1 /*
2 * Copyright (c) 1999, 2008, 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.reflect;
27
28 import java.lang.ref.Reference;
29 import java.lang.ref.WeakReference;
30 import java.util.Arrays;
31 import java.util.Collections;
32 import java.util.HashMap;
33 import java.util.HashSet;
34 import java.util.Map;
35 import java.util.Set;
36 import java.util.List;
37 import java.util.WeakHashMap;
38 import sun.misc.ProxyGenerator;
39
40 /**
41 * {@code Proxy} provides static methods for creating dynamic proxy
42 * classes and instances, and it is also the superclass of all
43 * dynamic proxy classes created by those methods.
44 *
45 * <p>To create a proxy for some interface {@code Foo}:
46 * <pre>
47 * InvocationHandler handler = new MyInvocationHandler(...);
48 * Class proxyClass = Proxy.getProxyClass(
49 * Foo.class.getClassLoader(), new Class[] { Foo.class });
50 * Foo f = (Foo) proxyClass.
51 * getConstructor(new Class[] { InvocationHandler.class }).
52 * newInstance(new Object[] { handler });
53 * </pre>
54 * or more simply:
55 * <pre>
56 * Foo f = (Foo) Proxy.newProxyInstance(Foo.class.getClassLoader(),
57 * new Class[] { Foo.class },
58 * handler);
59 * </pre>
60 *
61 * <p>A <i>dynamic proxy class</i> (simply referred to as a <i>proxy
62 * class</i> below) is a class that implements a list of interfaces
63 * specified at runtime when the class is created, with behavior as
64 * described below.
65 *
66 * A <i>proxy interface</i> is such an interface that is implemented
67 * by a proxy class.
68 *
69 * A <i>proxy instance</i> is an instance of a proxy class.
70 *
71 * Each proxy instance has an associated <i>invocation handler</i>
72 * object, which implements the interface {@link InvocationHandler}.
73 * A method invocation on a proxy instance through one of its proxy
74 * interfaces will be dispatched to the {@link InvocationHandler#invoke
75 * invoke} method of the instance's invocation handler, passing the proxy
76 * instance, a {@code java.lang.reflect.Method} object identifying
77 * the method that was invoked, and an array of type {@code Object}
78 * containing the arguments. The invocation handler processes the
79 * encoded method invocation as appropriate and the result that it
80 * returns will be returned as the result of the method invocation on
81 * the proxy instance.
82 *
83 * <p>A proxy class has the following properties:
84 *
85 * <ul>
86 * <li>Proxy classes are public, final, and not abstract.
87 *
88 * <li>The unqualified name of a proxy class is unspecified. The space
89 * of class names that begin with the string {@code "$Proxy"}
90 * should be, however, reserved for proxy classes.
91 *
92 * <li>A proxy class extends {@code java.lang.reflect.Proxy}.
93 *
94 * <li>A proxy class implements exactly the interfaces specified at its
95 * creation, in the same order.
96 *
97 * <li>If a proxy class implements a non-public interface, then it will
98 * be defined in the same package as that interface. Otherwise, the
99 * package of a proxy class is also unspecified. Note that package
100 * sealing will not prevent a proxy class from being successfully defined
101 * in a particular package at runtime, and neither will classes already
102 * defined by the same class loader and the same package with particular
103 * signers.
104 *
105 * <li>Since a proxy class implements all of the interfaces specified at
106 * its creation, invoking {@code getInterfaces} on its
107 * {@code Class} object will return an array containing the same
108 * list of interfaces (in the order specified at its creation), invoking
109 * {@code getMethods} on its {@code Class} object will return
110 * an array of {@code Method} objects that include all of the
111 * methods in those interfaces, and invoking {@code getMethod} will
112 * find methods in the proxy interfaces as would be expected.
113 *
114 * <li>The {@link Proxy#isProxyClass Proxy.isProxyClass} method will
115 * return true if it is passed a proxy class-- a class returned by
116 * {@code Proxy.getProxyClass} or the class of an object returned by
117 * {@code Proxy.newProxyInstance}-- and false otherwise.
118 *
119 * <li>The {@code java.security.ProtectionDomain} of a proxy class
120 * is the same as that of system classes loaded by the bootstrap class
121 * loader, such as {@code java.lang.Object}, because the code for a
122 * proxy class is generated by trusted system code. This protection
123 * domain will typically be granted
124 * {@code java.security.AllPermission}.
125 *
126 * <li>Each proxy class has one public constructor that takes one argument,
127 * an implementation of the interface {@link InvocationHandler}, to set
128 * the invocation handler for a proxy instance. Rather than having to use
129 * the reflection API to access the public constructor, a proxy instance
130 * can be also be created by calling the {@link Proxy#newProxyInstance
131 * Proxy.newProxyInstance} method, which combines the actions of calling
132 * {@link Proxy#getProxyClass Proxy.getProxyClass} with invoking the
133 * constructor with an invocation handler.
134 * </ul>
135 *
136 * <p>A proxy instance has the following properties:
137 *
138 * <ul>
139 * <li>Given a proxy instance {@code proxy} and one of the
140 * interfaces implemented by its proxy class {@code Foo}, the
141 * following expression will return true:
142 * <pre>
143 * {@code proxy instanceof Foo}
144 * </pre>
145 * and the following cast operation will succeed (rather than throwing
146 * a {@code ClassCastException}):
147 * <pre>
148 * {@code (Foo) proxy}
149 * </pre>
150 *
151 * <li>Each proxy instance has an associated invocation handler, the one
152 * that was passed to its constructor. The static
153 * {@link Proxy#getInvocationHandler Proxy.getInvocationHandler} method
154 * will return the invocation handler associated with the proxy instance
155 * passed as its argument.
156 *
157 * <li>An interface method invocation on a proxy instance will be
158 * encoded and dispatched to the invocation handler's {@link
159 * InvocationHandler#invoke invoke} method as described in the
160 * documentation for that method.
161 *
162 * <li>An invocation of the {@code hashCode},
163 * {@code equals}, or {@code toString} methods declared in
164 * {@code java.lang.Object} on a proxy instance will be encoded and
165 * dispatched to the invocation handler's {@code invoke} method in
166 * the same manner as interface method invocations are encoded and
167 * dispatched, as described above. The declaring class of the
168 * {@code Method} object passed to {@code invoke} will be
169 * {@code java.lang.Object}. Other public methods of a proxy
170 * instance inherited from {@code java.lang.Object} are not
171 * overridden by a proxy class, so invocations of those methods behave
172 * like they do for instances of {@code java.lang.Object}.
173 * </ul>
174 *
175 * <h3>Methods Duplicated in Multiple Proxy Interfaces</h3>
176 *
177 * <p>When two or more interfaces of a proxy class contain a method with
178 * the same name and parameter signature, the order of the proxy class's
179 * interfaces becomes significant. When such a <i>duplicate method</i>
180 * is invoked on a proxy instance, the {@code Method} object passed
181 * to the invocation handler will not necessarily be the one whose
182 * declaring class is assignable from the reference type of the interface
183 * that the proxy's method was invoked through. This limitation exists
184 * because the corresponding method implementation in the generated proxy
185 * class cannot determine which interface it was invoked through.
186 * Therefore, when a duplicate method is invoked on a proxy instance,
187 * the {@code Method} object for the method in the foremost interface
188 * that contains the method (either directly or inherited through a
189 * superinterface) in the proxy class's list of interfaces is passed to
190 * the invocation handler's {@code invoke} method, regardless of the
191 * reference type through which the method invocation occurred.
192 *
193 * <p>If a proxy interface contains a method with the same name and
194 * parameter signature as the {@code hashCode}, {@code equals},
195 * or {@code toString} methods of {@code java.lang.Object},
196 * when such a method is invoked on a proxy instance, the
197 * {@code Method} object passed to the invocation handler will have
198 * {@code java.lang.Object} as its declaring class. In other words,
199 * the public, non-final methods of {@code java.lang.Object}
200 * logically precede all of the proxy interfaces for the determination of
201 * which {@code Method} object to pass to the invocation handler.
202 *
203 * <p>Note also that when a duplicate method is dispatched to an
204 * invocation handler, the {@code invoke} method may only throw
205 * checked exception types that are assignable to one of the exception
206 * types in the {@code throws} clause of the method in <i>all</i> of
207 * the proxy interfaces that it can be invoked through. If the
208 * {@code invoke} method throws a checked exception that is not
209 * assignable to any of the exception types declared by the method in one
210 * of the proxy interfaces that it can be invoked through, then an
211 * unchecked {@code UndeclaredThrowableException} will be thrown by
212 * the invocation on the proxy instance. This restriction means that not
213 * all of the exception types returned by invoking
214 * {@code getExceptionTypes} on the {@code Method} object
215 * passed to the {@code invoke} method can necessarily be thrown
216 * successfully by the {@code invoke} method.
217 *
218 * @author Peter Jones
219 * @see InvocationHandler
220 * @since 1.3
221 */
222 public class Proxy implements java.io.Serializable {
223
224 private static final long serialVersionUID = -2222568056686623797L;
225
226 /** prefix for all proxy class names */
227 private final static String proxyClassNamePrefix = "$Proxy";
228
229 /** parameter types of a proxy class constructor */
230 private final static Class[] constructorParams =
231 { InvocationHandler.class };
232
233 /** maps a class loader to the proxy class cache for that loader */
234 private static Map<ClassLoader, Map<List<String>, Object>> loaderToCache
235 = new WeakHashMap<>();
236
237 /** marks that a particular proxy class is currently being generated */
238 private static Object pendingGenerationMarker = new Object();
239
240 /** next number to use for generation of unique proxy class names */
241 private static long nextUniqueNumber = 0;
242 private static Object nextUniqueNumberLock = new Object();
243
244 /** set of all generated proxy classes, for isProxyClass implementation */
245 private static Map<Class<?>, Void> proxyClasses =
246 Collections.synchronizedMap(new WeakHashMap<Class<?>, Void>());
247
248 /**
249 * the invocation handler for this proxy instance.
250 * @serial
251 */
252 protected InvocationHandler h;
253
254 /**
255 * Prohibits instantiation.
256 */
257 private Proxy() {
258 }
259
260 /**
261 * Constructs a new {@code Proxy} instance from a subclass
262 * (typically, a dynamic proxy class) with the specified value
263 * for its invocation handler.
264 *
265 * @param h the invocation handler for this proxy instance
266 */
267 protected Proxy(InvocationHandler h) {
268 this.h = h;
269 }
270
271 /**
272 * Returns the {@code java.lang.Class} object for a proxy class
273 * given a class loader and an array of interfaces. The proxy class
274 * will be defined by the specified class loader and will implement
275 * all of the supplied interfaces. If a proxy class for the same
276 * permutation of interfaces has already been defined by the class
277 * loader, then the existing proxy class will be returned; otherwise,
278 * a proxy class for those interfaces will be generated dynamically
279 * and defined by the class loader.
280 *
281 * <p>There are several restrictions on the parameters that may be
282 * passed to {@code Proxy.getProxyClass}:
283 *
284 * <ul>
285 * <li>All of the {@code Class} objects in the
286 * {@code interfaces} array must represent interfaces, not
287 * classes or primitive types.
288 *
289 * <li>No two elements in the {@code interfaces} array may
290 * refer to identical {@code Class} objects.
291 *
292 * <li>All of the interface types must be visible by name through the
293 * specified class loader. In other words, for class loader
294 * {@code cl} and every interface {@code i}, the following
295 * expression must be true:
296 * <pre>
297 * Class.forName(i.getName(), false, cl) == i
298 * </pre>
299 *
300 * <li>All non-public interfaces must be in the same package;
301 * otherwise, it would not be possible for the proxy class to
302 * implement all of the interfaces, regardless of what package it is
303 * defined in.
304 *
305 * <li>For any set of member methods of the specified interfaces
306 * that have the same signature:
307 * <ul>
308 * <li>If the return type of any of the methods is a primitive
309 * type or void, then all of the methods must have that same
310 * return type.
311 * <li>Otherwise, one of the methods must have a return type that
312 * is assignable to all of the return types of the rest of the
313 * methods.
314 * </ul>
315 *
316 * <li>The resulting proxy class must not exceed any limits imposed
317 * on classes by the virtual machine. For example, the VM may limit
318 * the number of interfaces that a class may implement to 65535; in
319 * that case, the size of the {@code interfaces} array must not
320 * exceed 65535.
321 * </ul>
322 *
323 * <p>If any of these restrictions are violated,
324 * {@code Proxy.getProxyClass} will throw an
325 * {@code IllegalArgumentException}. If the {@code interfaces}
326 * array argument or any of its elements are {@code null}, a
327 * {@code NullPointerException} will be thrown.
328 *
329 * <p>Note that the order of the specified proxy interfaces is
330 * significant: two requests for a proxy class with the same combination
331 * of interfaces but in a different order will result in two distinct
332 * proxy classes.
333 *
334 * @param loader the class loader to define the proxy class
335 * @param interfaces the list of interfaces for the proxy class
336 * to implement
337 * @return a proxy class that is defined in the specified class loader
338 * and that implements the specified interfaces
339 * @throws IllegalArgumentException if any of the restrictions on the
340 * parameters that may be passed to {@code getProxyClass}
341 * are violated
342 * @throws NullPointerException if the {@code interfaces} array
343 * argument or any of its elements are {@code null}
344 */
345 public static Class<?> getProxyClass(ClassLoader loader,
346 Class<?>... interfaces)
347 throws IllegalArgumentException
348 {
349 if (interfaces.length > 65535) {
350 throw new IllegalArgumentException("interface limit exceeded");
351 }
352
353 Class<?> proxyClass = null;
354
355 /* collect interface names to use as key for proxy class cache */
356 String[] interfaceNames = new String[interfaces.length];
357
358 // for detecting duplicates
359 Set<Class<?>> interfaceSet = new HashSet<>();
360
361 for (int i = 0; i < interfaces.length; i++) {
362 /*
363 * Verify that the class loader resolves the name of this
364 * interface to the same Class object.
365 */
366 String interfaceName = interfaces[i].getName();
367 Class<?> interfaceClass = null;
368 try {
369 interfaceClass = Class.forName(interfaceName, false, loader);
370 } catch (ClassNotFoundException e) {
371 }
372 if (interfaceClass != interfaces[i]) {
373 throw new IllegalArgumentException(
374 interfaces[i] + " is not visible from class loader");
375 }
376
377 /*
378 * Verify that the Class object actually represents an
379 * interface.
380 */
381 if (!interfaceClass.isInterface()) {
382 throw new IllegalArgumentException(
383 interfaceClass.getName() + " is not an interface");
384 }
385
386 /*
387 * Verify that this interface is not a duplicate.
388 */
389 if (interfaceSet.contains(interfaceClass)) {
390 throw new IllegalArgumentException(
391 "repeated interface: " + interfaceClass.getName());
392 }
393 interfaceSet.add(interfaceClass);
394
395 interfaceNames[i] = interfaceName;
396 }
397
398 /*
399 * Using string representations of the proxy interfaces as
400 * keys in the proxy class cache (instead of their Class
401 * objects) is sufficient because we require the proxy
402 * interfaces to be resolvable by name through the supplied
403 * class loader, and it has the advantage that using a string
404 * representation of a class makes for an implicit weak
405 * reference to the class.
406 */
407 List<String> key = Arrays.asList(interfaceNames);
408
409 /*
410 * Find or create the proxy class cache for the class loader.
411 */
412 Map<List<String>, Object> cache;
413 synchronized (loaderToCache) {
414 cache = loaderToCache.get(loader);
415 if (cache == null) {
416 cache = new HashMap<>();
417 loaderToCache.put(loader, cache);
418 }
419 /*
420 * This mapping will remain valid for the duration of this
421 * method, without further synchronization, because the mapping
422 * will only be removed if the class loader becomes unreachable.
423 */
424 }
425
426 /*
427 * Look up the list of interfaces in the proxy class cache using
428 * the key. This lookup will result in one of three possible
429 * kinds of values:
430 * null, if there is currently no proxy class for the list of
431 * interfaces in the class loader,
432 * the pendingGenerationMarker object, if a proxy class for the
433 * list of interfaces is currently being generated,
434 * or a weak reference to a Class object, if a proxy class for
435 * the list of interfaces has already been generated.
436 */
437 synchronized (cache) {
438 /*
439 * Note that we need not worry about reaping the cache for
440 * entries with cleared weak references because if a proxy class
441 * has been garbage collected, its class loader will have been
442 * garbage collected as well, so the entire cache will be reaped
443 * from the loaderToCache map.
444 */
445 do {
446 Object value = cache.get(key);
447 if (value instanceof Reference) {
448 proxyClass = (Class<?>) ((Reference) value).get();
449 }
450 if (proxyClass != null) {
451 // proxy class already generated: return it
452 return proxyClass;
453 } else if (value == pendingGenerationMarker) {
454 // proxy class being generated: wait for it
455 try {
456 cache.wait();
457 } catch (InterruptedException e) {
458 /*
459 * The class generation that we are waiting for should
460 * take a small, bounded time, so we can safely ignore
461 * thread interrupts here.
462 */
463 }
464 continue;
465 } else {
466 /*
467 * No proxy class for this list of interfaces has been
468 * generated or is being generated, so we will go and
469 * generate it now. Mark it as pending generation.
470 */
471 cache.put(key, pendingGenerationMarker);
472 break;
473 }
474 } while (true);
475 }
476
477 try {
478 String proxyPkg = null; // package to define proxy class in
479
480 /*
481 * Record the package of a non-public proxy interface so that the
482 * proxy class will be defined in the same package. Verify that
483 * all non-public proxy interfaces are in the same package.
484 */
485 for (int i = 0; i < interfaces.length; i++) {
486 int flags = interfaces[i].getModifiers();
487 if (!Modifier.isPublic(flags)) {
488 String name = interfaces[i].getName();
489 int n = name.lastIndexOf('.');
490 String pkg = ((n == -1) ? "" : name.substring(0, n + 1));
491 if (proxyPkg == null) {
492 proxyPkg = pkg;
493 } else if (!pkg.equals(proxyPkg)) {
494 throw new IllegalArgumentException(
495 "non-public interfaces from different packages");
496 }
497 }
498 }
499
500 if (proxyPkg == null) { // if no non-public proxy interfaces,
501 proxyPkg = ""; // use the unnamed package
502 }
503
504 {
505 /*
506 * Choose a name for the proxy class to generate.
507 */
508 long num;
509 synchronized (nextUniqueNumberLock) {
510 num = nextUniqueNumber++;
511 }
512 String proxyName = proxyPkg + proxyClassNamePrefix + num;
513 /*
514 * Verify that the class loader hasn't already
515 * defined a class with the chosen name.
516 */
517
518 /*
519 * Generate the specified proxy class.
520 */
521 byte[] proxyClassFile = ProxyGenerator.generateProxyClass(
522 proxyName, interfaces);
523 try {
524 proxyClass = defineClass0(loader, proxyName,
525 proxyClassFile, 0, proxyClassFile.length);
526 } catch (ClassFormatError e) {
527 /*
528 * A ClassFormatError here means that (barring bugs in the
529 * proxy class generation code) there was some other
530 * invalid aspect of the arguments supplied to the proxy
531 * class creation (such as virtual machine limitations
532 * exceeded).
533 */
534 throw new IllegalArgumentException(e.toString());
535 }
536 }
537 // add to set of all generated proxy classes, for isProxyClass
538 proxyClasses.put(proxyClass, null);
539
540 } finally {
541 /*
542 * We must clean up the "pending generation" state of the proxy
543 * class cache entry somehow. If a proxy class was successfully
544 * generated, store it in the cache (with a weak reference);
545 * otherwise, remove the reserved entry. In all cases, notify
546 * all waiters on reserved entries in this cache.
547 */
548 synchronized (cache) {
549 if (proxyClass != null) {
550 cache.put(key, new WeakReference<Class<?>>(proxyClass));
551 } else {
552 cache.remove(key);
553 }
554 cache.notifyAll();
555 }
556 }
557 return proxyClass;
558 }
559
560 /**
561 * Returns an instance of a proxy class for the specified interfaces
562 * that dispatches method invocations to the specified invocation
563 * handler. This method is equivalent to:
564 * <pre>
565 * Proxy.getProxyClass(loader, interfaces).
566 * getConstructor(new Class[] { InvocationHandler.class }).
567 * newInstance(new Object[] { handler });
568 * </pre>
569 *
570 * <p>{@code Proxy.newProxyInstance} throws
571 * {@code IllegalArgumentException} for the same reasons that
572 * {@code Proxy.getProxyClass} does.
573 *
574 * @param loader the class loader to define the proxy class
575 * @param interfaces the list of interfaces for the proxy class
576 * to implement
577 * @param h the invocation handler to dispatch method invocations to
578 * @return a proxy instance with the specified invocation handler of a
579 * proxy class that is defined by the specified class loader
580 * and that implements the specified interfaces
581 * @throws IllegalArgumentException if any of the restrictions on the
582 * parameters that may be passed to {@code getProxyClass}
583 * are violated
584 * @throws NullPointerException if the {@code interfaces} array
585 * argument or any of its elements are {@code null}, or
586 * if the invocation handler, {@code h}, is
587 * {@code null}
588 */
589 public static Object newProxyInstance(ClassLoader loader,
590 Class<?>[] interfaces,
591 InvocationHandler h)
592 throws IllegalArgumentException
593 {
594 if (h == null) {
595 throw new NullPointerException();
596 }
597
598 /*
599 * Look up or generate the designated proxy class.
600 */
601 Class<?> cl = getProxyClass(loader, interfaces);
602
603 /*
604 * Invoke its constructor with the designated invocation handler.
605 */
606 try {
607 Constructor cons = cl.getConstructor(constructorParams);
608 return cons.newInstance(new Object[] { h });
609 } catch (NoSuchMethodException e) {
610 throw new InternalError(e.toString());
611 } catch (IllegalAccessException e) {
612 throw new InternalError(e.toString());
613 } catch (InstantiationException e) {
614 throw new InternalError(e.toString());
615 } catch (InvocationTargetException e) {
616 throw new InternalError(e.toString());
617 }
618 }
619
620 /**
621 * Returns true if and only if the specified class was dynamically
622 * generated to be a proxy class using the {@code getProxyClass}
623 * method or the {@code newProxyInstance} method.
624 *
625 * <p>The reliability of this method is important for the ability
626 * to use it to make security decisions, so its implementation should
627 * not just test if the class in question extends {@code Proxy}.
628 *
629 * @param cl the class to test
630 * @return {@code true} if the class is a proxy class and
631 * {@code false} otherwise
632 * @throws NullPointerException if {@code cl} is {@code null}
633 */
634 public static boolean isProxyClass(Class<?> cl) {
635 if (cl == null) {
636 throw new NullPointerException();
637 }
638
639 return proxyClasses.containsKey(cl);
640 }
641
642 /**
643 * Returns the invocation handler for the specified proxy instance.
644 *
645 * @param proxy the proxy instance to return the invocation handler for
646 * @return the invocation handler for the proxy instance
647 * @throws IllegalArgumentException if the argument is not a
648 * proxy instance
649 */
650 public static InvocationHandler getInvocationHandler(Object proxy)
651 throws IllegalArgumentException
652 {
653 /*
654 * Verify that the object is actually a proxy instance.
655 */
656 if (!isProxyClass(proxy.getClass())) {
657 throw new IllegalArgumentException("not a proxy instance");
658 }
659
660 Proxy p = (Proxy) proxy;
661 return p.h;
662 }
663
664 private static native Class defineClass0(ClassLoader loader, String name,
665 byte[] b, int off, int len);
666 }