1 /*
2 * Copyright (c) 2008, 2013, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.lang.invoke;
27
28 import java.lang.reflect.*;
29 import java.security.AccessController;
30 import java.security.PrivilegedAction;
31 import java.util.List;
32 import java.util.ArrayList;
33 import java.util.Arrays;
34
35 import sun.invoke.util.ValueConversions;
36 import sun.invoke.util.VerifyAccess;
37 import sun.invoke.util.Wrapper;
38 import sun.reflect.CallerSensitive;
39 import sun.reflect.Reflection;
40 import sun.reflect.misc.ReflectUtil;
41 import sun.security.util.SecurityConstants;
42 import static java.lang.invoke.MethodHandleStatics.*;
43 import static java.lang.invoke.MethodHandleNatives.Constants.*;
44
45 /**
46 * This class consists exclusively of static methods that operate on or return
47 * method handles. They fall into several categories:
48 * <ul>
49 * <li>Lookup methods which help create method handles for methods and fields.
50 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
51 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
52 * <li>Wrapper methods which can convert between method handles and interface types.
53 * </ul>
54 * <p>
55 * @author John Rose, JSR 292 EG
56 */
57 public class MethodHandles {
58
59 private MethodHandles() { } // do not instantiate
60
61 private static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
62 static { MethodHandleImpl.initStatics(); }
63 // See IMPL_LOOKUP below.
64
65 //// Method handle creation from ordinary methods.
66
67 /**
68 * Returns a {@link Lookup lookup object} on the caller,
69 * which has the capability to access any method handle that the caller has access to,
70 * including direct method handles to private fields and methods.
71 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
72 * Do not store it in place where untrusted code can access it.
73 * @return a lookup object for the caller of this method
74 */
75 @CallerSensitive
76 public static Lookup lookup() {
77 return new Lookup(Reflection.getCallerClass());
78 }
79
80 /**
81 * Returns a {@link Lookup lookup object} which is trusted minimally.
82 * It can only be used to create method handles to
83 * publicly accessible fields and methods.
84 * <p>
85 * As a matter of pure convention, the {@linkplain Lookup#lookupClass lookup class}
86 * of this lookup object will be {@link java.lang.Object}.
87 * <p>
88 * The lookup class can be changed to any other class {@code C} using an expression of the form
89 * {@linkplain Lookup#in <code>publicLookup().in(C.class)</code>}.
90 * Since all classes have equal access to public names,
91 * such a change would confer no new access rights.
92 * @return a lookup object which is trusted minimally
93 */
94 public static Lookup publicLookup() {
95 return Lookup.PUBLIC_LOOKUP;
96 }
97
98 /**
99 * A <em>lookup object</em> is a factory for creating method handles,
100 * when the creation requires access checking.
101 * Method handles do not perform
102 * access checks when they are called, but rather when they are created.
103 * Therefore, method handle access
104 * restrictions must be enforced when a method handle is created.
105 * The caller class against which those restrictions are enforced
106 * is known as the {@linkplain #lookupClass lookup class}.
107 * <p>
108 * A lookup class which needs to create method handles will call
109 * {@link MethodHandles#lookup MethodHandles.lookup} to create a factory for itself.
110 * When the {@code Lookup} factory object is created, the identity of the lookup class is
111 * determined, and securely stored in the {@code Lookup} object.
112 * The lookup class (or its delegates) may then use factory methods
113 * on the {@code Lookup} object to create method handles for access-checked members.
114 * This includes all methods, constructors, and fields which are allowed to the lookup class,
115 * even private ones.
116 *
117 * <h1><a name="lookups"></a>Lookup Factory Methods</h1>
118 * The factory methods on a {@code Lookup} object correspond to all major
119 * use cases for methods, constructors, and fields.
120 * Here is a summary of the correspondence between these factory methods and
121 * the behavior the resulting method handles:
122 * <table border=1 cellpadding=5 summary="lookup method behaviors">
123 * <tr><th>lookup expression</th><th>member</th><th>behavior</th></tr>
124 * <tr>
125 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</td>
126 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
127 * </tr>
128 * <tr>
129 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</td>
130 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (T) C.f;}</td>
131 * </tr>
132 * <tr>
133 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</td>
134 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
135 * </tr>
136 * <tr>
137 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</td>
138 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
139 * </tr>
140 * <tr>
141 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</td>
142 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
143 * </tr>
144 * <tr>
145 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</td>
146 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
147 * </tr>
148 * <tr>
149 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</td>
150 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
151 * </tr>
152 * <tr>
153 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</td>
154 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
155 * </tr>
156 * <tr>
157 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</td>
158 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
159 * </tr>
160 * <tr>
161 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</td>
162 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
163 * </tr>
164 * <tr>
165 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
166 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
167 * </tr>
168 * <tr>
169 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</td>
170 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
171 * </tr>
172 * <tr>
173 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
174 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
175 * </tr>
176 * </table>
177 *
178 * Here, the type {@code C} is the class or interface being searched for a member,
179 * documented as a parameter named {@code refc} in the lookup methods.
180 * The method type {@code MT} is composed from the return type {@code T}
181 * and the sequence of argument types {@code A*}.
182 * The constructor also has a sequence of argument types {@code A*} and
183 * is deemed to return the newly-created object of type {@code C}.
184 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
185 * The formal parameter {@code this} stands for the self-reference of type {@code C};
186 * if it is present, it is always the leading argument to the method handle invocation.
187 * (In the case of some {@code protected} members, {@code this} may be
188 * restricted in type to the lookup class; see below.)
189 * The name {@code arg} stands for all the other method handle arguments.
190 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
191 * stands for a null reference if the accessed method or field is static,
192 * and {@code this} otherwise.
193 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
194 * for reflective objects corresponding to the given members.
195 * <p>
196 * In cases where the given member is of variable arity (i.e., a method or constructor)
197 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
198 * In all other cases, the returned method handle will be of fixed arity.
199 * <p>
200 * The equivalence between looked-up method handles and underlying
201 * class members can break down in a few ways:
202 * <ul>
203 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
204 * the lookup can still succeed, even when there is no equivalent
205 * Java expression or bytecoded constant.
206 * <li>Likewise, if {@code T} or {@code MT}
207 * is not symbolically accessible from the lookup class's loader,
208 * the lookup can still succeed.
209 * For example, lookups for {@code MethodHandle.invokeExact} and
210 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
211 * <li>If there is a security manager installed, it can forbid the lookup
212 * on various grounds (<a href="#secmgr">see below</a>).
213 * By contrast, the {@code ldc} instruction is not subject to
214 * security manager checks.
215 * </ul>
216 *
217 * <h1><a name="access"></a>Access checking</h1>
218 * Access checks are applied in the factory methods of {@code Lookup},
219 * when a method handle is created.
220 * This is a key difference from the Core Reflection API, since
221 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
222 * performs access checking against every caller, on every call.
223 * <p>
224 * All access checks start from a {@code Lookup} object, which
225 * compares its recorded lookup class against all requests to
226 * create method handles.
227 * A single {@code Lookup} object can be used to create any number
228 * of access-checked method handles, all checked against a single
229 * lookup class.
230 * <p>
231 * A {@code Lookup} object can be shared with other trusted code,
232 * such as a metaobject protocol.
233 * A shared {@code Lookup} object delegates the capability
234 * to create method handles on private members of the lookup class.
235 * Even if privileged code uses the {@code Lookup} object,
236 * the access checking is confined to the privileges of the
237 * original lookup class.
238 * <p>
239 * A lookup can fail, because
240 * the containing class is not accessible to the lookup class, or
241 * because the desired class member is missing, or because the
242 * desired class member is not accessible to the lookup class.
243 * In any of these cases, a {@code ReflectiveOperationException} will be
244 * thrown from the attempted lookup. The exact class will be one of
245 * the following:
246 * <ul>
247 * <li>NoSuchMethodException — if a method is requested but does not exist
248 * <li>NoSuchFieldException — if a field is requested but does not exist
249 * <li>IllegalAccessException — if the member exists but an access check fails
250 * </ul>
251 * <p>
252 * In general, the conditions under which a method handle may be
253 * looked up for a method {@code M} are exactly equivalent to the conditions
254 * under which the lookup class could have compiled and resolved a call to {@code M}.
255 * And the effect of invoking the method handle resulting from the lookup
256 * is exactly equivalent to executing the compiled and resolved call to {@code M}.
257 * The same point is true of fields and constructors.
258 * <p>
259 * If the desired member is {@code protected}, the usual JVM rules apply,
260 * including the requirement that the lookup class must be either be in the
261 * same package as the desired member, or must inherit that member.
262 * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.)
263 * In addition, if the desired member is a non-static field or method
264 * in a different package, the resulting method handle may only be applied
265 * to objects of the lookup class or one of its subclasses.
266 * This requirement is enforced by narrowing the type of the leading
267 * {@code this} parameter from {@code C}
268 * (which will necessarily be a superclass of the lookup class)
269 * to the lookup class itself.
270 * <p>
271 * In some cases, access between nested classes is obtained by the Java compiler by creating
272 * an wrapper method to access a private method of another class
273 * in the same top-level declaration.
274 * For example, a nested class {@code C.D}
275 * can access private members within other related classes such as
276 * {@code C}, {@code C.D.E}, or {@code C.B},
277 * but the Java compiler may need to generate wrapper methods in
278 * those related classes. In such cases, a {@code Lookup} object on
279 * {@code C.E} would be unable to those private members.
280 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
281 * which can transform a lookup on {@code C.E} into one on any of those other
282 * classes, without special elevation of privilege.
283 * <p>
284 * Although bytecode instructions can only refer to classes in
285 * a related class loader, this API can search for methods in any
286 * class, as long as a reference to its {@code Class} object is
287 * available. Such cross-loader references are also possible with the
288 * Core Reflection API, and are impossible to bytecode instructions
289 * such as {@code invokestatic} or {@code getfield}.
290 * There is a {@linkplain java.lang.SecurityManager security manager API}
291 * to allow applications to check such cross-loader references.
292 * These checks apply to both the {@code MethodHandles.Lookup} API
293 * and the Core Reflection API
294 * (as found on {@link java.lang.Class Class}).
295 * <p>
296 * Access checks only apply to named and reflected methods,
297 * constructors, and fields.
298 * Other method handle creation methods, such as
299 * {@link MethodHandle#asType MethodHandle.asType},
300 * do not require any access checks, and are done
301 * with static methods of {@link MethodHandles},
302 * independently of any {@code Lookup} object.
303 *
304 * <h1>Security manager interactions</h1>
305 * <a name="secmgr"></a>
306 * If a security manager is present, member lookups are subject to
307 * additional checks.
308 * From one to four calls are made to the security manager.
309 * Any of these calls can refuse access by throwing a
310 * {@link java.lang.SecurityException SecurityException}.
311 * Define {@code smgr} as the security manager,
312 * {@code refc} as the containing class in which the member
313 * is being sought, and {@code defc} as the class in which the
314 * member is actually defined.
315 * The calls are made according to the following rules:
316 * <ul>
317 * <li>In all cases, {@link SecurityManager#checkMemberAccess
318 * smgr.checkMemberAccess(refc, Member.PUBLIC)} is called.
319 * <li>If the class loader of the lookup class is not
320 * the same as or an ancestor of the class loader of {@code refc},
321 * then {@link SecurityManager#checkPackageAccess
322 * smgr.checkPackageAccess(refcPkg)} is called,
323 * where {@code refcPkg} is the package of {@code refc}.
324 * <li>If the retrieved member is not public,
325 * {@link SecurityManager#checkMemberAccess
326 * smgr.checkMemberAccess(defc, Member.DECLARED)} is called.
327 * (Note that {@code defc} might be the same as {@code refc}.)
328 * The default implementation of this security manager method
329 * inspects the stack to determine the original caller of
330 * the reflective request (such as {@code findStatic}),
331 * and performs additional permission checks if the
332 * class loader of {@code defc} differs from the class
333 * loader of the class from which the reflective request came.
334 * <li>If the retrieved member is not public,
335 * and if {@code defc} and {@code refc} are in different class loaders,
336 * and if the class loader of the lookup class is not
337 * the same as or an ancestor of the class loader of {@code defc},
338 * then {@link SecurityManager#checkPackageAccess
339 * smgr.checkPackageAccess(defcPkg)} is called,
340 * where {@code defcPkg} is the package of {@code defc}.
341 * </ul>
342 */
343 // 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
344 public static final
345 class Lookup {
346 /** The class on behalf of whom the lookup is being performed. */
347 private final Class<?> lookupClass;
348
349 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
350 private final int allowedModes;
351
352 /** A single-bit mask representing {@code public} access,
353 * which may contribute to the result of {@link #lookupModes lookupModes}.
354 * The value, {@code 0x01}, happens to be the same as the value of the
355 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
356 */
357 public static final int PUBLIC = Modifier.PUBLIC;
358
359 /** A single-bit mask representing {@code private} access,
360 * which may contribute to the result of {@link #lookupModes lookupModes}.
361 * The value, {@code 0x02}, happens to be the same as the value of the
362 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
363 */
364 public static final int PRIVATE = Modifier.PRIVATE;
365
366 /** A single-bit mask representing {@code protected} access,
367 * which may contribute to the result of {@link #lookupModes lookupModes}.
368 * The value, {@code 0x04}, happens to be the same as the value of the
369 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
370 */
371 public static final int PROTECTED = Modifier.PROTECTED;
372
373 /** A single-bit mask representing {@code package} access (default access),
374 * which may contribute to the result of {@link #lookupModes lookupModes}.
375 * The value is {@code 0x08}, which does not correspond meaningfully to
376 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
377 */
378 public static final int PACKAGE = Modifier.STATIC;
379
380 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE);
381 private static final int TRUSTED = -1;
382
383 private static int fixmods(int mods) {
384 mods &= (ALL_MODES - PACKAGE);
385 return (mods != 0) ? mods : PACKAGE;
386 }
387
388 /** Tells which class is performing the lookup. It is this class against
389 * which checks are performed for visibility and access permissions.
390 * <p>
391 * The class implies a maximum level of access permission,
392 * but the permissions may be additionally limited by the bitmask
393 * {@link #lookupModes lookupModes}, which controls whether non-public members
394 * can be accessed.
395 * @return the lookup class, on behalf of which this lookup object finds members
396 */
397 public Class<?> lookupClass() {
398 return lookupClass;
399 }
400
401 // This is just for calling out to MethodHandleImpl.
402 private Class<?> lookupClassOrNull() {
403 return (allowedModes == TRUSTED) ? null : lookupClass;
404 }
405
406 /** Tells which access-protection classes of members this lookup object can produce.
407 * The result is a bit-mask of the bits
408 * {@linkplain #PUBLIC PUBLIC (0x01)},
409 * {@linkplain #PRIVATE PRIVATE (0x02)},
410 * {@linkplain #PROTECTED PROTECTED (0x04)},
411 * and {@linkplain #PACKAGE PACKAGE (0x08)}.
412 * <p>
413 * A freshly-created lookup object
414 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class}
415 * has all possible bits set, since the caller class can access all its own members.
416 * A lookup object on a new lookup class
417 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
418 * may have some mode bits set to zero.
419 * The purpose of this is to restrict access via the new lookup object,
420 * so that it can access only names which can be reached by the original
421 * lookup object, and also by the new lookup class.
422 * @return the lookup modes, which limit the kinds of access performed by this lookup object
423 */
424 public int lookupModes() {
425 return allowedModes & ALL_MODES;
426 }
427
428 /** Embody the current class (the lookupClass) as a lookup class
429 * for method handle creation.
430 * Must be called by from a method in this package,
431 * which in turn is called by a method not in this package.
432 */
433 Lookup(Class<?> lookupClass) {
434 this(lookupClass, ALL_MODES);
435 // make sure we haven't accidentally picked up a privileged class:
436 checkUnprivilegedlookupClass(lookupClass);
437 }
438
439 private Lookup(Class<?> lookupClass, int allowedModes) {
440 this.lookupClass = lookupClass;
441 this.allowedModes = allowedModes;
442 }
443
444 /**
445 * Creates a lookup on the specified new lookup class.
446 * The resulting object will report the specified
447 * class as its own {@link #lookupClass lookupClass}.
448 * <p>
449 * However, the resulting {@code Lookup} object is guaranteed
450 * to have no more access capabilities than the original.
451 * In particular, access capabilities can be lost as follows:<ul>
452 * <li>If the new lookup class differs from the old one,
453 * protected members will not be accessible by virtue of inheritance.
454 * (Protected members may continue to be accessible because of package sharing.)
455 * <li>If the new lookup class is in a different package
456 * than the old one, protected and default (package) members will not be accessible.
457 * <li>If the new lookup class is not within the same package member
458 * as the old one, private members will not be accessible.
459 * <li>If the new lookup class is not accessible to the old lookup class,
460 * then no members, not even public members, will be accessible.
461 * (In all other cases, public members will continue to be accessible.)
462 * </ul>
463 *
464 * @param requestedLookupClass the desired lookup class for the new lookup object
465 * @return a lookup object which reports the desired lookup class
466 * @throws NullPointerException if the argument is null
467 */
468 public Lookup in(Class<?> requestedLookupClass) {
469 requestedLookupClass.getClass(); // null check
470 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
471 return new Lookup(requestedLookupClass, ALL_MODES);
472 if (requestedLookupClass == this.lookupClass)
473 return this; // keep same capabilities
474 int newModes = (allowedModes & (ALL_MODES & ~PROTECTED));
475 if ((newModes & PACKAGE) != 0
476 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
477 newModes &= ~(PACKAGE|PRIVATE);
478 }
479 // Allow nestmate lookups to be created without special privilege:
480 if ((newModes & PRIVATE) != 0
481 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
482 newModes &= ~PRIVATE;
483 }
484 if ((newModes & PUBLIC) != 0
485 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, allowedModes)) {
486 // The requested class it not accessible from the lookup class.
487 // No permissions.
488 newModes = 0;
489 }
490 checkUnprivilegedlookupClass(requestedLookupClass);
491 return new Lookup(requestedLookupClass, newModes);
492 }
493
494 // Make sure outer class is initialized first.
495 static { IMPL_NAMES.getClass(); }
496
497 /** Version of lookup which is trusted minimally.
498 * It can only be used to create method handles to
499 * publicly accessible members.
500 */
501 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, PUBLIC);
502
503 /** Package-private version of lookup which is trusted. */
504 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, TRUSTED);
505
506 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) {
507 String name = lookupClass.getName();
508 if (name.startsWith("java.lang.invoke."))
509 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
510 }
511
512 /**
513 * Displays the name of the class from which lookups are to be made.
514 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
515 * If there are restrictions on the access permitted to this lookup,
516 * this is indicated by adding a suffix to the class name, consisting
517 * of a slash and a keyword. The keyword represents the strongest
518 * allowed access, and is chosen as follows:
519 * <ul>
520 * <li>If no access is allowed, the suffix is "/noaccess".
521 * <li>If only public access is allowed, the suffix is "/public".
522 * <li>If only public and package access are allowed, the suffix is "/package".
523 * <li>If only public, package, and private access are allowed, the suffix is "/private".
524 * </ul>
525 * If none of the above cases apply, it is the case that full
526 * access (public, package, private, and protected) is allowed.
527 * In this case, no suffix is added.
528 * This is true only of an object obtained originally from
529 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
530 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
531 * always have restricted access, and will display a suffix.
532 * <p>
533 * (It may seem strange that protected access should be
534 * stronger than private access. Viewed independently from
535 * package access, protected access is the first to be lost,
536 * because it requires a direct subclass relationship between
537 * caller and callee.)
538 * @see #in
539 */
540 @Override
541 public String toString() {
542 String cname = lookupClass.getName();
543 switch (allowedModes) {
544 case 0: // no privileges
545 return cname + "/noaccess";
546 case PUBLIC:
547 return cname + "/public";
548 case PUBLIC|PACKAGE:
549 return cname + "/package";
550 case ALL_MODES & ~PROTECTED:
551 return cname + "/private";
552 case ALL_MODES:
553 return cname;
554 case TRUSTED:
555 return "/trusted"; // internal only; not exported
556 default: // Should not happen, but it's a bitfield...
557 cname = cname + "/" + Integer.toHexString(allowedModes);
558 assert(false) : cname;
559 return cname;
560 }
561 }
562
563 /**
564 * Produces a method handle for a static method.
565 * The type of the method handle will be that of the method.
566 * (Since static methods do not take receivers, there is no
567 * additional receiver argument inserted into the method handle type,
568 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
569 * The method and all its argument types must be accessible to the lookup class.
570 * If the method's class has not yet been initialized, that is done
571 * immediately, before the method handle is returned.
572 * <p>
573 * The returned method handle will have
574 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
575 * the method's variable arity modifier bit ({@code 0x0080}) is set.
576 * @param refc the class from which the method is accessed
577 * @param name the name of the method
578 * @param type the type of the method
579 * @return the desired method handle
580 * @throws NoSuchMethodException if the method does not exist
581 * @throws IllegalAccessException if access checking fails,
582 * or if the method is not {@code static},
583 * or if the method's variable arity modifier bit
584 * is set and {@code asVarargsCollector} fails
585 * @exception SecurityException if a security manager is present and it
586 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
587 * @throws NullPointerException if any argument is null
588 */
589 public
590 MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
591 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
592 checkSecurityManager(refc, method);
593 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method));
594 }
595
596 /**
597 * Produces a method handle for a virtual method.
598 * The type of the method handle will be that of the method,
599 * with the receiver type (usually {@code refc}) prepended.
600 * The method and all its argument types must be accessible to the lookup class.
601 * <p>
602 * When called, the handle will treat the first argument as a receiver
603 * and dispatch on the receiver's type to determine which method
604 * implementation to enter.
605 * (The dispatching action is identical with that performed by an
606 * {@code invokevirtual} or {@code invokeinterface} instruction.)
607 * <p>
608 * The first argument will be of type {@code refc} if the lookup
609 * class has full privileges to access the member. Otherwise
610 * the member must be {@code protected} and the first argument
611 * will be restricted in type to the lookup class.
612 * <p>
613 * The returned method handle will have
614 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
615 * the method's variable arity modifier bit ({@code 0x0080}) is set.
616 * <p>
617 * Because of the general equivalence between {@code invokevirtual}
618 * instructions and method handles produced by {@code findVirtual},
619 * if the class is {@code MethodHandle} and the name string is
620 * {@code invokeExact} or {@code invoke}, the resulting
621 * method handle is equivalent to one produced by
622 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
623 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
624 * with the same {@code type} argument.
625 *
626 * @param refc the class or interface from which the method is accessed
627 * @param name the name of the method
628 * @param type the type of the method, with the receiver argument omitted
629 * @return the desired method handle
630 * @throws NoSuchMethodException if the method does not exist
631 * @throws IllegalAccessException if access checking fails,
632 * or if the method is {@code static}
633 * or if the method's variable arity modifier bit
634 * is set and {@code asVarargsCollector} fails
635 * @exception SecurityException if a security manager is present and it
636 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
637 * @throws NullPointerException if any argument is null
638 */
639 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
640 if (refc == MethodHandle.class) {
641 MethodHandle mh = findVirtualForMH(name, type);
642 if (mh != null) return mh;
643 }
644 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
645 MemberName method = resolveOrFail(refKind, refc, name, type);
646 checkSecurityManager(refc, method);
647 return getDirectMethod(refKind, refc, method, findBoundCallerClass(method));
648 }
649 private MethodHandle findVirtualForMH(String name, MethodType type) {
650 // these names require special lookups because of the implicit MethodType argument
651 if ("invoke".equals(name))
652 return invoker(type);
653 if ("invokeExact".equals(name))
654 return exactInvoker(type);
655 return null;
656 }
657
658 /**
659 * Produces a method handle which creates an object and initializes it, using
660 * the constructor of the specified type.
661 * The parameter types of the method handle will be those of the constructor,
662 * while the return type will be a reference to the constructor's class.
663 * The constructor and all its argument types must be accessible to the lookup class.
664 * If the constructor's class has not yet been initialized, that is done
665 * immediately, before the method handle is returned.
666 * <p>
667 * Note: The requested type must have a return type of {@code void}.
668 * This is consistent with the JVM's treatment of constructor type descriptors.
669 * <p>
670 * The returned method handle will have
671 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
672 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
673 * @param refc the class or interface from which the method is accessed
674 * @param type the type of the method, with the receiver argument omitted, and a void return type
675 * @return the desired method handle
676 * @throws NoSuchMethodException if the constructor does not exist
677 * @throws IllegalAccessException if access checking fails
678 * or if the method's variable arity modifier bit
679 * is set and {@code asVarargsCollector} fails
680 * @exception SecurityException if a security manager is present and it
681 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
682 * @throws NullPointerException if any argument is null
683 */
684 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
685 String name = "<init>";
686 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
687 checkSecurityManager(refc, ctor);
688 return getDirectConstructor(refc, ctor);
689 }
690
691 /**
692 * Produces an early-bound method handle for a virtual method,
693 * as if called from an {@code invokespecial}
694 * instruction from {@code caller}.
695 * The type of the method handle will be that of the method,
696 * with a suitably restricted receiver type (such as {@code caller}) prepended.
697 * The method and all its argument types must be accessible
698 * to the caller.
699 * <p>
700 * When called, the handle will treat the first argument as a receiver,
701 * but will not dispatch on the receiver's type.
702 * (This direct invocation action is identical with that performed by an
703 * {@code invokespecial} instruction.)
704 * <p>
705 * If the explicitly specified caller class is not identical with the
706 * lookup class, or if this lookup object does not have private access
707 * privileges, the access fails.
708 * <p>
709 * The returned method handle will have
710 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
711 * the method's variable arity modifier bit ({@code 0x0080}) is set.
712 * @param refc the class or interface from which the method is accessed
713 * @param name the name of the method (which must not be "<init>")
714 * @param type the type of the method, with the receiver argument omitted
715 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
716 * @return the desired method handle
717 * @throws NoSuchMethodException if the method does not exist
718 * @throws IllegalAccessException if access checking fails
719 * or if the method's variable arity modifier bit
720 * is set and {@code asVarargsCollector} fails
721 * @exception SecurityException if a security manager is present and it
722 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
723 * @throws NullPointerException if any argument is null
724 */
725 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
726 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
727 checkSpecialCaller(specialCaller);
728 Lookup specialLookup = this.in(specialCaller);
729 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
730 checkSecurityManager(refc, method);
731 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
732 }
733
734 /**
735 * Produces a method handle giving read access to a non-static field.
736 * The type of the method handle will have a return type of the field's
737 * value type.
738 * The method handle's single argument will be the instance containing
739 * the field.
740 * Access checking is performed immediately on behalf of the lookup class.
741 * @param refc the class or interface from which the method is accessed
742 * @param name the field's name
743 * @param type the field's type
744 * @return a method handle which can load values from the field
745 * @throws NoSuchFieldException if the field does not exist
746 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
747 * @exception SecurityException if a security manager is present and it
748 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
749 * @throws NullPointerException if any argument is null
750 */
751 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
752 MemberName field = resolveOrFail(REF_getField, refc, name, type);
753 checkSecurityManager(refc, field);
754 return getDirectField(REF_getField, refc, field);
755 }
756
757 /**
758 * Produces a method handle giving write access to a non-static field.
759 * The type of the method handle will have a void return type.
760 * The method handle will take two arguments, the instance containing
761 * the field, and the value to be stored.
762 * The second argument will be of the field's value type.
763 * Access checking is performed immediately on behalf of the lookup class.
764 * @param refc the class or interface from which the method is accessed
765 * @param name the field's name
766 * @param type the field's type
767 * @return a method handle which can store values into the field
768 * @throws NoSuchFieldException if the field does not exist
769 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
770 * @exception SecurityException if a security manager is present and it
771 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
772 * @throws NullPointerException if any argument is null
773 */
774 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
775 MemberName field = resolveOrFail(REF_putField, refc, name, type);
776 checkSecurityManager(refc, field);
777 return getDirectField(REF_putField, refc, field);
778 }
779
780 /**
781 * Produces a method handle giving read access to a static field.
782 * The type of the method handle will have a return type of the field's
783 * value type.
784 * The method handle will take no arguments.
785 * Access checking is performed immediately on behalf of the lookup class.
786 * @param refc the class or interface from which the method is accessed
787 * @param name the field's name
788 * @param type the field's type
789 * @return a method handle which can load values from the field
790 * @throws NoSuchFieldException if the field does not exist
791 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
792 * @exception SecurityException if a security manager is present and it
793 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
794 * @throws NullPointerException if any argument is null
795 */
796 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
797 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
798 checkSecurityManager(refc, field);
799 return getDirectField(REF_getStatic, refc, field);
800 }
801
802 /**
803 * Produces a method handle giving write access to a static field.
804 * The type of the method handle will have a void return type.
805 * The method handle will take a single
806 * argument, of the field's value type, the value to be stored.
807 * Access checking is performed immediately on behalf of the lookup class.
808 * @param refc the class or interface from which the method is accessed
809 * @param name the field's name
810 * @param type the field's type
811 * @return a method handle which can store values into the field
812 * @throws NoSuchFieldException if the field does not exist
813 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
814 * @exception SecurityException if a security manager is present and it
815 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
816 * @throws NullPointerException if any argument is null
817 */
818 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
819 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
820 checkSecurityManager(refc, field);
821 return getDirectField(REF_putStatic, refc, field);
822 }
823
824 /**
825 * Produces an early-bound method handle for a non-static method.
826 * The receiver must have a supertype {@code defc} in which a method
827 * of the given name and type is accessible to the lookup class.
828 * The method and all its argument types must be accessible to the lookup class.
829 * The type of the method handle will be that of the method,
830 * without any insertion of an additional receiver parameter.
831 * The given receiver will be bound into the method handle,
832 * so that every call to the method handle will invoke the
833 * requested method on the given receiver.
834 * <p>
835 * The returned method handle will have
836 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
837 * the method's variable arity modifier bit ({@code 0x0080}) is set
838 * <em>and</em> the trailing array argument is not the only argument.
839 * (If the trailing array argument is the only argument,
840 * the given receiver value will be bound to it.)
841 * <p>
842 * This is equivalent to the following code:
843 * <blockquote><pre>
844 import static java.lang.invoke.MethodHandles.*;
845 import static java.lang.invoke.MethodType.*;
846 ...
847 MethodHandle mh0 = lookup().{@link #findVirtual findVirtual}(defc, name, type);
848 MethodHandle mh1 = mh0.{@link MethodHandle#bindTo bindTo}(receiver);
849 MethodType mt1 = mh1.type();
850 if (mh0.isVarargsCollector())
851 mh1 = mh1.asVarargsCollector(mt1.parameterType(mt1.parameterCount()-1));
852 return mh1;
853 * </pre></blockquote>
854 * where {@code defc} is either {@code receiver.getClass()} or a super
855 * type of that class, in which the requested method is accessible
856 * to the lookup class.
857 * (Note that {@code bindTo} does not preserve variable arity.)
858 * @param receiver the object from which the method is accessed
859 * @param name the name of the method
860 * @param type the type of the method, with the receiver argument omitted
861 * @return the desired method handle
862 * @throws NoSuchMethodException if the method does not exist
863 * @throws IllegalAccessException if access checking fails
864 * or if the method's variable arity modifier bit
865 * is set and {@code asVarargsCollector} fails
866 * @exception SecurityException if a security manager is present and it
867 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
868 * @throws NullPointerException if any argument is null
869 */
870 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
871 Class<? extends Object> refc = receiver.getClass(); // may get NPE
872 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
873 checkSecurityManager(refc, method);
874 MethodHandle mh = getDirectMethodNoRestrict(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
875 return mh.bindReceiver(receiver).setVarargs(method);
876 }
877
878 /**
879 * Makes a direct method handle to <i>m</i>, if the lookup class has permission.
880 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
881 * If <i>m</i> is virtual, overriding is respected on every call.
882 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
883 * The type of the method handle will be that of the method,
884 * with the receiver type prepended (but only if it is non-static).
885 * If the method's {@code accessible} flag is not set,
886 * access checking is performed immediately on behalf of the lookup class.
887 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
888 * <p>
889 * The returned method handle will have
890 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
891 * the method's variable arity modifier bit ({@code 0x0080}) is set.
892 * @param m the reflected method
893 * @return a method handle which can invoke the reflected method
894 * @throws IllegalAccessException if access checking fails
895 * or if the method's variable arity modifier bit
896 * is set and {@code asVarargsCollector} fails
897 * @throws NullPointerException if the argument is null
898 */
899 public MethodHandle unreflect(Method m) throws IllegalAccessException {
900 MemberName method = new MemberName(m);
901 byte refKind = method.getReferenceKind();
902 if (refKind == REF_invokeSpecial)
903 refKind = REF_invokeVirtual;
904 assert(method.isMethod());
905 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
906 return lookup.getDirectMethod(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method));
907 }
908
909 /**
910 * Produces a method handle for a reflected method.
911 * It will bypass checks for overriding methods on the receiver,
912 * as if by a {@code invokespecial} instruction from within the {@code specialCaller}.
913 * The type of the method handle will be that of the method,
914 * with the special caller type prepended (and <em>not</em> the receiver of the method).
915 * If the method's {@code accessible} flag is not set,
916 * access checking is performed immediately on behalf of the lookup class,
917 * as if {@code invokespecial} instruction were being linked.
918 * <p>
919 * The returned method handle will have
920 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
921 * the method's variable arity modifier bit ({@code 0x0080}) is set.
922 * @param m the reflected method
923 * @param specialCaller the class nominally calling the method
924 * @return a method handle which can invoke the reflected method
925 * @throws IllegalAccessException if access checking fails
926 * or if the method's variable arity modifier bit
927 * is set and {@code asVarargsCollector} fails
928 * @throws NullPointerException if any argument is null
929 */
930 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
931 checkSpecialCaller(specialCaller);
932 Lookup specialLookup = this.in(specialCaller);
933 MemberName method = new MemberName(m, true);
934 assert(method.isMethod());
935 // ignore m.isAccessible: this is a new kind of access
936 return specialLookup.getDirectMethod(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method));
937 }
938
939 /**
940 * Produces a method handle for a reflected constructor.
941 * The type of the method handle will be that of the constructor,
942 * with the return type changed to the declaring class.
943 * The method handle will perform a {@code newInstance} operation,
944 * creating a new instance of the constructor's class on the
945 * arguments passed to the method handle.
946 * <p>
947 * If the constructor's {@code accessible} flag is not set,
948 * access checking is performed immediately on behalf of the lookup class.
949 * <p>
950 * The returned method handle will have
951 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
952 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
953 * @param c the reflected constructor
954 * @return a method handle which can invoke the reflected constructor
955 * @throws IllegalAccessException if access checking fails
956 * or if the method's variable arity modifier bit
957 * is set and {@code asVarargsCollector} fails
958 * @throws NullPointerException if the argument is null
959 */
960 @SuppressWarnings("rawtypes") // Will be Constructor<?> after JSR 292 MR
961 public MethodHandle unreflectConstructor(Constructor c) throws IllegalAccessException {
962 MemberName ctor = new MemberName(c);
963 assert(ctor.isConstructor());
964 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
965 return lookup.getDirectConstructor(ctor.getDeclaringClass(), ctor);
966 }
967
968 /**
969 * Produces a method handle giving read access to a reflected field.
970 * The type of the method handle will have a return type of the field's
971 * value type.
972 * If the field is static, the method handle will take no arguments.
973 * Otherwise, its single argument will be the instance containing
974 * the field.
975 * If the field's {@code accessible} flag is not set,
976 * access checking is performed immediately on behalf of the lookup class.
977 * @param f the reflected field
978 * @return a method handle which can load values from the reflected field
979 * @throws IllegalAccessException if access checking fails
980 * @throws NullPointerException if the argument is null
981 */
982 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
983 return unreflectField(f, false);
984 }
985 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
986 MemberName field = new MemberName(f, isSetter);
987 assert(isSetter
988 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
989 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
990 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
991 return lookup.getDirectField(field.getReferenceKind(), f.getDeclaringClass(), field);
992 }
993
994 /**
995 * Produces a method handle giving write access to a reflected field.
996 * The type of the method handle will have a void return type.
997 * If the field is static, the method handle will take a single
998 * argument, of the field's value type, the value to be stored.
999 * Otherwise, the two arguments will be the instance containing
1000 * the field, and the value to be stored.
1001 * If the field's {@code accessible} flag is not set,
1002 * access checking is performed immediately on behalf of the lookup class.
1003 * @param f the reflected field
1004 * @return a method handle which can store values into the reflected field
1005 * @throws IllegalAccessException if access checking fails
1006 * @throws NullPointerException if the argument is null
1007 */
1008 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
1009 return unreflectField(f, true);
1010 }
1011
1012 /// Helper methods, all package-private.
1013
1014 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1015 checkSymbolicClass(refc); // do this before attempting to resolve
1016 name.getClass(); type.getClass(); // NPE
1017 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
1018 NoSuchFieldException.class);
1019 }
1020
1021 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1022 checkSymbolicClass(refc); // do this before attempting to resolve
1023 name.getClass(); type.getClass(); // NPE
1024 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
1025 NoSuchMethodException.class);
1026 }
1027
1028 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
1029 Class<?> caller = lookupClassOrNull();
1030 if (caller != null && !VerifyAccess.isClassAccessible(refc, caller, allowedModes))
1031 throw new MemberName(refc).makeAccessException("symbolic reference class is not public", this);
1032 }
1033
1034 /**
1035 * Find my trustable caller class if m is a caller sensitive method.
1036 * If this lookup object has private access, then the caller class is the lookupClass.
1037 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
1038 */
1039 Class<?> findBoundCallerClass(MemberName m) throws IllegalAccessException {
1040 Class<?> callerClass = null;
1041 if (MethodHandleNatives.isCallerSensitive(m)) {
1042 // Only full-power lookup is allowed to resolve caller-sensitive methods
1043 if (isFullPowerLookup()) {
1044 callerClass = lookupClass;
1045 } else {
1046 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
1047 }
1048 }
1049 return callerClass;
1050 }
1051
1052 private boolean isFullPowerLookup() {
1053 return (allowedModes & PRIVATE) != 0;
1054 }
1055
1056 /**
1057 * Determine whether a security manager has an overridden
1058 * SecurityManager.checkMemberAccess method.
1059 */
1060 private boolean isCheckMemberAccessOverridden(SecurityManager sm) {
1061 final Class<? extends SecurityManager> cls = sm.getClass();
1062 if (cls == SecurityManager.class) return false;
1063
1064 try {
1065 return cls.getMethod("checkMemberAccess", Class.class, int.class).
1066 getDeclaringClass() != SecurityManager.class;
1067 } catch (NoSuchMethodException e) {
1068 throw new InternalError("should not reach here");
1069 }
1070 }
1071
1072 /**
1073 * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
1074 * Determines a trustable caller class to compare with refc, the symbolic reference class.
1075 * If this lookup object has private access, then the caller class is the lookupClass.
1076 */
1077 void checkSecurityManager(Class<?> refc, MemberName m) {
1078 SecurityManager smgr = System.getSecurityManager();
1079 if (smgr == null) return;
1080 if (allowedModes == TRUSTED) return;
1081
1082 final boolean overridden = isCheckMemberAccessOverridden(smgr);
1083 // Step 1:
1084 {
1085 // Default policy is to allow Member.PUBLIC; no need to check
1086 // permission if SecurityManager is the default implementation
1087 final int which = Member.PUBLIC;
1088 final Class<?> clazz = refc;
1089 if (overridden) {
1090 // Don't refactor; otherwise break the stack depth for
1091 // checkMemberAccess of subclasses of SecurityManager as specified.
1092 smgr.checkMemberAccess(clazz, which);
1093 }
1094 }
1095
1096 // Step 2:
1097 if (!isFullPowerLookup() ||
1098 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
1099 ReflectUtil.checkPackageAccess(refc);
1100 }
1101
1102 // Step 3:
1103 if (m.isPublic()) return;
1104 Class<?> defc = m.getDeclaringClass();
1105 {
1106 // Inline SecurityManager.checkMemberAccess
1107 final int which = Member.DECLARED;
1108 final Class<?> clazz = defc;
1109 if (!overridden) {
1110 if (!isFullPowerLookup()) {
1111 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
1112 }
1113 } else {
1114 // Don't refactor; otherwise break the stack depth for
1115 // checkMemberAccess of subclasses of SecurityManager as specified.
1116 smgr.checkMemberAccess(clazz, which);
1117 }
1118 }
1119
1120 // Step 4:
1121 if (defc != refc) {
1122 ReflectUtil.checkPackageAccess(defc);
1123 }
1124 }
1125
1126 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1127 boolean wantStatic = (refKind == REF_invokeStatic);
1128 String message;
1129 if (m.isConstructor())
1130 message = "expected a method, not a constructor";
1131 else if (!m.isMethod())
1132 message = "expected a method";
1133 else if (wantStatic != m.isStatic())
1134 message = wantStatic ? "expected a static method" : "expected a non-static method";
1135 else
1136 { checkAccess(refKind, refc, m); return; }
1137 throw m.makeAccessException(message, this);
1138 }
1139
1140 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1141 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
1142 String message;
1143 if (wantStatic != m.isStatic())
1144 message = wantStatic ? "expected a static field" : "expected a non-static field";
1145 else
1146 { checkAccess(refKind, refc, m); return; }
1147 throw m.makeAccessException(message, this);
1148 }
1149
1150 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1151 assert(m.referenceKindIsConsistentWith(refKind) &&
1152 MethodHandleNatives.refKindIsValid(refKind) &&
1153 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
1154 int allowedModes = this.allowedModes;
1155 if (allowedModes == TRUSTED) return;
1156 int mods = m.getModifiers();
1157 if (Modifier.isFinal(mods) &&
1158 MethodHandleNatives.refKindIsSetter(refKind))
1159 throw m.makeAccessException("unexpected set of a final field", this);
1160 if (Modifier.isPublic(mods) && Modifier.isPublic(refc.getModifiers()) && allowedModes != 0)
1161 return; // common case
1162 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
1163 if ((requestedModes & allowedModes) != 0) {
1164 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
1165 mods, lookupClass(), allowedModes))
1166 return;
1167 } else {
1168 // Protected members can also be checked as if they were package-private.
1169 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
1170 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
1171 return;
1172 }
1173 throw m.makeAccessException(accessFailedMessage(refc, m), this);
1174 }
1175
1176 String accessFailedMessage(Class<?> refc, MemberName m) {
1177 Class<?> defc = m.getDeclaringClass();
1178 int mods = m.getModifiers();
1179 // check the class first:
1180 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
1181 (defc == refc ||
1182 Modifier.isPublic(refc.getModifiers())));
1183 if (!classOK && (allowedModes & PACKAGE) != 0) {
1184 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), ALL_MODES) &&
1185 (defc == refc ||
1186 VerifyAccess.isClassAccessible(refc, lookupClass(), ALL_MODES)));
1187 }
1188 if (!classOK)
1189 return "class is not public";
1190 if (Modifier.isPublic(mods))
1191 return "access to public member failed"; // (how?)
1192 if (Modifier.isPrivate(mods))
1193 return "member is private";
1194 if (Modifier.isProtected(mods))
1195 return "member is protected";
1196 return "member is private to package";
1197 }
1198
1199 private static final boolean ALLOW_NESTMATE_ACCESS = false;
1200
1201 private void checkSpecialCaller(Class<?> specialCaller) throws IllegalAccessException {
1202 int allowedModes = this.allowedModes;
1203 if (allowedModes == TRUSTED) return;
1204 if ((allowedModes & PRIVATE) == 0
1205 || (specialCaller != lookupClass()
1206 && !(ALLOW_NESTMATE_ACCESS &&
1207 VerifyAccess.isSamePackageMember(specialCaller, lookupClass()))))
1208 throw new MemberName(specialCaller).
1209 makeAccessException("no private access for invokespecial", this);
1210 }
1211
1212 private boolean restrictProtectedReceiver(MemberName method) {
1213 // The accessing class only has the right to use a protected member
1214 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
1215 if (!method.isProtected() || method.isStatic()
1216 || allowedModes == TRUSTED
1217 || method.getDeclaringClass() == lookupClass()
1218 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass())
1219 || (ALLOW_NESTMATE_ACCESS &&
1220 VerifyAccess.isSamePackageMember(method.getDeclaringClass(), lookupClass())))
1221 return false;
1222 return true;
1223 }
1224 private MethodHandle restrictReceiver(MemberName method, MethodHandle mh, Class<?> caller) throws IllegalAccessException {
1225 assert(!method.isStatic());
1226 // receiver type of mh is too wide; narrow to caller
1227 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
1228 throw method.makeAccessException("caller class must be a subclass below the method", caller);
1229 }
1230 MethodType rawType = mh.type();
1231 if (rawType.parameterType(0) == caller) return mh;
1232 MethodType narrowType = rawType.changeParameterType(0, caller);
1233 return mh.viewAsType(narrowType);
1234 }
1235
1236 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
1237 return getDirectMethodCommon(refKind, refc, method,
1238 (refKind == REF_invokeSpecial ||
1239 (MethodHandleNatives.refKindHasReceiver(refKind) &&
1240 restrictProtectedReceiver(method))), callerClass);
1241 }
1242 private MethodHandle getDirectMethodNoRestrict(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
1243 return getDirectMethodCommon(refKind, refc, method, false, callerClass);
1244 }
1245 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
1246 boolean doRestrict, Class<?> callerClass) throws IllegalAccessException {
1247 checkMethod(refKind, refc, method);
1248 if (method.isMethodHandleInvoke())
1249 return fakeMethodHandleInvoke(method);
1250
1251 Class<?> refcAsSuper;
1252 if (refKind == REF_invokeSpecial &&
1253 refc != lookupClass() &&
1254 refc != (refcAsSuper = lookupClass().getSuperclass()) &&
1255 refc.isAssignableFrom(lookupClass())) {
1256 assert(!method.getName().equals("<init>")); // not this code path
1257 // Per JVMS 6.5, desc. of invokespecial instruction:
1258 // If the method is in a superclass of the LC,
1259 // and if our original search was above LC.super,
1260 // repeat the search (symbolic lookup) from LC.super.
1261 // FIXME: MemberName.resolve should handle this instead.
1262 MemberName m2 = new MemberName(refcAsSuper,
1263 method.getName(),
1264 method.getMethodType(),
1265 REF_invokeSpecial);
1266 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull());
1267 if (m2 == null) throw new InternalError(method.toString());
1268 method = m2;
1269 refc = refcAsSuper;
1270 // redo basic checks
1271 checkMethod(refKind, refc, method);
1272 }
1273
1274 MethodHandle mh = DirectMethodHandle.make(refKind, refc, method);
1275 mh = maybeBindCaller(method, mh, callerClass);
1276 mh = mh.setVarargs(method);
1277 if (doRestrict)
1278 mh = restrictReceiver(method, mh, lookupClass());
1279 return mh;
1280 }
1281 private MethodHandle fakeMethodHandleInvoke(MemberName method) {
1282 return throwException(method.getReturnType(), UnsupportedOperationException.class);
1283 }
1284 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh,
1285 Class<?> callerClass)
1286 throws IllegalAccessException {
1287 if (allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
1288 return mh;
1289 Class<?> hostClass = lookupClass;
1290 if ((allowedModes & PRIVATE) == 0) // caller must use full-power lookup
1291 hostClass = callerClass; // callerClass came from a security manager style stack walk
1292 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, hostClass);
1293 // Note: caller will apply varargs after this step happens.
1294 return cbmh;
1295 }
1296 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
1297 checkField(refKind, refc, field);
1298 MethodHandle mh = DirectMethodHandle.make(refc, field);
1299 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
1300 restrictProtectedReceiver(field));
1301 if (doRestrict)
1302 mh = restrictReceiver(field, mh, lookupClass());
1303 return mh;
1304 }
1305 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
1306 assert(ctor.isConstructor());
1307 checkAccess(REF_newInvokeSpecial, refc, ctor);
1308 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
1309 return DirectMethodHandle.make(ctor).setVarargs(ctor);
1310 }
1311
1312 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
1313 */
1314 /*non-public*/
1315 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type) throws ReflectiveOperationException {
1316 MemberName resolved = null;
1317 if (type instanceof MemberName) {
1318 resolved = (MemberName) type;
1319 if (!resolved.isResolved()) throw new InternalError("unresolved MemberName");
1320 assert(name == null || name.equals(resolved.getName()));
1321 }
1322 if (MethodHandleNatives.refKindIsField(refKind)) {
1323 MemberName field = (resolved != null) ? resolved
1324 : resolveOrFail(refKind, defc, name, (Class<?>) type);
1325 return getDirectField(refKind, defc, field);
1326 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
1327 MemberName method = (resolved != null) ? resolved
1328 : resolveOrFail(refKind, defc, name, (MethodType) type);
1329 return getDirectMethod(refKind, defc, method, lookupClass);
1330 } else if (refKind == REF_newInvokeSpecial) {
1331 assert(name == null || name.equals("<init>"));
1332 MemberName ctor = (resolved != null) ? resolved
1333 : resolveOrFail(REF_newInvokeSpecial, defc, name, (MethodType) type);
1334 return getDirectConstructor(defc, ctor);
1335 }
1336 // oops
1337 throw new ReflectiveOperationException("bad MethodHandle constant #"+refKind+" "+name+" : "+type);
1338 }
1339 }
1340
1341 /**
1342 * Produces a method handle giving read access to elements of an array.
1343 * The type of the method handle will have a return type of the array's
1344 * element type. Its first argument will be the array type,
1345 * and the second will be {@code int}.
1346 * @param arrayClass an array type
1347 * @return a method handle which can load values from the given array type
1348 * @throws NullPointerException if the argument is null
1349 * @throws IllegalArgumentException if arrayClass is not an array type
1350 */
1351 public static
1352 MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
1353 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, false);
1354 }
1355
1356 /**
1357 * Produces a method handle giving write access to elements of an array.
1358 * The type of the method handle will have a void return type.
1359 * Its last argument will be the array's element type.
1360 * The first and second arguments will be the array type and int.
1361 * @param arrayClass the class of an array
1362 * @return a method handle which can store values into the array type
1363 * @throws NullPointerException if the argument is null
1364 * @throws IllegalArgumentException if arrayClass is not an array type
1365 */
1366 public static
1367 MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
1368 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, true);
1369 }
1370
1371 /// method handle invocation (reflective style)
1372
1373 /**
1374 * Produces a method handle which will invoke any method handle of the
1375 * given {@code type}, with a given number of trailing arguments replaced by
1376 * a single trailing {@code Object[]} array.
1377 * The resulting invoker will be a method handle with the following
1378 * arguments:
1379 * <ul>
1380 * <li>a single {@code MethodHandle} target
1381 * <li>zero or more leading values (counted by {@code leadingArgCount})
1382 * <li>an {@code Object[]} array containing trailing arguments
1383 * </ul>
1384 * <p>
1385 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
1386 * the indicated {@code type}.
1387 * That is, if the target is exactly of the given {@code type}, it will behave
1388 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
1389 * is used to convert the target to the required {@code type}.
1390 * <p>
1391 * The type of the returned invoker will not be the given {@code type}, but rather
1392 * will have all parameters except the first {@code leadingArgCount}
1393 * replaced by a single array of type {@code Object[]}, which will be
1394 * the final parameter.
1395 * <p>
1396 * Before invoking its target, the invoker will spread the final array, apply
1397 * reference casts as necessary, and unbox and widen primitive arguments.
1398 * <p>
1399 * This method is equivalent to the following code (though it may be more efficient):
1400 * <p><blockquote><pre>
1401 MethodHandle invoker = MethodHandles.invoker(type);
1402 int spreadArgCount = type.parameterCount() - leadingArgCount;
1403 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
1404 return invoker;
1405 * </pre></blockquote>
1406 * <p>
1407 * This method throws no reflective or security exceptions.
1408 * @param type the desired target type
1409 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
1410 * @return a method handle suitable for invoking any method handle of the given type
1411 * @throws NullPointerException if {@code type} is null
1412 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
1413 * the range from 0 to {@code type.parameterCount()} inclusive
1414 */
1415 static public
1416 MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
1417 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
1418 throw new IllegalArgumentException("bad argument count "+leadingArgCount);
1419 return type.invokers().spreadInvoker(leadingArgCount);
1420 }
1421
1422 /**
1423 * Produces a special <em>invoker method handle</em> which can be used to
1424 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
1425 * The resulting invoker will have a type which is
1426 * exactly equal to the desired type, except that it will accept
1427 * an additional leading argument of type {@code MethodHandle}.
1428 * <p>
1429 * This method is equivalent to the following code (though it may be more efficient):
1430 * <p><blockquote><pre>
1431 publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)
1432 * </pre></blockquote>
1433 *
1434 * <p style="font-size:smaller;">
1435 * <em>Discussion:</em>
1436 * Invoker method handles can be useful when working with variable method handles
1437 * of unknown types.
1438 * For example, to emulate an {@code invokeExact} call to a variable method
1439 * handle {@code M}, extract its type {@code T},
1440 * look up the invoker method {@code X} for {@code T},
1441 * and call the invoker method, as {@code X.invoke(T, A...)}.
1442 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
1443 * is unknown.)
1444 * If spreading, collecting, or other argument transformations are required,
1445 * they can be applied once to the invoker {@code X} and reused on many {@code M}
1446 * method handle values, as long as they are compatible with the type of {@code X}.
1447 * <p>
1448 * <em>(Note: The invoker method is not available via the Core Reflection API.
1449 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
1450 * on the declared {@code invokeExact} or {@code invoke} method will raise an
1451 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
1452 * <p>
1453 * This method throws no reflective or security exceptions.
1454 * @param type the desired target type
1455 * @return a method handle suitable for invoking any method handle of the given type
1456 */
1457 static public
1458 MethodHandle exactInvoker(MethodType type) {
1459 return type.invokers().exactInvoker();
1460 }
1461
1462 /**
1463 * Produces a special <em>invoker method handle</em> which can be used to
1464 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
1465 * The resulting invoker will have a type which is
1466 * exactly equal to the desired type, except that it will accept
1467 * an additional leading argument of type {@code MethodHandle}.
1468 * <p>
1469 * Before invoking its target, if the target differs from the expected type,
1470 * the invoker will apply reference casts as
1471 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
1472 * Similarly, the return value will be converted as necessary.
1473 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
1474 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
1475 * <p>
1476 * A {@linkplain MethodType#genericMethodType general method type},
1477 * mentions only {@code Object} arguments and return values.
1478 * An invoker for such a type is capable of calling any method handle
1479 * of the same arity as the general type.
1480 * <p>
1481 * This method is equivalent to the following code (though it may be more efficient):
1482 * <p><blockquote><pre>
1483 publicLookup().findVirtual(MethodHandle.class, "invoke", type)
1484 * </pre></blockquote>
1485 * <p>
1486 * This method throws no reflective or security exceptions.
1487 * @param type the desired target type
1488 * @return a method handle suitable for invoking any method handle convertible to the given type
1489 */
1490 static public
1491 MethodHandle invoker(MethodType type) {
1492 return type.invokers().generalInvoker();
1493 }
1494
1495 static /*non-public*/
1496 MethodHandle basicInvoker(MethodType type) {
1497 return type.form().basicInvoker();
1498 }
1499
1500 /// method handle modification (creation from other method handles)
1501
1502 /**
1503 * Produces a method handle which adapts the type of the
1504 * given method handle to a new type by pairwise argument and return type conversion.
1505 * The original type and new type must have the same number of arguments.
1506 * The resulting method handle is guaranteed to report a type
1507 * which is equal to the desired new type.
1508 * <p>
1509 * If the original type and new type are equal, returns target.
1510 * <p>
1511 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
1512 * and some additional conversions are also applied if those conversions fail.
1513 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
1514 * if possible, before or instead of any conversions done by {@code asType}:
1515 * <ul>
1516 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
1517 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
1518 * (This treatment of interfaces follows the usage of the bytecode verifier.)
1519 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
1520 * the boolean is converted to a byte value, 1 for true, 0 for false.
1521 * (This treatment follows the usage of the bytecode verifier.)
1522 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
1523 * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
1524 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
1525 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
1526 * then a Java casting conversion (JLS 5.5) is applied.
1527 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
1528 * widening and/or narrowing.)
1529 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
1530 * conversion will be applied at runtime, possibly followed
1531 * by a Java casting conversion (JLS 5.5) on the primitive value,
1532 * possibly followed by a conversion from byte to boolean by testing
1533 * the low-order bit.
1534 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
1535 * and if the reference is null at runtime, a zero value is introduced.
1536 * </ul>
1537 * @param target the method handle to invoke after arguments are retyped
1538 * @param newType the expected type of the new method handle
1539 * @return a method handle which delegates to the target after performing
1540 * any necessary argument conversions, and arranges for any
1541 * necessary return value conversions
1542 * @throws NullPointerException if either argument is null
1543 * @throws WrongMethodTypeException if the conversion cannot be made
1544 * @see MethodHandle#asType
1545 */
1546 public static
1547 MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
1548 if (!target.type().isCastableTo(newType)) {
1549 throw new WrongMethodTypeException("cannot explicitly cast "+target+" to "+newType);
1550 }
1551 return MethodHandleImpl.makePairwiseConvert(target, newType, 2);
1552 }
1553
1554 /**
1555 * Produces a method handle which adapts the calling sequence of the
1556 * given method handle to a new type, by reordering the arguments.
1557 * The resulting method handle is guaranteed to report a type
1558 * which is equal to the desired new type.
1559 * <p>
1560 * The given array controls the reordering.
1561 * Call {@code #I} the number of incoming parameters (the value
1562 * {@code newType.parameterCount()}, and call {@code #O} the number
1563 * of outgoing parameters (the value {@code target.type().parameterCount()}).
1564 * Then the length of the reordering array must be {@code #O},
1565 * and each element must be a non-negative number less than {@code #I}.
1566 * For every {@code N} less than {@code #O}, the {@code N}-th
1567 * outgoing argument will be taken from the {@code I}-th incoming
1568 * argument, where {@code I} is {@code reorder[N]}.
1569 * <p>
1570 * No argument or return value conversions are applied.
1571 * The type of each incoming argument, as determined by {@code newType},
1572 * must be identical to the type of the corresponding outgoing parameter
1573 * or parameters in the target method handle.
1574 * The return type of {@code newType} must be identical to the return
1575 * type of the original target.
1576 * <p>
1577 * The reordering array need not specify an actual permutation.
1578 * An incoming argument will be duplicated if its index appears
1579 * more than once in the array, and an incoming argument will be dropped
1580 * if its index does not appear in the array.
1581 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
1582 * incoming arguments which are not mentioned in the reordering array
1583 * are may be any type, as determined only by {@code newType}.
1584 * <blockquote><pre>{@code
1585 import static java.lang.invoke.MethodHandles.*;
1586 import static java.lang.invoke.MethodType.*;
1587 ...
1588 MethodType intfn1 = methodType(int.class, int.class);
1589 MethodType intfn2 = methodType(int.class, int.class, int.class);
1590 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
1591 assert(sub.type().equals(intfn2));
1592 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
1593 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
1594 assert((int)rsub.invokeExact(1, 100) == 99);
1595 MethodHandle add = ... (int x, int y) -> (x+y) ...;
1596 assert(add.type().equals(intfn2));
1597 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
1598 assert(twice.type().equals(intfn1));
1599 assert((int)twice.invokeExact(21) == 42);
1600 * }</pre></blockquote>
1601 * @param target the method handle to invoke after arguments are reordered
1602 * @param newType the expected type of the new method handle
1603 * @param reorder an index array which controls the reordering
1604 * @return a method handle which delegates to the target after it
1605 * drops unused arguments and moves and/or duplicates the other arguments
1606 * @throws NullPointerException if any argument is null
1607 * @throws IllegalArgumentException if the index array length is not equal to
1608 * the arity of the target, or if any index array element
1609 * not a valid index for a parameter of {@code newType},
1610 * or if two corresponding parameter types in
1611 * {@code target.type()} and {@code newType} are not identical,
1612 */
1613 public static
1614 MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
1615 checkReorder(reorder, newType, target.type());
1616 return target.permuteArguments(newType, reorder);
1617 }
1618
1619 private static void checkReorder(int[] reorder, MethodType newType, MethodType oldType) {
1620 if (newType.returnType() != oldType.returnType())
1621 throw newIllegalArgumentException("return types do not match",
1622 oldType, newType);
1623 if (reorder.length == oldType.parameterCount()) {
1624 int limit = newType.parameterCount();
1625 boolean bad = false;
1626 for (int j = 0; j < reorder.length; j++) {
1627 int i = reorder[j];
1628 if (i < 0 || i >= limit) {
1629 bad = true; break;
1630 }
1631 Class<?> src = newType.parameterType(i);
1632 Class<?> dst = oldType.parameterType(j);
1633 if (src != dst)
1634 throw newIllegalArgumentException("parameter types do not match after reorder",
1635 oldType, newType);
1636 }
1637 if (!bad) return;
1638 }
1639 throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
1640 }
1641
1642 /**
1643 * Produces a method handle of the requested return type which returns the given
1644 * constant value every time it is invoked.
1645 * <p>
1646 * Before the method handle is returned, the passed-in value is converted to the requested type.
1647 * If the requested type is primitive, widening primitive conversions are attempted,
1648 * else reference conversions are attempted.
1649 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
1650 * @param type the return type of the desired method handle
1651 * @param value the value to return
1652 * @return a method handle of the given return type and no arguments, which always returns the given value
1653 * @throws NullPointerException if the {@code type} argument is null
1654 * @throws ClassCastException if the value cannot be converted to the required return type
1655 * @throws IllegalArgumentException if the given type is {@code void.class}
1656 */
1657 public static
1658 MethodHandle constant(Class<?> type, Object value) {
1659 if (type.isPrimitive()) {
1660 if (type == void.class)
1661 throw newIllegalArgumentException("void type");
1662 Wrapper w = Wrapper.forPrimitiveType(type);
1663 return insertArguments(identity(type), 0, w.convert(value, type));
1664 } else {
1665 return identity(type).bindTo(type.cast(value));
1666 }
1667 }
1668
1669 /**
1670 * Produces a method handle which returns its sole argument when invoked.
1671 * @param type the type of the sole parameter and return value of the desired method handle
1672 * @return a unary method handle which accepts and returns the given type
1673 * @throws NullPointerException if the argument is null
1674 * @throws IllegalArgumentException if the given type is {@code void.class}
1675 */
1676 public static
1677 MethodHandle identity(Class<?> type) {
1678 if (type == void.class)
1679 throw newIllegalArgumentException("void type");
1680 else if (type == Object.class)
1681 return ValueConversions.identity();
1682 else if (type.isPrimitive())
1683 return ValueConversions.identity(Wrapper.forPrimitiveType(type));
1684 else
1685 return MethodHandleImpl.makeReferenceIdentity(type);
1686 }
1687
1688 /**
1689 * Provides a target method handle with one or more <em>bound arguments</em>
1690 * in advance of the method handle's invocation.
1691 * The formal parameters to the target corresponding to the bound
1692 * arguments are called <em>bound parameters</em>.
1693 * Returns a new method handle which saves away the bound arguments.
1694 * When it is invoked, it receives arguments for any non-bound parameters,
1695 * binds the saved arguments to their corresponding parameters,
1696 * and calls the original target.
1697 * <p>
1698 * The type of the new method handle will drop the types for the bound
1699 * parameters from the original target type, since the new method handle
1700 * will no longer require those arguments to be supplied by its callers.
1701 * <p>
1702 * Each given argument object must match the corresponding bound parameter type.
1703 * If a bound parameter type is a primitive, the argument object
1704 * must be a wrapper, and will be unboxed to produce the primitive value.
1705 * <p>
1706 * The {@code pos} argument selects which parameters are to be bound.
1707 * It may range between zero and <i>N-L</i> (inclusively),
1708 * where <i>N</i> is the arity of the target method handle
1709 * and <i>L</i> is the length of the values array.
1710 * @param target the method handle to invoke after the argument is inserted
1711 * @param pos where to insert the argument (zero for the first)
1712 * @param values the series of arguments to insert
1713 * @return a method handle which inserts an additional argument,
1714 * before calling the original method handle
1715 * @throws NullPointerException if the target or the {@code values} array is null
1716 * @see MethodHandle#bindTo
1717 */
1718 public static
1719 MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
1720 int insCount = values.length;
1721 MethodType oldType = target.type();
1722 int outargs = oldType.parameterCount();
1723 int inargs = outargs - insCount;
1724 if (inargs < 0)
1725 throw newIllegalArgumentException("too many values to insert");
1726 if (pos < 0 || pos > inargs)
1727 throw newIllegalArgumentException("no argument type to append");
1728 MethodHandle result = target;
1729 for (int i = 0; i < insCount; i++) {
1730 Object value = values[i];
1731 Class<?> ptype = oldType.parameterType(pos+i);
1732 if (ptype.isPrimitive()) {
1733 char btype = 'I';
1734 Wrapper w = Wrapper.forPrimitiveType(ptype);
1735 switch (w) {
1736 case LONG: btype = 'J'; break;
1737 case FLOAT: btype = 'F'; break;
1738 case DOUBLE: btype = 'D'; break;
1739 }
1740 // perform unboxing and/or primitive conversion
1741 value = w.convert(value, ptype);
1742 result = result.bindArgument(pos, btype, value);
1743 continue;
1744 }
1745 value = ptype.cast(value); // throw CCE if needed
1746 if (pos == 0) {
1747 result = result.bindReceiver(value);
1748 } else {
1749 result = result.bindArgument(pos, 'L', value);
1750 }
1751 }
1752 return result;
1753 }
1754
1755 /**
1756 * Produces a method handle which will discard some dummy arguments
1757 * before calling some other specified <i>target</i> method handle.
1758 * The type of the new method handle will be the same as the target's type,
1759 * except it will also include the dummy argument types,
1760 * at some given position.
1761 * <p>
1762 * The {@code pos} argument may range between zero and <i>N</i>,
1763 * where <i>N</i> is the arity of the target.
1764 * If {@code pos} is zero, the dummy arguments will precede
1765 * the target's real arguments; if {@code pos} is <i>N</i>
1766 * they will come after.
1767 * <p>
1768 * <b>Example:</b>
1769 * <p><blockquote><pre>
1770 import static java.lang.invoke.MethodHandles.*;
1771 import static java.lang.invoke.MethodType.*;
1772 ...
1773 MethodHandle cat = lookup().findVirtual(String.class,
1774 "concat", methodType(String.class, String.class));
1775 assertEquals("xy", (String) cat.invokeExact("x", "y"));
1776 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
1777 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
1778 assertEquals(bigType, d0.type());
1779 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
1780 * </pre></blockquote>
1781 * <p>
1782 * This method is also equivalent to the following code:
1783 * <p><blockquote><pre>
1784 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}(target, pos, valueTypes.toArray(new Class[0]))
1785 * </pre></blockquote>
1786 * @param target the method handle to invoke after the arguments are dropped
1787 * @param valueTypes the type(s) of the argument(s) to drop
1788 * @param pos position of first argument to drop (zero for the leftmost)
1789 * @return a method handle which drops arguments of the given types,
1790 * before calling the original method handle
1791 * @throws NullPointerException if the target is null,
1792 * or if the {@code valueTypes} list or any of its elements is null
1793 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
1794 * or if {@code pos} is negative or greater than the arity of the target,
1795 * or if the new method handle's type would have too many parameters
1796 */
1797 public static
1798 MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
1799 MethodType oldType = target.type(); // get NPE
1800 int dropped = valueTypes.size();
1801 MethodType.checkSlotCount(dropped);
1802 if (dropped == 0) return target;
1803 int outargs = oldType.parameterCount();
1804 int inargs = outargs + dropped;
1805 if (pos < 0 || pos >= inargs)
1806 throw newIllegalArgumentException("no argument type to remove");
1807 ArrayList<Class<?>> ptypes = new ArrayList<>(oldType.parameterList());
1808 ptypes.addAll(pos, valueTypes);
1809 MethodType newType = MethodType.methodType(oldType.returnType(), ptypes);
1810 return target.dropArguments(newType, pos, dropped);
1811 }
1812
1813 /**
1814 * Produces a method handle which will discard some dummy arguments
1815 * before calling some other specified <i>target</i> method handle.
1816 * The type of the new method handle will be the same as the target's type,
1817 * except it will also include the dummy argument types,
1818 * at some given position.
1819 * <p>
1820 * The {@code pos} argument may range between zero and <i>N</i>,
1821 * where <i>N</i> is the arity of the target.
1822 * If {@code pos} is zero, the dummy arguments will precede
1823 * the target's real arguments; if {@code pos} is <i>N</i>
1824 * they will come after.
1825 * <p>
1826 * <b>Example:</b>
1827 * <p><blockquote><pre>
1828 import static java.lang.invoke.MethodHandles.*;
1829 import static java.lang.invoke.MethodType.*;
1830 ...
1831 MethodHandle cat = lookup().findVirtual(String.class,
1832 "concat", methodType(String.class, String.class));
1833 assertEquals("xy", (String) cat.invokeExact("x", "y"));
1834 MethodHandle d0 = dropArguments(cat, 0, String.class);
1835 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
1836 MethodHandle d1 = dropArguments(cat, 1, String.class);
1837 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
1838 MethodHandle d2 = dropArguments(cat, 2, String.class);
1839 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
1840 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
1841 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
1842 * </pre></blockquote>
1843 * <p>
1844 * This method is also equivalent to the following code:
1845 * <p><blockquote><pre>
1846 * {@link #dropArguments(MethodHandle,int,List) dropArguments}(target, pos, Arrays.asList(valueTypes))
1847 * </pre></blockquote>
1848 * @param target the method handle to invoke after the arguments are dropped
1849 * @param valueTypes the type(s) of the argument(s) to drop
1850 * @param pos position of first argument to drop (zero for the leftmost)
1851 * @return a method handle which drops arguments of the given types,
1852 * before calling the original method handle
1853 * @throws NullPointerException if the target is null,
1854 * or if the {@code valueTypes} array or any of its elements is null
1855 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
1856 * or if {@code pos} is negative or greater than the arity of the target,
1857 * or if the new method handle's type would have too many parameters
1858 */
1859 public static
1860 MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
1861 return dropArguments(target, pos, Arrays.asList(valueTypes));
1862 }
1863
1864 /**
1865 * Adapts a target method handle by pre-processing
1866 * one or more of its arguments, each with its own unary filter function,
1867 * and then calling the target with each pre-processed argument
1868 * replaced by the result of its corresponding filter function.
1869 * <p>
1870 * The pre-processing is performed by one or more method handles,
1871 * specified in the elements of the {@code filters} array.
1872 * The first element of the filter array corresponds to the {@code pos}
1873 * argument of the target, and so on in sequence.
1874 * <p>
1875 * Null arguments in the array are treated as identity functions,
1876 * and the corresponding arguments left unchanged.
1877 * (If there are no non-null elements in the array, the original target is returned.)
1878 * Each filter is applied to the corresponding argument of the adapter.
1879 * <p>
1880 * If a filter {@code F} applies to the {@code N}th argument of
1881 * the target, then {@code F} must be a method handle which
1882 * takes exactly one argument. The type of {@code F}'s sole argument
1883 * replaces the corresponding argument type of the target
1884 * in the resulting adapted method handle.
1885 * The return type of {@code F} must be identical to the corresponding
1886 * parameter type of the target.
1887 * <p>
1888 * It is an error if there are elements of {@code filters}
1889 * (null or not)
1890 * which do not correspond to argument positions in the target.
1891 * <b>Example:</b>
1892 * <p><blockquote><pre>
1893 import static java.lang.invoke.MethodHandles.*;
1894 import static java.lang.invoke.MethodType.*;
1895 ...
1896 MethodHandle cat = lookup().findVirtual(String.class,
1897 "concat", methodType(String.class, String.class));
1898 MethodHandle upcase = lookup().findVirtual(String.class,
1899 "toUpperCase", methodType(String.class));
1900 assertEquals("xy", (String) cat.invokeExact("x", "y"));
1901 MethodHandle f0 = filterArguments(cat, 0, upcase);
1902 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
1903 MethodHandle f1 = filterArguments(cat, 1, upcase);
1904 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
1905 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
1906 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
1907 * </pre></blockquote>
1908 * <p> Here is pseudocode for the resulting adapter:
1909 * <blockquote><pre>
1910 * V target(P... p, A[i]... a[i], B... b);
1911 * A[i] filter[i](V[i]);
1912 * T adapter(P... p, V[i]... v[i], B... b) {
1913 * return target(p..., f[i](v[i])..., b...);
1914 * }
1915 * </pre></blockquote>
1916 *
1917 * @param target the method handle to invoke after arguments are filtered
1918 * @param pos the position of the first argument to filter
1919 * @param filters method handles to call initially on filtered arguments
1920 * @return method handle which incorporates the specified argument filtering logic
1921 * @throws NullPointerException if the target is null
1922 * or if the {@code filters} array is null
1923 * @throws IllegalArgumentException if a non-null element of {@code filters}
1924 * does not match a corresponding argument type of target as described above,
1925 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()}
1926 */
1927 public static
1928 MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
1929 MethodType targetType = target.type();
1930 MethodHandle adapter = target;
1931 MethodType adapterType = null;
1932 assert((adapterType = targetType) != null);
1933 int maxPos = targetType.parameterCount();
1934 if (pos + filters.length > maxPos)
1935 throw newIllegalArgumentException("too many filters");
1936 int curPos = pos-1; // pre-incremented
1937 for (MethodHandle filter : filters) {
1938 curPos += 1;
1939 if (filter == null) continue; // ignore null elements of filters
1940 adapter = filterArgument(adapter, curPos, filter);
1941 assert((adapterType = adapterType.changeParameterType(curPos, filter.type().parameterType(0))) != null);
1942 }
1943 assert(adapterType.equals(adapter.type()));
1944 return adapter;
1945 }
1946
1947 /*non-public*/ static
1948 MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
1949 MethodType targetType = target.type();
1950 MethodType filterType = filter.type();
1951 if (filterType.parameterCount() != 1
1952 || filterType.returnType() != targetType.parameterType(pos))
1953 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
1954 return MethodHandleImpl.makeCollectArguments(target, filter, pos, false);
1955 }
1956
1957 // FIXME: Make this public in M1.
1958 /*non-public*/ static
1959 MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle collector) {
1960 MethodType targetType = target.type();
1961 MethodType filterType = collector.type();
1962 if (filterType.returnType() != void.class &&
1963 filterType.returnType() != targetType.parameterType(pos))
1964 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
1965 return MethodHandleImpl.makeCollectArguments(target, collector, pos, false);
1966 }
1967
1968 /**
1969 * Adapts a target method handle by post-processing
1970 * its return value (if any) with a filter (another method handle).
1971 * The result of the filter is returned from the adapter.
1972 * <p>
1973 * If the target returns a value, the filter must accept that value as
1974 * its only argument.
1975 * If the target returns void, the filter must accept no arguments.
1976 * <p>
1977 * The return type of the filter
1978 * replaces the return type of the target
1979 * in the resulting adapted method handle.
1980 * The argument type of the filter (if any) must be identical to the
1981 * return type of the target.
1982 * <b>Example:</b>
1983 * <p><blockquote><pre>
1984 import static java.lang.invoke.MethodHandles.*;
1985 import static java.lang.invoke.MethodType.*;
1986 ...
1987 MethodHandle cat = lookup().findVirtual(String.class,
1988 "concat", methodType(String.class, String.class));
1989 MethodHandle length = lookup().findVirtual(String.class,
1990 "length", methodType(int.class));
1991 System.out.println((String) cat.invokeExact("x", "y")); // xy
1992 MethodHandle f0 = filterReturnValue(cat, length);
1993 System.out.println((int) f0.invokeExact("x", "y")); // 2
1994 * </pre></blockquote>
1995 * <p> Here is pseudocode for the resulting adapter:
1996 * <blockquote><pre>
1997 * V target(A...);
1998 * T filter(V);
1999 * T adapter(A... a) {
2000 * V v = target(a...);
2001 * return filter(v);
2002 * }
2003 * // and if the target has a void return:
2004 * void target2(A...);
2005 * T filter2();
2006 * T adapter2(A... a) {
2007 * target2(a...);
2008 * return filter2();
2009 * }
2010 * // and if the filter has a void return:
2011 * V target3(A...);
2012 * void filter3(V);
2013 * void adapter3(A... a) {
2014 * V v = target3(a...);
2015 * filter3(v);
2016 * }
2017 * </pre></blockquote>
2018 * @param target the method handle to invoke before filtering the return value
2019 * @param filter method handle to call on the return value
2020 * @return method handle which incorporates the specified return value filtering logic
2021 * @throws NullPointerException if either argument is null
2022 * @throws IllegalArgumentException if the argument list of {@code filter}
2023 * does not match the return type of target as described above
2024 */
2025 public static
2026 MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
2027 MethodType targetType = target.type();
2028 MethodType filterType = filter.type();
2029 Class<?> rtype = targetType.returnType();
2030 int filterValues = filterType.parameterCount();
2031 if (filterValues == 0
2032 ? (rtype != void.class)
2033 : (rtype != filterType.parameterType(0)))
2034 throw newIllegalArgumentException("target and filter types do not match", target, filter);
2035 // result = fold( lambda(retval, arg...) { filter(retval) },
2036 // lambda( arg...) { target(arg...) } )
2037 return MethodHandleImpl.makeCollectArguments(filter, target, 0, false);
2038 }
2039
2040 /**
2041 * Adapts a target method handle by pre-processing
2042 * some of its arguments, and then calling the target with
2043 * the result of the pre-processing, inserted into the original
2044 * sequence of arguments.
2045 * <p>
2046 * The pre-processing is performed by {@code combiner}, a second method handle.
2047 * Of the arguments passed to the adapter, the first {@code N} arguments
2048 * are copied to the combiner, which is then called.
2049 * (Here, {@code N} is defined as the parameter count of the combiner.)
2050 * After this, control passes to the target, with any result
2051 * from the combiner inserted before the original {@code N} incoming
2052 * arguments.
2053 * <p>
2054 * If the combiner returns a value, the first parameter type of the target
2055 * must be identical with the return type of the combiner, and the next
2056 * {@code N} parameter types of the target must exactly match the parameters
2057 * of the combiner.
2058 * <p>
2059 * If the combiner has a void return, no result will be inserted,
2060 * and the first {@code N} parameter types of the target
2061 * must exactly match the parameters of the combiner.
2062 * <p>
2063 * The resulting adapter is the same type as the target, except that the
2064 * first parameter type is dropped,
2065 * if it corresponds to the result of the combiner.
2066 * <p>
2067 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
2068 * that either the combiner or the target does not wish to receive.
2069 * If some of the incoming arguments are destined only for the combiner,
2070 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
2071 * arguments will not need to be live on the stack on entry to the
2072 * target.)
2073 * <b>Example:</b>
2074 * <p><blockquote><pre>
2075 import static java.lang.invoke.MethodHandles.*;
2076 import static java.lang.invoke.MethodType.*;
2077 ...
2078 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
2079 "println", methodType(void.class, String.class))
2080 .bindTo(System.out);
2081 MethodHandle cat = lookup().findVirtual(String.class,
2082 "concat", methodType(String.class, String.class));
2083 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
2084 MethodHandle catTrace = foldArguments(cat, trace);
2085 // also prints "boo":
2086 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
2087 * </pre></blockquote>
2088 * <p> Here is pseudocode for the resulting adapter:
2089 * <blockquote><pre>
2090 * // there are N arguments in A...
2091 * T target(V, A[N]..., B...);
2092 * V combiner(A...);
2093 * T adapter(A... a, B... b) {
2094 * V v = combiner(a...);
2095 * return target(v, a..., b...);
2096 * }
2097 * // and if the combiner has a void return:
2098 * T target2(A[N]..., B...);
2099 * void combiner2(A...);
2100 * T adapter2(A... a, B... b) {
2101 * combiner2(a...);
2102 * return target2(a..., b...);
2103 * }
2104 * </pre></blockquote>
2105 * @param target the method handle to invoke after arguments are combined
2106 * @param combiner method handle to call initially on the incoming arguments
2107 * @return method handle which incorporates the specified argument folding logic
2108 * @throws NullPointerException if either argument is null
2109 * @throws IllegalArgumentException if {@code combiner}'s return type
2110 * is non-void and not the same as the first argument type of
2111 * the target, or if the initial {@code N} argument types
2112 * of the target
2113 * (skipping one matching the {@code combiner}'s return type)
2114 * are not identical with the argument types of {@code combiner}
2115 */
2116 public static
2117 MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
2118 int pos = 0;
2119 MethodType targetType = target.type();
2120 MethodType combinerType = combiner.type();
2121 int foldPos = pos;
2122 int foldArgs = combinerType.parameterCount();
2123 int foldVals = combinerType.returnType() == void.class ? 0 : 1;
2124 int afterInsertPos = foldPos + foldVals;
2125 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
2126 if (ok && !(combinerType.parameterList()
2127 .equals(targetType.parameterList().subList(afterInsertPos,
2128 afterInsertPos + foldArgs))))
2129 ok = false;
2130 if (ok && foldVals != 0 && !combinerType.returnType().equals(targetType.parameterType(0)))
2131 ok = false;
2132 if (!ok)
2133 throw misMatchedTypes("target and combiner types", targetType, combinerType);
2134 MethodType newType = targetType.dropParameterTypes(foldPos, afterInsertPos);
2135 return MethodHandleImpl.makeCollectArguments(target, combiner, foldPos, true);
2136 }
2137
2138 /**
2139 * Makes a method handle which adapts a target method handle,
2140 * by guarding it with a test, a boolean-valued method handle.
2141 * If the guard fails, a fallback handle is called instead.
2142 * All three method handles must have the same corresponding
2143 * argument and return types, except that the return type
2144 * of the test must be boolean, and the test is allowed
2145 * to have fewer arguments than the other two method handles.
2146 * <p> Here is pseudocode for the resulting adapter:
2147 * <blockquote><pre>
2148 * boolean test(A...);
2149 * T target(A...,B...);
2150 * T fallback(A...,B...);
2151 * T adapter(A... a,B... b) {
2152 * if (test(a...))
2153 * return target(a..., b...);
2154 * else
2155 * return fallback(a..., b...);
2156 * }
2157 * </pre></blockquote>
2158 * Note that the test arguments ({@code a...} in the pseudocode) cannot
2159 * be modified by execution of the test, and so are passed unchanged
2160 * from the caller to the target or fallback as appropriate.
2161 * @param test method handle used for test, must return boolean
2162 * @param target method handle to call if test passes
2163 * @param fallback method handle to call if test fails
2164 * @return method handle which incorporates the specified if/then/else logic
2165 * @throws NullPointerException if any argument is null
2166 * @throws IllegalArgumentException if {@code test} does not return boolean,
2167 * or if all three method types do not match (with the return
2168 * type of {@code test} changed to match that of the target).
2169 */
2170 public static
2171 MethodHandle guardWithTest(MethodHandle test,
2172 MethodHandle target,
2173 MethodHandle fallback) {
2174 MethodType gtype = test.type();
2175 MethodType ttype = target.type();
2176 MethodType ftype = fallback.type();
2177 if (!ttype.equals(ftype))
2178 throw misMatchedTypes("target and fallback types", ttype, ftype);
2179 if (gtype.returnType() != boolean.class)
2180 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
2181 List<Class<?>> targs = ttype.parameterList();
2182 List<Class<?>> gargs = gtype.parameterList();
2183 if (!targs.equals(gargs)) {
2184 int gpc = gargs.size(), tpc = targs.size();
2185 if (gpc >= tpc || !targs.subList(0, gpc).equals(gargs))
2186 throw misMatchedTypes("target and test types", ttype, gtype);
2187 test = dropArguments(test, gpc, targs.subList(gpc, tpc));
2188 gtype = test.type();
2189 }
2190 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
2191 }
2192
2193 static RuntimeException misMatchedTypes(String what, MethodType t1, MethodType t2) {
2194 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
2195 }
2196
2197 /**
2198 * Makes a method handle which adapts a target method handle,
2199 * by running it inside an exception handler.
2200 * If the target returns normally, the adapter returns that value.
2201 * If an exception matching the specified type is thrown, the fallback
2202 * handle is called instead on the exception, plus the original arguments.
2203 * <p>
2204 * The target and handler must have the same corresponding
2205 * argument and return types, except that handler may omit trailing arguments
2206 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
2207 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
2208 * <p> Here is pseudocode for the resulting adapter:
2209 * <blockquote><pre>
2210 * T target(A..., B...);
2211 * T handler(ExType, A...);
2212 * T adapter(A... a, B... b) {
2213 * try {
2214 * return target(a..., b...);
2215 * } catch (ExType ex) {
2216 * return handler(ex, a...);
2217 * }
2218 * }
2219 * </pre></blockquote>
2220 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
2221 * be modified by execution of the target, and so are passed unchanged
2222 * from the caller to the handler, if the handler is invoked.
2223 * <p>
2224 * The target and handler must return the same type, even if the handler
2225 * always throws. (This might happen, for instance, because the handler
2226 * is simulating a {@code finally} clause).
2227 * To create such a throwing handler, compose the handler creation logic
2228 * with {@link #throwException throwException},
2229 * in order to create a method handle of the correct return type.
2230 * @param target method handle to call
2231 * @param exType the type of exception which the handler will catch
2232 * @param handler method handle to call if a matching exception is thrown
2233 * @return method handle which incorporates the specified try/catch logic
2234 * @throws NullPointerException if any argument is null
2235 * @throws IllegalArgumentException if {@code handler} does not accept
2236 * the given exception type, or if the method handle types do
2237 * not match in their return types and their
2238 * corresponding parameters
2239 */
2240 public static
2241 MethodHandle catchException(MethodHandle target,
2242 Class<? extends Throwable> exType,
2243 MethodHandle handler) {
2244 MethodType ttype = target.type();
2245 MethodType htype = handler.type();
2246 if (htype.parameterCount() < 1 ||
2247 !htype.parameterType(0).isAssignableFrom(exType))
2248 throw newIllegalArgumentException("handler does not accept exception type "+exType);
2249 if (htype.returnType() != ttype.returnType())
2250 throw misMatchedTypes("target and handler return types", ttype, htype);
2251 List<Class<?>> targs = ttype.parameterList();
2252 List<Class<?>> hargs = htype.parameterList();
2253 hargs = hargs.subList(1, hargs.size()); // omit leading parameter from handler
2254 if (!targs.equals(hargs)) {
2255 int hpc = hargs.size(), tpc = targs.size();
2256 if (hpc >= tpc || !targs.subList(0, hpc).equals(hargs))
2257 throw misMatchedTypes("target and handler types", ttype, htype);
2258 handler = dropArguments(handler, 1+hpc, targs.subList(hpc, tpc));
2259 htype = handler.type();
2260 }
2261 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
2262 }
2263
2264 /**
2265 * Produces a method handle which will throw exceptions of the given {@code exType}.
2266 * The method handle will accept a single argument of {@code exType},
2267 * and immediately throw it as an exception.
2268 * The method type will nominally specify a return of {@code returnType}.
2269 * The return type may be anything convenient: It doesn't matter to the
2270 * method handle's behavior, since it will never return normally.
2271 * @param returnType the return type of the desired method handle
2272 * @param exType the parameter type of the desired method handle
2273 * @return method handle which can throw the given exceptions
2274 * @throws NullPointerException if either argument is null
2275 */
2276 public static
2277 MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
2278 if (!Throwable.class.isAssignableFrom(exType))
2279 throw new ClassCastException(exType.getName());
2280 return MethodHandleImpl.throwException(MethodType.methodType(returnType, exType));
2281 }
2282 }