1 /*
2 * Copyright (c) 2008, 2014, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
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19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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24 */
25
26 package java.lang.invoke;
27
28 import java.lang.reflect.*;
29 import java.util.BitSet;
30 import java.util.List;
31 import java.util.Arrays;
32 import java.util.Objects;
33
34 import sun.invoke.util.ValueConversions;
35 import sun.invoke.util.VerifyAccess;
36 import sun.invoke.util.Wrapper;
37 import sun.reflect.CallerSensitive;
38 import sun.reflect.Reflection;
39 import sun.reflect.misc.ReflectUtil;
40 import sun.security.util.SecurityConstants;
41 import java.lang.invoke.LambdaForm.BasicType;
42 import static java.lang.invoke.LambdaForm.BasicType.*;
43 import static java.lang.invoke.MethodHandleStatics.*;
44 import static java.lang.invoke.MethodHandleImpl.Intrinsic;
45 import static java.lang.invoke.MethodHandleNatives.Constants.*;
46 import java.util.concurrent.ConcurrentHashMap;
47
48 /**
49 * This class consists exclusively of static methods that operate on or return
50 * method handles. They fall into several categories:
51 * <ul>
52 * <li>Lookup methods which help create method handles for methods and fields.
53 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
54 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
55 * </ul>
56 *
57 * @author John Rose, JSR 292 EG
58 * @since 1.7
59 */
60 public class MethodHandles {
61
62 private MethodHandles() { } // do not instantiate
63
64 private static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
65 static { MethodHandleImpl.initStatics(); }
66 // See IMPL_LOOKUP below.
67
68 //// Method handle creation from ordinary methods.
69
70 /**
71 * Returns a {@link Lookup lookup object} with
72 * full capabilities to emulate all supported bytecode behaviors of the caller.
73 * These capabilities include <a href="MethodHandles.Lookup.html#privacc">private access</a> to the caller.
74 * Factory methods on the lookup object can create
75 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
76 * for any member that the caller has access to via bytecodes,
77 * including protected and private fields and methods.
78 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
79 * Do not store it in place where untrusted code can access it.
80 * <p>
81 * This method is caller sensitive, which means that it may return different
82 * values to different callers.
83 * <p>
84 * For any given caller class {@code C}, the lookup object returned by this call
85 * has equivalent capabilities to any lookup object
86 * supplied by the JVM to the bootstrap method of an
87 * <a href="package-summary.html#indyinsn">invokedynamic instruction</a>
88 * executing in the same caller class {@code C}.
89 * @return a lookup object for the caller of this method, with private access
90 */
91 @CallerSensitive
92 public static Lookup lookup() {
93 return new Lookup(Reflection.getCallerClass());
94 }
95
96 /**
97 * Returns a {@link Lookup lookup object} which is trusted minimally.
98 * It can only be used to create method handles to
99 * publicly accessible fields and methods.
100 * <p>
101 * As a matter of pure convention, the {@linkplain Lookup#lookupClass lookup class}
102 * of this lookup object will be {@link java.lang.Object}.
103 *
104 * <p style="font-size:smaller;">
105 * <em>Discussion:</em>
106 * The lookup class can be changed to any other class {@code C} using an expression of the form
107 * {@link Lookup#in publicLookup().in(C.class)}.
108 * Since all classes have equal access to public names,
109 * such a change would confer no new access rights.
110 * A public lookup object is always subject to
111 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
112 * Also, it cannot access
113 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
114 * @return a lookup object which is trusted minimally
115 */
116 public static Lookup publicLookup() {
117 return Lookup.PUBLIC_LOOKUP;
118 }
119
120 /**
121 * Performs an unchecked "crack" of a
122 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
123 * The result is as if the user had obtained a lookup object capable enough
124 * to crack the target method handle, called
125 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
126 * on the target to obtain its symbolic reference, and then called
127 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
128 * to resolve the symbolic reference to a member.
129 * <p>
130 * If there is a security manager, its {@code checkPermission} method
131 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
132 * @param <T> the desired type of the result, either {@link Member} or a subtype
133 * @param target a direct method handle to crack into symbolic reference components
134 * @param expected a class object representing the desired result type {@code T}
135 * @return a reference to the method, constructor, or field object
136 * @exception SecurityException if the caller is not privileged to call {@code setAccessible}
137 * @exception NullPointerException if either argument is {@code null}
138 * @exception IllegalArgumentException if the target is not a direct method handle
139 * @exception ClassCastException if the member is not of the expected type
140 * @since 1.8
141 */
142 public static <T extends Member> T
143 reflectAs(Class<T> expected, MethodHandle target) {
144 SecurityManager smgr = System.getSecurityManager();
145 if (smgr != null) smgr.checkPermission(ACCESS_PERMISSION);
146 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
147 return lookup.revealDirect(target).reflectAs(expected, lookup);
148 }
149 // Copied from AccessibleObject, as used by Method.setAccessible, etc.:
150 private static final java.security.Permission ACCESS_PERMISSION =
151 new ReflectPermission("suppressAccessChecks");
152
153 /**
154 * A <em>lookup object</em> is a factory for creating method handles,
155 * when the creation requires access checking.
156 * Method handles do not perform
157 * access checks when they are called, but rather when they are created.
158 * Therefore, method handle access
159 * restrictions must be enforced when a method handle is created.
160 * The caller class against which those restrictions are enforced
161 * is known as the {@linkplain #lookupClass lookup class}.
162 * <p>
163 * A lookup class which needs to create method handles will call
164 * {@link MethodHandles#lookup MethodHandles.lookup} to create a factory for itself.
165 * When the {@code Lookup} factory object is created, the identity of the lookup class is
166 * determined, and securely stored in the {@code Lookup} object.
167 * The lookup class (or its delegates) may then use factory methods
168 * on the {@code Lookup} object to create method handles for access-checked members.
169 * This includes all methods, constructors, and fields which are allowed to the lookup class,
170 * even private ones.
171 *
172 * <h1><a name="lookups"></a>Lookup Factory Methods</h1>
173 * The factory methods on a {@code Lookup} object correspond to all major
174 * use cases for methods, constructors, and fields.
175 * Each method handle created by a factory method is the functional
176 * equivalent of a particular <em>bytecode behavior</em>.
177 * (Bytecode behaviors are described in section 5.4.3.5 of the Java Virtual Machine Specification.)
178 * Here is a summary of the correspondence between these factory methods and
179 * the behavior the resulting method handles:
180 * <table border=1 cellpadding=5 summary="lookup method behaviors">
181 * <tr>
182 * <th><a name="equiv"></a>lookup expression</th>
183 * <th>member</th>
184 * <th>bytecode behavior</th>
185 * </tr>
186 * <tr>
187 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</td>
188 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
189 * </tr>
190 * <tr>
191 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</td>
192 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (T) C.f;}</td>
193 * </tr>
194 * <tr>
195 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</td>
196 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
197 * </tr>
198 * <tr>
199 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</td>
200 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
201 * </tr>
202 * <tr>
203 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</td>
204 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
205 * </tr>
206 * <tr>
207 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</td>
208 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
209 * </tr>
210 * <tr>
211 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</td>
212 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
213 * </tr>
214 * <tr>
215 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</td>
216 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
217 * </tr>
218 * <tr>
219 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</td>
220 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
221 * </tr>
222 * <tr>
223 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</td>
224 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
225 * </tr>
226 * <tr>
227 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
228 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
229 * </tr>
230 * <tr>
231 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</td>
232 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
233 * </tr>
234 * <tr>
235 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
236 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
237 * </tr>
238 * </table>
239 *
240 * Here, the type {@code C} is the class or interface being searched for a member,
241 * documented as a parameter named {@code refc} in the lookup methods.
242 * The method type {@code MT} is composed from the return type {@code T}
243 * and the sequence of argument types {@code A*}.
244 * The constructor also has a sequence of argument types {@code A*} and
245 * is deemed to return the newly-created object of type {@code C}.
246 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
247 * The formal parameter {@code this} stands for the self-reference of type {@code C};
248 * if it is present, it is always the leading argument to the method handle invocation.
249 * (In the case of some {@code protected} members, {@code this} may be
250 * restricted in type to the lookup class; see below.)
251 * The name {@code arg} stands for all the other method handle arguments.
252 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
253 * stands for a null reference if the accessed method or field is static,
254 * and {@code this} otherwise.
255 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
256 * for reflective objects corresponding to the given members.
257 * <p>
258 * In cases where the given member is of variable arity (i.e., a method or constructor)
259 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
260 * In all other cases, the returned method handle will be of fixed arity.
261 * <p style="font-size:smaller;">
262 * <em>Discussion:</em>
263 * The equivalence between looked-up method handles and underlying
264 * class members and bytecode behaviors
265 * can break down in a few ways:
266 * <ul style="font-size:smaller;">
267 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
268 * the lookup can still succeed, even when there is no equivalent
269 * Java expression or bytecoded constant.
270 * <li>Likewise, if {@code T} or {@code MT}
271 * is not symbolically accessible from the lookup class's loader,
272 * the lookup can still succeed.
273 * For example, lookups for {@code MethodHandle.invokeExact} and
274 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
275 * <li>If there is a security manager installed, it can forbid the lookup
276 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
277 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
278 * constant is not subject to security manager checks.
279 * <li>If the looked-up method has a
280 * <a href="MethodHandle.html#maxarity">very large arity</a>,
281 * the method handle creation may fail, due to the method handle
282 * type having too many parameters.
283 * </ul>
284 *
285 * <h1><a name="access"></a>Access checking</h1>
286 * Access checks are applied in the factory methods of {@code Lookup},
287 * when a method handle is created.
288 * This is a key difference from the Core Reflection API, since
289 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
290 * performs access checking against every caller, on every call.
291 * <p>
292 * All access checks start from a {@code Lookup} object, which
293 * compares its recorded lookup class against all requests to
294 * create method handles.
295 * A single {@code Lookup} object can be used to create any number
296 * of access-checked method handles, all checked against a single
297 * lookup class.
298 * <p>
299 * A {@code Lookup} object can be shared with other trusted code,
300 * such as a metaobject protocol.
301 * A shared {@code Lookup} object delegates the capability
302 * to create method handles on private members of the lookup class.
303 * Even if privileged code uses the {@code Lookup} object,
304 * the access checking is confined to the privileges of the
305 * original lookup class.
306 * <p>
307 * A lookup can fail, because
308 * the containing class is not accessible to the lookup class, or
309 * because the desired class member is missing, or because the
310 * desired class member is not accessible to the lookup class, or
311 * because the lookup object is not trusted enough to access the member.
312 * In any of these cases, a {@code ReflectiveOperationException} will be
313 * thrown from the attempted lookup. The exact class will be one of
314 * the following:
315 * <ul>
316 * <li>NoSuchMethodException — if a method is requested but does not exist
317 * <li>NoSuchFieldException — if a field is requested but does not exist
318 * <li>IllegalAccessException — if the member exists but an access check fails
319 * </ul>
320 * <p>
321 * In general, the conditions under which a method handle may be
322 * looked up for a method {@code M} are no more restrictive than the conditions
323 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
324 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
325 * a method handle lookup will generally raise a corresponding
326 * checked exception, such as {@code NoSuchMethodException}.
327 * And the effect of invoking the method handle resulting from the lookup
328 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
329 * to executing the compiled, verified, and resolved call to {@code M}.
330 * The same point is true of fields and constructors.
331 * <p style="font-size:smaller;">
332 * <em>Discussion:</em>
333 * Access checks only apply to named and reflected methods,
334 * constructors, and fields.
335 * Other method handle creation methods, such as
336 * {@link MethodHandle#asType MethodHandle.asType},
337 * do not require any access checks, and are used
338 * independently of any {@code Lookup} object.
339 * <p>
340 * If the desired member is {@code protected}, the usual JVM rules apply,
341 * including the requirement that the lookup class must be either be in the
342 * same package as the desired member, or must inherit that member.
343 * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.)
344 * In addition, if the desired member is a non-static field or method
345 * in a different package, the resulting method handle may only be applied
346 * to objects of the lookup class or one of its subclasses.
347 * This requirement is enforced by narrowing the type of the leading
348 * {@code this} parameter from {@code C}
349 * (which will necessarily be a superclass of the lookup class)
350 * to the lookup class itself.
351 * <p>
352 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
353 * that the receiver argument must match both the resolved method <em>and</em>
354 * the current class. Again, this requirement is enforced by narrowing the
355 * type of the leading parameter to the resulting method handle.
356 * (See the Java Virtual Machine Specification, section 4.10.1.9.)
357 * <p>
358 * The JVM represents constructors and static initializer blocks as internal methods
359 * with special names ({@code "<init>"} and {@code "<clinit>"}).
360 * The internal syntax of invocation instructions allows them to refer to such internal
361 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
362 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
363 * <p>
364 * In some cases, access between nested classes is obtained by the Java compiler by creating
365 * an wrapper method to access a private method of another class
366 * in the same top-level declaration.
367 * For example, a nested class {@code C.D}
368 * can access private members within other related classes such as
369 * {@code C}, {@code C.D.E}, or {@code C.B},
370 * but the Java compiler may need to generate wrapper methods in
371 * those related classes. In such cases, a {@code Lookup} object on
372 * {@code C.E} would be unable to those private members.
373 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
374 * which can transform a lookup on {@code C.E} into one on any of those other
375 * classes, without special elevation of privilege.
376 * <p>
377 * The accesses permitted to a given lookup object may be limited,
378 * according to its set of {@link #lookupModes lookupModes},
379 * to a subset of members normally accessible to the lookup class.
380 * For example, the {@link MethodHandles#publicLookup publicLookup}
381 * method produces a lookup object which is only allowed to access
382 * public members in public classes.
383 * The caller sensitive method {@link MethodHandles#lookup lookup}
384 * produces a lookup object with full capabilities relative to
385 * its caller class, to emulate all supported bytecode behaviors.
386 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
387 * with fewer access modes than the original lookup object.
388 *
389 * <p style="font-size:smaller;">
390 * <a name="privacc"></a>
391 * <em>Discussion of private access:</em>
392 * We say that a lookup has <em>private access</em>
393 * if its {@linkplain #lookupModes lookup modes}
394 * include the possibility of accessing {@code private} members.
395 * As documented in the relevant methods elsewhere,
396 * only lookups with private access possess the following capabilities:
397 * <ul style="font-size:smaller;">
398 * <li>access private fields, methods, and constructors of the lookup class
399 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
400 * such as {@code Class.forName}
401 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
402 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
403 * for classes accessible to the lookup class
404 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
405 * within the same package member
406 * </ul>
407 * <p style="font-size:smaller;">
408 * Each of these permissions is a consequence of the fact that a lookup object
409 * with private access can be securely traced back to an originating class,
410 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
411 * can be reliably determined and emulated by method handles.
412 *
413 * <h1><a name="secmgr"></a>Security manager interactions</h1>
414 * Although bytecode instructions can only refer to classes in
415 * a related class loader, this API can search for methods in any
416 * class, as long as a reference to its {@code Class} object is
417 * available. Such cross-loader references are also possible with the
418 * Core Reflection API, and are impossible to bytecode instructions
419 * such as {@code invokestatic} or {@code getfield}.
420 * There is a {@linkplain java.lang.SecurityManager security manager API}
421 * to allow applications to check such cross-loader references.
422 * These checks apply to both the {@code MethodHandles.Lookup} API
423 * and the Core Reflection API
424 * (as found on {@link java.lang.Class Class}).
425 * <p>
426 * If a security manager is present, member lookups are subject to
427 * additional checks.
428 * From one to three calls are made to the security manager.
429 * Any of these calls can refuse access by throwing a
430 * {@link java.lang.SecurityException SecurityException}.
431 * Define {@code smgr} as the security manager,
432 * {@code lookc} as the lookup class of the current lookup object,
433 * {@code refc} as the containing class in which the member
434 * is being sought, and {@code defc} as the class in which the
435 * member is actually defined.
436 * The value {@code lookc} is defined as <em>not present</em>
437 * if the current lookup object does not have
438 * <a href="MethodHandles.Lookup.html#privacc">private access</a>.
439 * The calls are made according to the following rules:
440 * <ul>
441 * <li><b>Step 1:</b>
442 * If {@code lookc} is not present, or if its class loader is not
443 * the same as or an ancestor of the class loader of {@code refc},
444 * then {@link SecurityManager#checkPackageAccess
445 * smgr.checkPackageAccess(refcPkg)} is called,
446 * where {@code refcPkg} is the package of {@code refc}.
447 * <li><b>Step 2:</b>
448 * If the retrieved member is not public and
449 * {@code lookc} is not present, then
450 * {@link SecurityManager#checkPermission smgr.checkPermission}
451 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
452 * <li><b>Step 3:</b>
453 * If the retrieved member is not public,
454 * and if {@code lookc} is not present,
455 * and if {@code defc} and {@code refc} are different,
456 * then {@link SecurityManager#checkPackageAccess
457 * smgr.checkPackageAccess(defcPkg)} is called,
458 * where {@code defcPkg} is the package of {@code defc}.
459 * </ul>
460 * Security checks are performed after other access checks have passed.
461 * Therefore, the above rules presuppose a member that is public,
462 * or else that is being accessed from a lookup class that has
463 * rights to access the member.
464 *
465 * <h1><a name="callsens"></a>Caller sensitive methods</h1>
466 * A small number of Java methods have a special property called caller sensitivity.
467 * A <em>caller-sensitive</em> method can behave differently depending on the
468 * identity of its immediate caller.
469 * <p>
470 * If a method handle for a caller-sensitive method is requested,
471 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
472 * but they take account of the lookup class in a special way.
473 * The resulting method handle behaves as if it were called
474 * from an instruction contained in the lookup class,
475 * so that the caller-sensitive method detects the lookup class.
476 * (By contrast, the invoker of the method handle is disregarded.)
477 * Thus, in the case of caller-sensitive methods,
478 * different lookup classes may give rise to
479 * differently behaving method handles.
480 * <p>
481 * In cases where the lookup object is
482 * {@link MethodHandles#publicLookup() publicLookup()},
483 * or some other lookup object without
484 * <a href="MethodHandles.Lookup.html#privacc">private access</a>,
485 * the lookup class is disregarded.
486 * In such cases, no caller-sensitive method handle can be created,
487 * access is forbidden, and the lookup fails with an
488 * {@code IllegalAccessException}.
489 * <p style="font-size:smaller;">
490 * <em>Discussion:</em>
491 * For example, the caller-sensitive method
492 * {@link java.lang.Class#forName(String) Class.forName(x)}
493 * can return varying classes or throw varying exceptions,
494 * depending on the class loader of the class that calls it.
495 * A public lookup of {@code Class.forName} will fail, because
496 * there is no reasonable way to determine its bytecode behavior.
497 * <p style="font-size:smaller;">
498 * If an application caches method handles for broad sharing,
499 * it should use {@code publicLookup()} to create them.
500 * If there is a lookup of {@code Class.forName}, it will fail,
501 * and the application must take appropriate action in that case.
502 * It may be that a later lookup, perhaps during the invocation of a
503 * bootstrap method, can incorporate the specific identity
504 * of the caller, making the method accessible.
505 * <p style="font-size:smaller;">
506 * The function {@code MethodHandles.lookup} is caller sensitive
507 * so that there can be a secure foundation for lookups.
508 * Nearly all other methods in the JSR 292 API rely on lookup
509 * objects to check access requests.
510 */
511 public static final
512 class Lookup {
513 /** The class on behalf of whom the lookup is being performed. */
514 private final Class<?> lookupClass;
515
516 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
517 private final int allowedModes;
518
519 /** A single-bit mask representing {@code public} access,
520 * which may contribute to the result of {@link #lookupModes lookupModes}.
521 * The value, {@code 0x01}, happens to be the same as the value of the
522 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
523 */
524 public static final int PUBLIC = Modifier.PUBLIC;
525
526 /** A single-bit mask representing {@code private} access,
527 * which may contribute to the result of {@link #lookupModes lookupModes}.
528 * The value, {@code 0x02}, happens to be the same as the value of the
529 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
530 */
531 public static final int PRIVATE = Modifier.PRIVATE;
532
533 /** A single-bit mask representing {@code protected} access,
534 * which may contribute to the result of {@link #lookupModes lookupModes}.
535 * The value, {@code 0x04}, happens to be the same as the value of the
536 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
537 */
538 public static final int PROTECTED = Modifier.PROTECTED;
539
540 /** A single-bit mask representing {@code package} access (default access),
541 * which may contribute to the result of {@link #lookupModes lookupModes}.
542 * The value is {@code 0x08}, which does not correspond meaningfully to
543 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
544 */
545 public static final int PACKAGE = Modifier.STATIC;
546
547 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE);
548 private static final int TRUSTED = -1;
549
550 private static int fixmods(int mods) {
551 mods &= (ALL_MODES - PACKAGE);
552 return (mods != 0) ? mods : PACKAGE;
553 }
554
555 /** Tells which class is performing the lookup. It is this class against
556 * which checks are performed for visibility and access permissions.
557 * <p>
558 * The class implies a maximum level of access permission,
559 * but the permissions may be additionally limited by the bitmask
560 * {@link #lookupModes lookupModes}, which controls whether non-public members
561 * can be accessed.
562 * @return the lookup class, on behalf of which this lookup object finds members
563 */
564 public Class<?> lookupClass() {
565 return lookupClass;
566 }
567
568 // This is just for calling out to MethodHandleImpl.
569 private Class<?> lookupClassOrNull() {
570 return (allowedModes == TRUSTED) ? null : lookupClass;
571 }
572
573 /** Tells which access-protection classes of members this lookup object can produce.
574 * The result is a bit-mask of the bits
575 * {@linkplain #PUBLIC PUBLIC (0x01)},
576 * {@linkplain #PRIVATE PRIVATE (0x02)},
577 * {@linkplain #PROTECTED PROTECTED (0x04)},
578 * and {@linkplain #PACKAGE PACKAGE (0x08)}.
579 * <p>
580 * A freshly-created lookup object
581 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class}
582 * has all possible bits set, since the caller class can access all its own members.
583 * A lookup object on a new lookup class
584 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
585 * may have some mode bits set to zero.
586 * The purpose of this is to restrict access via the new lookup object,
587 * so that it can access only names which can be reached by the original
588 * lookup object, and also by the new lookup class.
589 * @return the lookup modes, which limit the kinds of access performed by this lookup object
590 */
591 public int lookupModes() {
592 return allowedModes & ALL_MODES;
593 }
594
595 /** Embody the current class (the lookupClass) as a lookup class
596 * for method handle creation.
597 * Must be called by from a method in this package,
598 * which in turn is called by a method not in this package.
599 */
600 Lookup(Class<?> lookupClass) {
601 this(lookupClass, ALL_MODES);
602 // make sure we haven't accidentally picked up a privileged class:
603 checkUnprivilegedlookupClass(lookupClass, ALL_MODES);
604 }
605
606 private Lookup(Class<?> lookupClass, int allowedModes) {
607 this.lookupClass = lookupClass;
608 this.allowedModes = allowedModes;
609 }
610
611 /**
612 * Creates a lookup on the specified new lookup class.
613 * The resulting object will report the specified
614 * class as its own {@link #lookupClass lookupClass}.
615 * <p>
616 * However, the resulting {@code Lookup} object is guaranteed
617 * to have no more access capabilities than the original.
618 * In particular, access capabilities can be lost as follows:<ul>
619 * <li>If the new lookup class differs from the old one,
620 * protected members will not be accessible by virtue of inheritance.
621 * (Protected members may continue to be accessible because of package sharing.)
622 * <li>If the new lookup class is in a different package
623 * than the old one, protected and default (package) members will not be accessible.
624 * <li>If the new lookup class is not within the same package member
625 * as the old one, private members will not be accessible.
626 * <li>If the new lookup class is not accessible to the old lookup class,
627 * then no members, not even public members, will be accessible.
628 * (In all other cases, public members will continue to be accessible.)
629 * </ul>
630 *
631 * @param requestedLookupClass the desired lookup class for the new lookup object
632 * @return a lookup object which reports the desired lookup class
633 * @throws NullPointerException if the argument is null
634 */
635 public Lookup in(Class<?> requestedLookupClass) {
636 Objects.requireNonNull(requestedLookupClass);
637 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
638 return new Lookup(requestedLookupClass, ALL_MODES);
639 if (requestedLookupClass == this.lookupClass)
640 return this; // keep same capabilities
641 int newModes = (allowedModes & (ALL_MODES & ~PROTECTED));
642 if ((newModes & PACKAGE) != 0
643 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
644 newModes &= ~(PACKAGE|PRIVATE);
645 }
646 // Allow nestmate lookups to be created without special privilege:
647 if ((newModes & PRIVATE) != 0
648 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
649 newModes &= ~PRIVATE;
650 }
651 if ((newModes & PUBLIC) != 0
652 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, allowedModes)) {
653 // The requested class it not accessible from the lookup class.
654 // No permissions.
655 newModes = 0;
656 }
657 checkUnprivilegedlookupClass(requestedLookupClass, newModes);
658 return new Lookup(requestedLookupClass, newModes);
659 }
660
661 // Make sure outer class is initialized first.
662 static { IMPL_NAMES.getClass(); }
663
664 /** Version of lookup which is trusted minimally.
665 * It can only be used to create method handles to
666 * publicly accessible members.
667 */
668 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, PUBLIC);
669
670 /** Package-private version of lookup which is trusted. */
671 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, TRUSTED);
672
673 private static void checkUnprivilegedlookupClass(Class<?> lookupClass, int allowedModes) {
674 String name = lookupClass.getName();
675 if (name.startsWith("java.lang.invoke."))
676 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
677
678 // For caller-sensitive MethodHandles.lookup()
679 // disallow lookup more restricted packages
680 if (allowedModes == ALL_MODES && lookupClass.getClassLoader() == null) {
681 if (name.startsWith("java.") ||
682 (name.startsWith("sun.") && !name.startsWith("sun.invoke."))) {
683 throw newIllegalArgumentException("illegal lookupClass: " + lookupClass);
684 }
685 }
686 }
687
688 /**
689 * Displays the name of the class from which lookups are to be made.
690 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
691 * If there are restrictions on the access permitted to this lookup,
692 * this is indicated by adding a suffix to the class name, consisting
693 * of a slash and a keyword. The keyword represents the strongest
694 * allowed access, and is chosen as follows:
695 * <ul>
696 * <li>If no access is allowed, the suffix is "/noaccess".
697 * <li>If only public access is allowed, the suffix is "/public".
698 * <li>If only public and package access are allowed, the suffix is "/package".
699 * <li>If only public, package, and private access are allowed, the suffix is "/private".
700 * </ul>
701 * If none of the above cases apply, it is the case that full
702 * access (public, package, private, and protected) is allowed.
703 * In this case, no suffix is added.
704 * This is true only of an object obtained originally from
705 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
706 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
707 * always have restricted access, and will display a suffix.
708 * <p>
709 * (It may seem strange that protected access should be
710 * stronger than private access. Viewed independently from
711 * package access, protected access is the first to be lost,
712 * because it requires a direct subclass relationship between
713 * caller and callee.)
714 * @see #in
715 */
716 @Override
717 public String toString() {
718 String cname = lookupClass.getName();
719 switch (allowedModes) {
720 case 0: // no privileges
721 return cname + "/noaccess";
722 case PUBLIC:
723 return cname + "/public";
724 case PUBLIC|PACKAGE:
725 return cname + "/package";
726 case ALL_MODES & ~PROTECTED:
727 return cname + "/private";
728 case ALL_MODES:
729 return cname;
730 case TRUSTED:
731 return "/trusted"; // internal only; not exported
732 default: // Should not happen, but it's a bitfield...
733 cname = cname + "/" + Integer.toHexString(allowedModes);
734 assert(false) : cname;
735 return cname;
736 }
737 }
738
739 /**
740 * Produces a method handle for a static method.
741 * The type of the method handle will be that of the method.
742 * (Since static methods do not take receivers, there is no
743 * additional receiver argument inserted into the method handle type,
744 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
745 * The method and all its argument types must be accessible to the lookup object.
746 * <p>
747 * The returned method handle will have
748 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
749 * the method's variable arity modifier bit ({@code 0x0080}) is set.
750 * <p>
751 * If the returned method handle is invoked, the method's class will
752 * be initialized, if it has not already been initialized.
753 * <p><b>Example:</b>
754 * <blockquote><pre>{@code
755 import static java.lang.invoke.MethodHandles.*;
756 import static java.lang.invoke.MethodType.*;
757 ...
758 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
759 "asList", methodType(List.class, Object[].class));
760 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
761 * }</pre></blockquote>
762 * @param refc the class from which the method is accessed
763 * @param name the name of the method
764 * @param type the type of the method
765 * @return the desired method handle
766 * @throws NoSuchMethodException if the method does not exist
767 * @throws IllegalAccessException if access checking fails,
768 * or if the method is not {@code static},
769 * or if the method's variable arity modifier bit
770 * is set and {@code asVarargsCollector} fails
771 * @exception SecurityException if a security manager is present and it
772 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
773 * @throws NullPointerException if any argument is null
774 */
775 public
776 MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
777 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
778 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method));
779 }
780
781 /**
782 * Produces a method handle for a virtual method.
783 * The type of the method handle will be that of the method,
784 * with the receiver type (usually {@code refc}) prepended.
785 * The method and all its argument types must be accessible to the lookup object.
786 * <p>
787 * When called, the handle will treat the first argument as a receiver
788 * and dispatch on the receiver's type to determine which method
789 * implementation to enter.
790 * (The dispatching action is identical with that performed by an
791 * {@code invokevirtual} or {@code invokeinterface} instruction.)
792 * <p>
793 * The first argument will be of type {@code refc} if the lookup
794 * class has full privileges to access the member. Otherwise
795 * the member must be {@code protected} and the first argument
796 * will be restricted in type to the lookup class.
797 * <p>
798 * The returned method handle will have
799 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
800 * the method's variable arity modifier bit ({@code 0x0080}) is set.
801 * <p>
802 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
803 * instructions and method handles produced by {@code findVirtual},
804 * if the class is {@code MethodHandle} and the name string is
805 * {@code invokeExact} or {@code invoke}, the resulting
806 * method handle is equivalent to one produced by
807 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
808 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
809 * with the same {@code type} argument.
810 *
811 * <b>Example:</b>
812 * <blockquote><pre>{@code
813 import static java.lang.invoke.MethodHandles.*;
814 import static java.lang.invoke.MethodType.*;
815 ...
816 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
817 "concat", methodType(String.class, String.class));
818 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
819 "hashCode", methodType(int.class));
820 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
821 "hashCode", methodType(int.class));
822 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
823 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
824 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
825 // interface method:
826 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
827 "subSequence", methodType(CharSequence.class, int.class, int.class));
828 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
829 // constructor "internal method" must be accessed differently:
830 MethodType MT_newString = methodType(void.class); //()V for new String()
831 try { assertEquals("impossible", lookup()
832 .findVirtual(String.class, "<init>", MT_newString));
833 } catch (NoSuchMethodException ex) { } // OK
834 MethodHandle MH_newString = publicLookup()
835 .findConstructor(String.class, MT_newString);
836 assertEquals("", (String) MH_newString.invokeExact());
837 * }</pre></blockquote>
838 *
839 * @param refc the class or interface from which the method is accessed
840 * @param name the name of the method
841 * @param type the type of the method, with the receiver argument omitted
842 * @return the desired method handle
843 * @throws NoSuchMethodException if the method does not exist
844 * @throws IllegalAccessException if access checking fails,
845 * or if the method is {@code static}
846 * or if the method's variable arity modifier bit
847 * is set and {@code asVarargsCollector} fails
848 * @exception SecurityException if a security manager is present and it
849 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
850 * @throws NullPointerException if any argument is null
851 */
852 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
853 if (refc == MethodHandle.class) {
854 MethodHandle mh = findVirtualForMH(name, type);
855 if (mh != null) return mh;
856 }
857 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
858 MemberName method = resolveOrFail(refKind, refc, name, type);
859 return getDirectMethod(refKind, refc, method, findBoundCallerClass(method));
860 }
861 private MethodHandle findVirtualForMH(String name, MethodType type) {
862 // these names require special lookups because of the implicit MethodType argument
863 if ("invoke".equals(name))
864 return invoker(type);
865 if ("invokeExact".equals(name))
866 return exactInvoker(type);
867 if ("invokeBasic".equals(name))
868 return basicInvoker(type);
869 assert(!MemberName.isMethodHandleInvokeName(name));
870 return null;
871 }
872
873 /**
874 * Produces a method handle which creates an object and initializes it, using
875 * the constructor of the specified type.
876 * The parameter types of the method handle will be those of the constructor,
877 * while the return type will be a reference to the constructor's class.
878 * The constructor and all its argument types must be accessible to the lookup object.
879 * <p>
880 * The requested type must have a return type of {@code void}.
881 * (This is consistent with the JVM's treatment of constructor type descriptors.)
882 * <p>
883 * The returned method handle will have
884 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
885 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
886 * <p>
887 * If the returned method handle is invoked, the constructor's class will
888 * be initialized, if it has not already been initialized.
889 * <p><b>Example:</b>
890 * <blockquote><pre>{@code
891 import static java.lang.invoke.MethodHandles.*;
892 import static java.lang.invoke.MethodType.*;
893 ...
894 MethodHandle MH_newArrayList = publicLookup().findConstructor(
895 ArrayList.class, methodType(void.class, Collection.class));
896 Collection orig = Arrays.asList("x", "y");
897 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
898 assert(orig != copy);
899 assertEquals(orig, copy);
900 // a variable-arity constructor:
901 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
902 ProcessBuilder.class, methodType(void.class, String[].class));
903 ProcessBuilder pb = (ProcessBuilder)
904 MH_newProcessBuilder.invoke("x", "y", "z");
905 assertEquals("[x, y, z]", pb.command().toString());
906 * }</pre></blockquote>
907 * @param refc the class or interface from which the method is accessed
908 * @param type the type of the method, with the receiver argument omitted, and a void return type
909 * @return the desired method handle
910 * @throws NoSuchMethodException if the constructor does not exist
911 * @throws IllegalAccessException if access checking fails
912 * or if the method's variable arity modifier bit
913 * is set and {@code asVarargsCollector} fails
914 * @exception SecurityException if a security manager is present and it
915 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
916 * @throws NullPointerException if any argument is null
917 */
918 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
919 String name = "<init>";
920 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
921 return getDirectConstructor(refc, ctor);
922 }
923
924 /**
925 * Produces an early-bound method handle for a virtual method.
926 * It will bypass checks for overriding methods on the receiver,
927 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
928 * instruction from within the explicitly specified {@code specialCaller}.
929 * The type of the method handle will be that of the method,
930 * with a suitably restricted receiver type prepended.
931 * (The receiver type will be {@code specialCaller} or a subtype.)
932 * The method and all its argument types must be accessible
933 * to the lookup object.
934 * <p>
935 * Before method resolution,
936 * if the explicitly specified caller class is not identical with the
937 * lookup class, or if this lookup object does not have
938 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
939 * privileges, the access fails.
940 * <p>
941 * The returned method handle will have
942 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
943 * the method's variable arity modifier bit ({@code 0x0080}) is set.
944 * <p style="font-size:smaller;">
945 * <em>(Note: JVM internal methods named {@code "<init>"} are not visible to this API,
946 * even though the {@code invokespecial} instruction can refer to them
947 * in special circumstances. Use {@link #findConstructor findConstructor}
948 * to access instance initialization methods in a safe manner.)</em>
949 * <p><b>Example:</b>
950 * <blockquote><pre>{@code
951 import static java.lang.invoke.MethodHandles.*;
952 import static java.lang.invoke.MethodType.*;
953 ...
954 static class Listie extends ArrayList {
955 public String toString() { return "[wee Listie]"; }
956 static Lookup lookup() { return MethodHandles.lookup(); }
957 }
958 ...
959 // no access to constructor via invokeSpecial:
960 MethodHandle MH_newListie = Listie.lookup()
961 .findConstructor(Listie.class, methodType(void.class));
962 Listie l = (Listie) MH_newListie.invokeExact();
963 try { assertEquals("impossible", Listie.lookup().findSpecial(
964 Listie.class, "<init>", methodType(void.class), Listie.class));
965 } catch (NoSuchMethodException ex) { } // OK
966 // access to super and self methods via invokeSpecial:
967 MethodHandle MH_super = Listie.lookup().findSpecial(
968 ArrayList.class, "toString" , methodType(String.class), Listie.class);
969 MethodHandle MH_this = Listie.lookup().findSpecial(
970 Listie.class, "toString" , methodType(String.class), Listie.class);
971 MethodHandle MH_duper = Listie.lookup().findSpecial(
972 Object.class, "toString" , methodType(String.class), Listie.class);
973 assertEquals("[]", (String) MH_super.invokeExact(l));
974 assertEquals(""+l, (String) MH_this.invokeExact(l));
975 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
976 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
977 String.class, "toString", methodType(String.class), Listie.class));
978 } catch (IllegalAccessException ex) { } // OK
979 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
980 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
981 * }</pre></blockquote>
982 *
983 * @param refc the class or interface from which the method is accessed
984 * @param name the name of the method (which must not be "<init>")
985 * @param type the type of the method, with the receiver argument omitted
986 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
987 * @return the desired method handle
988 * @throws NoSuchMethodException if the method does not exist
989 * @throws IllegalAccessException if access checking fails
990 * or if the method's variable arity modifier bit
991 * is set and {@code asVarargsCollector} fails
992 * @exception SecurityException if a security manager is present and it
993 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
994 * @throws NullPointerException if any argument is null
995 */
996 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
997 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
998 checkSpecialCaller(specialCaller);
999 Lookup specialLookup = this.in(specialCaller);
1000 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
1001 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1002 }
1003
1004 /**
1005 * Produces a method handle giving read access to a non-static field.
1006 * The type of the method handle will have a return type of the field's
1007 * value type.
1008 * The method handle's single argument will be the instance containing
1009 * the field.
1010 * Access checking is performed immediately on behalf of the lookup class.
1011 * @param refc the class or interface from which the method is accessed
1012 * @param name the field's name
1013 * @param type the field's type
1014 * @return a method handle which can load values from the field
1015 * @throws NoSuchFieldException if the field does not exist
1016 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1017 * @exception SecurityException if a security manager is present and it
1018 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1019 * @throws NullPointerException if any argument is null
1020 */
1021 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1022 MemberName field = resolveOrFail(REF_getField, refc, name, type);
1023 return getDirectField(REF_getField, refc, field);
1024 }
1025
1026 /**
1027 * Produces a method handle giving write access to a non-static field.
1028 * The type of the method handle will have a void return type.
1029 * The method handle will take two arguments, the instance containing
1030 * the field, and the value to be stored.
1031 * The second argument will be of the field's value type.
1032 * Access checking is performed immediately on behalf of the lookup class.
1033 * @param refc the class or interface from which the method is accessed
1034 * @param name the field's name
1035 * @param type the field's type
1036 * @return a method handle which can store values into the field
1037 * @throws NoSuchFieldException if the field does not exist
1038 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1039 * @exception SecurityException if a security manager is present and it
1040 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1041 * @throws NullPointerException if any argument is null
1042 */
1043 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1044 MemberName field = resolveOrFail(REF_putField, refc, name, type);
1045 return getDirectField(REF_putField, refc, field);
1046 }
1047
1048 /**
1049 * Produces a method handle giving read access to a static field.
1050 * The type of the method handle will have a return type of the field's
1051 * value type.
1052 * The method handle will take no arguments.
1053 * Access checking is performed immediately on behalf of the lookup class.
1054 * <p>
1055 * If the returned method handle is invoked, the field's class will
1056 * be initialized, if it has not already been initialized.
1057 * @param refc the class or interface from which the method is accessed
1058 * @param name the field's name
1059 * @param type the field's type
1060 * @return a method handle which can load values from the field
1061 * @throws NoSuchFieldException if the field does not exist
1062 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1063 * @exception SecurityException if a security manager is present and it
1064 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1065 * @throws NullPointerException if any argument is null
1066 */
1067 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1068 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
1069 return getDirectField(REF_getStatic, refc, field);
1070 }
1071
1072 /**
1073 * Produces a method handle giving write access to a static field.
1074 * The type of the method handle will have a void return type.
1075 * The method handle will take a single
1076 * argument, of the field's value type, the value to be stored.
1077 * Access checking is performed immediately on behalf of the lookup class.
1078 * <p>
1079 * If the returned method handle is invoked, the field's class will
1080 * be initialized, if it has not already been initialized.
1081 * @param refc the class or interface from which the method is accessed
1082 * @param name the field's name
1083 * @param type the field's type
1084 * @return a method handle which can store values into the field
1085 * @throws NoSuchFieldException if the field does not exist
1086 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1087 * @exception SecurityException if a security manager is present and it
1088 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1089 * @throws NullPointerException if any argument is null
1090 */
1091 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1092 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
1093 return getDirectField(REF_putStatic, refc, field);
1094 }
1095
1096 /**
1097 * Produces an early-bound method handle for a non-static method.
1098 * The receiver must have a supertype {@code defc} in which a method
1099 * of the given name and type is accessible to the lookup class.
1100 * The method and all its argument types must be accessible to the lookup object.
1101 * The type of the method handle will be that of the method,
1102 * without any insertion of an additional receiver parameter.
1103 * The given receiver will be bound into the method handle,
1104 * so that every call to the method handle will invoke the
1105 * requested method on the given receiver.
1106 * <p>
1107 * The returned method handle will have
1108 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1109 * the method's variable arity modifier bit ({@code 0x0080}) is set
1110 * <em>and</em> the trailing array argument is not the only argument.
1111 * (If the trailing array argument is the only argument,
1112 * the given receiver value will be bound to it.)
1113 * <p>
1114 * This is equivalent to the following code:
1115 * <blockquote><pre>{@code
1116 import static java.lang.invoke.MethodHandles.*;
1117 import static java.lang.invoke.MethodType.*;
1118 ...
1119 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
1120 MethodHandle mh1 = mh0.bindTo(receiver);
1121 MethodType mt1 = mh1.type();
1122 if (mh0.isVarargsCollector())
1123 mh1 = mh1.asVarargsCollector(mt1.parameterType(mt1.parameterCount()-1));
1124 return mh1;
1125 * }</pre></blockquote>
1126 * where {@code defc} is either {@code receiver.getClass()} or a super
1127 * type of that class, in which the requested method is accessible
1128 * to the lookup class.
1129 * (Note that {@code bindTo} does not preserve variable arity.)
1130 * @param receiver the object from which the method is accessed
1131 * @param name the name of the method
1132 * @param type the type of the method, with the receiver argument omitted
1133 * @return the desired method handle
1134 * @throws NoSuchMethodException if the method does not exist
1135 * @throws IllegalAccessException if access checking fails
1136 * or if the method's variable arity modifier bit
1137 * is set and {@code asVarargsCollector} fails
1138 * @exception SecurityException if a security manager is present and it
1139 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1140 * @throws NullPointerException if any argument is null
1141 * @see MethodHandle#bindTo
1142 * @see #findVirtual
1143 */
1144 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1145 Class<? extends Object> refc = receiver.getClass(); // may get NPE
1146 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
1147 MethodHandle mh = getDirectMethodNoRestrict(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1148 return mh.bindArgumentL(0, receiver).setVarargs(method);
1149 }
1150
1151 /**
1152 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1153 * to <i>m</i>, if the lookup class has permission.
1154 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
1155 * If <i>m</i> is virtual, overriding is respected on every call.
1156 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
1157 * The type of the method handle will be that of the method,
1158 * with the receiver type prepended (but only if it is non-static).
1159 * If the method's {@code accessible} flag is not set,
1160 * access checking is performed immediately on behalf of the lookup class.
1161 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
1162 * <p>
1163 * The returned method handle will have
1164 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1165 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1166 * <p>
1167 * If <i>m</i> is static, and
1168 * if the returned method handle is invoked, the method's class will
1169 * be initialized, if it has not already been initialized.
1170 * @param m the reflected method
1171 * @return a method handle which can invoke the reflected method
1172 * @throws IllegalAccessException if access checking fails
1173 * or if the method's variable arity modifier bit
1174 * is set and {@code asVarargsCollector} fails
1175 * @throws NullPointerException if the argument is null
1176 */
1177 public MethodHandle unreflect(Method m) throws IllegalAccessException {
1178 if (m.getDeclaringClass() == MethodHandle.class) {
1179 MethodHandle mh = unreflectForMH(m);
1180 if (mh != null) return mh;
1181 }
1182 MemberName method = new MemberName(m);
1183 byte refKind = method.getReferenceKind();
1184 if (refKind == REF_invokeSpecial)
1185 refKind = REF_invokeVirtual;
1186 assert(method.isMethod());
1187 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
1188 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method));
1189 }
1190 private MethodHandle unreflectForMH(Method m) {
1191 // these names require special lookups because they throw UnsupportedOperationException
1192 if (MemberName.isMethodHandleInvokeName(m.getName()))
1193 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
1194 return null;
1195 }
1196
1197 /**
1198 * Produces a method handle for a reflected method.
1199 * It will bypass checks for overriding methods on the receiver,
1200 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1201 * instruction from within the explicitly specified {@code specialCaller}.
1202 * The type of the method handle will be that of the method,
1203 * with a suitably restricted receiver type prepended.
1204 * (The receiver type will be {@code specialCaller} or a subtype.)
1205 * If the method's {@code accessible} flag is not set,
1206 * access checking is performed immediately on behalf of the lookup class,
1207 * as if {@code invokespecial} instruction were being linked.
1208 * <p>
1209 * Before method resolution,
1210 * if the explicitly specified caller class is not identical with the
1211 * lookup class, or if this lookup object does not have
1212 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1213 * privileges, the access fails.
1214 * <p>
1215 * The returned method handle will have
1216 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1217 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1218 * @param m the reflected method
1219 * @param specialCaller the class nominally calling the method
1220 * @return a method handle which can invoke the reflected method
1221 * @throws IllegalAccessException if access checking fails
1222 * or if the method's variable arity modifier bit
1223 * is set and {@code asVarargsCollector} fails
1224 * @throws NullPointerException if any argument is null
1225 */
1226 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
1227 checkSpecialCaller(specialCaller);
1228 Lookup specialLookup = this.in(specialCaller);
1229 MemberName method = new MemberName(m, true);
1230 assert(method.isMethod());
1231 // ignore m.isAccessible: this is a new kind of access
1232 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method));
1233 }
1234
1235 /**
1236 * Produces a method handle for a reflected constructor.
1237 * The type of the method handle will be that of the constructor,
1238 * with the return type changed to the declaring class.
1239 * The method handle will perform a {@code newInstance} operation,
1240 * creating a new instance of the constructor's class on the
1241 * arguments passed to the method handle.
1242 * <p>
1243 * If the constructor's {@code accessible} flag is not set,
1244 * access checking is performed immediately on behalf of the lookup class.
1245 * <p>
1246 * The returned method handle will have
1247 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1248 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1249 * <p>
1250 * If the returned method handle is invoked, the constructor's class will
1251 * be initialized, if it has not already been initialized.
1252 * @param c the reflected constructor
1253 * @return a method handle which can invoke the reflected constructor
1254 * @throws IllegalAccessException if access checking fails
1255 * or if the method's variable arity modifier bit
1256 * is set and {@code asVarargsCollector} fails
1257 * @throws NullPointerException if the argument is null
1258 */
1259 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
1260 MemberName ctor = new MemberName(c);
1261 assert(ctor.isConstructor());
1262 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
1263 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
1264 }
1265
1266 /**
1267 * Produces a method handle giving read access to a reflected field.
1268 * The type of the method handle will have a return type of the field's
1269 * value type.
1270 * If the field is static, the method handle will take no arguments.
1271 * Otherwise, its single argument will be the instance containing
1272 * the field.
1273 * If the field's {@code accessible} flag is not set,
1274 * access checking is performed immediately on behalf of the lookup class.
1275 * <p>
1276 * If the field is static, and
1277 * if the returned method handle is invoked, the field's class will
1278 * be initialized, if it has not already been initialized.
1279 * @param f the reflected field
1280 * @return a method handle which can load values from the reflected field
1281 * @throws IllegalAccessException if access checking fails
1282 * @throws NullPointerException if the argument is null
1283 */
1284 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
1285 return unreflectField(f, false);
1286 }
1287 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
1288 MemberName field = new MemberName(f, isSetter);
1289 assert(isSetter
1290 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
1291 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
1292 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
1293 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
1294 }
1295
1296 /**
1297 * Produces a method handle giving write access to a reflected field.
1298 * The type of the method handle will have a void return type.
1299 * If the field is static, the method handle will take a single
1300 * argument, of the field's value type, the value to be stored.
1301 * Otherwise, the two arguments will be the instance containing
1302 * the field, and the value to be stored.
1303 * If the field's {@code accessible} flag is not set,
1304 * access checking is performed immediately on behalf of the lookup class.
1305 * <p>
1306 * If the field is static, and
1307 * if the returned method handle is invoked, the field's class will
1308 * be initialized, if it has not already been initialized.
1309 * @param f the reflected field
1310 * @return a method handle which can store values into the reflected field
1311 * @throws IllegalAccessException if access checking fails
1312 * @throws NullPointerException if the argument is null
1313 */
1314 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
1315 return unreflectField(f, true);
1316 }
1317
1318 /**
1319 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1320 * created by this lookup object or a similar one.
1321 * Security and access checks are performed to ensure that this lookup object
1322 * is capable of reproducing the target method handle.
1323 * This means that the cracking may fail if target is a direct method handle
1324 * but was created by an unrelated lookup object.
1325 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
1326 * and was created by a lookup object for a different class.
1327 * @param target a direct method handle to crack into symbolic reference components
1328 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
1329 * @exception SecurityException if a security manager is present and it
1330 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1331 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
1332 * @exception NullPointerException if the target is {@code null}
1333 * @see MethodHandleInfo
1334 * @since 1.8
1335 */
1336 public MethodHandleInfo revealDirect(MethodHandle target) {
1337 MemberName member = target.internalMemberName();
1338 if (member == null || (!member.isResolved() && !member.isMethodHandleInvoke()))
1339 throw newIllegalArgumentException("not a direct method handle");
1340 Class<?> defc = member.getDeclaringClass();
1341 byte refKind = member.getReferenceKind();
1342 assert(MethodHandleNatives.refKindIsValid(refKind));
1343 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
1344 // Devirtualized method invocation is usually formally virtual.
1345 // To avoid creating extra MemberName objects for this common case,
1346 // we encode this extra degree of freedom using MH.isInvokeSpecial.
1347 refKind = REF_invokeVirtual;
1348 if (refKind == REF_invokeVirtual && defc.isInterface())
1349 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
1350 refKind = REF_invokeInterface;
1351 // Check SM permissions and member access before cracking.
1352 try {
1353 checkAccess(refKind, defc, member);
1354 checkSecurityManager(defc, member);
1355 } catch (IllegalAccessException ex) {
1356 throw new IllegalArgumentException(ex);
1357 }
1358 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
1359 Class<?> callerClass = target.internalCallerClass();
1360 if (!hasPrivateAccess() || callerClass != lookupClass())
1361 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
1362 }
1363 // Produce the handle to the results.
1364 return new InfoFromMemberName(this, member, refKind);
1365 }
1366
1367 /// Helper methods, all package-private.
1368
1369 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1370 checkSymbolicClass(refc); // do this before attempting to resolve
1371 Objects.requireNonNull(name);
1372 Objects.requireNonNull(type);
1373 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
1374 NoSuchFieldException.class);
1375 }
1376
1377 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1378 checkSymbolicClass(refc); // do this before attempting to resolve
1379 Objects.requireNonNull(name);
1380 Objects.requireNonNull(type);
1381 checkMethodName(refKind, name); // NPE check on name
1382 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
1383 NoSuchMethodException.class);
1384 }
1385
1386 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
1387 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
1388 Objects.requireNonNull(member.getName());
1389 Objects.requireNonNull(member.getType());
1390 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
1391 ReflectiveOperationException.class);
1392 }
1393
1394 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
1395 Objects.requireNonNull(refc);
1396 Class<?> caller = lookupClassOrNull();
1397 if (caller != null && !VerifyAccess.isClassAccessible(refc, caller, allowedModes))
1398 throw new MemberName(refc).makeAccessException("symbolic reference class is not public", this);
1399 }
1400
1401 /** Check name for an illegal leading "<" character. */
1402 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
1403 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
1404 throw new NoSuchMethodException("illegal method name: "+name);
1405 }
1406
1407
1408 /**
1409 * Find my trustable caller class if m is a caller sensitive method.
1410 * If this lookup object has private access, then the caller class is the lookupClass.
1411 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
1412 */
1413 Class<?> findBoundCallerClass(MemberName m) throws IllegalAccessException {
1414 Class<?> callerClass = null;
1415 if (MethodHandleNatives.isCallerSensitive(m)) {
1416 // Only lookups with private access are allowed to resolve caller-sensitive methods
1417 if (hasPrivateAccess()) {
1418 callerClass = lookupClass;
1419 } else {
1420 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
1421 }
1422 }
1423 return callerClass;
1424 }
1425
1426 private boolean hasPrivateAccess() {
1427 return (allowedModes & PRIVATE) != 0;
1428 }
1429
1430 /**
1431 * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
1432 * Determines a trustable caller class to compare with refc, the symbolic reference class.
1433 * If this lookup object has private access, then the caller class is the lookupClass.
1434 */
1435 void checkSecurityManager(Class<?> refc, MemberName m) {
1436 SecurityManager smgr = System.getSecurityManager();
1437 if (smgr == null) return;
1438 if (allowedModes == TRUSTED) return;
1439
1440 // Step 1:
1441 boolean fullPowerLookup = hasPrivateAccess();
1442 if (!fullPowerLookup ||
1443 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
1444 ReflectUtil.checkPackageAccess(refc);
1445 }
1446
1447 // Step 2:
1448 if (m.isPublic()) return;
1449 if (!fullPowerLookup) {
1450 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
1451 }
1452
1453 // Step 3:
1454 Class<?> defc = m.getDeclaringClass();
1455 if (!fullPowerLookup && defc != refc) {
1456 ReflectUtil.checkPackageAccess(defc);
1457 }
1458 }
1459
1460 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1461 boolean wantStatic = (refKind == REF_invokeStatic);
1462 String message;
1463 if (m.isConstructor())
1464 message = "expected a method, not a constructor";
1465 else if (!m.isMethod())
1466 message = "expected a method";
1467 else if (wantStatic != m.isStatic())
1468 message = wantStatic ? "expected a static method" : "expected a non-static method";
1469 else
1470 { checkAccess(refKind, refc, m); return; }
1471 throw m.makeAccessException(message, this);
1472 }
1473
1474 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1475 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
1476 String message;
1477 if (wantStatic != m.isStatic())
1478 message = wantStatic ? "expected a static field" : "expected a non-static field";
1479 else
1480 { checkAccess(refKind, refc, m); return; }
1481 throw m.makeAccessException(message, this);
1482 }
1483
1484 /** Check public/protected/private bits on the symbolic reference class and its member. */
1485 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1486 assert(m.referenceKindIsConsistentWith(refKind) &&
1487 MethodHandleNatives.refKindIsValid(refKind) &&
1488 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
1489 int allowedModes = this.allowedModes;
1490 if (allowedModes == TRUSTED) return;
1491 int mods = m.getModifiers();
1492 if (Modifier.isProtected(mods) &&
1493 refKind == REF_invokeVirtual &&
1494 m.getDeclaringClass() == Object.class &&
1495 m.getName().equals("clone") &&
1496 refc.isArray()) {
1497 // The JVM does this hack also.
1498 // (See ClassVerifier::verify_invoke_instructions
1499 // and LinkResolver::check_method_accessability.)
1500 // Because the JVM does not allow separate methods on array types,
1501 // there is no separate method for int[].clone.
1502 // All arrays simply inherit Object.clone.
1503 // But for access checking logic, we make Object.clone
1504 // (normally protected) appear to be public.
1505 // Later on, when the DirectMethodHandle is created,
1506 // its leading argument will be restricted to the
1507 // requested array type.
1508 // N.B. The return type is not adjusted, because
1509 // that is *not* the bytecode behavior.
1510 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
1511 }
1512 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
1513 // cannot "new" a protected ctor in a different package
1514 mods ^= Modifier.PROTECTED;
1515 }
1516 if (Modifier.isFinal(mods) &&
1517 MethodHandleNatives.refKindIsSetter(refKind))
1518 throw m.makeAccessException("unexpected set of a final field", this);
1519 if (Modifier.isPublic(mods) && Modifier.isPublic(refc.getModifiers()) && allowedModes != 0)
1520 return; // common case
1521 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
1522 if ((requestedModes & allowedModes) != 0) {
1523 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
1524 mods, lookupClass(), allowedModes))
1525 return;
1526 } else {
1527 // Protected members can also be checked as if they were package-private.
1528 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
1529 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
1530 return;
1531 }
1532 throw m.makeAccessException(accessFailedMessage(refc, m), this);
1533 }
1534
1535 String accessFailedMessage(Class<?> refc, MemberName m) {
1536 Class<?> defc = m.getDeclaringClass();
1537 int mods = m.getModifiers();
1538 // check the class first:
1539 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
1540 (defc == refc ||
1541 Modifier.isPublic(refc.getModifiers())));
1542 if (!classOK && (allowedModes & PACKAGE) != 0) {
1543 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), ALL_MODES) &&
1544 (defc == refc ||
1545 VerifyAccess.isClassAccessible(refc, lookupClass(), ALL_MODES)));
1546 }
1547 if (!classOK)
1548 return "class is not public";
1549 if (Modifier.isPublic(mods))
1550 return "access to public member failed"; // (how?)
1551 if (Modifier.isPrivate(mods))
1552 return "member is private";
1553 if (Modifier.isProtected(mods))
1554 return "member is protected";
1555 return "member is private to package";
1556 }
1557
1558 private static final boolean ALLOW_NESTMATE_ACCESS = false;
1559
1560 private void checkSpecialCaller(Class<?> specialCaller) throws IllegalAccessException {
1561 int allowedModes = this.allowedModes;
1562 if (allowedModes == TRUSTED) return;
1563 if (!hasPrivateAccess()
1564 || (specialCaller != lookupClass()
1565 && !(ALLOW_NESTMATE_ACCESS &&
1566 VerifyAccess.isSamePackageMember(specialCaller, lookupClass()))))
1567 throw new MemberName(specialCaller).
1568 makeAccessException("no private access for invokespecial", this);
1569 }
1570
1571 private boolean restrictProtectedReceiver(MemberName method) {
1572 // The accessing class only has the right to use a protected member
1573 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
1574 if (!method.isProtected() || method.isStatic()
1575 || allowedModes == TRUSTED
1576 || method.getDeclaringClass() == lookupClass()
1577 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass())
1578 || (ALLOW_NESTMATE_ACCESS &&
1579 VerifyAccess.isSamePackageMember(method.getDeclaringClass(), lookupClass())))
1580 return false;
1581 return true;
1582 }
1583 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
1584 assert(!method.isStatic());
1585 // receiver type of mh is too wide; narrow to caller
1586 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
1587 throw method.makeAccessException("caller class must be a subclass below the method", caller);
1588 }
1589 MethodType rawType = mh.type();
1590 if (rawType.parameterType(0) == caller) return mh;
1591 MethodType narrowType = rawType.changeParameterType(0, caller);
1592 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
1593 assert(mh.viewAsTypeChecks(narrowType, true));
1594 return mh.copyWith(narrowType, mh.form);
1595 }
1596
1597 /** Check access and get the requested method. */
1598 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
1599 final boolean doRestrict = true;
1600 final boolean checkSecurity = true;
1601 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
1602 }
1603 /** Check access and get the requested method, eliding receiver narrowing rules. */
1604 private MethodHandle getDirectMethodNoRestrict(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
1605 final boolean doRestrict = false;
1606 final boolean checkSecurity = true;
1607 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
1608 }
1609 /** Check access and get the requested method, eliding security manager checks. */
1610 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
1611 final boolean doRestrict = true;
1612 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
1613 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
1614 }
1615 /** Common code for all methods; do not call directly except from immediately above. */
1616 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
1617 boolean checkSecurity,
1618 boolean doRestrict, Class<?> callerClass) throws IllegalAccessException {
1619 checkMethod(refKind, refc, method);
1620 // Optionally check with the security manager; this isn't needed for unreflect* calls.
1621 if (checkSecurity)
1622 checkSecurityManager(refc, method);
1623 assert(!method.isMethodHandleInvoke());
1624
1625 if (refKind == REF_invokeSpecial &&
1626 refc != lookupClass() &&
1627 !refc.isInterface() &&
1628 refc != lookupClass().getSuperclass() &&
1629 refc.isAssignableFrom(lookupClass())) {
1630 assert(!method.getName().equals("<init>")); // not this code path
1631 // Per JVMS 6.5, desc. of invokespecial instruction:
1632 // If the method is in a superclass of the LC,
1633 // and if our original search was above LC.super,
1634 // repeat the search (symbolic lookup) from LC.super
1635 // and continue with the direct superclass of that class,
1636 // and so forth, until a match is found or no further superclasses exist.
1637 // FIXME: MemberName.resolve should handle this instead.
1638 Class<?> refcAsSuper = lookupClass();
1639 MemberName m2;
1640 do {
1641 refcAsSuper = refcAsSuper.getSuperclass();
1642 m2 = new MemberName(refcAsSuper,
1643 method.getName(),
1644 method.getMethodType(),
1645 REF_invokeSpecial);
1646 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull());
1647 } while (m2 == null && // no method is found yet
1648 refc != refcAsSuper); // search up to refc
1649 if (m2 == null) throw new InternalError(method.toString());
1650 method = m2;
1651 refc = refcAsSuper;
1652 // redo basic checks
1653 checkMethod(refKind, refc, method);
1654 }
1655
1656 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method);
1657 MethodHandle mh = dmh;
1658 // Optionally narrow the receiver argument to refc using restrictReceiver.
1659 if (doRestrict &&
1660 (refKind == REF_invokeSpecial ||
1661 (MethodHandleNatives.refKindHasReceiver(refKind) &&
1662 restrictProtectedReceiver(method)))) {
1663 mh = restrictReceiver(method, dmh, lookupClass());
1664 }
1665 mh = maybeBindCaller(method, mh, callerClass);
1666 mh = mh.setVarargs(method);
1667 return mh;
1668 }
1669 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh,
1670 Class<?> callerClass)
1671 throws IllegalAccessException {
1672 if (allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
1673 return mh;
1674 Class<?> hostClass = lookupClass;
1675 if (!hasPrivateAccess()) // caller must have private access
1676 hostClass = callerClass; // callerClass came from a security manager style stack walk
1677 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, hostClass);
1678 // Note: caller will apply varargs after this step happens.
1679 return cbmh;
1680 }
1681 /** Check access and get the requested field. */
1682 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
1683 final boolean checkSecurity = true;
1684 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
1685 }
1686 /** Check access and get the requested field, eliding security manager checks. */
1687 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
1688 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
1689 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
1690 }
1691 /** Common code for all fields; do not call directly except from immediately above. */
1692 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
1693 boolean checkSecurity) throws IllegalAccessException {
1694 checkField(refKind, refc, field);
1695 // Optionally check with the security manager; this isn't needed for unreflect* calls.
1696 if (checkSecurity)
1697 checkSecurityManager(refc, field);
1698 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
1699 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
1700 restrictProtectedReceiver(field));
1701 if (doRestrict)
1702 return restrictReceiver(field, dmh, lookupClass());
1703 return dmh;
1704 }
1705 /** Check access and get the requested constructor. */
1706 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
1707 final boolean checkSecurity = true;
1708 return getDirectConstructorCommon(refc, ctor, checkSecurity);
1709 }
1710 /** Check access and get the requested constructor, eliding security manager checks. */
1711 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
1712 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
1713 return getDirectConstructorCommon(refc, ctor, checkSecurity);
1714 }
1715 /** Common code for all constructors; do not call directly except from immediately above. */
1716 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
1717 boolean checkSecurity) throws IllegalAccessException {
1718 assert(ctor.isConstructor());
1719 checkAccess(REF_newInvokeSpecial, refc, ctor);
1720 // Optionally check with the security manager; this isn't needed for unreflect* calls.
1721 if (checkSecurity)
1722 checkSecurityManager(refc, ctor);
1723 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
1724 return DirectMethodHandle.make(ctor).setVarargs(ctor);
1725 }
1726
1727 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
1728 */
1729 /*non-public*/
1730 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type) throws ReflectiveOperationException {
1731 if (!(type instanceof Class || type instanceof MethodType))
1732 throw new InternalError("unresolved MemberName");
1733 MemberName member = new MemberName(refKind, defc, name, type);
1734 MethodHandle mh = LOOKASIDE_TABLE.get(member);
1735 if (mh != null) {
1736 checkSymbolicClass(defc);
1737 return mh;
1738 }
1739 // Treat MethodHandle.invoke and invokeExact specially.
1740 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
1741 mh = findVirtualForMH(member.getName(), member.getMethodType());
1742 if (mh != null) {
1743 return mh;
1744 }
1745 }
1746 MemberName resolved = resolveOrFail(refKind, member);
1747 mh = getDirectMethodForConstant(refKind, defc, resolved);
1748 if (mh instanceof DirectMethodHandle
1749 && canBeCached(refKind, defc, resolved)) {
1750 MemberName key = mh.internalMemberName();
1751 if (key != null) {
1752 key = key.asNormalOriginal();
1753 }
1754 if (member.equals(key)) { // better safe than sorry
1755 LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh);
1756 }
1757 }
1758 return mh;
1759 }
1760 private
1761 boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
1762 if (refKind == REF_invokeSpecial) {
1763 return false;
1764 }
1765 if (!Modifier.isPublic(defc.getModifiers()) ||
1766 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
1767 !member.isPublic() ||
1768 member.isCallerSensitive()) {
1769 return false;
1770 }
1771 ClassLoader loader = defc.getClassLoader();
1772 if (!sun.misc.VM.isSystemDomainLoader(loader)) {
1773 ClassLoader sysl = ClassLoader.getSystemClassLoader();
1774 boolean found = false;
1775 while (sysl != null) {
1776 if (loader == sysl) { found = true; break; }
1777 sysl = sysl.getParent();
1778 }
1779 if (!found) {
1780 return false;
1781 }
1782 }
1783 try {
1784 MemberName resolved2 = publicLookup().resolveOrFail(refKind,
1785 new MemberName(refKind, defc, member.getName(), member.getType()));
1786 checkSecurityManager(defc, resolved2);
1787 } catch (ReflectiveOperationException | SecurityException ex) {
1788 return false;
1789 }
1790 return true;
1791 }
1792 private
1793 MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
1794 throws ReflectiveOperationException {
1795 if (MethodHandleNatives.refKindIsField(refKind)) {
1796 return getDirectFieldNoSecurityManager(refKind, defc, member);
1797 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
1798 return getDirectMethodNoSecurityManager(refKind, defc, member, lookupClass);
1799 } else if (refKind == REF_newInvokeSpecial) {
1800 return getDirectConstructorNoSecurityManager(defc, member);
1801 }
1802 // oops
1803 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
1804 }
1805
1806 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
1807 }
1808
1809 /**
1810 * Produces a method handle giving read access to elements of an array.
1811 * The type of the method handle will have a return type of the array's
1812 * element type. Its first argument will be the array type,
1813 * and the second will be {@code int}.
1814 * @param arrayClass an array type
1815 * @return a method handle which can load values from the given array type
1816 * @throws NullPointerException if the argument is null
1817 * @throws IllegalArgumentException if arrayClass is not an array type
1818 */
1819 public static
1820 MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
1821 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, false);
1822 }
1823
1824 /**
1825 * Produces a method handle giving write access to elements of an array.
1826 * The type of the method handle will have a void return type.
1827 * Its last argument will be the array's element type.
1828 * The first and second arguments will be the array type and int.
1829 * @param arrayClass the class of an array
1830 * @return a method handle which can store values into the array type
1831 * @throws NullPointerException if the argument is null
1832 * @throws IllegalArgumentException if arrayClass is not an array type
1833 */
1834 public static
1835 MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
1836 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, true);
1837 }
1838
1839 /// method handle invocation (reflective style)
1840
1841 /**
1842 * Produces a method handle which will invoke any method handle of the
1843 * given {@code type}, with a given number of trailing arguments replaced by
1844 * a single trailing {@code Object[]} array.
1845 * The resulting invoker will be a method handle with the following
1846 * arguments:
1847 * <ul>
1848 * <li>a single {@code MethodHandle} target
1849 * <li>zero or more leading values (counted by {@code leadingArgCount})
1850 * <li>an {@code Object[]} array containing trailing arguments
1851 * </ul>
1852 * <p>
1853 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
1854 * the indicated {@code type}.
1855 * That is, if the target is exactly of the given {@code type}, it will behave
1856 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
1857 * is used to convert the target to the required {@code type}.
1858 * <p>
1859 * The type of the returned invoker will not be the given {@code type}, but rather
1860 * will have all parameters except the first {@code leadingArgCount}
1861 * replaced by a single array of type {@code Object[]}, which will be
1862 * the final parameter.
1863 * <p>
1864 * Before invoking its target, the invoker will spread the final array, apply
1865 * reference casts as necessary, and unbox and widen primitive arguments.
1866 * If, when the invoker is called, the supplied array argument does
1867 * not have the correct number of elements, the invoker will throw
1868 * an {@link IllegalArgumentException} instead of invoking the target.
1869 * <p>
1870 * This method is equivalent to the following code (though it may be more efficient):
1871 * <blockquote><pre>{@code
1872 MethodHandle invoker = MethodHandles.invoker(type);
1873 int spreadArgCount = type.parameterCount() - leadingArgCount;
1874 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
1875 return invoker;
1876 * }</pre></blockquote>
1877 * This method throws no reflective or security exceptions.
1878 * @param type the desired target type
1879 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
1880 * @return a method handle suitable for invoking any method handle of the given type
1881 * @throws NullPointerException if {@code type} is null
1882 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
1883 * the range from 0 to {@code type.parameterCount()} inclusive,
1884 * or if the resulting method handle's type would have
1885 * <a href="MethodHandle.html#maxarity">too many parameters</a>
1886 */
1887 public static
1888 MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
1889 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
1890 throw newIllegalArgumentException("bad argument count", leadingArgCount);
1891 type = type.asSpreaderType(Object[].class, type.parameterCount() - leadingArgCount);
1892 return type.invokers().spreadInvoker(leadingArgCount);
1893 }
1894
1895 /**
1896 * Produces a special <em>invoker method handle</em> which can be used to
1897 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
1898 * The resulting invoker will have a type which is
1899 * exactly equal to the desired type, except that it will accept
1900 * an additional leading argument of type {@code MethodHandle}.
1901 * <p>
1902 * This method is equivalent to the following code (though it may be more efficient):
1903 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
1904 *
1905 * <p style="font-size:smaller;">
1906 * <em>Discussion:</em>
1907 * Invoker method handles can be useful when working with variable method handles
1908 * of unknown types.
1909 * For example, to emulate an {@code invokeExact} call to a variable method
1910 * handle {@code M}, extract its type {@code T},
1911 * look up the invoker method {@code X} for {@code T},
1912 * and call the invoker method, as {@code X.invoke(T, A...)}.
1913 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
1914 * is unknown.)
1915 * If spreading, collecting, or other argument transformations are required,
1916 * they can be applied once to the invoker {@code X} and reused on many {@code M}
1917 * method handle values, as long as they are compatible with the type of {@code X}.
1918 * <p style="font-size:smaller;">
1919 * <em>(Note: The invoker method is not available via the Core Reflection API.
1920 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
1921 * on the declared {@code invokeExact} or {@code invoke} method will raise an
1922 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
1923 * <p>
1924 * This method throws no reflective or security exceptions.
1925 * @param type the desired target type
1926 * @return a method handle suitable for invoking any method handle of the given type
1927 * @throws IllegalArgumentException if the resulting method handle's type would have
1928 * <a href="MethodHandle.html#maxarity">too many parameters</a>
1929 */
1930 public static
1931 MethodHandle exactInvoker(MethodType type) {
1932 return type.invokers().exactInvoker();
1933 }
1934
1935 /**
1936 * Produces a special <em>invoker method handle</em> which can be used to
1937 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
1938 * The resulting invoker will have a type which is
1939 * exactly equal to the desired type, except that it will accept
1940 * an additional leading argument of type {@code MethodHandle}.
1941 * <p>
1942 * Before invoking its target, if the target differs from the expected type,
1943 * the invoker will apply reference casts as
1944 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
1945 * Similarly, the return value will be converted as necessary.
1946 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
1947 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
1948 * <p>
1949 * This method is equivalent to the following code (though it may be more efficient):
1950 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
1951 * <p style="font-size:smaller;">
1952 * <em>Discussion:</em>
1953 * A {@linkplain MethodType#genericMethodType general method type} is one which
1954 * mentions only {@code Object} arguments and return values.
1955 * An invoker for such a type is capable of calling any method handle
1956 * of the same arity as the general type.
1957 * <p style="font-size:smaller;">
1958 * <em>(Note: The invoker method is not available via the Core Reflection API.
1959 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
1960 * on the declared {@code invokeExact} or {@code invoke} method will raise an
1961 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
1962 * <p>
1963 * This method throws no reflective or security exceptions.
1964 * @param type the desired target type
1965 * @return a method handle suitable for invoking any method handle convertible to the given type
1966 * @throws IllegalArgumentException if the resulting method handle's type would have
1967 * <a href="MethodHandle.html#maxarity">too many parameters</a>
1968 */
1969 public static
1970 MethodHandle invoker(MethodType type) {
1971 return type.invokers().genericInvoker();
1972 }
1973
1974 static /*non-public*/
1975 MethodHandle basicInvoker(MethodType type) {
1976 return type.invokers().basicInvoker();
1977 }
1978
1979 /// method handle modification (creation from other method handles)
1980
1981 /**
1982 * Produces a method handle which adapts the type of the
1983 * given method handle to a new type by pairwise argument and return type conversion.
1984 * The original type and new type must have the same number of arguments.
1985 * The resulting method handle is guaranteed to report a type
1986 * which is equal to the desired new type.
1987 * <p>
1988 * If the original type and new type are equal, returns target.
1989 * <p>
1990 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
1991 * and some additional conversions are also applied if those conversions fail.
1992 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
1993 * if possible, before or instead of any conversions done by {@code asType}:
1994 * <ul>
1995 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
1996 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
1997 * (This treatment of interfaces follows the usage of the bytecode verifier.)
1998 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
1999 * the boolean is converted to a byte value, 1 for true, 0 for false.
2000 * (This treatment follows the usage of the bytecode verifier.)
2001 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
2002 * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
2003 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
2004 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
2005 * then a Java casting conversion (JLS 5.5) is applied.
2006 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
2007 * widening and/or narrowing.)
2008 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
2009 * conversion will be applied at runtime, possibly followed
2010 * by a Java casting conversion (JLS 5.5) on the primitive value,
2011 * possibly followed by a conversion from byte to boolean by testing
2012 * the low-order bit.
2013 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
2014 * and if the reference is null at runtime, a zero value is introduced.
2015 * </ul>
2016 * @param target the method handle to invoke after arguments are retyped
2017 * @param newType the expected type of the new method handle
2018 * @return a method handle which delegates to the target after performing
2019 * any necessary argument conversions, and arranges for any
2020 * necessary return value conversions
2021 * @throws NullPointerException if either argument is null
2022 * @throws WrongMethodTypeException if the conversion cannot be made
2023 * @see MethodHandle#asType
2024 */
2025 public static
2026 MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
2027 explicitCastArgumentsChecks(target, newType);
2028 // use the asTypeCache when possible:
2029 MethodType oldType = target.type();
2030 if (oldType == newType) return target;
2031 if (oldType.explicitCastEquivalentToAsType(newType)) {
2032 return target.asFixedArity().asType(newType);
2033 }
2034 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
2035 }
2036
2037 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
2038 if (target.type().parameterCount() != newType.parameterCount()) {
2039 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
2040 }
2041 }
2042
2043 /**
2044 * Produces a method handle which adapts the calling sequence of the
2045 * given method handle to a new type, by reordering the arguments.
2046 * The resulting method handle is guaranteed to report a type
2047 * which is equal to the desired new type.
2048 * <p>
2049 * The given array controls the reordering.
2050 * Call {@code #I} the number of incoming parameters (the value
2051 * {@code newType.parameterCount()}, and call {@code #O} the number
2052 * of outgoing parameters (the value {@code target.type().parameterCount()}).
2053 * Then the length of the reordering array must be {@code #O},
2054 * and each element must be a non-negative number less than {@code #I}.
2055 * For every {@code N} less than {@code #O}, the {@code N}-th
2056 * outgoing argument will be taken from the {@code I}-th incoming
2057 * argument, where {@code I} is {@code reorder[N]}.
2058 * <p>
2059 * No argument or return value conversions are applied.
2060 * The type of each incoming argument, as determined by {@code newType},
2061 * must be identical to the type of the corresponding outgoing parameter
2062 * or parameters in the target method handle.
2063 * The return type of {@code newType} must be identical to the return
2064 * type of the original target.
2065 * <p>
2066 * The reordering array need not specify an actual permutation.
2067 * An incoming argument will be duplicated if its index appears
2068 * more than once in the array, and an incoming argument will be dropped
2069 * if its index does not appear in the array.
2070 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
2071 * incoming arguments which are not mentioned in the reordering array
2072 * are may be any type, as determined only by {@code newType}.
2073 * <blockquote><pre>{@code
2074 import static java.lang.invoke.MethodHandles.*;
2075 import static java.lang.invoke.MethodType.*;
2076 ...
2077 MethodType intfn1 = methodType(int.class, int.class);
2078 MethodType intfn2 = methodType(int.class, int.class, int.class);
2079 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
2080 assert(sub.type().equals(intfn2));
2081 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
2082 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
2083 assert((int)rsub.invokeExact(1, 100) == 99);
2084 MethodHandle add = ... (int x, int y) -> (x+y) ...;
2085 assert(add.type().equals(intfn2));
2086 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
2087 assert(twice.type().equals(intfn1));
2088 assert((int)twice.invokeExact(21) == 42);
2089 * }</pre></blockquote>
2090 * @param target the method handle to invoke after arguments are reordered
2091 * @param newType the expected type of the new method handle
2092 * @param reorder an index array which controls the reordering
2093 * @return a method handle which delegates to the target after it
2094 * drops unused arguments and moves and/or duplicates the other arguments
2095 * @throws NullPointerException if any argument is null
2096 * @throws IllegalArgumentException if the index array length is not equal to
2097 * the arity of the target, or if any index array element
2098 * not a valid index for a parameter of {@code newType},
2099 * or if two corresponding parameter types in
2100 * {@code target.type()} and {@code newType} are not identical,
2101 */
2102 public static
2103 MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
2104 reorder = reorder.clone(); // get a private copy
2105 MethodType oldType = target.type();
2106 permuteArgumentChecks(reorder, newType, oldType);
2107 // first detect dropped arguments and handle them separately
2108 int[] originalReorder = reorder;
2109 BoundMethodHandle result = target.rebind();
2110 LambdaForm form = result.form;
2111 int newArity = newType.parameterCount();
2112 // Normalize the reordering into a real permutation,
2113 // by removing duplicates and adding dropped elements.
2114 // This somewhat improves lambda form caching, as well
2115 // as simplifying the transform by breaking it up into steps.
2116 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
2117 if (ddIdx > 0) {
2118 // We found a duplicated entry at reorder[ddIdx].
2119 // Example: (x,y,z)->asList(x,y,z)
2120 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
2121 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
2122 // The starred element corresponds to the argument
2123 // deleted by the dupArgumentForm transform.
2124 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
2125 boolean killFirst = false;
2126 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
2127 // Set killFirst if the dup is larger than an intervening position.
2128 // This will remove at least one inversion from the permutation.
2129 if (dupVal > val) killFirst = true;
2130 }
2131 if (!killFirst) {
2132 srcPos = dstPos;
2133 dstPos = ddIdx;
2134 }
2135 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
2136 assert (reorder[srcPos] == reorder[dstPos]);
2137 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
2138 // contract the reordering by removing the element at dstPos
2139 int tailPos = dstPos + 1;
2140 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
2141 reorder = Arrays.copyOf(reorder, reorder.length - 1);
2142 } else {
2143 int dropVal = ~ddIdx, insPos = 0;
2144 while (insPos < reorder.length && reorder[insPos] < dropVal) {
2145 // Find first element of reorder larger than dropVal.
2146 // This is where we will insert the dropVal.
2147 insPos += 1;
2148 }
2149 Class<?> ptype = newType.parameterType(dropVal);
2150 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
2151 oldType = oldType.insertParameterTypes(insPos, ptype);
2152 // expand the reordering by inserting an element at insPos
2153 int tailPos = insPos + 1;
2154 reorder = Arrays.copyOf(reorder, reorder.length + 1);
2155 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
2156 reorder[insPos] = dropVal;
2157 }
2158 assert (permuteArgumentChecks(reorder, newType, oldType));
2159 }
2160 assert (reorder.length == newArity); // a perfect permutation
2161 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
2162 form = form.editor().permuteArgumentsForm(1, reorder);
2163 if (newType == result.type() && form == result.internalForm())
2164 return result;
2165 return result.copyWith(newType, form);
2166 }
2167
2168 /**
2169 * Return an indication of any duplicate or omission in reorder.
2170 * If the reorder contains a duplicate entry, return the index of the second occurrence.
2171 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
2172 * Otherwise, return zero.
2173 * If an element not in [0..newArity-1] is encountered, return reorder.length.
2174 */
2175 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
2176 final int BIT_LIMIT = 63; // max number of bits in bit mask
2177 if (newArity < BIT_LIMIT) {
2178 long mask = 0;
2179 for (int i = 0; i < reorder.length; i++) {
2180 int arg = reorder[i];
2181 if (arg >= newArity) {
2182 return reorder.length;
2183 }
2184 long bit = 1L << arg;
2185 if ((mask & bit) != 0) {
2186 return i; // >0 indicates a dup
2187 }
2188 mask |= bit;
2189 }
2190 if (mask == (1L << newArity) - 1) {
2191 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
2192 return 0;
2193 }
2194 // find first zero
2195 long zeroBit = Long.lowestOneBit(~mask);
2196 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
2197 assert(zeroPos <= newArity);
2198 if (zeroPos == newArity) {
2199 return 0;
2200 }
2201 return ~zeroPos;
2202 } else {
2203 // same algorithm, different bit set
2204 BitSet mask = new BitSet(newArity);
2205 for (int i = 0; i < reorder.length; i++) {
2206 int arg = reorder[i];
2207 if (arg >= newArity) {
2208 return reorder.length;
2209 }
2210 if (mask.get(arg)) {
2211 return i; // >0 indicates a dup
2212 }
2213 mask.set(arg);
2214 }
2215 int zeroPos = mask.nextClearBit(0);
2216 assert(zeroPos <= newArity);
2217 if (zeroPos == newArity) {
2218 return 0;
2219 }
2220 return ~zeroPos;
2221 }
2222 }
2223
2224 private static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
2225 if (newType.returnType() != oldType.returnType())
2226 throw newIllegalArgumentException("return types do not match",
2227 oldType, newType);
2228 if (reorder.length == oldType.parameterCount()) {
2229 int limit = newType.parameterCount();
2230 boolean bad = false;
2231 for (int j = 0; j < reorder.length; j++) {
2232 int i = reorder[j];
2233 if (i < 0 || i >= limit) {
2234 bad = true; break;
2235 }
2236 Class<?> src = newType.parameterType(i);
2237 Class<?> dst = oldType.parameterType(j);
2238 if (src != dst)
2239 throw newIllegalArgumentException("parameter types do not match after reorder",
2240 oldType, newType);
2241 }
2242 if (!bad) return true;
2243 }
2244 throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
2245 }
2246
2247 /**
2248 * Produces a method handle of the requested return type which returns the given
2249 * constant value every time it is invoked.
2250 * <p>
2251 * Before the method handle is returned, the passed-in value is converted to the requested type.
2252 * If the requested type is primitive, widening primitive conversions are attempted,
2253 * else reference conversions are attempted.
2254 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
2255 * @param type the return type of the desired method handle
2256 * @param value the value to return
2257 * @return a method handle of the given return type and no arguments, which always returns the given value
2258 * @throws NullPointerException if the {@code type} argument is null
2259 * @throws ClassCastException if the value cannot be converted to the required return type
2260 * @throws IllegalArgumentException if the given type is {@code void.class}
2261 */
2262 public static
2263 MethodHandle constant(Class<?> type, Object value) {
2264 if (type.isPrimitive()) {
2265 if (type == void.class)
2266 throw newIllegalArgumentException("void type");
2267 Wrapper w = Wrapper.forPrimitiveType(type);
2268 value = w.convert(value, type);
2269 if (w.zero().equals(value))
2270 return zero(w, type);
2271 return insertArguments(identity(type), 0, value);
2272 } else {
2273 if (value == null)
2274 return zero(Wrapper.OBJECT, type);
2275 return identity(type).bindTo(value);
2276 }
2277 }
2278
2279 /**
2280 * Produces a method handle which returns its sole argument when invoked.
2281 * @param type the type of the sole parameter and return value of the desired method handle
2282 * @return a unary method handle which accepts and returns the given type
2283 * @throws NullPointerException if the argument is null
2284 * @throws IllegalArgumentException if the given type is {@code void.class}
2285 */
2286 public static
2287 MethodHandle identity(Class<?> type) {
2288 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
2289 int pos = btw.ordinal();
2290 MethodHandle ident = IDENTITY_MHS[pos];
2291 if (ident == null) {
2292 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
2293 }
2294 if (ident.type().returnType() == type)
2295 return ident;
2296 // something like identity(Foo.class); do not bother to intern these
2297 assert(btw == Wrapper.OBJECT);
2298 return makeIdentity(type);
2299 }
2300 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.values().length];
2301 private static MethodHandle makeIdentity(Class<?> ptype) {
2302 MethodType mtype = MethodType.methodType(ptype, ptype);
2303 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
2304 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
2305 }
2306
2307 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
2308 int pos = btw.ordinal();
2309 MethodHandle zero = ZERO_MHS[pos];
2310 if (zero == null) {
2311 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
2312 }
2313 if (zero.type().returnType() == rtype)
2314 return zero;
2315 assert(btw == Wrapper.OBJECT);
2316 return makeZero(rtype);
2317 }
2318 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.values().length];
2319 private static MethodHandle makeZero(Class<?> rtype) {
2320 MethodType mtype = MethodType.methodType(rtype);
2321 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
2322 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
2323 }
2324
2325 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
2326 // Simulate a CAS, to avoid racy duplication of results.
2327 MethodHandle prev = cache[pos];
2328 if (prev != null) return prev;
2329 return cache[pos] = value;
2330 }
2331
2332 /**
2333 * Provides a target method handle with one or more <em>bound arguments</em>
2334 * in advance of the method handle's invocation.
2335 * The formal parameters to the target corresponding to the bound
2336 * arguments are called <em>bound parameters</em>.
2337 * Returns a new method handle which saves away the bound arguments.
2338 * When it is invoked, it receives arguments for any non-bound parameters,
2339 * binds the saved arguments to their corresponding parameters,
2340 * and calls the original target.
2341 * <p>
2342 * The type of the new method handle will drop the types for the bound
2343 * parameters from the original target type, since the new method handle
2344 * will no longer require those arguments to be supplied by its callers.
2345 * <p>
2346 * Each given argument object must match the corresponding bound parameter type.
2347 * If a bound parameter type is a primitive, the argument object
2348 * must be a wrapper, and will be unboxed to produce the primitive value.
2349 * <p>
2350 * The {@code pos} argument selects which parameters are to be bound.
2351 * It may range between zero and <i>N-L</i> (inclusively),
2352 * where <i>N</i> is the arity of the target method handle
2353 * and <i>L</i> is the length of the values array.
2354 * @param target the method handle to invoke after the argument is inserted
2355 * @param pos where to insert the argument (zero for the first)
2356 * @param values the series of arguments to insert
2357 * @return a method handle which inserts an additional argument,
2358 * before calling the original method handle
2359 * @throws NullPointerException if the target or the {@code values} array is null
2360 * @see MethodHandle#bindTo
2361 */
2362 public static
2363 MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
2364 int insCount = values.length;
2365 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
2366 if (insCount == 0) return target;
2367 BoundMethodHandle result = target.rebind();
2368 for (int i = 0; i < insCount; i++) {
2369 Object value = values[i];
2370 Class<?> ptype = ptypes[pos+i];
2371 if (ptype.isPrimitive()) {
2372 result = insertArgumentPrimitive(result, pos, ptype, value);
2373 } else {
2374 value = ptype.cast(value); // throw CCE if needed
2375 result = result.bindArgumentL(pos, value);
2376 }
2377 }
2378 return result;
2379 }
2380
2381 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
2382 Class<?> ptype, Object value) {
2383 Wrapper w = Wrapper.forPrimitiveType(ptype);
2384 // perform unboxing and/or primitive conversion
2385 value = w.convert(value, ptype);
2386 switch (w) {
2387 case INT: return result.bindArgumentI(pos, (int)value);
2388 case LONG: return result.bindArgumentJ(pos, (long)value);
2389 case FLOAT: return result.bindArgumentF(pos, (float)value);
2390 case DOUBLE: return result.bindArgumentD(pos, (double)value);
2391 default: return result.bindArgumentI(pos, ValueConversions.widenSubword(value));
2392 }
2393 }
2394
2395 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
2396 MethodType oldType = target.type();
2397 int outargs = oldType.parameterCount();
2398 int inargs = outargs - insCount;
2399 if (inargs < 0)
2400 throw newIllegalArgumentException("too many values to insert");
2401 if (pos < 0 || pos > inargs)
2402 throw newIllegalArgumentException("no argument type to append");
2403 return oldType.ptypes();
2404 }
2405
2406 /**
2407 * Produces a method handle which will discard some dummy arguments
2408 * before calling some other specified <i>target</i> method handle.
2409 * The type of the new method handle will be the same as the target's type,
2410 * except it will also include the dummy argument types,
2411 * at some given position.
2412 * <p>
2413 * The {@code pos} argument may range between zero and <i>N</i>,
2414 * where <i>N</i> is the arity of the target.
2415 * If {@code pos} is zero, the dummy arguments will precede
2416 * the target's real arguments; if {@code pos} is <i>N</i>
2417 * they will come after.
2418 * <p>
2419 * <b>Example:</b>
2420 * <blockquote><pre>{@code
2421 import static java.lang.invoke.MethodHandles.*;
2422 import static java.lang.invoke.MethodType.*;
2423 ...
2424 MethodHandle cat = lookup().findVirtual(String.class,
2425 "concat", methodType(String.class, String.class));
2426 assertEquals("xy", (String) cat.invokeExact("x", "y"));
2427 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
2428 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
2429 assertEquals(bigType, d0.type());
2430 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
2431 * }</pre></blockquote>
2432 * <p>
2433 * This method is also equivalent to the following code:
2434 * <blockquote><pre>
2435 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
2436 * </pre></blockquote>
2437 * @param target the method handle to invoke after the arguments are dropped
2438 * @param valueTypes the type(s) of the argument(s) to drop
2439 * @param pos position of first argument to drop (zero for the leftmost)
2440 * @return a method handle which drops arguments of the given types,
2441 * before calling the original method handle
2442 * @throws NullPointerException if the target is null,
2443 * or if the {@code valueTypes} list or any of its elements is null
2444 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
2445 * or if {@code pos} is negative or greater than the arity of the target,
2446 * or if the new method handle's type would have too many parameters
2447 */
2448 public static
2449 MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
2450 MethodType oldType = target.type(); // get NPE
2451 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
2452 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
2453 if (dropped == 0) return target;
2454 BoundMethodHandle result = target.rebind();
2455 LambdaForm lform = result.form;
2456 int insertFormArg = 1 + pos;
2457 for (Class<?> ptype : valueTypes) {
2458 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
2459 }
2460 result = result.copyWith(newType, lform);
2461 return result;
2462 }
2463
2464 private static int dropArgumentChecks(MethodType oldType, int pos, List<Class<?>> valueTypes) {
2465 int dropped = valueTypes.size();
2466 MethodType.checkSlotCount(dropped);
2467 int outargs = oldType.parameterCount();
2468 int inargs = outargs + dropped;
2469 if (pos < 0 || pos > outargs)
2470 throw newIllegalArgumentException("no argument type to remove"
2471 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
2472 );
2473 return dropped;
2474 }
2475
2476 /**
2477 * Produces a method handle which will discard some dummy arguments
2478 * before calling some other specified <i>target</i> method handle.
2479 * The type of the new method handle will be the same as the target's type,
2480 * except it will also include the dummy argument types,
2481 * at some given position.
2482 * <p>
2483 * The {@code pos} argument may range between zero and <i>N</i>,
2484 * where <i>N</i> is the arity of the target.
2485 * If {@code pos} is zero, the dummy arguments will precede
2486 * the target's real arguments; if {@code pos} is <i>N</i>
2487 * they will come after.
2488 * <p>
2489 * <b>Example:</b>
2490 * <blockquote><pre>{@code
2491 import static java.lang.invoke.MethodHandles.*;
2492 import static java.lang.invoke.MethodType.*;
2493 ...
2494 MethodHandle cat = lookup().findVirtual(String.class,
2495 "concat", methodType(String.class, String.class));
2496 assertEquals("xy", (String) cat.invokeExact("x", "y"));
2497 MethodHandle d0 = dropArguments(cat, 0, String.class);
2498 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
2499 MethodHandle d1 = dropArguments(cat, 1, String.class);
2500 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
2501 MethodHandle d2 = dropArguments(cat, 2, String.class);
2502 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
2503 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
2504 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
2505 * }</pre></blockquote>
2506 * <p>
2507 * This method is also equivalent to the following code:
2508 * <blockquote><pre>
2509 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
2510 * </pre></blockquote>
2511 * @param target the method handle to invoke after the arguments are dropped
2512 * @param valueTypes the type(s) of the argument(s) to drop
2513 * @param pos position of first argument to drop (zero for the leftmost)
2514 * @return a method handle which drops arguments of the given types,
2515 * before calling the original method handle
2516 * @throws NullPointerException if the target is null,
2517 * or if the {@code valueTypes} array or any of its elements is null
2518 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
2519 * or if {@code pos} is negative or greater than the arity of the target,
2520 * or if the new method handle's type would have
2521 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2522 */
2523 public static
2524 MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
2525 return dropArguments(target, pos, Arrays.asList(valueTypes));
2526 }
2527
2528 /**
2529 * Adapts a target method handle by pre-processing
2530 * one or more of its arguments, each with its own unary filter function,
2531 * and then calling the target with each pre-processed argument
2532 * replaced by the result of its corresponding filter function.
2533 * <p>
2534 * The pre-processing is performed by one or more method handles,
2535 * specified in the elements of the {@code filters} array.
2536 * The first element of the filter array corresponds to the {@code pos}
2537 * argument of the target, and so on in sequence.
2538 * <p>
2539 * Null arguments in the array are treated as identity functions,
2540 * and the corresponding arguments left unchanged.
2541 * (If there are no non-null elements in the array, the original target is returned.)
2542 * Each filter is applied to the corresponding argument of the adapter.
2543 * <p>
2544 * If a filter {@code F} applies to the {@code N}th argument of
2545 * the target, then {@code F} must be a method handle which
2546 * takes exactly one argument. The type of {@code F}'s sole argument
2547 * replaces the corresponding argument type of the target
2548 * in the resulting adapted method handle.
2549 * The return type of {@code F} must be identical to the corresponding
2550 * parameter type of the target.
2551 * <p>
2552 * It is an error if there are elements of {@code filters}
2553 * (null or not)
2554 * which do not correspond to argument positions in the target.
2555 * <p><b>Example:</b>
2556 * <blockquote><pre>{@code
2557 import static java.lang.invoke.MethodHandles.*;
2558 import static java.lang.invoke.MethodType.*;
2559 ...
2560 MethodHandle cat = lookup().findVirtual(String.class,
2561 "concat", methodType(String.class, String.class));
2562 MethodHandle upcase = lookup().findVirtual(String.class,
2563 "toUpperCase", methodType(String.class));
2564 assertEquals("xy", (String) cat.invokeExact("x", "y"));
2565 MethodHandle f0 = filterArguments(cat, 0, upcase);
2566 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
2567 MethodHandle f1 = filterArguments(cat, 1, upcase);
2568 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
2569 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
2570 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
2571 * }</pre></blockquote>
2572 * <p> Here is pseudocode for the resulting adapter:
2573 * <blockquote><pre>{@code
2574 * V target(P... p, A[i]... a[i], B... b);
2575 * A[i] filter[i](V[i]);
2576 * T adapter(P... p, V[i]... v[i], B... b) {
2577 * return target(p..., f[i](v[i])..., b...);
2578 * }
2579 * }</pre></blockquote>
2580 *
2581 * @param target the method handle to invoke after arguments are filtered
2582 * @param pos the position of the first argument to filter
2583 * @param filters method handles to call initially on filtered arguments
2584 * @return method handle which incorporates the specified argument filtering logic
2585 * @throws NullPointerException if the target is null
2586 * or if the {@code filters} array is null
2587 * @throws IllegalArgumentException if a non-null element of {@code filters}
2588 * does not match a corresponding argument type of target as described above,
2589 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
2590 * or if the resulting method handle's type would have
2591 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2592 */
2593 public static
2594 MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
2595 filterArgumentsCheckArity(target, pos, filters);
2596 MethodHandle adapter = target;
2597 int curPos = pos-1; // pre-incremented
2598 for (MethodHandle filter : filters) {
2599 curPos += 1;
2600 if (filter == null) continue; // ignore null elements of filters
2601 adapter = filterArgument(adapter, curPos, filter);
2602 }
2603 return adapter;
2604 }
2605
2606 /*non-public*/ static
2607 MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
2608 filterArgumentChecks(target, pos, filter);
2609 MethodType targetType = target.type();
2610 MethodType filterType = filter.type();
2611 BoundMethodHandle result = target.rebind();
2612 Class<?> newParamType = filterType.parameterType(0);
2613 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
2614 MethodType newType = targetType.changeParameterType(pos, newParamType);
2615 result = result.copyWithExtendL(newType, lform, filter);
2616 return result;
2617 }
2618
2619 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
2620 MethodType targetType = target.type();
2621 int maxPos = targetType.parameterCount();
2622 if (pos + filters.length > maxPos)
2623 throw newIllegalArgumentException("too many filters");
2624 }
2625
2626 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
2627 MethodType targetType = target.type();
2628 MethodType filterType = filter.type();
2629 if (filterType.parameterCount() != 1
2630 || filterType.returnType() != targetType.parameterType(pos))
2631 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
2632 }
2633
2634 /**
2635 * Adapts a target method handle by pre-processing
2636 * a sub-sequence of its arguments with a filter (another method handle).
2637 * The pre-processed arguments are replaced by the result (if any) of the
2638 * filter function.
2639 * The target is then called on the modified (usually shortened) argument list.
2640 * <p>
2641 * If the filter returns a value, the target must accept that value as
2642 * its argument in position {@code pos}, preceded and/or followed by
2643 * any arguments not passed to the filter.
2644 * If the filter returns void, the target must accept all arguments
2645 * not passed to the filter.
2646 * No arguments are reordered, and a result returned from the filter
2647 * replaces (in order) the whole subsequence of arguments originally
2648 * passed to the adapter.
2649 * <p>
2650 * The argument types (if any) of the filter
2651 * replace zero or one argument types of the target, at position {@code pos},
2652 * in the resulting adapted method handle.
2653 * The return type of the filter (if any) must be identical to the
2654 * argument type of the target at position {@code pos}, and that target argument
2655 * is supplied by the return value of the filter.
2656 * <p>
2657 * In all cases, {@code pos} must be greater than or equal to zero, and
2658 * {@code pos} must also be less than or equal to the target's arity.
2659 * <p><b>Example:</b>
2660 * <blockquote><pre>{@code
2661 import static java.lang.invoke.MethodHandles.*;
2662 import static java.lang.invoke.MethodType.*;
2663 ...
2664 MethodHandle deepToString = publicLookup()
2665 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
2666
2667 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
2668 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
2669
2670 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
2671 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
2672
2673 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
2674 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
2675 assertEquals("[top, [up, down], strange]",
2676 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
2677
2678 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
2679 assertEquals("[top, [up, down], [strange]]",
2680 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
2681
2682 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
2683 assertEquals("[top, [[up, down, strange], charm], bottom]",
2684 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
2685 * }</pre></blockquote>
2686 * <p> Here is pseudocode for the resulting adapter:
2687 * <blockquote><pre>{@code
2688 * T target(A...,V,C...);
2689 * V filter(B...);
2690 * T adapter(A... a,B... b,C... c) {
2691 * V v = filter(b...);
2692 * return target(a...,v,c...);
2693 * }
2694 * // and if the filter has no arguments:
2695 * T target2(A...,V,C...);
2696 * V filter2();
2697 * T adapter2(A... a,C... c) {
2698 * V v = filter2();
2699 * return target2(a...,v,c...);
2700 * }
2701 * // and if the filter has a void return:
2702 * T target3(A...,C...);
2703 * void filter3(B...);
2704 * void adapter3(A... a,B... b,C... c) {
2705 * filter3(b...);
2706 * return target3(a...,c...);
2707 * }
2708 * }</pre></blockquote>
2709 * <p>
2710 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
2711 * one which first "folds" the affected arguments, and then drops them, in separate
2712 * steps as follows:
2713 * <blockquote><pre>{@code
2714 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
2715 * mh = MethodHandles.foldArguments(mh, coll); //step 1
2716 * }</pre></blockquote>
2717 * If the target method handle consumes no arguments besides than the result
2718 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
2719 * is equivalent to {@code filterReturnValue(coll, mh)}.
2720 * If the filter method handle {@code coll} consumes one argument and produces
2721 * a non-void result, then {@code collectArguments(mh, N, coll)}
2722 * is equivalent to {@code filterArguments(mh, N, coll)}.
2723 * Other equivalences are possible but would require argument permutation.
2724 *
2725 * @param target the method handle to invoke after filtering the subsequence of arguments
2726 * @param pos the position of the first adapter argument to pass to the filter,
2727 * and/or the target argument which receives the result of the filter
2728 * @param filter method handle to call on the subsequence of arguments
2729 * @return method handle which incorporates the specified argument subsequence filtering logic
2730 * @throws NullPointerException if either argument is null
2731 * @throws IllegalArgumentException if the return type of {@code filter}
2732 * is non-void and is not the same as the {@code pos} argument of the target,
2733 * or if {@code pos} is not between 0 and the target's arity, inclusive,
2734 * or if the resulting method handle's type would have
2735 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2736 * @see MethodHandles#foldArguments
2737 * @see MethodHandles#filterArguments
2738 * @see MethodHandles#filterReturnValue
2739 */
2740 public static
2741 MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
2742 MethodType newType = collectArgumentsChecks(target, pos, filter);
2743 MethodType collectorType = filter.type();
2744 BoundMethodHandle result = target.rebind();
2745 LambdaForm lform;
2746 if (collectorType.returnType().isArray() && filter.intrinsicName() == Intrinsic.NEW_ARRAY) {
2747 lform = result.editor().collectArgumentArrayForm(1 + pos, filter);
2748 if (lform != null) {
2749 return result.copyWith(newType, lform);
2750 }
2751 }
2752 lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
2753 return result.copyWithExtendL(newType, lform, filter);
2754 }
2755
2756 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
2757 MethodType targetType = target.type();
2758 MethodType filterType = filter.type();
2759 Class<?> rtype = filterType.returnType();
2760 List<Class<?>> filterArgs = filterType.parameterList();
2761 if (rtype == void.class) {
2762 return targetType.insertParameterTypes(pos, filterArgs);
2763 }
2764 if (rtype != targetType.parameterType(pos)) {
2765 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
2766 }
2767 return targetType.dropParameterTypes(pos, pos+1).insertParameterTypes(pos, filterArgs);
2768 }
2769
2770 /**
2771 * Adapts a target method handle by post-processing
2772 * its return value (if any) with a filter (another method handle).
2773 * The result of the filter is returned from the adapter.
2774 * <p>
2775 * If the target returns a value, the filter must accept that value as
2776 * its only argument.
2777 * If the target returns void, the filter must accept no arguments.
2778 * <p>
2779 * The return type of the filter
2780 * replaces the return type of the target
2781 * in the resulting adapted method handle.
2782 * The argument type of the filter (if any) must be identical to the
2783 * return type of the target.
2784 * <p><b>Example:</b>
2785 * <blockquote><pre>{@code
2786 import static java.lang.invoke.MethodHandles.*;
2787 import static java.lang.invoke.MethodType.*;
2788 ...
2789 MethodHandle cat = lookup().findVirtual(String.class,
2790 "concat", methodType(String.class, String.class));
2791 MethodHandle length = lookup().findVirtual(String.class,
2792 "length", methodType(int.class));
2793 System.out.println((String) cat.invokeExact("x", "y")); // xy
2794 MethodHandle f0 = filterReturnValue(cat, length);
2795 System.out.println((int) f0.invokeExact("x", "y")); // 2
2796 * }</pre></blockquote>
2797 * <p> Here is pseudocode for the resulting adapter:
2798 * <blockquote><pre>{@code
2799 * V target(A...);
2800 * T filter(V);
2801 * T adapter(A... a) {
2802 * V v = target(a...);
2803 * return filter(v);
2804 * }
2805 * // and if the target has a void return:
2806 * void target2(A...);
2807 * T filter2();
2808 * T adapter2(A... a) {
2809 * target2(a...);
2810 * return filter2();
2811 * }
2812 * // and if the filter has a void return:
2813 * V target3(A...);
2814 * void filter3(V);
2815 * void adapter3(A... a) {
2816 * V v = target3(a...);
2817 * filter3(v);
2818 * }
2819 * }</pre></blockquote>
2820 * @param target the method handle to invoke before filtering the return value
2821 * @param filter method handle to call on the return value
2822 * @return method handle which incorporates the specified return value filtering logic
2823 * @throws NullPointerException if either argument is null
2824 * @throws IllegalArgumentException if the argument list of {@code filter}
2825 * does not match the return type of target as described above
2826 */
2827 public static
2828 MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
2829 MethodType targetType = target.type();
2830 MethodType filterType = filter.type();
2831 filterReturnValueChecks(targetType, filterType);
2832 BoundMethodHandle result = target.rebind();
2833 BasicType rtype = BasicType.basicType(filterType.returnType());
2834 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
2835 MethodType newType = targetType.changeReturnType(filterType.returnType());
2836 result = result.copyWithExtendL(newType, lform, filter);
2837 return result;
2838 }
2839
2840 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
2841 Class<?> rtype = targetType.returnType();
2842 int filterValues = filterType.parameterCount();
2843 if (filterValues == 0
2844 ? (rtype != void.class)
2845 : (rtype != filterType.parameterType(0)))
2846 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
2847 }
2848
2849 /**
2850 * Adapts a target method handle by pre-processing
2851 * some of its arguments, and then calling the target with
2852 * the result of the pre-processing, inserted into the original
2853 * sequence of arguments.
2854 * <p>
2855 * The pre-processing is performed by {@code combiner}, a second method handle.
2856 * Of the arguments passed to the adapter, the first {@code N} arguments
2857 * are copied to the combiner, which is then called.
2858 * (Here, {@code N} is defined as the parameter count of the combiner.)
2859 * After this, control passes to the target, with any result
2860 * from the combiner inserted before the original {@code N} incoming
2861 * arguments.
2862 * <p>
2863 * If the combiner returns a value, the first parameter type of the target
2864 * must be identical with the return type of the combiner, and the next
2865 * {@code N} parameter types of the target must exactly match the parameters
2866 * of the combiner.
2867 * <p>
2868 * If the combiner has a void return, no result will be inserted,
2869 * and the first {@code N} parameter types of the target
2870 * must exactly match the parameters of the combiner.
2871 * <p>
2872 * The resulting adapter is the same type as the target, except that the
2873 * first parameter type is dropped,
2874 * if it corresponds to the result of the combiner.
2875 * <p>
2876 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
2877 * that either the combiner or the target does not wish to receive.
2878 * If some of the incoming arguments are destined only for the combiner,
2879 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
2880 * arguments will not need to be live on the stack on entry to the
2881 * target.)
2882 * <p><b>Example:</b>
2883 * <blockquote><pre>{@code
2884 import static java.lang.invoke.MethodHandles.*;
2885 import static java.lang.invoke.MethodType.*;
2886 ...
2887 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
2888 "println", methodType(void.class, String.class))
2889 .bindTo(System.out);
2890 MethodHandle cat = lookup().findVirtual(String.class,
2891 "concat", methodType(String.class, String.class));
2892 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
2893 MethodHandle catTrace = foldArguments(cat, trace);
2894 // also prints "boo":
2895 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
2896 * }</pre></blockquote>
2897 * <p> Here is pseudocode for the resulting adapter:
2898 * <blockquote><pre>{@code
2899 * // there are N arguments in A...
2900 * T target(V, A[N]..., B...);
2901 * V combiner(A...);
2902 * T adapter(A... a, B... b) {
2903 * V v = combiner(a...);
2904 * return target(v, a..., b...);
2905 * }
2906 * // and if the combiner has a void return:
2907 * T target2(A[N]..., B...);
2908 * void combiner2(A...);
2909 * T adapter2(A... a, B... b) {
2910 * combiner2(a...);
2911 * return target2(a..., b...);
2912 * }
2913 * }</pre></blockquote>
2914 * @param target the method handle to invoke after arguments are combined
2915 * @param combiner method handle to call initially on the incoming arguments
2916 * @return method handle which incorporates the specified argument folding logic
2917 * @throws NullPointerException if either argument is null
2918 * @throws IllegalArgumentException if {@code combiner}'s return type
2919 * is non-void and not the same as the first argument type of
2920 * the target, or if the initial {@code N} argument types
2921 * of the target
2922 * (skipping one matching the {@code combiner}'s return type)
2923 * are not identical with the argument types of {@code combiner}
2924 */
2925 public static
2926 MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
2927 int foldPos = 0;
2928 MethodType targetType = target.type();
2929 MethodType combinerType = combiner.type();
2930 Class<?> rtype = foldArgumentChecks(foldPos, targetType, combinerType);
2931 BoundMethodHandle result = target.rebind();
2932 boolean dropResult = (rtype == void.class);
2933 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
2934 LambdaForm lform = result.editor().foldArgumentsForm(1 + foldPos, dropResult, combinerType.basicType());
2935 MethodType newType = targetType;
2936 if (!dropResult)
2937 newType = newType.dropParameterTypes(foldPos, foldPos + 1);
2938 result = result.copyWithExtendL(newType, lform, combiner);
2939 return result;
2940 }
2941
2942 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
2943 int foldArgs = combinerType.parameterCount();
2944 Class<?> rtype = combinerType.returnType();
2945 int foldVals = rtype == void.class ? 0 : 1;
2946 int afterInsertPos = foldPos + foldVals;
2947 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
2948 if (ok && !(combinerType.parameterList()
2949 .equals(targetType.parameterList().subList(afterInsertPos,
2950 afterInsertPos + foldArgs))))
2951 ok = false;
2952 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(0))
2953 ok = false;
2954 if (!ok)
2955 throw misMatchedTypes("target and combiner types", targetType, combinerType);
2956 return rtype;
2957 }
2958
2959 /**
2960 * Makes a method handle which adapts a target method handle,
2961 * by guarding it with a test, a boolean-valued method handle.
2962 * If the guard fails, a fallback handle is called instead.
2963 * All three method handles must have the same corresponding
2964 * argument and return types, except that the return type
2965 * of the test must be boolean, and the test is allowed
2966 * to have fewer arguments than the other two method handles.
2967 * <p> Here is pseudocode for the resulting adapter:
2968 * <blockquote><pre>{@code
2969 * boolean test(A...);
2970 * T target(A...,B...);
2971 * T fallback(A...,B...);
2972 * T adapter(A... a,B... b) {
2973 * if (test(a...))
2974 * return target(a..., b...);
2975 * else
2976 * return fallback(a..., b...);
2977 * }
2978 * }</pre></blockquote>
2979 * Note that the test arguments ({@code a...} in the pseudocode) cannot
2980 * be modified by execution of the test, and so are passed unchanged
2981 * from the caller to the target or fallback as appropriate.
2982 * @param test method handle used for test, must return boolean
2983 * @param target method handle to call if test passes
2984 * @param fallback method handle to call if test fails
2985 * @return method handle which incorporates the specified if/then/else logic
2986 * @throws NullPointerException if any argument is null
2987 * @throws IllegalArgumentException if {@code test} does not return boolean,
2988 * or if all three method types do not match (with the return
2989 * type of {@code test} changed to match that of the target).
2990 */
2991 public static
2992 MethodHandle guardWithTest(MethodHandle test,
2993 MethodHandle target,
2994 MethodHandle fallback) {
2995 MethodType gtype = test.type();
2996 MethodType ttype = target.type();
2997 MethodType ftype = fallback.type();
2998 if (!ttype.equals(ftype))
2999 throw misMatchedTypes("target and fallback types", ttype, ftype);
3000 if (gtype.returnType() != boolean.class)
3001 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
3002 List<Class<?>> targs = ttype.parameterList();
3003 List<Class<?>> gargs = gtype.parameterList();
3004 if (!targs.equals(gargs)) {
3005 int gpc = gargs.size(), tpc = targs.size();
3006 if (gpc >= tpc || !targs.subList(0, gpc).equals(gargs))
3007 throw misMatchedTypes("target and test types", ttype, gtype);
3008 test = dropArguments(test, gpc, targs.subList(gpc, tpc));
3009 gtype = test.type();
3010 }
3011 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
3012 }
3013
3014 static RuntimeException misMatchedTypes(String what, MethodType t1, MethodType t2) {
3015 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
3016 }
3017
3018 /**
3019 * Makes a method handle which adapts a target method handle,
3020 * by running it inside an exception handler.
3021 * If the target returns normally, the adapter returns that value.
3022 * If an exception matching the specified type is thrown, the fallback
3023 * handle is called instead on the exception, plus the original arguments.
3024 * <p>
3025 * The target and handler must have the same corresponding
3026 * argument and return types, except that handler may omit trailing arguments
3027 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
3028 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
3029 * <p> Here is pseudocode for the resulting adapter:
3030 * <blockquote><pre>{@code
3031 * T target(A..., B...);
3032 * T handler(ExType, A...);
3033 * T adapter(A... a, B... b) {
3034 * try {
3035 * return target(a..., b...);
3036 * } catch (ExType ex) {
3037 * return handler(ex, a...);
3038 * }
3039 * }
3040 * }</pre></blockquote>
3041 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
3042 * be modified by execution of the target, and so are passed unchanged
3043 * from the caller to the handler, if the handler is invoked.
3044 * <p>
3045 * The target and handler must return the same type, even if the handler
3046 * always throws. (This might happen, for instance, because the handler
3047 * is simulating a {@code finally} clause).
3048 * To create such a throwing handler, compose the handler creation logic
3049 * with {@link #throwException throwException},
3050 * in order to create a method handle of the correct return type.
3051 * @param target method handle to call
3052 * @param exType the type of exception which the handler will catch
3053 * @param handler method handle to call if a matching exception is thrown
3054 * @return method handle which incorporates the specified try/catch logic
3055 * @throws NullPointerException if any argument is null
3056 * @throws IllegalArgumentException if {@code handler} does not accept
3057 * the given exception type, or if the method handle types do
3058 * not match in their return types and their
3059 * corresponding parameters
3060 */
3061 public static
3062 MethodHandle catchException(MethodHandle target,
3063 Class<? extends Throwable> exType,
3064 MethodHandle handler) {
3065 MethodType ttype = target.type();
3066 MethodType htype = handler.type();
3067 if (htype.parameterCount() < 1 ||
3068 !htype.parameterType(0).isAssignableFrom(exType))
3069 throw newIllegalArgumentException("handler does not accept exception type "+exType);
3070 if (htype.returnType() != ttype.returnType())
3071 throw misMatchedTypes("target and handler return types", ttype, htype);
3072 List<Class<?>> targs = ttype.parameterList();
3073 List<Class<?>> hargs = htype.parameterList();
3074 hargs = hargs.subList(1, hargs.size()); // omit leading parameter from handler
3075 if (!targs.equals(hargs)) {
3076 int hpc = hargs.size(), tpc = targs.size();
3077 if (hpc >= tpc || !targs.subList(0, hpc).equals(hargs))
3078 throw misMatchedTypes("target and handler types", ttype, htype);
3079 handler = dropArguments(handler, 1+hpc, targs.subList(hpc, tpc));
3080 htype = handler.type();
3081 }
3082 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
3083 }
3084
3085 /**
3086 * Produces a method handle which will throw exceptions of the given {@code exType}.
3087 * The method handle will accept a single argument of {@code exType},
3088 * and immediately throw it as an exception.
3089 * The method type will nominally specify a return of {@code returnType}.
3090 * The return type may be anything convenient: It doesn't matter to the
3091 * method handle's behavior, since it will never return normally.
3092 * @param returnType the return type of the desired method handle
3093 * @param exType the parameter type of the desired method handle
3094 * @return method handle which can throw the given exceptions
3095 * @throws NullPointerException if either argument is null
3096 */
3097 public static
3098 MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
3099 if (!Throwable.class.isAssignableFrom(exType))
3100 throw new ClassCastException(exType.getName());
3101 return MethodHandleImpl.throwException(MethodType.methodType(returnType, exType));
3102 }
3103 }