1 /*
2 * Copyright (c) 2013, 2020, Oracle and/or its affiliates. All rights reserved.
3 * Copyright (c) 2019, Azul Systems, Inc. All rights reserved.
4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
5 *
6 * This code is free software; you can redistribute it and/or modify it
7 * under the terms of the GNU General Public License version 2 only, as
8 * published by the Free Software Foundation. Oracle designates this
9 * particular file as subject to the "Classpath" exception as provided
10 * by Oracle in the LICENSE file that accompanied this code.
11 *
12 * This code is distributed in the hope that it will be useful, but WITHOUT
13 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
14 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
15 * version 2 for more details (a copy is included in the LICENSE file that
16 * accompanied this code).
17 *
18 * You should have received a copy of the GNU General Public License version
19 * 2 along with this work; if not, write to the Free Software Foundation,
20 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
21 *
22 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
23 * or visit www.oracle.com if you need additional information or have any
24 * questions.
25 */
26
27 package java.lang;
28
29 import java.io.InputStream;
30 import java.io.IOException;
31 import java.io.UncheckedIOException;
32 import java.io.File;
33 import java.lang.reflect.Constructor;
34 import java.lang.reflect.InvocationTargetException;
35 import java.net.URL;
36 import java.security.AccessController;
37 import java.security.AccessControlContext;
38 import java.security.CodeSource;
39 import java.security.PrivilegedAction;
40 import java.security.ProtectionDomain;
41 import java.security.cert.Certificate;
42 import java.util.ArrayList;
43 import java.util.Collections;
44 import java.util.Enumeration;
45 import java.util.HashMap;
46 import java.util.Map;
47 import java.util.NoSuchElementException;
48 import java.util.Objects;
49 import java.util.Set;
50 import java.util.Spliterator;
51 import java.util.Spliterators;
52 import java.util.WeakHashMap;
53 import java.util.concurrent.ConcurrentHashMap;
54 import java.util.function.Supplier;
55 import java.util.stream.Stream;
56 import java.util.stream.StreamSupport;
57
58 import jdk.internal.loader.BootLoader;
59 import jdk.internal.loader.BuiltinClassLoader;
60 import jdk.internal.loader.ClassLoaders;
61 import jdk.internal.loader.NativeLibrary;
62 import jdk.internal.loader.NativeLibraries;
63 import jdk.internal.perf.PerfCounter;
64 import jdk.internal.misc.Unsafe;
65 import jdk.internal.misc.VM;
66 import jdk.internal.reflect.CallerSensitive;
67 import jdk.internal.reflect.Reflection;
68 import jdk.internal.util.StaticProperty;
69 import sun.reflect.misc.ReflectUtil;
70 import sun.security.util.SecurityConstants;
71
72 /**
73 * A class loader is an object that is responsible for loading classes. The
74 * class {@code ClassLoader} is an abstract class. Given the <a
75 * href="#binary-name">binary name</a> of a class, a class loader should attempt to
76 * locate or generate data that constitutes a definition for the class. A
77 * typical strategy is to transform the name into a file name and then read a
78 * "class file" of that name from a file system.
79 *
80 * <p> Every {@link java.lang.Class Class} object contains a {@link
81 * Class#getClassLoader() reference} to the {@code ClassLoader} that defined
82 * it.
83 *
84 * <p> {@code Class} objects for array classes are not created by class
85 * loaders, but are created automatically as required by the Java runtime.
86 * The class loader for an array class, as returned by {@link
87 * Class#getClassLoader()} is the same as the class loader for its element
88 * type; if the element type is a primitive type, then the array class has no
89 * class loader.
90 *
91 * <p> Applications implement subclasses of {@code ClassLoader} in order to
92 * extend the manner in which the Java virtual machine dynamically loads
93 * classes.
94 *
95 * <p> Class loaders may typically be used by security managers to indicate
96 * security domains.
97 *
98 * <p> In addition to loading classes, a class loader is also responsible for
99 * locating resources. A resource is some data (a "{@code .class}" file,
100 * configuration data, or an image for example) that is identified with an
101 * abstract '/'-separated path name. Resources are typically packaged with an
102 * application or library so that they can be located by code in the
103 * application or library. In some cases, the resources are included so that
104 * they can be located by other libraries.
105 *
106 * <p> The {@code ClassLoader} class uses a delegation model to search for
107 * classes and resources. Each instance of {@code ClassLoader} has an
108 * associated parent class loader. When requested to find a class or
109 * resource, a {@code ClassLoader} instance will usually delegate the search
110 * for the class or resource to its parent class loader before attempting to
111 * find the class or resource itself.
112 *
113 * <p> Class loaders that support concurrent loading of classes are known as
114 * <em>{@linkplain #isRegisteredAsParallelCapable() parallel capable}</em> class
115 * loaders and are required to register themselves at their class initialization
116 * time by invoking the {@link
117 * #registerAsParallelCapable ClassLoader.registerAsParallelCapable}
118 * method. Note that the {@code ClassLoader} class is registered as parallel
119 * capable by default. However, its subclasses still need to register themselves
120 * if they are parallel capable.
121 * In environments in which the delegation model is not strictly
122 * hierarchical, class loaders need to be parallel capable, otherwise class
123 * loading can lead to deadlocks because the loader lock is held for the
124 * duration of the class loading process (see {@link #loadClass
125 * loadClass} methods).
126 *
127 * <h2> <a id="builtinLoaders">Run-time Built-in Class Loaders</a></h2>
128 *
129 * The Java run-time has the following built-in class loaders:
130 *
131 * <ul>
132 * <li><p>Bootstrap class loader.
133 * It is the virtual machine's built-in class loader, typically represented
134 * as {@code null}, and does not have a parent.</li>
135 * <li><p>{@linkplain #getPlatformClassLoader() Platform class loader}.
136 * All <em>platform classes</em> are visible to the platform class loader
137 * that can be used as the parent of a {@code ClassLoader} instance.
138 * Platform classes include Java SE platform APIs, their implementation
139 * classes and JDK-specific run-time classes that are defined by the
140 * platform class loader or its ancestors.
141 * <p> To allow for upgrading/overriding of modules defined to the platform
142 * class loader, and where upgraded modules read modules defined to class
143 * loaders other than the platform class loader and its ancestors, then
144 * the platform class loader may have to delegate to other class loaders,
145 * the application class loader for example.
146 * In other words, classes in named modules defined to class loaders
147 * other than the platform class loader and its ancestors may be visible
148 * to the platform class loader. </li>
149 * <li><p>{@linkplain #getSystemClassLoader() System class loader}.
150 * It is also known as <em>application class loader</em> and is distinct
151 * from the platform class loader.
152 * The system class loader is typically used to define classes on the
153 * application class path, module path, and JDK-specific tools.
154 * The platform class loader is a parent or an ancestor of the system class
155 * loader that all platform classes are visible to it.</li>
156 * </ul>
157 *
158 * <p> Normally, the Java virtual machine loads classes from the local file
159 * system in a platform-dependent manner.
160 * However, some classes may not originate from a file; they may originate
161 * from other sources, such as the network, or they could be constructed by an
162 * application. The method {@link #defineClass(String, byte[], int, int)
163 * defineClass} converts an array of bytes into an instance of class
164 * {@code Class}. Instances of this newly defined class can be created using
165 * {@link Class#newInstance Class.newInstance}.
166 *
167 * <p> The methods and constructors of objects created by a class loader may
168 * reference other classes. To determine the class(es) referred to, the Java
169 * virtual machine invokes the {@link #loadClass loadClass} method of
170 * the class loader that originally created the class.
171 *
172 * <p> For example, an application could create a network class loader to
173 * download class files from a server. Sample code might look like:
174 *
175 * <blockquote><pre>
176 * ClassLoader loader = new NetworkClassLoader(host, port);
177 * Object main = loader.loadClass("Main", true).newInstance();
178 * . . .
179 * </pre></blockquote>
180 *
181 * <p> The network class loader subclass must define the methods {@link
182 * #findClass findClass} and {@code loadClassData} to load a class
183 * from the network. Once it has downloaded the bytes that make up the class,
184 * it should use the method {@link #defineClass defineClass} to
185 * create a class instance. A sample implementation is:
186 *
187 * <blockquote><pre>
188 * class NetworkClassLoader extends ClassLoader {
189 * String host;
190 * int port;
191 *
192 * public Class findClass(String name) {
193 * byte[] b = loadClassData(name);
194 * return defineClass(name, b, 0, b.length);
195 * }
196 *
197 * private byte[] loadClassData(String name) {
198 * // load the class data from the connection
199 * . . .
200 * }
201 * }
202 * </pre></blockquote>
203 *
204 * <h3> <a id="binary-name">Binary names</a> </h3>
205 *
206 * <p> Any class name provided as a {@code String} parameter to methods in
207 * {@code ClassLoader} must be a binary name as defined by
208 * <cite>The Java™ Language Specification</cite>.
209 *
210 * <p> Examples of valid class names include:
211 * <blockquote><pre>
212 * "java.lang.String"
213 * "javax.swing.JSpinner$DefaultEditor"
214 * "java.security.KeyStore$Builder$FileBuilder$1"
215 * "java.net.URLClassLoader$3$1"
216 * </pre></blockquote>
217 *
218 * <p> Any package name provided as a {@code String} parameter to methods in
219 * {@code ClassLoader} must be either the empty string (denoting an unnamed package)
220 * or a fully qualified name as defined by
221 * <cite>The Java™ Language Specification</cite>.
222 *
223 * @jls 6.7 Fully Qualified Names
224 * @jls 13.1 The Form of a Binary
225 * @see #resolveClass(Class)
226 * @since 1.0
227 * @revised 9
228 * @spec JPMS
229 */
230 public abstract class ClassLoader {
231
232 private static native void registerNatives();
233 static {
234 registerNatives();
235 }
236
237 // The parent class loader for delegation
238 // Note: VM hardcoded the offset of this field, thus all new fields
239 // must be added *after* it.
240 private final ClassLoader parent;
241
242 // class loader name
243 private final String name;
244
245 // the unnamed module for this ClassLoader
246 private final Module unnamedModule;
247
248 // a string for exception message printing
249 private final String nameAndId;
250
251 /**
252 * Encapsulates the set of parallel capable loader types.
253 */
254 private static class ParallelLoaders {
255 private ParallelLoaders() {}
256
257 // the set of parallel capable loader types
258 private static final Set<Class<? extends ClassLoader>> loaderTypes =
259 Collections.newSetFromMap(new WeakHashMap<>());
260 static {
261 synchronized (loaderTypes) { loaderTypes.add(ClassLoader.class); }
262 }
263
264 /**
265 * Registers the given class loader type as parallel capable.
266 * Returns {@code true} is successfully registered; {@code false} if
267 * loader's super class is not registered.
268 */
269 static boolean register(Class<? extends ClassLoader> c) {
270 synchronized (loaderTypes) {
271 if (loaderTypes.contains(c.getSuperclass())) {
272 // register the class loader as parallel capable
273 // if and only if all of its super classes are.
274 // Note: given current classloading sequence, if
275 // the immediate super class is parallel capable,
276 // all the super classes higher up must be too.
277 loaderTypes.add(c);
278 return true;
279 } else {
280 return false;
281 }
282 }
283 }
284
285 /**
286 * Returns {@code true} if the given class loader type is
287 * registered as parallel capable.
288 */
289 static boolean isRegistered(Class<? extends ClassLoader> c) {
290 synchronized (loaderTypes) {
291 return loaderTypes.contains(c);
292 }
293 }
294 }
295
296 // Maps class name to the corresponding lock object when the current
297 // class loader is parallel capable.
298 // Note: VM also uses this field to decide if the current class loader
299 // is parallel capable and the appropriate lock object for class loading.
300 private final ConcurrentHashMap<String, Object> parallelLockMap;
301
302 // Maps packages to certs
303 private final ConcurrentHashMap<String, Certificate[]> package2certs;
304
305 // Shared among all packages with unsigned classes
306 private static final Certificate[] nocerts = new Certificate[0];
307
308 // The classes loaded by this class loader. The only purpose of this table
309 // is to keep the classes from being GC'ed until the loader is GC'ed.
310 private final ArrayList<Class<?>> classes = new ArrayList<>();
311
312 // The "default" domain. Set as the default ProtectionDomain on newly
313 // created classes.
314 private final ProtectionDomain defaultDomain =
315 new ProtectionDomain(new CodeSource(null, (Certificate[]) null),
316 null, this, null);
317
318 // Invoked by the VM to record every loaded class with this loader.
319 void addClass(Class<?> c) {
320 synchronized (classes) {
321 classes.add(c);
322 }
323 }
324
325 // The packages defined in this class loader. Each package name is
326 // mapped to its corresponding NamedPackage object.
327 //
328 // The value is a Package object if ClassLoader::definePackage,
329 // Class::getPackage, ClassLoader::getDefinePackage(s) or
330 // Package::getPackage(s) method is called to define it.
331 // Otherwise, the value is a NamedPackage object.
332 private final ConcurrentHashMap<String, NamedPackage> packages
333 = new ConcurrentHashMap<>();
334
335 /*
336 * Returns a named package for the given module.
337 */
338 private NamedPackage getNamedPackage(String pn, Module m) {
339 NamedPackage p = packages.get(pn);
340 if (p == null) {
341 p = new NamedPackage(pn, m);
342
343 NamedPackage value = packages.putIfAbsent(pn, p);
344 if (value != null) {
345 // Package object already be defined for the named package
346 p = value;
347 // if definePackage is called by this class loader to define
348 // a package in a named module, this will return Package
349 // object of the same name. Package object may contain
350 // unexpected information but it does not impact the runtime.
351 // this assertion may be helpful for troubleshooting
352 assert value.module() == m;
353 }
354 }
355 return p;
356 }
357
358 private static Void checkCreateClassLoader() {
359 return checkCreateClassLoader(null);
360 }
361
362 private static Void checkCreateClassLoader(String name) {
363 if (name != null && name.isEmpty()) {
364 throw new IllegalArgumentException("name must be non-empty or null");
365 }
366
367 SecurityManager security = System.getSecurityManager();
368 if (security != null) {
369 security.checkCreateClassLoader();
370 }
371 return null;
372 }
373
374 private ClassLoader(Void unused, String name, ClassLoader parent) {
375 this.name = name;
376 this.parent = parent;
377 this.unnamedModule = new Module(this);
378 if (ParallelLoaders.isRegistered(this.getClass())) {
379 parallelLockMap = new ConcurrentHashMap<>();
380 assertionLock = new Object();
381 } else {
382 // no finer-grained lock; lock on the classloader instance
383 parallelLockMap = null;
384 assertionLock = this;
385 }
386 this.package2certs = new ConcurrentHashMap<>();
387 this.nameAndId = nameAndId(this);
388 }
389
390 /**
391 * If the defining loader has a name explicitly set then
392 * '<loader-name>' @<id>
393 * If the defining loader has no name then
394 * <qualified-class-name> @<id>
395 * If it's built-in loader then omit `@<id>` as there is only one instance.
396 */
397 private static String nameAndId(ClassLoader ld) {
398 String nid = ld.getName() != null ? "\'" + ld.getName() + "\'"
399 : ld.getClass().getName();
400 if (!(ld instanceof BuiltinClassLoader)) {
401 String id = Integer.toHexString(System.identityHashCode(ld));
402 nid = nid + " @" + id;
403 }
404 return nid;
405 }
406
407 /**
408 * Creates a new class loader of the specified name and using the
409 * specified parent class loader for delegation.
410 *
411 * @apiNote If the parent is specified as {@code null} (for the
412 * bootstrap class loader) then there is no guarantee that all platform
413 * classes are visible.
414 *
415 * @param name class loader name; or {@code null} if not named
416 * @param parent the parent class loader
417 *
418 * @throws IllegalArgumentException if the given name is empty.
419 *
420 * @throws SecurityException
421 * If a security manager exists and its
422 * {@link SecurityManager#checkCreateClassLoader()}
423 * method doesn't allow creation of a new class loader.
424 *
425 * @since 9
426 * @spec JPMS
427 */
428 protected ClassLoader(String name, ClassLoader parent) {
429 this(checkCreateClassLoader(name), name, parent);
430 }
431
432 /**
433 * Creates a new class loader using the specified parent class loader for
434 * delegation.
435 *
436 * <p> If there is a security manager, its {@link
437 * SecurityManager#checkCreateClassLoader() checkCreateClassLoader} method
438 * is invoked. This may result in a security exception. </p>
439 *
440 * @apiNote If the parent is specified as {@code null} (for the
441 * bootstrap class loader) then there is no guarantee that all platform
442 * classes are visible.
443 *
444 * @param parent
445 * The parent class loader
446 *
447 * @throws SecurityException
448 * If a security manager exists and its
449 * {@code checkCreateClassLoader} method doesn't allow creation
450 * of a new class loader.
451 *
452 * @since 1.2
453 */
454 protected ClassLoader(ClassLoader parent) {
455 this(checkCreateClassLoader(), null, parent);
456 }
457
458 /**
459 * Creates a new class loader using the {@code ClassLoader} returned by
460 * the method {@link #getSystemClassLoader()
461 * getSystemClassLoader()} as the parent class loader.
462 *
463 * <p> If there is a security manager, its {@link
464 * SecurityManager#checkCreateClassLoader()
465 * checkCreateClassLoader} method is invoked. This may result in
466 * a security exception. </p>
467 *
468 * @throws SecurityException
469 * If a security manager exists and its
470 * {@code checkCreateClassLoader} method doesn't allow creation
471 * of a new class loader.
472 */
473 protected ClassLoader() {
474 this(checkCreateClassLoader(), null, getSystemClassLoader());
475 }
476
477 /**
478 * Returns the name of this class loader or {@code null} if
479 * this class loader is not named.
480 *
481 * @apiNote This method is non-final for compatibility. If this
482 * method is overridden, this method must return the same name
483 * as specified when this class loader was instantiated.
484 *
485 * @return name of this class loader; or {@code null} if
486 * this class loader is not named.
487 *
488 * @since 9
489 * @spec JPMS
490 */
491 public String getName() {
492 return name;
493 }
494
495 // package-private used by StackTraceElement to avoid
496 // calling the overrideable getName method
497 final String name() {
498 return name;
499 }
500
501 // -- Class --
502
503 /**
504 * Loads the class with the specified <a href="#binary-name">binary name</a>.
505 * This method searches for classes in the same manner as the {@link
506 * #loadClass(String, boolean)} method. It is invoked by the Java virtual
507 * machine to resolve class references. Invoking this method is equivalent
508 * to invoking {@link #loadClass(String, boolean) loadClass(name,
509 * false)}.
510 *
511 * @param name
512 * The <a href="#binary-name">binary name</a> of the class
513 *
514 * @return The resulting {@code Class} object
515 *
516 * @throws ClassNotFoundException
517 * If the class was not found
518 */
519 public Class<?> loadClass(String name) throws ClassNotFoundException {
520 return loadClass(name, false);
521 }
522
523 /**
524 * Loads the class with the specified <a href="#binary-name">binary name</a>. The
525 * default implementation of this method searches for classes in the
526 * following order:
527 *
528 * <ol>
529 *
530 * <li><p> Invoke {@link #findLoadedClass(String)} to check if the class
531 * has already been loaded. </p></li>
532 *
533 * <li><p> Invoke the {@link #loadClass(String) loadClass} method
534 * on the parent class loader. If the parent is {@code null} the class
535 * loader built into the virtual machine is used, instead. </p></li>
536 *
537 * <li><p> Invoke the {@link #findClass(String)} method to find the
538 * class. </p></li>
539 *
540 * </ol>
541 *
542 * <p> If the class was found using the above steps, and the
543 * {@code resolve} flag is true, this method will then invoke the {@link
544 * #resolveClass(Class)} method on the resulting {@code Class} object.
545 *
546 * <p> Subclasses of {@code ClassLoader} are encouraged to override {@link
547 * #findClass(String)}, rather than this method. </p>
548 *
549 * <p> Unless overridden, this method synchronizes on the result of
550 * {@link #getClassLoadingLock getClassLoadingLock} method
551 * during the entire class loading process.
552 *
553 * @param name
554 * The <a href="#binary-name">binary name</a> of the class
555 *
556 * @param resolve
557 * If {@code true} then resolve the class
558 *
559 * @return The resulting {@code Class} object
560 *
561 * @throws ClassNotFoundException
562 * If the class could not be found
563 */
564 protected Class<?> loadClass(String name, boolean resolve)
565 throws ClassNotFoundException
566 {
567 synchronized (getClassLoadingLock(name)) {
568 // First, check if the class has already been loaded
569 Class<?> c = findLoadedClass(name);
570 if (c == null) {
571 long t0 = System.nanoTime();
572 try {
573 if (parent != null) {
574 c = parent.loadClass(name, false);
575 } else {
576 c = findBootstrapClassOrNull(name);
577 }
578 } catch (ClassNotFoundException e) {
579 // ClassNotFoundException thrown if class not found
580 // from the non-null parent class loader
581 }
582
583 if (c == null) {
584 // If still not found, then invoke findClass in order
585 // to find the class.
586 long t1 = System.nanoTime();
587 c = findClass(name);
588
589 // this is the defining class loader; record the stats
590 PerfCounter.getParentDelegationTime().addTime(t1 - t0);
591 PerfCounter.getFindClassTime().addElapsedTimeFrom(t1);
592 PerfCounter.getFindClasses().increment();
593 }
594 }
595 if (resolve) {
596 resolveClass(c);
597 }
598 return c;
599 }
600 }
601
602 /**
603 * Loads the class with the specified <a href="#binary-name">binary name</a>
604 * in a module defined to this class loader. This method returns {@code null}
605 * if the class could not be found.
606 *
607 * @apiNote This method does not delegate to the parent class loader.
608 *
609 * @implSpec The default implementation of this method searches for classes
610 * in the following order:
611 *
612 * <ol>
613 * <li>Invoke {@link #findLoadedClass(String)} to check if the class
614 * has already been loaded.</li>
615 * <li>Invoke the {@link #findClass(String, String)} method to find the
616 * class in the given module.</li>
617 * </ol>
618 *
619 * @param module
620 * The module
621 * @param name
622 * The <a href="#binary-name">binary name</a> of the class
623 *
624 * @return The resulting {@code Class} object in a module defined by
625 * this class loader, or {@code null} if the class could not be found.
626 */
627 final Class<?> loadClass(Module module, String name) {
628 synchronized (getClassLoadingLock(name)) {
629 // First, check if the class has already been loaded
630 Class<?> c = findLoadedClass(name);
631 if (c == null) {
632 c = findClass(module.getName(), name);
633 }
634 if (c != null && c.getModule() == module) {
635 return c;
636 } else {
637 return null;
638 }
639 }
640 }
641
642 /**
643 * Returns the lock object for class loading operations.
644 * For backward compatibility, the default implementation of this method
645 * behaves as follows. If this ClassLoader object is registered as
646 * parallel capable, the method returns a dedicated object associated
647 * with the specified class name. Otherwise, the method returns this
648 * ClassLoader object.
649 *
650 * @param className
651 * The name of the to-be-loaded class
652 *
653 * @return the lock for class loading operations
654 *
655 * @throws NullPointerException
656 * If registered as parallel capable and {@code className} is null
657 *
658 * @see #loadClass(String, boolean)
659 *
660 * @since 1.7
661 */
662 protected Object getClassLoadingLock(String className) {
663 Object lock = this;
664 if (parallelLockMap != null) {
665 Object newLock = new Object();
666 lock = parallelLockMap.putIfAbsent(className, newLock);
667 if (lock == null) {
668 lock = newLock;
669 }
670 }
671 return lock;
672 }
673
674 // Invoked by the VM after loading class with this loader.
675 private void checkPackageAccess(Class<?> cls, ProtectionDomain pd) {
676 final SecurityManager sm = System.getSecurityManager();
677 if (sm != null) {
678 if (ReflectUtil.isNonPublicProxyClass(cls)) {
679 for (Class<?> intf: cls.getInterfaces()) {
680 checkPackageAccess(intf, pd);
681 }
682 return;
683 }
684
685 final String packageName = cls.getPackageName();
686 if (!packageName.isEmpty()) {
687 AccessController.doPrivileged(new PrivilegedAction<>() {
688 public Void run() {
689 sm.checkPackageAccess(packageName);
690 return null;
691 }
692 }, new AccessControlContext(new ProtectionDomain[] {pd}));
693 }
694 }
695 }
696
697 /**
698 * Finds the class with the specified <a href="#binary-name">binary name</a>.
699 * This method should be overridden by class loader implementations that
700 * follow the delegation model for loading classes, and will be invoked by
701 * the {@link #loadClass loadClass} method after checking the
702 * parent class loader for the requested class.
703 *
704 * @implSpec The default implementation throws {@code ClassNotFoundException}.
705 *
706 * @param name
707 * The <a href="#binary-name">binary name</a> of the class
708 *
709 * @return The resulting {@code Class} object
710 *
711 * @throws ClassNotFoundException
712 * If the class could not be found
713 *
714 * @since 1.2
715 */
716 protected Class<?> findClass(String name) throws ClassNotFoundException {
717 throw new ClassNotFoundException(name);
718 }
719
720 /**
721 * Finds the class with the given <a href="#binary-name">binary name</a>
722 * in a module defined to this class loader.
723 * Class loader implementations that support loading from modules
724 * should override this method.
725 *
726 * @apiNote This method returns {@code null} rather than throwing
727 * {@code ClassNotFoundException} if the class could not be found.
728 *
729 * @implSpec The default implementation attempts to find the class by
730 * invoking {@link #findClass(String)} when the {@code moduleName} is
731 * {@code null}. It otherwise returns {@code null}.
732 *
733 * @param moduleName
734 * The module name; or {@code null} to find the class in the
735 * {@linkplain #getUnnamedModule() unnamed module} for this
736 * class loader
737
738 * @param name
739 * The <a href="#binary-name">binary name</a> of the class
740 *
741 * @return The resulting {@code Class} object, or {@code null}
742 * if the class could not be found.
743 *
744 * @since 9
745 * @spec JPMS
746 */
747 protected Class<?> findClass(String moduleName, String name) {
748 if (moduleName == null) {
749 try {
750 return findClass(name);
751 } catch (ClassNotFoundException ignore) { }
752 }
753 return null;
754 }
755
756
757 /**
758 * Converts an array of bytes into an instance of class {@code Class}.
759 * Before the {@code Class} can be used it must be resolved. This method
760 * is deprecated in favor of the version that takes a <a
761 * href="#binary-name">binary name</a> as its first argument, and is more secure.
762 *
763 * @param b
764 * The bytes that make up the class data. The bytes in positions
765 * {@code off} through {@code off+len-1} should have the format
766 * of a valid class file as defined by
767 * <cite>The Java™ Virtual Machine Specification</cite>.
768 *
769 * @param off
770 * The start offset in {@code b} of the class data
771 *
772 * @param len
773 * The length of the class data
774 *
775 * @return The {@code Class} object that was created from the specified
776 * class data
777 *
778 * @throws ClassFormatError
779 * If the data did not contain a valid class
780 *
781 * @throws IndexOutOfBoundsException
782 * If either {@code off} or {@code len} is negative, or if
783 * {@code off+len} is greater than {@code b.length}.
784 *
785 * @throws SecurityException
786 * If an attempt is made to add this class to a package that
787 * contains classes that were signed by a different set of
788 * certificates than this class, or if an attempt is made
789 * to define a class in a package with a fully-qualified name
790 * that starts with "{@code java.}".
791 *
792 * @see #loadClass(String, boolean)
793 * @see #resolveClass(Class)
794 *
795 * @deprecated Replaced by {@link #defineClass(String, byte[], int, int)
796 * defineClass(String, byte[], int, int)}
797 */
798 @Deprecated(since="1.1")
799 protected final Class<?> defineClass(byte[] b, int off, int len)
800 throws ClassFormatError
801 {
802 return defineClass(null, b, off, len, null);
803 }
804
805 /**
806 * Converts an array of bytes into an instance of class {@code Class}.
807 * Before the {@code Class} can be used it must be resolved.
808 *
809 * <p> This method assigns a default {@link java.security.ProtectionDomain
810 * ProtectionDomain} to the newly defined class. The
811 * {@code ProtectionDomain} is effectively granted the same set of
812 * permissions returned when {@link
813 * java.security.Policy#getPermissions(java.security.CodeSource)
814 * Policy.getPolicy().getPermissions(new CodeSource(null, null))}
815 * is invoked. The default protection domain is created on the first invocation
816 * of {@link #defineClass(String, byte[], int, int) defineClass},
817 * and re-used on subsequent invocations.
818 *
819 * <p> To assign a specific {@code ProtectionDomain} to the class, use
820 * the {@link #defineClass(String, byte[], int, int,
821 * java.security.ProtectionDomain) defineClass} method that takes a
822 * {@code ProtectionDomain} as one of its arguments. </p>
823 *
824 * <p>
825 * This method defines a package in this class loader corresponding to the
826 * package of the {@code Class} (if such a package has not already been defined
827 * in this class loader). The name of the defined package is derived from
828 * the <a href="#binary-name">binary name</a> of the class specified by
829 * the byte array {@code b}.
830 * Other properties of the defined package are as specified by {@link Package}.
831 *
832 * @param name
833 * The expected <a href="#binary-name">binary name</a> of the class, or
834 * {@code null} if not known
835 *
836 * @param b
837 * The bytes that make up the class data. The bytes in positions
838 * {@code off} through {@code off+len-1} should have the format
839 * of a valid class file as defined by
840 * <cite>The Java™ Virtual Machine Specification</cite>.
841 *
842 * @param off
843 * The start offset in {@code b} of the class data
844 *
845 * @param len
846 * The length of the class data
847 *
848 * @return The {@code Class} object that was created from the specified
849 * class data.
850 *
851 * @throws ClassFormatError
852 * If the data did not contain a valid class
853 *
854 * @throws IndexOutOfBoundsException
855 * If either {@code off} or {@code len} is negative, or if
856 * {@code off+len} is greater than {@code b.length}.
857 *
858 * @throws SecurityException
859 * If an attempt is made to add this class to a package that
860 * contains classes that were signed by a different set of
861 * certificates than this class (which is unsigned), or if
862 * {@code name} begins with "{@code java.}".
863 *
864 * @see #loadClass(String, boolean)
865 * @see #resolveClass(Class)
866 * @see java.security.CodeSource
867 * @see java.security.SecureClassLoader
868 *
869 * @since 1.1
870 * @revised 9
871 * @spec JPMS
872 */
873 protected final Class<?> defineClass(String name, byte[] b, int off, int len)
874 throws ClassFormatError
875 {
876 return defineClass(name, b, off, len, null);
877 }
878
879 /* Determine protection domain, and check that:
880 - not define java.* class,
881 - signer of this class matches signers for the rest of the classes in
882 package.
883 */
884 private ProtectionDomain preDefineClass(String name,
885 ProtectionDomain pd)
886 {
887 if (!checkName(name))
888 throw new NoClassDefFoundError("IllegalName: " + name);
889
890 // Note: Checking logic in java.lang.invoke.MemberName.checkForTypeAlias
891 // relies on the fact that spoofing is impossible if a class has a name
892 // of the form "java.*"
893 if ((name != null) && name.startsWith("java.")
894 && this != getBuiltinPlatformClassLoader()) {
895 throw new SecurityException
896 ("Prohibited package name: " +
897 name.substring(0, name.lastIndexOf('.')));
898 }
899 if (pd == null) {
900 pd = defaultDomain;
901 }
902
903 if (name != null) {
904 checkCerts(name, pd.getCodeSource());
905 }
906
907 return pd;
908 }
909
910 private String defineClassSourceLocation(ProtectionDomain pd) {
911 CodeSource cs = pd.getCodeSource();
912 String source = null;
913 if (cs != null && cs.getLocation() != null) {
914 source = cs.getLocation().toString();
915 }
916 return source;
917 }
918
919 private void postDefineClass(Class<?> c, ProtectionDomain pd) {
920 // define a named package, if not present
921 getNamedPackage(c.getPackageName(), c.getModule());
922
923 if (pd.getCodeSource() != null) {
924 Certificate certs[] = pd.getCodeSource().getCertificates();
925 if (certs != null)
926 setSigners(c, certs);
927 }
928 }
929
930 /**
931 * Converts an array of bytes into an instance of class {@code Class},
932 * with a given {@code ProtectionDomain}.
933 *
934 * <p> If the given {@code ProtectionDomain} is {@code null},
935 * then a default protection domain will be assigned to the class as specified
936 * in the documentation for {@link #defineClass(String, byte[], int, int)}.
937 * Before the class can be used it must be resolved.
938 *
939 * <p> The first class defined in a package determines the exact set of
940 * certificates that all subsequent classes defined in that package must
941 * contain. The set of certificates for a class is obtained from the
942 * {@link java.security.CodeSource CodeSource} within the
943 * {@code ProtectionDomain} of the class. Any classes added to that
944 * package must contain the same set of certificates or a
945 * {@code SecurityException} will be thrown. Note that if
946 * {@code name} is {@code null}, this check is not performed.
947 * You should always pass in the <a href="#binary-name">binary name</a> of the
948 * class you are defining as well as the bytes. This ensures that the
949 * class you are defining is indeed the class you think it is.
950 *
951 * <p> If the specified {@code name} begins with "{@code java.}", it can
952 * only be defined by the {@linkplain #getPlatformClassLoader()
953 * platform class loader} or its ancestors; otherwise {@code SecurityException}
954 * will be thrown. If {@code name} is not {@code null}, it must be equal to
955 * the <a href="#binary-name">binary name</a> of the class
956 * specified by the byte array {@code b}, otherwise a {@link
957 * NoClassDefFoundError NoClassDefFoundError} will be thrown.
958 *
959 * <p> This method defines a package in this class loader corresponding to the
960 * package of the {@code Class} (if such a package has not already been defined
961 * in this class loader). The name of the defined package is derived from
962 * the <a href="#binary-name">binary name</a> of the class specified by
963 * the byte array {@code b}.
964 * Other properties of the defined package are as specified by {@link Package}.
965 *
966 * @param name
967 * The expected <a href="#binary-name">binary name</a> of the class, or
968 * {@code null} if not known
969 *
970 * @param b
971 * The bytes that make up the class data. The bytes in positions
972 * {@code off} through {@code off+len-1} should have the format
973 * of a valid class file as defined by
974 * <cite>The Java™ Virtual Machine Specification</cite>.
975 *
976 * @param off
977 * The start offset in {@code b} of the class data
978 *
979 * @param len
980 * The length of the class data
981 *
982 * @param protectionDomain
983 * The {@code ProtectionDomain} of the class
984 *
985 * @return The {@code Class} object created from the data,
986 * and {@code ProtectionDomain}.
987 *
988 * @throws ClassFormatError
989 * If the data did not contain a valid class
990 *
991 * @throws NoClassDefFoundError
992 * If {@code name} is not {@code null} and not equal to the
993 * <a href="#binary-name">binary name</a> of the class specified by {@code b}
994 *
995 * @throws IndexOutOfBoundsException
996 * If either {@code off} or {@code len} is negative, or if
997 * {@code off+len} is greater than {@code b.length}.
998 *
999 * @throws SecurityException
1000 * If an attempt is made to add this class to a package that
1001 * contains classes that were signed by a different set of
1002 * certificates than this class, or if {@code name} begins with
1003 * "{@code java.}" and this class loader is not the platform
1004 * class loader or its ancestor.
1005 *
1006 * @revised 9
1007 * @spec JPMS
1008 */
1009 protected final Class<?> defineClass(String name, byte[] b, int off, int len,
1010 ProtectionDomain protectionDomain)
1011 throws ClassFormatError
1012 {
1013 protectionDomain = preDefineClass(name, protectionDomain);
1014 String source = defineClassSourceLocation(protectionDomain);
1015 Class<?> c = defineClass1(this, name, b, off, len, protectionDomain, source);
1016 postDefineClass(c, protectionDomain);
1017 return c;
1018 }
1019
1020 /**
1021 * Converts a {@link java.nio.ByteBuffer ByteBuffer} into an instance
1022 * of class {@code Class}, with the given {@code ProtectionDomain}.
1023 * If the given {@code ProtectionDomain} is {@code null}, then a default
1024 * protection domain will be assigned to the class as
1025 * specified in the documentation for {@link #defineClass(String, byte[],
1026 * int, int)}. Before the class can be used it must be resolved.
1027 *
1028 * <p>The rules about the first class defined in a package determining the
1029 * set of certificates for the package, the restrictions on class names,
1030 * and the defined package of the class
1031 * are identical to those specified in the documentation for {@link
1032 * #defineClass(String, byte[], int, int, ProtectionDomain)}.
1033 *
1034 * <p> An invocation of this method of the form
1035 * <i>cl</i>{@code .defineClass(}<i>name</i>{@code ,}
1036 * <i>bBuffer</i>{@code ,} <i>pd</i>{@code )} yields exactly the same
1037 * result as the statements
1038 *
1039 *<p> <code>
1040 * ...<br>
1041 * byte[] temp = new byte[bBuffer.{@link
1042 * java.nio.ByteBuffer#remaining remaining}()];<br>
1043 * bBuffer.{@link java.nio.ByteBuffer#get(byte[])
1044 * get}(temp);<br>
1045 * return {@link #defineClass(String, byte[], int, int, ProtectionDomain)
1046 * cl.defineClass}(name, temp, 0,
1047 * temp.length, pd);<br>
1048 * </code></p>
1049 *
1050 * @param name
1051 * The expected <a href="#binary-name">binary name</a>. of the class, or
1052 * {@code null} if not known
1053 *
1054 * @param b
1055 * The bytes that make up the class data. The bytes from positions
1056 * {@code b.position()} through {@code b.position() + b.limit() -1
1057 * } should have the format of a valid class file as defined by
1058 * <cite>The Java™ Virtual Machine Specification</cite>.
1059 *
1060 * @param protectionDomain
1061 * The {@code ProtectionDomain} of the class, or {@code null}.
1062 *
1063 * @return The {@code Class} object created from the data,
1064 * and {@code ProtectionDomain}.
1065 *
1066 * @throws ClassFormatError
1067 * If the data did not contain a valid class.
1068 *
1069 * @throws NoClassDefFoundError
1070 * If {@code name} is not {@code null} and not equal to the
1071 * <a href="#binary-name">binary name</a> of the class specified by {@code b}
1072 *
1073 * @throws SecurityException
1074 * If an attempt is made to add this class to a package that
1075 * contains classes that were signed by a different set of
1076 * certificates than this class, or if {@code name} begins with
1077 * "{@code java.}".
1078 *
1079 * @see #defineClass(String, byte[], int, int, ProtectionDomain)
1080 *
1081 * @since 1.5
1082 * @revised 9
1083 * @spec JPMS
1084 */
1085 protected final Class<?> defineClass(String name, java.nio.ByteBuffer b,
1086 ProtectionDomain protectionDomain)
1087 throws ClassFormatError
1088 {
1089 int len = b.remaining();
1090
1091 // Use byte[] if not a direct ByteBuffer:
1092 if (!b.isDirect()) {
1093 if (b.hasArray()) {
1094 return defineClass(name, b.array(),
1095 b.position() + b.arrayOffset(), len,
1096 protectionDomain);
1097 } else {
1098 // no array, or read-only array
1099 byte[] tb = new byte[len];
1100 b.get(tb); // get bytes out of byte buffer.
1101 return defineClass(name, tb, 0, len, protectionDomain);
1102 }
1103 }
1104
1105 protectionDomain = preDefineClass(name, protectionDomain);
1106 String source = defineClassSourceLocation(protectionDomain);
1107 Class<?> c = defineClass2(this, name, b, b.position(), len, protectionDomain, source);
1108 postDefineClass(c, protectionDomain);
1109 return c;
1110 }
1111
1112 static native Class<?> defineClass1(ClassLoader loader, String name, byte[] b, int off, int len,
1113 ProtectionDomain pd, String source);
1114
1115 static native Class<?> defineClass2(ClassLoader loader, String name, java.nio.ByteBuffer b,
1116 int off, int len, ProtectionDomain pd,
1117 String source);
1118
1119 /**
1120 * Defines a class of the given flags via Lookup.defineClass.
1121 *
1122 * @param loader the defining loader
1123 * @param lookup nest host of the Class to be defined
1124 * @param name the binary name or {@code null} if not findable
1125 * @param b class bytes
1126 * @param off the start offset in {@code b} of the class bytes
1127 * @param len the length of the class bytes
1128 * @param pd protection domain
1129 * @param initialize initialize the class
1130 * @param flags flags
1131 * @param classData class data
1132 */
1133 static native Class<?> defineClass0(ClassLoader loader,
1134 Class<?> lookup,
1135 String name,
1136 byte[] b, int off, int len,
1137 ProtectionDomain pd,
1138 boolean initialize,
1139 int flags,
1140 Object classData);
1141
1142 // true if the name is null or has the potential to be a valid binary name
1143 private boolean checkName(String name) {
1144 if ((name == null) || (name.isEmpty()))
1145 return true;
1146 if ((name.indexOf('/') != -1) || (name.charAt(0) == '['))
1147 return false;
1148 return true;
1149 }
1150
1151 private void checkCerts(String name, CodeSource cs) {
1152 int i = name.lastIndexOf('.');
1153 String pname = (i == -1) ? "" : name.substring(0, i);
1154
1155 Certificate[] certs = null;
1156 if (cs != null) {
1157 certs = cs.getCertificates();
1158 }
1159 certs = certs == null ? nocerts : certs;
1160 Certificate[] pcerts = package2certs.putIfAbsent(pname, certs);
1161 if (pcerts != null && !compareCerts(pcerts, certs)) {
1162 throw new SecurityException("class \"" + name
1163 + "\"'s signer information does not match signer information"
1164 + " of other classes in the same package");
1165 }
1166 }
1167
1168 /**
1169 * check to make sure the certs for the new class (certs) are the same as
1170 * the certs for the first class inserted in the package (pcerts)
1171 */
1172 private boolean compareCerts(Certificate[] pcerts, Certificate[] certs) {
1173 // empty array fast-path
1174 if (certs.length == 0)
1175 return pcerts.length == 0;
1176
1177 // the length must be the same at this point
1178 if (certs.length != pcerts.length)
1179 return false;
1180
1181 // go through and make sure all the certs in one array
1182 // are in the other and vice-versa.
1183 boolean match;
1184 for (Certificate cert : certs) {
1185 match = false;
1186 for (Certificate pcert : pcerts) {
1187 if (cert.equals(pcert)) {
1188 match = true;
1189 break;
1190 }
1191 }
1192 if (!match) return false;
1193 }
1194
1195 // now do the same for pcerts
1196 for (Certificate pcert : pcerts) {
1197 match = false;
1198 for (Certificate cert : certs) {
1199 if (pcert.equals(cert)) {
1200 match = true;
1201 break;
1202 }
1203 }
1204 if (!match) return false;
1205 }
1206
1207 return true;
1208 }
1209
1210 /**
1211 * Links the specified class. This (misleadingly named) method may be
1212 * used by a class loader to link a class. If the class {@code c} has
1213 * already been linked, then this method simply returns. Otherwise, the
1214 * class is linked as described in the "Execution" chapter of
1215 * <cite>The Java™ Language Specification</cite>.
1216 *
1217 * @param c
1218 * The class to link
1219 *
1220 * @throws NullPointerException
1221 * If {@code c} is {@code null}.
1222 *
1223 * @see #defineClass(String, byte[], int, int)
1224 */
1225 protected final void resolveClass(Class<?> c) {
1226 if (c == null) {
1227 throw new NullPointerException();
1228 }
1229 }
1230
1231 /**
1232 * Finds a class with the specified <a href="#binary-name">binary name</a>,
1233 * loading it if necessary.
1234 *
1235 * <p> This method loads the class through the system class loader (see
1236 * {@link #getSystemClassLoader()}). The {@code Class} object returned
1237 * might have more than one {@code ClassLoader} associated with it.
1238 * Subclasses of {@code ClassLoader} need not usually invoke this method,
1239 * because most class loaders need to override just {@link
1240 * #findClass(String)}. </p>
1241 *
1242 * @param name
1243 * The <a href="#binary-name">binary name</a> of the class
1244 *
1245 * @return The {@code Class} object for the specified {@code name}
1246 *
1247 * @throws ClassNotFoundException
1248 * If the class could not be found
1249 *
1250 * @see #ClassLoader(ClassLoader)
1251 * @see #getParent()
1252 */
1253 protected final Class<?> findSystemClass(String name)
1254 throws ClassNotFoundException
1255 {
1256 return getSystemClassLoader().loadClass(name);
1257 }
1258
1259 /**
1260 * Returns a class loaded by the bootstrap class loader;
1261 * or return null if not found.
1262 */
1263 Class<?> findBootstrapClassOrNull(String name) {
1264 if (!checkName(name)) return null;
1265
1266 return findBootstrapClass(name);
1267 }
1268
1269 // return null if not found
1270 private native Class<?> findBootstrapClass(String name);
1271
1272 /**
1273 * Returns the class with the given <a href="#binary-name">binary name</a> if this
1274 * loader has been recorded by the Java virtual machine as an initiating
1275 * loader of a class with that <a href="#binary-name">binary name</a>. Otherwise
1276 * {@code null} is returned.
1277 *
1278 * @param name
1279 * The <a href="#binary-name">binary name</a> of the class
1280 *
1281 * @return The {@code Class} object, or {@code null} if the class has
1282 * not been loaded
1283 *
1284 * @since 1.1
1285 */
1286 protected final Class<?> findLoadedClass(String name) {
1287 if (!checkName(name))
1288 return null;
1289 return findLoadedClass0(name);
1290 }
1291
1292 private final native Class<?> findLoadedClass0(String name);
1293
1294 /**
1295 * Sets the signers of a class. This should be invoked after defining a
1296 * class.
1297 *
1298 * @param c
1299 * The {@code Class} object
1300 *
1301 * @param signers
1302 * The signers for the class
1303 *
1304 * @since 1.1
1305 */
1306 protected final void setSigners(Class<?> c, Object[] signers) {
1307 c.setSigners(signers);
1308 }
1309
1310
1311 // -- Resources --
1312
1313 /**
1314 * Returns a URL to a resource in a module defined to this class loader.
1315 * Class loader implementations that support loading from modules
1316 * should override this method.
1317 *
1318 * @apiNote This method is the basis for the {@link
1319 * Class#getResource Class.getResource}, {@link Class#getResourceAsStream
1320 * Class.getResourceAsStream}, and {@link Module#getResourceAsStream
1321 * Module.getResourceAsStream} methods. It is not subject to the rules for
1322 * encapsulation specified by {@code Module.getResourceAsStream}.
1323 *
1324 * @implSpec The default implementation attempts to find the resource by
1325 * invoking {@link #findResource(String)} when the {@code moduleName} is
1326 * {@code null}. It otherwise returns {@code null}.
1327 *
1328 * @param moduleName
1329 * The module name; or {@code null} to find a resource in the
1330 * {@linkplain #getUnnamedModule() unnamed module} for this
1331 * class loader
1332 * @param name
1333 * The resource name
1334 *
1335 * @return A URL to the resource; {@code null} if the resource could not be
1336 * found, a URL could not be constructed to locate the resource,
1337 * access to the resource is denied by the security manager, or
1338 * there isn't a module of the given name defined to the class
1339 * loader.
1340 *
1341 * @throws IOException
1342 * If I/O errors occur
1343 *
1344 * @see java.lang.module.ModuleReader#find(String)
1345 * @since 9
1346 * @spec JPMS
1347 */
1348 protected URL findResource(String moduleName, String name) throws IOException {
1349 if (moduleName == null) {
1350 return findResource(name);
1351 } else {
1352 return null;
1353 }
1354 }
1355
1356 /**
1357 * Finds the resource with the given name. A resource is some data
1358 * (images, audio, text, etc) that can be accessed by class code in a way
1359 * that is independent of the location of the code.
1360 *
1361 * <p> The name of a resource is a '{@code /}'-separated path name that
1362 * identifies the resource. </p>
1363 *
1364 * <p> Resources in named modules are subject to the encapsulation rules
1365 * specified by {@link Module#getResourceAsStream Module.getResourceAsStream}.
1366 * Additionally, and except for the special case where the resource has a
1367 * name ending with "{@code .class}", this method will only find resources in
1368 * packages of named modules when the package is {@link Module#isOpen(String)
1369 * opened} unconditionally (even if the caller of this method is in the
1370 * same module as the resource). </p>
1371 *
1372 * @implSpec The default implementation will first search the parent class
1373 * loader for the resource; if the parent is {@code null} the path of the
1374 * class loader built into the virtual machine is searched. If not found,
1375 * this method will invoke {@link #findResource(String)} to find the resource.
1376 *
1377 * @apiNote Where several modules are defined to the same class loader,
1378 * and where more than one module contains a resource with the given name,
1379 * then the ordering that modules are searched is not specified and may be
1380 * very unpredictable.
1381 * When overriding this method it is recommended that an implementation
1382 * ensures that any delegation is consistent with the {@link
1383 * #getResources(java.lang.String) getResources(String)} method.
1384 *
1385 * @param name
1386 * The resource name
1387 *
1388 * @return {@code URL} object for reading the resource; {@code null} if
1389 * the resource could not be found, a {@code URL} could not be
1390 * constructed to locate the resource, the resource is in a package
1391 * that is not opened unconditionally, or access to the resource is
1392 * denied by the security manager.
1393 *
1394 * @throws NullPointerException If {@code name} is {@code null}
1395 *
1396 * @since 1.1
1397 * @revised 9
1398 * @spec JPMS
1399 */
1400 public URL getResource(String name) {
1401 Objects.requireNonNull(name);
1402 URL url;
1403 if (parent != null) {
1404 url = parent.getResource(name);
1405 } else {
1406 url = BootLoader.findResource(name);
1407 }
1408 if (url == null) {
1409 url = findResource(name);
1410 }
1411 return url;
1412 }
1413
1414 /**
1415 * Finds all the resources with the given name. A resource is some data
1416 * (images, audio, text, etc) that can be accessed by class code in a way
1417 * that is independent of the location of the code.
1418 *
1419 * <p> The name of a resource is a {@code /}-separated path name that
1420 * identifies the resource. </p>
1421 *
1422 * <p> Resources in named modules are subject to the encapsulation rules
1423 * specified by {@link Module#getResourceAsStream Module.getResourceAsStream}.
1424 * Additionally, and except for the special case where the resource has a
1425 * name ending with "{@code .class}", this method will only find resources in
1426 * packages of named modules when the package is {@link Module#isOpen(String)
1427 * opened} unconditionally (even if the caller of this method is in the
1428 * same module as the resource). </p>
1429 *
1430 * @implSpec The default implementation will first search the parent class
1431 * loader for the resource; if the parent is {@code null} the path of the
1432 * class loader built into the virtual machine is searched. It then
1433 * invokes {@link #findResources(String)} to find the resources with the
1434 * name in this class loader. It returns an enumeration whose elements
1435 * are the URLs found by searching the parent class loader followed by
1436 * the elements found with {@code findResources}.
1437 *
1438 * @apiNote Where several modules are defined to the same class loader,
1439 * and where more than one module contains a resource with the given name,
1440 * then the ordering is not specified and may be very unpredictable.
1441 * When overriding this method it is recommended that an
1442 * implementation ensures that any delegation is consistent with the {@link
1443 * #getResource(java.lang.String) getResource(String)} method. This should
1444 * ensure that the first element returned by the Enumeration's
1445 * {@code nextElement} method is the same resource that the
1446 * {@code getResource(String)} method would return.
1447 *
1448 * @param name
1449 * The resource name
1450 *
1451 * @return An enumeration of {@link java.net.URL URL} objects for the
1452 * resource. If no resources could be found, the enumeration will
1453 * be empty. Resources for which a {@code URL} cannot be
1454 * constructed, are in a package that is not opened
1455 * unconditionally, or access to the resource is denied by the
1456 * security manager, are not returned in the enumeration.
1457 *
1458 * @throws IOException
1459 * If I/O errors occur
1460 * @throws NullPointerException If {@code name} is {@code null}
1461 *
1462 * @since 1.2
1463 * @revised 9
1464 * @spec JPMS
1465 */
1466 public Enumeration<URL> getResources(String name) throws IOException {
1467 Objects.requireNonNull(name);
1468 @SuppressWarnings("unchecked")
1469 Enumeration<URL>[] tmp = (Enumeration<URL>[]) new Enumeration<?>[2];
1470 if (parent != null) {
1471 tmp[0] = parent.getResources(name);
1472 } else {
1473 tmp[0] = BootLoader.findResources(name);
1474 }
1475 tmp[1] = findResources(name);
1476
1477 return new CompoundEnumeration<>(tmp);
1478 }
1479
1480 /**
1481 * Returns a stream whose elements are the URLs of all the resources with
1482 * the given name. A resource is some data (images, audio, text, etc) that
1483 * can be accessed by class code in a way that is independent of the
1484 * location of the code.
1485 *
1486 * <p> The name of a resource is a {@code /}-separated path name that
1487 * identifies the resource.
1488 *
1489 * <p> The resources will be located when the returned stream is evaluated.
1490 * If the evaluation results in an {@code IOException} then the I/O
1491 * exception is wrapped in an {@link UncheckedIOException} that is then
1492 * thrown.
1493 *
1494 * <p> Resources in named modules are subject to the encapsulation rules
1495 * specified by {@link Module#getResourceAsStream Module.getResourceAsStream}.
1496 * Additionally, and except for the special case where the resource has a
1497 * name ending with "{@code .class}", this method will only find resources in
1498 * packages of named modules when the package is {@link Module#isOpen(String)
1499 * opened} unconditionally (even if the caller of this method is in the
1500 * same module as the resource). </p>
1501 *
1502 * @implSpec The default implementation invokes {@link #getResources(String)
1503 * getResources} to find all the resources with the given name and returns
1504 * a stream with the elements in the enumeration as the source.
1505 *
1506 * @apiNote When overriding this method it is recommended that an
1507 * implementation ensures that any delegation is consistent with the {@link
1508 * #getResource(java.lang.String) getResource(String)} method. This should
1509 * ensure that the first element returned by the stream is the same
1510 * resource that the {@code getResource(String)} method would return.
1511 *
1512 * @param name
1513 * The resource name
1514 *
1515 * @return A stream of resource {@link java.net.URL URL} objects. If no
1516 * resources could be found, the stream will be empty. Resources
1517 * for which a {@code URL} cannot be constructed, are in a package
1518 * that is not opened unconditionally, or access to the resource
1519 * is denied by the security manager, will not be in the stream.
1520 *
1521 * @throws NullPointerException If {@code name} is {@code null}
1522 *
1523 * @since 9
1524 */
1525 public Stream<URL> resources(String name) {
1526 Objects.requireNonNull(name);
1527 int characteristics = Spliterator.NONNULL | Spliterator.IMMUTABLE;
1528 Supplier<Spliterator<URL>> si = () -> {
1529 try {
1530 return Spliterators.spliteratorUnknownSize(
1531 getResources(name).asIterator(), characteristics);
1532 } catch (IOException e) {
1533 throw new UncheckedIOException(e);
1534 }
1535 };
1536 return StreamSupport.stream(si, characteristics, false);
1537 }
1538
1539 /**
1540 * Finds the resource with the given name. Class loader implementations
1541 * should override this method.
1542 *
1543 * <p> For resources in named modules then the method must implement the
1544 * rules for encapsulation specified in the {@code Module} {@link
1545 * Module#getResourceAsStream getResourceAsStream} method. Additionally,
1546 * it must not find non-"{@code .class}" resources in packages of named
1547 * modules unless the package is {@link Module#isOpen(String) opened}
1548 * unconditionally. </p>
1549 *
1550 * @implSpec The default implementation returns {@code null}.
1551 *
1552 * @param name
1553 * The resource name
1554 *
1555 * @return {@code URL} object for reading the resource; {@code null} if
1556 * the resource could not be found, a {@code URL} could not be
1557 * constructed to locate the resource, the resource is in a package
1558 * that is not opened unconditionally, or access to the resource is
1559 * denied by the security manager.
1560 *
1561 * @since 1.2
1562 * @revised 9
1563 * @spec JPMS
1564 */
1565 protected URL findResource(String name) {
1566 return null;
1567 }
1568
1569 /**
1570 * Returns an enumeration of {@link java.net.URL URL} objects
1571 * representing all the resources with the given name. Class loader
1572 * implementations should override this method.
1573 *
1574 * <p> For resources in named modules then the method must implement the
1575 * rules for encapsulation specified in the {@code Module} {@link
1576 * Module#getResourceAsStream getResourceAsStream} method. Additionally,
1577 * it must not find non-"{@code .class}" resources in packages of named
1578 * modules unless the package is {@link Module#isOpen(String) opened}
1579 * unconditionally. </p>
1580 *
1581 * @implSpec The default implementation returns an enumeration that
1582 * contains no elements.
1583 *
1584 * @param name
1585 * The resource name
1586 *
1587 * @return An enumeration of {@link java.net.URL URL} objects for
1588 * the resource. If no resources could be found, the enumeration
1589 * will be empty. Resources for which a {@code URL} cannot be
1590 * constructed, are in a package that is not opened unconditionally,
1591 * or access to the resource is denied by the security manager,
1592 * are not returned in the enumeration.
1593 *
1594 * @throws IOException
1595 * If I/O errors occur
1596 *
1597 * @since 1.2
1598 * @revised 9
1599 * @spec JPMS
1600 */
1601 protected Enumeration<URL> findResources(String name) throws IOException {
1602 return Collections.emptyEnumeration();
1603 }
1604
1605 /**
1606 * Registers the caller as
1607 * {@linkplain #isRegisteredAsParallelCapable() parallel capable}.
1608 * The registration succeeds if and only if all of the following
1609 * conditions are met:
1610 * <ol>
1611 * <li> no instance of the caller has been created</li>
1612 * <li> all of the super classes (except class Object) of the caller are
1613 * registered as parallel capable</li>
1614 * </ol>
1615 * <p>Note that once a class loader is registered as parallel capable, there
1616 * is no way to change it back.</p>
1617 *
1618 * @return {@code true} if the caller is successfully registered as
1619 * parallel capable and {@code false} if otherwise.
1620 *
1621 * @see #isRegisteredAsParallelCapable()
1622 *
1623 * @since 1.7
1624 */
1625 @CallerSensitive
1626 protected static boolean registerAsParallelCapable() {
1627 Class<? extends ClassLoader> callerClass =
1628 Reflection.getCallerClass().asSubclass(ClassLoader.class);
1629 return ParallelLoaders.register(callerClass);
1630 }
1631
1632 /**
1633 * Returns {@code true} if this class loader is registered as
1634 * {@linkplain #registerAsParallelCapable parallel capable}, otherwise
1635 * {@code false}.
1636 *
1637 * @return {@code true} if this class loader is parallel capable,
1638 * otherwise {@code false}.
1639 *
1640 * @see #registerAsParallelCapable()
1641 *
1642 * @since 9
1643 */
1644 public final boolean isRegisteredAsParallelCapable() {
1645 return ParallelLoaders.isRegistered(this.getClass());
1646 }
1647
1648 /**
1649 * Find a resource of the specified name from the search path used to load
1650 * classes. This method locates the resource through the system class
1651 * loader (see {@link #getSystemClassLoader()}).
1652 *
1653 * <p> Resources in named modules are subject to the encapsulation rules
1654 * specified by {@link Module#getResourceAsStream Module.getResourceAsStream}.
1655 * Additionally, and except for the special case where the resource has a
1656 * name ending with "{@code .class}", this method will only find resources in
1657 * packages of named modules when the package is {@link Module#isOpen(String)
1658 * opened} unconditionally. </p>
1659 *
1660 * @param name
1661 * The resource name
1662 *
1663 * @return A {@link java.net.URL URL} to the resource; {@code
1664 * null} if the resource could not be found, a URL could not be
1665 * constructed to locate the resource, the resource is in a package
1666 * that is not opened unconditionally or access to the resource is
1667 * denied by the security manager.
1668 *
1669 * @since 1.1
1670 * @revised 9
1671 * @spec JPMS
1672 */
1673 public static URL getSystemResource(String name) {
1674 return getSystemClassLoader().getResource(name);
1675 }
1676
1677 /**
1678 * Finds all resources of the specified name from the search path used to
1679 * load classes. The resources thus found are returned as an
1680 * {@link java.util.Enumeration Enumeration} of {@link
1681 * java.net.URL URL} objects.
1682 *
1683 * <p> The search order is described in the documentation for {@link
1684 * #getSystemResource(String)}. </p>
1685 *
1686 * <p> Resources in named modules are subject to the encapsulation rules
1687 * specified by {@link Module#getResourceAsStream Module.getResourceAsStream}.
1688 * Additionally, and except for the special case where the resource has a
1689 * name ending with "{@code .class}", this method will only find resources in
1690 * packages of named modules when the package is {@link Module#isOpen(String)
1691 * opened} unconditionally. </p>
1692 *
1693 * @param name
1694 * The resource name
1695 *
1696 * @return An enumeration of {@link java.net.URL URL} objects for
1697 * the resource. If no resources could be found, the enumeration
1698 * will be empty. Resources for which a {@code URL} cannot be
1699 * constructed, are in a package that is not opened unconditionally,
1700 * or access to the resource is denied by the security manager,
1701 * are not returned in the enumeration.
1702 *
1703 * @throws IOException
1704 * If I/O errors occur
1705 *
1706 * @since 1.2
1707 * @revised 9
1708 * @spec JPMS
1709 */
1710 public static Enumeration<URL> getSystemResources(String name)
1711 throws IOException
1712 {
1713 return getSystemClassLoader().getResources(name);
1714 }
1715
1716 /**
1717 * Returns an input stream for reading the specified resource.
1718 *
1719 * <p> The search order is described in the documentation for {@link
1720 * #getResource(String)}. </p>
1721 *
1722 * <p> Resources in named modules are subject to the encapsulation rules
1723 * specified by {@link Module#getResourceAsStream Module.getResourceAsStream}.
1724 * Additionally, and except for the special case where the resource has a
1725 * name ending with "{@code .class}", this method will only find resources in
1726 * packages of named modules when the package is {@link Module#isOpen(String)
1727 * opened} unconditionally. </p>
1728 *
1729 * @param name
1730 * The resource name
1731 *
1732 * @return An input stream for reading the resource; {@code null} if the
1733 * resource could not be found, the resource is in a package that
1734 * is not opened unconditionally, or access to the resource is
1735 * denied by the security manager.
1736 *
1737 * @throws NullPointerException If {@code name} is {@code null}
1738 *
1739 * @since 1.1
1740 * @revised 9
1741 * @spec JPMS
1742 */
1743 public InputStream getResourceAsStream(String name) {
1744 Objects.requireNonNull(name);
1745 URL url = getResource(name);
1746 try {
1747 return url != null ? url.openStream() : null;
1748 } catch (IOException e) {
1749 return null;
1750 }
1751 }
1752
1753 /**
1754 * Open for reading, a resource of the specified name from the search path
1755 * used to load classes. This method locates the resource through the
1756 * system class loader (see {@link #getSystemClassLoader()}).
1757 *
1758 * <p> Resources in named modules are subject to the encapsulation rules
1759 * specified by {@link Module#getResourceAsStream Module.getResourceAsStream}.
1760 * Additionally, and except for the special case where the resource has a
1761 * name ending with "{@code .class}", this method will only find resources in
1762 * packages of named modules when the package is {@link Module#isOpen(String)
1763 * opened} unconditionally. </p>
1764 *
1765 * @param name
1766 * The resource name
1767 *
1768 * @return An input stream for reading the resource; {@code null} if the
1769 * resource could not be found, the resource is in a package that
1770 * is not opened unconditionally, or access to the resource is
1771 * denied by the security manager.
1772 *
1773 * @since 1.1
1774 * @revised 9
1775 * @spec JPMS
1776 */
1777 public static InputStream getSystemResourceAsStream(String name) {
1778 URL url = getSystemResource(name);
1779 try {
1780 return url != null ? url.openStream() : null;
1781 } catch (IOException e) {
1782 return null;
1783 }
1784 }
1785
1786
1787 // -- Hierarchy --
1788
1789 /**
1790 * Returns the parent class loader for delegation. Some implementations may
1791 * use {@code null} to represent the bootstrap class loader. This method
1792 * will return {@code null} in such implementations if this class loader's
1793 * parent is the bootstrap class loader.
1794 *
1795 * @return The parent {@code ClassLoader}
1796 *
1797 * @throws SecurityException
1798 * If a security manager is present, and the caller's class loader
1799 * is not {@code null} and is not an ancestor of this class loader,
1800 * and the caller does not have the
1801 * {@link RuntimePermission}{@code ("getClassLoader")}
1802 *
1803 * @since 1.2
1804 */
1805 @CallerSensitive
1806 public final ClassLoader getParent() {
1807 if (parent == null)
1808 return null;
1809 SecurityManager sm = System.getSecurityManager();
1810 if (sm != null) {
1811 // Check access to the parent class loader
1812 // If the caller's class loader is same as this class loader,
1813 // permission check is performed.
1814 checkClassLoaderPermission(parent, Reflection.getCallerClass());
1815 }
1816 return parent;
1817 }
1818
1819 /**
1820 * Returns the unnamed {@code Module} for this class loader.
1821 *
1822 * @return The unnamed Module for this class loader
1823 *
1824 * @see Module#isNamed()
1825 * @since 9
1826 * @spec JPMS
1827 */
1828 public final Module getUnnamedModule() {
1829 return unnamedModule;
1830 }
1831
1832 /**
1833 * Returns the platform class loader. All
1834 * <a href="#builtinLoaders">platform classes</a> are visible to
1835 * the platform class loader.
1836 *
1837 * @implNote The name of the builtin platform class loader is
1838 * {@code "platform"}.
1839 *
1840 * @return The platform {@code ClassLoader}.
1841 *
1842 * @throws SecurityException
1843 * If a security manager is present, and the caller's class loader is
1844 * not {@code null}, and the caller's class loader is not the same
1845 * as or an ancestor of the platform class loader,
1846 * and the caller does not have the
1847 * {@link RuntimePermission}{@code ("getClassLoader")}
1848 *
1849 * @since 9
1850 * @spec JPMS
1851 */
1852 @CallerSensitive
1853 public static ClassLoader getPlatformClassLoader() {
1854 SecurityManager sm = System.getSecurityManager();
1855 ClassLoader loader = getBuiltinPlatformClassLoader();
1856 if (sm != null) {
1857 checkClassLoaderPermission(loader, Reflection.getCallerClass());
1858 }
1859 return loader;
1860 }
1861
1862 /**
1863 * Returns the system class loader. This is the default
1864 * delegation parent for new {@code ClassLoader} instances, and is
1865 * typically the class loader used to start the application.
1866 *
1867 * <p> This method is first invoked early in the runtime's startup
1868 * sequence, at which point it creates the system class loader. This
1869 * class loader will be the context class loader for the main application
1870 * thread (for example, the thread that invokes the {@code main} method of
1871 * the main class).
1872 *
1873 * <p> The default system class loader is an implementation-dependent
1874 * instance of this class.
1875 *
1876 * <p> If the system property "{@systemProperty java.system.class.loader}"
1877 * is defined when this method is first invoked then the value of that
1878 * property is taken to be the name of a class that will be returned as the
1879 * system class loader. The class is loaded using the default system class
1880 * loader and must define a public constructor that takes a single parameter
1881 * of type {@code ClassLoader} which is used as the delegation parent. An
1882 * instance is then created using this constructor with the default system
1883 * class loader as the parameter. The resulting class loader is defined
1884 * to be the system class loader. During construction, the class loader
1885 * should take great care to avoid calling {@code getSystemClassLoader()}.
1886 * If circular initialization of the system class loader is detected then
1887 * an {@code IllegalStateException} is thrown.
1888 *
1889 * @implNote The system property to override the system class loader is not
1890 * examined until the VM is almost fully initialized. Code that executes
1891 * this method during startup should take care not to cache the return
1892 * value until the system is fully initialized.
1893 *
1894 * <p> The name of the built-in system class loader is {@code "app"}.
1895 * The system property "{@code java.class.path}" is read during early
1896 * initialization of the VM to determine the class path.
1897 * An empty value of "{@code java.class.path}" property is interpreted
1898 * differently depending on whether the initial module (the module
1899 * containing the main class) is named or unnamed:
1900 * If named, the built-in system class loader will have no class path and
1901 * will search for classes and resources using the application module path;
1902 * otherwise, if unnamed, it will set the class path to the current
1903 * working directory.
1904 *
1905 * <p> JAR files on the class path may contain a {@code Class-Path} manifest
1906 * attribute to specify dependent JAR files to be included in the class path.
1907 * {@code Class-Path} entries must meet certain conditions for validity (see
1908 * the <a href="{@docRoot}/../specs/jar/jar.html#class-path-attribute">
1909 * JAR File Specification</a> for details). Invalid {@code Class-Path}
1910 * entries are ignored. For debugging purposes, ignored entries can be
1911 * printed to the console if the
1912 * {@systemProperty jdk.net.URLClassPath.showIgnoredClassPathEntries} system
1913 * property is set to {@code true}.
1914 *
1915 * @return The system {@code ClassLoader}
1916 *
1917 * @throws SecurityException
1918 * If a security manager is present, and the caller's class loader
1919 * is not {@code null} and is not the same as or an ancestor of the
1920 * system class loader, and the caller does not have the
1921 * {@link RuntimePermission}{@code ("getClassLoader")}
1922 *
1923 * @throws IllegalStateException
1924 * If invoked recursively during the construction of the class
1925 * loader specified by the "{@code java.system.class.loader}"
1926 * property.
1927 *
1928 * @throws Error
1929 * If the system property "{@code java.system.class.loader}"
1930 * is defined but the named class could not be loaded, the
1931 * provider class does not define the required constructor, or an
1932 * exception is thrown by that constructor when it is invoked. The
1933 * underlying cause of the error can be retrieved via the
1934 * {@link Throwable#getCause()} method.
1935 *
1936 * @revised 1.4
1937 * @revised 9
1938 * @spec JPMS
1939 */
1940 @CallerSensitive
1941 public static ClassLoader getSystemClassLoader() {
1942 switch (VM.initLevel()) {
1943 case 0:
1944 case 1:
1945 case 2:
1946 // the system class loader is the built-in app class loader during startup
1947 return getBuiltinAppClassLoader();
1948 case 3:
1949 String msg = "getSystemClassLoader cannot be called during the system class loader instantiation";
1950 throw new IllegalStateException(msg);
1951 default:
1952 // system fully initialized
1953 assert VM.isBooted() && scl != null;
1954 SecurityManager sm = System.getSecurityManager();
1955 if (sm != null) {
1956 checkClassLoaderPermission(scl, Reflection.getCallerClass());
1957 }
1958 return scl;
1959 }
1960 }
1961
1962 static ClassLoader getBuiltinPlatformClassLoader() {
1963 return ClassLoaders.platformClassLoader();
1964 }
1965
1966 static ClassLoader getBuiltinAppClassLoader() {
1967 return ClassLoaders.appClassLoader();
1968 }
1969
1970 /*
1971 * Initialize the system class loader that may be a custom class on the
1972 * application class path or application module path.
1973 *
1974 * @see java.lang.System#initPhase3
1975 */
1976 static synchronized ClassLoader initSystemClassLoader() {
1977 if (VM.initLevel() != 3) {
1978 throw new InternalError("system class loader cannot be set at initLevel " +
1979 VM.initLevel());
1980 }
1981
1982 // detect recursive initialization
1983 if (scl != null) {
1984 throw new IllegalStateException("recursive invocation");
1985 }
1986
1987 ClassLoader builtinLoader = getBuiltinAppClassLoader();
1988
1989 // All are privileged frames. No need to call doPrivileged.
1990 String cn = System.getProperty("java.system.class.loader");
1991 if (cn != null) {
1992 try {
1993 // custom class loader is only supported to be loaded from unnamed module
1994 Constructor<?> ctor = Class.forName(cn, false, builtinLoader)
1995 .getDeclaredConstructor(ClassLoader.class);
1996 scl = (ClassLoader) ctor.newInstance(builtinLoader);
1997 } catch (Exception e) {
1998 Throwable cause = e;
1999 if (e instanceof InvocationTargetException) {
2000 cause = e.getCause();
2001 if (cause instanceof Error) {
2002 throw (Error) cause;
2003 }
2004 }
2005 if (cause instanceof RuntimeException) {
2006 throw (RuntimeException) cause;
2007 }
2008 throw new Error(cause.getMessage(), cause);
2009 }
2010 } else {
2011 scl = builtinLoader;
2012 }
2013 return scl;
2014 }
2015
2016 // Returns true if the specified class loader can be found in this class
2017 // loader's delegation chain.
2018 boolean isAncestor(ClassLoader cl) {
2019 ClassLoader acl = this;
2020 do {
2021 acl = acl.parent;
2022 if (cl == acl) {
2023 return true;
2024 }
2025 } while (acl != null);
2026 return false;
2027 }
2028
2029 // Tests if class loader access requires "getClassLoader" permission
2030 // check. A class loader 'from' can access class loader 'to' if
2031 // class loader 'from' is same as class loader 'to' or an ancestor
2032 // of 'to'. The class loader in a system domain can access
2033 // any class loader.
2034 private static boolean needsClassLoaderPermissionCheck(ClassLoader from,
2035 ClassLoader to)
2036 {
2037 if (from == to)
2038 return false;
2039
2040 if (from == null)
2041 return false;
2042
2043 return !to.isAncestor(from);
2044 }
2045
2046 // Returns the class's class loader, or null if none.
2047 static ClassLoader getClassLoader(Class<?> caller) {
2048 // This can be null if the VM is requesting it
2049 if (caller == null) {
2050 return null;
2051 }
2052 // Circumvent security check since this is package-private
2053 return caller.getClassLoader0();
2054 }
2055
2056 /*
2057 * Checks RuntimePermission("getClassLoader") permission
2058 * if caller's class loader is not null and caller's class loader
2059 * is not the same as or an ancestor of the given cl argument.
2060 */
2061 static void checkClassLoaderPermission(ClassLoader cl, Class<?> caller) {
2062 SecurityManager sm = System.getSecurityManager();
2063 if (sm != null) {
2064 // caller can be null if the VM is requesting it
2065 ClassLoader ccl = getClassLoader(caller);
2066 if (needsClassLoaderPermissionCheck(ccl, cl)) {
2067 sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
2068 }
2069 }
2070 }
2071
2072 // The system class loader
2073 // @GuardedBy("ClassLoader.class")
2074 private static volatile ClassLoader scl;
2075
2076 // -- Package --
2077
2078 /**
2079 * Define a Package of the given Class object.
2080 *
2081 * If the given class represents an array type, a primitive type or void,
2082 * this method returns {@code null}.
2083 *
2084 * This method does not throw IllegalArgumentException.
2085 */
2086 Package definePackage(Class<?> c) {
2087 if (c.isPrimitive() || c.isArray()) {
2088 return null;
2089 }
2090
2091 return definePackage(c.getPackageName(), c.getModule());
2092 }
2093
2094 /**
2095 * Defines a Package of the given name and module
2096 *
2097 * This method does not throw IllegalArgumentException.
2098 *
2099 * @param name package name
2100 * @param m module
2101 */
2102 Package definePackage(String name, Module m) {
2103 if (name.isEmpty() && m.isNamed()) {
2104 throw new InternalError("unnamed package in " + m);
2105 }
2106
2107 // check if Package object is already defined
2108 NamedPackage pkg = packages.get(name);
2109 if (pkg instanceof Package)
2110 return (Package)pkg;
2111
2112 return (Package)packages.compute(name, (n, p) -> toPackage(n, p, m));
2113 }
2114
2115 /*
2116 * Returns a Package object for the named package
2117 */
2118 private Package toPackage(String name, NamedPackage p, Module m) {
2119 // define Package object if the named package is not yet defined
2120 if (p == null)
2121 return NamedPackage.toPackage(name, m);
2122
2123 // otherwise, replace the NamedPackage object with Package object
2124 if (p instanceof Package)
2125 return (Package)p;
2126
2127 return NamedPackage.toPackage(p.packageName(), p.module());
2128 }
2129
2130 /**
2131 * Defines a package by <a href="#binary-name">name</a> in this {@code ClassLoader}.
2132 * <p>
2133 * <a href="#binary-name">Package names</a> must be unique within a class loader and
2134 * cannot be redefined or changed once created.
2135 * <p>
2136 * If a class loader wishes to define a package with specific properties,
2137 * such as version information, then the class loader should call this
2138 * {@code definePackage} method before calling {@code defineClass}.
2139 * Otherwise, the
2140 * {@link #defineClass(String, byte[], int, int, ProtectionDomain) defineClass}
2141 * method will define a package in this class loader corresponding to the package
2142 * of the newly defined class; the properties of this defined package are
2143 * specified by {@link Package}.
2144 *
2145 * @apiNote
2146 * A class loader that wishes to define a package for classes in a JAR
2147 * typically uses the specification and implementation titles, versions, and
2148 * vendors from the JAR's manifest. If the package is specified as
2149 * {@linkplain java.util.jar.Attributes.Name#SEALED sealed} in the JAR's manifest,
2150 * the {@code URL} of the JAR file is typically used as the {@code sealBase}.
2151 * If classes of package {@code 'p'} defined by this class loader
2152 * are loaded from multiple JARs, the {@code Package} object may contain
2153 * different information depending on the first class of package {@code 'p'}
2154 * defined and which JAR's manifest is read first to explicitly define
2155 * package {@code 'p'}.
2156 *
2157 * <p> It is strongly recommended that a class loader does not call this
2158 * method to explicitly define packages in <em>named modules</em>; instead,
2159 * the package will be automatically defined when a class is {@linkplain
2160 * #defineClass(String, byte[], int, int, ProtectionDomain) being defined}.
2161 * If it is desirable to define {@code Package} explicitly, it should ensure
2162 * that all packages in a named module are defined with the properties
2163 * specified by {@link Package}. Otherwise, some {@code Package} objects
2164 * in a named module may be for example sealed with different seal base.
2165 *
2166 * @param name
2167 * The <a href="#binary-name">package name</a>
2168 *
2169 * @param specTitle
2170 * The specification title
2171 *
2172 * @param specVersion
2173 * The specification version
2174 *
2175 * @param specVendor
2176 * The specification vendor
2177 *
2178 * @param implTitle
2179 * The implementation title
2180 *
2181 * @param implVersion
2182 * The implementation version
2183 *
2184 * @param implVendor
2185 * The implementation vendor
2186 *
2187 * @param sealBase
2188 * If not {@code null}, then this package is sealed with
2189 * respect to the given code source {@link java.net.URL URL}
2190 * object. Otherwise, the package is not sealed.
2191 *
2192 * @return The newly defined {@code Package} object
2193 *
2194 * @throws NullPointerException
2195 * if {@code name} is {@code null}.
2196 *
2197 * @throws IllegalArgumentException
2198 * if a package of the given {@code name} is already
2199 * defined by this class loader
2200 *
2201 *
2202 * @since 1.2
2203 * @revised 9
2204 * @spec JPMS
2205 *
2206 * @jvms 5.3 Creation and Loading
2207 * @see <a href="{@docRoot}/../specs/jar/jar.html#package-sealing">
2208 * The JAR File Specification: Package Sealing</a>
2209 */
2210 protected Package definePackage(String name, String specTitle,
2211 String specVersion, String specVendor,
2212 String implTitle, String implVersion,
2213 String implVendor, URL sealBase)
2214 {
2215 Objects.requireNonNull(name);
2216
2217 // definePackage is not final and may be overridden by custom class loader
2218 Package p = new Package(name, specTitle, specVersion, specVendor,
2219 implTitle, implVersion, implVendor,
2220 sealBase, this);
2221
2222 if (packages.putIfAbsent(name, p) != null)
2223 throw new IllegalArgumentException(name);
2224
2225 return p;
2226 }
2227
2228 /**
2229 * Returns a {@code Package} of the given <a href="#binary-name">name</a> that
2230 * has been defined by this class loader.
2231 *
2232 * @param name The <a href="#binary-name">package name</a>
2233 *
2234 * @return The {@code Package} of the given name that has been defined
2235 * by this class loader, or {@code null} if not found
2236 *
2237 * @throws NullPointerException
2238 * if {@code name} is {@code null}.
2239 *
2240 * @jvms 5.3 Creation and Loading
2241 *
2242 * @since 9
2243 * @spec JPMS
2244 */
2245 public final Package getDefinedPackage(String name) {
2246 Objects.requireNonNull(name, "name cannot be null");
2247
2248 NamedPackage p = packages.get(name);
2249 if (p == null)
2250 return null;
2251
2252 return definePackage(name, p.module());
2253 }
2254
2255 /**
2256 * Returns all of the {@code Package}s that have been defined by
2257 * this class loader. The returned array has no duplicated {@code Package}s
2258 * of the same name.
2259 *
2260 * @apiNote This method returns an array rather than a {@code Set} or {@code Stream}
2261 * for consistency with the existing {@link #getPackages} method.
2262 *
2263 * @return The array of {@code Package} objects that have been defined by
2264 * this class loader; or an zero length array if no package has been
2265 * defined by this class loader.
2266 *
2267 * @jvms 5.3 Creation and Loading
2268 *
2269 * @since 9
2270 * @spec JPMS
2271 */
2272 public final Package[] getDefinedPackages() {
2273 return packages().toArray(Package[]::new);
2274 }
2275
2276 /**
2277 * Finds a package by <a href="#binary-name">name</a> in this class loader and its ancestors.
2278 * <p>
2279 * If this class loader defines a {@code Package} of the given name,
2280 * the {@code Package} is returned. Otherwise, the ancestors of
2281 * this class loader are searched recursively (parent by parent)
2282 * for a {@code Package} of the given name.
2283 *
2284 * @apiNote The {@link #getPlatformClassLoader() platform class loader}
2285 * may delegate to the application class loader but the application class
2286 * loader is not its ancestor. When invoked on the platform class loader,
2287 * this method will not find packages defined to the application
2288 * class loader.
2289 *
2290 * @param name
2291 * The <a href="#binary-name">package name</a>
2292 *
2293 * @return The {@code Package} of the given name that has been defined by
2294 * this class loader or its ancestors, or {@code null} if not found.
2295 *
2296 * @throws NullPointerException
2297 * if {@code name} is {@code null}.
2298 *
2299 * @deprecated
2300 * If multiple class loaders delegate to each other and define classes
2301 * with the same package name, and one such loader relies on the lookup
2302 * behavior of {@code getPackage} to return a {@code Package} from
2303 * a parent loader, then the properties exposed by the {@code Package}
2304 * may not be as expected in the rest of the program.
2305 * For example, the {@code Package} will only expose annotations from the
2306 * {@code package-info.class} file defined by the parent loader, even if
2307 * annotations exist in a {@code package-info.class} file defined by
2308 * a child loader. A more robust approach is to use the
2309 * {@link ClassLoader#getDefinedPackage} method which returns
2310 * a {@code Package} for the specified class loader.
2311 *
2312 * @see ClassLoader#getDefinedPackage(String)
2313 *
2314 * @since 1.2
2315 * @revised 9
2316 * @spec JPMS
2317 */
2318 @Deprecated(since="9")
2319 protected Package getPackage(String name) {
2320 Package pkg = getDefinedPackage(name);
2321 if (pkg == null) {
2322 if (parent != null) {
2323 pkg = parent.getPackage(name);
2324 } else {
2325 pkg = BootLoader.getDefinedPackage(name);
2326 }
2327 }
2328 return pkg;
2329 }
2330
2331 /**
2332 * Returns all of the {@code Package}s that have been defined by
2333 * this class loader and its ancestors. The returned array may contain
2334 * more than one {@code Package} object of the same package name, each
2335 * defined by a different class loader in the class loader hierarchy.
2336 *
2337 * @apiNote The {@link #getPlatformClassLoader() platform class loader}
2338 * may delegate to the application class loader. In other words,
2339 * packages in modules defined to the application class loader may be
2340 * visible to the platform class loader. On the other hand,
2341 * the application class loader is not its ancestor and hence
2342 * when invoked on the platform class loader, this method will not
2343 * return any packages defined to the application class loader.
2344 *
2345 * @return The array of {@code Package} objects that have been defined by
2346 * this class loader and its ancestors
2347 *
2348 * @see ClassLoader#getDefinedPackages()
2349 *
2350 * @since 1.2
2351 * @revised 9
2352 * @spec JPMS
2353 */
2354 protected Package[] getPackages() {
2355 Stream<Package> pkgs = packages();
2356 ClassLoader ld = parent;
2357 while (ld != null) {
2358 pkgs = Stream.concat(ld.packages(), pkgs);
2359 ld = ld.parent;
2360 }
2361 return Stream.concat(BootLoader.packages(), pkgs)
2362 .toArray(Package[]::new);
2363 }
2364
2365
2366
2367 // package-private
2368
2369 /**
2370 * Returns a stream of Packages defined in this class loader
2371 */
2372 Stream<Package> packages() {
2373 return packages.values().stream()
2374 .map(p -> definePackage(p.packageName(), p.module()));
2375 }
2376
2377 // -- Native library access --
2378
2379 /**
2380 * Returns the absolute path name of a native library. The VM invokes this
2381 * method to locate the native libraries that belong to classes loaded with
2382 * this class loader. If this method returns {@code null}, the VM
2383 * searches the library along the path specified as the
2384 * "{@code java.library.path}" property.
2385 *
2386 * @param libname
2387 * The library name
2388 *
2389 * @return The absolute path of the native library
2390 *
2391 * @see System#loadLibrary(String)
2392 * @see System#mapLibraryName(String)
2393 *
2394 * @since 1.2
2395 */
2396 protected String findLibrary(String libname) {
2397 return null;
2398 }
2399
2400 private final NativeLibraries libraries = NativeLibraries.jniNativeLibraries(this);
2401
2402 // Invoked in the java.lang.Runtime class to implement load and loadLibrary.
2403 static NativeLibrary loadLibrary(Class<?> fromClass, File file) {
2404 ClassLoader loader = (fromClass == null) ? null : fromClass.getClassLoader();
2405 NativeLibraries libs = loader != null ? loader.libraries : BootLoader.getNativeLibraries();
2406 NativeLibrary nl = libs.loadLibrary(fromClass, file);
2407 if (nl != null) {
2408 return nl;
2409 }
2410 throw new UnsatisfiedLinkError("Can't load library: " + file);
2411 }
2412 static NativeLibrary loadLibrary(Class<?> fromClass, String name) {
2413 ClassLoader loader = (fromClass == null) ? null : fromClass.getClassLoader();
2414 if (loader == null) {
2415 NativeLibrary nl = BootLoader.getNativeLibraries().loadLibrary(fromClass, name);
2416 if (nl != null) {
2417 return nl;
2418 }
2419 throw new UnsatisfiedLinkError("no " + name +
2420 " in system library path: " + StaticProperty.sunBootLibraryPath());
2421 }
2422
2423 NativeLibraries libs = loader.libraries;
2424 // First load from the file returned from ClassLoader::findLibrary, if found.
2425 String libfilename = loader.findLibrary(name);
2426 if (libfilename != null) {
2427 File libfile = new File(libfilename);
2428 if (!libfile.isAbsolute()) {
2429 throw new UnsatisfiedLinkError(
2430 "ClassLoader.findLibrary failed to return an absolute path: " + libfilename);
2431 }
2432 NativeLibrary nl = libs.loadLibrary(fromClass, libfile);
2433 if (nl != null) {
2434 return nl;
2435 }
2436 throw new UnsatisfiedLinkError("Can't load " + libfilename);
2437 }
2438 // Then load from system library path and java library path
2439 NativeLibrary nl = libs.loadLibrary(fromClass, name);
2440 if (nl != null) {
2441 return nl;
2442 }
2443
2444 // Oops, it failed
2445 throw new UnsatisfiedLinkError("no " + name +
2446 " in java.library.path: " + StaticProperty.javaLibraryPath());
2447 }
2448
2449 /*
2450 * Invoked in the VM class linking code.
2451 */
2452 private static long findNative(ClassLoader loader, String entryName) {
2453 if (loader == null) {
2454 return BootLoader.getNativeLibraries().find(entryName);
2455 } else {
2456 return loader.libraries.find(entryName);
2457 }
2458 }
2459
2460 // -- Assertion management --
2461
2462 final Object assertionLock;
2463
2464 // The default toggle for assertion checking.
2465 // @GuardedBy("assertionLock")
2466 private boolean defaultAssertionStatus = false;
2467
2468 // Maps String packageName to Boolean package default assertion status Note
2469 // that the default package is placed under a null map key. If this field
2470 // is null then we are delegating assertion status queries to the VM, i.e.,
2471 // none of this ClassLoader's assertion status modification methods have
2472 // been invoked.
2473 // @GuardedBy("assertionLock")
2474 private Map<String, Boolean> packageAssertionStatus = null;
2475
2476 // Maps String fullyQualifiedClassName to Boolean assertionStatus If this
2477 // field is null then we are delegating assertion status queries to the VM,
2478 // i.e., none of this ClassLoader's assertion status modification methods
2479 // have been invoked.
2480 // @GuardedBy("assertionLock")
2481 Map<String, Boolean> classAssertionStatus = null;
2482
2483 /**
2484 * Sets the default assertion status for this class loader. This setting
2485 * determines whether classes loaded by this class loader and initialized
2486 * in the future will have assertions enabled or disabled by default.
2487 * This setting may be overridden on a per-package or per-class basis by
2488 * invoking {@link #setPackageAssertionStatus(String, boolean)} or {@link
2489 * #setClassAssertionStatus(String, boolean)}.
2490 *
2491 * @param enabled
2492 * {@code true} if classes loaded by this class loader will
2493 * henceforth have assertions enabled by default, {@code false}
2494 * if they will have assertions disabled by default.
2495 *
2496 * @since 1.4
2497 */
2498 public void setDefaultAssertionStatus(boolean enabled) {
2499 synchronized (assertionLock) {
2500 if (classAssertionStatus == null)
2501 initializeJavaAssertionMaps();
2502
2503 defaultAssertionStatus = enabled;
2504 }
2505 }
2506
2507 /**
2508 * Sets the package default assertion status for the named package. The
2509 * package default assertion status determines the assertion status for
2510 * classes initialized in the future that belong to the named package or
2511 * any of its "subpackages".
2512 *
2513 * <p> A subpackage of a package named p is any package whose name begins
2514 * with "{@code p.}". For example, {@code javax.swing.text} is a
2515 * subpackage of {@code javax.swing}, and both {@code java.util} and
2516 * {@code java.lang.reflect} are subpackages of {@code java}.
2517 *
2518 * <p> In the event that multiple package defaults apply to a given class,
2519 * the package default pertaining to the most specific package takes
2520 * precedence over the others. For example, if {@code javax.lang} and
2521 * {@code javax.lang.reflect} both have package defaults associated with
2522 * them, the latter package default applies to classes in
2523 * {@code javax.lang.reflect}.
2524 *
2525 * <p> Package defaults take precedence over the class loader's default
2526 * assertion status, and may be overridden on a per-class basis by invoking
2527 * {@link #setClassAssertionStatus(String, boolean)}. </p>
2528 *
2529 * @param packageName
2530 * The name of the package whose package default assertion status
2531 * is to be set. A {@code null} value indicates the unnamed
2532 * package that is "current"
2533 * (see section 7.4.2 of
2534 * <cite>The Java™ Language Specification</cite>.)
2535 *
2536 * @param enabled
2537 * {@code true} if classes loaded by this classloader and
2538 * belonging to the named package or any of its subpackages will
2539 * have assertions enabled by default, {@code false} if they will
2540 * have assertions disabled by default.
2541 *
2542 * @since 1.4
2543 */
2544 public void setPackageAssertionStatus(String packageName,
2545 boolean enabled) {
2546 synchronized (assertionLock) {
2547 if (packageAssertionStatus == null)
2548 initializeJavaAssertionMaps();
2549
2550 packageAssertionStatus.put(packageName, enabled);
2551 }
2552 }
2553
2554 /**
2555 * Sets the desired assertion status for the named top-level class in this
2556 * class loader and any nested classes contained therein. This setting
2557 * takes precedence over the class loader's default assertion status, and
2558 * over any applicable per-package default. This method has no effect if
2559 * the named class has already been initialized. (Once a class is
2560 * initialized, its assertion status cannot change.)
2561 *
2562 * <p> If the named class is not a top-level class, this invocation will
2563 * have no effect on the actual assertion status of any class. </p>
2564 *
2565 * @param className
2566 * The fully qualified class name of the top-level class whose
2567 * assertion status is to be set.
2568 *
2569 * @param enabled
2570 * {@code true} if the named class is to have assertions
2571 * enabled when (and if) it is initialized, {@code false} if the
2572 * class is to have assertions disabled.
2573 *
2574 * @since 1.4
2575 */
2576 public void setClassAssertionStatus(String className, boolean enabled) {
2577 synchronized (assertionLock) {
2578 if (classAssertionStatus == null)
2579 initializeJavaAssertionMaps();
2580
2581 classAssertionStatus.put(className, enabled);
2582 }
2583 }
2584
2585 /**
2586 * Sets the default assertion status for this class loader to
2587 * {@code false} and discards any package defaults or class assertion
2588 * status settings associated with the class loader. This method is
2589 * provided so that class loaders can be made to ignore any command line or
2590 * persistent assertion status settings and "start with a clean slate."
2591 *
2592 * @since 1.4
2593 */
2594 public void clearAssertionStatus() {
2595 /*
2596 * Whether or not "Java assertion maps" are initialized, set
2597 * them to empty maps, effectively ignoring any present settings.
2598 */
2599 synchronized (assertionLock) {
2600 classAssertionStatus = new HashMap<>();
2601 packageAssertionStatus = new HashMap<>();
2602 defaultAssertionStatus = false;
2603 }
2604 }
2605
2606 /**
2607 * Returns the assertion status that would be assigned to the specified
2608 * class if it were to be initialized at the time this method is invoked.
2609 * If the named class has had its assertion status set, the most recent
2610 * setting will be returned; otherwise, if any package default assertion
2611 * status pertains to this class, the most recent setting for the most
2612 * specific pertinent package default assertion status is returned;
2613 * otherwise, this class loader's default assertion status is returned.
2614 * </p>
2615 *
2616 * @param className
2617 * The fully qualified class name of the class whose desired
2618 * assertion status is being queried.
2619 *
2620 * @return The desired assertion status of the specified class.
2621 *
2622 * @see #setClassAssertionStatus(String, boolean)
2623 * @see #setPackageAssertionStatus(String, boolean)
2624 * @see #setDefaultAssertionStatus(boolean)
2625 *
2626 * @since 1.4
2627 */
2628 boolean desiredAssertionStatus(String className) {
2629 synchronized (assertionLock) {
2630 // assert classAssertionStatus != null;
2631 // assert packageAssertionStatus != null;
2632
2633 // Check for a class entry
2634 Boolean result = classAssertionStatus.get(className);
2635 if (result != null)
2636 return result.booleanValue();
2637
2638 // Check for most specific package entry
2639 int dotIndex = className.lastIndexOf('.');
2640 if (dotIndex < 0) { // default package
2641 result = packageAssertionStatus.get(null);
2642 if (result != null)
2643 return result.booleanValue();
2644 }
2645 while(dotIndex > 0) {
2646 className = className.substring(0, dotIndex);
2647 result = packageAssertionStatus.get(className);
2648 if (result != null)
2649 return result.booleanValue();
2650 dotIndex = className.lastIndexOf('.', dotIndex-1);
2651 }
2652
2653 // Return the classloader default
2654 return defaultAssertionStatus;
2655 }
2656 }
2657
2658 // Set up the assertions with information provided by the VM.
2659 // Note: Should only be called inside a synchronized block
2660 private void initializeJavaAssertionMaps() {
2661 // assert Thread.holdsLock(assertionLock);
2662
2663 classAssertionStatus = new HashMap<>();
2664 packageAssertionStatus = new HashMap<>();
2665 AssertionStatusDirectives directives = retrieveDirectives();
2666
2667 for(int i = 0; i < directives.classes.length; i++)
2668 classAssertionStatus.put(directives.classes[i],
2669 directives.classEnabled[i]);
2670
2671 for(int i = 0; i < directives.packages.length; i++)
2672 packageAssertionStatus.put(directives.packages[i],
2673 directives.packageEnabled[i]);
2674
2675 defaultAssertionStatus = directives.deflt;
2676 }
2677
2678 // Retrieves the assertion directives from the VM.
2679 private static native AssertionStatusDirectives retrieveDirectives();
2680
2681
2682 // -- Misc --
2683
2684 /**
2685 * Returns the ConcurrentHashMap used as a storage for ClassLoaderValue(s)
2686 * associated with this ClassLoader, creating it if it doesn't already exist.
2687 */
2688 ConcurrentHashMap<?, ?> createOrGetClassLoaderValueMap() {
2689 ConcurrentHashMap<?, ?> map = classLoaderValueMap;
2690 if (map == null) {
2691 map = new ConcurrentHashMap<>();
2692 boolean set = trySetObjectField("classLoaderValueMap", map);
2693 if (!set) {
2694 // beaten by someone else
2695 map = classLoaderValueMap;
2696 }
2697 }
2698 return map;
2699 }
2700
2701 // the storage for ClassLoaderValue(s) associated with this ClassLoader
2702 private volatile ConcurrentHashMap<?, ?> classLoaderValueMap;
2703
2704 /**
2705 * Attempts to atomically set a volatile field in this object. Returns
2706 * {@code true} if not beaten by another thread. Avoids the use of
2707 * AtomicReferenceFieldUpdater in this class.
2708 */
2709 private boolean trySetObjectField(String name, Object obj) {
2710 Unsafe unsafe = Unsafe.getUnsafe();
2711 Class<?> k = ClassLoader.class;
2712 long offset;
2713 offset = unsafe.objectFieldOffset(k, name);
2714 return unsafe.compareAndSetReference(this, offset, null, obj);
2715 }
2716 }
2717
2718 /*
2719 * A utility class that will enumerate over an array of enumerations.
2720 */
2721 final class CompoundEnumeration<E> implements Enumeration<E> {
2722 private final Enumeration<E>[] enums;
2723 private int index;
2724
2725 public CompoundEnumeration(Enumeration<E>[] enums) {
2726 this.enums = enums;
2727 }
2728
2729 private boolean next() {
2730 while (index < enums.length) {
2731 if (enums[index] != null && enums[index].hasMoreElements()) {
2732 return true;
2733 }
2734 index++;
2735 }
2736 return false;
2737 }
2738
2739 public boolean hasMoreElements() {
2740 return next();
2741 }
2742
2743 public E nextElement() {
2744 if (!next()) {
2745 throw new NoSuchElementException();
2746 }
2747 return enums[index].nextElement();
2748 }
2749 }