1 /*
2 * Copyright (c) 2008, 2013, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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24 */
25
26 package java.lang.invoke;
27
28 import java.lang.reflect.*;
29 import java.util.List;
30 import java.util.ArrayList;
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.MethodHandleNatives.Constants.*;
44 import java.util.concurrent.ConcurrentHashMap;
45
46 /**
47 * This class consists exclusively of static methods that operate on or return
48 * method handles. They fall into several categories:
49 * <ul>
50 * <li>Lookup methods which help create method handles for methods and fields.
51 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
52 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
53 * </ul>
54 * <p>
55 * @author John Rose, JSR 292 EG
56 * @since 1.7
57 */
58 public class MethodHandles {
59
60 private MethodHandles() { } // do not instantiate
61
62 private static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
63 static { MethodHandleImpl.initStatics(); }
64 // See IMPL_LOOKUP below.
65
66 //// Method handle creation from ordinary methods.
67
68 /**
69 * Returns a {@link Lookup lookup object} with
70 * full capabilities to emulate all supported bytecode behaviors of the caller.
71 * These capabilities include <a href="MethodHandles.Lookup.html#privacc">private access</a> to the caller.
72 * Factory methods on the lookup object can create
73 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
74 * for any member that the caller has access to via bytecodes,
75 * including protected and private fields and methods.
76 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
77 * Do not store it in place where untrusted code can access it.
78 * <p>
79 * This method is caller sensitive, which means that it may return different
80 * values to different callers.
81 * <p>
82 * For any given caller class {@code C}, the lookup object returned by this call
83 * has equivalent capabilities to any lookup object
84 * supplied by the JVM to the bootstrap method of an
85 * <a href="package-summary.html#indyinsn">invokedynamic instruction</a>
86 * executing in the same caller class {@code C}.
87 * @return a lookup object for the caller of this method, with private access
88 */
89 @CallerSensitive
90 public static Lookup lookup() {
91 return new Lookup(Reflection.getCallerClass());
92 }
93
94 /**
95 * Returns a {@link Lookup lookup object} which is trusted minimally.
96 * It can only be used to create method handles to
97 * publicly accessible fields and methods.
98 * <p>
99 * As a matter of pure convention, the {@linkplain Lookup#lookupClass lookup class}
100 * of this lookup object will be {@link java.lang.Object}.
101 *
102 * <p style="font-size:smaller;">
103 * <em>Discussion:</em>
104 * The lookup class can be changed to any other class {@code C} using an expression of the form
105 * {@link Lookup#in publicLookup().in(C.class)}.
106 * Since all classes have equal access to public names,
107 * such a change would confer no new access rights.
108 * A public lookup object is always subject to
109 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
110 * Also, it cannot access
111 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
112 * @return a lookup object which is trusted minimally
113 */
114 public static Lookup publicLookup() {
115 return Lookup.PUBLIC_LOOKUP;
116 }
117
118 /**
119 * Performs an unchecked "crack" of a
120 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
121 * The result is as if the user had obtained a lookup object capable enough
122 * to crack the target method handle, called
123 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
124 * on the target to obtain its symbolic reference, and then called
125 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
126 * to resolve the symbolic reference to a member.
127 * <p>
128 * If there is a security manager, its {@code checkPermission} method
129 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
130 * @param <T> the desired type of the result, either {@link Member} or a subtype
131 * @param target a direct method handle to crack into symbolic reference components
132 * @param expected a class object representing the desired result type {@code T}
133 * @return a reference to the method, constructor, or field object
134 * @exception SecurityException if the caller is not privileged to call {@code setAccessible}
135 * @exception NullPointerException if either argument is {@code null}
136 * @exception IllegalArgumentException if the target is not a direct method handle
137 * @exception ClassCastException if the member is not of the expected type
138 * @since 1.8
139 */
140 public static <T extends Member> T
141 reflectAs(Class<T> expected, MethodHandle target) {
142 SecurityManager smgr = System.getSecurityManager();
143 if (smgr != null) smgr.checkPermission(ACCESS_PERMISSION);
144 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
145 return lookup.revealDirect(target).reflectAs(expected, lookup);
146 }
147 // Copied from AccessibleObject, as used by Method.setAccessible, etc.:
148 static final private java.security.Permission ACCESS_PERMISSION =
149 new ReflectPermission("suppressAccessChecks");
150
151 /**
152 * A <em>lookup object</em> is a factory for creating method handles,
153 * when the creation requires access checking.
154 * Method handles do not perform
155 * access checks when they are called, but rather when they are created.
156 * Therefore, method handle access
157 * restrictions must be enforced when a method handle is created.
158 * The caller class against which those restrictions are enforced
159 * is known as the {@linkplain #lookupClass lookup class}.
160 * <p>
161 * A lookup class which needs to create method handles will call
162 * {@link MethodHandles#lookup MethodHandles.lookup} to create a factory for itself.
163 * When the {@code Lookup} factory object is created, the identity of the lookup class is
164 * determined, and securely stored in the {@code Lookup} object.
165 * The lookup class (or its delegates) may then use factory methods
166 * on the {@code Lookup} object to create method handles for access-checked members.
167 * This includes all methods, constructors, and fields which are allowed to the lookup class,
168 * even private ones.
169 *
170 * <h1><a name="lookups"></a>Lookup Factory Methods</h1>
171 * The factory methods on a {@code Lookup} object correspond to all major
172 * use cases for methods, constructors, and fields.
173 * Each method handle created by a factory method is the functional
174 * equivalent of a particular <em>bytecode behavior</em>.
175 * (Bytecode behaviors are described in section 5.4.3.5 of the Java Virtual Machine Specification.)
176 * Here is a summary of the correspondence between these factory methods and
177 * the behavior the resulting method handles:
178 * <table border=1 cellpadding=5 summary="lookup method behaviors">
179 * <tr>
180 * <th><a name="equiv"></a>lookup expression</th>
181 * <th>member</th>
182 * <th>bytecode behavior</th>
183 * </tr>
184 * <tr>
185 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</td>
186 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
187 * </tr>
188 * <tr>
189 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</td>
190 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (T) C.f;}</td>
191 * </tr>
192 * <tr>
193 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</td>
194 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
195 * </tr>
196 * <tr>
197 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</td>
198 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
199 * </tr>
200 * <tr>
201 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</td>
202 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
203 * </tr>
204 * <tr>
205 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</td>
206 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
207 * </tr>
208 * <tr>
209 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</td>
210 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
211 * </tr>
212 * <tr>
213 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</td>
214 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
215 * </tr>
216 * <tr>
217 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</td>
218 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
219 * </tr>
220 * <tr>
221 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</td>
222 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
223 * </tr>
224 * <tr>
225 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
226 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
227 * </tr>
228 * <tr>
229 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</td>
230 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
231 * </tr>
232 * <tr>
233 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
234 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
235 * </tr>
236 * </table>
237 *
238 * Here, the type {@code C} is the class or interface being searched for a member,
239 * documented as a parameter named {@code refc} in the lookup methods.
240 * The method type {@code MT} is composed from the return type {@code T}
241 * and the sequence of argument types {@code A*}.
242 * The constructor also has a sequence of argument types {@code A*} and
243 * is deemed to return the newly-created object of type {@code C}.
244 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
245 * The formal parameter {@code this} stands for the self-reference of type {@code C};
246 * if it is present, it is always the leading argument to the method handle invocation.
247 * (In the case of some {@code protected} members, {@code this} may be
248 * restricted in type to the lookup class; see below.)
249 * The name {@code arg} stands for all the other method handle arguments.
250 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
251 * stands for a null reference if the accessed method or field is static,
252 * and {@code this} otherwise.
253 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
254 * for reflective objects corresponding to the given members.
255 * <p>
256 * In cases where the given member is of variable arity (i.e., a method or constructor)
257 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
258 * In all other cases, the returned method handle will be of fixed arity.
259 * <p style="font-size:smaller;">
260 * <em>Discussion:</em>
261 * The equivalence between looked-up method handles and underlying
262 * class members and bytecode behaviors
263 * can break down in a few ways:
264 * <ul style="font-size:smaller;">
265 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
266 * the lookup can still succeed, even when there is no equivalent
267 * Java expression or bytecoded constant.
268 * <li>Likewise, if {@code T} or {@code MT}
269 * is not symbolically accessible from the lookup class's loader,
270 * the lookup can still succeed.
271 * For example, lookups for {@code MethodHandle.invokeExact} and
272 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
273 * <li>If there is a security manager installed, it can forbid the lookup
274 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
275 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
276 * constant is not subject to security manager checks.
277 * <li>If the looked-up method has a
278 * <a href="MethodHandle.html#maxarity">very large arity</a>,
279 * the method handle creation may fail, due to the method handle
280 * type having too many parameters.
281 * </ul>
282 *
283 * <h1><a name="access"></a>Access checking</h1>
284 * Access checks are applied in the factory methods of {@code Lookup},
285 * when a method handle is created.
286 * This is a key difference from the Core Reflection API, since
287 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
288 * performs access checking against every caller, on every call.
289 * <p>
290 * All access checks start from a {@code Lookup} object, which
291 * compares its recorded lookup class against all requests to
292 * create method handles.
293 * A single {@code Lookup} object can be used to create any number
294 * of access-checked method handles, all checked against a single
295 * lookup class.
296 * <p>
297 * A {@code Lookup} object can be shared with other trusted code,
298 * such as a metaobject protocol.
299 * A shared {@code Lookup} object delegates the capability
300 * to create method handles on private members of the lookup class.
301 * Even if privileged code uses the {@code Lookup} object,
302 * the access checking is confined to the privileges of the
303 * original lookup class.
304 * <p>
305 * A lookup can fail, because
306 * the containing class is not accessible to the lookup class, or
307 * because the desired class member is missing, or because the
308 * desired class member is not accessible to the lookup class, or
309 * because the lookup object is not trusted enough to access the member.
310 * In any of these cases, a {@code ReflectiveOperationException} will be
311 * thrown from the attempted lookup. The exact class will be one of
312 * the following:
313 * <ul>
314 * <li>NoSuchMethodException — if a method is requested but does not exist
315 * <li>NoSuchFieldException — if a field is requested but does not exist
316 * <li>IllegalAccessException — if the member exists but an access check fails
317 * </ul>
318 * <p>
319 * In general, the conditions under which a method handle may be
320 * looked up for a method {@code M} are no more restrictive than the conditions
321 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
322 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
323 * a method handle lookup will generally raise a corresponding
324 * checked exception, such as {@code NoSuchMethodException}.
325 * And the effect of invoking the method handle resulting from the lookup
326 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
327 * to executing the compiled, verified, and resolved call to {@code M}.
328 * The same point is true of fields and constructors.
329 * <p style="font-size:smaller;">
330 * <em>Discussion:</em>
331 * Access checks only apply to named and reflected methods,
332 * constructors, and fields.
333 * Other method handle creation methods, such as
334 * {@link MethodHandle#asType MethodHandle.asType},
335 * do not require any access checks, and are used
336 * independently of any {@code Lookup} object.
337 * <p>
338 * If the desired member is {@code protected}, the usual JVM rules apply,
339 * including the requirement that the lookup class must be either be in the
340 * same package as the desired member, or must inherit that member.
341 * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.)
342 * In addition, if the desired member is a non-static field or method
343 * in a different package, the resulting method handle may only be applied
344 * to objects of the lookup class or one of its subclasses.
345 * This requirement is enforced by narrowing the type of the leading
346 * {@code this} parameter from {@code C}
347 * (which will necessarily be a superclass of the lookup class)
348 * to the lookup class itself.
349 * <p>
350 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
351 * that the receiver argument must match both the resolved method <em>and</em>
352 * the current class. Again, this requirement is enforced by narrowing the
353 * type of the leading parameter to the resulting method handle.
354 * (See the Java Virtual Machine Specification, section 4.10.1.9.)
355 * <p>
356 * The JVM represents constructors and static initializer blocks as internal methods
357 * with special names ({@code "<init>"} and {@code "<clinit>"}).
358 * The internal syntax of invocation instructions allows them to refer to such internal
359 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
360 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
361 * <p>
362 * In some cases, access between nested classes is obtained by the Java compiler by creating
363 * an wrapper method to access a private method of another class
364 * in the same top-level declaration.
365 * For example, a nested class {@code C.D}
366 * can access private members within other related classes such as
367 * {@code C}, {@code C.D.E}, or {@code C.B},
368 * but the Java compiler may need to generate wrapper methods in
369 * those related classes. In such cases, a {@code Lookup} object on
370 * {@code C.E} would be unable to those private members.
371 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
372 * which can transform a lookup on {@code C.E} into one on any of those other
373 * classes, without special elevation of privilege.
374 * <p>
375 * The accesses permitted to a given lookup object may be limited,
376 * according to its set of {@link #lookupModes lookupModes},
377 * to a subset of members normally accessible to the lookup class.
378 * For example, the {@link MethodHandles#publicLookup publicLookup}
379 * method produces a lookup object which is only allowed to access
380 * public members in public classes.
381 * The caller sensitive method {@link MethodHandles#lookup lookup}
382 * produces a lookup object with full capabilities relative to
383 * its caller class, to emulate all supported bytecode behaviors.
384 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
385 * with fewer access modes than the original lookup object.
386 *
387 * <p style="font-size:smaller;">
388 * <a name="privacc"></a>
389 * <em>Discussion of private access:</em>
390 * We say that a lookup has <em>private access</em>
391 * if its {@linkplain #lookupModes lookup modes}
392 * include the possibility of accessing {@code private} members.
393 * As documented in the relevant methods elsewhere,
394 * only lookups with private access possess the following capabilities:
395 * <ul style="font-size:smaller;">
396 * <li>access private fields, methods, and constructors of the lookup class
397 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
398 * such as {@code Class.forName}
399 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
400 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
401 * for classes accessible to the lookup class
402 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
403 * within the same package member
404 * </ul>
405 * <p style="font-size:smaller;">
406 * Each of these permissions is a consequence of the fact that a lookup object
407 * with private access can be securely traced back to an originating class,
408 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
409 * can be reliably determined and emulated by method handles.
410 *
411 * <h1><a name="secmgr"></a>Security manager interactions</h1>
412 * Although bytecode instructions can only refer to classes in
413 * a related class loader, this API can search for methods in any
414 * class, as long as a reference to its {@code Class} object is
415 * available. Such cross-loader references are also possible with the
416 * Core Reflection API, and are impossible to bytecode instructions
417 * such as {@code invokestatic} or {@code getfield}.
418 * There is a {@linkplain java.lang.SecurityManager security manager API}
419 * to allow applications to check such cross-loader references.
420 * These checks apply to both the {@code MethodHandles.Lookup} API
421 * and the Core Reflection API
422 * (as found on {@link java.lang.Class Class}).
423 * <p>
424 * If a security manager is present, member lookups are subject to
425 * additional checks.
426 * From one to three calls are made to the security manager.
427 * Any of these calls can refuse access by throwing a
428 * {@link java.lang.SecurityException SecurityException}.
429 * Define {@code smgr} as the security manager,
430 * {@code lookc} as the lookup class of the current lookup object,
431 * {@code refc} as the containing class in which the member
432 * is being sought, and {@code defc} as the class in which the
433 * member is actually defined.
434 * The value {@code lookc} is defined as <em>not present</em>
435 * if the current lookup object does not have
436 * <a href="MethodHandles.Lookup.html#privacc">private access</a>.
437 * The calls are made according to the following rules:
438 * <ul>
439 * <li><b>Step 1:</b>
440 * If {@code lookc} is not present, or if its class loader is not
441 * the same as or an ancestor of the class loader of {@code refc},
442 * then {@link SecurityManager#checkPackageAccess
443 * smgr.checkPackageAccess(refcPkg)} is called,
444 * where {@code refcPkg} is the package of {@code refc}.
445 * <li><b>Step 2:</b>
446 * If the retrieved member is not public and
447 * {@code lookc} is not present, then
448 * {@link SecurityManager#checkPermission smgr.checkPermission}
449 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
450 * <li><b>Step 3:</b>
451 * If the retrieved member is not public,
452 * and if {@code lookc} is not present,
453 * and if {@code defc} and {@code refc} are different,
454 * then {@link SecurityManager#checkPackageAccess
455 * smgr.checkPackageAccess(defcPkg)} is called,
456 * where {@code defcPkg} is the package of {@code defc}.
457 * </ul>
458 * Security checks are performed after other access checks have passed.
459 * Therefore, the above rules presuppose a member that is public,
460 * or else that is being accessed from a lookup class that has
461 * rights to access the member.
462 *
463 * <h1><a name="callsens"></a>Caller sensitive methods</h1>
464 * A small number of Java methods have a special property called caller sensitivity.
465 * A <em>caller-sensitive</em> method can behave differently depending on the
466 * identity of its immediate caller.
467 * <p>
468 * If a method handle for a caller-sensitive method is requested,
469 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
470 * but they take account of the lookup class in a special way.
471 * The resulting method handle behaves as if it were called
472 * from an instruction contained in the lookup class,
473 * so that the caller-sensitive method detects the lookup class.
474 * (By contrast, the invoker of the method handle is disregarded.)
475 * Thus, in the case of caller-sensitive methods,
476 * different lookup classes may give rise to
477 * differently behaving method handles.
478 * <p>
479 * In cases where the lookup object is
480 * {@link MethodHandles#publicLookup() publicLookup()},
481 * or some other lookup object without
482 * <a href="MethodHandles.Lookup.html#privacc">private access</a>,
483 * the lookup class is disregarded.
484 * In such cases, no caller-sensitive method handle can be created,
485 * access is forbidden, and the lookup fails with an
486 * {@code IllegalAccessException}.
487 * <p style="font-size:smaller;">
488 * <em>Discussion:</em>
489 * For example, the caller-sensitive method
490 * {@link java.lang.Class#forName(String) Class.forName(x)}
491 * can return varying classes or throw varying exceptions,
492 * depending on the class loader of the class that calls it.
493 * A public lookup of {@code Class.forName} will fail, because
494 * there is no reasonable way to determine its bytecode behavior.
495 * <p style="font-size:smaller;">
496 * If an application caches method handles for broad sharing,
497 * it should use {@code publicLookup()} to create them.
498 * If there is a lookup of {@code Class.forName}, it will fail,
499 * and the application must take appropriate action in that case.
500 * It may be that a later lookup, perhaps during the invocation of a
501 * bootstrap method, can incorporate the specific identity
502 * of the caller, making the method accessible.
503 * <p style="font-size:smaller;">
504 * The function {@code MethodHandles.lookup} is caller sensitive
505 * so that there can be a secure foundation for lookups.
506 * Nearly all other methods in the JSR 292 API rely on lookup
507 * objects to check access requests.
508 */
509 public static final
510 class Lookup {
511 /** The class on behalf of whom the lookup is being performed. */
512 private final Class<?> lookupClass;
513
514 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
515 private final int allowedModes;
516
517 /** A single-bit mask representing {@code public} access,
518 * which may contribute to the result of {@link #lookupModes lookupModes}.
519 * The value, {@code 0x01}, happens to be the same as the value of the
520 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
521 */
522 public static final int PUBLIC = Modifier.PUBLIC;
523
524 /** A single-bit mask representing {@code private} access,
525 * which may contribute to the result of {@link #lookupModes lookupModes}.
526 * The value, {@code 0x02}, happens to be the same as the value of the
527 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
528 */
529 public static final int PRIVATE = Modifier.PRIVATE;
530
531 /** A single-bit mask representing {@code protected} access,
532 * which may contribute to the result of {@link #lookupModes lookupModes}.
533 * The value, {@code 0x04}, happens to be the same as the value of the
534 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
535 */
536 public static final int PROTECTED = Modifier.PROTECTED;
537
538 /** A single-bit mask representing {@code package} access (default access),
539 * which may contribute to the result of {@link #lookupModes lookupModes}.
540 * The value is {@code 0x08}, which does not correspond meaningfully to
541 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
542 */
543 public static final int PACKAGE = Modifier.STATIC;
544
545 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE);
546 private static final int TRUSTED = -1;
547
548 private static int fixmods(int mods) {
549 mods &= (ALL_MODES - PACKAGE);
550 return (mods != 0) ? mods : PACKAGE;
551 }
552
553 /** Tells which class is performing the lookup. It is this class against
554 * which checks are performed for visibility and access permissions.
555 * <p>
556 * The class implies a maximum level of access permission,
557 * but the permissions may be additionally limited by the bitmask
558 * {@link #lookupModes lookupModes}, which controls whether non-public members
559 * can be accessed.
560 * @return the lookup class, on behalf of which this lookup object finds members
561 */
562 public Class<?> lookupClass() {
563 return lookupClass;
564 }
565
566 // This is just for calling out to MethodHandleImpl.
567 private Class<?> lookupClassOrNull() {
568 return (allowedModes == TRUSTED) ? null : lookupClass;
569 }
570
571 /** Tells which access-protection classes of members this lookup object can produce.
572 * The result is a bit-mask of the bits
573 * {@linkplain #PUBLIC PUBLIC (0x01)},
574 * {@linkplain #PRIVATE PRIVATE (0x02)},
575 * {@linkplain #PROTECTED PROTECTED (0x04)},
576 * and {@linkplain #PACKAGE PACKAGE (0x08)}.
577 * <p>
578 * A freshly-created lookup object
579 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class}
580 * has all possible bits set, since the caller class can access all its own members.
581 * A lookup object on a new lookup class
582 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
583 * may have some mode bits set to zero.
584 * The purpose of this is to restrict access via the new lookup object,
585 * so that it can access only names which can be reached by the original
586 * lookup object, and also by the new lookup class.
587 * @return the lookup modes, which limit the kinds of access performed by this lookup object
588 */
589 public int lookupModes() {
590 return allowedModes & ALL_MODES;
591 }
592
593 /** Embody the current class (the lookupClass) as a lookup class
594 * for method handle creation.
595 * Must be called by from a method in this package,
596 * which in turn is called by a method not in this package.
597 */
598 Lookup(Class<?> lookupClass) {
599 this(lookupClass, ALL_MODES);
600 // make sure we haven't accidentally picked up a privileged class:
601 checkUnprivilegedlookupClass(lookupClass, ALL_MODES);
602 }
603
604 private Lookup(Class<?> lookupClass, int allowedModes) {
605 this.lookupClass = lookupClass;
606 this.allowedModes = allowedModes;
607 }
608
609 /**
610 * Creates a lookup on the specified new lookup class.
611 * The resulting object will report the specified
612 * class as its own {@link #lookupClass lookupClass}.
613 * <p>
614 * However, the resulting {@code Lookup} object is guaranteed
615 * to have no more access capabilities than the original.
616 * In particular, access capabilities can be lost as follows:<ul>
617 * <li>If the new lookup class differs from the old one,
618 * protected members will not be accessible by virtue of inheritance.
619 * (Protected members may continue to be accessible because of package sharing.)
620 * <li>If the new lookup class is in a different package
621 * than the old one, protected and default (package) members will not be accessible.
622 * <li>If the new lookup class is not within the same package member
623 * as the old one, private members will not be accessible.
624 * <li>If the new lookup class is not accessible to the old lookup class,
625 * then no members, not even public members, will be accessible.
626 * (In all other cases, public members will continue to be accessible.)
627 * </ul>
628 *
629 * @param requestedLookupClass the desired lookup class for the new lookup object
630 * @return a lookup object which reports the desired lookup class
631 * @throws NullPointerException if the argument is null
632 */
633 public Lookup in(Class<?> requestedLookupClass) {
634 requestedLookupClass.getClass(); // null check
635 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
636 return new Lookup(requestedLookupClass, ALL_MODES);
637 if (requestedLookupClass == this.lookupClass)
638 return this; // keep same capabilities
639 int newModes = (allowedModes & (ALL_MODES & ~PROTECTED));
640 if ((newModes & PACKAGE) != 0
641 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
642 newModes &= ~(PACKAGE|PRIVATE);
643 }
644 // Allow nestmate lookups to be created without special privilege:
645 if ((newModes & PRIVATE) != 0
646 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
647 newModes &= ~PRIVATE;
648 }
649 if ((newModes & PUBLIC) != 0
650 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, allowedModes)) {
651 // The requested class it not accessible from the lookup class.
652 // No permissions.
653 newModes = 0;
654 }
655 checkUnprivilegedlookupClass(requestedLookupClass, newModes);
656 return new Lookup(requestedLookupClass, newModes);
657 }
658
659 // Make sure outer class is initialized first.
660 static { IMPL_NAMES.getClass(); }
661
662 /** Version of lookup which is trusted minimally.
663 * It can only be used to create method handles to
664 * publicly accessible members.
665 */
666 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, PUBLIC);
667
668 /** Package-private version of lookup which is trusted. */
669 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, TRUSTED);
670
671 private static void checkUnprivilegedlookupClass(Class<?> lookupClass, int allowedModes) {
672 String name = lookupClass.getName();
673 if (name.startsWith("java.lang.invoke."))
674 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
675
676 // For caller-sensitive MethodHandles.lookup()
677 // disallow lookup more restricted packages
678 if (allowedModes == ALL_MODES && lookupClass.getClassLoader() == null) {
679 if (name.startsWith("java.") ||
680 (name.startsWith("sun.") && !name.startsWith("sun.invoke."))) {
681 throw newIllegalArgumentException("illegal lookupClass: " + lookupClass);
682 }
683 }
684 }
685
686 /**
687 * Displays the name of the class from which lookups are to be made.
688 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
689 * If there are restrictions on the access permitted to this lookup,
690 * this is indicated by adding a suffix to the class name, consisting
691 * of a slash and a keyword. The keyword represents the strongest
692 * allowed access, and is chosen as follows:
693 * <ul>
694 * <li>If no access is allowed, the suffix is "/noaccess".
695 * <li>If only public access is allowed, the suffix is "/public".
696 * <li>If only public and package access are allowed, the suffix is "/package".
697 * <li>If only public, package, and private access are allowed, the suffix is "/private".
698 * </ul>
699 * If none of the above cases apply, it is the case that full
700 * access (public, package, private, and protected) is allowed.
701 * In this case, no suffix is added.
702 * This is true only of an object obtained originally from
703 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
704 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
705 * always have restricted access, and will display a suffix.
706 * <p>
707 * (It may seem strange that protected access should be
708 * stronger than private access. Viewed independently from
709 * package access, protected access is the first to be lost,
710 * because it requires a direct subclass relationship between
711 * caller and callee.)
712 * @see #in
713 */
714 @Override
715 public String toString() {
716 String cname = lookupClass.getName();
717 switch (allowedModes) {
718 case 0: // no privileges
719 return cname + "/noaccess";
720 case PUBLIC:
721 return cname + "/public";
722 case PUBLIC|PACKAGE:
723 return cname + "/package";
724 case ALL_MODES & ~PROTECTED:
725 return cname + "/private";
726 case ALL_MODES:
727 return cname;
728 case TRUSTED:
729 return "/trusted"; // internal only; not exported
730 default: // Should not happen, but it's a bitfield...
731 cname = cname + "/" + Integer.toHexString(allowedModes);
732 assert(false) : cname;
733 return cname;
734 }
735 }
736
737 /**
738 * Produces a method handle for a static method.
739 * The type of the method handle will be that of the method.
740 * (Since static methods do not take receivers, there is no
741 * additional receiver argument inserted into the method handle type,
742 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
743 * The method and all its argument types must be accessible to the lookup object.
744 * <p>
745 * The returned method handle will have
746 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
747 * the method's variable arity modifier bit ({@code 0x0080}) is set.
748 * <p>
749 * If the returned method handle is invoked, the method's class will
750 * be initialized, if it has not already been initialized.
751 * <p><b>Example:</b>
752 * <blockquote><pre>{@code
753 import static java.lang.invoke.MethodHandles.*;
754 import static java.lang.invoke.MethodType.*;
755 ...
756 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
757 "asList", methodType(List.class, Object[].class));
758 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
759 * }</pre></blockquote>
760 * @param refc the class from which the method is accessed
761 * @param name the name of the method
762 * @param type the type of the method
763 * @return the desired method handle
764 * @throws NoSuchMethodException if the method does not exist
765 * @throws IllegalAccessException if access checking fails,
766 * or if the method is not {@code static},
767 * or if the method's variable arity modifier bit
768 * is set and {@code asVarargsCollector} fails
769 * @exception SecurityException if a security manager is present and it
770 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
771 * @throws NullPointerException if any argument is null
772 */
773 public
774 MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
775 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
776 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method));
777 }
778
779 /**
780 * Produces a method handle for a virtual method.
781 * The type of the method handle will be that of the method,
782 * with the receiver type (usually {@code refc}) prepended.
783 * The method and all its argument types must be accessible to the lookup object.
784 * <p>
785 * When called, the handle will treat the first argument as a receiver
786 * and dispatch on the receiver's type to determine which method
787 * implementation to enter.
788 * (The dispatching action is identical with that performed by an
789 * {@code invokevirtual} or {@code invokeinterface} instruction.)
790 * <p>
791 * The first argument will be of type {@code refc} if the lookup
792 * class has full privileges to access the member. Otherwise
793 * the member must be {@code protected} and the first argument
794 * will be restricted in type to the lookup class.
795 * <p>
796 * The returned method handle will have
797 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
798 * the method's variable arity modifier bit ({@code 0x0080}) is set.
799 * <p>
800 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
801 * instructions and method handles produced by {@code findVirtual},
802 * if the class is {@code MethodHandle} and the name string is
803 * {@code invokeExact} or {@code invoke}, the resulting
804 * method handle is equivalent to one produced by
805 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
806 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
807 * with the same {@code type} argument.
808 *
809 * <b>Example:</b>
810 * <blockquote><pre>{@code
811 import static java.lang.invoke.MethodHandles.*;
812 import static java.lang.invoke.MethodType.*;
813 ...
814 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
815 "concat", methodType(String.class, String.class));
816 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
817 "hashCode", methodType(int.class));
818 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
819 "hashCode", methodType(int.class));
820 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
821 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
822 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
823 // interface method:
824 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
825 "subSequence", methodType(CharSequence.class, int.class, int.class));
826 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
827 // constructor "internal method" must be accessed differently:
828 MethodType MT_newString = methodType(void.class); //()V for new String()
829 try { assertEquals("impossible", lookup()
830 .findVirtual(String.class, "<init>", MT_newString));
831 } catch (NoSuchMethodException ex) { } // OK
832 MethodHandle MH_newString = publicLookup()
833 .findConstructor(String.class, MT_newString);
834 assertEquals("", (String) MH_newString.invokeExact());
835 * }</pre></blockquote>
836 *
837 * @param refc the class or interface from which the method is accessed
838 * @param name the name of the method
839 * @param type the type of the method, with the receiver argument omitted
840 * @return the desired method handle
841 * @throws NoSuchMethodException if the method does not exist
842 * @throws IllegalAccessException if access checking fails,
843 * or if the method is {@code static}
844 * or if the method's variable arity modifier bit
845 * is set and {@code asVarargsCollector} fails
846 * @exception SecurityException if a security manager is present and it
847 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
848 * @throws NullPointerException if any argument is null
849 */
850 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
851 if (refc == MethodHandle.class) {
852 MethodHandle mh = findVirtualForMH(name, type);
853 if (mh != null) return mh;
854 }
855 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
856 MemberName method = resolveOrFail(refKind, refc, name, type);
857 return getDirectMethod(refKind, refc, method, findBoundCallerClass(method));
858 }
859 private MethodHandle findVirtualForMH(String name, MethodType type) {
860 // these names require special lookups because of the implicit MethodType argument
861 if ("invoke".equals(name))
862 return invoker(type);
863 if ("invokeExact".equals(name))
864 return exactInvoker(type);
865 assert(!MemberName.isMethodHandleInvokeName(name));
866 return null;
867 }
868
869 /**
870 * Produces a method handle which creates an object and initializes it, using
871 * the constructor of the specified type.
872 * The parameter types of the method handle will be those of the constructor,
873 * while the return type will be a reference to the constructor's class.
874 * The constructor and all its argument types must be accessible to the lookup object.
875 * <p>
876 * The requested type must have a return type of {@code void}.
877 * (This is consistent with the JVM's treatment of constructor type descriptors.)
878 * <p>
879 * The returned method handle will have
880 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
881 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
882 * <p>
883 * If the returned method handle is invoked, the constructor's class will
884 * be initialized, if it has not already been initialized.
885 * <p><b>Example:</b>
886 * <blockquote><pre>{@code
887 import static java.lang.invoke.MethodHandles.*;
888 import static java.lang.invoke.MethodType.*;
889 ...
890 MethodHandle MH_newArrayList = publicLookup().findConstructor(
891 ArrayList.class, methodType(void.class, Collection.class));
892 Collection orig = Arrays.asList("x", "y");
893 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
894 assert(orig != copy);
895 assertEquals(orig, copy);
896 // a variable-arity constructor:
897 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
898 ProcessBuilder.class, methodType(void.class, String[].class));
899 ProcessBuilder pb = (ProcessBuilder)
900 MH_newProcessBuilder.invoke("x", "y", "z");
901 assertEquals("[x, y, z]", pb.command().toString());
902 * }</pre></blockquote>
903 * @param refc the class or interface from which the method is accessed
904 * @param type the type of the method, with the receiver argument omitted, and a void return type
905 * @return the desired method handle
906 * @throws NoSuchMethodException if the constructor does not exist
907 * @throws IllegalAccessException if access checking fails
908 * or if the method's variable arity modifier bit
909 * is set and {@code asVarargsCollector} fails
910 * @exception SecurityException if a security manager is present and it
911 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
912 * @throws NullPointerException if any argument is null
913 */
914 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
915 String name = "<init>";
916 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
917 return getDirectConstructor(refc, ctor);
918 }
919
920 /**
921 * Produces an early-bound method handle for a virtual method.
922 * It will bypass checks for overriding methods on the receiver,
923 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
924 * instruction from within the explicitly specified {@code specialCaller}.
925 * The type of the method handle will be that of the method,
926 * with a suitably restricted receiver type prepended.
927 * (The receiver type will be {@code specialCaller} or a subtype.)
928 * The method and all its argument types must be accessible
929 * to the lookup object.
930 * <p>
931 * Before method resolution,
932 * if the explicitly specified caller class is not identical with the
933 * lookup class, or if this lookup object does not have
934 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
935 * privileges, the access fails.
936 * <p>
937 * The returned method handle will have
938 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
939 * the method's variable arity modifier bit ({@code 0x0080}) is set.
940 * <p style="font-size:smaller;">
941 * <em>(Note: JVM internal methods named {@code "<init>"} are not visible to this API,
942 * even though the {@code invokespecial} instruction can refer to them
943 * in special circumstances. Use {@link #findConstructor findConstructor}
944 * to access instance initialization methods in a safe manner.)</em>
945 * <p><b>Example:</b>
946 * <blockquote><pre>{@code
947 import static java.lang.invoke.MethodHandles.*;
948 import static java.lang.invoke.MethodType.*;
949 ...
950 static class Listie extends ArrayList {
951 public String toString() { return "[wee Listie]"; }
952 static Lookup lookup() { return MethodHandles.lookup(); }
953 }
954 ...
955 // no access to constructor via invokeSpecial:
956 MethodHandle MH_newListie = Listie.lookup()
957 .findConstructor(Listie.class, methodType(void.class));
958 Listie l = (Listie) MH_newListie.invokeExact();
959 try { assertEquals("impossible", Listie.lookup().findSpecial(
960 Listie.class, "<init>", methodType(void.class), Listie.class));
961 } catch (NoSuchMethodException ex) { } // OK
962 // access to super and self methods via invokeSpecial:
963 MethodHandle MH_super = Listie.lookup().findSpecial(
964 ArrayList.class, "toString" , methodType(String.class), Listie.class);
965 MethodHandle MH_this = Listie.lookup().findSpecial(
966 Listie.class, "toString" , methodType(String.class), Listie.class);
967 MethodHandle MH_duper = Listie.lookup().findSpecial(
968 Object.class, "toString" , methodType(String.class), Listie.class);
969 assertEquals("[]", (String) MH_super.invokeExact(l));
970 assertEquals(""+l, (String) MH_this.invokeExact(l));
971 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
972 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
973 String.class, "toString", methodType(String.class), Listie.class));
974 } catch (IllegalAccessException ex) { } // OK
975 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
976 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
977 * }</pre></blockquote>
978 *
979 * @param refc the class or interface from which the method is accessed
980 * @param name the name of the method (which must not be "<init>")
981 * @param type the type of the method, with the receiver argument omitted
982 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
983 * @return the desired method handle
984 * @throws NoSuchMethodException if the method does not exist
985 * @throws IllegalAccessException if access checking fails
986 * or if the method's variable arity modifier bit
987 * is set and {@code asVarargsCollector} fails
988 * @exception SecurityException if a security manager is present and it
989 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
990 * @throws NullPointerException if any argument is null
991 */
992 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
993 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
994 checkSpecialCaller(specialCaller);
995 Lookup specialLookup = this.in(specialCaller);
996 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
997 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
998 }
999
1000 /**
1001 * Produces a method handle giving read access to a non-static field.
1002 * The type of the method handle will have a return type of the field's
1003 * value type.
1004 * The method handle's single argument will be the instance containing
1005 * the field.
1006 * Access checking is performed immediately on behalf of the lookup class.
1007 * @param refc the class or interface from which the method is accessed
1008 * @param name the field's name
1009 * @param type the field's type
1010 * @return a method handle which can load values from the field
1011 * @throws NoSuchFieldException if the field does not exist
1012 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1013 * @exception SecurityException if a security manager is present and it
1014 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1015 * @throws NullPointerException if any argument is null
1016 */
1017 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1018 MemberName field = resolveOrFail(REF_getField, refc, name, type);
1019 return getDirectField(REF_getField, refc, field);
1020 }
1021
1022 /**
1023 * Produces a method handle giving write access to a non-static field.
1024 * The type of the method handle will have a void return type.
1025 * The method handle will take two arguments, the instance containing
1026 * the field, and the value to be stored.
1027 * The second argument will be of the field's value type.
1028 * Access checking is performed immediately on behalf of the lookup class.
1029 * @param refc the class or interface from which the method is accessed
1030 * @param name the field's name
1031 * @param type the field's type
1032 * @return a method handle which can store values into the field
1033 * @throws NoSuchFieldException if the field does not exist
1034 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1035 * @exception SecurityException if a security manager is present and it
1036 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1037 * @throws NullPointerException if any argument is null
1038 */
1039 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1040 MemberName field = resolveOrFail(REF_putField, refc, name, type);
1041 return getDirectField(REF_putField, refc, field);
1042 }
1043
1044 /**
1045 * Produces a method handle giving read access to a static field.
1046 * The type of the method handle will have a return type of the field's
1047 * value type.
1048 * The method handle will take no arguments.
1049 * Access checking is performed immediately on behalf of the lookup class.
1050 * <p>
1051 * If the returned method handle is invoked, the field's class will
1052 * be initialized, if it has not already been initialized.
1053 * @param refc the class or interface from which the method is accessed
1054 * @param name the field's name
1055 * @param type the field's type
1056 * @return a method handle which can load values from the field
1057 * @throws NoSuchFieldException if the field does not exist
1058 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1059 * @exception SecurityException if a security manager is present and it
1060 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1061 * @throws NullPointerException if any argument is null
1062 */
1063 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1064 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
1065 return getDirectField(REF_getStatic, refc, field);
1066 }
1067
1068 /**
1069 * Produces a method handle giving write access to a static field.
1070 * The type of the method handle will have a void return type.
1071 * The method handle will take a single
1072 * argument, of the field's value type, the value to be stored.
1073 * Access checking is performed immediately on behalf of the lookup class.
1074 * <p>
1075 * If the returned method handle is invoked, the field's class will
1076 * be initialized, if it has not already been initialized.
1077 * @param refc the class or interface from which the method is accessed
1078 * @param name the field's name
1079 * @param type the field's type
1080 * @return a method handle which can store values into the field
1081 * @throws NoSuchFieldException if the field does not exist
1082 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1083 * @exception SecurityException if a security manager is present and it
1084 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1085 * @throws NullPointerException if any argument is null
1086 */
1087 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1088 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
1089 return getDirectField(REF_putStatic, refc, field);
1090 }
1091
1092 /**
1093 * Produces an early-bound method handle for a non-static method.
1094 * The receiver must have a supertype {@code defc} in which a method
1095 * of the given name and type is accessible to the lookup class.
1096 * The method and all its argument types must be accessible to the lookup object.
1097 * The type of the method handle will be that of the method,
1098 * without any insertion of an additional receiver parameter.
1099 * The given receiver will be bound into the method handle,
1100 * so that every call to the method handle will invoke the
1101 * requested method on the given receiver.
1102 * <p>
1103 * The returned method handle will have
1104 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1105 * the method's variable arity modifier bit ({@code 0x0080}) is set
1106 * <em>and</em> the trailing array argument is not the only argument.
1107 * (If the trailing array argument is the only argument,
1108 * the given receiver value will be bound to it.)
1109 * <p>
1110 * This is equivalent to the following code:
1111 * <blockquote><pre>{@code
1112 import static java.lang.invoke.MethodHandles.*;
1113 import static java.lang.invoke.MethodType.*;
1114 ...
1115 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
1116 MethodHandle mh1 = mh0.bindTo(receiver);
1117 MethodType mt1 = mh1.type();
1118 if (mh0.isVarargsCollector())
1119 mh1 = mh1.asVarargsCollector(mt1.parameterType(mt1.parameterCount()-1));
1120 return mh1;
1121 * }</pre></blockquote>
1122 * where {@code defc} is either {@code receiver.getClass()} or a super
1123 * type of that class, in which the requested method is accessible
1124 * to the lookup class.
1125 * (Note that {@code bindTo} does not preserve variable arity.)
1126 * @param receiver the object from which the method is accessed
1127 * @param name the name of the method
1128 * @param type the type of the method, with the receiver argument omitted
1129 * @return the desired method handle
1130 * @throws NoSuchMethodException if the method does not exist
1131 * @throws IllegalAccessException if access checking fails
1132 * or if the method's variable arity modifier bit
1133 * is set and {@code asVarargsCollector} fails
1134 * @exception SecurityException if a security manager is present and it
1135 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1136 * @throws NullPointerException if any argument is null
1137 * @see MethodHandle#bindTo
1138 * @see #findVirtual
1139 */
1140 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1141 Class<? extends Object> refc = receiver.getClass(); // may get NPE
1142 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
1143 MethodHandle mh = getDirectMethodNoRestrict(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1144 return mh.bindReceiver(receiver).setVarargs(method);
1145 }
1146
1147 /**
1148 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1149 * to <i>m</i>, if the lookup class has permission.
1150 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
1151 * If <i>m</i> is virtual, overriding is respected on every call.
1152 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
1153 * The type of the method handle will be that of the method,
1154 * with the receiver type prepended (but only if it is non-static).
1155 * If the method's {@code accessible} flag is not set,
1156 * access checking is performed immediately on behalf of the lookup class.
1157 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
1158 * <p>
1159 * The returned method handle will have
1160 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1161 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1162 * <p>
1163 * If <i>m</i> is static, and
1164 * if the returned method handle is invoked, the method's class will
1165 * be initialized, if it has not already been initialized.
1166 * @param m the reflected method
1167 * @return a method handle which can invoke the reflected method
1168 * @throws IllegalAccessException if access checking fails
1169 * or if the method's variable arity modifier bit
1170 * is set and {@code asVarargsCollector} fails
1171 * @throws NullPointerException if the argument is null
1172 */
1173 public MethodHandle unreflect(Method m) throws IllegalAccessException {
1174 if (m.getDeclaringClass() == MethodHandle.class) {
1175 MethodHandle mh = unreflectForMH(m);
1176 if (mh != null) return mh;
1177 }
1178 MemberName method = new MemberName(m);
1179 byte refKind = method.getReferenceKind();
1180 if (refKind == REF_invokeSpecial)
1181 refKind = REF_invokeVirtual;
1182 assert(method.isMethod());
1183 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
1184 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method));
1185 }
1186 private MethodHandle unreflectForMH(Method m) {
1187 // these names require special lookups because they throw UnsupportedOperationException
1188 if (MemberName.isMethodHandleInvokeName(m.getName()))
1189 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
1190 return null;
1191 }
1192
1193 /**
1194 * Produces a method handle for a reflected method.
1195 * It will bypass checks for overriding methods on the receiver,
1196 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1197 * instruction from within the explicitly specified {@code specialCaller}.
1198 * The type of the method handle will be that of the method,
1199 * with a suitably restricted receiver type prepended.
1200 * (The receiver type will be {@code specialCaller} or a subtype.)
1201 * If the method's {@code accessible} flag is not set,
1202 * access checking is performed immediately on behalf of the lookup class,
1203 * as if {@code invokespecial} instruction were being linked.
1204 * <p>
1205 * Before method resolution,
1206 * if the explicitly specified caller class is not identical with the
1207 * lookup class, or if this lookup object does not have
1208 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1209 * privileges, the access fails.
1210 * <p>
1211 * The returned method handle will have
1212 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1213 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1214 * @param m the reflected method
1215 * @param specialCaller the class nominally calling the method
1216 * @return a method handle which can invoke the reflected method
1217 * @throws IllegalAccessException if access checking fails
1218 * or if the method's variable arity modifier bit
1219 * is set and {@code asVarargsCollector} fails
1220 * @throws NullPointerException if any argument is null
1221 */
1222 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
1223 checkSpecialCaller(specialCaller);
1224 Lookup specialLookup = this.in(specialCaller);
1225 MemberName method = new MemberName(m, true);
1226 assert(method.isMethod());
1227 // ignore m.isAccessible: this is a new kind of access
1228 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method));
1229 }
1230
1231 /**
1232 * Produces a method handle for a reflected constructor.
1233 * The type of the method handle will be that of the constructor,
1234 * with the return type changed to the declaring class.
1235 * The method handle will perform a {@code newInstance} operation,
1236 * creating a new instance of the constructor's class on the
1237 * arguments passed to the method handle.
1238 * <p>
1239 * If the constructor's {@code accessible} flag is not set,
1240 * access checking is performed immediately on behalf of the lookup class.
1241 * <p>
1242 * The returned method handle will have
1243 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1244 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1245 * <p>
1246 * If the returned method handle is invoked, the constructor's class will
1247 * be initialized, if it has not already been initialized.
1248 * @param c the reflected constructor
1249 * @return a method handle which can invoke the reflected constructor
1250 * @throws IllegalAccessException if access checking fails
1251 * or if the method's variable arity modifier bit
1252 * is set and {@code asVarargsCollector} fails
1253 * @throws NullPointerException if the argument is null
1254 */
1255 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
1256 MemberName ctor = new MemberName(c);
1257 assert(ctor.isConstructor());
1258 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
1259 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
1260 }
1261
1262 /**
1263 * Produces a method handle giving read access to a reflected field.
1264 * The type of the method handle will have a return type of the field's
1265 * value type.
1266 * If the field is static, the method handle will take no arguments.
1267 * Otherwise, its single argument will be the instance containing
1268 * the field.
1269 * If the field's {@code accessible} flag is not set,
1270 * access checking is performed immediately on behalf of the lookup class.
1271 * <p>
1272 * If the field is static, and
1273 * if the returned method handle is invoked, the field's class will
1274 * be initialized, if it has not already been initialized.
1275 * @param f the reflected field
1276 * @return a method handle which can load values from the reflected field
1277 * @throws IllegalAccessException if access checking fails
1278 * @throws NullPointerException if the argument is null
1279 */
1280 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
1281 return unreflectField(f, false);
1282 }
1283 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
1284 MemberName field = new MemberName(f, isSetter);
1285 assert(isSetter
1286 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
1287 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
1288 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
1289 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
1290 }
1291
1292 /**
1293 * Produces a method handle giving write access to a reflected field.
1294 * The type of the method handle will have a void return type.
1295 * If the field is static, the method handle will take a single
1296 * argument, of the field's value type, the value to be stored.
1297 * Otherwise, the two arguments will be the instance containing
1298 * the field, and the value to be stored.
1299 * If the field's {@code accessible} flag is not set,
1300 * access checking is performed immediately on behalf of the lookup class.
1301 * <p>
1302 * If the field is static, and
1303 * if the returned method handle is invoked, the field's class will
1304 * be initialized, if it has not already been initialized.
1305 * @param f the reflected field
1306 * @return a method handle which can store values into the reflected field
1307 * @throws IllegalAccessException if access checking fails
1308 * @throws NullPointerException if the argument is null
1309 */
1310 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
1311 return unreflectField(f, true);
1312 }
1313
1314 /**
1315 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1316 * created by this lookup object or a similar one.
1317 * Security and access checks are performed to ensure that this lookup object
1318 * is capable of reproducing the target method handle.
1319 * This means that the cracking may fail if target is a direct method handle
1320 * but was created by an unrelated lookup object.
1321 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
1322 * and was created by a lookup object for a different class.
1323 * @param target a direct method handle to crack into symbolic reference components
1324 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
1325 * @exception SecurityException if a security manager is present and it
1326 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1327 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
1328 * @exception NullPointerException if the target is {@code null}
1329 * @see MethodHandleInfo
1330 * @since 1.8
1331 */
1332 public MethodHandleInfo revealDirect(MethodHandle target) {
1333 MemberName member = target.internalMemberName();
1334 if (member == null || (!member.isResolved() && !member.isMethodHandleInvoke()))
1335 throw newIllegalArgumentException("not a direct method handle");
1336 Class<?> defc = member.getDeclaringClass();
1337 byte refKind = member.getReferenceKind();
1338 assert(MethodHandleNatives.refKindIsValid(refKind));
1339 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
1340 // Devirtualized method invocation is usually formally virtual.
1341 // To avoid creating extra MemberName objects for this common case,
1342 // we encode this extra degree of freedom using MH.isInvokeSpecial.
1343 refKind = REF_invokeVirtual;
1344 if (refKind == REF_invokeVirtual && defc.isInterface())
1345 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
1346 refKind = REF_invokeInterface;
1347 // Check SM permissions and member access before cracking.
1348 try {
1349 checkAccess(refKind, defc, member);
1350 checkSecurityManager(defc, member);
1351 } catch (IllegalAccessException ex) {
1352 throw new IllegalArgumentException(ex);
1353 }
1354 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
1355 Class<?> callerClass = target.internalCallerClass();
1356 if (!hasPrivateAccess() || callerClass != lookupClass())
1357 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
1358 }
1359 // Produce the handle to the results.
1360 return new InfoFromMemberName(this, member, refKind);
1361 }
1362
1363 /// Helper methods, all package-private.
1364
1365 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1366 checkSymbolicClass(refc); // do this before attempting to resolve
1367 name.getClass(); // NPE
1368 type.getClass(); // NPE
1369 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
1370 NoSuchFieldException.class);
1371 }
1372
1373 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1374 checkSymbolicClass(refc); // do this before attempting to resolve
1375 name.getClass(); // NPE
1376 type.getClass(); // NPE
1377 checkMethodName(refKind, name); // NPE check on name
1378 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
1379 NoSuchMethodException.class);
1380 }
1381
1382 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
1383 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
1384 member.getName().getClass(); // NPE
1385 member.getType().getClass(); // NPE
1386 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
1387 ReflectiveOperationException.class);
1388 }
1389
1390 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
1391 refc.getClass(); // NPE
1392 Class<?> caller = lookupClassOrNull();
1393 if (caller != null && !VerifyAccess.isClassAccessible(refc, caller, allowedModes))
1394 throw new MemberName(refc).makeAccessException("symbolic reference class is not public", this);
1395 }
1396
1397 /** Check name for an illegal leading "<" character. */
1398 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
1399 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
1400 throw new NoSuchMethodException("illegal method name: "+name);
1401 }
1402
1403
1404 /**
1405 * Find my trustable caller class if m is a caller sensitive method.
1406 * If this lookup object has private access, then the caller class is the lookupClass.
1407 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
1408 */
1409 Class<?> findBoundCallerClass(MemberName m) throws IllegalAccessException {
1410 Class<?> callerClass = null;
1411 if (MethodHandleNatives.isCallerSensitive(m)) {
1412 // Only lookups with private access are allowed to resolve caller-sensitive methods
1413 if (hasPrivateAccess()) {
1414 callerClass = lookupClass;
1415 } else {
1416 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
1417 }
1418 }
1419 return callerClass;
1420 }
1421
1422 private boolean hasPrivateAccess() {
1423 return (allowedModes & PRIVATE) != 0;
1424 }
1425
1426 /**
1427 * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
1428 * Determines a trustable caller class to compare with refc, the symbolic reference class.
1429 * If this lookup object has private access, then the caller class is the lookupClass.
1430 */
1431 void checkSecurityManager(Class<?> refc, MemberName m) {
1432 SecurityManager smgr = System.getSecurityManager();
1433 if (smgr == null) return;
1434 if (allowedModes == TRUSTED) return;
1435
1436 // Step 1:
1437 boolean fullPowerLookup = hasPrivateAccess();
1438 if (!fullPowerLookup ||
1439 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
1440 ReflectUtil.checkPackageAccess(refc);
1441 }
1442
1443 // Step 2:
1444 if (m.isPublic()) return;
1445 if (!fullPowerLookup) {
1446 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
1447 }
1448
1449 // Step 3:
1450 Class<?> defc = m.getDeclaringClass();
1451 if (!fullPowerLookup && defc != refc) {
1452 ReflectUtil.checkPackageAccess(defc);
1453 }
1454 }
1455
1456 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1457 boolean wantStatic = (refKind == REF_invokeStatic);
1458 String message;
1459 if (m.isConstructor())
1460 message = "expected a method, not a constructor";
1461 else if (!m.isMethod())
1462 message = "expected a method";
1463 else if (wantStatic != m.isStatic())
1464 message = wantStatic ? "expected a static method" : "expected a non-static method";
1465 else
1466 { checkAccess(refKind, refc, m); return; }
1467 throw m.makeAccessException(message, this);
1468 }
1469
1470 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1471 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
1472 String message;
1473 if (wantStatic != m.isStatic())
1474 message = wantStatic ? "expected a static field" : "expected a non-static field";
1475 else
1476 { checkAccess(refKind, refc, m); return; }
1477 throw m.makeAccessException(message, this);
1478 }
1479
1480 /** Check public/protected/private bits on the symbolic reference class and its member. */
1481 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1482 assert(m.referenceKindIsConsistentWith(refKind) &&
1483 MethodHandleNatives.refKindIsValid(refKind) &&
1484 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
1485 int allowedModes = this.allowedModes;
1486 if (allowedModes == TRUSTED) return;
1487 int mods = m.getModifiers();
1488 if (Modifier.isProtected(mods) &&
1489 refKind == REF_invokeVirtual &&
1490 m.getDeclaringClass() == Object.class &&
1491 m.getName().equals("clone") &&
1492 refc.isArray()) {
1493 // The JVM does this hack also.
1494 // (See ClassVerifier::verify_invoke_instructions
1495 // and LinkResolver::check_method_accessability.)
1496 // Because the JVM does not allow separate methods on array types,
1497 // there is no separate method for int[].clone.
1498 // All arrays simply inherit Object.clone.
1499 // But for access checking logic, we make Object.clone
1500 // (normally protected) appear to be public.
1501 // Later on, when the DirectMethodHandle is created,
1502 // its leading argument will be restricted to the
1503 // requested array type.
1504 // N.B. The return type is not adjusted, because
1505 // that is *not* the bytecode behavior.
1506 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
1507 }
1508 if (Modifier.isFinal(mods) &&
1509 MethodHandleNatives.refKindIsSetter(refKind))
1510 throw m.makeAccessException("unexpected set of a final field", this);
1511 if (Modifier.isPublic(mods) && Modifier.isPublic(refc.getModifiers()) && allowedModes != 0)
1512 return; // common case
1513 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
1514 if ((requestedModes & allowedModes) != 0) {
1515 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
1516 mods, lookupClass(), allowedModes))
1517 return;
1518 } else {
1519 // Protected members can also be checked as if they were package-private.
1520 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
1521 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
1522 return;
1523 }
1524 throw m.makeAccessException(accessFailedMessage(refc, m), this);
1525 }
1526
1527 String accessFailedMessage(Class<?> refc, MemberName m) {
1528 Class<?> defc = m.getDeclaringClass();
1529 int mods = m.getModifiers();
1530 // check the class first:
1531 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
1532 (defc == refc ||
1533 Modifier.isPublic(refc.getModifiers())));
1534 if (!classOK && (allowedModes & PACKAGE) != 0) {
1535 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), ALL_MODES) &&
1536 (defc == refc ||
1537 VerifyAccess.isClassAccessible(refc, lookupClass(), ALL_MODES)));
1538 }
1539 if (!classOK)
1540 return "class is not public";
1541 if (Modifier.isPublic(mods))
1542 return "access to public member failed"; // (how?)
1543 if (Modifier.isPrivate(mods))
1544 return "member is private";
1545 if (Modifier.isProtected(mods))
1546 return "member is protected";
1547 return "member is private to package";
1548 }
1549
1550 private static final boolean ALLOW_NESTMATE_ACCESS = false;
1551
1552 private void checkSpecialCaller(Class<?> specialCaller) throws IllegalAccessException {
1553 int allowedModes = this.allowedModes;
1554 if (allowedModes == TRUSTED) return;
1555 if (!hasPrivateAccess()
1556 || (specialCaller != lookupClass()
1557 && !(ALLOW_NESTMATE_ACCESS &&
1558 VerifyAccess.isSamePackageMember(specialCaller, lookupClass()))))
1559 throw new MemberName(specialCaller).
1560 makeAccessException("no private access for invokespecial", this);
1561 }
1562
1563 private boolean restrictProtectedReceiver(MemberName method) {
1564 // The accessing class only has the right to use a protected member
1565 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
1566 if (!method.isProtected() || method.isStatic()
1567 || allowedModes == TRUSTED
1568 || method.getDeclaringClass() == lookupClass()
1569 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass())
1570 || (ALLOW_NESTMATE_ACCESS &&
1571 VerifyAccess.isSamePackageMember(method.getDeclaringClass(), lookupClass())))
1572 return false;
1573 return true;
1574 }
1575 private MethodHandle restrictReceiver(MemberName method, MethodHandle mh, Class<?> caller) throws IllegalAccessException {
1576 assert(!method.isStatic());
1577 // receiver type of mh is too wide; narrow to caller
1578 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
1579 throw method.makeAccessException("caller class must be a subclass below the method", caller);
1580 }
1581 MethodType rawType = mh.type();
1582 if (rawType.parameterType(0) == caller) return mh;
1583 MethodType narrowType = rawType.changeParameterType(0, caller);
1584 return mh.viewAsType(narrowType);
1585 }
1586
1587 /** Check access and get the requested method. */
1588 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
1589 final boolean doRestrict = true;
1590 final boolean checkSecurity = true;
1591 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
1592 }
1593 /** Check access and get the requested method, eliding receiver narrowing rules. */
1594 private MethodHandle getDirectMethodNoRestrict(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
1595 final boolean doRestrict = false;
1596 final boolean checkSecurity = true;
1597 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
1598 }
1599 /** Check access and get the requested method, eliding security manager checks. */
1600 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
1601 final boolean doRestrict = true;
1602 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
1603 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
1604 }
1605 /** Common code for all methods; do not call directly except from immediately above. */
1606 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
1607 boolean checkSecurity,
1608 boolean doRestrict, Class<?> callerClass) throws IllegalAccessException {
1609 checkMethod(refKind, refc, method);
1610 // Optionally check with the security manager; this isn't needed for unreflect* calls.
1611 if (checkSecurity)
1612 checkSecurityManager(refc, method);
1613 assert(!method.isMethodHandleInvoke());
1614
1615 Class<?> refcAsSuper;
1616 if (refKind == REF_invokeSpecial &&
1617 refc != lookupClass() &&
1618 !refc.isInterface() &&
1619 refc != (refcAsSuper = lookupClass().getSuperclass()) &&
1620 refc.isAssignableFrom(lookupClass())) {
1621 assert(!method.getName().equals("<init>")); // not this code path
1622 // Per JVMS 6.5, desc. of invokespecial instruction:
1623 // If the method is in a superclass of the LC,
1624 // and if our original search was above LC.super,
1625 // repeat the search (symbolic lookup) from LC.super.
1626 // FIXME: MemberName.resolve should handle this instead.
1627 MemberName m2 = new MemberName(refcAsSuper,
1628 method.getName(),
1629 method.getMethodType(),
1630 REF_invokeSpecial);
1631 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull());
1632 if (m2 == null) throw new InternalError(method.toString());
1633 method = m2;
1634 refc = refcAsSuper;
1635 // redo basic checks
1636 checkMethod(refKind, refc, method);
1637 }
1638
1639 MethodHandle mh = DirectMethodHandle.make(refKind, refc, method);
1640 mh = maybeBindCaller(method, mh, callerClass);
1641 mh = mh.setVarargs(method);
1642 // Optionally narrow the receiver argument to refc using restrictReceiver.
1643 if (doRestrict &&
1644 (refKind == REF_invokeSpecial ||
1645 (MethodHandleNatives.refKindHasReceiver(refKind) &&
1646 restrictProtectedReceiver(method))))
1647 mh = restrictReceiver(method, mh, lookupClass());
1648 return mh;
1649 }
1650 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh,
1651 Class<?> callerClass)
1652 throws IllegalAccessException {
1653 if (allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
1654 return mh;
1655 Class<?> hostClass = lookupClass;
1656 if (!hasPrivateAccess()) // caller must have private access
1657 hostClass = callerClass; // callerClass came from a security manager style stack walk
1658 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, hostClass);
1659 // Note: caller will apply varargs after this step happens.
1660 return cbmh;
1661 }
1662 /** Check access and get the requested field. */
1663 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
1664 final boolean checkSecurity = true;
1665 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
1666 }
1667 /** Check access and get the requested field, eliding security manager checks. */
1668 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
1669 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
1670 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
1671 }
1672 /** Common code for all fields; do not call directly except from immediately above. */
1673 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
1674 boolean checkSecurity) throws IllegalAccessException {
1675 checkField(refKind, refc, field);
1676 // Optionally check with the security manager; this isn't needed for unreflect* calls.
1677 if (checkSecurity)
1678 checkSecurityManager(refc, field);
1679 MethodHandle mh = DirectMethodHandle.make(refc, field);
1680 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
1681 restrictProtectedReceiver(field));
1682 if (doRestrict)
1683 mh = restrictReceiver(field, mh, lookupClass());
1684 return mh;
1685 }
1686 /** Check access and get the requested constructor. */
1687 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
1688 final boolean checkSecurity = true;
1689 return getDirectConstructorCommon(refc, ctor, checkSecurity);
1690 }
1691 /** Check access and get the requested constructor, eliding security manager checks. */
1692 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
1693 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
1694 return getDirectConstructorCommon(refc, ctor, checkSecurity);
1695 }
1696 /** Common code for all constructors; do not call directly except from immediately above. */
1697 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
1698 boolean checkSecurity) throws IllegalAccessException {
1699 assert(ctor.isConstructor());
1700 checkAccess(REF_newInvokeSpecial, refc, ctor);
1701 // Optionally check with the security manager; this isn't needed for unreflect* calls.
1702 if (checkSecurity)
1703 checkSecurityManager(refc, ctor);
1704 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
1705 return DirectMethodHandle.make(ctor).setVarargs(ctor);
1706 }
1707
1708 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
1709 */
1710 /*non-public*/
1711 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type) throws ReflectiveOperationException {
1712 if (!(type instanceof Class || type instanceof MethodType))
1713 throw new InternalError("unresolved MemberName");
1714 MemberName member = new MemberName(refKind, defc, name, type);
1715 MethodHandle mh = LOOKASIDE_TABLE.get(member);
1716 if (mh != null) {
1717 checkSymbolicClass(defc);
1718 return mh;
1719 }
1720 // Treat MethodHandle.invoke and invokeExact specially.
1721 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
1722 mh = findVirtualForMH(member.getName(), member.getMethodType());
1723 if (mh != null) {
1724 return mh;
1725 }
1726 }
1727 MemberName resolved = resolveOrFail(refKind, member);
1728 mh = getDirectMethodForConstant(refKind, defc, resolved);
1729 if (mh instanceof DirectMethodHandle
1730 && canBeCached(refKind, defc, resolved)) {
1731 MemberName key = mh.internalMemberName();
1732 if (key != null) {
1733 key = key.asNormalOriginal();
1734 }
1735 if (member.equals(key)) { // better safe than sorry
1736 LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh);
1737 }
1738 }
1739 return mh;
1740 }
1741 private
1742 boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
1743 if (refKind == REF_invokeSpecial) {
1744 return false;
1745 }
1746 if (!Modifier.isPublic(defc.getModifiers()) ||
1747 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
1748 !member.isPublic() ||
1749 member.isCallerSensitive()) {
1750 return false;
1751 }
1752 ClassLoader loader = defc.getClassLoader();
1753 if (!sun.misc.VM.isSystemDomainLoader(loader)) {
1754 ClassLoader sysl = ClassLoader.getSystemClassLoader();
1755 boolean found = false;
1756 while (sysl != null) {
1757 if (loader == sysl) { found = true; break; }
1758 sysl = sysl.getParent();
1759 }
1760 if (!found) {
1761 return false;
1762 }
1763 }
1764 try {
1765 MemberName resolved2 = publicLookup().resolveOrFail(refKind,
1766 new MemberName(refKind, defc, member.getName(), member.getType()));
1767 checkSecurityManager(defc, resolved2);
1768 } catch (ReflectiveOperationException | SecurityException ex) {
1769 return false;
1770 }
1771 return true;
1772 }
1773 private
1774 MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
1775 throws ReflectiveOperationException {
1776 if (MethodHandleNatives.refKindIsField(refKind)) {
1777 return getDirectFieldNoSecurityManager(refKind, defc, member);
1778 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
1779 return getDirectMethodNoSecurityManager(refKind, defc, member, lookupClass);
1780 } else if (refKind == REF_newInvokeSpecial) {
1781 return getDirectConstructorNoSecurityManager(defc, member);
1782 }
1783 // oops
1784 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
1785 }
1786
1787 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
1788 }
1789
1790 /**
1791 * Produces a method handle giving read access to elements of an array.
1792 * The type of the method handle will have a return type of the array's
1793 * element type. Its first argument will be the array type,
1794 * and the second will be {@code int}.
1795 * @param arrayClass an array type
1796 * @return a method handle which can load values from the given array type
1797 * @throws NullPointerException if the argument is null
1798 * @throws IllegalArgumentException if arrayClass is not an array type
1799 */
1800 public static
1801 MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
1802 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, false);
1803 }
1804
1805 /**
1806 * Produces a method handle giving write access to elements of an array.
1807 * The type of the method handle will have a void return type.
1808 * Its last argument will be the array's element type.
1809 * The first and second arguments will be the array type and int.
1810 * @param arrayClass the class of an array
1811 * @return a method handle which can store values into the array type
1812 * @throws NullPointerException if the argument is null
1813 * @throws IllegalArgumentException if arrayClass is not an array type
1814 */
1815 public static
1816 MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
1817 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, true);
1818 }
1819
1820 /// method handle invocation (reflective style)
1821
1822 /**
1823 * Produces a method handle which will invoke any method handle of the
1824 * given {@code type}, with a given number of trailing arguments replaced by
1825 * a single trailing {@code Object[]} array.
1826 * The resulting invoker will be a method handle with the following
1827 * arguments:
1828 * <ul>
1829 * <li>a single {@code MethodHandle} target
1830 * <li>zero or more leading values (counted by {@code leadingArgCount})
1831 * <li>an {@code Object[]} array containing trailing arguments
1832 * </ul>
1833 * <p>
1834 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
1835 * the indicated {@code type}.
1836 * That is, if the target is exactly of the given {@code type}, it will behave
1837 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
1838 * is used to convert the target to the required {@code type}.
1839 * <p>
1840 * The type of the returned invoker will not be the given {@code type}, but rather
1841 * will have all parameters except the first {@code leadingArgCount}
1842 * replaced by a single array of type {@code Object[]}, which will be
1843 * the final parameter.
1844 * <p>
1845 * Before invoking its target, the invoker will spread the final array, apply
1846 * reference casts as necessary, and unbox and widen primitive arguments.
1847 * If, when the invoker is called, the supplied array argument does
1848 * not have the correct number of elements, the invoker will throw
1849 * an {@link IllegalArgumentException} instead of invoking the target.
1850 * <p>
1851 * This method is equivalent to the following code (though it may be more efficient):
1852 * <blockquote><pre>{@code
1853 MethodHandle invoker = MethodHandles.invoker(type);
1854 int spreadArgCount = type.parameterCount() - leadingArgCount;
1855 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
1856 return invoker;
1857 * }</pre></blockquote>
1858 * This method throws no reflective or security exceptions.
1859 * @param type the desired target type
1860 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
1861 * @return a method handle suitable for invoking any method handle of the given type
1862 * @throws NullPointerException if {@code type} is null
1863 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
1864 * the range from 0 to {@code type.parameterCount()} inclusive,
1865 * or if the resulting method handle's type would have
1866 * <a href="MethodHandle.html#maxarity">too many parameters</a>
1867 */
1868 static public
1869 MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
1870 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
1871 throw new IllegalArgumentException("bad argument count "+leadingArgCount);
1872 return type.invokers().spreadInvoker(leadingArgCount);
1873 }
1874
1875 /**
1876 * Produces a special <em>invoker method handle</em> which can be used to
1877 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
1878 * The resulting invoker will have a type which is
1879 * exactly equal to the desired type, except that it will accept
1880 * an additional leading argument of type {@code MethodHandle}.
1881 * <p>
1882 * This method is equivalent to the following code (though it may be more efficient):
1883 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
1884 *
1885 * <p style="font-size:smaller;">
1886 * <em>Discussion:</em>
1887 * Invoker method handles can be useful when working with variable method handles
1888 * of unknown types.
1889 * For example, to emulate an {@code invokeExact} call to a variable method
1890 * handle {@code M}, extract its type {@code T},
1891 * look up the invoker method {@code X} for {@code T},
1892 * and call the invoker method, as {@code X.invoke(T, A...)}.
1893 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
1894 * is unknown.)
1895 * If spreading, collecting, or other argument transformations are required,
1896 * they can be applied once to the invoker {@code X} and reused on many {@code M}
1897 * method handle values, as long as they are compatible with the type of {@code X}.
1898 * <p style="font-size:smaller;">
1899 * <em>(Note: The invoker method is not available via the Core Reflection API.
1900 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
1901 * on the declared {@code invokeExact} or {@code invoke} method will raise an
1902 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
1903 * <p>
1904 * This method throws no reflective or security exceptions.
1905 * @param type the desired target type
1906 * @return a method handle suitable for invoking any method handle of the given type
1907 * @throws IllegalArgumentException if the resulting method handle's type would have
1908 * <a href="MethodHandle.html#maxarity">too many parameters</a>
1909 */
1910 static public
1911 MethodHandle exactInvoker(MethodType type) {
1912 return type.invokers().exactInvoker();
1913 }
1914
1915 /**
1916 * Produces a special <em>invoker method handle</em> which can be used to
1917 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
1918 * The resulting invoker will have a type which is
1919 * exactly equal to the desired type, except that it will accept
1920 * an additional leading argument of type {@code MethodHandle}.
1921 * <p>
1922 * Before invoking its target, if the target differs from the expected type,
1923 * the invoker will apply reference casts as
1924 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
1925 * Similarly, the return value will be converted as necessary.
1926 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
1927 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
1928 * <p>
1929 * This method is equivalent to the following code (though it may be more efficient):
1930 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
1931 * <p style="font-size:smaller;">
1932 * <em>Discussion:</em>
1933 * A {@linkplain MethodType#genericMethodType general method type} is one which
1934 * mentions only {@code Object} arguments and return values.
1935 * An invoker for such a type is capable of calling any method handle
1936 * of the same arity as the general type.
1937 * <p style="font-size:smaller;">
1938 * <em>(Note: The invoker method is not available via the Core Reflection API.
1939 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
1940 * on the declared {@code invokeExact} or {@code invoke} method will raise an
1941 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
1942 * <p>
1943 * This method throws no reflective or security exceptions.
1944 * @param type the desired target type
1945 * @return a method handle suitable for invoking any method handle convertible to the given type
1946 * @throws IllegalArgumentException if the resulting method handle's type would have
1947 * <a href="MethodHandle.html#maxarity">too many parameters</a>
1948 */
1949 static public
1950 MethodHandle invoker(MethodType type) {
1951 return type.invokers().generalInvoker();
1952 }
1953
1954 static /*non-public*/
1955 MethodHandle basicInvoker(MethodType type) {
1956 return type.form().basicInvoker();
1957 }
1958
1959 /// method handle modification (creation from other method handles)
1960
1961 /**
1962 * Produces a method handle which adapts the type of the
1963 * given method handle to a new type by pairwise argument and return type conversion.
1964 * The original type and new type must have the same number of arguments.
1965 * The resulting method handle is guaranteed to report a type
1966 * which is equal to the desired new type.
1967 * <p>
1968 * If the original type and new type are equal, returns target.
1969 * <p>
1970 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
1971 * and some additional conversions are also applied if those conversions fail.
1972 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
1973 * if possible, before or instead of any conversions done by {@code asType}:
1974 * <ul>
1975 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
1976 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
1977 * (This treatment of interfaces follows the usage of the bytecode verifier.)
1978 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
1979 * the boolean is converted to a byte value, 1 for true, 0 for false.
1980 * (This treatment follows the usage of the bytecode verifier.)
1981 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
1982 * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
1983 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
1984 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
1985 * then a Java casting conversion (JLS 5.5) is applied.
1986 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
1987 * widening and/or narrowing.)
1988 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
1989 * conversion will be applied at runtime, possibly followed
1990 * by a Java casting conversion (JLS 5.5) on the primitive value,
1991 * possibly followed by a conversion from byte to boolean by testing
1992 * the low-order bit.
1993 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
1994 * and if the reference is null at runtime, a zero value is introduced.
1995 * </ul>
1996 * @param target the method handle to invoke after arguments are retyped
1997 * @param newType the expected type of the new method handle
1998 * @return a method handle which delegates to the target after performing
1999 * any necessary argument conversions, and arranges for any
2000 * necessary return value conversions
2001 * @throws NullPointerException if either argument is null
2002 * @throws WrongMethodTypeException if the conversion cannot be made
2003 * @see MethodHandle#asType
2004 */
2005 public static
2006 MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
2007 if (!target.type().isCastableTo(newType)) {
2008 throw new WrongMethodTypeException("cannot explicitly cast "+target+" to "+newType);
2009 }
2010 return MethodHandleImpl.makePairwiseConvert(target, newType, 2);
2011 }
2012
2013 /**
2014 * Produces a method handle which adapts the calling sequence of the
2015 * given method handle to a new type, by reordering the arguments.
2016 * The resulting method handle is guaranteed to report a type
2017 * which is equal to the desired new type.
2018 * <p>
2019 * The given array controls the reordering.
2020 * Call {@code #I} the number of incoming parameters (the value
2021 * {@code newType.parameterCount()}, and call {@code #O} the number
2022 * of outgoing parameters (the value {@code target.type().parameterCount()}).
2023 * Then the length of the reordering array must be {@code #O},
2024 * and each element must be a non-negative number less than {@code #I}.
2025 * For every {@code N} less than {@code #O}, the {@code N}-th
2026 * outgoing argument will be taken from the {@code I}-th incoming
2027 * argument, where {@code I} is {@code reorder[N]}.
2028 * <p>
2029 * No argument or return value conversions are applied.
2030 * The type of each incoming argument, as determined by {@code newType},
2031 * must be identical to the type of the corresponding outgoing parameter
2032 * or parameters in the target method handle.
2033 * The return type of {@code newType} must be identical to the return
2034 * type of the original target.
2035 * <p>
2036 * The reordering array need not specify an actual permutation.
2037 * An incoming argument will be duplicated if its index appears
2038 * more than once in the array, and an incoming argument will be dropped
2039 * if its index does not appear in the array.
2040 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
2041 * incoming arguments which are not mentioned in the reordering array
2042 * are may be any type, as determined only by {@code newType}.
2043 * <blockquote><pre>{@code
2044 import static java.lang.invoke.MethodHandles.*;
2045 import static java.lang.invoke.MethodType.*;
2046 ...
2047 MethodType intfn1 = methodType(int.class, int.class);
2048 MethodType intfn2 = methodType(int.class, int.class, int.class);
2049 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
2050 assert(sub.type().equals(intfn2));
2051 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
2052 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
2053 assert((int)rsub.invokeExact(1, 100) == 99);
2054 MethodHandle add = ... (int x, int y) -> (x+y) ...;
2055 assert(add.type().equals(intfn2));
2056 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
2057 assert(twice.type().equals(intfn1));
2058 assert((int)twice.invokeExact(21) == 42);
2059 * }</pre></blockquote>
2060 * @param target the method handle to invoke after arguments are reordered
2061 * @param newType the expected type of the new method handle
2062 * @param reorder an index array which controls the reordering
2063 * @return a method handle which delegates to the target after it
2064 * drops unused arguments and moves and/or duplicates the other arguments
2065 * @throws NullPointerException if any argument is null
2066 * @throws IllegalArgumentException if the index array length is not equal to
2067 * the arity of the target, or if any index array element
2068 * not a valid index for a parameter of {@code newType},
2069 * or if two corresponding parameter types in
2070 * {@code target.type()} and {@code newType} are not identical,
2071 */
2072 public static
2073 MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
2074 checkReorder(reorder, newType, target.type());
2075 return target.permuteArguments(newType, reorder);
2076 }
2077
2078 private static void checkReorder(int[] reorder, MethodType newType, MethodType oldType) {
2079 if (newType.returnType() != oldType.returnType())
2080 throw newIllegalArgumentException("return types do not match",
2081 oldType, newType);
2082 if (reorder.length == oldType.parameterCount()) {
2083 int limit = newType.parameterCount();
2084 boolean bad = false;
2085 for (int j = 0; j < reorder.length; j++) {
2086 int i = reorder[j];
2087 if (i < 0 || i >= limit) {
2088 bad = true; break;
2089 }
2090 Class<?> src = newType.parameterType(i);
2091 Class<?> dst = oldType.parameterType(j);
2092 if (src != dst)
2093 throw newIllegalArgumentException("parameter types do not match after reorder",
2094 oldType, newType);
2095 }
2096 if (!bad) return;
2097 }
2098 throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
2099 }
2100
2101 /**
2102 * Produces a method handle of the requested return type which returns the given
2103 * constant value every time it is invoked.
2104 * <p>
2105 * Before the method handle is returned, the passed-in value is converted to the requested type.
2106 * If the requested type is primitive, widening primitive conversions are attempted,
2107 * else reference conversions are attempted.
2108 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
2109 * @param type the return type of the desired method handle
2110 * @param value the value to return
2111 * @return a method handle of the given return type and no arguments, which always returns the given value
2112 * @throws NullPointerException if the {@code type} argument is null
2113 * @throws ClassCastException if the value cannot be converted to the required return type
2114 * @throws IllegalArgumentException if the given type is {@code void.class}
2115 */
2116 public static
2117 MethodHandle constant(Class<?> type, Object value) {
2118 if (type.isPrimitive()) {
2119 if (type == void.class)
2120 throw newIllegalArgumentException("void type");
2121 Wrapper w = Wrapper.forPrimitiveType(type);
2122 return insertArguments(identity(type), 0, w.convert(value, type));
2123 } else {
2124 return identity(type).bindTo(type.cast(value));
2125 }
2126 }
2127
2128 /**
2129 * Produces a method handle which returns its sole argument when invoked.
2130 * @param type the type of the sole parameter and return value of the desired method handle
2131 * @return a unary method handle which accepts and returns the given type
2132 * @throws NullPointerException if the argument is null
2133 * @throws IllegalArgumentException if the given type is {@code void.class}
2134 */
2135 public static
2136 MethodHandle identity(Class<?> type) {
2137 if (type == void.class)
2138 throw newIllegalArgumentException("void type");
2139 else if (type == Object.class)
2140 return ValueConversions.identity();
2141 else if (type.isPrimitive())
2142 return ValueConversions.identity(Wrapper.forPrimitiveType(type));
2143 else
2144 return MethodHandleImpl.makeReferenceIdentity(type);
2145 }
2146
2147 /**
2148 * Provides a target method handle with one or more <em>bound arguments</em>
2149 * in advance of the method handle's invocation.
2150 * The formal parameters to the target corresponding to the bound
2151 * arguments are called <em>bound parameters</em>.
2152 * Returns a new method handle which saves away the bound arguments.
2153 * When it is invoked, it receives arguments for any non-bound parameters,
2154 * binds the saved arguments to their corresponding parameters,
2155 * and calls the original target.
2156 * <p>
2157 * The type of the new method handle will drop the types for the bound
2158 * parameters from the original target type, since the new method handle
2159 * will no longer require those arguments to be supplied by its callers.
2160 * <p>
2161 * Each given argument object must match the corresponding bound parameter type.
2162 * If a bound parameter type is a primitive, the argument object
2163 * must be a wrapper, and will be unboxed to produce the primitive value.
2164 * <p>
2165 * The {@code pos} argument selects which parameters are to be bound.
2166 * It may range between zero and <i>N-L</i> (inclusively),
2167 * where <i>N</i> is the arity of the target method handle
2168 * and <i>L</i> is the length of the values array.
2169 * @param target the method handle to invoke after the argument is inserted
2170 * @param pos where to insert the argument (zero for the first)
2171 * @param values the series of arguments to insert
2172 * @return a method handle which inserts an additional argument,
2173 * before calling the original method handle
2174 * @throws NullPointerException if the target or the {@code values} array is null
2175 * @see MethodHandle#bindTo
2176 */
2177 public static
2178 MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
2179 int insCount = values.length;
2180 MethodType oldType = target.type();
2181 int outargs = oldType.parameterCount();
2182 int inargs = outargs - insCount;
2183 if (inargs < 0)
2184 throw newIllegalArgumentException("too many values to insert");
2185 if (pos < 0 || pos > inargs)
2186 throw newIllegalArgumentException("no argument type to append");
2187 MethodHandle result = target;
2188 for (int i = 0; i < insCount; i++) {
2189 Object value = values[i];
2190 Class<?> ptype = oldType.parameterType(pos+i);
2191 if (ptype.isPrimitive()) {
2192 BasicType btype = I_TYPE;
2193 Wrapper w = Wrapper.forPrimitiveType(ptype);
2194 switch (w) {
2195 case LONG: btype = J_TYPE; break;
2196 case FLOAT: btype = F_TYPE; break;
2197 case DOUBLE: btype = D_TYPE; break;
2198 }
2199 // perform unboxing and/or primitive conversion
2200 value = w.convert(value, ptype);
2201 result = result.bindArgument(pos, btype, value);
2202 continue;
2203 }
2204 value = ptype.cast(value); // throw CCE if needed
2205 if (pos == 0) {
2206 result = result.bindReceiver(value);
2207 } else {
2208 result = result.bindArgument(pos, L_TYPE, value);
2209 }
2210 }
2211 return result;
2212 }
2213
2214 /**
2215 * Produces a method handle which will discard some dummy arguments
2216 * before calling some other specified <i>target</i> method handle.
2217 * The type of the new method handle will be the same as the target's type,
2218 * except it will also include the dummy argument types,
2219 * at some given position.
2220 * <p>
2221 * The {@code pos} argument may range between zero and <i>N</i>,
2222 * where <i>N</i> is the arity of the target.
2223 * If {@code pos} is zero, the dummy arguments will precede
2224 * the target's real arguments; if {@code pos} is <i>N</i>
2225 * they will come after.
2226 * <p>
2227 * <b>Example:</b>
2228 * <blockquote><pre>{@code
2229 import static java.lang.invoke.MethodHandles.*;
2230 import static java.lang.invoke.MethodType.*;
2231 ...
2232 MethodHandle cat = lookup().findVirtual(String.class,
2233 "concat", methodType(String.class, String.class));
2234 assertEquals("xy", (String) cat.invokeExact("x", "y"));
2235 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
2236 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
2237 assertEquals(bigType, d0.type());
2238 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
2239 * }</pre></blockquote>
2240 * <p>
2241 * This method is also equivalent to the following code:
2242 * <blockquote><pre>
2243 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
2244 * </pre></blockquote>
2245 * @param target the method handle to invoke after the arguments are dropped
2246 * @param valueTypes the type(s) of the argument(s) to drop
2247 * @param pos position of first argument to drop (zero for the leftmost)
2248 * @return a method handle which drops arguments of the given types,
2249 * before calling the original method handle
2250 * @throws NullPointerException if the target is null,
2251 * or if the {@code valueTypes} list or any of its elements is null
2252 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
2253 * or if {@code pos} is negative or greater than the arity of the target,
2254 * or if the new method handle's type would have too many parameters
2255 */
2256 public static
2257 MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
2258 MethodType oldType = target.type(); // get NPE
2259 int dropped = valueTypes.size();
2260 MethodType.checkSlotCount(dropped);
2261 if (dropped == 0) return target;
2262 int outargs = oldType.parameterCount();
2263 int inargs = outargs + dropped;
2264 if (pos < 0 || pos >= inargs)
2265 throw newIllegalArgumentException("no argument type to remove");
2266 ArrayList<Class<?>> ptypes = new ArrayList<>(oldType.parameterList());
2267 ptypes.addAll(pos, valueTypes);
2268 MethodType newType = MethodType.methodType(oldType.returnType(), ptypes);
2269 return target.dropArguments(newType, pos, dropped);
2270 }
2271
2272 /**
2273 * Produces a method handle which will discard some dummy arguments
2274 * before calling some other specified <i>target</i> method handle.
2275 * The type of the new method handle will be the same as the target's type,
2276 * except it will also include the dummy argument types,
2277 * at some given position.
2278 * <p>
2279 * The {@code pos} argument may range between zero and <i>N</i>,
2280 * where <i>N</i> is the arity of the target.
2281 * If {@code pos} is zero, the dummy arguments will precede
2282 * the target's real arguments; if {@code pos} is <i>N</i>
2283 * they will come after.
2284 * <p>
2285 * <b>Example:</b>
2286 * <blockquote><pre>{@code
2287 import static java.lang.invoke.MethodHandles.*;
2288 import static java.lang.invoke.MethodType.*;
2289 ...
2290 MethodHandle cat = lookup().findVirtual(String.class,
2291 "concat", methodType(String.class, String.class));
2292 assertEquals("xy", (String) cat.invokeExact("x", "y"));
2293 MethodHandle d0 = dropArguments(cat, 0, String.class);
2294 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
2295 MethodHandle d1 = dropArguments(cat, 1, String.class);
2296 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
2297 MethodHandle d2 = dropArguments(cat, 2, String.class);
2298 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
2299 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
2300 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
2301 * }</pre></blockquote>
2302 * <p>
2303 * This method is also equivalent to the following code:
2304 * <blockquote><pre>
2305 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
2306 * </pre></blockquote>
2307 * @param target the method handle to invoke after the arguments are dropped
2308 * @param valueTypes the type(s) of the argument(s) to drop
2309 * @param pos position of first argument to drop (zero for the leftmost)
2310 * @return a method handle which drops arguments of the given types,
2311 * before calling the original method handle
2312 * @throws NullPointerException if the target is null,
2313 * or if the {@code valueTypes} array or any of its elements is null
2314 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
2315 * or if {@code pos} is negative or greater than the arity of the target,
2316 * or if the new method handle's type would have
2317 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2318 */
2319 public static
2320 MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
2321 return dropArguments(target, pos, Arrays.asList(valueTypes));
2322 }
2323
2324 /**
2325 * Adapts a target method handle by pre-processing
2326 * one or more of its arguments, each with its own unary filter function,
2327 * and then calling the target with each pre-processed argument
2328 * replaced by the result of its corresponding filter function.
2329 * <p>
2330 * The pre-processing is performed by one or more method handles,
2331 * specified in the elements of the {@code filters} array.
2332 * The first element of the filter array corresponds to the {@code pos}
2333 * argument of the target, and so on in sequence.
2334 * <p>
2335 * Null arguments in the array are treated as identity functions,
2336 * and the corresponding arguments left unchanged.
2337 * (If there are no non-null elements in the array, the original target is returned.)
2338 * Each filter is applied to the corresponding argument of the adapter.
2339 * <p>
2340 * If a filter {@code F} applies to the {@code N}th argument of
2341 * the target, then {@code F} must be a method handle which
2342 * takes exactly one argument. The type of {@code F}'s sole argument
2343 * replaces the corresponding argument type of the target
2344 * in the resulting adapted method handle.
2345 * The return type of {@code F} must be identical to the corresponding
2346 * parameter type of the target.
2347 * <p>
2348 * It is an error if there are elements of {@code filters}
2349 * (null or not)
2350 * which do not correspond to argument positions in the target.
2351 * <p><b>Example:</b>
2352 * <blockquote><pre>{@code
2353 import static java.lang.invoke.MethodHandles.*;
2354 import static java.lang.invoke.MethodType.*;
2355 ...
2356 MethodHandle cat = lookup().findVirtual(String.class,
2357 "concat", methodType(String.class, String.class));
2358 MethodHandle upcase = lookup().findVirtual(String.class,
2359 "toUpperCase", methodType(String.class));
2360 assertEquals("xy", (String) cat.invokeExact("x", "y"));
2361 MethodHandle f0 = filterArguments(cat, 0, upcase);
2362 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
2363 MethodHandle f1 = filterArguments(cat, 1, upcase);
2364 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
2365 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
2366 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
2367 * }</pre></blockquote>
2368 * <p> Here is pseudocode for the resulting adapter:
2369 * <blockquote><pre>{@code
2370 * V target(P... p, A[i]... a[i], B... b);
2371 * A[i] filter[i](V[i]);
2372 * T adapter(P... p, V[i]... v[i], B... b) {
2373 * return target(p..., f[i](v[i])..., b...);
2374 * }
2375 * }</pre></blockquote>
2376 *
2377 * @param target the method handle to invoke after arguments are filtered
2378 * @param pos the position of the first argument to filter
2379 * @param filters method handles to call initially on filtered arguments
2380 * @return method handle which incorporates the specified argument filtering logic
2381 * @throws NullPointerException if the target is null
2382 * or if the {@code filters} array is null
2383 * @throws IllegalArgumentException if a non-null element of {@code filters}
2384 * does not match a corresponding argument type of target as described above,
2385 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
2386 * or if the resulting method handle's type would have
2387 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2388 */
2389 public static
2390 MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
2391 MethodType targetType = target.type();
2392 MethodHandle adapter = target;
2393 MethodType adapterType = null;
2394 assert((adapterType = targetType) != null);
2395 int maxPos = targetType.parameterCount();
2396 if (pos + filters.length > maxPos)
2397 throw newIllegalArgumentException("too many filters");
2398 int curPos = pos-1; // pre-incremented
2399 for (MethodHandle filter : filters) {
2400 curPos += 1;
2401 if (filter == null) continue; // ignore null elements of filters
2402 adapter = filterArgument(adapter, curPos, filter);
2403 assert((adapterType = adapterType.changeParameterType(curPos, filter.type().parameterType(0))) != null);
2404 }
2405 assert(adapterType.equals(adapter.type()));
2406 return adapter;
2407 }
2408
2409 /*non-public*/ static
2410 MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
2411 MethodType targetType = target.type();
2412 MethodType filterType = filter.type();
2413 if (filterType.parameterCount() != 1
2414 || filterType.returnType() != targetType.parameterType(pos))
2415 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
2416 return MethodHandleImpl.makeCollectArguments(target, filter, pos, false);
2417 }
2418
2419 /**
2420 * Adapts a target method handle by pre-processing
2421 * a sub-sequence of its arguments with a filter (another method handle).
2422 * The pre-processed arguments are replaced by the result (if any) of the
2423 * filter function.
2424 * The target is then called on the modified (usually shortened) argument list.
2425 * <p>
2426 * If the filter returns a value, the target must accept that value as
2427 * its argument in position {@code pos}, preceded and/or followed by
2428 * any arguments not passed to the filter.
2429 * If the filter returns void, the target must accept all arguments
2430 * not passed to the filter.
2431 * No arguments are reordered, and a result returned from the filter
2432 * replaces (in order) the whole subsequence of arguments originally
2433 * passed to the adapter.
2434 * <p>
2435 * The argument types (if any) of the filter
2436 * replace zero or one argument types of the target, at position {@code pos},
2437 * in the resulting adapted method handle.
2438 * The return type of the filter (if any) must be identical to the
2439 * argument type of the target at position {@code pos}, and that target argument
2440 * is supplied by the return value of the filter.
2441 * <p>
2442 * In all cases, {@code pos} must be greater than or equal to zero, and
2443 * {@code pos} must also be less than or equal to the target's arity.
2444 * <p><b>Example:</b>
2445 * <blockquote><pre>{@code
2446 import static java.lang.invoke.MethodHandles.*;
2447 import static java.lang.invoke.MethodType.*;
2448 ...
2449 MethodHandle deepToString = publicLookup()
2450 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
2451
2452 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
2453 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
2454
2455 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
2456 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
2457
2458 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
2459 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
2460 assertEquals("[top, [up, down], strange]",
2461 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
2462
2463 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
2464 assertEquals("[top, [up, down], [strange]]",
2465 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
2466
2467 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
2468 assertEquals("[top, [[up, down, strange], charm], bottom]",
2469 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
2470 * }</pre></blockquote>
2471 * <p> Here is pseudocode for the resulting adapter:
2472 * <blockquote><pre>{@code
2473 * T target(A...,V,C...);
2474 * V filter(B...);
2475 * T adapter(A... a,B... b,C... c) {
2476 * V v = filter(b...);
2477 * return target(a...,v,c...);
2478 * }
2479 * // and if the filter has no arguments:
2480 * T target2(A...,V,C...);
2481 * V filter2();
2482 * T adapter2(A... a,C... c) {
2483 * V v = filter2();
2484 * return target2(a...,v,c...);
2485 * }
2486 * // and if the filter has a void return:
2487 * T target3(A...,C...);
2488 * void filter3(B...);
2489 * void adapter3(A... a,B... b,C... c) {
2490 * filter3(b...);
2491 * return target3(a...,c...);
2492 * }
2493 * }</pre></blockquote>
2494 * <p>
2495 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
2496 * one which first "folds" the affected arguments, and then drops them, in separate
2497 * steps as follows:
2498 * <blockquote><pre>{@code
2499 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
2500 * mh = MethodHandles.foldArguments(mh, coll); //step 1
2501 * }</pre></blockquote>
2502 * If the target method handle consumes no arguments besides than the result
2503 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
2504 * is equivalent to {@code filterReturnValue(coll, mh)}.
2505 * If the filter method handle {@code coll} consumes one argument and produces
2506 * a non-void result, then {@code collectArguments(mh, N, coll)}
2507 * is equivalent to {@code filterArguments(mh, N, coll)}.
2508 * Other equivalences are possible but would require argument permutation.
2509 *
2510 * @param target the method handle to invoke after filtering the subsequence of arguments
2511 * @param pos the position of the first adapter argument to pass to the filter,
2512 * and/or the target argument which receives the result of the filter
2513 * @param filter method handle to call on the subsequence of arguments
2514 * @return method handle which incorporates the specified argument subsequence filtering logic
2515 * @throws NullPointerException if either argument is null
2516 * @throws IllegalArgumentException if the return type of {@code filter}
2517 * is non-void and is not the same as the {@code pos} argument of the target,
2518 * or if {@code pos} is not between 0 and the target's arity, inclusive,
2519 * or if the resulting method handle's type would have
2520 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2521 * @see MethodHandles#foldArguments
2522 * @see MethodHandles#filterArguments
2523 * @see MethodHandles#filterReturnValue
2524 */
2525 public static
2526 MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
2527 MethodType targetType = target.type();
2528 MethodType filterType = filter.type();
2529 if (filterType.returnType() != void.class &&
2530 filterType.returnType() != targetType.parameterType(pos))
2531 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
2532 return MethodHandleImpl.makeCollectArguments(target, filter, pos, false);
2533 }
2534
2535 /**
2536 * Adapts a target method handle by post-processing
2537 * its return value (if any) with a filter (another method handle).
2538 * The result of the filter is returned from the adapter.
2539 * <p>
2540 * If the target returns a value, the filter must accept that value as
2541 * its only argument.
2542 * If the target returns void, the filter must accept no arguments.
2543 * <p>
2544 * The return type of the filter
2545 * replaces the return type of the target
2546 * in the resulting adapted method handle.
2547 * The argument type of the filter (if any) must be identical to the
2548 * return type of the target.
2549 * <p><b>Example:</b>
2550 * <blockquote><pre>{@code
2551 import static java.lang.invoke.MethodHandles.*;
2552 import static java.lang.invoke.MethodType.*;
2553 ...
2554 MethodHandle cat = lookup().findVirtual(String.class,
2555 "concat", methodType(String.class, String.class));
2556 MethodHandle length = lookup().findVirtual(String.class,
2557 "length", methodType(int.class));
2558 System.out.println((String) cat.invokeExact("x", "y")); // xy
2559 MethodHandle f0 = filterReturnValue(cat, length);
2560 System.out.println((int) f0.invokeExact("x", "y")); // 2
2561 * }</pre></blockquote>
2562 * <p> Here is pseudocode for the resulting adapter:
2563 * <blockquote><pre>{@code
2564 * V target(A...);
2565 * T filter(V);
2566 * T adapter(A... a) {
2567 * V v = target(a...);
2568 * return filter(v);
2569 * }
2570 * // and if the target has a void return:
2571 * void target2(A...);
2572 * T filter2();
2573 * T adapter2(A... a) {
2574 * target2(a...);
2575 * return filter2();
2576 * }
2577 * // and if the filter has a void return:
2578 * V target3(A...);
2579 * void filter3(V);
2580 * void adapter3(A... a) {
2581 * V v = target3(a...);
2582 * filter3(v);
2583 * }
2584 * }</pre></blockquote>
2585 * @param target the method handle to invoke before filtering the return value
2586 * @param filter method handle to call on the return value
2587 * @return method handle which incorporates the specified return value filtering logic
2588 * @throws NullPointerException if either argument is null
2589 * @throws IllegalArgumentException if the argument list of {@code filter}
2590 * does not match the return type of target as described above
2591 */
2592 public static
2593 MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
2594 MethodType targetType = target.type();
2595 MethodType filterType = filter.type();
2596 Class<?> rtype = targetType.returnType();
2597 int filterValues = filterType.parameterCount();
2598 if (filterValues == 0
2599 ? (rtype != void.class)
2600 : (rtype != filterType.parameterType(0)))
2601 throw newIllegalArgumentException("target and filter types do not match", target, filter);
2602 // result = fold( lambda(retval, arg...) { filter(retval) },
2603 // lambda( arg...) { target(arg...) } )
2604 return MethodHandleImpl.makeCollectArguments(filter, target, 0, false);
2605 }
2606
2607 /**
2608 * Adapts a target method handle by pre-processing
2609 * some of its arguments, and then calling the target with
2610 * the result of the pre-processing, inserted into the original
2611 * sequence of arguments.
2612 * <p>
2613 * The pre-processing is performed by {@code combiner}, a second method handle.
2614 * Of the arguments passed to the adapter, the first {@code N} arguments
2615 * are copied to the combiner, which is then called.
2616 * (Here, {@code N} is defined as the parameter count of the combiner.)
2617 * After this, control passes to the target, with any result
2618 * from the combiner inserted before the original {@code N} incoming
2619 * arguments.
2620 * <p>
2621 * If the combiner returns a value, the first parameter type of the target
2622 * must be identical with the return type of the combiner, and the next
2623 * {@code N} parameter types of the target must exactly match the parameters
2624 * of the combiner.
2625 * <p>
2626 * If the combiner has a void return, no result will be inserted,
2627 * and the first {@code N} parameter types of the target
2628 * must exactly match the parameters of the combiner.
2629 * <p>
2630 * The resulting adapter is the same type as the target, except that the
2631 * first parameter type is dropped,
2632 * if it corresponds to the result of the combiner.
2633 * <p>
2634 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
2635 * that either the combiner or the target does not wish to receive.
2636 * If some of the incoming arguments are destined only for the combiner,
2637 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
2638 * arguments will not need to be live on the stack on entry to the
2639 * target.)
2640 * <p><b>Example:</b>
2641 * <blockquote><pre>{@code
2642 import static java.lang.invoke.MethodHandles.*;
2643 import static java.lang.invoke.MethodType.*;
2644 ...
2645 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
2646 "println", methodType(void.class, String.class))
2647 .bindTo(System.out);
2648 MethodHandle cat = lookup().findVirtual(String.class,
2649 "concat", methodType(String.class, String.class));
2650 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
2651 MethodHandle catTrace = foldArguments(cat, trace);
2652 // also prints "boo":
2653 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
2654 * }</pre></blockquote>
2655 * <p> Here is pseudocode for the resulting adapter:
2656 * <blockquote><pre>{@code
2657 * // there are N arguments in A...
2658 * T target(V, A[N]..., B...);
2659 * V combiner(A...);
2660 * T adapter(A... a, B... b) {
2661 * V v = combiner(a...);
2662 * return target(v, a..., b...);
2663 * }
2664 * // and if the combiner has a void return:
2665 * T target2(A[N]..., B...);
2666 * void combiner2(A...);
2667 * T adapter2(A... a, B... b) {
2668 * combiner2(a...);
2669 * return target2(a..., b...);
2670 * }
2671 * }</pre></blockquote>
2672 * @param target the method handle to invoke after arguments are combined
2673 * @param combiner method handle to call initially on the incoming arguments
2674 * @return method handle which incorporates the specified argument folding logic
2675 * @throws NullPointerException if either argument is null
2676 * @throws IllegalArgumentException if {@code combiner}'s return type
2677 * is non-void and not the same as the first argument type of
2678 * the target, or if the initial {@code N} argument types
2679 * of the target
2680 * (skipping one matching the {@code combiner}'s return type)
2681 * are not identical with the argument types of {@code combiner}
2682 */
2683 public static
2684 MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
2685 int pos = 0;
2686 MethodType targetType = target.type();
2687 MethodType combinerType = combiner.type();
2688 int foldPos = pos;
2689 int foldArgs = combinerType.parameterCount();
2690 int foldVals = combinerType.returnType() == void.class ? 0 : 1;
2691 int afterInsertPos = foldPos + foldVals;
2692 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
2693 if (ok && !(combinerType.parameterList()
2694 .equals(targetType.parameterList().subList(afterInsertPos,
2695 afterInsertPos + foldArgs))))
2696 ok = false;
2697 if (ok && foldVals != 0 && !combinerType.returnType().equals(targetType.parameterType(0)))
2698 ok = false;
2699 if (!ok)
2700 throw misMatchedTypes("target and combiner types", targetType, combinerType);
2701 MethodType newType = targetType.dropParameterTypes(foldPos, afterInsertPos);
2702 return MethodHandleImpl.makeCollectArguments(target, combiner, foldPos, true);
2703 }
2704
2705 /**
2706 * Makes a method handle which adapts a target method handle,
2707 * by guarding it with a test, a boolean-valued method handle.
2708 * If the guard fails, a fallback handle is called instead.
2709 * All three method handles must have the same corresponding
2710 * argument and return types, except that the return type
2711 * of the test must be boolean, and the test is allowed
2712 * to have fewer arguments than the other two method handles.
2713 * <p> Here is pseudocode for the resulting adapter:
2714 * <blockquote><pre>{@code
2715 * boolean test(A...);
2716 * T target(A...,B...);
2717 * T fallback(A...,B...);
2718 * T adapter(A... a,B... b) {
2719 * if (test(a...))
2720 * return target(a..., b...);
2721 * else
2722 * return fallback(a..., b...);
2723 * }
2724 * }</pre></blockquote>
2725 * Note that the test arguments ({@code a...} in the pseudocode) cannot
2726 * be modified by execution of the test, and so are passed unchanged
2727 * from the caller to the target or fallback as appropriate.
2728 * @param test method handle used for test, must return boolean
2729 * @param target method handle to call if test passes
2730 * @param fallback method handle to call if test fails
2731 * @return method handle which incorporates the specified if/then/else logic
2732 * @throws NullPointerException if any argument is null
2733 * @throws IllegalArgumentException if {@code test} does not return boolean,
2734 * or if all three method types do not match (with the return
2735 * type of {@code test} changed to match that of the target).
2736 */
2737 public static
2738 MethodHandle guardWithTest(MethodHandle test,
2739 MethodHandle target,
2740 MethodHandle fallback) {
2741 MethodType gtype = test.type();
2742 MethodType ttype = target.type();
2743 MethodType ftype = fallback.type();
2744 if (!ttype.equals(ftype))
2745 throw misMatchedTypes("target and fallback types", ttype, ftype);
2746 if (gtype.returnType() != boolean.class)
2747 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
2748 List<Class<?>> targs = ttype.parameterList();
2749 List<Class<?>> gargs = gtype.parameterList();
2750 if (!targs.equals(gargs)) {
2751 int gpc = gargs.size(), tpc = targs.size();
2752 if (gpc >= tpc || !targs.subList(0, gpc).equals(gargs))
2753 throw misMatchedTypes("target and test types", ttype, gtype);
2754 test = dropArguments(test, gpc, targs.subList(gpc, tpc));
2755 gtype = test.type();
2756 }
2757 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
2758 }
2759
2760 static RuntimeException misMatchedTypes(String what, MethodType t1, MethodType t2) {
2761 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
2762 }
2763
2764 /**
2765 * Makes a method handle which adapts a target method handle,
2766 * by running it inside an exception handler.
2767 * If the target returns normally, the adapter returns that value.
2768 * If an exception matching the specified type is thrown, the fallback
2769 * handle is called instead on the exception, plus the original arguments.
2770 * <p>
2771 * The target and handler must have the same corresponding
2772 * argument and return types, except that handler may omit trailing arguments
2773 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
2774 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
2775 * <p> Here is pseudocode for the resulting adapter:
2776 * <blockquote><pre>{@code
2777 * T target(A..., B...);
2778 * T handler(ExType, A...);
2779 * T adapter(A... a, B... b) {
2780 * try {
2781 * return target(a..., b...);
2782 * } catch (ExType ex) {
2783 * return handler(ex, a...);
2784 * }
2785 * }
2786 * }</pre></blockquote>
2787 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
2788 * be modified by execution of the target, and so are passed unchanged
2789 * from the caller to the handler, if the handler is invoked.
2790 * <p>
2791 * The target and handler must return the same type, even if the handler
2792 * always throws. (This might happen, for instance, because the handler
2793 * is simulating a {@code finally} clause).
2794 * To create such a throwing handler, compose the handler creation logic
2795 * with {@link #throwException throwException},
2796 * in order to create a method handle of the correct return type.
2797 * @param target method handle to call
2798 * @param exType the type of exception which the handler will catch
2799 * @param handler method handle to call if a matching exception is thrown
2800 * @return method handle which incorporates the specified try/catch logic
2801 * @throws NullPointerException if any argument is null
2802 * @throws IllegalArgumentException if {@code handler} does not accept
2803 * the given exception type, or if the method handle types do
2804 * not match in their return types and their
2805 * corresponding parameters
2806 */
2807 public static
2808 MethodHandle catchException(MethodHandle target,
2809 Class<? extends Throwable> exType,
2810 MethodHandle handler) {
2811 MethodType ttype = target.type();
2812 MethodType htype = handler.type();
2813 if (htype.parameterCount() < 1 ||
2814 !htype.parameterType(0).isAssignableFrom(exType))
2815 throw newIllegalArgumentException("handler does not accept exception type "+exType);
2816 if (htype.returnType() != ttype.returnType())
2817 throw misMatchedTypes("target and handler return types", ttype, htype);
2818 List<Class<?>> targs = ttype.parameterList();
2819 List<Class<?>> hargs = htype.parameterList();
2820 hargs = hargs.subList(1, hargs.size()); // omit leading parameter from handler
2821 if (!targs.equals(hargs)) {
2822 int hpc = hargs.size(), tpc = targs.size();
2823 if (hpc >= tpc || !targs.subList(0, hpc).equals(hargs))
2824 throw misMatchedTypes("target and handler types", ttype, htype);
2825 handler = dropArguments(handler, 1+hpc, targs.subList(hpc, tpc));
2826 htype = handler.type();
2827 }
2828 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
2829 }
2830
2831 /**
2832 * Produces a method handle which will throw exceptions of the given {@code exType}.
2833 * The method handle will accept a single argument of {@code exType},
2834 * and immediately throw it as an exception.
2835 * The method type will nominally specify a return of {@code returnType}.
2836 * The return type may be anything convenient: It doesn't matter to the
2837 * method handle's behavior, since it will never return normally.
2838 * @param returnType the return type of the desired method handle
2839 * @param exType the parameter type of the desired method handle
2840 * @return method handle which can throw the given exceptions
2841 * @throws NullPointerException if either argument is null
2842 */
2843 public static
2844 MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
2845 if (!Throwable.class.isAssignableFrom(exType))
2846 throw new ClassCastException(exType.getName());
2847 return MethodHandleImpl.throwException(MethodType.methodType(returnType, exType));
2848 }
2849 }