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