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.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.lang.invoke;
27
28 import java.lang.reflect.*;
29 import java.security.AccessController;
30 import java.security.PrivilegedAction;
31 import java.util.List;
32 import java.util.ArrayList;
33 import java.util.Arrays;
34 import sun.invoke.util.ValueConversions;
35 import sun.invoke.util.VerifyAccess;
36 import sun.invoke.util.Wrapper;
37 import sun.reflect.CallerSensitive;
38 import sun.reflect.Reflection;
39 import sun.security.util.SecurityConstants;
40 import static java.lang.invoke.MethodHandleStatics.*;
41 import static java.lang.invoke.MethodHandleNatives.Constants.*;
42
43 /**
44 * This class consists exclusively of static methods that operate on or return
45 * method handles. They fall into several categories:
46 * <ul>
47 * <li>Lookup methods which help create method handles for methods and fields.
48 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
49 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
50 * <li>Wrapper methods which can convert between method handles and interface types.
51 * </ul>
52 * <p>
53 * @author John Rose, JSR 292 EG
54 */
55 public class MethodHandles {
56
57 private MethodHandles() { } // do not instantiate
58
59 private static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
60 static { MethodHandleImpl.initStatics(); }
61 // See IMPL_LOOKUP below.
62
63 //// Method handle creation from ordinary methods.
64
65 /**
66 * Returns a {@link Lookup lookup object} on the caller,
67 * which has the capability to access any method handle that the caller has access to,
68 * including direct method handles to private fields and methods.
69 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
70 * Do not store it in place where untrusted code can access it.
71 */
72 @CallerSensitive
73 public static Lookup lookup() {
74 return new Lookup(Reflection.getCallerClass());
75 }
76
77 /**
78 * Returns a {@link Lookup lookup object} which is trusted minimally.
79 * It can only be used to create method handles to
80 * publicly accessible fields and methods.
81 * <p>
82 * As a matter of pure convention, the {@linkplain Lookup#lookupClass lookup class}
83 * of this lookup object will be {@link java.lang.Object}.
84 * <p>
85 * The lookup class can be changed to any other class {@code C} using an expression of the form
86 * {@linkplain Lookup#in <code>publicLookup().in(C.class)</code>}.
87 * Since all classes have equal access to public names,
88 * such a change would confer no new access rights.
89 */
90 public static Lookup publicLookup() {
91 return Lookup.PUBLIC_LOOKUP;
92 }
93
94 /**
95 * A <em>lookup object</em> is a factory for creating method handles,
96 * when the creation requires access checking.
97 * Method handles do not perform
98 * access checks when they are called, but rather when they are created.
99 * Therefore, method handle access
100 * restrictions must be enforced when a method handle is created.
101 * The caller class against which those restrictions are enforced
102 * is known as the {@linkplain #lookupClass lookup class}.
103 * <p>
104 * A lookup class which needs to create method handles will call
105 * {@link MethodHandles#lookup MethodHandles.lookup} to create a factory for itself.
106 * When the {@code Lookup} factory object is created, the identity of the lookup class is
107 * determined, and securely stored in the {@code Lookup} object.
108 * The lookup class (or its delegates) may then use factory methods
109 * on the {@code Lookup} object to create method handles for access-checked members.
110 * This includes all methods, constructors, and fields which are allowed to the lookup class,
111 * even private ones.
112 * <p>
113 * The factory methods on a {@code Lookup} object correspond to all major
114 * use cases for methods, constructors, and fields.
115 * Here is a summary of the correspondence between these factory methods and
116 * the behavior the resulting method handles:
117 * <code>
118 * <table border=1 cellpadding=5 summary="lookup method behaviors">
119 * <tr><th>lookup expression</th><th>member</th><th>behavior</th></tr>
120 * <tr>
121 * <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</td>
122 * <td>FT f;</td><td>(T) this.f;</td>
123 * </tr>
124 * <tr>
125 * <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</td>
126 * <td>static<br>FT f;</td><td>(T) C.f;</td>
127 * </tr>
128 * <tr>
129 * <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</td>
130 * <td>FT f;</td><td>this.f = x;</td>
131 * </tr>
132 * <tr>
133 * <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</td>
134 * <td>static<br>FT f;</td><td>C.f = arg;</td>
135 * </tr>
136 * <tr>
137 * <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</td>
138 * <td>T m(A*);</td><td>(T) this.m(arg*);</td>
139 * </tr>
140 * <tr>
141 * <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</td>
142 * <td>static<br>T m(A*);</td><td>(T) C.m(arg*);</td>
143 * </tr>
144 * <tr>
145 * <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</td>
146 * <td>T m(A*);</td><td>(T) super.m(arg*);</td>
147 * </tr>
148 * <tr>
149 * <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</td>
150 * <td>C(A*);</td><td>(T) new C(arg*);</td>
151 * </tr>
152 * <tr>
153 * <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</td>
154 * <td>(static)?<br>FT f;</td><td>(FT) aField.get(thisOrNull);</td>
155 * </tr>
156 * <tr>
157 * <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</td>
158 * <td>(static)?<br>FT f;</td><td>aField.set(thisOrNull, arg);</td>
159 * </tr>
160 * <tr>
161 * <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
162 * <td>(static)?<br>T m(A*);</td><td>(T) aMethod.invoke(thisOrNull, arg*);</td>
163 * </tr>
164 * <tr>
165 * <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</td>
166 * <td>C(A*);</td><td>(C) aConstructor.newInstance(arg*);</td>
167 * </tr>
168 * <tr>
169 * <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
170 * <td>(static)?<br>T m(A*);</td><td>(T) aMethod.invoke(thisOrNull, arg*);</td>
171 * </tr>
172 * </table>
173 * </code>
174 * Here, the type {@code C} is the class or interface being searched for a member,
175 * documented as a parameter named {@code refc} in the lookup methods.
176 * The method or constructor type {@code MT} is composed from the return type {@code T}
177 * and the sequence of argument types {@code A*}.
178 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
179 * The formal parameter {@code this} stands for the self-reference of type {@code C};
180 * if it is present, it is always the leading argument to the method handle invocation.
181 * (In the case of some {@code protected} members, {@code this} may be
182 * restricted in type to the lookup class; see below.)
183 * The name {@code arg} stands for all the other method handle arguments.
184 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
185 * stands for a null reference if the accessed method or field is static,
186 * and {@code this} otherwise.
187 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
188 * for reflective objects corresponding to the given members.
189 * <p>
190 * In cases where the given member is of variable arity (i.e., a method or constructor)
191 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
192 * In all other cases, the returned method handle will be of fixed arity.
193 * <p>
194 * The equivalence between looked-up method handles and underlying
195 * class members can break down in a few ways:
196 * <ul>
197 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
198 * the lookup can still succeed, even when there is no equivalent
199 * Java expression or bytecoded constant.
200 * <li>Likewise, if {@code T} or {@code MT}
201 * is not symbolically accessible from the lookup class's loader,
202 * the lookup can still succeed.
203 * For example, lookups for {@code MethodHandle.invokeExact} and
204 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
205 * <li>If there is a security manager installed, it can forbid the lookup
206 * on various grounds (<a href="#secmgr">see below</a>).
207 * By contrast, the {@code ldc} instruction is not subject to
208 * security manager checks.
209 * </ul>
210 *
211 * <h3><a name="access"></a>Access checking</h3>
212 * Access checks are applied in the factory methods of {@code Lookup},
213 * when a method handle is created.
214 * This is a key difference from the Core Reflection API, since
215 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
216 * performs access checking against every caller, on every call.
217 * <p>
218 * All access checks start from a {@code Lookup} object, which
219 * compares its recorded lookup class against all requests to
220 * create method handles.
221 * A single {@code Lookup} object can be used to create any number
222 * of access-checked method handles, all checked against a single
223 * lookup class.
224 * <p>
225 * A {@code Lookup} object can be shared with other trusted code,
226 * such as a metaobject protocol.
227 * A shared {@code Lookup} object delegates the capability
228 * to create method handles on private members of the lookup class.
229 * Even if privileged code uses the {@code Lookup} object,
230 * the access checking is confined to the privileges of the
231 * original lookup class.
232 * <p>
233 * A lookup can fail, because
234 * the containing class is not accessible to the lookup class, or
235 * because the desired class member is missing, or because the
236 * desired class member is not accessible to the lookup class.
237 * In any of these cases, a {@code ReflectiveOperationException} will be
238 * thrown from the attempted lookup. The exact class will be one of
239 * the following:
240 * <ul>
241 * <li>NoSuchMethodException — if a method is requested but does not exist
242 * <li>NoSuchFieldException — if a field is requested but does not exist
243 * <li>IllegalAccessException — if the member exists but an access check fails
244 * </ul>
245 * <p>
246 * In general, the conditions under which a method handle may be
247 * looked up for a method {@code M} are exactly equivalent to the conditions
248 * under which the lookup class could have compiled and resolved a call to {@code M}.
249 * And the effect of invoking the method handle resulting from the lookup
250 * is exactly equivalent to executing the compiled and resolved call to {@code M}.
251 * The same point is true of fields and constructors.
252 * <p>
253 * If the desired member is {@code protected}, the usual JVM rules apply,
254 * including the requirement that the lookup class must be either be in the
255 * same package as the desired member, or must inherit that member.
256 * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.)
257 * In addition, if the desired member is a non-static field or method
258 * in a different package, the resulting method handle may only be applied
259 * to objects of the lookup class or one of its subclasses.
260 * This requirement is enforced by narrowing the type of the leading
261 * {@code this} parameter from {@code C}
262 * (which will necessarily be a superclass of the lookup class)
263 * to the lookup class itself.
264 * <p>
265 * In some cases, access between nested classes is obtained by the Java compiler by creating
266 * an wrapper method to access a private method of another class
267 * in the same top-level declaration.
268 * For example, a nested class {@code C.D}
269 * can access private members within other related classes such as
270 * {@code C}, {@code C.D.E}, or {@code C.B},
271 * but the Java compiler may need to generate wrapper methods in
272 * those related classes. In such cases, a {@code Lookup} object on
273 * {@code C.E} would be unable to those private members.
274 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
275 * which can transform a lookup on {@code C.E} into one on any of those other
276 * classes, without special elevation of privilege.
277 * <p>
278 * Although bytecode instructions can only refer to classes in
279 * a related class loader, this API can search for methods in any
280 * class, as long as a reference to its {@code Class} object is
281 * available. Such cross-loader references are also possible with the
282 * Core Reflection API, and are impossible to bytecode instructions
283 * such as {@code invokestatic} or {@code getfield}.
284 * There is a {@linkplain java.lang.SecurityManager security manager API}
285 * to allow applications to check such cross-loader references.
286 * These checks apply to both the {@code MethodHandles.Lookup} API
287 * and the Core Reflection API
288 * (as found on {@link java.lang.Class Class}).
289 * <p>
290 * Access checks only apply to named and reflected methods,
291 * constructors, and fields.
292 * Other method handle creation methods, such as
293 * {@link MethodHandle#asType MethodHandle.asType},
294 * do not require any access checks, and are done
295 * with static methods of {@link MethodHandles},
296 * independently of any {@code Lookup} object.
297 *
298 * <h3>Security manager interactions</h3>
299 * <a name="secmgr"></a>
300 * If a security manager is present, member lookups are subject to
301 * additional checks.
302 * From one to four calls are made to the security manager.
303 * Any of these calls can refuse access by throwing a
304 * {@link java.lang.SecurityException SecurityException}.
305 * Define {@code smgr} as the security manager,
306 * {@code refc} as the containing class in which the member
307 * is being sought, and {@code defc} as the class in which the
308 * member is actually defined.
309 * The calls are made according to the following rules:
310 * <ul>
311 * <li>In all cases, {@link SecurityManager#checkMemberAccess
312 * smgr.checkMemberAccess(refc, Member.PUBLIC)} is called.
313 * <li>If the class loader of the lookup class is not
314 * the same as or an ancestor of the class loader of {@code refc},
315 * then {@link SecurityManager#checkPackageAccess
316 * smgr.checkPackageAccess(refcPkg)} is called,
317 * where {@code refcPkg} is the package of {@code refc}.
318 * <li>If the retrieved member is not public,
319 * {@link SecurityManager#checkMemberAccess
320 * smgr.checkMemberAccess(defc, Member.DECLARED)} is called.
321 * (Note that {@code defc} might be the same as {@code refc}.)
322 * The default implementation of this security manager method
323 * inspects the stack to determine the original caller of
324 * the reflective request (such as {@code findStatic}),
325 * and performs additional permission checks if the
326 * class loader of {@code defc} differs from the class
327 * loader of the class from which the reflective request came.
328 * <li>If the retrieved member is not public,
329 * and if {@code defc} and {@code refc} are in different class loaders,
330 * and if the class loader of the lookup class is not
331 * the same as or an ancestor of the class loader of {@code defc},
332 * then {@link SecurityManager#checkPackageAccess
333 * smgr.checkPackageAccess(defcPkg)} is called,
334 * where {@code defcPkg} is the package of {@code defc}.
335 * </ul>
336 */
337 // FIXME in MR1: clarify that the bytecode behavior of a caller-ID method (like Class.forName) is relative to the lookupClass used to create the method handle, not the dynamic caller of the method handle
338 public static final
339 class Lookup {
340 /** The class on behalf of whom the lookup is being performed. */
341 private final Class<?> lookupClass;
342
343 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
344 private final int allowedModes;
345
346 /** A single-bit mask representing {@code public} access,
347 * which may contribute to the result of {@link #lookupModes lookupModes}.
348 * The value, {@code 0x01}, happens to be the same as the value of the
349 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
350 */
351 public static final int PUBLIC = Modifier.PUBLIC;
352
353 /** A single-bit mask representing {@code private} access,
354 * which may contribute to the result of {@link #lookupModes lookupModes}.
355 * The value, {@code 0x02}, happens to be the same as the value of the
356 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
357 */
358 public static final int PRIVATE = Modifier.PRIVATE;
359
360 /** A single-bit mask representing {@code protected} access,
361 * which may contribute to the result of {@link #lookupModes lookupModes}.
362 * The value, {@code 0x04}, happens to be the same as the value of the
363 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
364 */
365 public static final int PROTECTED = Modifier.PROTECTED;
366
367 /** A single-bit mask representing {@code package} access (default access),
368 * which may contribute to the result of {@link #lookupModes lookupModes}.
369 * The value is {@code 0x08}, which does not correspond meaningfully to
370 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
371 */
372 public static final int PACKAGE = Modifier.STATIC;
373
374 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE);
375 private static final int TRUSTED = -1;
376
377 private static int fixmods(int mods) {
378 mods &= (ALL_MODES - PACKAGE);
379 return (mods != 0) ? mods : PACKAGE;
380 }
381
382 /** Tells which class is performing the lookup. It is this class against
383 * which checks are performed for visibility and access permissions.
384 * <p>
385 * The class implies a maximum level of access permission,
386 * but the permissions may be additionally limited by the bitmask
387 * {@link #lookupModes lookupModes}, which controls whether non-public members
388 * can be accessed.
389 */
390 public Class<?> lookupClass() {
391 return lookupClass;
392 }
393
394 // This is just for calling out to MethodHandleImpl.
395 private Class<?> lookupClassOrNull() {
396 return (allowedModes == TRUSTED) ? null : lookupClass;
397 }
398
399 /** Tells which access-protection classes of members this lookup object can produce.
400 * The result is a bit-mask of the bits
401 * {@linkplain #PUBLIC PUBLIC (0x01)},
402 * {@linkplain #PRIVATE PRIVATE (0x02)},
403 * {@linkplain #PROTECTED PROTECTED (0x04)},
404 * and {@linkplain #PACKAGE PACKAGE (0x08)}.
405 * <p>
406 * A freshly-created lookup object
407 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class}
408 * has all possible bits set, since the caller class can access all its own members.
409 * A lookup object on a new lookup class
410 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
411 * may have some mode bits set to zero.
412 * The purpose of this is to restrict access via the new lookup object,
413 * so that it can access only names which can be reached by the original
414 * lookup object, and also by the new lookup class.
415 */
416 public int lookupModes() {
417 return allowedModes & ALL_MODES;
418 }
419
420 /** Embody the current class (the lookupClass) as a lookup class
421 * for method handle creation.
422 * Must be called by from a method in this package,
423 * which in turn is called by a method not in this package.
424 */
425 Lookup(Class<?> lookupClass) {
426 this(lookupClass, ALL_MODES);
427 // make sure we haven't accidentally picked up a privileged class:
428 checkUnprivilegedlookupClass(lookupClass);
429 }
430
431 private Lookup(Class<?> lookupClass, int allowedModes) {
432 this.lookupClass = lookupClass;
433 this.allowedModes = allowedModes;
434 }
435
436 /**
437 * Creates a lookup on the specified new lookup class.
438 * The resulting object will report the specified
439 * class as its own {@link #lookupClass lookupClass}.
440 * <p>
441 * However, the resulting {@code Lookup} object is guaranteed
442 * to have no more access capabilities than the original.
443 * In particular, access capabilities can be lost as follows:<ul>
444 * <li>If the new lookup class differs from the old one,
445 * protected members will not be accessible by virtue of inheritance.
446 * (Protected members may continue to be accessible because of package sharing.)
447 * <li>If the new lookup class is in a different package
448 * than the old one, protected and default (package) members will not be accessible.
449 * <li>If the new lookup class is not within the same package member
450 * as the old one, private members will not be accessible.
451 * <li>If the new lookup class is not accessible to the old lookup class,
452 * then no members, not even public members, will be accessible.
453 * (In all other cases, public members will continue to be accessible.)
454 * </ul>
455 *
456 * @param requestedLookupClass the desired lookup class for the new lookup object
457 * @return a lookup object which reports the desired lookup class
458 * @throws NullPointerException if the argument is null
459 */
460 public Lookup in(Class<?> requestedLookupClass) {
461 requestedLookupClass.getClass(); // null check
462 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
463 return new Lookup(requestedLookupClass, ALL_MODES);
464 if (requestedLookupClass == this.lookupClass)
465 return this; // keep same capabilities
466 int newModes = (allowedModes & (ALL_MODES & ~PROTECTED));
467 if ((newModes & PACKAGE) != 0
468 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
469 newModes &= ~(PACKAGE|PRIVATE);
470 }
471 // Allow nestmate lookups to be created without special privilege:
472 if ((newModes & PRIVATE) != 0
473 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
474 newModes &= ~PRIVATE;
475 }
476 if ((newModes & PUBLIC) != 0
477 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, allowedModes)) {
478 // The requested class it not accessible from the lookup class.
479 // No permissions.
480 newModes = 0;
481 }
482 checkUnprivilegedlookupClass(requestedLookupClass);
483 return new Lookup(requestedLookupClass, newModes);
484 }
485
486 // Make sure outer class is initialized first.
487 static { IMPL_NAMES.getClass(); }
488
489 /** Version of lookup which is trusted minimally.
490 * It can only be used to create method handles to
491 * publicly accessible members.
492 */
493 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, PUBLIC);
494
495 /** Package-private version of lookup which is trusted. */
496 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, TRUSTED);
497
498 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) {
499 String name = lookupClass.getName();
500 if (name.startsWith("java.lang.invoke."))
501 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
502 }
503
504 /**
505 * Displays the name of the class from which lookups are to be made.
506 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
507 * If there are restrictions on the access permitted to this lookup,
508 * this is indicated by adding a suffix to the class name, consisting
509 * of a slash and a keyword. The keyword represents the strongest
510 * allowed access, and is chosen as follows:
511 * <ul>
512 * <li>If no access is allowed, the suffix is "/noaccess".
513 * <li>If only public access is allowed, the suffix is "/public".
514 * <li>If only public and package access are allowed, the suffix is "/package".
515 * <li>If only public, package, and private access are allowed, the suffix is "/private".
516 * </ul>
517 * If none of the above cases apply, it is the case that full
518 * access (public, package, private, and protected) is allowed.
519 * In this case, no suffix is added.
520 * This is true only of an object obtained originally from
521 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
522 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
523 * always have restricted access, and will display a suffix.
524 * <p>
525 * (It may seem strange that protected access should be
526 * stronger than private access. Viewed independently from
527 * package access, protected access is the first to be lost,
528 * because it requires a direct subclass relationship between
529 * caller and callee.)
530 * @see #in
531 */
532 @Override
533 public String toString() {
534 String cname = lookupClass.getName();
535 switch (allowedModes) {
536 case 0: // no privileges
537 return cname + "/noaccess";
538 case PUBLIC:
539 return cname + "/public";
540 case PUBLIC|PACKAGE:
541 return cname + "/package";
542 case ALL_MODES & ~PROTECTED:
543 return cname + "/private";
544 case ALL_MODES:
545 return cname;
546 case TRUSTED:
547 return "/trusted"; // internal only; not exported
548 default: // Should not happen, but it's a bitfield...
549 cname = cname + "/" + Integer.toHexString(allowedModes);
550 assert(false) : cname;
551 return cname;
552 }
553 }
554
555 /**
556 * Produces a method handle for a static method.
557 * The type of the method handle will be that of the method.
558 * (Since static methods do not take receivers, there is no
559 * additional receiver argument inserted into the method handle type,
560 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
561 * The method and all its argument types must be accessible to the lookup class.
562 * If the method's class has not yet been initialized, that is done
563 * immediately, before the method handle is returned.
564 * <p>
565 * The returned method handle will have
566 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
567 * the method's variable arity modifier bit ({@code 0x0080}) is set.
568 * @param refc the class from which the method is accessed
569 * @param name the name of the method
570 * @param type the type of the method
571 * @return the desired method handle
572 * @throws NoSuchMethodException if the method does not exist
573 * @throws IllegalAccessException if access checking fails,
574 * or if the method is not {@code static},
575 * or if the method's variable arity modifier bit
576 * is set and {@code asVarargsCollector} fails
577 * @exception SecurityException if a security manager is present and it
578 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
579 * @throws NullPointerException if any argument is null
580 */
581 @CallerSensitive
582 public
583 MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
584 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
585 Class<?> callerClass = Reflection.getCallerClass();
586 checkSecurityManager(refc, method, callerClass);
587 return getDirectMethod(REF_invokeStatic, refc, method,
588 findBoundCallerClass(method, callerClass));
589 }
590
591 /**
592 * Produces a method handle for a virtual method.
593 * The type of the method handle will be that of the method,
594 * with the receiver type (usually {@code refc}) prepended.
595 * The method and all its argument types must be accessible to the lookup class.
596 * <p>
597 * When called, the handle will treat the first argument as a receiver
598 * and dispatch on the receiver's type to determine which method
599 * implementation to enter.
600 * (The dispatching action is identical with that performed by an
601 * {@code invokevirtual} or {@code invokeinterface} instruction.)
602 * <p>
603 * The first argument will be of type {@code refc} if the lookup
604 * class has full privileges to access the member. Otherwise
605 * the member must be {@code protected} and the first argument
606 * will be restricted in type to the lookup class.
607 * <p>
608 * The returned method handle will have
609 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
610 * the method's variable arity modifier bit ({@code 0x0080}) is set.
611 * <p>
612 * Because of the general equivalence between {@code invokevirtual}
613 * instructions and method handles produced by {@code findVirtual},
614 * if the class is {@code MethodHandle} and the name string is
615 * {@code invokeExact} or {@code invoke}, the resulting
616 * method handle is equivalent to one produced by
617 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
618 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
619 * with the same {@code type} argument.
620 *
621 * @param refc the class or interface from which the method is accessed
622 * @param name the name of the method
623 * @param type the type of the method, with the receiver argument omitted
624 * @return the desired method handle
625 * @throws NoSuchMethodException if the method does not exist
626 * @throws IllegalAccessException if access checking fails,
627 * or if the method is {@code static}
628 * or if the method's variable arity modifier bit
629 * is set and {@code asVarargsCollector} fails
630 * @exception SecurityException if a security manager is present and it
631 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
632 * @throws NullPointerException if any argument is null
633 */
634 @CallerSensitive
635 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
636 if (refc == MethodHandle.class) {
637 MethodHandle mh = findVirtualForMH(name, type);
638 if (mh != null) return mh;
639 }
640 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
641 MemberName method = resolveOrFail(refKind, refc, name, type);
642 Class<?> callerClass = Reflection.getCallerClass();
643 checkSecurityManager(refc, method, callerClass);
644 return getDirectMethod(refKind, refc, method,
645 findBoundCallerClass(method, callerClass));
646 }
647 private MethodHandle findVirtualForMH(String name, MethodType type) {
648 // these names require special lookups because of the implicit MethodType argument
649 if ("invoke".equals(name))
650 return invoker(type);
651 if ("invokeExact".equals(name))
652 return exactInvoker(type);
653 return null;
654 }
655
656 /**
657 * Produces a method handle which creates an object and initializes it, using
658 * the constructor of the specified type.
659 * The parameter types of the method handle will be those of the constructor,
660 * while the return type will be a reference to the constructor's class.
661 * The constructor and all its argument types must be accessible to the lookup class.
662 * If the constructor's class has not yet been initialized, that is done
663 * immediately, before the method handle is returned.
664 * <p>
665 * Note: The requested type must have a return type of {@code void}.
666 * This is consistent with the JVM's treatment of constructor type descriptors.
667 * <p>
668 * The returned method handle will have
669 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
670 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
671 * @param refc the class or interface from which the method is accessed
672 * @param type the type of the method, with the receiver argument omitted, and a void return type
673 * @return the desired method handle
674 * @throws NoSuchMethodException if the constructor does not exist
675 * @throws IllegalAccessException if access checking fails
676 * or if the method's variable arity modifier bit
677 * is set and {@code asVarargsCollector} fails
678 * @exception SecurityException if a security manager is present and it
679 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
680 * @throws NullPointerException if any argument is null
681 */
682 @CallerSensitive
683 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
684 String name = "<init>";
685 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
686 checkSecurityManager(refc, ctor, Reflection.getCallerClass());
687 return getDirectConstructor(refc, ctor);
688 }
689
690 /**
691 * Produces an early-bound method handle for a virtual method,
692 * as if called from an {@code invokespecial}
693 * instruction from {@code caller}.
694 * The type of the method handle will be that of the method,
695 * with a suitably restricted receiver type (such as {@code caller}) prepended.
696 * The method and all its argument types must be accessible
697 * to the caller.
698 * <p>
699 * When called, the handle will treat the first argument as a receiver,
700 * but will not dispatch on the receiver's type.
701 * (This direct invocation action is identical with that performed by an
702 * {@code invokespecial} instruction.)
703 * <p>
704 * If the explicitly specified caller class is not identical with the
705 * lookup class, or if this lookup object does not have private access
706 * privileges, the access fails.
707 * <p>
708 * The returned method handle will have
709 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
710 * the method's variable arity modifier bit ({@code 0x0080}) is set.
711 * @param refc the class or interface from which the method is accessed
712 * @param name the name of the method (which must not be "<init>")
713 * @param type the type of the method, with the receiver argument omitted
714 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
715 * @return the desired method handle
716 * @throws NoSuchMethodException if the method does not exist
717 * @throws IllegalAccessException if access checking fails
718 * or if the method's variable arity modifier bit
719 * is set and {@code asVarargsCollector} fails
720 * @exception SecurityException if a security manager is present and it
721 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
722 * @throws NullPointerException if any argument is null
723 */
724 @CallerSensitive
725 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
726 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
727 checkSpecialCaller(specialCaller);
728 Lookup specialLookup = this.in(specialCaller);
729 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
730 Class<?> callerClass = Reflection.getCallerClass();
731 checkSecurityManager(refc, method, callerClass);
732 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method,
733 findBoundCallerClass(method, callerClass));
734 }
735
736 /**
737 * Produces a method handle giving read access to a non-static field.
738 * The type of the method handle will have a return type of the field's
739 * value type.
740 * The method handle's single argument will be the instance containing
741 * the field.
742 * Access checking is performed immediately on behalf of the lookup class.
743 * @param refc the class or interface from which the method is accessed
744 * @param name the field's name
745 * @param type the field's type
746 * @return a method handle which can load values from the field
747 * @throws NoSuchFieldException if the field does not exist
748 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
749 * @exception SecurityException if a security manager is present and it
750 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
751 * @throws NullPointerException if any argument is null
752 */
753 @CallerSensitive
754 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
755 MemberName field = resolveOrFail(REF_getField, refc, name, type);
756 checkSecurityManager(refc, field, Reflection.getCallerClass());
757 return getDirectField(REF_getField, refc, field);
758 }
759
760 /**
761 * Produces a method handle giving write access to a non-static field.
762 * The type of the method handle will have a void return type.
763 * The method handle will take two arguments, the instance containing
764 * the field, and the value to be stored.
765 * The second argument will be of the field's value type.
766 * Access checking is performed immediately on behalf of the lookup class.
767 * @param refc the class or interface from which the method is accessed
768 * @param name the field's name
769 * @param type the field's type
770 * @return a method handle which can store values into the field
771 * @throws NoSuchFieldException if the field does not exist
772 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
773 * @exception SecurityException if a security manager is present and it
774 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
775 * @throws NullPointerException if any argument is null
776 */
777 @CallerSensitive
778 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
779 MemberName field = resolveOrFail(REF_putField, refc, name, type);
780 checkSecurityManager(refc, field, Reflection.getCallerClass());
781 return getDirectField(REF_putField, refc, field);
782 }
783
784 /**
785 * Produces a method handle giving read access to a static field.
786 * The type of the method handle will have a return type of the field's
787 * value type.
788 * The method handle will take no arguments.
789 * Access checking is performed immediately on behalf of the lookup class.
790 * @param refc the class or interface from which the method is accessed
791 * @param name the field's name
792 * @param type the field's type
793 * @return a method handle which can load values from the field
794 * @throws NoSuchFieldException if the field does not exist
795 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
796 * @exception SecurityException if a security manager is present and it
797 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
798 * @throws NullPointerException if any argument is null
799 */
800 @CallerSensitive
801 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
802 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
803 checkSecurityManager(refc, field, Reflection.getCallerClass());
804 return getDirectField(REF_getStatic, refc, field);
805 }
806
807 /**
808 * Produces a method handle giving write access to a static field.
809 * The type of the method handle will have a void return type.
810 * The method handle will take a single
811 * argument, of the field's value type, the value to be stored.
812 * Access checking is performed immediately on behalf of the lookup class.
813 * @param refc the class or interface from which the method is accessed
814 * @param name the field's name
815 * @param type the field's type
816 * @return a method handle which can store values into the field
817 * @throws NoSuchFieldException if the field does not exist
818 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
819 * @exception SecurityException if a security manager is present and it
820 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
821 * @throws NullPointerException if any argument is null
822 */
823 @CallerSensitive
824 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
825 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
826 checkSecurityManager(refc, field, Reflection.getCallerClass());
827 return getDirectField(REF_putStatic, refc, field);
828 }
829
830 /**
831 * Produces an early-bound method handle for a non-static method.
832 * The receiver must have a supertype {@code defc} in which a method
833 * of the given name and type is accessible to the lookup class.
834 * The method and all its argument types must be accessible to the lookup class.
835 * The type of the method handle will be that of the method,
836 * without any insertion of an additional receiver parameter.
837 * The given receiver will be bound into the method handle,
838 * so that every call to the method handle will invoke the
839 * requested method on the given receiver.
840 * <p>
841 * The returned method handle will have
842 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
843 * the method's variable arity modifier bit ({@code 0x0080}) is set
844 * <em>and</em> the trailing array argument is not the only argument.
845 * (If the trailing array argument is the only argument,
846 * the given receiver value will be bound to it.)
847 * <p>
848 * This is equivalent to the following code:
849 * <blockquote><pre>
850 import static java.lang.invoke.MethodHandles.*;
851 import static java.lang.invoke.MethodType.*;
852 ...
853 MethodHandle mh0 = lookup().{@link #findVirtual findVirtual}(defc, name, type);
854 MethodHandle mh1 = mh0.{@link MethodHandle#bindTo bindTo}(receiver);
855 MethodType mt1 = mh1.type();
856 if (mh0.isVarargsCollector())
857 mh1 = mh1.asVarargsCollector(mt1.parameterType(mt1.parameterCount()-1));
858 return mh1;
859 * </pre></blockquote>
860 * where {@code defc} is either {@code receiver.getClass()} or a super
861 * type of that class, in which the requested method is accessible
862 * to the lookup class.
863 * (Note that {@code bindTo} does not preserve variable arity.)
864 * @param receiver the object from which the method is accessed
865 * @param name the name of the method
866 * @param type the type of the method, with the receiver argument omitted
867 * @return the desired method handle
868 * @throws NoSuchMethodException if the method does not exist
869 * @throws IllegalAccessException if access checking fails
870 * or if the method's variable arity modifier bit
871 * is set and {@code asVarargsCollector} fails
872 * @exception SecurityException if a security manager is present and it
873 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
874 * @throws NullPointerException if any argument is null
875 */
876 @CallerSensitive
877 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
878 Class<? extends Object> refc = receiver.getClass(); // may get NPE
879 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
880 Class<?> callerClass = Reflection.getCallerClass();
881 checkSecurityManager(refc, method, callerClass);
882 MethodHandle mh = getDirectMethodNoRestrict(REF_invokeSpecial, refc, method,
883 findBoundCallerClass(method, callerClass));
884 return mh.bindReceiver(receiver).setVarargs(method);
885 }
886
887 /**
888 * Makes a direct method handle to <i>m</i>, if the lookup class has permission.
889 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
890 * If <i>m</i> is virtual, overriding is respected on every call.
891 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
892 * The type of the method handle will be that of the method,
893 * with the receiver type prepended (but only if it is non-static).
894 * If the method's {@code accessible} flag is not set,
895 * access checking is performed immediately on behalf of the lookup class.
896 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
897 * <p>
898 * The returned method handle will have
899 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
900 * the method's variable arity modifier bit ({@code 0x0080}) is set.
901 * @param m the reflected method
902 * @return a method handle which can invoke the reflected method
903 * @throws IllegalAccessException if access checking fails
904 * or if the method's variable arity modifier bit
905 * is set and {@code asVarargsCollector} fails
906 * @throws NullPointerException if the argument is null
907 */
908 @CallerSensitive
909 public MethodHandle unreflect(Method m) throws IllegalAccessException {
910 MemberName method = new MemberName(m);
911 byte refKind = method.getReferenceKind();
912 if (refKind == REF_invokeSpecial)
913 refKind = REF_invokeVirtual;
914 assert(method.isMethod());
915 Class<?> callerClass = findBoundCallerClass(method, Reflection.getCallerClass());
916 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
917 return lookup.getDirectMethod(refKind, method.getDeclaringClass(), method, callerClass);
918 }
919
920 /**
921 * Produces a method handle for a reflected method.
922 * It will bypass checks for overriding methods on the receiver,
923 * as if by a {@code invokespecial} instruction from within the {@code specialCaller}.
924 * The type of the method handle will be that of the method,
925 * with the special caller type prepended (and <em>not</em> the receiver of the method).
926 * If the method's {@code accessible} flag is not set,
927 * access checking is performed immediately on behalf of the lookup class,
928 * as if {@code invokespecial} instruction were being linked.
929 * <p>
930 * The returned method handle will have
931 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
932 * the method's variable arity modifier bit ({@code 0x0080}) is set.
933 * @param m the reflected method
934 * @param specialCaller the class nominally calling the method
935 * @return a method handle which can invoke the reflected method
936 * @throws IllegalAccessException if access checking fails
937 * or if the method's variable arity modifier bit
938 * is set and {@code asVarargsCollector} fails
939 * @throws NullPointerException if any argument is null
940 */
941 @CallerSensitive
942 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
943 checkSpecialCaller(specialCaller);
944 Lookup specialLookup = this.in(specialCaller);
945 MemberName method = new MemberName(m, true);
946 assert(method.isMethod());
947 Class<?> callerClass = findBoundCallerClass(method, Reflection.getCallerClass());
948 // ignore m.isAccessible: this is a new kind of access
949 return specialLookup.getDirectMethod(REF_invokeSpecial, method.getDeclaringClass(), method, callerClass);
950 }
951
952 /**
953 * Produces a method handle for a reflected constructor.
954 * The type of the method handle will be that of the constructor,
955 * with the return type changed to the declaring class.
956 * The method handle will perform a {@code newInstance} operation,
957 * creating a new instance of the constructor's class on the
958 * arguments passed to the method handle.
959 * <p>
960 * If the constructor's {@code accessible} flag is not set,
961 * access checking is performed immediately on behalf of the lookup class.
962 * <p>
963 * The returned method handle will have
964 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
965 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
966 * @param c the reflected constructor
967 * @return a method handle which can invoke the reflected constructor
968 * @throws IllegalAccessException if access checking fails
969 * or if the method's variable arity modifier bit
970 * is set and {@code asVarargsCollector} fails
971 * @throws NullPointerException if the argument is null
972 */
973 @SuppressWarnings("rawtypes") // Will be Constructor<?> after JSR 292 MR
974 public MethodHandle unreflectConstructor(Constructor c) throws IllegalAccessException {
975 MemberName ctor = new MemberName(c);
976 assert(ctor.isConstructor());
977 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
978 return lookup.getDirectConstructor(ctor.getDeclaringClass(), ctor);
979 }
980
981 /**
982 * Produces a method handle giving read access to a reflected field.
983 * The type of the method handle will have a return type of the field's
984 * value type.
985 * If the field is static, the method handle will take no arguments.
986 * Otherwise, its single argument will be the instance containing
987 * the field.
988 * If the field's {@code accessible} flag is not set,
989 * access checking is performed immediately on behalf of the lookup class.
990 * @param f the reflected field
991 * @return a method handle which can load values from the reflected field
992 * @throws IllegalAccessException if access checking fails
993 * @throws NullPointerException if the argument is null
994 */
995 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
996 return unreflectField(f, false);
997 }
998 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
999 MemberName field = new MemberName(f, isSetter);
1000 assert(isSetter
1001 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
1002 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
1003 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
1004 return lookup.getDirectField(field.getReferenceKind(), f.getDeclaringClass(), field);
1005 }
1006
1007 /**
1008 * Produces a method handle giving write access to a reflected field.
1009 * The type of the method handle will have a void return type.
1010 * If the field is static, the method handle will take a single
1011 * argument, of the field's value type, the value to be stored.
1012 * Otherwise, the two arguments will be the instance containing
1013 * the field, and the value to be stored.
1014 * If the field's {@code accessible} flag is not set,
1015 * access checking is performed immediately on behalf of the lookup class.
1016 * @param f the reflected field
1017 * @return a method handle which can store values into the reflected field
1018 * @throws IllegalAccessException if access checking fails
1019 * @throws NullPointerException if the argument is null
1020 */
1021 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
1022 return unreflectField(f, true);
1023 }
1024
1025 /// Helper methods, all package-private.
1026
1027 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1028 checkSymbolicClass(refc); // do this before attempting to resolve
1029 name.getClass(); type.getClass(); // NPE
1030 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
1031 NoSuchFieldException.class);
1032 }
1033
1034 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1035 checkSymbolicClass(refc); // do this before attempting to resolve
1036 name.getClass(); type.getClass(); // NPE
1037 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
1038 NoSuchMethodException.class);
1039 }
1040
1041 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
1042 Class<?> caller = lookupClassOrNull();
1043 if (caller != null && !VerifyAccess.isClassAccessible(refc, caller, allowedModes))
1044 throw new MemberName(refc).makeAccessException("symbolic reference class is not public", this);
1045 }
1046
1047 /**
1048 * Find my trustable caller class if m is a caller sensitive method.
1049 * If this lookup object has private access, then the caller class is the lookupClass.
1050 * Otherwise, it is the caller of the currently executing public API method (e.g., findVirtual).
1051 * This is the same caller class as is used by checkSecurityManager.
1052 */
1053 Class<?> findBoundCallerClass(MemberName m, Class<?> callerAtEntryPoint) {
1054 Class<?> callerClass = null;
1055 if (MethodHandleNatives.isCallerSensitive(m)) {
1056 // Do not refactor this to a more "logical" place, since it is stack walk magic.
1057 // Note that this is the same expression as in Step 2 below in checkSecurityManager.
1058 callerClass = ((allowedModes & PRIVATE) != 0
1059 ? lookupClass // for strong access modes, no extra check
1060 : callerAtEntryPoint);
1061 }
1062 return callerClass;
1063 }
1064
1065 /**
1066 * Determine whether a security manager has an overridden
1067 * SecurityManager.checkMemberAccess method.
1068 */
1069 private boolean isCheckMemberAccessOverridden(SecurityManager sm) {
1070 final Class<? extends SecurityManager> cls = sm.getClass();
1071 if (cls == SecurityManager.class) return false;
1072
1073 try {
1074 return cls.getMethod("checkMemberAccess", Class.class, int.class).
1075 getDeclaringClass() != SecurityManager.class;
1076 } catch (NoSuchMethodException e) {
1077 throw new InternalError("should not reach here");
1078 }
1079 }
1080
1081 /**
1082 * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
1083 * Determines a trustable caller class to compare with refc, the symbolic reference class.
1084 * If this lookup object has private access, then the caller class is the lookupClass.
1085 * Otherwise, it is the caller of the currently executing public API method (e.g., findVirtual).
1086 * This function performs stack walk magic: do not refactor it.
1087 */
1088 void checkSecurityManager(Class<?> refc, MemberName m, Class<?> caller) {
1089 SecurityManager smgr = System.getSecurityManager();
1090 if (smgr == null) return;
1091 if (allowedModes == TRUSTED) return;
1092
1093 final boolean overridden = isCheckMemberAccessOverridden(smgr);
1094 // Step 1:
1095 {
1096 // Default policy is to allow Member.PUBLIC; no need to check
1097 // permission if SecurityManager is the default implementation
1098 final int which = Member.PUBLIC;
1099 final Class<?> clazz = refc;
1100 if (overridden) {
1101 // Don't refactor; otherwise break the stack depth for
1102 // checkMemberAccess of subclasses of SecurityManager as specified.
1103 smgr.checkMemberAccess(clazz, which);
1104 }
1105 }
1106
1107 // Step 2:
1108 Class<?> callerClass = ((allowedModes & PRIVATE) != 0
1109 ? lookupClass // for strong access modes, no extra check
1110 : caller);
1111 if (!VerifyAccess.classLoaderIsAncestor(lookupClass, refc) ||
1112 (callerClass != lookupClass &&
1113 !VerifyAccess.classLoaderIsAncestor(callerClass, refc)))
1114 smgr.checkPackageAccess(VerifyAccess.getPackageName(refc));
1115
1116 // Step 3:
1117 if (m.isPublic()) return;
1118 Class<?> defc = m.getDeclaringClass();
1119 {
1120 // Inline SecurityManager.checkMemberAccess
1121 final int which = Member.DECLARED;
1122 final Class<?> clazz = defc;
1123 if (!overridden) {
1124 if (caller.getClassLoader() != clazz.getClassLoader()) {
1125 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
1126 }
1127 } else {
1128 // Don't refactor; otherwise break the stack depth for
1129 // checkMemberAccess of subclasses of SecurityManager as specified.
1130 smgr.checkMemberAccess(clazz, which);
1131 }
1132 }
1133
1134 // Step 4:
1135 if (defc != refc)
1136 smgr.checkPackageAccess(VerifyAccess.getPackageName(defc));
1137 }
1138
1139 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1140 boolean wantStatic = (refKind == REF_invokeStatic);
1141 String message;
1142 if (m.isConstructor())
1143 message = "expected a method, not a constructor";
1144 else if (!m.isMethod())
1145 message = "expected a method";
1146 else if (wantStatic != m.isStatic())
1147 message = wantStatic ? "expected a static method" : "expected a non-static method";
1148 else
1149 { checkAccess(refKind, refc, m); return; }
1150 throw m.makeAccessException(message, this);
1151 }
1152
1153 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1154 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
1155 String message;
1156 if (wantStatic != m.isStatic())
1157 message = wantStatic ? "expected a static field" : "expected a non-static field";
1158 else
1159 { checkAccess(refKind, refc, m); return; }
1160 throw m.makeAccessException(message, this);
1161 }
1162
1163 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1164 assert(m.referenceKindIsConsistentWith(refKind) &&
1165 MethodHandleNatives.refKindIsValid(refKind) &&
1166 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
1167 int allowedModes = this.allowedModes;
1168 if (allowedModes == TRUSTED) return;
1169 int mods = m.getModifiers();
1170 if (Modifier.isFinal(mods) &&
1171 MethodHandleNatives.refKindIsSetter(refKind))
1172 throw m.makeAccessException("unexpected set of a final field", this);
1173 if (Modifier.isPublic(mods) && Modifier.isPublic(refc.getModifiers()) && allowedModes != 0)
1174 return; // common case
1175 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
1176 if ((requestedModes & allowedModes) != 0) {
1177 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
1178 mods, lookupClass(), allowedModes))
1179 return;
1180 } else {
1181 // Protected members can also be checked as if they were package-private.
1182 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
1183 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
1184 return;
1185 }
1186 throw m.makeAccessException(accessFailedMessage(refc, m), this);
1187 }
1188
1189 String accessFailedMessage(Class<?> refc, MemberName m) {
1190 Class<?> defc = m.getDeclaringClass();
1191 int mods = m.getModifiers();
1192 // check the class first:
1193 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
1194 (defc == refc ||
1195 Modifier.isPublic(refc.getModifiers())));
1196 if (!classOK && (allowedModes & PACKAGE) != 0) {
1197 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), ALL_MODES) &&
1198 (defc == refc ||
1199 VerifyAccess.isClassAccessible(refc, lookupClass(), ALL_MODES)));
1200 }
1201 if (!classOK)
1202 return "class is not public";
1203 if (Modifier.isPublic(mods))
1204 return "access to public member failed"; // (how?)
1205 if (Modifier.isPrivate(mods))
1206 return "member is private";
1207 if (Modifier.isProtected(mods))
1208 return "member is protected";
1209 return "member is private to package";
1210 }
1211
1212 private static final boolean ALLOW_NESTMATE_ACCESS = false;
1213
1214 private void checkSpecialCaller(Class<?> specialCaller) throws IllegalAccessException {
1215 int allowedModes = this.allowedModes;
1216 if (allowedModes == TRUSTED) return;
1217 if ((allowedModes & PRIVATE) == 0
1218 || (specialCaller != lookupClass()
1219 && !(ALLOW_NESTMATE_ACCESS &&
1220 VerifyAccess.isSamePackageMember(specialCaller, lookupClass()))))
1221 throw new MemberName(specialCaller).
1222 makeAccessException("no private access for invokespecial", this);
1223 }
1224
1225 private boolean restrictProtectedReceiver(MemberName method) {
1226 // The accessing class only has the right to use a protected member
1227 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
1228 if (!method.isProtected() || method.isStatic()
1229 || allowedModes == TRUSTED
1230 || method.getDeclaringClass() == lookupClass()
1231 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass())
1232 || (ALLOW_NESTMATE_ACCESS &&
1233 VerifyAccess.isSamePackageMember(method.getDeclaringClass(), lookupClass())))
1234 return false;
1235 return true;
1236 }
1237 private MethodHandle restrictReceiver(MemberName method, MethodHandle mh, Class<?> caller) throws IllegalAccessException {
1238 assert(!method.isStatic());
1239 // receiver type of mh is too wide; narrow to caller
1240 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
1241 throw method.makeAccessException("caller class must be a subclass below the method", caller);
1242 }
1243 MethodType rawType = mh.type();
1244 if (rawType.parameterType(0) == caller) return mh;
1245 MethodType narrowType = rawType.changeParameterType(0, caller);
1246 return mh.viewAsType(narrowType);
1247 }
1248
1249 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
1250 return getDirectMethodCommon(refKind, refc, method,
1251 (refKind == REF_invokeSpecial ||
1252 (MethodHandleNatives.refKindHasReceiver(refKind) &&
1253 restrictProtectedReceiver(method))), callerClass);
1254 }
1255 private MethodHandle getDirectMethodNoRestrict(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
1256 return getDirectMethodCommon(refKind, refc, method, false, callerClass);
1257 }
1258 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
1259 boolean doRestrict, Class<?> callerClass) throws IllegalAccessException {
1260 checkMethod(refKind, refc, method);
1261 if (method.isMethodHandleInvoke())
1262 return fakeMethodHandleInvoke(method);
1263
1264 Class<?> refcAsSuper;
1265 if (refKind == REF_invokeSpecial &&
1266 refc != lookupClass() &&
1267 refc != (refcAsSuper = lookupClass().getSuperclass()) &&
1268 refc.isAssignableFrom(lookupClass())) {
1269 assert(!method.getName().equals("<init>")); // not this code path
1270 // Per JVMS 6.5, desc. of invokespecial instruction:
1271 // If the method is in a superclass of the LC,
1272 // and if our original search was above LC.super,
1273 // repeat the search (symbolic lookup) from LC.super.
1274 // FIXME: MemberName.resolve should handle this instead.
1275 MemberName m2 = new MemberName(refcAsSuper,
1276 method.getName(),
1277 method.getMethodType(),
1278 REF_invokeSpecial);
1279 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull());
1280 if (m2 == null) throw new InternalError(method.toString());
1281 method = m2;
1282 refc = refcAsSuper;
1283 // redo basic checks
1284 checkMethod(refKind, refc, method);
1285 }
1286
1287 MethodHandle mh = DirectMethodHandle.make(refKind, refc, method);
1288 mh = maybeBindCaller(method, mh, callerClass);
1289 mh = mh.setVarargs(method);
1290 if (doRestrict)
1291 mh = restrictReceiver(method, mh, lookupClass());
1292 return mh;
1293 }
1294 private MethodHandle fakeMethodHandleInvoke(MemberName method) {
1295 return throwException(method.getReturnType(), UnsupportedOperationException.class);
1296 }
1297 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh,
1298 Class<?> callerClass)
1299 throws IllegalAccessException {
1300 if (allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
1301 return mh;
1302 Class<?> hostClass = lookupClass;
1303 if ((allowedModes & PRIVATE) == 0) // caller must use full-power lookup
1304 hostClass = callerClass; // callerClass came from a security manager style stack walk
1305 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, hostClass);
1306 // Note: caller will apply varargs after this step happens.
1307 return cbmh;
1308 }
1309 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
1310 checkField(refKind, refc, field);
1311 MethodHandle mh = DirectMethodHandle.make(refc, field);
1312 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
1313 restrictProtectedReceiver(field));
1314 if (doRestrict)
1315 mh = restrictReceiver(field, mh, lookupClass());
1316 return mh;
1317 }
1318 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
1319 assert(ctor.isConstructor());
1320 checkAccess(REF_newInvokeSpecial, refc, ctor);
1321 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
1322 return DirectMethodHandle.make(ctor).setVarargs(ctor);
1323 }
1324
1325 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
1326 */
1327 /*non-public*/
1328 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type) throws ReflectiveOperationException {
1329 MemberName resolved = null;
1330 if (type instanceof MemberName) {
1331 resolved = (MemberName) type;
1332 if (!resolved.isResolved()) throw new InternalError("unresolved MemberName");
1333 assert(name == null || name.equals(resolved.getName()));
1334 }
1335 if (MethodHandleNatives.refKindIsField(refKind)) {
1336 MemberName field = (resolved != null) ? resolved
1337 : resolveOrFail(refKind, defc, name, (Class<?>) type);
1338 return getDirectField(refKind, defc, field);
1339 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
1340 MemberName method = (resolved != null) ? resolved
1341 : resolveOrFail(refKind, defc, name, (MethodType) type);
1342 return getDirectMethod(refKind, defc, method, lookupClass);
1343 } else if (refKind == REF_newInvokeSpecial) {
1344 assert(name == null || name.equals("<init>"));
1345 MemberName ctor = (resolved != null) ? resolved
1346 : resolveOrFail(REF_newInvokeSpecial, defc, name, (MethodType) type);
1347 return getDirectConstructor(defc, ctor);
1348 }
1349 // oops
1350 throw new ReflectiveOperationException("bad MethodHandle constant #"+refKind+" "+name+" : "+type);
1351 }
1352 }
1353
1354 /**
1355 * Produces a method handle giving read access to elements of an array.
1356 * The type of the method handle will have a return type of the array's
1357 * element type. Its first argument will be the array type,
1358 * and the second will be {@code int}.
1359 * @param arrayClass an array type
1360 * @return a method handle which can load values from the given array type
1361 * @throws NullPointerException if the argument is null
1362 * @throws IllegalArgumentException if arrayClass is not an array type
1363 */
1364 public static
1365 MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
1366 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, false);
1367 }
1368
1369 /**
1370 * Produces a method handle giving write access to elements of an array.
1371 * The type of the method handle will have a void return type.
1372 * Its last argument will be the array's element type.
1373 * The first and second arguments will be the array type and int.
1374 * @return a method handle which can store values into the array type
1375 * @throws NullPointerException if the argument is null
1376 * @throws IllegalArgumentException if arrayClass is not an array type
1377 */
1378 public static
1379 MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
1380 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, true);
1381 }
1382
1383 /// method handle invocation (reflective style)
1384
1385 /**
1386 * Produces a method handle which will invoke any method handle of the
1387 * given {@code type}, with a given number of trailing arguments replaced by
1388 * a single trailing {@code Object[]} array.
1389 * The resulting invoker will be a method handle with the following
1390 * arguments:
1391 * <ul>
1392 * <li>a single {@code MethodHandle} target
1393 * <li>zero or more leading values (counted by {@code leadingArgCount})
1394 * <li>an {@code Object[]} array containing trailing arguments
1395 * </ul>
1396 * <p>
1397 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
1398 * the indicated {@code type}.
1399 * That is, if the target is exactly of the given {@code type}, it will behave
1400 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
1401 * is used to convert the target to the required {@code type}.
1402 * <p>
1403 * The type of the returned invoker will not be the given {@code type}, but rather
1404 * will have all parameters except the first {@code leadingArgCount}
1405 * replaced by a single array of type {@code Object[]}, which will be
1406 * the final parameter.
1407 * <p>
1408 * Before invoking its target, the invoker will spread the final array, apply
1409 * reference casts as necessary, and unbox and widen primitive arguments.
1410 * <p>
1411 * This method is equivalent to the following code (though it may be more efficient):
1412 * <p><blockquote><pre>
1413 MethodHandle invoker = MethodHandles.invoker(type);
1414 int spreadArgCount = type.parameterCount() - leadingArgCount;
1415 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
1416 return invoker;
1417 * </pre></blockquote>
1418 * <p>
1419 * This method throws no reflective or security exceptions.
1420 * @param type the desired target type
1421 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
1422 * @return a method handle suitable for invoking any method handle of the given type
1423 * @throws NullPointerException if {@code type} is null
1424 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
1425 * the range from 0 to {@code type.parameterCount()} inclusive
1426 */
1427 static public
1428 MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
1429 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
1430 throw new IllegalArgumentException("bad argument count "+leadingArgCount);
1431 return type.invokers().spreadInvoker(leadingArgCount);
1432 }
1433
1434 /**
1435 * Produces a special <em>invoker method handle</em> which can be used to
1436 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
1437 * The resulting invoker will have a type which is
1438 * exactly equal to the desired type, except that it will accept
1439 * an additional leading argument of type {@code MethodHandle}.
1440 * <p>
1441 * This method is equivalent to the following code (though it may be more efficient):
1442 * <p><blockquote><pre>
1443 publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)
1444 * </pre></blockquote>
1445 *
1446 * <p style="font-size:smaller;">
1447 * <em>Discussion:</em>
1448 * Invoker method handles can be useful when working with variable method handles
1449 * of unknown types.
1450 * For example, to emulate an {@code invokeExact} call to a variable method
1451 * handle {@code M}, extract its type {@code T},
1452 * look up the invoker method {@code X} for {@code T},
1453 * and call the invoker method, as {@code X.invoke(T, A...)}.
1454 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
1455 * is unknown.)
1456 * If spreading, collecting, or other argument transformations are required,
1457 * they can be applied once to the invoker {@code X} and reused on many {@code M}
1458 * method handle values, as long as they are compatible with the type of {@code X}.
1459 * <p>
1460 * <em>(Note: The invoker method is not available via the Core Reflection API.
1461 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
1462 * on the declared {@code invokeExact} or {@code invoke} method will raise an
1463 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
1464 * <p>
1465 * This method throws no reflective or security exceptions.
1466 * @param type the desired target type
1467 * @return a method handle suitable for invoking any method handle of the given type
1468 */
1469 static public
1470 MethodHandle exactInvoker(MethodType type) {
1471 return type.invokers().exactInvoker();
1472 }
1473
1474 /**
1475 * Produces a special <em>invoker method handle</em> which can be used to
1476 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
1477 * The resulting invoker will have a type which is
1478 * exactly equal to the desired type, except that it will accept
1479 * an additional leading argument of type {@code MethodHandle}.
1480 * <p>
1481 * Before invoking its target, if the target differs from the expected type,
1482 * the invoker will apply reference casts as
1483 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
1484 * Similarly, the return value will be converted as necessary.
1485 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
1486 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
1487 * <p>
1488 * A {@linkplain MethodType#genericMethodType general method type},
1489 * mentions only {@code Object} arguments and return values.
1490 * An invoker for such a type is capable of calling any method handle
1491 * of the same arity as the general type.
1492 * <p>
1493 * This method is equivalent to the following code (though it may be more efficient):
1494 * <p><blockquote><pre>
1495 publicLookup().findVirtual(MethodHandle.class, "invoke", type)
1496 * </pre></blockquote>
1497 * <p>
1498 * This method throws no reflective or security exceptions.
1499 * @param type the desired target type
1500 * @return a method handle suitable for invoking any method handle convertible to the given type
1501 */
1502 static public
1503 MethodHandle invoker(MethodType type) {
1504 return type.invokers().generalInvoker();
1505 }
1506
1507 static /*non-public*/
1508 MethodHandle basicInvoker(MethodType type) {
1509 return type.form().basicInvoker();
1510 }
1511
1512 /// method handle modification (creation from other method handles)
1513
1514 /**
1515 * Produces a method handle which adapts the type of the
1516 * given method handle to a new type by pairwise argument and return type conversion.
1517 * The original type and new type must have the same number of arguments.
1518 * The resulting method handle is guaranteed to report a type
1519 * which is equal to the desired new type.
1520 * <p>
1521 * If the original type and new type are equal, returns target.
1522 * <p>
1523 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
1524 * and some additional conversions are also applied if those conversions fail.
1525 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
1526 * if possible, before or instead of any conversions done by {@code asType}:
1527 * <ul>
1528 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
1529 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
1530 * (This treatment of interfaces follows the usage of the bytecode verifier.)
1531 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
1532 * the boolean is converted to a byte value, 1 for true, 0 for false.
1533 * (This treatment follows the usage of the bytecode verifier.)
1534 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
1535 * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
1536 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
1537 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
1538 * then a Java casting conversion (JLS 5.5) is applied.
1539 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
1540 * widening and/or narrowing.)
1541 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
1542 * conversion will be applied at runtime, possibly followed
1543 * by a Java casting conversion (JLS 5.5) on the primitive value,
1544 * possibly followed by a conversion from byte to boolean by testing
1545 * the low-order bit.
1546 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
1547 * and if the reference is null at runtime, a zero value is introduced.
1548 * </ul>
1549 * @param target the method handle to invoke after arguments are retyped
1550 * @param newType the expected type of the new method handle
1551 * @return a method handle which delegates to the target after performing
1552 * any necessary argument conversions, and arranges for any
1553 * necessary return value conversions
1554 * @throws NullPointerException if either argument is null
1555 * @throws WrongMethodTypeException if the conversion cannot be made
1556 * @see MethodHandle#asType
1557 */
1558 public static
1559 MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
1560 if (!target.type().isCastableTo(newType)) {
1561 throw new WrongMethodTypeException("cannot explicitly cast "+target+" to "+newType);
1562 }
1563 return MethodHandleImpl.makePairwiseConvert(target, newType, 2);
1564 }
1565
1566 /**
1567 * Produces a method handle which adapts the calling sequence of the
1568 * given method handle to a new type, by reordering the arguments.
1569 * The resulting method handle is guaranteed to report a type
1570 * which is equal to the desired new type.
1571 * <p>
1572 * The given array controls the reordering.
1573 * Call {@code #I} the number of incoming parameters (the value
1574 * {@code newType.parameterCount()}, and call {@code #O} the number
1575 * of outgoing parameters (the value {@code target.type().parameterCount()}).
1576 * Then the length of the reordering array must be {@code #O},
1577 * and each element must be a non-negative number less than {@code #I}.
1578 * For every {@code N} less than {@code #O}, the {@code N}-th
1579 * outgoing argument will be taken from the {@code I}-th incoming
1580 * argument, where {@code I} is {@code reorder[N]}.
1581 * <p>
1582 * No argument or return value conversions are applied.
1583 * The type of each incoming argument, as determined by {@code newType},
1584 * must be identical to the type of the corresponding outgoing parameter
1585 * or parameters in the target method handle.
1586 * The return type of {@code newType} must be identical to the return
1587 * type of the original target.
1588 * <p>
1589 * The reordering array need not specify an actual permutation.
1590 * An incoming argument will be duplicated if its index appears
1591 * more than once in the array, and an incoming argument will be dropped
1592 * if its index does not appear in the array.
1593 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
1594 * incoming arguments which are not mentioned in the reordering array
1595 * are may be any type, as determined only by {@code newType}.
1596 * <blockquote><pre>
1597 import static java.lang.invoke.MethodHandles.*;
1598 import static java.lang.invoke.MethodType.*;
1599 ...
1600 MethodType intfn1 = methodType(int.class, int.class);
1601 MethodType intfn2 = methodType(int.class, int.class, int.class);
1602 MethodHandle sub = ... {int x, int y => x-y} ...;
1603 assert(sub.type().equals(intfn2));
1604 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
1605 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
1606 assert((int)rsub.invokeExact(1, 100) == 99);
1607 MethodHandle add = ... {int x, int y => x+y} ...;
1608 assert(add.type().equals(intfn2));
1609 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
1610 assert(twice.type().equals(intfn1));
1611 assert((int)twice.invokeExact(21) == 42);
1612 * </pre></blockquote>
1613 * @param target the method handle to invoke after arguments are reordered
1614 * @param newType the expected type of the new method handle
1615 * @param reorder an index array which controls the reordering
1616 * @return a method handle which delegates to the target after it
1617 * drops unused arguments and moves and/or duplicates the other arguments
1618 * @throws NullPointerException if any argument is null
1619 * @throws IllegalArgumentException if the index array length is not equal to
1620 * the arity of the target, or if any index array element
1621 * not a valid index for a parameter of {@code newType},
1622 * or if two corresponding parameter types in
1623 * {@code target.type()} and {@code newType} are not identical,
1624 */
1625 public static
1626 MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
1627 checkReorder(reorder, newType, target.type());
1628 return target.permuteArguments(newType, reorder);
1629 }
1630
1631 private static void checkReorder(int[] reorder, MethodType newType, MethodType oldType) {
1632 if (newType.returnType() != oldType.returnType())
1633 throw newIllegalArgumentException("return types do not match",
1634 oldType, newType);
1635 if (reorder.length == oldType.parameterCount()) {
1636 int limit = newType.parameterCount();
1637 boolean bad = false;
1638 for (int j = 0; j < reorder.length; j++) {
1639 int i = reorder[j];
1640 if (i < 0 || i >= limit) {
1641 bad = true; break;
1642 }
1643 Class<?> src = newType.parameterType(i);
1644 Class<?> dst = oldType.parameterType(j);
1645 if (src != dst)
1646 throw newIllegalArgumentException("parameter types do not match after reorder",
1647 oldType, newType);
1648 }
1649 if (!bad) return;
1650 }
1651 throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
1652 }
1653
1654 /**
1655 * Produces a method handle of the requested return type which returns the given
1656 * constant value every time it is invoked.
1657 * <p>
1658 * Before the method handle is returned, the passed-in value is converted to the requested type.
1659 * If the requested type is primitive, widening primitive conversions are attempted,
1660 * else reference conversions are attempted.
1661 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
1662 * @param type the return type of the desired method handle
1663 * @param value the value to return
1664 * @return a method handle of the given return type and no arguments, which always returns the given value
1665 * @throws NullPointerException if the {@code type} argument is null
1666 * @throws ClassCastException if the value cannot be converted to the required return type
1667 * @throws IllegalArgumentException if the given type is {@code void.class}
1668 */
1669 public static
1670 MethodHandle constant(Class<?> type, Object value) {
1671 if (type.isPrimitive()) {
1672 if (type == void.class)
1673 throw newIllegalArgumentException("void type");
1674 Wrapper w = Wrapper.forPrimitiveType(type);
1675 return insertArguments(identity(type), 0, w.convert(value, type));
1676 } else {
1677 return identity(type).bindTo(type.cast(value));
1678 }
1679 }
1680
1681 /**
1682 * Produces a method handle which returns its sole argument when invoked.
1683 * @param type the type of the sole parameter and return value of the desired method handle
1684 * @return a unary method handle which accepts and returns the given type
1685 * @throws NullPointerException if the argument is null
1686 * @throws IllegalArgumentException if the given type is {@code void.class}
1687 */
1688 public static
1689 MethodHandle identity(Class<?> type) {
1690 if (type == void.class)
1691 throw newIllegalArgumentException("void type");
1692 else if (type == Object.class)
1693 return ValueConversions.identity();
1694 else if (type.isPrimitive())
1695 return ValueConversions.identity(Wrapper.forPrimitiveType(type));
1696 else
1697 return MethodHandleImpl.makeReferenceIdentity(type);
1698 }
1699
1700 /**
1701 * Provides a target method handle with one or more <em>bound arguments</em>
1702 * in advance of the method handle's invocation.
1703 * The formal parameters to the target corresponding to the bound
1704 * arguments are called <em>bound parameters</em>.
1705 * Returns a new method handle which saves away the bound arguments.
1706 * When it is invoked, it receives arguments for any non-bound parameters,
1707 * binds the saved arguments to their corresponding parameters,
1708 * and calls the original target.
1709 * <p>
1710 * The type of the new method handle will drop the types for the bound
1711 * parameters from the original target type, since the new method handle
1712 * will no longer require those arguments to be supplied by its callers.
1713 * <p>
1714 * Each given argument object must match the corresponding bound parameter type.
1715 * If a bound parameter type is a primitive, the argument object
1716 * must be a wrapper, and will be unboxed to produce the primitive value.
1717 * <p>
1718 * The {@code pos} argument selects which parameters are to be bound.
1719 * It may range between zero and <i>N-L</i> (inclusively),
1720 * where <i>N</i> is the arity of the target method handle
1721 * and <i>L</i> is the length of the values array.
1722 * @param target the method handle to invoke after the argument is inserted
1723 * @param pos where to insert the argument (zero for the first)
1724 * @param values the series of arguments to insert
1725 * @return a method handle which inserts an additional argument,
1726 * before calling the original method handle
1727 * @throws NullPointerException if the target or the {@code values} array is null
1728 * @see MethodHandle#bindTo
1729 */
1730 public static
1731 MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
1732 int insCount = values.length;
1733 MethodType oldType = target.type();
1734 int outargs = oldType.parameterCount();
1735 int inargs = outargs - insCount;
1736 if (inargs < 0)
1737 throw newIllegalArgumentException("too many values to insert");
1738 if (pos < 0 || pos > inargs)
1739 throw newIllegalArgumentException("no argument type to append");
1740 MethodHandle result = target;
1741 for (int i = 0; i < insCount; i++) {
1742 Object value = values[i];
1743 Class<?> ptype = oldType.parameterType(pos+i);
1744 if (ptype.isPrimitive()) {
1745 char btype = 'I';
1746 Wrapper w = Wrapper.forPrimitiveType(ptype);
1747 switch (w) {
1748 case LONG: btype = 'J'; break;
1749 case FLOAT: btype = 'F'; break;
1750 case DOUBLE: btype = 'D'; break;
1751 }
1752 // perform unboxing and/or primitive conversion
1753 value = w.convert(value, ptype);
1754 result = result.bindArgument(pos, btype, value);
1755 continue;
1756 }
1757 value = ptype.cast(value); // throw CCE if needed
1758 if (pos == 0) {
1759 result = result.bindReceiver(value);
1760 } else {
1761 result = result.bindArgument(pos, 'L', value);
1762 }
1763 }
1764 return result;
1765 }
1766
1767 /**
1768 * Produces a method handle which will discard some dummy arguments
1769 * before calling some other specified <i>target</i> method handle.
1770 * The type of the new method handle will be the same as the target's type,
1771 * except it will also include the dummy argument types,
1772 * at some given position.
1773 * <p>
1774 * The {@code pos} argument may range between zero and <i>N</i>,
1775 * where <i>N</i> is the arity of the target.
1776 * If {@code pos} is zero, the dummy arguments will precede
1777 * the target's real arguments; if {@code pos} is <i>N</i>
1778 * they will come after.
1779 * <p>
1780 * <b>Example:</b>
1781 * <p><blockquote><pre>
1782 import static java.lang.invoke.MethodHandles.*;
1783 import static java.lang.invoke.MethodType.*;
1784 ...
1785 MethodHandle cat = lookup().findVirtual(String.class,
1786 "concat", methodType(String.class, String.class));
1787 assertEquals("xy", (String) cat.invokeExact("x", "y"));
1788 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
1789 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
1790 assertEquals(bigType, d0.type());
1791 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
1792 * </pre></blockquote>
1793 * <p>
1794 * This method is also equivalent to the following code:
1795 * <p><blockquote><pre>
1796 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}(target, pos, valueTypes.toArray(new Class[0]))
1797 * </pre></blockquote>
1798 * @param target the method handle to invoke after the arguments are dropped
1799 * @param valueTypes the type(s) of the argument(s) to drop
1800 * @param pos position of first argument to drop (zero for the leftmost)
1801 * @return a method handle which drops arguments of the given types,
1802 * before calling the original method handle
1803 * @throws NullPointerException if the target is null,
1804 * or if the {@code valueTypes} list or any of its elements is null
1805 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
1806 * or if {@code pos} is negative or greater than the arity of the target,
1807 * or if the new method handle's type would have too many parameters
1808 */
1809 public static
1810 MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
1811 MethodType oldType = target.type(); // get NPE
1812 int dropped = valueTypes.size();
1813 MethodType.checkSlotCount(dropped);
1814 if (dropped == 0) return target;
1815 int outargs = oldType.parameterCount();
1816 int inargs = outargs + dropped;
1817 if (pos < 0 || pos >= inargs)
1818 throw newIllegalArgumentException("no argument type to remove");
1819 ArrayList<Class<?>> ptypes = new ArrayList<>(oldType.parameterList());
1820 ptypes.addAll(pos, valueTypes);
1821 MethodType newType = MethodType.methodType(oldType.returnType(), ptypes);
1822 return target.dropArguments(newType, pos, dropped);
1823 }
1824
1825 /**
1826 * Produces a method handle which will discard some dummy arguments
1827 * before calling some other specified <i>target</i> method handle.
1828 * The type of the new method handle will be the same as the target's type,
1829 * except it will also include the dummy argument types,
1830 * at some given position.
1831 * <p>
1832 * The {@code pos} argument may range between zero and <i>N</i>,
1833 * where <i>N</i> is the arity of the target.
1834 * If {@code pos} is zero, the dummy arguments will precede
1835 * the target's real arguments; if {@code pos} is <i>N</i>
1836 * they will come after.
1837 * <p>
1838 * <b>Example:</b>
1839 * <p><blockquote><pre>
1840 import static java.lang.invoke.MethodHandles.*;
1841 import static java.lang.invoke.MethodType.*;
1842 ...
1843 MethodHandle cat = lookup().findVirtual(String.class,
1844 "concat", methodType(String.class, String.class));
1845 assertEquals("xy", (String) cat.invokeExact("x", "y"));
1846 MethodHandle d0 = dropArguments(cat, 0, String.class);
1847 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
1848 MethodHandle d1 = dropArguments(cat, 1, String.class);
1849 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
1850 MethodHandle d2 = dropArguments(cat, 2, String.class);
1851 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
1852 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
1853 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
1854 * </pre></blockquote>
1855 * <p>
1856 * This method is also equivalent to the following code:
1857 * <p><blockquote><pre>
1858 * {@link #dropArguments(MethodHandle,int,List) dropArguments}(target, pos, Arrays.asList(valueTypes))
1859 * </pre></blockquote>
1860 * @param target the method handle to invoke after the arguments are dropped
1861 * @param valueTypes the type(s) of the argument(s) to drop
1862 * @param pos position of first argument to drop (zero for the leftmost)
1863 * @return a method handle which drops arguments of the given types,
1864 * before calling the original method handle
1865 * @throws NullPointerException if the target is null,
1866 * or if the {@code valueTypes} array or any of its elements is null
1867 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
1868 * or if {@code pos} is negative or greater than the arity of the target,
1869 * or if the new method handle's type would have too many parameters
1870 */
1871 public static
1872 MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
1873 return dropArguments(target, pos, Arrays.asList(valueTypes));
1874 }
1875
1876 /**
1877 * Adapts a target method handle by pre-processing
1878 * one or more of its arguments, each with its own unary filter function,
1879 * and then calling the target with each pre-processed argument
1880 * replaced by the result of its corresponding filter function.
1881 * <p>
1882 * The pre-processing is performed by one or more method handles,
1883 * specified in the elements of the {@code filters} array.
1884 * The first element of the filter array corresponds to the {@code pos}
1885 * argument of the target, and so on in sequence.
1886 * <p>
1887 * Null arguments in the array are treated as identity functions,
1888 * and the corresponding arguments left unchanged.
1889 * (If there are no non-null elements in the array, the original target is returned.)
1890 * Each filter is applied to the corresponding argument of the adapter.
1891 * <p>
1892 * If a filter {@code F} applies to the {@code N}th argument of
1893 * the target, then {@code F} must be a method handle which
1894 * takes exactly one argument. The type of {@code F}'s sole argument
1895 * replaces the corresponding argument type of the target
1896 * in the resulting adapted method handle.
1897 * The return type of {@code F} must be identical to the corresponding
1898 * parameter type of the target.
1899 * <p>
1900 * It is an error if there are elements of {@code filters}
1901 * (null or not)
1902 * which do not correspond to argument positions in the target.
1903 * <b>Example:</b>
1904 * <p><blockquote><pre>
1905 import static java.lang.invoke.MethodHandles.*;
1906 import static java.lang.invoke.MethodType.*;
1907 ...
1908 MethodHandle cat = lookup().findVirtual(String.class,
1909 "concat", methodType(String.class, String.class));
1910 MethodHandle upcase = lookup().findVirtual(String.class,
1911 "toUpperCase", methodType(String.class));
1912 assertEquals("xy", (String) cat.invokeExact("x", "y"));
1913 MethodHandle f0 = filterArguments(cat, 0, upcase);
1914 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
1915 MethodHandle f1 = filterArguments(cat, 1, upcase);
1916 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
1917 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
1918 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
1919 * </pre></blockquote>
1920 * <p> Here is pseudocode for the resulting adapter:
1921 * <blockquote><pre>
1922 * V target(P... p, A[i]... a[i], B... b);
1923 * A[i] filter[i](V[i]);
1924 * T adapter(P... p, V[i]... v[i], B... b) {
1925 * return target(p..., f[i](v[i])..., b...);
1926 * }
1927 * </pre></blockquote>
1928 *
1929 * @param target the method handle to invoke after arguments are filtered
1930 * @param pos the position of the first argument to filter
1931 * @param filters method handles to call initially on filtered arguments
1932 * @return method handle which incorporates the specified argument filtering logic
1933 * @throws NullPointerException if the target is null
1934 * or if the {@code filters} array is null
1935 * @throws IllegalArgumentException if a non-null element of {@code filters}
1936 * does not match a corresponding argument type of target as described above,
1937 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()}
1938 */
1939 public static
1940 MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
1941 MethodType targetType = target.type();
1942 MethodHandle adapter = target;
1943 MethodType adapterType = null;
1944 assert((adapterType = targetType) != null);
1945 int maxPos = targetType.parameterCount();
1946 if (pos + filters.length > maxPos)
1947 throw newIllegalArgumentException("too many filters");
1948 int curPos = pos-1; // pre-incremented
1949 for (MethodHandle filter : filters) {
1950 curPos += 1;
1951 if (filter == null) continue; // ignore null elements of filters
1952 adapter = filterArgument(adapter, curPos, filter);
1953 assert((adapterType = adapterType.changeParameterType(curPos, filter.type().parameterType(0))) != null);
1954 }
1955 assert(adapterType.equals(adapter.type()));
1956 return adapter;
1957 }
1958
1959 /*non-public*/ static
1960 MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
1961 MethodType targetType = target.type();
1962 MethodType filterType = filter.type();
1963 if (filterType.parameterCount() != 1
1964 || filterType.returnType() != targetType.parameterType(pos))
1965 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
1966 return MethodHandleImpl.makeCollectArguments(target, filter, pos, false);
1967 }
1968
1969 // FIXME: Make this public in M1.
1970 /*non-public*/ static
1971 MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle collector) {
1972 MethodType targetType = target.type();
1973 MethodType filterType = collector.type();
1974 if (filterType.returnType() != void.class &&
1975 filterType.returnType() != targetType.parameterType(pos))
1976 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
1977 return MethodHandleImpl.makeCollectArguments(target, collector, pos, false);
1978 }
1979
1980 /**
1981 * Adapts a target method handle by post-processing
1982 * its return value (if any) with a filter (another method handle).
1983 * The result of the filter is returned from the adapter.
1984 * <p>
1985 * If the target returns a value, the filter must accept that value as
1986 * its only argument.
1987 * If the target returns void, the filter must accept no arguments.
1988 * <p>
1989 * The return type of the filter
1990 * replaces the return type of the target
1991 * in the resulting adapted method handle.
1992 * The argument type of the filter (if any) must be identical to the
1993 * return type of the target.
1994 * <b>Example:</b>
1995 * <p><blockquote><pre>
1996 import static java.lang.invoke.MethodHandles.*;
1997 import static java.lang.invoke.MethodType.*;
1998 ...
1999 MethodHandle cat = lookup().findVirtual(String.class,
2000 "concat", methodType(String.class, String.class));
2001 MethodHandle length = lookup().findVirtual(String.class,
2002 "length", methodType(int.class));
2003 System.out.println((String) cat.invokeExact("x", "y")); // xy
2004 MethodHandle f0 = filterReturnValue(cat, length);
2005 System.out.println((int) f0.invokeExact("x", "y")); // 2
2006 * </pre></blockquote>
2007 * <p> Here is pseudocode for the resulting adapter:
2008 * <blockquote><pre>
2009 * V target(A...);
2010 * T filter(V);
2011 * T adapter(A... a) {
2012 * V v = target(a...);
2013 * return filter(v);
2014 * }
2015 * // and if the target has a void return:
2016 * void target2(A...);
2017 * T filter2();
2018 * T adapter2(A... a) {
2019 * target2(a...);
2020 * return filter2();
2021 * }
2022 * // and if the filter has a void return:
2023 * V target3(A...);
2024 * void filter3(V);
2025 * void adapter3(A... a) {
2026 * V v = target3(a...);
2027 * filter3(v);
2028 * }
2029 * </pre></blockquote>
2030 * @param target the method handle to invoke before filtering the return value
2031 * @param filter method handle to call on the return value
2032 * @return method handle which incorporates the specified return value filtering logic
2033 * @throws NullPointerException if either argument is null
2034 * @throws IllegalArgumentException if the argument list of {@code filter}
2035 * does not match the return type of target as described above
2036 */
2037 public static
2038 MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
2039 MethodType targetType = target.type();
2040 MethodType filterType = filter.type();
2041 Class<?> rtype = targetType.returnType();
2042 int filterValues = filterType.parameterCount();
2043 if (filterValues == 0
2044 ? (rtype != void.class)
2045 : (rtype != filterType.parameterType(0)))
2046 throw newIllegalArgumentException("target and filter types do not match", target, filter);
2047 // result = fold( lambda(retval, arg...) { filter(retval) },
2048 // lambda( arg...) { target(arg...) } )
2049 return MethodHandleImpl.makeCollectArguments(filter, target, 0, false);
2050 }
2051
2052 /**
2053 * Adapts a target method handle by pre-processing
2054 * some of its arguments, and then calling the target with
2055 * the result of the pre-processing, inserted into the original
2056 * sequence of arguments.
2057 * <p>
2058 * The pre-processing is performed by {@code combiner}, a second method handle.
2059 * Of the arguments passed to the adapter, the first {@code N} arguments
2060 * are copied to the combiner, which is then called.
2061 * (Here, {@code N} is defined as the parameter count of the combiner.)
2062 * After this, control passes to the target, with any result
2063 * from the combiner inserted before the original {@code N} incoming
2064 * arguments.
2065 * <p>
2066 * If the combiner returns a value, the first parameter type of the target
2067 * must be identical with the return type of the combiner, and the next
2068 * {@code N} parameter types of the target must exactly match the parameters
2069 * of the combiner.
2070 * <p>
2071 * If the combiner has a void return, no result will be inserted,
2072 * and the first {@code N} parameter types of the target
2073 * must exactly match the parameters of the combiner.
2074 * <p>
2075 * The resulting adapter is the same type as the target, except that the
2076 * first parameter type is dropped,
2077 * if it corresponds to the result of the combiner.
2078 * <p>
2079 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
2080 * that either the combiner or the target does not wish to receive.
2081 * If some of the incoming arguments are destined only for the combiner,
2082 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
2083 * arguments will not need to be live on the stack on entry to the
2084 * target.)
2085 * <b>Example:</b>
2086 * <p><blockquote><pre>
2087 import static java.lang.invoke.MethodHandles.*;
2088 import static java.lang.invoke.MethodType.*;
2089 ...
2090 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
2091 "println", methodType(void.class, String.class))
2092 .bindTo(System.out);
2093 MethodHandle cat = lookup().findVirtual(String.class,
2094 "concat", methodType(String.class, String.class));
2095 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
2096 MethodHandle catTrace = foldArguments(cat, trace);
2097 // also prints "boo":
2098 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
2099 * </pre></blockquote>
2100 * <p> Here is pseudocode for the resulting adapter:
2101 * <blockquote><pre>
2102 * // there are N arguments in A...
2103 * T target(V, A[N]..., B...);
2104 * V combiner(A...);
2105 * T adapter(A... a, B... b) {
2106 * V v = combiner(a...);
2107 * return target(v, a..., b...);
2108 * }
2109 * // and if the combiner has a void return:
2110 * T target2(A[N]..., B...);
2111 * void combiner2(A...);
2112 * T adapter2(A... a, B... b) {
2113 * combiner2(a...);
2114 * return target2(a..., b...);
2115 * }
2116 * </pre></blockquote>
2117 * @param target the method handle to invoke after arguments are combined
2118 * @param combiner method handle to call initially on the incoming arguments
2119 * @return method handle which incorporates the specified argument folding logic
2120 * @throws NullPointerException if either argument is null
2121 * @throws IllegalArgumentException if {@code combiner}'s return type
2122 * is non-void and not the same as the first argument type of
2123 * the target, or if the initial {@code N} argument types
2124 * of the target
2125 * (skipping one matching the {@code combiner}'s return type)
2126 * are not identical with the argument types of {@code combiner}
2127 */
2128 public static
2129 MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
2130 int pos = 0;
2131 MethodType targetType = target.type();
2132 MethodType combinerType = combiner.type();
2133 int foldPos = pos;
2134 int foldArgs = combinerType.parameterCount();
2135 int foldVals = combinerType.returnType() == void.class ? 0 : 1;
2136 int afterInsertPos = foldPos + foldVals;
2137 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
2138 if (ok && !(combinerType.parameterList()
2139 .equals(targetType.parameterList().subList(afterInsertPos,
2140 afterInsertPos + foldArgs))))
2141 ok = false;
2142 if (ok && foldVals != 0 && !combinerType.returnType().equals(targetType.parameterType(0)))
2143 ok = false;
2144 if (!ok)
2145 throw misMatchedTypes("target and combiner types", targetType, combinerType);
2146 MethodType newType = targetType.dropParameterTypes(foldPos, afterInsertPos);
2147 return MethodHandleImpl.makeCollectArguments(target, combiner, foldPos, true);
2148 }
2149
2150 /**
2151 * Makes a method handle which adapts a target method handle,
2152 * by guarding it with a test, a boolean-valued method handle.
2153 * If the guard fails, a fallback handle is called instead.
2154 * All three method handles must have the same corresponding
2155 * argument and return types, except that the return type
2156 * of the test must be boolean, and the test is allowed
2157 * to have fewer arguments than the other two method handles.
2158 * <p> Here is pseudocode for the resulting adapter:
2159 * <blockquote><pre>
2160 * boolean test(A...);
2161 * T target(A...,B...);
2162 * T fallback(A...,B...);
2163 * T adapter(A... a,B... b) {
2164 * if (test(a...))
2165 * return target(a..., b...);
2166 * else
2167 * return fallback(a..., b...);
2168 * }
2169 * </pre></blockquote>
2170 * Note that the test arguments ({@code a...} in the pseudocode) cannot
2171 * be modified by execution of the test, and so are passed unchanged
2172 * from the caller to the target or fallback as appropriate.
2173 * @param test method handle used for test, must return boolean
2174 * @param target method handle to call if test passes
2175 * @param fallback method handle to call if test fails
2176 * @return method handle which incorporates the specified if/then/else logic
2177 * @throws NullPointerException if any argument is null
2178 * @throws IllegalArgumentException if {@code test} does not return boolean,
2179 * or if all three method types do not match (with the return
2180 * type of {@code test} changed to match that of the target).
2181 */
2182 public static
2183 MethodHandle guardWithTest(MethodHandle test,
2184 MethodHandle target,
2185 MethodHandle fallback) {
2186 MethodType gtype = test.type();
2187 MethodType ttype = target.type();
2188 MethodType ftype = fallback.type();
2189 if (!ttype.equals(ftype))
2190 throw misMatchedTypes("target and fallback types", ttype, ftype);
2191 if (gtype.returnType() != boolean.class)
2192 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
2193 List<Class<?>> targs = ttype.parameterList();
2194 List<Class<?>> gargs = gtype.parameterList();
2195 if (!targs.equals(gargs)) {
2196 int gpc = gargs.size(), tpc = targs.size();
2197 if (gpc >= tpc || !targs.subList(0, gpc).equals(gargs))
2198 throw misMatchedTypes("target and test types", ttype, gtype);
2199 test = dropArguments(test, gpc, targs.subList(gpc, tpc));
2200 gtype = test.type();
2201 }
2202 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
2203 }
2204
2205 static RuntimeException misMatchedTypes(String what, MethodType t1, MethodType t2) {
2206 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
2207 }
2208
2209 /**
2210 * Makes a method handle which adapts a target method handle,
2211 * by running it inside an exception handler.
2212 * If the target returns normally, the adapter returns that value.
2213 * If an exception matching the specified type is thrown, the fallback
2214 * handle is called instead on the exception, plus the original arguments.
2215 * <p>
2216 * The target and handler must have the same corresponding
2217 * argument and return types, except that handler may omit trailing arguments
2218 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
2219 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
2220 * <p> Here is pseudocode for the resulting adapter:
2221 * <blockquote><pre>
2222 * T target(A..., B...);
2223 * T handler(ExType, A...);
2224 * T adapter(A... a, B... b) {
2225 * try {
2226 * return target(a..., b...);
2227 * } catch (ExType ex) {
2228 * return handler(ex, a...);
2229 * }
2230 * }
2231 * </pre></blockquote>
2232 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
2233 * be modified by execution of the target, and so are passed unchanged
2234 * from the caller to the handler, if the handler is invoked.
2235 * <p>
2236 * The target and handler must return the same type, even if the handler
2237 * always throws. (This might happen, for instance, because the handler
2238 * is simulating a {@code finally} clause).
2239 * To create such a throwing handler, compose the handler creation logic
2240 * with {@link #throwException throwException},
2241 * in order to create a method handle of the correct return type.
2242 * @param target method handle to call
2243 * @param exType the type of exception which the handler will catch
2244 * @param handler method handle to call if a matching exception is thrown
2245 * @return method handle which incorporates the specified try/catch logic
2246 * @throws NullPointerException if any argument is null
2247 * @throws IllegalArgumentException if {@code handler} does not accept
2248 * the given exception type, or if the method handle types do
2249 * not match in their return types and their
2250 * corresponding parameters
2251 */
2252 public static
2253 MethodHandle catchException(MethodHandle target,
2254 Class<? extends Throwable> exType,
2255 MethodHandle handler) {
2256 MethodType ttype = target.type();
2257 MethodType htype = handler.type();
2258 if (htype.parameterCount() < 1 ||
2259 !htype.parameterType(0).isAssignableFrom(exType))
2260 throw newIllegalArgumentException("handler does not accept exception type "+exType);
2261 if (htype.returnType() != ttype.returnType())
2262 throw misMatchedTypes("target and handler return types", ttype, htype);
2263 List<Class<?>> targs = ttype.parameterList();
2264 List<Class<?>> hargs = htype.parameterList();
2265 hargs = hargs.subList(1, hargs.size()); // omit leading parameter from handler
2266 if (!targs.equals(hargs)) {
2267 int hpc = hargs.size(), tpc = targs.size();
2268 if (hpc >= tpc || !targs.subList(0, hpc).equals(hargs))
2269 throw misMatchedTypes("target and handler types", ttype, htype);
2270 handler = dropArguments(handler, 1+hpc, targs.subList(hpc, tpc));
2271 htype = handler.type();
2272 }
2273 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
2274 }
2275
2276 /**
2277 * Produces a method handle which will throw exceptions of the given {@code exType}.
2278 * The method handle will accept a single argument of {@code exType},
2279 * and immediately throw it as an exception.
2280 * The method type will nominally specify a return of {@code returnType}.
2281 * The return type may be anything convenient: It doesn't matter to the
2282 * method handle's behavior, since it will never return normally.
2283 * @return method handle which can throw the given exceptions
2284 * @throws NullPointerException if either argument is null
2285 */
2286 public static
2287 MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
2288 if (!Throwable.class.isAssignableFrom(exType))
2289 throw new ClassCastException(exType.getName());
2290 return MethodHandleImpl.throwException(MethodType.methodType(returnType, exType));
2291 }
2292 }