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 * @param name
738 * The <a href="#binary-name">binary name</a> of the class
739 *
740 * @return The resulting {@code Class} object, or {@code null}
741 * if the class could not be found.
742 *
743 * @since 9
744 * @spec JPMS
745 */
746 protected Class<?> findClass(String moduleName, String name) {
747 if (moduleName == null) {
748 try {
749 return findClass(name);
750 } catch (ClassNotFoundException ignore) { }
751 }
752 return null;
753 }
754
755
756 /**
757 * Converts an array of bytes into an instance of class {@code Class}.
758 * Before the {@code Class} can be used it must be resolved. This method
759 * is deprecated in favor of the version that takes a <a
760 * href="#binary-name">binary name</a> as its first argument, and is more secure.
761 *
762 * @param b
763 * The bytes that make up the class data. The bytes in positions
764 * {@code off} through {@code off+len-1} should have the format
765 * of a valid class file as defined by
766 * <cite>The Java™ Virtual Machine Specification</cite>.
767 *
768 * @param off
769 * The start offset in {@code b} of the class data
770 *
771 * @param len
772 * The length of the class data
773 *
774 * @return The {@code Class} object that was created from the specified
775 * class data
776 *
777 * @throws ClassFormatError
778 * If the data did not contain a valid class
779 *
780 * @throws IndexOutOfBoundsException
781 * If either {@code off} or {@code len} is negative, or if
782 * {@code off+len} is greater than {@code b.length}.
783 *
784 * @throws SecurityException
785 * If an attempt is made to add this class to a package that
786 * contains classes that were signed by a different set of
787 * certificates than this class, or if an attempt is made
788 * to define a class in a package with a fully-qualified name
789 * that starts with "{@code java.}".
790 *
791 * @see #loadClass(String, boolean)
792 * @see #resolveClass(Class)
793 *
794 * @deprecated Replaced by {@link #defineClass(String, byte[], int, int)
795 * defineClass(String, byte[], int, int)}
796 */
797 @Deprecated(since="1.1")
798 protected final Class<?> defineClass(byte[] b, int off, int len)
799 throws ClassFormatError
800 {
801 return defineClass(null, b, off, len, null);
802 }
803
804 /**
805 * Converts an array of bytes into an instance of class {@code Class}.
806 * Before the {@code Class} can be used it must be resolved.
807 *
808 * <p> This method assigns a default {@link java.security.ProtectionDomain
809 * ProtectionDomain} to the newly defined class. The
810 * {@code ProtectionDomain} is effectively granted the same set of
811 * permissions returned when {@link
812 * java.security.Policy#getPermissions(java.security.CodeSource)
813 * Policy.getPolicy().getPermissions(new CodeSource(null, null))}
814 * is invoked. The default protection domain is created on the first invocation
815 * of {@link #defineClass(String, byte[], int, int) defineClass},
816 * and re-used on subsequent invocations.
817 *
818 * <p> To assign a specific {@code ProtectionDomain} to the class, use
819 * the {@link #defineClass(String, byte[], int, int,
820 * java.security.ProtectionDomain) defineClass} method that takes a
821 * {@code ProtectionDomain} as one of its arguments. </p>
822 *
823 * <p>
824 * This method defines a package in this class loader corresponding to the
825 * package of the {@code Class} (if such a package has not already been defined
826 * in this class loader). The name of the defined package is derived from
827 * the <a href="#binary-name">binary name</a> of the class specified by
828 * the byte array {@code b}.
829 * Other properties of the defined package are as specified by {@link Package}.
830 *
831 * @param name
832 * The expected <a href="#binary-name">binary name</a> of the class, or
833 * {@code null} if not known
834 *
835 * @param b
836 * The bytes that make up the class data. The bytes in positions
837 * {@code off} through {@code off+len-1} should have the format
838 * of a valid class file as defined by
839 * <cite>The Java™ Virtual Machine Specification</cite>.
840 *
841 * @param off
842 * The start offset in {@code b} of the class data
843 *
844 * @param len
845 * The length of the class data
846 *
847 * @return The {@code Class} object that was created from the specified
848 * class data.
849 *
850 * @throws ClassFormatError
851 * If the data did not contain a valid class
852 *
853 * @throws IndexOutOfBoundsException
854 * If either {@code off} or {@code len} is negative, or if
855 * {@code off+len} is greater than {@code b.length}.
856 *
857 * @throws SecurityException
858 * If an attempt is made to add this class to a package that
859 * contains classes that were signed by a different set of
860 * certificates than this class (which is unsigned), or if
861 * {@code name} begins with "{@code java.}".
862 *
863 * @see #loadClass(String, boolean)
864 * @see #resolveClass(Class)
865 * @see java.security.CodeSource
866 * @see java.security.SecureClassLoader
867 *
868 * @since 1.1
869 * @revised 9
870 * @spec JPMS
871 */
872 protected final Class<?> defineClass(String name, byte[] b, int off, int len)
873 throws ClassFormatError
874 {
875 return defineClass(name, b, off, len, null);
876 }
877
878 /* Determine protection domain, and check that:
879 - not define java.* class,
880 - signer of this class matches signers for the rest of the classes in
881 package.
882 */
883 private ProtectionDomain preDefineClass(String name,
884 ProtectionDomain pd)
885 {
886 if (!checkName(name))
887 throw new NoClassDefFoundError("IllegalName: " + name);
888
889 // Note: Checking logic in java.lang.invoke.MemberName.checkForTypeAlias
890 // relies on the fact that spoofing is impossible if a class has a name
891 // of the form "java.*"
892 if ((name != null) && name.startsWith("java.")
893 && this != getBuiltinPlatformClassLoader()) {
894 throw new SecurityException
895 ("Prohibited package name: " +
896 name.substring(0, name.lastIndexOf('.')));
897 }
898 if (pd == null) {
899 pd = defaultDomain;
900 }
901
902 if (name != null) {
903 checkCerts(name, pd.getCodeSource());
904 }
905
906 return pd;
907 }
908
909 private String defineClassSourceLocation(ProtectionDomain pd) {
910 CodeSource cs = pd.getCodeSource();
911 String source = null;
912 if (cs != null && cs.getLocation() != null) {
913 source = cs.getLocation().toString();
914 }
915 return source;
916 }
917
918 private void postDefineClass(Class<?> c, ProtectionDomain pd) {
919 // define a named package, if not present
920 getNamedPackage(c.getPackageName(), c.getModule());
921
922 if (pd.getCodeSource() != null) {
923 Certificate certs[] = pd.getCodeSource().getCertificates();
924 if (certs != null)
925 setSigners(c, certs);
926 }
927 }
928
929 /**
930 * Converts an array of bytes into an instance of class {@code Class},
931 * with a given {@code ProtectionDomain}.
932 *
933 * <p> If the given {@code ProtectionDomain} is {@code null},
934 * then a default protection domain will be assigned to the class as specified
935 * in the documentation for {@link #defineClass(String, byte[], int, int)}.
936 * Before the class can be used it must be resolved.
937 *
938 * <p> The first class defined in a package determines the exact set of
939 * certificates that all subsequent classes defined in that package must
940 * contain. The set of certificates for a class is obtained from the
941 * {@link java.security.CodeSource CodeSource} within the
942 * {@code ProtectionDomain} of the class. Any classes added to that
943 * package must contain the same set of certificates or a
944 * {@code SecurityException} will be thrown. Note that if
945 * {@code name} is {@code null}, this check is not performed.
946 * You should always pass in the <a href="#binary-name">binary name</a> of the
947 * class you are defining as well as the bytes. This ensures that the
948 * class you are defining is indeed the class you think it is.
949 *
950 * <p> If the specified {@code name} begins with "{@code java.}", it can
951 * only be defined by the {@linkplain #getPlatformClassLoader()
952 * platform class loader} or its ancestors; otherwise {@code SecurityException}
953 * will be thrown. If {@code name} is not {@code null}, it must be equal to
954 * the <a href="#binary-name">binary name</a> of the class
955 * specified by the byte array {@code b}, otherwise a {@link
956 * NoClassDefFoundError NoClassDefFoundError} will be thrown.
957 *
958 * <p> This method defines a package in this class loader corresponding to the
959 * package of the {@code Class} (if such a package has not already been defined
960 * in this class loader). The name of the defined package is derived from
961 * the <a href="#binary-name">binary name</a> of the class specified by
962 * the byte array {@code b}.
963 * Other properties of the defined package are as specified by {@link Package}.
964 *
965 * @param name
966 * The expected <a href="#binary-name">binary name</a> of the class, or
967 * {@code null} if not known
968 *
969 * @param b
970 * The bytes that make up the class data. The bytes in positions
971 * {@code off} through {@code off+len-1} should have the format
972 * of a valid class file as defined by
973 * <cite>The Java™ Virtual Machine Specification</cite>.
974 *
975 * @param off
976 * The start offset in {@code b} of the class data
977 *
978 * @param len
979 * The length of the class data
980 *
981 * @param protectionDomain
982 * The {@code ProtectionDomain} of the class
983 *
984 * @return The {@code Class} object created from the data,
985 * and {@code ProtectionDomain}.
986 *
987 * @throws ClassFormatError
988 * If the data did not contain a valid class
989 *
990 * @throws NoClassDefFoundError
991 * If {@code name} is not {@code null} and not equal to the
992 * <a href="#binary-name">binary name</a> of the class specified by {@code b}
993 *
994 * @throws IndexOutOfBoundsException
995 * If either {@code off} or {@code len} is negative, or if
996 * {@code off+len} is greater than {@code b.length}.
997 *
998 * @throws SecurityException
999 * If an attempt is made to add this class to a package that
1000 * contains classes that were signed by a different set of
1001 * certificates than this class, or if {@code name} begins with
1002 * "{@code java.}" and this class loader is not the platform
1003 * class loader or its ancestor.
1004 *
1005 * @revised 9
1006 * @spec JPMS
1007 */
1008 protected final Class<?> defineClass(String name, byte[] b, int off, int len,
1009 ProtectionDomain protectionDomain)
1010 throws ClassFormatError
1011 {
1012 protectionDomain = preDefineClass(name, protectionDomain);
1013 String source = defineClassSourceLocation(protectionDomain);
1014 Class<?> c = defineClass1(this, name, b, off, len, protectionDomain, source);
1015 postDefineClass(c, protectionDomain);
1016 return c;
1017 }
1018
1019 /**
1020 * Converts a {@link java.nio.ByteBuffer ByteBuffer} into an instance
1021 * of class {@code Class}, with the given {@code ProtectionDomain}.
1022 * If the given {@code ProtectionDomain} is {@code null}, then a default
1023 * protection domain will be assigned to the class as
1024 * specified in the documentation for {@link #defineClass(String, byte[],
1025 * int, int)}. Before the class can be used it must be resolved.
1026 *
1027 * <p>The rules about the first class defined in a package determining the
1028 * set of certificates for the package, the restrictions on class names,
1029 * and the defined package of the class
1030 * are identical to those specified in the documentation for {@link
1031 * #defineClass(String, byte[], int, int, ProtectionDomain)}.
1032 *
1033 * <p> An invocation of this method of the form
1034 * <i>cl</i>{@code .defineClass(}<i>name</i>{@code ,}
1035 * <i>bBuffer</i>{@code ,} <i>pd</i>{@code )} yields exactly the same
1036 * result as the statements
1037 *
1038 *<p> <code>
1039 * ...<br>
1040 * byte[] temp = new byte[bBuffer.{@link
1041 * java.nio.ByteBuffer#remaining remaining}()];<br>
1042 * bBuffer.{@link java.nio.ByteBuffer#get(byte[])
1043 * get}(temp);<br>
1044 * return {@link #defineClass(String, byte[], int, int, ProtectionDomain)
1045 * cl.defineClass}(name, temp, 0,
1046 * temp.length, pd);<br>
1047 * </code></p>
1048 *
1049 * @param name
1050 * The expected <a href="#binary-name">binary name</a>. of the class, or
1051 * {@code null} if not known
1052 *
1053 * @param b
1054 * The bytes that make up the class data. The bytes from positions
1055 * {@code b.position()} through {@code b.position() + b.limit() -1
1056 * } should have the format of a valid class file as defined by
1057 * <cite>The Java™ Virtual Machine Specification</cite>.
1058 *
1059 * @param protectionDomain
1060 * The {@code ProtectionDomain} of the class, or {@code null}.
1061 *
1062 * @return The {@code Class} object created from the data,
1063 * and {@code ProtectionDomain}.
1064 *
1065 * @throws ClassFormatError
1066 * If the data did not contain a valid class.
1067 *
1068 * @throws NoClassDefFoundError
1069 * If {@code name} is not {@code null} and not equal to the
1070 * <a href="#binary-name">binary name</a> of the class specified by {@code b}
1071 *
1072 * @throws SecurityException
1073 * If an attempt is made to add this class to a package that
1074 * contains classes that were signed by a different set of
1075 * certificates than this class, or if {@code name} begins with
1076 * "{@code java.}".
1077 *
1078 * @see #defineClass(String, byte[], int, int, ProtectionDomain)
1079 *
1080 * @since 1.5
1081 * @revised 9
1082 * @spec JPMS
1083 */
1084 protected final Class<?> defineClass(String name, java.nio.ByteBuffer b,
1085 ProtectionDomain protectionDomain)
1086 throws ClassFormatError
1087 {
1088 int len = b.remaining();
1089
1090 // Use byte[] if not a direct ByteBuffer:
1091 if (!b.isDirect()) {
1092 if (b.hasArray()) {
1093 return defineClass(name, b.array(),
1094 b.position() + b.arrayOffset(), len,
1095 protectionDomain);
1096 } else {
1097 // no array, or read-only array
1098 byte[] tb = new byte[len];
1099 b.get(tb); // get bytes out of byte buffer.
1100 return defineClass(name, tb, 0, len, protectionDomain);
1101 }
1102 }
1103
1104 protectionDomain = preDefineClass(name, protectionDomain);
1105 String source = defineClassSourceLocation(protectionDomain);
1106 Class<?> c = defineClass2(this, name, b, b.position(), len, protectionDomain, source);
1107 postDefineClass(c, protectionDomain);
1108 return c;
1109 }
1110
1111 static native Class<?> defineClass1(ClassLoader loader, String name, byte[] b, int off, int len,
1112 ProtectionDomain pd, String source);
1113
1114 static native Class<?> defineClass2(ClassLoader loader, String name, java.nio.ByteBuffer b,
1115 int off, int len, ProtectionDomain pd,
1116 String source);
1117
1118 /**
1119 * Defines a class of the given flags via Lookup.defineClass.
1120 *
1121 * @param loader the defining loader
1122 * @param lookup nest host of the Class to be defined
1123 * @param name the binary name or {@code null} if not findable
1124 * @param b class bytes
1125 * @param off the start offset in {@code b} of the class bytes
1126 * @param len the length of the class bytes
1127 * @param pd protection domain
1128 * @param initialize initialize the class
1129 * @param flags flags
1130 * @param classData class data
1131 */
1132 static native Class<?> defineClass0(ClassLoader loader,
1133 Class<?> lookup,
1134 String name,
1135 byte[] b, int off, int len,
1136 ProtectionDomain pd,
1137 boolean initialize,
1138 int flags,
1139 Object classData);
1140
1141 // true if the name is null or has the potential to be a valid binary name
1142 private boolean checkName(String name) {
1143 if ((name == null) || (name.isEmpty()))
1144 return true;
1145 if ((name.indexOf('/') != -1) || (name.charAt(0) == '['))
1146 return false;
1147 return true;
1148 }
1149
1150 private void checkCerts(String name, CodeSource cs) {
1151 int i = name.lastIndexOf('.');
1152 String pname = (i == -1) ? "" : name.substring(0, i);
1153
1154 Certificate[] certs = null;
1155 if (cs != null) {
1156 certs = cs.getCertificates();
1157 }
1158 certs = certs == null ? nocerts : certs;
1159 Certificate[] pcerts = package2certs.putIfAbsent(pname, certs);
1160 if (pcerts != null && !compareCerts(pcerts, certs)) {
1161 throw new SecurityException("class \"" + name
1162 + "\"'s signer information does not match signer information"
1163 + " of other classes in the same package");
1164 }
1165 }
1166
1167 /**
1168 * check to make sure the certs for the new class (certs) are the same as
1169 * the certs for the first class inserted in the package (pcerts)
1170 */
1171 private boolean compareCerts(Certificate[] pcerts, Certificate[] certs) {
1172 // empty array fast-path
1173 if (certs.length == 0)
1174 return pcerts.length == 0;
1175
1176 // the length must be the same at this point
1177 if (certs.length != pcerts.length)
1178 return false;
1179
1180 // go through and make sure all the certs in one array
1181 // are in the other and vice-versa.
1182 boolean match;
1183 for (Certificate cert : certs) {
1184 match = false;
1185 for (Certificate pcert : pcerts) {
1186 if (cert.equals(pcert)) {
1187 match = true;
1188 break;
1189 }
1190 }
1191 if (!match) return false;
1192 }
1193
1194 // now do the same for pcerts
1195 for (Certificate pcert : pcerts) {
1196 match = false;
1197 for (Certificate cert : certs) {
1198 if (pcert.equals(cert)) {
1199 match = true;
1200 break;
1201 }
1202 }
1203 if (!match) return false;
1204 }
1205
1206 return true;
1207 }
1208
1209 /**
1210 * Links the specified class. This (misleadingly named) method may be
1211 * used by a class loader to link a class. If the class {@code c} has
1212 * already been linked, then this method simply returns. Otherwise, the
1213 * class is linked as described in the "Execution" chapter of
1214 * <cite>The Java™ Language Specification</cite>.
1215 *
1216 * @param c
1217 * The class to link
1218 *
1219 * @throws NullPointerException
1220 * If {@code c} is {@code null}.
1221 *
1222 * @see #defineClass(String, byte[], int, int)
1223 */
1224 protected final void resolveClass(Class<?> c) {
1225 if (c == null) {
1226 throw new NullPointerException();
1227 }
1228 }
1229
1230 /**
1231 * Finds a class with the specified <a href="#binary-name">binary name</a>,
1232 * loading it if necessary.
1233 *
1234 * <p> This method loads the class through the system class loader (see
1235 * {@link #getSystemClassLoader()}). The {@code Class} object returned
1236 * might have more than one {@code ClassLoader} associated with it.
1237 * Subclasses of {@code ClassLoader} need not usually invoke this method,
1238 * because most class loaders need to override just {@link
1239 * #findClass(String)}. </p>
1240 *
1241 * @param name
1242 * The <a href="#binary-name">binary name</a> of the class
1243 *
1244 * @return The {@code Class} object for the specified {@code name}
1245 *
1246 * @throws ClassNotFoundException
1247 * If the class could not be found
1248 *
1249 * @see #ClassLoader(ClassLoader)
1250 * @see #getParent()
1251 */
1252 protected final Class<?> findSystemClass(String name)
1253 throws ClassNotFoundException
1254 {
1255 return getSystemClassLoader().loadClass(name);
1256 }
1257
1258 /**
1259 * Returns a class loaded by the bootstrap class loader;
1260 * or return null if not found.
1261 */
1262 Class<?> findBootstrapClassOrNull(String name) {
1263 if (!checkName(name)) return null;
1264
1265 return findBootstrapClass(name);
1266 }
1267
1268 // return null if not found
1269 private native Class<?> findBootstrapClass(String name);
1270
1271 /**
1272 * Returns the class with the given <a href="#binary-name">binary name</a> if this
1273 * loader has been recorded by the Java virtual machine as an initiating
1274 * loader of a class with that <a href="#binary-name">binary name</a>. Otherwise
1275 * {@code null} is returned.
1276 *
1277 * @param name
1278 * The <a href="#binary-name">binary name</a> of the class
1279 *
1280 * @return The {@code Class} object, or {@code null} if the class has
1281 * not been loaded
1282 *
1283 * @since 1.1
1284 */
1285 protected final Class<?> findLoadedClass(String name) {
1286 if (!checkName(name))
1287 return null;
1288 return findLoadedClass0(name);
1289 }
1290
1291 private final native Class<?> findLoadedClass0(String name);
1292
1293 /**
1294 * Sets the signers of a class. This should be invoked after defining a
1295 * class.
1296 *
1297 * @param c
1298 * The {@code Class} object
1299 *
1300 * @param signers
1301 * The signers for the class
1302 *
1303 * @since 1.1
1304 */
1305 protected final void setSigners(Class<?> c, Object[] signers) {
1306 c.setSigners(signers);
1307 }
1308
1309
1310 // -- Resources --
1311
1312 /**
1313 * Returns a URL to a resource in a module defined to this class loader.
1314 * Class loader implementations that support loading from modules
1315 * should override this method.
1316 *
1317 * @apiNote This method is the basis for the {@link
1318 * Class#getResource Class.getResource}, {@link Class#getResourceAsStream
1319 * Class.getResourceAsStream}, and {@link Module#getResourceAsStream
1320 * Module.getResourceAsStream} methods. It is not subject to the rules for
1321 * encapsulation specified by {@code Module.getResourceAsStream}.
1322 *
1323 * @implSpec The default implementation attempts to find the resource by
1324 * invoking {@link #findResource(String)} when the {@code moduleName} is
1325 * {@code null}. It otherwise returns {@code null}.
1326 *
1327 * @param moduleName
1328 * The module name; or {@code null} to find a resource in the
1329 * {@linkplain #getUnnamedModule() unnamed module} for this
1330 * class loader
1331 * @param name
1332 * The resource name
1333 *
1334 * @return A URL to the resource; {@code null} if the resource could not be
1335 * found, a URL could not be constructed to locate the resource,
1336 * access to the resource is denied by the security manager, or
1337 * there isn't a module of the given name defined to the class
1338 * loader.
1339 *
1340 * @throws IOException
1341 * If I/O errors occur
1342 *
1343 * @see java.lang.module.ModuleReader#find(String)
1344 * @since 9
1345 * @spec JPMS
1346 */
1347 protected URL findResource(String moduleName, String name) throws IOException {
1348 if (moduleName == null) {
1349 return findResource(name);
1350 } else {
1351 return null;
1352 }
1353 }
1354
1355 /**
1356 * Finds the resource with the given name. A resource is some data
1357 * (images, audio, text, etc) that can be accessed by class code in a way
1358 * that is independent of the location of the code.
1359 *
1360 * <p> The name of a resource is a '{@code /}'-separated path name that
1361 * identifies the resource. </p>
1362 *
1363 * <p> Resources in named modules are subject to the encapsulation rules
1364 * specified by {@link Module#getResourceAsStream Module.getResourceAsStream}.
1365 * Additionally, and except for the special case where the resource has a
1366 * name ending with "{@code .class}", this method will only find resources in
1367 * packages of named modules when the package is {@link Module#isOpen(String)
1368 * opened} unconditionally (even if the caller of this method is in the
1369 * same module as the resource). </p>
1370 *
1371 * @implSpec The default implementation will first search the parent class
1372 * loader for the resource; if the parent is {@code null} the path of the
1373 * class loader built into the virtual machine is searched. If not found,
1374 * this method will invoke {@link #findResource(String)} to find the resource.
1375 *
1376 * @apiNote Where several modules are defined to the same class loader,
1377 * and where more than one module contains a resource with the given name,
1378 * then the ordering that modules are searched is not specified and may be
1379 * very unpredictable.
1380 * When overriding this method it is recommended that an implementation
1381 * ensures that any delegation is consistent with the {@link
1382 * #getResources(java.lang.String) getResources(String)} method.
1383 *
1384 * @param name
1385 * The resource name
1386 *
1387 * @return {@code URL} object for reading the resource; {@code null} if
1388 * the resource could not be found, a {@code URL} could not be
1389 * constructed to locate the resource, the resource is in a package
1390 * that is not opened unconditionally, or access to the resource is
1391 * denied by the security manager.
1392 *
1393 * @throws NullPointerException If {@code name} is {@code null}
1394 *
1395 * @since 1.1
1396 * @revised 9
1397 * @spec JPMS
1398 */
1399 public URL getResource(String name) {
1400 Objects.requireNonNull(name);
1401 URL url;
1402 if (parent != null) {
1403 url = parent.getResource(name);
1404 } else {
1405 url = BootLoader.findResource(name);
1406 }
1407 if (url == null) {
1408 url = findResource(name);
1409 }
1410 return url;
1411 }
1412
1413 /**
1414 * Finds all the resources with the given name. A resource is some data
1415 * (images, audio, text, etc) that can be accessed by class code in a way
1416 * that is independent of the location of the code.
1417 *
1418 * <p> The name of a resource is a {@code /}-separated path name that
1419 * identifies the resource. </p>
1420 *
1421 * <p> Resources in named modules are subject to the encapsulation rules
1422 * specified by {@link Module#getResourceAsStream Module.getResourceAsStream}.
1423 * Additionally, and except for the special case where the resource has a
1424 * name ending with "{@code .class}", this method will only find resources in
1425 * packages of named modules when the package is {@link Module#isOpen(String)
1426 * opened} unconditionally (even if the caller of this method is in the
1427 * same module as the resource). </p>
1428 *
1429 * @implSpec The default implementation will first search the parent class
1430 * loader for the resource; if the parent is {@code null} the path of the
1431 * class loader built into the virtual machine is searched. It then
1432 * invokes {@link #findResources(String)} to find the resources with the
1433 * name in this class loader. It returns an enumeration whose elements
1434 * are the URLs found by searching the parent class loader followed by
1435 * the elements found with {@code findResources}.
1436 *
1437 * @apiNote Where several modules are defined to the same class loader,
1438 * and where more than one module contains a resource with the given name,
1439 * then the ordering is not specified and may be very unpredictable.
1440 * When overriding this method it is recommended that an
1441 * implementation ensures that any delegation is consistent with the {@link
1442 * #getResource(java.lang.String) getResource(String)} method. This should
1443 * ensure that the first element returned by the Enumeration's
1444 * {@code nextElement} method is the same resource that the
1445 * {@code getResource(String)} method would return.
1446 *
1447 * @param name
1448 * The resource name
1449 *
1450 * @return An enumeration of {@link java.net.URL URL} objects for the
1451 * resource. If no resources could be found, the enumeration will
1452 * be empty. Resources for which a {@code URL} cannot be
1453 * constructed, are in a package that is not opened
1454 * unconditionally, or access to the resource is denied by the
1455 * security manager, are not returned in the enumeration.
1456 *
1457 * @throws IOException
1458 * If I/O errors occur
1459 * @throws NullPointerException If {@code name} is {@code null}
1460 *
1461 * @since 1.2
1462 * @revised 9
1463 * @spec JPMS
1464 */
1465 public Enumeration<URL> getResources(String name) throws IOException {
1466 Objects.requireNonNull(name);
1467 @SuppressWarnings("unchecked")
1468 Enumeration<URL>[] tmp = (Enumeration<URL>[]) new Enumeration<?>[2];
1469 if (parent != null) {
1470 tmp[0] = parent.getResources(name);
1471 } else {
1472 tmp[0] = BootLoader.findResources(name);
1473 }
1474 tmp[1] = findResources(name);
1475
1476 return new CompoundEnumeration<>(tmp);
1477 }
1478
1479 /**
1480 * Returns a stream whose elements are the URLs of all the resources with
1481 * the given name. A resource is some data (images, audio, text, etc) that
1482 * can be accessed by class code in a way that is independent of the
1483 * location of the code.
1484 *
1485 * <p> The name of a resource is a {@code /}-separated path name that
1486 * identifies the resource.
1487 *
1488 * <p> The resources will be located when the returned stream is evaluated.
1489 * If the evaluation results in an {@code IOException} then the I/O
1490 * exception is wrapped in an {@link UncheckedIOException} that is then
1491 * thrown.
1492 *
1493 * <p> Resources in named modules are subject to the encapsulation rules
1494 * specified by {@link Module#getResourceAsStream Module.getResourceAsStream}.
1495 * Additionally, and except for the special case where the resource has a
1496 * name ending with "{@code .class}", this method will only find resources in
1497 * packages of named modules when the package is {@link Module#isOpen(String)
1498 * opened} unconditionally (even if the caller of this method is in the
1499 * same module as the resource). </p>
1500 *
1501 * @implSpec The default implementation invokes {@link #getResources(String)
1502 * getResources} to find all the resources with the given name and returns
1503 * a stream with the elements in the enumeration as the source.
1504 *
1505 * @apiNote When overriding this method it is recommended that an
1506 * implementation ensures that any delegation is consistent with the {@link
1507 * #getResource(java.lang.String) getResource(String)} method. This should
1508 * ensure that the first element returned by the stream is the same
1509 * resource that the {@code getResource(String)} method would return.
1510 *
1511 * @param name
1512 * The resource name
1513 *
1514 * @return A stream of resource {@link java.net.URL URL} objects. If no
1515 * resources could be found, the stream will be empty. Resources
1516 * for which a {@code URL} cannot be constructed, are in a package
1517 * that is not opened unconditionally, or access to the resource
1518 * is denied by the security manager, will not be in the stream.
1519 *
1520 * @throws NullPointerException If {@code name} is {@code null}
1521 *
1522 * @since 9
1523 */
1524 public Stream<URL> resources(String name) {
1525 Objects.requireNonNull(name);
1526 int characteristics = Spliterator.NONNULL | Spliterator.IMMUTABLE;
1527 Supplier<Spliterator<URL>> si = () -> {
1528 try {
1529 return Spliterators.spliteratorUnknownSize(
1530 getResources(name).asIterator(), characteristics);
1531 } catch (IOException e) {
1532 throw new UncheckedIOException(e);
1533 }
1534 };
1535 return StreamSupport.stream(si, characteristics, false);
1536 }
1537
1538 /**
1539 * Finds the resource with the given name. Class loader implementations
1540 * should override this method.
1541 *
1542 * <p> For resources in named modules then the method must implement the
1543 * rules for encapsulation specified in the {@code Module} {@link
1544 * Module#getResourceAsStream getResourceAsStream} method. Additionally,
1545 * it must not find non-"{@code .class}" resources in packages of named
1546 * modules unless the package is {@link Module#isOpen(String) opened}
1547 * unconditionally. </p>
1548 *
1549 * @implSpec The default implementation returns {@code null}.
1550 *
1551 * @param name
1552 * The resource name
1553 *
1554 * @return {@code URL} object for reading the resource; {@code null} if
1555 * the resource could not be found, a {@code URL} could not be
1556 * constructed to locate the resource, the resource is in a package
1557 * that is not opened unconditionally, or access to the resource is
1558 * denied by the security manager.
1559 *
1560 * @since 1.2
1561 * @revised 9
1562 * @spec JPMS
1563 */
1564 protected URL findResource(String name) {
1565 return null;
1566 }
1567
1568 /**
1569 * Returns an enumeration of {@link java.net.URL URL} objects
1570 * representing all the resources with the given name. Class loader
1571 * implementations should override this method.
1572 *
1573 * <p> For resources in named modules then the method must implement the
1574 * rules for encapsulation specified in the {@code Module} {@link
1575 * Module#getResourceAsStream getResourceAsStream} method. Additionally,
1576 * it must not find non-"{@code .class}" resources in packages of named
1577 * modules unless the package is {@link Module#isOpen(String) opened}
1578 * unconditionally. </p>
1579 *
1580 * @implSpec The default implementation returns an enumeration that
1581 * contains no elements.
1582 *
1583 * @param name
1584 * The resource name
1585 *
1586 * @return An enumeration of {@link java.net.URL URL} objects for
1587 * the resource. If no resources could be found, the enumeration
1588 * will be empty. Resources for which a {@code URL} cannot be
1589 * constructed, are in a package that is not opened unconditionally,
1590 * or access to the resource is denied by the security manager,
1591 * are not returned in the enumeration.
1592 *
1593 * @throws IOException
1594 * If I/O errors occur
1595 *
1596 * @since 1.2
1597 * @revised 9
1598 * @spec JPMS
1599 */
1600 protected Enumeration<URL> findResources(String name) throws IOException {
1601 return Collections.emptyEnumeration();
1602 }
1603
1604 /**
1605 * Registers the caller as
1606 * {@linkplain #isRegisteredAsParallelCapable() parallel capable}.
1607 * The registration succeeds if and only if all of the following
1608 * conditions are met:
1609 * <ol>
1610 * <li> no instance of the caller has been created</li>
1611 * <li> all of the super classes (except class Object) of the caller are
1612 * registered as parallel capable</li>
1613 * </ol>
1614 * <p>Note that once a class loader is registered as parallel capable, there
1615 * is no way to change it back.</p>
1616 *
1617 * @return {@code true} if the caller is successfully registered as
1618 * parallel capable and {@code false} if otherwise.
1619 *
1620 * @see #isRegisteredAsParallelCapable()
1621 *
1622 * @since 1.7
1623 */
1624 @CallerSensitive
1625 protected static boolean registerAsParallelCapable() {
1626 Class<? extends ClassLoader> callerClass =
1627 Reflection.getCallerClass().asSubclass(ClassLoader.class);
1628 return ParallelLoaders.register(callerClass);
1629 }
1630
1631 /**
1632 * Returns {@code true} if this class loader is registered as
1633 * {@linkplain #registerAsParallelCapable parallel capable}, otherwise
1634 * {@code false}.
1635 *
1636 * @return {@code true} if this class loader is parallel capable,
1637 * otherwise {@code false}.
1638 *
1639 * @see #registerAsParallelCapable()
1640 *
1641 * @since 9
1642 */
1643 public final boolean isRegisteredAsParallelCapable() {
1644 return ParallelLoaders.isRegistered(this.getClass());
1645 }
1646
1647 /**
1648 * Find a resource of the specified name from the search path used to load
1649 * classes. This method locates the resource through the system class
1650 * loader (see {@link #getSystemClassLoader()}).
1651 *
1652 * <p> Resources in named modules are subject to the encapsulation rules
1653 * specified by {@link Module#getResourceAsStream Module.getResourceAsStream}.
1654 * Additionally, and except for the special case where the resource has a
1655 * name ending with "{@code .class}", this method will only find resources in
1656 * packages of named modules when the package is {@link Module#isOpen(String)
1657 * opened} unconditionally. </p>
1658 *
1659 * @param name
1660 * The resource name
1661 *
1662 * @return A {@link java.net.URL URL} to the resource; {@code
1663 * null} if the resource could not be found, a URL could not be
1664 * constructed to locate the resource, the resource is in a package
1665 * that is not opened unconditionally or access to the resource is
1666 * denied by the security manager.
1667 *
1668 * @since 1.1
1669 * @revised 9
1670 * @spec JPMS
1671 */
1672 public static URL getSystemResource(String name) {
1673 return getSystemClassLoader().getResource(name);
1674 }
1675
1676 /**
1677 * Finds all resources of the specified name from the search path used to
1678 * load classes. The resources thus found are returned as an
1679 * {@link java.util.Enumeration Enumeration} of {@link
1680 * java.net.URL URL} objects.
1681 *
1682 * <p> The search order is described in the documentation for {@link
1683 * #getSystemResource(String)}. </p>
1684 *
1685 * <p> Resources in named modules are subject to the encapsulation rules
1686 * specified by {@link Module#getResourceAsStream Module.getResourceAsStream}.
1687 * Additionally, and except for the special case where the resource has a
1688 * name ending with "{@code .class}", this method will only find resources in
1689 * packages of named modules when the package is {@link Module#isOpen(String)
1690 * opened} unconditionally. </p>
1691 *
1692 * @param name
1693 * The resource name
1694 *
1695 * @return An enumeration of {@link java.net.URL URL} objects for
1696 * the resource. If no resources could be found, the enumeration
1697 * will be empty. Resources for which a {@code URL} cannot be
1698 * constructed, are in a package that is not opened unconditionally,
1699 * or access to the resource is denied by the security manager,
1700 * are not returned in the enumeration.
1701 *
1702 * @throws IOException
1703 * If I/O errors occur
1704 *
1705 * @since 1.2
1706 * @revised 9
1707 * @spec JPMS
1708 */
1709 public static Enumeration<URL> getSystemResources(String name)
1710 throws IOException
1711 {
1712 return getSystemClassLoader().getResources(name);
1713 }
1714
1715 /**
1716 * Returns an input stream for reading the specified resource.
1717 *
1718 * <p> The search order is described in the documentation for {@link
1719 * #getResource(String)}. </p>
1720 *
1721 * <p> Resources in named modules are subject to the encapsulation rules
1722 * specified by {@link Module#getResourceAsStream Module.getResourceAsStream}.
1723 * Additionally, and except for the special case where the resource has a
1724 * name ending with "{@code .class}", this method will only find resources in
1725 * packages of named modules when the package is {@link Module#isOpen(String)
1726 * opened} unconditionally. </p>
1727 *
1728 * @param name
1729 * The resource name
1730 *
1731 * @return An input stream for reading the resource; {@code null} if the
1732 * resource could not be found, the resource is in a package that
1733 * is not opened unconditionally, or access to the resource is
1734 * denied by the security manager.
1735 *
1736 * @throws NullPointerException If {@code name} is {@code null}
1737 *
1738 * @since 1.1
1739 * @revised 9
1740 * @spec JPMS
1741 */
1742 public InputStream getResourceAsStream(String name) {
1743 Objects.requireNonNull(name);
1744 URL url = getResource(name);
1745 try {
1746 return url != null ? url.openStream() : null;
1747 } catch (IOException e) {
1748 return null;
1749 }
1750 }
1751
1752 /**
1753 * Open for reading, a resource of the specified name from the search path
1754 * used to load classes. This method locates the resource through the
1755 * system class loader (see {@link #getSystemClassLoader()}).
1756 *
1757 * <p> Resources in named modules are subject to the encapsulation rules
1758 * specified by {@link Module#getResourceAsStream Module.getResourceAsStream}.
1759 * Additionally, and except for the special case where the resource has a
1760 * name ending with "{@code .class}", this method will only find resources in
1761 * packages of named modules when the package is {@link Module#isOpen(String)
1762 * opened} unconditionally. </p>
1763 *
1764 * @param name
1765 * The resource name
1766 *
1767 * @return An input stream for reading the resource; {@code null} if the
1768 * resource could not be found, the resource is in a package that
1769 * is not opened unconditionally, or access to the resource is
1770 * denied by the security manager.
1771 *
1772 * @since 1.1
1773 * @revised 9
1774 * @spec JPMS
1775 */
1776 public static InputStream getSystemResourceAsStream(String name) {
1777 URL url = getSystemResource(name);
1778 try {
1779 return url != null ? url.openStream() : null;
1780 } catch (IOException e) {
1781 return null;
1782 }
1783 }
1784
1785
1786 // -- Hierarchy --
1787
1788 /**
1789 * Returns the parent class loader for delegation. Some implementations may
1790 * use {@code null} to represent the bootstrap class loader. This method
1791 * will return {@code null} in such implementations if this class loader's
1792 * parent is the bootstrap class loader.
1793 *
1794 * @return The parent {@code ClassLoader}
1795 *
1796 * @throws SecurityException
1797 * If a security manager is present, and the caller's class loader
1798 * is not {@code null} and is not an ancestor of this class loader,
1799 * and the caller does not have the
1800 * {@link RuntimePermission}{@code ("getClassLoader")}
1801 *
1802 * @since 1.2
1803 */
1804 @CallerSensitive
1805 public final ClassLoader getParent() {
1806 if (parent == null)
1807 return null;
1808 SecurityManager sm = System.getSecurityManager();
1809 if (sm != null) {
1810 // Check access to the parent class loader
1811 // If the caller's class loader is same as this class loader,
1812 // permission check is performed.
1813 checkClassLoaderPermission(parent, Reflection.getCallerClass());
1814 }
1815 return parent;
1816 }
1817
1818 /**
1819 * Returns the unnamed {@code Module} for this class loader.
1820 *
1821 * @return The unnamed Module for this class loader
1822 *
1823 * @see Module#isNamed()
1824 * @since 9
1825 * @spec JPMS
1826 */
1827 public final Module getUnnamedModule() {
1828 return unnamedModule;
1829 }
1830
1831 /**
1832 * Returns the platform class loader. All
1833 * <a href="#builtinLoaders">platform classes</a> are visible to
1834 * the platform class loader.
1835 *
1836 * @implNote The name of the builtin platform class loader is
1837 * {@code "platform"}.
1838 *
1839 * @return The platform {@code ClassLoader}.
1840 *
1841 * @throws SecurityException
1842 * If a security manager is present, and the caller's class loader is
1843 * not {@code null}, and the caller's class loader is not the same
1844 * as or an ancestor of the platform class loader,
1845 * and the caller does not have the
1846 * {@link RuntimePermission}{@code ("getClassLoader")}
1847 *
1848 * @since 9
1849 * @spec JPMS
1850 */
1851 @CallerSensitive
1852 public static ClassLoader getPlatformClassLoader() {
1853 SecurityManager sm = System.getSecurityManager();
1854 ClassLoader loader = getBuiltinPlatformClassLoader();
1855 if (sm != null) {
1856 checkClassLoaderPermission(loader, Reflection.getCallerClass());
1857 }
1858 return loader;
1859 }
1860
1861 /**
1862 * Returns the system class loader. This is the default
1863 * delegation parent for new {@code ClassLoader} instances, and is
1864 * typically the class loader used to start the application.
1865 *
1866 * <p> This method is first invoked early in the runtime's startup
1867 * sequence, at which point it creates the system class loader. This
1868 * class loader will be the context class loader for the main application
1869 * thread (for example, the thread that invokes the {@code main} method of
1870 * the main class).
1871 *
1872 * <p> The default system class loader is an implementation-dependent
1873 * instance of this class.
1874 *
1875 * <p> If the system property "{@systemProperty java.system.class.loader}"
1876 * is defined when this method is first invoked then the value of that
1877 * property is taken to be the name of a class that will be returned as the
1878 * system class loader. The class is loaded using the default system class
1879 * loader and must define a public constructor that takes a single parameter
1880 * of type {@code ClassLoader} which is used as the delegation parent. An
1881 * instance is then created using this constructor with the default system
1882 * class loader as the parameter. The resulting class loader is defined
1883 * to be the system class loader. During construction, the class loader
1884 * should take great care to avoid calling {@code getSystemClassLoader()}.
1885 * If circular initialization of the system class loader is detected then
1886 * an {@code IllegalStateException} is thrown.
1887 *
1888 * @implNote The system property to override the system class loader is not
1889 * examined until the VM is almost fully initialized. Code that executes
1890 * this method during startup should take care not to cache the return
1891 * value until the system is fully initialized.
1892 *
1893 * <p> The name of the built-in system class loader is {@code "app"}.
1894 * The system property "{@code java.class.path}" is read during early
1895 * initialization of the VM to determine the class path.
1896 * An empty value of "{@code java.class.path}" property is interpreted
1897 * differently depending on whether the initial module (the module
1898 * containing the main class) is named or unnamed:
1899 * If named, the built-in system class loader will have no class path and
1900 * will search for classes and resources using the application module path;
1901 * otherwise, if unnamed, it will set the class path to the current
1902 * working directory.
1903 *
1904 * <p> JAR files on the class path may contain a {@code Class-Path} manifest
1905 * attribute to specify dependent JAR files to be included in the class path.
1906 * {@code Class-Path} entries must meet certain conditions for validity (see
1907 * the <a href="{@docRoot}/../specs/jar/jar.html#class-path-attribute">
1908 * JAR File Specification</a> for details). Invalid {@code Class-Path}
1909 * entries are ignored. For debugging purposes, ignored entries can be
1910 * printed to the console if the
1911 * {@systemProperty jdk.net.URLClassPath.showIgnoredClassPathEntries} system
1912 * property is set to {@code true}.
1913 *
1914 * @return The system {@code ClassLoader}
1915 *
1916 * @throws SecurityException
1917 * If a security manager is present, and the caller's class loader
1918 * is not {@code null} and is not the same as or an ancestor of the
1919 * system class loader, and the caller does not have the
1920 * {@link RuntimePermission}{@code ("getClassLoader")}
1921 *
1922 * @throws IllegalStateException
1923 * If invoked recursively during the construction of the class
1924 * loader specified by the "{@code java.system.class.loader}"
1925 * property.
1926 *
1927 * @throws Error
1928 * If the system property "{@code java.system.class.loader}"
1929 * is defined but the named class could not be loaded, the
1930 * provider class does not define the required constructor, or an
1931 * exception is thrown by that constructor when it is invoked. The
1932 * underlying cause of the error can be retrieved via the
1933 * {@link Throwable#getCause()} method.
1934 *
1935 * @revised 1.4
1936 * @revised 9
1937 * @spec JPMS
1938 */
1939 @CallerSensitive
1940 public static ClassLoader getSystemClassLoader() {
1941 switch (VM.initLevel()) {
1942 case 0:
1943 case 1:
1944 case 2:
1945 // the system class loader is the built-in app class loader during startup
1946 return getBuiltinAppClassLoader();
1947 case 3:
1948 String msg = "getSystemClassLoader cannot be called during the system class loader instantiation";
1949 throw new IllegalStateException(msg);
1950 default:
1951 // system fully initialized
1952 assert VM.isBooted() && scl != null;
1953 SecurityManager sm = System.getSecurityManager();
1954 if (sm != null) {
1955 checkClassLoaderPermission(scl, Reflection.getCallerClass());
1956 }
1957 return scl;
1958 }
1959 }
1960
1961 static ClassLoader getBuiltinPlatformClassLoader() {
1962 return ClassLoaders.platformClassLoader();
1963 }
1964
1965 static ClassLoader getBuiltinAppClassLoader() {
1966 return ClassLoaders.appClassLoader();
1967 }
1968
1969 /*
1970 * Initialize the system class loader that may be a custom class on the
1971 * application class path or application module path.
1972 *
1973 * @see java.lang.System#initPhase3
1974 */
1975 static synchronized ClassLoader initSystemClassLoader() {
1976 if (VM.initLevel() != 3) {
1977 throw new InternalError("system class loader cannot be set at initLevel " +
1978 VM.initLevel());
1979 }
1980
1981 // detect recursive initialization
1982 if (scl != null) {
1983 throw new IllegalStateException("recursive invocation");
1984 }
1985
1986 ClassLoader builtinLoader = getBuiltinAppClassLoader();
1987
1988 // All are privileged frames. No need to call doPrivileged.
1989 String cn = System.getProperty("java.system.class.loader");
1990 if (cn != null) {
1991 try {
1992 // custom class loader is only supported to be loaded from unnamed module
1993 Constructor<?> ctor = Class.forName(cn, false, builtinLoader)
1994 .getDeclaredConstructor(ClassLoader.class);
1995 scl = (ClassLoader) ctor.newInstance(builtinLoader);
1996 } catch (Exception e) {
1997 Throwable cause = e;
1998 if (e instanceof InvocationTargetException) {
1999 cause = e.getCause();
2000 if (cause instanceof Error) {
2001 throw (Error) cause;
2002 }
2003 }
2004 if (cause instanceof RuntimeException) {
2005 throw (RuntimeException) cause;
2006 }
2007 throw new Error(cause.getMessage(), cause);
2008 }
2009 } else {
2010 scl = builtinLoader;
2011 }
2012 return scl;
2013 }
2014
2015 // Returns true if the specified class loader can be found in this class
2016 // loader's delegation chain.
2017 boolean isAncestor(ClassLoader cl) {
2018 ClassLoader acl = this;
2019 do {
2020 acl = acl.parent;
2021 if (cl == acl) {
2022 return true;
2023 }
2024 } while (acl != null);
2025 return false;
2026 }
2027
2028 // Tests if class loader access requires "getClassLoader" permission
2029 // check. A class loader 'from' can access class loader 'to' if
2030 // class loader 'from' is same as class loader 'to' or an ancestor
2031 // of 'to'. The class loader in a system domain can access
2032 // any class loader.
2033 private static boolean needsClassLoaderPermissionCheck(ClassLoader from,
2034 ClassLoader to)
2035 {
2036 if (from == to)
2037 return false;
2038
2039 if (from == null)
2040 return false;
2041
2042 return !to.isAncestor(from);
2043 }
2044
2045 // Returns the class's class loader, or null if none.
2046 static ClassLoader getClassLoader(Class<?> caller) {
2047 // This can be null if the VM is requesting it
2048 if (caller == null) {
2049 return null;
2050 }
2051 // Circumvent security check since this is package-private
2052 return caller.getClassLoader0();
2053 }
2054
2055 /*
2056 * Checks RuntimePermission("getClassLoader") permission
2057 * if caller's class loader is not null and caller's class loader
2058 * is not the same as or an ancestor of the given cl argument.
2059 */
2060 static void checkClassLoaderPermission(ClassLoader cl, Class<?> caller) {
2061 SecurityManager sm = System.getSecurityManager();
2062 if (sm != null) {
2063 // caller can be null if the VM is requesting it
2064 ClassLoader ccl = getClassLoader(caller);
2065 if (needsClassLoaderPermissionCheck(ccl, cl)) {
2066 sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
2067 }
2068 }
2069 }
2070
2071 // The system class loader
2072 // @GuardedBy("ClassLoader.class")
2073 private static volatile ClassLoader scl;
2074
2075 // -- Package --
2076
2077 /**
2078 * Define a Package of the given Class object.
2079 *
2080 * If the given class represents an array type, a primitive type or void,
2081 * this method returns {@code null}.
2082 *
2083 * This method does not throw IllegalArgumentException.
2084 */
2085 Package definePackage(Class<?> c) {
2086 if (c.isPrimitive() || c.isArray()) {
2087 return null;
2088 }
2089
2090 return definePackage(c.getPackageName(), c.getModule());
2091 }
2092
2093 /**
2094 * Defines a Package of the given name and module
2095 *
2096 * This method does not throw IllegalArgumentException.
2097 *
2098 * @param name package name
2099 * @param m module
2100 */
2101 Package definePackage(String name, Module m) {
2102 if (name.isEmpty() && m.isNamed()) {
2103 throw new InternalError("unnamed package in " + m);
2104 }
2105
2106 // check if Package object is already defined
2107 NamedPackage pkg = packages.get(name);
2108 if (pkg instanceof Package)
2109 return (Package)pkg;
2110
2111 return (Package)packages.compute(name, (n, p) -> toPackage(n, p, m));
2112 }
2113
2114 /*
2115 * Returns a Package object for the named package
2116 */
2117 private Package toPackage(String name, NamedPackage p, Module m) {
2118 // define Package object if the named package is not yet defined
2119 if (p == null)
2120 return NamedPackage.toPackage(name, m);
2121
2122 // otherwise, replace the NamedPackage object with Package object
2123 if (p instanceof Package)
2124 return (Package)p;
2125
2126 return NamedPackage.toPackage(p.packageName(), p.module());
2127 }
2128
2129 /**
2130 * Defines a package by <a href="#binary-name">name</a> in this {@code ClassLoader}.
2131 * <p>
2132 * <a href="#binary-name">Package names</a> must be unique within a class loader and
2133 * cannot be redefined or changed once created.
2134 * <p>
2135 * If a class loader wishes to define a package with specific properties,
2136 * such as version information, then the class loader should call this
2137 * {@code definePackage} method before calling {@code defineClass}.
2138 * Otherwise, the
2139 * {@link #defineClass(String, byte[], int, int, ProtectionDomain) defineClass}
2140 * method will define a package in this class loader corresponding to the package
2141 * of the newly defined class; the properties of this defined package are
2142 * specified by {@link Package}.
2143 *
2144 * @apiNote
2145 * A class loader that wishes to define a package for classes in a JAR
2146 * typically uses the specification and implementation titles, versions, and
2147 * vendors from the JAR's manifest. If the package is specified as
2148 * {@linkplain java.util.jar.Attributes.Name#SEALED sealed} in the JAR's manifest,
2149 * the {@code URL} of the JAR file is typically used as the {@code sealBase}.
2150 * If classes of package {@code 'p'} defined by this class loader
2151 * are loaded from multiple JARs, the {@code Package} object may contain
2152 * different information depending on the first class of package {@code 'p'}
2153 * defined and which JAR's manifest is read first to explicitly define
2154 * package {@code 'p'}.
2155 *
2156 * <p> It is strongly recommended that a class loader does not call this
2157 * method to explicitly define packages in <em>named modules</em>; instead,
2158 * the package will be automatically defined when a class is {@linkplain
2159 * #defineClass(String, byte[], int, int, ProtectionDomain) being defined}.
2160 * If it is desirable to define {@code Package} explicitly, it should ensure
2161 * that all packages in a named module are defined with the properties
2162 * specified by {@link Package}. Otherwise, some {@code Package} objects
2163 * in a named module may be for example sealed with different seal base.
2164 *
2165 * @param name
2166 * The <a href="#binary-name">package name</a>
2167 *
2168 * @param specTitle
2169 * The specification title
2170 *
2171 * @param specVersion
2172 * The specification version
2173 *
2174 * @param specVendor
2175 * The specification vendor
2176 *
2177 * @param implTitle
2178 * The implementation title
2179 *
2180 * @param implVersion
2181 * The implementation version
2182 *
2183 * @param implVendor
2184 * The implementation vendor
2185 *
2186 * @param sealBase
2187 * If not {@code null}, then this package is sealed with
2188 * respect to the given code source {@link java.net.URL URL}
2189 * object. Otherwise, the package is not sealed.
2190 *
2191 * @return The newly defined {@code Package} object
2192 *
2193 * @throws NullPointerException
2194 * if {@code name} is {@code null}.
2195 *
2196 * @throws IllegalArgumentException
2197 * if a package of the given {@code name} is already
2198 * defined by this class loader
2199 *
2200 *
2201 * @since 1.2
2202 * @revised 9
2203 * @spec JPMS
2204 *
2205 * @jvms 5.3 Creation and Loading
2206 * @see <a href="{@docRoot}/../specs/jar/jar.html#package-sealing">
2207 * The JAR File Specification: Package Sealing</a>
2208 */
2209 protected Package definePackage(String name, String specTitle,
2210 String specVersion, String specVendor,
2211 String implTitle, String implVersion,
2212 String implVendor, URL sealBase)
2213 {
2214 Objects.requireNonNull(name);
2215
2216 // definePackage is not final and may be overridden by custom class loader
2217 Package p = new Package(name, specTitle, specVersion, specVendor,
2218 implTitle, implVersion, implVendor,
2219 sealBase, this);
2220
2221 if (packages.putIfAbsent(name, p) != null)
2222 throw new IllegalArgumentException(name);
2223
2224 return p;
2225 }
2226
2227 /**
2228 * Returns a {@code Package} of the given <a href="#binary-name">name</a> that
2229 * has been defined by this class loader.
2230 *
2231 * @param name The <a href="#binary-name">package name</a>
2232 *
2233 * @return The {@code Package} of the given name that has been defined
2234 * by this class loader, or {@code null} if not found
2235 *
2236 * @throws NullPointerException
2237 * if {@code name} is {@code null}.
2238 *
2239 * @jvms 5.3 Creation and Loading
2240 *
2241 * @since 9
2242 * @spec JPMS
2243 */
2244 public final Package getDefinedPackage(String name) {
2245 Objects.requireNonNull(name, "name cannot be null");
2246
2247 NamedPackage p = packages.get(name);
2248 if (p == null)
2249 return null;
2250
2251 return definePackage(name, p.module());
2252 }
2253
2254 /**
2255 * Returns all of the {@code Package}s that have been defined by
2256 * this class loader. The returned array has no duplicated {@code Package}s
2257 * of the same name.
2258 *
2259 * @apiNote This method returns an array rather than a {@code Set} or {@code Stream}
2260 * for consistency with the existing {@link #getPackages} method.
2261 *
2262 * @return The array of {@code Package} objects that have been defined by
2263 * this class loader; or an zero length array if no package has been
2264 * defined by this class loader.
2265 *
2266 * @jvms 5.3 Creation and Loading
2267 *
2268 * @since 9
2269 * @spec JPMS
2270 */
2271 public final Package[] getDefinedPackages() {
2272 return packages().toArray(Package[]::new);
2273 }
2274
2275 /**
2276 * Finds a package by <a href="#binary-name">name</a> in this class loader and its ancestors.
2277 * <p>
2278 * If this class loader defines a {@code Package} of the given name,
2279 * the {@code Package} is returned. Otherwise, the ancestors of
2280 * this class loader are searched recursively (parent by parent)
2281 * for a {@code Package} of the given name.
2282 *
2283 * @apiNote The {@link #getPlatformClassLoader() platform class loader}
2284 * may delegate to the application class loader but the application class
2285 * loader is not its ancestor. When invoked on the platform class loader,
2286 * this method will not find packages defined to the application
2287 * class loader.
2288 *
2289 * @param name
2290 * The <a href="#binary-name">package name</a>
2291 *
2292 * @return The {@code Package} of the given name that has been defined by
2293 * this class loader or its ancestors, or {@code null} if not found.
2294 *
2295 * @throws NullPointerException
2296 * if {@code name} is {@code null}.
2297 *
2298 * @deprecated
2299 * If multiple class loaders delegate to each other and define classes
2300 * with the same package name, and one such loader relies on the lookup
2301 * behavior of {@code getPackage} to return a {@code Package} from
2302 * a parent loader, then the properties exposed by the {@code Package}
2303 * may not be as expected in the rest of the program.
2304 * For example, the {@code Package} will only expose annotations from the
2305 * {@code package-info.class} file defined by the parent loader, even if
2306 * annotations exist in a {@code package-info.class} file defined by
2307 * a child loader. A more robust approach is to use the
2308 * {@link ClassLoader#getDefinedPackage} method which returns
2309 * a {@code Package} for the specified class loader.
2310 *
2311 * @see ClassLoader#getDefinedPackage(String)
2312 *
2313 * @since 1.2
2314 * @revised 9
2315 * @spec JPMS
2316 */
2317 @Deprecated(since="9")
2318 protected Package getPackage(String name) {
2319 Package pkg = getDefinedPackage(name);
2320 if (pkg == null) {
2321 if (parent != null) {
2322 pkg = parent.getPackage(name);
2323 } else {
2324 pkg = BootLoader.getDefinedPackage(name);
2325 }
2326 }
2327 return pkg;
2328 }
2329
2330 /**
2331 * Returns all of the {@code Package}s that have been defined by
2332 * this class loader and its ancestors. The returned array may contain
2333 * more than one {@code Package} object of the same package name, each
2334 * defined by a different class loader in the class loader hierarchy.
2335 *
2336 * @apiNote The {@link #getPlatformClassLoader() platform class loader}
2337 * may delegate to the application class loader. In other words,
2338 * packages in modules defined to the application class loader may be
2339 * visible to the platform class loader. On the other hand,
2340 * the application class loader is not its ancestor and hence
2341 * when invoked on the platform class loader, this method will not
2342 * return any packages defined to the application class loader.
2343 *
2344 * @return The array of {@code Package} objects that have been defined by
2345 * this class loader and its ancestors
2346 *
2347 * @see ClassLoader#getDefinedPackages()
2348 *
2349 * @since 1.2
2350 * @revised 9
2351 * @spec JPMS
2352 */
2353 protected Package[] getPackages() {
2354 Stream<Package> pkgs = packages();
2355 ClassLoader ld = parent;
2356 while (ld != null) {
2357 pkgs = Stream.concat(ld.packages(), pkgs);
2358 ld = ld.parent;
2359 }
2360 return Stream.concat(BootLoader.packages(), pkgs)
2361 .toArray(Package[]::new);
2362 }
2363
2364
2365
2366 // package-private
2367
2368 /**
2369 * Returns a stream of Packages defined in this class loader
2370 */
2371 Stream<Package> packages() {
2372 return packages.values().stream()
2373 .map(p -> definePackage(p.packageName(), p.module()));
2374 }
2375
2376 // -- Native library access --
2377
2378 /**
2379 * Returns the absolute path name of a native library. The VM invokes this
2380 * method to locate the native libraries that belong to classes loaded with
2381 * this class loader. If this method returns {@code null}, the VM
2382 * searches the library along the path specified as the
2383 * "{@code java.library.path}" property.
2384 *
2385 * @param libname
2386 * The library name
2387 *
2388 * @return The absolute path of the native library
2389 *
2390 * @see System#loadLibrary(String)
2391 * @see System#mapLibraryName(String)
2392 *
2393 * @since 1.2
2394 */
2395 protected String findLibrary(String libname) {
2396 return null;
2397 }
2398
2399 private final NativeLibraries libraries = NativeLibraries.jniNativeLibraries(this);
2400
2401 // Invoked in the java.lang.Runtime class to implement load and loadLibrary.
2402 static NativeLibrary loadLibrary(Class<?> fromClass, File file) {
2403 ClassLoader loader = (fromClass == null) ? null : fromClass.getClassLoader();
2404 NativeLibraries libs = loader != null ? loader.libraries : BootLoader.getNativeLibraries();
2405 NativeLibrary nl = libs.loadLibrary(fromClass, file);
2406 if (nl != null) {
2407 return nl;
2408 }
2409 throw new UnsatisfiedLinkError("Can't load library: " + file);
2410 }
2411 static NativeLibrary loadLibrary(Class<?> fromClass, String name) {
2412 ClassLoader loader = (fromClass == null) ? null : fromClass.getClassLoader();
2413 if (loader == null) {
2414 NativeLibrary nl = BootLoader.getNativeLibraries().loadLibrary(fromClass, name);
2415 if (nl != null) {
2416 return nl;
2417 }
2418 throw new UnsatisfiedLinkError("no " + name +
2419 " in system library path: " + StaticProperty.sunBootLibraryPath());
2420 }
2421
2422 NativeLibraries libs = loader.libraries;
2423 // First load from the file returned from ClassLoader::findLibrary, if found.
2424 String libfilename = loader.findLibrary(name);
2425 if (libfilename != null) {
2426 File libfile = new File(libfilename);
2427 if (!libfile.isAbsolute()) {
2428 throw new UnsatisfiedLinkError(
2429 "ClassLoader.findLibrary failed to return an absolute path: " + libfilename);
2430 }
2431 NativeLibrary nl = libs.loadLibrary(fromClass, libfile);
2432 if (nl != null) {
2433 return nl;
2434 }
2435 throw new UnsatisfiedLinkError("Can't load " + libfilename);
2436 }
2437 // Then load from system library path and java library path
2438 NativeLibrary nl = libs.loadLibrary(fromClass, name);
2439 if (nl != null) {
2440 return nl;
2441 }
2442
2443 // Oops, it failed
2444 throw new UnsatisfiedLinkError("no " + name +
2445 " in java.library.path: " + StaticProperty.javaLibraryPath());
2446 }
2447
2448 /*
2449 * Invoked in the VM class linking code.
2450 */
2451 private static long findNative(ClassLoader loader, String entryName) {
2452 if (loader == null) {
2453 return BootLoader.getNativeLibraries().find(entryName);
2454 } else {
2455 return loader.libraries.find(entryName);
2456 }
2457 }
2458
2459 // -- Assertion management --
2460
2461 final Object assertionLock;
2462
2463 // The default toggle for assertion checking.
2464 // @GuardedBy("assertionLock")
2465 private boolean defaultAssertionStatus = false;
2466
2467 // Maps String packageName to Boolean package default assertion status Note
2468 // that the default package is placed under a null map key. If this field
2469 // is null then we are delegating assertion status queries to the VM, i.e.,
2470 // none of this ClassLoader's assertion status modification methods have
2471 // been invoked.
2472 // @GuardedBy("assertionLock")
2473 private Map<String, Boolean> packageAssertionStatus = null;
2474
2475 // Maps String fullyQualifiedClassName to Boolean assertionStatus If this
2476 // field is null then we are delegating assertion status queries to the VM,
2477 // i.e., none of this ClassLoader's assertion status modification methods
2478 // have been invoked.
2479 // @GuardedBy("assertionLock")
2480 Map<String, Boolean> classAssertionStatus = null;
2481
2482 /**
2483 * Sets the default assertion status for this class loader. This setting
2484 * determines whether classes loaded by this class loader and initialized
2485 * in the future will have assertions enabled or disabled by default.
2486 * This setting may be overridden on a per-package or per-class basis by
2487 * invoking {@link #setPackageAssertionStatus(String, boolean)} or {@link
2488 * #setClassAssertionStatus(String, boolean)}.
2489 *
2490 * @param enabled
2491 * {@code true} if classes loaded by this class loader will
2492 * henceforth have assertions enabled by default, {@code false}
2493 * if they will have assertions disabled by default.
2494 *
2495 * @since 1.4
2496 */
2497 public void setDefaultAssertionStatus(boolean enabled) {
2498 synchronized (assertionLock) {
2499 if (classAssertionStatus == null)
2500 initializeJavaAssertionMaps();
2501
2502 defaultAssertionStatus = enabled;
2503 }
2504 }
2505
2506 /**
2507 * Sets the package default assertion status for the named package. The
2508 * package default assertion status determines the assertion status for
2509 * classes initialized in the future that belong to the named package or
2510 * any of its "subpackages".
2511 *
2512 * <p> A subpackage of a package named p is any package whose name begins
2513 * with "{@code p.}". For example, {@code javax.swing.text} is a
2514 * subpackage of {@code javax.swing}, and both {@code java.util} and
2515 * {@code java.lang.reflect} are subpackages of {@code java}.
2516 *
2517 * <p> In the event that multiple package defaults apply to a given class,
2518 * the package default pertaining to the most specific package takes
2519 * precedence over the others. For example, if {@code javax.lang} and
2520 * {@code javax.lang.reflect} both have package defaults associated with
2521 * them, the latter package default applies to classes in
2522 * {@code javax.lang.reflect}.
2523 *
2524 * <p> Package defaults take precedence over the class loader's default
2525 * assertion status, and may be overridden on a per-class basis by invoking
2526 * {@link #setClassAssertionStatus(String, boolean)}. </p>
2527 *
2528 * @param packageName
2529 * The name of the package whose package default assertion status
2530 * is to be set. A {@code null} value indicates the unnamed
2531 * package that is "current"
2532 * (see section 7.4.2 of
2533 * <cite>The Java™ Language Specification</cite>.)
2534 *
2535 * @param enabled
2536 * {@code true} if classes loaded by this classloader and
2537 * belonging to the named package or any of its subpackages will
2538 * have assertions enabled by default, {@code false} if they will
2539 * have assertions disabled by default.
2540 *
2541 * @since 1.4
2542 */
2543 public void setPackageAssertionStatus(String packageName,
2544 boolean enabled) {
2545 synchronized (assertionLock) {
2546 if (packageAssertionStatus == null)
2547 initializeJavaAssertionMaps();
2548
2549 packageAssertionStatus.put(packageName, enabled);
2550 }
2551 }
2552
2553 /**
2554 * Sets the desired assertion status for the named top-level class in this
2555 * class loader and any nested classes contained therein. This setting
2556 * takes precedence over the class loader's default assertion status, and
2557 * over any applicable per-package default. This method has no effect if
2558 * the named class has already been initialized. (Once a class is
2559 * initialized, its assertion status cannot change.)
2560 *
2561 * <p> If the named class is not a top-level class, this invocation will
2562 * have no effect on the actual assertion status of any class. </p>
2563 *
2564 * @param className
2565 * The fully qualified class name of the top-level class whose
2566 * assertion status is to be set.
2567 *
2568 * @param enabled
2569 * {@code true} if the named class is to have assertions
2570 * enabled when (and if) it is initialized, {@code false} if the
2571 * class is to have assertions disabled.
2572 *
2573 * @since 1.4
2574 */
2575 public void setClassAssertionStatus(String className, boolean enabled) {
2576 synchronized (assertionLock) {
2577 if (classAssertionStatus == null)
2578 initializeJavaAssertionMaps();
2579
2580 classAssertionStatus.put(className, enabled);
2581 }
2582 }
2583
2584 /**
2585 * Sets the default assertion status for this class loader to
2586 * {@code false} and discards any package defaults or class assertion
2587 * status settings associated with the class loader. This method is
2588 * provided so that class loaders can be made to ignore any command line or
2589 * persistent assertion status settings and "start with a clean slate."
2590 *
2591 * @since 1.4
2592 */
2593 public void clearAssertionStatus() {
2594 /*
2595 * Whether or not "Java assertion maps" are initialized, set
2596 * them to empty maps, effectively ignoring any present settings.
2597 */
2598 synchronized (assertionLock) {
2599 classAssertionStatus = new HashMap<>();
2600 packageAssertionStatus = new HashMap<>();
2601 defaultAssertionStatus = false;
2602 }
2603 }
2604
2605 /**
2606 * Returns the assertion status that would be assigned to the specified
2607 * class if it were to be initialized at the time this method is invoked.
2608 * If the named class has had its assertion status set, the most recent
2609 * setting will be returned; otherwise, if any package default assertion
2610 * status pertains to this class, the most recent setting for the most
2611 * specific pertinent package default assertion status is returned;
2612 * otherwise, this class loader's default assertion status is returned.
2613 * </p>
2614 *
2615 * @param className
2616 * The fully qualified class name of the class whose desired
2617 * assertion status is being queried.
2618 *
2619 * @return The desired assertion status of the specified class.
2620 *
2621 * @see #setClassAssertionStatus(String, boolean)
2622 * @see #setPackageAssertionStatus(String, boolean)
2623 * @see #setDefaultAssertionStatus(boolean)
2624 *
2625 * @since 1.4
2626 */
2627 boolean desiredAssertionStatus(String className) {
2628 synchronized (assertionLock) {
2629 // assert classAssertionStatus != null;
2630 // assert packageAssertionStatus != null;
2631
2632 // Check for a class entry
2633 Boolean result = classAssertionStatus.get(className);
2634 if (result != null)
2635 return result.booleanValue();
2636
2637 // Check for most specific package entry
2638 int dotIndex = className.lastIndexOf('.');
2639 if (dotIndex < 0) { // default package
2640 result = packageAssertionStatus.get(null);
2641 if (result != null)
2642 return result.booleanValue();
2643 }
2644 while(dotIndex > 0) {
2645 className = className.substring(0, dotIndex);
2646 result = packageAssertionStatus.get(className);
2647 if (result != null)
2648 return result.booleanValue();
2649 dotIndex = className.lastIndexOf('.', dotIndex-1);
2650 }
2651
2652 // Return the classloader default
2653 return defaultAssertionStatus;
2654 }
2655 }
2656
2657 // Set up the assertions with information provided by the VM.
2658 // Note: Should only be called inside a synchronized block
2659 private void initializeJavaAssertionMaps() {
2660 // assert Thread.holdsLock(assertionLock);
2661
2662 classAssertionStatus = new HashMap<>();
2663 packageAssertionStatus = new HashMap<>();
2664 AssertionStatusDirectives directives = retrieveDirectives();
2665
2666 for(int i = 0; i < directives.classes.length; i++)
2667 classAssertionStatus.put(directives.classes[i],
2668 directives.classEnabled[i]);
2669
2670 for(int i = 0; i < directives.packages.length; i++)
2671 packageAssertionStatus.put(directives.packages[i],
2672 directives.packageEnabled[i]);
2673
2674 defaultAssertionStatus = directives.deflt;
2675 }
2676
2677 // Retrieves the assertion directives from the VM.
2678 private static native AssertionStatusDirectives retrieveDirectives();
2679
2680
2681 // -- Misc --
2682
2683 /**
2684 * Returns the ConcurrentHashMap used as a storage for ClassLoaderValue(s)
2685 * associated with this ClassLoader, creating it if it doesn't already exist.
2686 */
2687 ConcurrentHashMap<?, ?> createOrGetClassLoaderValueMap() {
2688 ConcurrentHashMap<?, ?> map = classLoaderValueMap;
2689 if (map == null) {
2690 map = new ConcurrentHashMap<>();
2691 boolean set = trySetObjectField("classLoaderValueMap", map);
2692 if (!set) {
2693 // beaten by someone else
2694 map = classLoaderValueMap;
2695 }
2696 }
2697 return map;
2698 }
2699
2700 // the storage for ClassLoaderValue(s) associated with this ClassLoader
2701 private volatile ConcurrentHashMap<?, ?> classLoaderValueMap;
2702
2703 /**
2704 * Attempts to atomically set a volatile field in this object. Returns
2705 * {@code true} if not beaten by another thread. Avoids the use of
2706 * AtomicReferenceFieldUpdater in this class.
2707 */
2708 private boolean trySetObjectField(String name, Object obj) {
2709 Unsafe unsafe = Unsafe.getUnsafe();
2710 Class<?> k = ClassLoader.class;
2711 long offset;
2712 offset = unsafe.objectFieldOffset(k, name);
2713 return unsafe.compareAndSetReference(this, offset, null, obj);
2714 }
2715 }
2716
2717 /*
2718 * A utility class that will enumerate over an array of enumerations.
2719 */
2720 final class CompoundEnumeration<E> implements Enumeration<E> {
2721 private final Enumeration<E>[] enums;
2722 private int index;
2723
2724 public CompoundEnumeration(Enumeration<E>[] enums) {
2725 this.enums = enums;
2726 }
2727
2728 private boolean next() {
2729 while (index < enums.length) {
2730 if (enums[index] != null && enums[index].hasMoreElements()) {
2731 return true;
2732 }
2733 index++;
2734 }
2735 return false;
2736 }
2737
2738 public boolean hasMoreElements() {
2739 return next();
2740 }
2741
2742 public E nextElement() {
2743 if (!next()) {
2744 throw new NoSuchElementException();
2745 }
2746 return enums[index].nextElement();
2747 }
2748 }