1 /*
2 * Copyright (c) 2008, 2016, 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).
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17 * You should have received a copy of the GNU General Public License version
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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
33 import sun.invoke.util.ValueConversions;
34 import sun.invoke.util.VerifyAccess;
35 import sun.invoke.util.Wrapper;
36 import sun.reflect.CallerSensitive;
37 import sun.reflect.Reflection;
38 import sun.reflect.misc.ReflectUtil;
39 import sun.security.util.SecurityConstants;
40 import java.lang.invoke.LambdaForm.BasicType;
41 import static java.lang.invoke.LambdaForm.BasicType.*;
42 import static java.lang.invoke.MethodHandleStatics.*;
43 import static java.lang.invoke.MethodHandleImpl.Intrinsic;
44 import static java.lang.invoke.MethodHandleNatives.Constants.*;
45
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 * <p>
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 static final private 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 requestedLookupClass.getClass(); // null check
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 if (refc.isArray()) {
920 throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
921 }
922 String name = "<init>";
923 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
924 return getDirectConstructor(refc, ctor);
925 }
926
927 /**
928 * Produces an early-bound method handle for a virtual method.
929 * It will bypass checks for overriding methods on the receiver,
930 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
931 * instruction from within the explicitly specified {@code specialCaller}.
932 * The type of the method handle will be that of the method,
933 * with a suitably restricted receiver type prepended.
934 * (The receiver type will be {@code specialCaller} or a subtype.)
935 * The method and all its argument types must be accessible
936 * to the lookup object.
937 * <p>
938 * Before method resolution,
939 * if the explicitly specified caller class is not identical with the
940 * lookup class, or if this lookup object does not have
941 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
942 * privileges, the access fails.
943 * <p>
944 * The returned method handle will have
945 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
946 * the method's variable arity modifier bit ({@code 0x0080}) is set.
947 * <p style="font-size:smaller;">
948 * <em>(Note: JVM internal methods named {@code "<init>"} are not visible to this API,
949 * even though the {@code invokespecial} instruction can refer to them
950 * in special circumstances. Use {@link #findConstructor findConstructor}
951 * to access instance initialization methods in a safe manner.)</em>
952 * <p><b>Example:</b>
953 * <blockquote><pre>{@code
954 import static java.lang.invoke.MethodHandles.*;
955 import static java.lang.invoke.MethodType.*;
956 ...
957 static class Listie extends ArrayList {
958 public String toString() { return "[wee Listie]"; }
959 static Lookup lookup() { return MethodHandles.lookup(); }
960 }
961 ...
962 // no access to constructor via invokeSpecial:
963 MethodHandle MH_newListie = Listie.lookup()
964 .findConstructor(Listie.class, methodType(void.class));
965 Listie l = (Listie) MH_newListie.invokeExact();
966 try { assertEquals("impossible", Listie.lookup().findSpecial(
967 Listie.class, "<init>", methodType(void.class), Listie.class));
968 } catch (NoSuchMethodException ex) { } // OK
969 // access to super and self methods via invokeSpecial:
970 MethodHandle MH_super = Listie.lookup().findSpecial(
971 ArrayList.class, "toString" , methodType(String.class), Listie.class);
972 MethodHandle MH_this = Listie.lookup().findSpecial(
973 Listie.class, "toString" , methodType(String.class), Listie.class);
974 MethodHandle MH_duper = Listie.lookup().findSpecial(
975 Object.class, "toString" , methodType(String.class), Listie.class);
976 assertEquals("[]", (String) MH_super.invokeExact(l));
977 assertEquals(""+l, (String) MH_this.invokeExact(l));
978 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
979 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
980 String.class, "toString", methodType(String.class), Listie.class));
981 } catch (IllegalAccessException ex) { } // OK
982 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
983 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
984 * }</pre></blockquote>
985 *
986 * @param refc the class or interface from which the method is accessed
987 * @param name the name of the method (which must not be "<init>")
988 * @param type the type of the method, with the receiver argument omitted
989 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
990 * @return the desired method handle
991 * @throws NoSuchMethodException if the method does not exist
992 * @throws IllegalAccessException if access checking fails
993 * or if the method's variable arity modifier bit
994 * is set and {@code asVarargsCollector} fails
995 * @exception SecurityException if a security manager is present and it
996 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
997 * @throws NullPointerException if any argument is null
998 */
999 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
1000 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
1001 checkSpecialCaller(specialCaller);
1002 Lookup specialLookup = this.in(specialCaller);
1003 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
1004 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1005 }
1006
1007 /**
1008 * Produces a method handle giving read access to a non-static field.
1009 * The type of the method handle will have a return type of the field's
1010 * value type.
1011 * The method handle's single argument will be the instance containing
1012 * the field.
1013 * Access checking is performed immediately on behalf of the lookup class.
1014 * @param refc the class or interface from which the method is accessed
1015 * @param name the field's name
1016 * @param type the field's type
1017 * @return a method handle which can load values from the field
1018 * @throws NoSuchFieldException if the field does not exist
1019 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1020 * @exception SecurityException if a security manager is present and it
1021 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1022 * @throws NullPointerException if any argument is null
1023 */
1024 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1025 MemberName field = resolveOrFail(REF_getField, refc, name, type);
1026 return getDirectField(REF_getField, refc, field);
1027 }
1028
1029 /**
1030 * Produces a method handle giving write access to a non-static field.
1031 * The type of the method handle will have a void return type.
1032 * The method handle will take two arguments, the instance containing
1033 * the field, and the value to be stored.
1034 * The second argument will be of the field's value type.
1035 * Access checking is performed immediately on behalf of the lookup class.
1036 * @param refc the class or interface from which the method is accessed
1037 * @param name the field's name
1038 * @param type the field's type
1039 * @return a method handle which can store values into the field
1040 * @throws NoSuchFieldException if the field does not exist
1041 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1042 * @exception SecurityException if a security manager is present and it
1043 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1044 * @throws NullPointerException if any argument is null
1045 */
1046 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1047 MemberName field = resolveOrFail(REF_putField, refc, name, type);
1048 return getDirectField(REF_putField, refc, field);
1049 }
1050
1051 /**
1052 * Produces a method handle giving read access to a static field.
1053 * The type of the method handle will have a return type of the field's
1054 * value type.
1055 * The method handle will take no arguments.
1056 * Access checking is performed immediately on behalf of the lookup class.
1057 * <p>
1058 * If the returned method handle is invoked, the field's class will
1059 * be initialized, if it has not already been initialized.
1060 * @param refc the class or interface from which the method is accessed
1061 * @param name the field's name
1062 * @param type the field's type
1063 * @return a method handle which can load values from the field
1064 * @throws NoSuchFieldException if the field does not exist
1065 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1066 * @exception SecurityException if a security manager is present and it
1067 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1068 * @throws NullPointerException if any argument is null
1069 */
1070 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1071 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
1072 return getDirectField(REF_getStatic, refc, field);
1073 }
1074
1075 /**
1076 * Produces a method handle giving write access to a static field.
1077 * The type of the method handle will have a void return type.
1078 * The method handle will take a single
1079 * argument, of the field's value type, the value to be stored.
1080 * Access checking is performed immediately on behalf of the lookup class.
1081 * <p>
1082 * If the returned method handle is invoked, the field's class will
1083 * be initialized, if it has not already been initialized.
1084 * @param refc the class or interface from which the method is accessed
1085 * @param name the field's name
1086 * @param type the field's type
1087 * @return a method handle which can store values into the field
1088 * @throws NoSuchFieldException if the field does not exist
1089 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1090 * @exception SecurityException if a security manager is present and it
1091 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1092 * @throws NullPointerException if any argument is null
1093 */
1094 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1095 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
1096 return getDirectField(REF_putStatic, refc, field);
1097 }
1098
1099 /**
1100 * Produces an early-bound method handle for a non-static method.
1101 * The receiver must have a supertype {@code defc} in which a method
1102 * of the given name and type is accessible to the lookup class.
1103 * The method and all its argument types must be accessible to the lookup object.
1104 * The type of the method handle will be that of the method,
1105 * without any insertion of an additional receiver parameter.
1106 * The given receiver will be bound into the method handle,
1107 * so that every call to the method handle will invoke the
1108 * requested method on the given receiver.
1109 * <p>
1110 * The returned method handle will have
1111 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1112 * the method's variable arity modifier bit ({@code 0x0080}) is set
1113 * <em>and</em> the trailing array argument is not the only argument.
1114 * (If the trailing array argument is the only argument,
1115 * the given receiver value will be bound to it.)
1116 * <p>
1117 * This is equivalent to the following code:
1118 * <blockquote><pre>{@code
1119 import static java.lang.invoke.MethodHandles.*;
1120 import static java.lang.invoke.MethodType.*;
1121 ...
1122 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
1123 MethodHandle mh1 = mh0.bindTo(receiver);
1124 MethodType mt1 = mh1.type();
1125 if (mh0.isVarargsCollector())
1126 mh1 = mh1.asVarargsCollector(mt1.parameterType(mt1.parameterCount()-1));
1127 return mh1;
1128 * }</pre></blockquote>
1129 * where {@code defc} is either {@code receiver.getClass()} or a super
1130 * type of that class, in which the requested method is accessible
1131 * to the lookup class.
1132 * (Note that {@code bindTo} does not preserve variable arity.)
1133 * @param receiver the object from which the method is accessed
1134 * @param name the name of the method
1135 * @param type the type of the method, with the receiver argument omitted
1136 * @return the desired method handle
1137 * @throws NoSuchMethodException if the method does not exist
1138 * @throws IllegalAccessException if access checking fails
1139 * or if the method's variable arity modifier bit
1140 * is set and {@code asVarargsCollector} fails
1141 * @exception SecurityException if a security manager is present and it
1142 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1143 * @throws NullPointerException if any argument is null
1144 * @see MethodHandle#bindTo
1145 * @see #findVirtual
1146 */
1147 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1148 Class<? extends Object> refc = receiver.getClass(); // may get NPE
1149 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
1150 MethodHandle mh = getDirectMethodNoRestrict(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1151 return mh.bindArgumentL(0, receiver).setVarargs(method);
1152 }
1153
1154 /**
1155 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1156 * to <i>m</i>, if the lookup class has permission.
1157 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
1158 * If <i>m</i> is virtual, overriding is respected on every call.
1159 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
1160 * The type of the method handle will be that of the method,
1161 * with the receiver type prepended (but only if it is non-static).
1162 * If the method's {@code accessible} flag is not set,
1163 * access checking is performed immediately on behalf of the lookup class.
1164 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
1165 * <p>
1166 * The returned method handle will have
1167 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1168 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1169 * <p>
1170 * If <i>m</i> is static, and
1171 * if the returned method handle is invoked, the method's class will
1172 * be initialized, if it has not already been initialized.
1173 * @param m the reflected method
1174 * @return a method handle which can invoke the reflected method
1175 * @throws IllegalAccessException if access checking fails
1176 * or if the method's variable arity modifier bit
1177 * is set and {@code asVarargsCollector} fails
1178 * @throws NullPointerException if the argument is null
1179 */
1180 public MethodHandle unreflect(Method m) throws IllegalAccessException {
1181 if (m.getDeclaringClass() == MethodHandle.class) {
1182 MethodHandle mh = unreflectForMH(m);
1183 if (mh != null) return mh;
1184 }
1185 MemberName method = new MemberName(m);
1186 byte refKind = method.getReferenceKind();
1187 if (refKind == REF_invokeSpecial)
1188 refKind = REF_invokeVirtual;
1189 assert(method.isMethod());
1190 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
1191 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method));
1192 }
1193 private MethodHandle unreflectForMH(Method m) {
1194 // these names require special lookups because they throw UnsupportedOperationException
1195 if (MemberName.isMethodHandleInvokeName(m.getName()))
1196 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
1197 return null;
1198 }
1199
1200 /**
1201 * Produces a method handle for a reflected method.
1202 * It will bypass checks for overriding methods on the receiver,
1203 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1204 * instruction from within the explicitly specified {@code specialCaller}.
1205 * The type of the method handle will be that of the method,
1206 * with a suitably restricted receiver type prepended.
1207 * (The receiver type will be {@code specialCaller} or a subtype.)
1208 * If the method's {@code accessible} flag is not set,
1209 * access checking is performed immediately on behalf of the lookup class,
1210 * as if {@code invokespecial} instruction were being linked.
1211 * <p>
1212 * Before method resolution,
1213 * if the explicitly specified caller class is not identical with the
1214 * lookup class, or if this lookup object does not have
1215 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1216 * privileges, the access fails.
1217 * <p>
1218 * The returned method handle will have
1219 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1220 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1221 * @param m the reflected method
1222 * @param specialCaller the class nominally calling the method
1223 * @return a method handle which can invoke the reflected method
1224 * @throws IllegalAccessException if access checking fails
1225 * or if the method's variable arity modifier bit
1226 * is set and {@code asVarargsCollector} fails
1227 * @throws NullPointerException if any argument is null
1228 */
1229 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
1230 checkSpecialCaller(specialCaller);
1231 Lookup specialLookup = this.in(specialCaller);
1232 MemberName method = new MemberName(m, true);
1233 assert(method.isMethod());
1234 // ignore m.isAccessible: this is a new kind of access
1235 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method));
1236 }
1237
1238 /**
1239 * Produces a method handle for a reflected constructor.
1240 * The type of the method handle will be that of the constructor,
1241 * with the return type changed to the declaring class.
1242 * The method handle will perform a {@code newInstance} operation,
1243 * creating a new instance of the constructor's class on the
1244 * arguments passed to the method handle.
1245 * <p>
1246 * If the constructor's {@code accessible} flag is not set,
1247 * access checking is performed immediately on behalf of the lookup class.
1248 * <p>
1249 * The returned method handle will have
1250 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1251 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1252 * <p>
1253 * If the returned method handle is invoked, the constructor's class will
1254 * be initialized, if it has not already been initialized.
1255 * @param c the reflected constructor
1256 * @return a method handle which can invoke the reflected constructor
1257 * @throws IllegalAccessException if access checking fails
1258 * or if the method's variable arity modifier bit
1259 * is set and {@code asVarargsCollector} fails
1260 * @throws NullPointerException if the argument is null
1261 */
1262 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
1263 MemberName ctor = new MemberName(c);
1264 assert(ctor.isConstructor());
1265 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
1266 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
1267 }
1268
1269 /**
1270 * Produces a method handle giving read access to a reflected field.
1271 * The type of the method handle will have a return type of the field's
1272 * value type.
1273 * If the field is static, the method handle will take no arguments.
1274 * Otherwise, its single argument will be the instance containing
1275 * the field.
1276 * If the field's {@code accessible} flag is not set,
1277 * access checking is performed immediately on behalf of the lookup class.
1278 * <p>
1279 * If the field is static, and
1280 * if the returned method handle is invoked, the field's class will
1281 * be initialized, if it has not already been initialized.
1282 * @param f the reflected field
1283 * @return a method handle which can load values from the reflected field
1284 * @throws IllegalAccessException if access checking fails
1285 * @throws NullPointerException if the argument is null
1286 */
1287 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
1288 return unreflectField(f, false);
1289 }
1290 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
1291 MemberName field = new MemberName(f, isSetter);
1292 assert(isSetter
1293 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
1294 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
1295 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
1296 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
1297 }
1298
1299 /**
1300 * Produces a method handle giving write access to a reflected field.
1301 * The type of the method handle will have a void return type.
1302 * If the field is static, the method handle will take a single
1303 * argument, of the field's value type, the value to be stored.
1304 * Otherwise, the two arguments will be the instance containing
1305 * the field, and the value to be stored.
1306 * If the field's {@code accessible} flag is not set,
1307 * access checking is performed immediately on behalf of the lookup class.
1308 * <p>
1309 * If the field is static, and
1310 * if the returned method handle is invoked, the field's class will
1311 * be initialized, if it has not already been initialized.
1312 * @param f the reflected field
1313 * @return a method handle which can store values into the reflected field
1314 * @throws IllegalAccessException if access checking fails
1315 * @throws NullPointerException if the argument is null
1316 */
1317 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
1318 return unreflectField(f, true);
1319 }
1320
1321 /**
1322 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1323 * created by this lookup object or a similar one.
1324 * Security and access checks are performed to ensure that this lookup object
1325 * is capable of reproducing the target method handle.
1326 * This means that the cracking may fail if target is a direct method handle
1327 * but was created by an unrelated lookup object.
1328 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
1329 * and was created by a lookup object for a different class.
1330 * @param target a direct method handle to crack into symbolic reference components
1331 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
1332 * @exception SecurityException if a security manager is present and it
1333 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1334 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
1335 * @exception NullPointerException if the target is {@code null}
1336 * @see MethodHandleInfo
1337 * @since 1.8
1338 */
1339 public MethodHandleInfo revealDirect(MethodHandle target) {
1340 MemberName member = target.internalMemberName();
1341 if (member == null || (!member.isResolved() && !member.isMethodHandleInvoke()))
1342 throw newIllegalArgumentException("not a direct method handle");
1343 Class<?> defc = member.getDeclaringClass();
1344 byte refKind = member.getReferenceKind();
1345 assert(MethodHandleNatives.refKindIsValid(refKind));
1346 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
1347 // Devirtualized method invocation is usually formally virtual.
1348 // To avoid creating extra MemberName objects for this common case,
1349 // we encode this extra degree of freedom using MH.isInvokeSpecial.
1350 refKind = REF_invokeVirtual;
1351 if (refKind == REF_invokeVirtual && defc.isInterface())
1352 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
1353 refKind = REF_invokeInterface;
1354 // Check SM permissions and member access before cracking.
1355 try {
1356 checkAccess(refKind, defc, member);
1357 checkSecurityManager(defc, member);
1358 } catch (IllegalAccessException ex) {
1359 throw new IllegalArgumentException(ex);
1360 }
1361 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
1362 Class<?> callerClass = target.internalCallerClass();
1363 if (!hasPrivateAccess() || callerClass != lookupClass())
1364 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
1365 }
1366 // Produce the handle to the results.
1367 return new InfoFromMemberName(this, member, refKind);
1368 }
1369
1370 /// Helper methods, all package-private.
1371
1372 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1373 checkSymbolicClass(refc); // do this before attempting to resolve
1374 name.getClass(); // NPE
1375 type.getClass(); // NPE
1376 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
1377 NoSuchFieldException.class);
1378 }
1379
1380 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1381 checkSymbolicClass(refc); // do this before attempting to resolve
1382 name.getClass(); // NPE
1383 type.getClass(); // NPE
1384 checkMethodName(refKind, name); // NPE check on name
1385 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
1386 NoSuchMethodException.class);
1387 }
1388
1389 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
1390 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
1391 member.getName().getClass(); // NPE
1392 member.getType().getClass(); // NPE
1393 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
1394 ReflectiveOperationException.class);
1395 }
1396
1397 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
1398 refc.getClass(); // NPE
1399 Class<?> caller = lookupClassOrNull();
1400 if (caller != null && !VerifyAccess.isClassAccessible(refc, caller, allowedModes))
1401 throw new MemberName(refc).makeAccessException("symbolic reference class is not public", this);
1402 }
1403
1404 /** Check name for an illegal leading "<" character. */
1405 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
1406 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
1407 throw new NoSuchMethodException("illegal method name: "+name);
1408 }
1409
1410
1411 /**
1412 * Find my trustable caller class if m is a caller sensitive method.
1413 * If this lookup object has private access, then the caller class is the lookupClass.
1414 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
1415 */
1416 Class<?> findBoundCallerClass(MemberName m) throws IllegalAccessException {
1417 Class<?> callerClass = null;
1418 if (MethodHandleNatives.isCallerSensitive(m)) {
1419 // Only lookups with private access are allowed to resolve caller-sensitive methods
1420 if (hasPrivateAccess()) {
1421 callerClass = lookupClass;
1422 } else {
1423 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
1424 }
1425 }
1426 return callerClass;
1427 }
1428
1429 private boolean hasPrivateAccess() {
1430 return (allowedModes & PRIVATE) != 0;
1431 }
1432
1433 /**
1434 * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
1435 * Determines a trustable caller class to compare with refc, the symbolic reference class.
1436 * If this lookup object has private access, then the caller class is the lookupClass.
1437 */
1438 void checkSecurityManager(Class<?> refc, MemberName m) {
1439 SecurityManager smgr = System.getSecurityManager();
1440 if (smgr == null) return;
1441 if (allowedModes == TRUSTED) return;
1442
1443 // Step 1:
1444 boolean fullPowerLookup = hasPrivateAccess();
1445 if (!fullPowerLookup ||
1446 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
1447 ReflectUtil.checkPackageAccess(refc);
1448 }
1449
1450 // Step 2:
1451 if (m.isPublic()) return;
1452 if (!fullPowerLookup) {
1453 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
1454 }
1455
1456 // Step 3:
1457 Class<?> defc = m.getDeclaringClass();
1458 if (!fullPowerLookup && defc != refc) {
1459 ReflectUtil.checkPackageAccess(defc);
1460 }
1461 }
1462
1463 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1464 boolean wantStatic = (refKind == REF_invokeStatic);
1465 String message;
1466 if (m.isConstructor())
1467 message = "expected a method, not a constructor";
1468 else if (!m.isMethod())
1469 message = "expected a method";
1470 else if (wantStatic != m.isStatic())
1471 message = wantStatic ? "expected a static method" : "expected a non-static method";
1472 else
1473 { checkAccess(refKind, refc, m); return; }
1474 throw m.makeAccessException(message, this);
1475 }
1476
1477 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1478 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
1479 String message;
1480 if (wantStatic != m.isStatic())
1481 message = wantStatic ? "expected a static field" : "expected a non-static field";
1482 else
1483 { checkAccess(refKind, refc, m); return; }
1484 throw m.makeAccessException(message, this);
1485 }
1486
1487 /** Check public/protected/private bits on the symbolic reference class and its member. */
1488 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1489 assert(m.referenceKindIsConsistentWith(refKind) &&
1490 MethodHandleNatives.refKindIsValid(refKind) &&
1491 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
1492 int allowedModes = this.allowedModes;
1493 if (allowedModes == TRUSTED) return;
1494 int mods = m.getModifiers();
1495 if (Modifier.isProtected(mods) &&
1496 refKind == REF_invokeVirtual &&
1497 m.getDeclaringClass() == Object.class &&
1498 m.getName().equals("clone") &&
1499 refc.isArray()) {
1500 // The JVM does this hack also.
1501 // (See ClassVerifier::verify_invoke_instructions
1502 // and LinkResolver::check_method_accessability.)
1503 // Because the JVM does not allow separate methods on array types,
1504 // there is no separate method for int[].clone.
1505 // All arrays simply inherit Object.clone.
1506 // But for access checking logic, we make Object.clone
1507 // (normally protected) appear to be public.
1508 // Later on, when the DirectMethodHandle is created,
1509 // its leading argument will be restricted to the
1510 // requested array type.
1511 // N.B. The return type is not adjusted, because
1512 // that is *not* the bytecode behavior.
1513 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
1514 }
1515 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
1516 // cannot "new" a protected ctor in a different package
1517 mods ^= Modifier.PROTECTED;
1518 }
1519 if (Modifier.isFinal(mods) &&
1520 MethodHandleNatives.refKindIsSetter(refKind))
1521 throw m.makeAccessException("unexpected set of a final field", this);
1522 if (Modifier.isPublic(mods) && Modifier.isPublic(refc.getModifiers()) && allowedModes != 0)
1523 return; // common case
1524 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
1525 if ((requestedModes & allowedModes) != 0) {
1526 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
1527 mods, lookupClass(), allowedModes))
1528 return;
1529 } else {
1530 // Protected members can also be checked as if they were package-private.
1531 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
1532 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
1533 return;
1534 }
1535 throw m.makeAccessException(accessFailedMessage(refc, m), this);
1536 }
1537
1538 String accessFailedMessage(Class<?> refc, MemberName m) {
1539 Class<?> defc = m.getDeclaringClass();
1540 int mods = m.getModifiers();
1541 // check the class first:
1542 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
1543 (defc == refc ||
1544 Modifier.isPublic(refc.getModifiers())));
1545 if (!classOK && (allowedModes & PACKAGE) != 0) {
1546 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), ALL_MODES) &&
1547 (defc == refc ||
1548 VerifyAccess.isClassAccessible(refc, lookupClass(), ALL_MODES)));
1549 }
1550 if (!classOK)
1551 return "class is not public";
1552 if (Modifier.isPublic(mods))
1553 return "access to public member failed"; // (how?)
1554 if (Modifier.isPrivate(mods))
1555 return "member is private";
1556 if (Modifier.isProtected(mods))
1557 return "member is protected";
1558 return "member is private to package";
1559 }
1560
1561 private static final boolean ALLOW_NESTMATE_ACCESS = false;
1562
1563 private void checkSpecialCaller(Class<?> specialCaller) throws IllegalAccessException {
1564 int allowedModes = this.allowedModes;
1565 if (allowedModes == TRUSTED) return;
1566 if (!hasPrivateAccess()
1567 || (specialCaller != lookupClass()
1568 && !(ALLOW_NESTMATE_ACCESS &&
1569 VerifyAccess.isSamePackageMember(specialCaller, lookupClass()))))
1570 throw new MemberName(specialCaller).
1571 makeAccessException("no private access for invokespecial", this);
1572 }
1573
1574 private boolean restrictProtectedReceiver(MemberName method) {
1575 // The accessing class only has the right to use a protected member
1576 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
1577 if (!method.isProtected() || method.isStatic()
1578 || allowedModes == TRUSTED
1579 || method.getDeclaringClass() == lookupClass()
1580 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass())
1581 || (ALLOW_NESTMATE_ACCESS &&
1582 VerifyAccess.isSamePackageMember(method.getDeclaringClass(), lookupClass())))
1583 return false;
1584 return true;
1585 }
1586 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
1587 assert(!method.isStatic());
1588 // receiver type of mh is too wide; narrow to caller
1589 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
1590 throw method.makeAccessException("caller class must be a subclass below the method", caller);
1591 }
1592 MethodType rawType = mh.type();
1593 if (rawType.parameterType(0) == caller) return mh;
1594 MethodType narrowType = rawType.changeParameterType(0, caller);
1595 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
1596 assert(mh.viewAsTypeChecks(narrowType, true));
1597 return mh.copyWith(narrowType, mh.form);
1598 }
1599
1600 /** Check access and get the requested method. */
1601 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
1602 final boolean doRestrict = true;
1603 final boolean checkSecurity = true;
1604 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
1605 }
1606 /** Check access and get the requested method, eliding receiver narrowing rules. */
1607 private MethodHandle getDirectMethodNoRestrict(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
1608 final boolean doRestrict = false;
1609 final boolean checkSecurity = true;
1610 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
1611 }
1612 /** Check access and get the requested method, eliding security manager checks. */
1613 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
1614 final boolean doRestrict = true;
1615 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
1616 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
1617 }
1618 /** Common code for all methods; do not call directly except from immediately above. */
1619 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
1620 boolean checkSecurity,
1621 boolean doRestrict, Class<?> callerClass) throws IllegalAccessException {
1622 checkMethod(refKind, refc, method);
1623 // Optionally check with the security manager; this isn't needed for unreflect* calls.
1624 if (checkSecurity)
1625 checkSecurityManager(refc, method);
1626 assert(!method.isMethodHandleInvoke());
1627
1628 if (refKind == REF_invokeSpecial &&
1629 refc != lookupClass() &&
1630 !refc.isInterface() &&
1631 refc != lookupClass().getSuperclass() &&
1632 refc.isAssignableFrom(lookupClass())) {
1633 assert(!method.getName().equals("<init>")); // not this code path
1634 // Per JVMS 6.5, desc. of invokespecial instruction:
1635 // If the method is in a superclass of the LC,
1636 // and if our original search was above LC.super,
1637 // repeat the search (symbolic lookup) from LC.super
1638 // and continue with the direct superclass of that class,
1639 // and so forth, until a match is found or no further superclasses exist.
1640 // FIXME: MemberName.resolve should handle this instead.
1641 Class<?> refcAsSuper = lookupClass();
1642 MemberName m2;
1643 do {
1644 refcAsSuper = refcAsSuper.getSuperclass();
1645 m2 = new MemberName(refcAsSuper,
1646 method.getName(),
1647 method.getMethodType(),
1648 REF_invokeSpecial);
1649 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull());
1650 } while (m2 == null && // no method is found yet
1651 refc != refcAsSuper); // search up to refc
1652 if (m2 == null) throw new InternalError(method.toString());
1653 method = m2;
1654 refc = refcAsSuper;
1655 // redo basic checks
1656 checkMethod(refKind, refc, method);
1657 }
1658
1659 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method);
1660 MethodHandle mh = dmh;
1661 // Optionally narrow the receiver argument to refc using restrictReceiver.
1662 if (doRestrict &&
1663 (refKind == REF_invokeSpecial ||
1664 (MethodHandleNatives.refKindHasReceiver(refKind) &&
1665 restrictProtectedReceiver(method)))) {
1666 mh = restrictReceiver(method, dmh, lookupClass());
1667 }
1668 mh = maybeBindCaller(method, mh, callerClass);
1669 mh = mh.setVarargs(method);
1670 return mh;
1671 }
1672 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh,
1673 Class<?> callerClass)
1674 throws IllegalAccessException {
1675 if (allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
1676 return mh;
1677 Class<?> hostClass = lookupClass;
1678 if (!hasPrivateAccess()) // caller must have private access
1679 hostClass = callerClass; // callerClass came from a security manager style stack walk
1680 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, hostClass);
1681 // Note: caller will apply varargs after this step happens.
1682 return cbmh;
1683 }
1684 /** Check access and get the requested field. */
1685 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
1686 final boolean checkSecurity = true;
1687 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
1688 }
1689 /** Check access and get the requested field, eliding security manager checks. */
1690 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
1691 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
1692 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
1693 }
1694 /** Common code for all fields; do not call directly except from immediately above. */
1695 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
1696 boolean checkSecurity) throws IllegalAccessException {
1697 checkField(refKind, refc, field);
1698 // Optionally check with the security manager; this isn't needed for unreflect* calls.
1699 if (checkSecurity)
1700 checkSecurityManager(refc, field);
1701 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
1702 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
1703 restrictProtectedReceiver(field));
1704 if (doRestrict)
1705 return restrictReceiver(field, dmh, lookupClass());
1706 return dmh;
1707 }
1708 /** Check access and get the requested constructor. */
1709 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
1710 final boolean checkSecurity = true;
1711 return getDirectConstructorCommon(refc, ctor, checkSecurity);
1712 }
1713 /** Check access and get the requested constructor, eliding security manager checks. */
1714 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
1715 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
1716 return getDirectConstructorCommon(refc, ctor, checkSecurity);
1717 }
1718 /** Common code for all constructors; do not call directly except from immediately above. */
1719 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
1720 boolean checkSecurity) throws IllegalAccessException {
1721 assert(ctor.isConstructor());
1722 checkAccess(REF_newInvokeSpecial, refc, ctor);
1723 // Optionally check with the security manager; this isn't needed for unreflect* calls.
1724 if (checkSecurity)
1725 checkSecurityManager(refc, ctor);
1726 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
1727 return DirectMethodHandle.make(ctor).setVarargs(ctor);
1728 }
1729
1730 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
1731 */
1732 /*non-public*/
1733 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type) throws ReflectiveOperationException {
1734 if (!(type instanceof Class || type instanceof MethodType))
1735 throw new InternalError("unresolved MemberName");
1736 MemberName member = new MemberName(refKind, defc, name, type);
1737 MethodHandle mh = LOOKASIDE_TABLE.get(member);
1738 if (mh != null) {
1739 checkSymbolicClass(defc);
1740 return mh;
1741 }
1742 // Treat MethodHandle.invoke and invokeExact specially.
1743 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
1744 mh = findVirtualForMH(member.getName(), member.getMethodType());
1745 if (mh != null) {
1746 return mh;
1747 }
1748 }
1749 MemberName resolved = resolveOrFail(refKind, member);
1750 mh = getDirectMethodForConstant(refKind, defc, resolved);
1751 if (mh instanceof DirectMethodHandle
1752 && canBeCached(refKind, defc, resolved)) {
1753 MemberName key = mh.internalMemberName();
1754 if (key != null) {
1755 key = key.asNormalOriginal();
1756 }
1757 if (member.equals(key)) { // better safe than sorry
1758 LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh);
1759 }
1760 }
1761 return mh;
1762 }
1763 private
1764 boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
1765 if (refKind == REF_invokeSpecial) {
1766 return false;
1767 }
1768 if (!Modifier.isPublic(defc.getModifiers()) ||
1769 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
1770 !member.isPublic() ||
1771 member.isCallerSensitive()) {
1772 return false;
1773 }
1774 ClassLoader loader = defc.getClassLoader();
1775 if (!sun.misc.VM.isSystemDomainLoader(loader)) {
1776 ClassLoader sysl = ClassLoader.getSystemClassLoader();
1777 boolean found = false;
1778 while (sysl != null) {
1779 if (loader == sysl) { found = true; break; }
1780 sysl = sysl.getParent();
1781 }
1782 if (!found) {
1783 return false;
1784 }
1785 }
1786 try {
1787 MemberName resolved2 = publicLookup().resolveOrFail(refKind,
1788 new MemberName(refKind, defc, member.getName(), member.getType()));
1789 checkSecurityManager(defc, resolved2);
1790 } catch (ReflectiveOperationException | SecurityException ex) {
1791 return false;
1792 }
1793 return true;
1794 }
1795 private
1796 MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
1797 throws ReflectiveOperationException {
1798 if (MethodHandleNatives.refKindIsField(refKind)) {
1799 return getDirectFieldNoSecurityManager(refKind, defc, member);
1800 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
1801 return getDirectMethodNoSecurityManager(refKind, defc, member, lookupClass);
1802 } else if (refKind == REF_newInvokeSpecial) {
1803 return getDirectConstructorNoSecurityManager(defc, member);
1804 }
1805 // oops
1806 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
1807 }
1808
1809 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
1810 }
1811
1812 /**
1813 * Produces a method handle giving read access to elements of an array.
1814 * The type of the method handle will have a return type of the array's
1815 * element type. Its first argument will be the array type,
1816 * and the second will be {@code int}.
1817 * @param arrayClass an array type
1818 * @return a method handle which can load values from the given array type
1819 * @throws NullPointerException if the argument is null
1820 * @throws IllegalArgumentException if arrayClass is not an array type
1821 */
1822 public static
1823 MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
1824 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, false);
1825 }
1826
1827 /**
1828 * Produces a method handle giving write access to elements of an array.
1829 * The type of the method handle will have a void return type.
1830 * Its last argument will be the array's element type.
1831 * The first and second arguments will be the array type and int.
1832 * @param arrayClass the class of an array
1833 * @return a method handle which can store values into the array type
1834 * @throws NullPointerException if the argument is null
1835 * @throws IllegalArgumentException if arrayClass is not an array type
1836 */
1837 public static
1838 MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
1839 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, true);
1840 }
1841
1842 /// method handle invocation (reflective style)
1843
1844 /**
1845 * Produces a method handle which will invoke any method handle of the
1846 * given {@code type}, with a given number of trailing arguments replaced by
1847 * a single trailing {@code Object[]} array.
1848 * The resulting invoker will be a method handle with the following
1849 * arguments:
1850 * <ul>
1851 * <li>a single {@code MethodHandle} target
1852 * <li>zero or more leading values (counted by {@code leadingArgCount})
1853 * <li>an {@code Object[]} array containing trailing arguments
1854 * </ul>
1855 * <p>
1856 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
1857 * the indicated {@code type}.
1858 * That is, if the target is exactly of the given {@code type}, it will behave
1859 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
1860 * is used to convert the target to the required {@code type}.
1861 * <p>
1862 * The type of the returned invoker will not be the given {@code type}, but rather
1863 * will have all parameters except the first {@code leadingArgCount}
1864 * replaced by a single array of type {@code Object[]}, which will be
1865 * the final parameter.
1866 * <p>
1867 * Before invoking its target, the invoker will spread the final array, apply
1868 * reference casts as necessary, and unbox and widen primitive arguments.
1869 * If, when the invoker is called, the supplied array argument does
1870 * not have the correct number of elements, the invoker will throw
1871 * an {@link IllegalArgumentException} instead of invoking the target.
1872 * <p>
1873 * This method is equivalent to the following code (though it may be more efficient):
1874 * <blockquote><pre>{@code
1875 MethodHandle invoker = MethodHandles.invoker(type);
1876 int spreadArgCount = type.parameterCount() - leadingArgCount;
1877 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
1878 return invoker;
1879 * }</pre></blockquote>
1880 * This method throws no reflective or security exceptions.
1881 * @param type the desired target type
1882 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
1883 * @return a method handle suitable for invoking any method handle of the given type
1884 * @throws NullPointerException if {@code type} is null
1885 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
1886 * the range from 0 to {@code type.parameterCount()} inclusive,
1887 * or if the resulting method handle's type would have
1888 * <a href="MethodHandle.html#maxarity">too many parameters</a>
1889 */
1890 static public
1891 MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
1892 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
1893 throw newIllegalArgumentException("bad argument count", leadingArgCount);
1894 type = type.asSpreaderType(Object[].class, type.parameterCount() - leadingArgCount);
1895 return type.invokers().spreadInvoker(leadingArgCount);
1896 }
1897
1898 /**
1899 * Produces a special <em>invoker method handle</em> which can be used to
1900 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
1901 * The resulting invoker will have a type which is
1902 * exactly equal to the desired type, except that it will accept
1903 * an additional leading argument of type {@code MethodHandle}.
1904 * <p>
1905 * This method is equivalent to the following code (though it may be more efficient):
1906 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
1907 *
1908 * <p style="font-size:smaller;">
1909 * <em>Discussion:</em>
1910 * Invoker method handles can be useful when working with variable method handles
1911 * of unknown types.
1912 * For example, to emulate an {@code invokeExact} call to a variable method
1913 * handle {@code M}, extract its type {@code T},
1914 * look up the invoker method {@code X} for {@code T},
1915 * and call the invoker method, as {@code X.invoke(T, A...)}.
1916 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
1917 * is unknown.)
1918 * If spreading, collecting, or other argument transformations are required,
1919 * they can be applied once to the invoker {@code X} and reused on many {@code M}
1920 * method handle values, as long as they are compatible with the type of {@code X}.
1921 * <p style="font-size:smaller;">
1922 * <em>(Note: The invoker method is not available via the Core Reflection API.
1923 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
1924 * on the declared {@code invokeExact} or {@code invoke} method will raise an
1925 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
1926 * <p>
1927 * This method throws no reflective or security exceptions.
1928 * @param type the desired target type
1929 * @return a method handle suitable for invoking any method handle of the given type
1930 * @throws IllegalArgumentException if the resulting method handle's type would have
1931 * <a href="MethodHandle.html#maxarity">too many parameters</a>
1932 */
1933 static public
1934 MethodHandle exactInvoker(MethodType type) {
1935 return type.invokers().exactInvoker();
1936 }
1937
1938 /**
1939 * Produces a special <em>invoker method handle</em> which can be used to
1940 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
1941 * The resulting invoker will have a type which is
1942 * exactly equal to the desired type, except that it will accept
1943 * an additional leading argument of type {@code MethodHandle}.
1944 * <p>
1945 * Before invoking its target, if the target differs from the expected type,
1946 * the invoker will apply reference casts as
1947 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
1948 * Similarly, the return value will be converted as necessary.
1949 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
1950 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
1951 * <p>
1952 * This method is equivalent to the following code (though it may be more efficient):
1953 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
1954 * <p style="font-size:smaller;">
1955 * <em>Discussion:</em>
1956 * A {@linkplain MethodType#genericMethodType general method type} is one which
1957 * mentions only {@code Object} arguments and return values.
1958 * An invoker for such a type is capable of calling any method handle
1959 * of the same arity as the general type.
1960 * <p style="font-size:smaller;">
1961 * <em>(Note: The invoker method is not available via the Core Reflection API.
1962 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
1963 * on the declared {@code invokeExact} or {@code invoke} method will raise an
1964 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
1965 * <p>
1966 * This method throws no reflective or security exceptions.
1967 * @param type the desired target type
1968 * @return a method handle suitable for invoking any method handle convertible to the given type
1969 * @throws IllegalArgumentException if the resulting method handle's type would have
1970 * <a href="MethodHandle.html#maxarity">too many parameters</a>
1971 */
1972 static public
1973 MethodHandle invoker(MethodType type) {
1974 return type.invokers().genericInvoker();
1975 }
1976
1977 static /*non-public*/
1978 MethodHandle basicInvoker(MethodType type) {
1979 return type.invokers().basicInvoker();
1980 }
1981
1982 /// method handle modification (creation from other method handles)
1983
1984 /**
1985 * Produces a method handle which adapts the type of the
1986 * given method handle to a new type by pairwise argument and return type conversion.
1987 * The original type and new type must have the same number of arguments.
1988 * The resulting method handle is guaranteed to report a type
1989 * which is equal to the desired new type.
1990 * <p>
1991 * If the original type and new type are equal, returns target.
1992 * <p>
1993 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
1994 * and some additional conversions are also applied if those conversions fail.
1995 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
1996 * if possible, before or instead of any conversions done by {@code asType}:
1997 * <ul>
1998 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
1999 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
2000 * (This treatment of interfaces follows the usage of the bytecode verifier.)
2001 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
2002 * the boolean is converted to a byte value, 1 for true, 0 for false.
2003 * (This treatment follows the usage of the bytecode verifier.)
2004 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
2005 * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
2006 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
2007 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
2008 * then a Java casting conversion (JLS 5.5) is applied.
2009 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
2010 * widening and/or narrowing.)
2011 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
2012 * conversion will be applied at runtime, possibly followed
2013 * by a Java casting conversion (JLS 5.5) on the primitive value,
2014 * possibly followed by a conversion from byte to boolean by testing
2015 * the low-order bit.
2016 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
2017 * and if the reference is null at runtime, a zero value is introduced.
2018 * </ul>
2019 * @param target the method handle to invoke after arguments are retyped
2020 * @param newType the expected type of the new method handle
2021 * @return a method handle which delegates to the target after performing
2022 * any necessary argument conversions, and arranges for any
2023 * necessary return value conversions
2024 * @throws NullPointerException if either argument is null
2025 * @throws WrongMethodTypeException if the conversion cannot be made
2026 * @see MethodHandle#asType
2027 */
2028 public static
2029 MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
2030 explicitCastArgumentsChecks(target, newType);
2031 // use the asTypeCache when possible:
2032 MethodType oldType = target.type();
2033 if (oldType == newType) return target;
2034 if (oldType.explicitCastEquivalentToAsType(newType)) {
2035 return target.asFixedArity().asType(newType);
2036 }
2037 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
2038 }
2039
2040 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
2041 if (target.type().parameterCount() != newType.parameterCount()) {
2042 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
2043 }
2044 }
2045
2046 /**
2047 * Produces a method handle which adapts the calling sequence of the
2048 * given method handle to a new type, by reordering the arguments.
2049 * The resulting method handle is guaranteed to report a type
2050 * which is equal to the desired new type.
2051 * <p>
2052 * The given array controls the reordering.
2053 * Call {@code #I} the number of incoming parameters (the value
2054 * {@code newType.parameterCount()}, and call {@code #O} the number
2055 * of outgoing parameters (the value {@code target.type().parameterCount()}).
2056 * Then the length of the reordering array must be {@code #O},
2057 * and each element must be a non-negative number less than {@code #I}.
2058 * For every {@code N} less than {@code #O}, the {@code N}-th
2059 * outgoing argument will be taken from the {@code I}-th incoming
2060 * argument, where {@code I} is {@code reorder[N]}.
2061 * <p>
2062 * No argument or return value conversions are applied.
2063 * The type of each incoming argument, as determined by {@code newType},
2064 * must be identical to the type of the corresponding outgoing parameter
2065 * or parameters in the target method handle.
2066 * The return type of {@code newType} must be identical to the return
2067 * type of the original target.
2068 * <p>
2069 * The reordering array need not specify an actual permutation.
2070 * An incoming argument will be duplicated if its index appears
2071 * more than once in the array, and an incoming argument will be dropped
2072 * if its index does not appear in the array.
2073 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
2074 * incoming arguments which are not mentioned in the reordering array
2075 * are may be any type, as determined only by {@code newType}.
2076 * <blockquote><pre>{@code
2077 import static java.lang.invoke.MethodHandles.*;
2078 import static java.lang.invoke.MethodType.*;
2079 ...
2080 MethodType intfn1 = methodType(int.class, int.class);
2081 MethodType intfn2 = methodType(int.class, int.class, int.class);
2082 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
2083 assert(sub.type().equals(intfn2));
2084 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
2085 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
2086 assert((int)rsub.invokeExact(1, 100) == 99);
2087 MethodHandle add = ... (int x, int y) -> (x+y) ...;
2088 assert(add.type().equals(intfn2));
2089 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
2090 assert(twice.type().equals(intfn1));
2091 assert((int)twice.invokeExact(21) == 42);
2092 * }</pre></blockquote>
2093 * @param target the method handle to invoke after arguments are reordered
2094 * @param newType the expected type of the new method handle
2095 * @param reorder an index array which controls the reordering
2096 * @return a method handle which delegates to the target after it
2097 * drops unused arguments and moves and/or duplicates the other arguments
2098 * @throws NullPointerException if any argument is null
2099 * @throws IllegalArgumentException if the index array length is not equal to
2100 * the arity of the target, or if any index array element
2101 * not a valid index for a parameter of {@code newType},
2102 * or if two corresponding parameter types in
2103 * {@code target.type()} and {@code newType} are not identical,
2104 */
2105 public static
2106 MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
2107 reorder = reorder.clone(); // get a private copy
2108 MethodType oldType = target.type();
2109 permuteArgumentChecks(reorder, newType, oldType);
2110 // first detect dropped arguments and handle them separately
2111 int[] originalReorder = reorder;
2112 BoundMethodHandle result = target.rebind();
2113 LambdaForm form = result.form;
2114 int newArity = newType.parameterCount();
2115 // Normalize the reordering into a real permutation,
2116 // by removing duplicates and adding dropped elements.
2117 // This somewhat improves lambda form caching, as well
2118 // as simplifying the transform by breaking it up into steps.
2119 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
2120 if (ddIdx > 0) {
2121 // We found a duplicated entry at reorder[ddIdx].
2122 // Example: (x,y,z)->asList(x,y,z)
2123 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
2124 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
2125 // The starred element corresponds to the argument
2126 // deleted by the dupArgumentForm transform.
2127 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
2128 boolean killFirst = false;
2129 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
2130 // Set killFirst if the dup is larger than an intervening position.
2131 // This will remove at least one inversion from the permutation.
2132 if (dupVal > val) killFirst = true;
2133 }
2134 if (!killFirst) {
2135 srcPos = dstPos;
2136 dstPos = ddIdx;
2137 }
2138 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
2139 assert (reorder[srcPos] == reorder[dstPos]);
2140 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
2141 // contract the reordering by removing the element at dstPos
2142 int tailPos = dstPos + 1;
2143 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
2144 reorder = Arrays.copyOf(reorder, reorder.length - 1);
2145 } else {
2146 int dropVal = ~ddIdx, insPos = 0;
2147 while (insPos < reorder.length && reorder[insPos] < dropVal) {
2148 // Find first element of reorder larger than dropVal.
2149 // This is where we will insert the dropVal.
2150 insPos += 1;
2151 }
2152 Class<?> ptype = newType.parameterType(dropVal);
2153 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
2154 oldType = oldType.insertParameterTypes(insPos, ptype);
2155 // expand the reordering by inserting an element at insPos
2156 int tailPos = insPos + 1;
2157 reorder = Arrays.copyOf(reorder, reorder.length + 1);
2158 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
2159 reorder[insPos] = dropVal;
2160 }
2161 assert (permuteArgumentChecks(reorder, newType, oldType));
2162 }
2163 assert (reorder.length == newArity); // a perfect permutation
2164 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
2165 form = form.editor().permuteArgumentsForm(1, reorder);
2166 if (newType == result.type() && form == result.internalForm())
2167 return result;
2168 return result.copyWith(newType, form);
2169 }
2170
2171 /**
2172 * Return an indication of any duplicate or omission in reorder.
2173 * If the reorder contains a duplicate entry, return the index of the second occurrence.
2174 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
2175 * Otherwise, return zero.
2176 * If an element not in [0..newArity-1] is encountered, return reorder.length.
2177 */
2178 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
2179 final int BIT_LIMIT = 63; // max number of bits in bit mask
2180 if (newArity < BIT_LIMIT) {
2181 long mask = 0;
2182 for (int i = 0; i < reorder.length; i++) {
2183 int arg = reorder[i];
2184 if (arg >= newArity) {
2185 return reorder.length;
2186 }
2187 long bit = 1L << arg;
2188 if ((mask & bit) != 0) {
2189 return i; // >0 indicates a dup
2190 }
2191 mask |= bit;
2192 }
2193 if (mask == (1L << newArity) - 1) {
2194 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
2195 return 0;
2196 }
2197 // find first zero
2198 long zeroBit = Long.lowestOneBit(~mask);
2199 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
2200 assert(zeroPos <= newArity);
2201 if (zeroPos == newArity) {
2202 return 0;
2203 }
2204 return ~zeroPos;
2205 } else {
2206 // same algorithm, different bit set
2207 BitSet mask = new BitSet(newArity);
2208 for (int i = 0; i < reorder.length; i++) {
2209 int arg = reorder[i];
2210 if (arg >= newArity) {
2211 return reorder.length;
2212 }
2213 if (mask.get(arg)) {
2214 return i; // >0 indicates a dup
2215 }
2216 mask.set(arg);
2217 }
2218 int zeroPos = mask.nextClearBit(0);
2219 assert(zeroPos <= newArity);
2220 if (zeroPos == newArity) {
2221 return 0;
2222 }
2223 return ~zeroPos;
2224 }
2225 }
2226
2227 private static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
2228 if (newType.returnType() != oldType.returnType())
2229 throw newIllegalArgumentException("return types do not match",
2230 oldType, newType);
2231 if (reorder.length == oldType.parameterCount()) {
2232 int limit = newType.parameterCount();
2233 boolean bad = false;
2234 for (int j = 0; j < reorder.length; j++) {
2235 int i = reorder[j];
2236 if (i < 0 || i >= limit) {
2237 bad = true; break;
2238 }
2239 Class<?> src = newType.parameterType(i);
2240 Class<?> dst = oldType.parameterType(j);
2241 if (src != dst)
2242 throw newIllegalArgumentException("parameter types do not match after reorder",
2243 oldType, newType);
2244 }
2245 if (!bad) return true;
2246 }
2247 throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
2248 }
2249
2250 /**
2251 * Produces a method handle of the requested return type which returns the given
2252 * constant value every time it is invoked.
2253 * <p>
2254 * Before the method handle is returned, the passed-in value is converted to the requested type.
2255 * If the requested type is primitive, widening primitive conversions are attempted,
2256 * else reference conversions are attempted.
2257 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
2258 * @param type the return type of the desired method handle
2259 * @param value the value to return
2260 * @return a method handle of the given return type and no arguments, which always returns the given value
2261 * @throws NullPointerException if the {@code type} argument is null
2262 * @throws ClassCastException if the value cannot be converted to the required return type
2263 * @throws IllegalArgumentException if the given type is {@code void.class}
2264 */
2265 public static
2266 MethodHandle constant(Class<?> type, Object value) {
2267 if (type.isPrimitive()) {
2268 if (type == void.class)
2269 throw newIllegalArgumentException("void type");
2270 Wrapper w = Wrapper.forPrimitiveType(type);
2271 value = w.convert(value, type);
2272 if (w.zero().equals(value))
2273 return zero(w, type);
2274 return insertArguments(identity(type), 0, value);
2275 } else {
2276 if (value == null)
2277 return zero(Wrapper.OBJECT, type);
2278 return identity(type).bindTo(value);
2279 }
2280 }
2281
2282 /**
2283 * Produces a method handle which returns its sole argument when invoked.
2284 * @param type the type of the sole parameter and return value of the desired method handle
2285 * @return a unary method handle which accepts and returns the given type
2286 * @throws NullPointerException if the argument is null
2287 * @throws IllegalArgumentException if the given type is {@code void.class}
2288 */
2289 public static
2290 MethodHandle identity(Class<?> type) {
2291 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
2292 int pos = btw.ordinal();
2293 MethodHandle ident = IDENTITY_MHS[pos];
2294 if (ident == null) {
2295 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
2296 }
2297 if (ident.type().returnType() == type)
2298 return ident;
2299 // something like identity(Foo.class); do not bother to intern these
2300 assert(btw == Wrapper.OBJECT);
2301 return makeIdentity(type);
2302 }
2303 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.values().length];
2304 private static MethodHandle makeIdentity(Class<?> ptype) {
2305 MethodType mtype = MethodType.methodType(ptype, ptype);
2306 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
2307 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
2308 }
2309
2310 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
2311 int pos = btw.ordinal();
2312 MethodHandle zero = ZERO_MHS[pos];
2313 if (zero == null) {
2314 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
2315 }
2316 if (zero.type().returnType() == rtype)
2317 return zero;
2318 assert(btw == Wrapper.OBJECT);
2319 return makeZero(rtype);
2320 }
2321 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.values().length];
2322 private static MethodHandle makeZero(Class<?> rtype) {
2323 MethodType mtype = MethodType.methodType(rtype);
2324 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
2325 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
2326 }
2327
2328 synchronized private static MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
2329 // Simulate a CAS, to avoid racy duplication of results.
2330 MethodHandle prev = cache[pos];
2331 if (prev != null) return prev;
2332 return cache[pos] = value;
2333 }
2334
2335 /**
2336 * Provides a target method handle with one or more <em>bound arguments</em>
2337 * in advance of the method handle's invocation.
2338 * The formal parameters to the target corresponding to the bound
2339 * arguments are called <em>bound parameters</em>.
2340 * Returns a new method handle which saves away the bound arguments.
2341 * When it is invoked, it receives arguments for any non-bound parameters,
2342 * binds the saved arguments to their corresponding parameters,
2343 * and calls the original target.
2344 * <p>
2345 * The type of the new method handle will drop the types for the bound
2346 * parameters from the original target type, since the new method handle
2347 * will no longer require those arguments to be supplied by its callers.
2348 * <p>
2349 * Each given argument object must match the corresponding bound parameter type.
2350 * If a bound parameter type is a primitive, the argument object
2351 * must be a wrapper, and will be unboxed to produce the primitive value.
2352 * <p>
2353 * The {@code pos} argument selects which parameters are to be bound.
2354 * It may range between zero and <i>N-L</i> (inclusively),
2355 * where <i>N</i> is the arity of the target method handle
2356 * and <i>L</i> is the length of the values array.
2357 * @param target the method handle to invoke after the argument is inserted
2358 * @param pos where to insert the argument (zero for the first)
2359 * @param values the series of arguments to insert
2360 * @return a method handle which inserts an additional argument,
2361 * before calling the original method handle
2362 * @throws NullPointerException if the target or the {@code values} array is null
2363 * @see MethodHandle#bindTo
2364 */
2365 public static
2366 MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
2367 int insCount = values.length;
2368 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
2369 if (insCount == 0) return target;
2370 BoundMethodHandle result = target.rebind();
2371 for (int i = 0; i < insCount; i++) {
2372 Object value = values[i];
2373 Class<?> ptype = ptypes[pos+i];
2374 if (ptype.isPrimitive()) {
2375 result = insertArgumentPrimitive(result, pos, ptype, value);
2376 } else {
2377 value = ptype.cast(value); // throw CCE if needed
2378 result = result.bindArgumentL(pos, value);
2379 }
2380 }
2381 return result;
2382 }
2383
2384 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
2385 Class<?> ptype, Object value) {
2386 Wrapper w = Wrapper.forPrimitiveType(ptype);
2387 // perform unboxing and/or primitive conversion
2388 value = w.convert(value, ptype);
2389 switch (w) {
2390 case INT: return result.bindArgumentI(pos, (int)value);
2391 case LONG: return result.bindArgumentJ(pos, (long)value);
2392 case FLOAT: return result.bindArgumentF(pos, (float)value);
2393 case DOUBLE: return result.bindArgumentD(pos, (double)value);
2394 default: return result.bindArgumentI(pos, ValueConversions.widenSubword(value));
2395 }
2396 }
2397
2398 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
2399 MethodType oldType = target.type();
2400 int outargs = oldType.parameterCount();
2401 int inargs = outargs - insCount;
2402 if (inargs < 0)
2403 throw newIllegalArgumentException("too many values to insert");
2404 if (pos < 0 || pos > inargs)
2405 throw newIllegalArgumentException("no argument type to append");
2406 return oldType.ptypes();
2407 }
2408
2409 /**
2410 * Produces a method handle which will discard some dummy arguments
2411 * before calling some other specified <i>target</i> method handle.
2412 * The type of the new method handle will be the same as the target's type,
2413 * except it will also include the dummy argument types,
2414 * at some given position.
2415 * <p>
2416 * The {@code pos} argument may range between zero and <i>N</i>,
2417 * where <i>N</i> is the arity of the target.
2418 * If {@code pos} is zero, the dummy arguments will precede
2419 * the target's real arguments; if {@code pos} is <i>N</i>
2420 * they will come after.
2421 * <p>
2422 * <b>Example:</b>
2423 * <blockquote><pre>{@code
2424 import static java.lang.invoke.MethodHandles.*;
2425 import static java.lang.invoke.MethodType.*;
2426 ...
2427 MethodHandle cat = lookup().findVirtual(String.class,
2428 "concat", methodType(String.class, String.class));
2429 assertEquals("xy", (String) cat.invokeExact("x", "y"));
2430 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
2431 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
2432 assertEquals(bigType, d0.type());
2433 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
2434 * }</pre></blockquote>
2435 * <p>
2436 * This method is also equivalent to the following code:
2437 * <blockquote><pre>
2438 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
2439 * </pre></blockquote>
2440 * @param target the method handle to invoke after the arguments are dropped
2441 * @param valueTypes the type(s) of the argument(s) to drop
2442 * @param pos position of first argument to drop (zero for the leftmost)
2443 * @return a method handle which drops arguments of the given types,
2444 * before calling the original method handle
2445 * @throws NullPointerException if the target is null,
2446 * or if the {@code valueTypes} list or any of its elements is null
2447 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
2448 * or if {@code pos} is negative or greater than the arity of the target,
2449 * or if the new method handle's type would have too many parameters
2450 */
2451 public static
2452 MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
2453 MethodType oldType = target.type(); // get NPE
2454 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
2455 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
2456 if (dropped == 0) return target;
2457 BoundMethodHandle result = target.rebind();
2458 LambdaForm lform = result.form;
2459 int insertFormArg = 1 + pos;
2460 for (Class<?> ptype : valueTypes) {
2461 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
2462 }
2463 result = result.copyWith(newType, lform);
2464 return result;
2465 }
2466
2467 private static int dropArgumentChecks(MethodType oldType, int pos, List<Class<?>> valueTypes) {
2468 int dropped = valueTypes.size();
2469 MethodType.checkSlotCount(dropped);
2470 int outargs = oldType.parameterCount();
2471 int inargs = outargs + dropped;
2472 if (pos < 0 || pos > outargs)
2473 throw newIllegalArgumentException("no argument type to remove"
2474 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
2475 );
2476 return dropped;
2477 }
2478
2479 /**
2480 * Produces a method handle which will discard some dummy arguments
2481 * before calling some other specified <i>target</i> method handle.
2482 * The type of the new method handle will be the same as the target's type,
2483 * except it will also include the dummy argument types,
2484 * at some given position.
2485 * <p>
2486 * The {@code pos} argument may range between zero and <i>N</i>,
2487 * where <i>N</i> is the arity of the target.
2488 * If {@code pos} is zero, the dummy arguments will precede
2489 * the target's real arguments; if {@code pos} is <i>N</i>
2490 * they will come after.
2491 * <p>
2492 * <b>Example:</b>
2493 * <blockquote><pre>{@code
2494 import static java.lang.invoke.MethodHandles.*;
2495 import static java.lang.invoke.MethodType.*;
2496 ...
2497 MethodHandle cat = lookup().findVirtual(String.class,
2498 "concat", methodType(String.class, String.class));
2499 assertEquals("xy", (String) cat.invokeExact("x", "y"));
2500 MethodHandle d0 = dropArguments(cat, 0, String.class);
2501 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
2502 MethodHandle d1 = dropArguments(cat, 1, String.class);
2503 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
2504 MethodHandle d2 = dropArguments(cat, 2, String.class);
2505 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
2506 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
2507 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
2508 * }</pre></blockquote>
2509 * <p>
2510 * This method is also equivalent to the following code:
2511 * <blockquote><pre>
2512 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
2513 * </pre></blockquote>
2514 * @param target the method handle to invoke after the arguments are dropped
2515 * @param valueTypes the type(s) of the argument(s) to drop
2516 * @param pos position of first argument to drop (zero for the leftmost)
2517 * @return a method handle which drops arguments of the given types,
2518 * before calling the original method handle
2519 * @throws NullPointerException if the target is null,
2520 * or if the {@code valueTypes} array or any of its elements is null
2521 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
2522 * or if {@code pos} is negative or greater than the arity of the target,
2523 * or if the new method handle's type would have
2524 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2525 */
2526 public static
2527 MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
2528 return dropArguments(target, pos, Arrays.asList(valueTypes));
2529 }
2530
2531 /**
2532 * Adapts a target method handle by pre-processing
2533 * one or more of its arguments, each with its own unary filter function,
2534 * and then calling the target with each pre-processed argument
2535 * replaced by the result of its corresponding filter function.
2536 * <p>
2537 * The pre-processing is performed by one or more method handles,
2538 * specified in the elements of the {@code filters} array.
2539 * The first element of the filter array corresponds to the {@code pos}
2540 * argument of the target, and so on in sequence.
2541 * <p>
2542 * Null arguments in the array are treated as identity functions,
2543 * and the corresponding arguments left unchanged.
2544 * (If there are no non-null elements in the array, the original target is returned.)
2545 * Each filter is applied to the corresponding argument of the adapter.
2546 * <p>
2547 * If a filter {@code F} applies to the {@code N}th argument of
2548 * the target, then {@code F} must be a method handle which
2549 * takes exactly one argument. The type of {@code F}'s sole argument
2550 * replaces the corresponding argument type of the target
2551 * in the resulting adapted method handle.
2552 * The return type of {@code F} must be identical to the corresponding
2553 * parameter type of the target.
2554 * <p>
2555 * It is an error if there are elements of {@code filters}
2556 * (null or not)
2557 * which do not correspond to argument positions in the target.
2558 * <p><b>Example:</b>
2559 * <blockquote><pre>{@code
2560 import static java.lang.invoke.MethodHandles.*;
2561 import static java.lang.invoke.MethodType.*;
2562 ...
2563 MethodHandle cat = lookup().findVirtual(String.class,
2564 "concat", methodType(String.class, String.class));
2565 MethodHandle upcase = lookup().findVirtual(String.class,
2566 "toUpperCase", methodType(String.class));
2567 assertEquals("xy", (String) cat.invokeExact("x", "y"));
2568 MethodHandle f0 = filterArguments(cat, 0, upcase);
2569 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
2570 MethodHandle f1 = filterArguments(cat, 1, upcase);
2571 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
2572 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
2573 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
2574 * }</pre></blockquote>
2575 * <p> Here is pseudocode for the resulting adapter:
2576 * <blockquote><pre>{@code
2577 * V target(P... p, A[i]... a[i], B... b);
2578 * A[i] filter[i](V[i]);
2579 * T adapter(P... p, V[i]... v[i], B... b) {
2580 * return target(p..., f[i](v[i])..., b...);
2581 * }
2582 * }</pre></blockquote>
2583 *
2584 * @param target the method handle to invoke after arguments are filtered
2585 * @param pos the position of the first argument to filter
2586 * @param filters method handles to call initially on filtered arguments
2587 * @return method handle which incorporates the specified argument filtering logic
2588 * @throws NullPointerException if the target is null
2589 * or if the {@code filters} array is null
2590 * @throws IllegalArgumentException if a non-null element of {@code filters}
2591 * does not match a corresponding argument type of target as described above,
2592 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
2593 * or if the resulting method handle's type would have
2594 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2595 */
2596 public static
2597 MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
2598 filterArgumentsCheckArity(target, pos, filters);
2599 MethodHandle adapter = target;
2600 int curPos = pos-1; // pre-incremented
2601 for (MethodHandle filter : filters) {
2602 curPos += 1;
2603 if (filter == null) continue; // ignore null elements of filters
2604 adapter = filterArgument(adapter, curPos, filter);
2605 }
2606 return adapter;
2607 }
2608
2609 /*non-public*/ static
2610 MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
2611 filterArgumentChecks(target, pos, filter);
2612 MethodType targetType = target.type();
2613 MethodType filterType = filter.type();
2614 BoundMethodHandle result = target.rebind();
2615 Class<?> newParamType = filterType.parameterType(0);
2616 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
2617 MethodType newType = targetType.changeParameterType(pos, newParamType);
2618 result = result.copyWithExtendL(newType, lform, filter);
2619 return result;
2620 }
2621
2622 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
2623 MethodType targetType = target.type();
2624 int maxPos = targetType.parameterCount();
2625 if (pos + filters.length > maxPos)
2626 throw newIllegalArgumentException("too many filters");
2627 }
2628
2629 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
2630 MethodType targetType = target.type();
2631 MethodType filterType = filter.type();
2632 if (filterType.parameterCount() != 1
2633 || filterType.returnType() != targetType.parameterType(pos))
2634 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
2635 }
2636
2637 /**
2638 * Adapts a target method handle by pre-processing
2639 * a sub-sequence of its arguments with a filter (another method handle).
2640 * The pre-processed arguments are replaced by the result (if any) of the
2641 * filter function.
2642 * The target is then called on the modified (usually shortened) argument list.
2643 * <p>
2644 * If the filter returns a value, the target must accept that value as
2645 * its argument in position {@code pos}, preceded and/or followed by
2646 * any arguments not passed to the filter.
2647 * If the filter returns void, the target must accept all arguments
2648 * not passed to the filter.
2649 * No arguments are reordered, and a result returned from the filter
2650 * replaces (in order) the whole subsequence of arguments originally
2651 * passed to the adapter.
2652 * <p>
2653 * The argument types (if any) of the filter
2654 * replace zero or one argument types of the target, at position {@code pos},
2655 * in the resulting adapted method handle.
2656 * The return type of the filter (if any) must be identical to the
2657 * argument type of the target at position {@code pos}, and that target argument
2658 * is supplied by the return value of the filter.
2659 * <p>
2660 * In all cases, {@code pos} must be greater than or equal to zero, and
2661 * {@code pos} must also be less than or equal to the target's arity.
2662 * <p><b>Example:</b>
2663 * <blockquote><pre>{@code
2664 import static java.lang.invoke.MethodHandles.*;
2665 import static java.lang.invoke.MethodType.*;
2666 ...
2667 MethodHandle deepToString = publicLookup()
2668 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
2669
2670 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
2671 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
2672
2673 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
2674 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
2675
2676 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
2677 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
2678 assertEquals("[top, [up, down], strange]",
2679 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
2680
2681 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
2682 assertEquals("[top, [up, down], [strange]]",
2683 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
2684
2685 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
2686 assertEquals("[top, [[up, down, strange], charm], bottom]",
2687 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
2688 * }</pre></blockquote>
2689 * <p> Here is pseudocode for the resulting adapter:
2690 * <blockquote><pre>{@code
2691 * T target(A...,V,C...);
2692 * V filter(B...);
2693 * T adapter(A... a,B... b,C... c) {
2694 * V v = filter(b...);
2695 * return target(a...,v,c...);
2696 * }
2697 * // and if the filter has no arguments:
2698 * T target2(A...,V,C...);
2699 * V filter2();
2700 * T adapter2(A... a,C... c) {
2701 * V v = filter2();
2702 * return target2(a...,v,c...);
2703 * }
2704 * // and if the filter has a void return:
2705 * T target3(A...,C...);
2706 * void filter3(B...);
2707 * void adapter3(A... a,B... b,C... c) {
2708 * filter3(b...);
2709 * return target3(a...,c...);
2710 * }
2711 * }</pre></blockquote>
2712 * <p>
2713 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
2714 * one which first "folds" the affected arguments, and then drops them, in separate
2715 * steps as follows:
2716 * <blockquote><pre>{@code
2717 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
2718 * mh = MethodHandles.foldArguments(mh, coll); //step 1
2719 * }</pre></blockquote>
2720 * If the target method handle consumes no arguments besides than the result
2721 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
2722 * is equivalent to {@code filterReturnValue(coll, mh)}.
2723 * If the filter method handle {@code coll} consumes one argument and produces
2724 * a non-void result, then {@code collectArguments(mh, N, coll)}
2725 * is equivalent to {@code filterArguments(mh, N, coll)}.
2726 * Other equivalences are possible but would require argument permutation.
2727 *
2728 * @param target the method handle to invoke after filtering the subsequence of arguments
2729 * @param pos the position of the first adapter argument to pass to the filter,
2730 * and/or the target argument which receives the result of the filter
2731 * @param filter method handle to call on the subsequence of arguments
2732 * @return method handle which incorporates the specified argument subsequence filtering logic
2733 * @throws NullPointerException if either argument is null
2734 * @throws IllegalArgumentException if the return type of {@code filter}
2735 * is non-void and is not the same as the {@code pos} argument of the target,
2736 * or if {@code pos} is not between 0 and the target's arity, inclusive,
2737 * or if the resulting method handle's type would have
2738 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2739 * @see MethodHandles#foldArguments
2740 * @see MethodHandles#filterArguments
2741 * @see MethodHandles#filterReturnValue
2742 */
2743 public static
2744 MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
2745 MethodType newType = collectArgumentsChecks(target, pos, filter);
2746 MethodType collectorType = filter.type();
2747 BoundMethodHandle result = target.rebind();
2748 LambdaForm lform;
2749 if (collectorType.returnType().isArray() && filter.intrinsicName() == Intrinsic.NEW_ARRAY) {
2750 lform = result.editor().collectArgumentArrayForm(1 + pos, filter);
2751 if (lform != null) {
2752 return result.copyWith(newType, lform);
2753 }
2754 }
2755 lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
2756 return result.copyWithExtendL(newType, lform, filter);
2757 }
2758
2759 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
2760 MethodType targetType = target.type();
2761 MethodType filterType = filter.type();
2762 Class<?> rtype = filterType.returnType();
2763 List<Class<?>> filterArgs = filterType.parameterList();
2764 if (rtype == void.class) {
2765 return targetType.insertParameterTypes(pos, filterArgs);
2766 }
2767 if (rtype != targetType.parameterType(pos)) {
2768 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
2769 }
2770 return targetType.dropParameterTypes(pos, pos+1).insertParameterTypes(pos, filterArgs);
2771 }
2772
2773 /**
2774 * Adapts a target method handle by post-processing
2775 * its return value (if any) with a filter (another method handle).
2776 * The result of the filter is returned from the adapter.
2777 * <p>
2778 * If the target returns a value, the filter must accept that value as
2779 * its only argument.
2780 * If the target returns void, the filter must accept no arguments.
2781 * <p>
2782 * The return type of the filter
2783 * replaces the return type of the target
2784 * in the resulting adapted method handle.
2785 * The argument type of the filter (if any) must be identical to the
2786 * return type of the target.
2787 * <p><b>Example:</b>
2788 * <blockquote><pre>{@code
2789 import static java.lang.invoke.MethodHandles.*;
2790 import static java.lang.invoke.MethodType.*;
2791 ...
2792 MethodHandle cat = lookup().findVirtual(String.class,
2793 "concat", methodType(String.class, String.class));
2794 MethodHandle length = lookup().findVirtual(String.class,
2795 "length", methodType(int.class));
2796 System.out.println((String) cat.invokeExact("x", "y")); // xy
2797 MethodHandle f0 = filterReturnValue(cat, length);
2798 System.out.println((int) f0.invokeExact("x", "y")); // 2
2799 * }</pre></blockquote>
2800 * <p> Here is pseudocode for the resulting adapter:
2801 * <blockquote><pre>{@code
2802 * V target(A...);
2803 * T filter(V);
2804 * T adapter(A... a) {
2805 * V v = target(a...);
2806 * return filter(v);
2807 * }
2808 * // and if the target has a void return:
2809 * void target2(A...);
2810 * T filter2();
2811 * T adapter2(A... a) {
2812 * target2(a...);
2813 * return filter2();
2814 * }
2815 * // and if the filter has a void return:
2816 * V target3(A...);
2817 * void filter3(V);
2818 * void adapter3(A... a) {
2819 * V v = target3(a...);
2820 * filter3(v);
2821 * }
2822 * }</pre></blockquote>
2823 * @param target the method handle to invoke before filtering the return value
2824 * @param filter method handle to call on the return value
2825 * @return method handle which incorporates the specified return value filtering logic
2826 * @throws NullPointerException if either argument is null
2827 * @throws IllegalArgumentException if the argument list of {@code filter}
2828 * does not match the return type of target as described above
2829 */
2830 public static
2831 MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
2832 MethodType targetType = target.type();
2833 MethodType filterType = filter.type();
2834 filterReturnValueChecks(targetType, filterType);
2835 BoundMethodHandle result = target.rebind();
2836 BasicType rtype = BasicType.basicType(filterType.returnType());
2837 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
2838 MethodType newType = targetType.changeReturnType(filterType.returnType());
2839 result = result.copyWithExtendL(newType, lform, filter);
2840 return result;
2841 }
2842
2843 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
2844 Class<?> rtype = targetType.returnType();
2845 int filterValues = filterType.parameterCount();
2846 if (filterValues == 0
2847 ? (rtype != void.class)
2848 : (rtype != filterType.parameterType(0)))
2849 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
2850 }
2851
2852 /**
2853 * Adapts a target method handle by pre-processing
2854 * some of its arguments, and then calling the target with
2855 * the result of the pre-processing, inserted into the original
2856 * sequence of arguments.
2857 * <p>
2858 * The pre-processing is performed by {@code combiner}, a second method handle.
2859 * Of the arguments passed to the adapter, the first {@code N} arguments
2860 * are copied to the combiner, which is then called.
2861 * (Here, {@code N} is defined as the parameter count of the combiner.)
2862 * After this, control passes to the target, with any result
2863 * from the combiner inserted before the original {@code N} incoming
2864 * arguments.
2865 * <p>
2866 * If the combiner returns a value, the first parameter type of the target
2867 * must be identical with the return type of the combiner, and the next
2868 * {@code N} parameter types of the target must exactly match the parameters
2869 * of the combiner.
2870 * <p>
2871 * If the combiner has a void return, no result will be inserted,
2872 * and the first {@code N} parameter types of the target
2873 * must exactly match the parameters of the combiner.
2874 * <p>
2875 * The resulting adapter is the same type as the target, except that the
2876 * first parameter type is dropped,
2877 * if it corresponds to the result of the combiner.
2878 * <p>
2879 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
2880 * that either the combiner or the target does not wish to receive.
2881 * If some of the incoming arguments are destined only for the combiner,
2882 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
2883 * arguments will not need to be live on the stack on entry to the
2884 * target.)
2885 * <p><b>Example:</b>
2886 * <blockquote><pre>{@code
2887 import static java.lang.invoke.MethodHandles.*;
2888 import static java.lang.invoke.MethodType.*;
2889 ...
2890 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
2891 "println", methodType(void.class, String.class))
2892 .bindTo(System.out);
2893 MethodHandle cat = lookup().findVirtual(String.class,
2894 "concat", methodType(String.class, String.class));
2895 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
2896 MethodHandle catTrace = foldArguments(cat, trace);
2897 // also prints "boo":
2898 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
2899 * }</pre></blockquote>
2900 * <p> Here is pseudocode for the resulting adapter:
2901 * <blockquote><pre>{@code
2902 * // there are N arguments in A...
2903 * T target(V, A[N]..., B...);
2904 * V combiner(A...);
2905 * T adapter(A... a, B... b) {
2906 * V v = combiner(a...);
2907 * return target(v, a..., b...);
2908 * }
2909 * // and if the combiner has a void return:
2910 * T target2(A[N]..., B...);
2911 * void combiner2(A...);
2912 * T adapter2(A... a, B... b) {
2913 * combiner2(a...);
2914 * return target2(a..., b...);
2915 * }
2916 * }</pre></blockquote>
2917 * @param target the method handle to invoke after arguments are combined
2918 * @param combiner method handle to call initially on the incoming arguments
2919 * @return method handle which incorporates the specified argument folding logic
2920 * @throws NullPointerException if either argument is null
2921 * @throws IllegalArgumentException if {@code combiner}'s return type
2922 * is non-void and not the same as the first argument type of
2923 * the target, or if the initial {@code N} argument types
2924 * of the target
2925 * (skipping one matching the {@code combiner}'s return type)
2926 * are not identical with the argument types of {@code combiner}
2927 */
2928 public static
2929 MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
2930 int foldPos = 0;
2931 MethodType targetType = target.type();
2932 MethodType combinerType = combiner.type();
2933 Class<?> rtype = foldArgumentChecks(foldPos, targetType, combinerType);
2934 BoundMethodHandle result = target.rebind();
2935 boolean dropResult = (rtype == void.class);
2936 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
2937 LambdaForm lform = result.editor().foldArgumentsForm(1 + foldPos, dropResult, combinerType.basicType());
2938 MethodType newType = targetType;
2939 if (!dropResult)
2940 newType = newType.dropParameterTypes(foldPos, foldPos + 1);
2941 result = result.copyWithExtendL(newType, lform, combiner);
2942 return result;
2943 }
2944
2945 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
2946 int foldArgs = combinerType.parameterCount();
2947 Class<?> rtype = combinerType.returnType();
2948 int foldVals = rtype == void.class ? 0 : 1;
2949 int afterInsertPos = foldPos + foldVals;
2950 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
2951 if (ok && !(combinerType.parameterList()
2952 .equals(targetType.parameterList().subList(afterInsertPos,
2953 afterInsertPos + foldArgs))))
2954 ok = false;
2955 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(0))
2956 ok = false;
2957 if (!ok)
2958 throw misMatchedTypes("target and combiner types", targetType, combinerType);
2959 return rtype;
2960 }
2961
2962 /**
2963 * Makes a method handle which adapts a target method handle,
2964 * by guarding it with a test, a boolean-valued method handle.
2965 * If the guard fails, a fallback handle is called instead.
2966 * All three method handles must have the same corresponding
2967 * argument and return types, except that the return type
2968 * of the test must be boolean, and the test is allowed
2969 * to have fewer arguments than the other two method handles.
2970 * <p> Here is pseudocode for the resulting adapter:
2971 * <blockquote><pre>{@code
2972 * boolean test(A...);
2973 * T target(A...,B...);
2974 * T fallback(A...,B...);
2975 * T adapter(A... a,B... b) {
2976 * if (test(a...))
2977 * return target(a..., b...);
2978 * else
2979 * return fallback(a..., b...);
2980 * }
2981 * }</pre></blockquote>
2982 * Note that the test arguments ({@code a...} in the pseudocode) cannot
2983 * be modified by execution of the test, and so are passed unchanged
2984 * from the caller to the target or fallback as appropriate.
2985 * @param test method handle used for test, must return boolean
2986 * @param target method handle to call if test passes
2987 * @param fallback method handle to call if test fails
2988 * @return method handle which incorporates the specified if/then/else logic
2989 * @throws NullPointerException if any argument is null
2990 * @throws IllegalArgumentException if {@code test} does not return boolean,
2991 * or if all three method types do not match (with the return
2992 * type of {@code test} changed to match that of the target).
2993 */
2994 public static
2995 MethodHandle guardWithTest(MethodHandle test,
2996 MethodHandle target,
2997 MethodHandle fallback) {
2998 MethodType gtype = test.type();
2999 MethodType ttype = target.type();
3000 MethodType ftype = fallback.type();
3001 if (!ttype.equals(ftype))
3002 throw misMatchedTypes("target and fallback types", ttype, ftype);
3003 if (gtype.returnType() != boolean.class)
3004 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
3005 List<Class<?>> targs = ttype.parameterList();
3006 List<Class<?>> gargs = gtype.parameterList();
3007 if (!targs.equals(gargs)) {
3008 int gpc = gargs.size(), tpc = targs.size();
3009 if (gpc >= tpc || !targs.subList(0, gpc).equals(gargs))
3010 throw misMatchedTypes("target and test types", ttype, gtype);
3011 test = dropArguments(test, gpc, targs.subList(gpc, tpc));
3012 gtype = test.type();
3013 }
3014 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
3015 }
3016
3017 static RuntimeException misMatchedTypes(String what, MethodType t1, MethodType t2) {
3018 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
3019 }
3020
3021 /**
3022 * Makes a method handle which adapts a target method handle,
3023 * by running it inside an exception handler.
3024 * If the target returns normally, the adapter returns that value.
3025 * If an exception matching the specified type is thrown, the fallback
3026 * handle is called instead on the exception, plus the original arguments.
3027 * <p>
3028 * The target and handler must have the same corresponding
3029 * argument and return types, except that handler may omit trailing arguments
3030 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
3031 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
3032 * <p> Here is pseudocode for the resulting adapter:
3033 * <blockquote><pre>{@code
3034 * T target(A..., B...);
3035 * T handler(ExType, A...);
3036 * T adapter(A... a, B... b) {
3037 * try {
3038 * return target(a..., b...);
3039 * } catch (ExType ex) {
3040 * return handler(ex, a...);
3041 * }
3042 * }
3043 * }</pre></blockquote>
3044 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
3045 * be modified by execution of the target, and so are passed unchanged
3046 * from the caller to the handler, if the handler is invoked.
3047 * <p>
3048 * The target and handler must return the same type, even if the handler
3049 * always throws. (This might happen, for instance, because the handler
3050 * is simulating a {@code finally} clause).
3051 * To create such a throwing handler, compose the handler creation logic
3052 * with {@link #throwException throwException},
3053 * in order to create a method handle of the correct return type.
3054 * @param target method handle to call
3055 * @param exType the type of exception which the handler will catch
3056 * @param handler method handle to call if a matching exception is thrown
3057 * @return method handle which incorporates the specified try/catch logic
3058 * @throws NullPointerException if any argument is null
3059 * @throws IllegalArgumentException if {@code handler} does not accept
3060 * the given exception type, or if the method handle types do
3061 * not match in their return types and their
3062 * corresponding parameters
3063 */
3064 public static
3065 MethodHandle catchException(MethodHandle target,
3066 Class<? extends Throwable> exType,
3067 MethodHandle handler) {
3068 MethodType ttype = target.type();
3069 MethodType htype = handler.type();
3070 if (htype.parameterCount() < 1 ||
3071 !htype.parameterType(0).isAssignableFrom(exType))
3072 throw newIllegalArgumentException("handler does not accept exception type "+exType);
3073 if (htype.returnType() != ttype.returnType())
3074 throw misMatchedTypes("target and handler return types", ttype, htype);
3075 List<Class<?>> targs = ttype.parameterList();
3076 List<Class<?>> hargs = htype.parameterList();
3077 hargs = hargs.subList(1, hargs.size()); // omit leading parameter from handler
3078 if (!targs.equals(hargs)) {
3079 int hpc = hargs.size(), tpc = targs.size();
3080 if (hpc >= tpc || !targs.subList(0, hpc).equals(hargs))
3081 throw misMatchedTypes("target and handler types", ttype, htype);
3082 handler = dropArguments(handler, 1+hpc, targs.subList(hpc, tpc));
3083 htype = handler.type();
3084 }
3085 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
3086 }
3087
3088 /**
3089 * Produces a method handle which will throw exceptions of the given {@code exType}.
3090 * The method handle will accept a single argument of {@code exType},
3091 * and immediately throw it as an exception.
3092 * The method type will nominally specify a return of {@code returnType}.
3093 * The return type may be anything convenient: It doesn't matter to the
3094 * method handle's behavior, since it will never return normally.
3095 * @param returnType the return type of the desired method handle
3096 * @param exType the parameter type of the desired method handle
3097 * @return method handle which can throw the given exceptions
3098 * @throws NullPointerException if either argument is null
3099 */
3100 public static
3101 MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
3102 if (!Throwable.class.isAssignableFrom(exType))
3103 throw new ClassCastException(exType.getName());
3104 return MethodHandleImpl.throwException(MethodType.methodType(returnType, exType));
3105 }
3106 }