1 /*
   2  * Copyright (c) 2013, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 package java.lang;
  26 
  27 import java.io.InputStream;
  28 import java.io.IOException;
  29 import java.io.File;
  30 import java.lang.reflect.Constructor;
  31 import java.lang.reflect.InvocationTargetException;
  32 import java.net.URL;
  33 import java.security.AccessController;
  34 import java.security.AccessControlContext;
  35 import java.security.CodeSource;
  36 import java.security.PrivilegedAction;
  37 import java.security.PrivilegedActionException;
  38 import java.security.PrivilegedExceptionAction;
  39 import java.security.ProtectionDomain;
  40 import java.security.cert.Certificate;
  41 import java.util.Collections;
  42 import java.util.Enumeration;
  43 import java.util.HashMap;
  44 import java.util.HashSet;
  45 import java.util.Set;
  46 import java.util.Stack;
  47 import java.util.Map;
  48 import java.util.Vector;
  49 import java.util.Hashtable;
  50 import java.util.WeakHashMap;
  51 import java.util.concurrent.ConcurrentHashMap;
  52 import sun.misc.CompoundEnumeration;
  53 import sun.misc.Resource;
  54 import sun.misc.URLClassPath;
  55 import sun.reflect.CallerSensitive;
  56 import sun.reflect.Reflection;
  57 import sun.reflect.misc.ReflectUtil;
  58 import sun.security.util.SecurityConstants;
  59 
  60 /**
  61  * A class loader is an object that is responsible for loading classes. The
  62  * class <tt>ClassLoader</tt> is an abstract class.  Given the <a
  63  * href="#name">binary name</a> of a class, a class loader should attempt to
  64  * locate or generate data that constitutes a definition for the class.  A
  65  * typical strategy is to transform the name into a file name and then read a
  66  * "class file" of that name from a file system.
  67  *
  68  * <p> Every {@link Class <tt>Class</tt>} object contains a {@link
  69  * Class#getClassLoader() reference} to the <tt>ClassLoader</tt> that defined
  70  * it.
  71  *
  72  * <p> <tt>Class</tt> objects for array classes are not created by class
  73  * loaders, but are created automatically as required by the Java runtime.
  74  * The class loader for an array class, as returned by {@link
  75  * Class#getClassLoader()} is the same as the class loader for its element
  76  * type; if the element type is a primitive type, then the array class has no
  77  * class loader.
  78  *
  79  * <p> Applications implement subclasses of <tt>ClassLoader</tt> in order to
  80  * extend the manner in which the Java virtual machine dynamically loads
  81  * classes.
  82  *
  83  * <p> Class loaders may typically be used by security managers to indicate
  84  * security domains.
  85  *
  86  * <p> The <tt>ClassLoader</tt> class uses a delegation model to search for
  87  * classes and resources.  Each instance of <tt>ClassLoader</tt> has an
  88  * associated parent class loader.  When requested to find a class or
  89  * resource, a <tt>ClassLoader</tt> instance will delegate the search for the
  90  * class or resource to its parent class loader before attempting to find the
  91  * class or resource itself.  The virtual machine's built-in class loader,
  92  * called the "bootstrap class loader", does not itself have a parent but may
  93  * serve as the parent of a <tt>ClassLoader</tt> instance.
  94  *
  95  * <p> Class loaders that support concurrent loading of classes are known as
  96  * <em>parallel capable</em> class loaders and are required to register
  97  * themselves at their class initialization time by invoking the
  98  * {@link
  99  * #registerAsParallelCapable <tt>ClassLoader.registerAsParallelCapable</tt>}
 100  * method. Note that the <tt>ClassLoader</tt> class is registered as parallel
 101  * capable by default. However, its subclasses still need to register themselves
 102  * if they are parallel capable. <br>
 103  * In environments in which the delegation model is not strictly
 104  * hierarchical, class loaders need to be parallel capable, otherwise class
 105  * loading can lead to deadlocks because the loader lock is held for the
 106  * duration of the class loading process (see {@link #loadClass
 107  * <tt>loadClass</tt>} methods).
 108  *
 109  * <p> Normally, the Java virtual machine loads classes from the local file
 110  * system in a platform-dependent manner.  For example, on UNIX systems, the
 111  * virtual machine loads classes from the directory defined by the
 112  * <tt>CLASSPATH</tt> environment variable.
 113  *
 114  * <p> However, some classes may not originate from a file; they may originate
 115  * from other sources, such as the network, or they could be constructed by an
 116  * application.  The method {@link #defineClass(String, byte[], int, int)
 117  * <tt>defineClass</tt>} converts an array of bytes into an instance of class
 118  * <tt>Class</tt>. Instances of this newly defined class can be created using
 119  * {@link Class#newInstance <tt>Class.newInstance</tt>}.
 120  *
 121  * <p> The methods and constructors of objects created by a class loader may
 122  * reference other classes.  To determine the class(es) referred to, the Java
 123  * virtual machine invokes the {@link #loadClass <tt>loadClass</tt>} method of
 124  * the class loader that originally created the class.
 125  *
 126  * <p> For example, an application could create a network class loader to
 127  * download class files from a server.  Sample code might look like:
 128  *
 129  * <blockquote><pre>
 130  *   ClassLoader loader&nbsp;= new NetworkClassLoader(host,&nbsp;port);
 131  *   Object main&nbsp;= loader.loadClass("Main", true).newInstance();
 132  *       &nbsp;.&nbsp;.&nbsp;.
 133  * </pre></blockquote>
 134  *
 135  * <p> The network class loader subclass must define the methods {@link
 136  * #findClass <tt>findClass</tt>} and <tt>loadClassData</tt> to load a class
 137  * from the network.  Once it has downloaded the bytes that make up the class,
 138  * it should use the method {@link #defineClass <tt>defineClass</tt>} to
 139  * create a class instance.  A sample implementation is:
 140  *
 141  * <blockquote><pre>
 142  *     class NetworkClassLoader extends ClassLoader {
 143  *         String host;
 144  *         int port;
 145  *
 146  *         public Class findClass(String name) {
 147  *             byte[] b = loadClassData(name);
 148  *             return defineClass(name, b, 0, b.length);
 149  *         }
 150  *
 151  *         private byte[] loadClassData(String name) {
 152  *             // load the class data from the connection
 153  *             &nbsp;.&nbsp;.&nbsp;.
 154  *         }
 155  *     }
 156  * </pre></blockquote>
 157  *
 158  * <h3> <a name="name">Binary names</a> </h3>
 159  *
 160  * <p> Any class name provided as a {@link String} parameter to methods in
 161  * <tt>ClassLoader</tt> must be a binary name as defined by
 162  * <cite>The Java&trade; Language Specification</cite>.
 163  *
 164  * <p> Examples of valid class names include:
 165  * <blockquote><pre>
 166  *   "java.lang.String"
 167  *   "javax.swing.JSpinner$DefaultEditor"
 168  *   "java.security.KeyStore$Builder$FileBuilder$1"
 169  *   "java.net.URLClassLoader$3$1"
 170  * </pre></blockquote>
 171  *
 172  * {@code Class} objects for array classes are not created by {@code ClassLoader};
 173  * use the {@link Class#forName} method instead.
 174  *
 175  * @jls 13.1 The Form of a Binary
 176  * @see      #resolveClass(Class)
 177  * @since 1.0
 178  */
 179 public abstract class ClassLoader {
 180 
 181     private static native void registerNatives();
 182     static {
 183         registerNatives();
 184     }
 185 
 186     // The parent class loader for delegation
 187     // Note: VM hardcoded the offset of this field, thus all new fields
 188     // must be added *after* it.
 189     private final ClassLoader parent;
 190 
 191     /**
 192      * Encapsulates the set of parallel capable loader types.
 193      */
 194     private static class ParallelLoaders {
 195         private ParallelLoaders() {}
 196 
 197         // the set of parallel capable loader types
 198         private static final Set<Class<? extends ClassLoader>> loaderTypes =
 199             Collections.newSetFromMap(new WeakHashMap<>());
 200         static {
 201             synchronized (loaderTypes) { loaderTypes.add(ClassLoader.class); }
 202         }
 203 
 204         /**
 205          * Registers the given class loader type as parallel capable.
 206          * Returns {@code true} is successfully registered; {@code false} if
 207          * loader's super class is not registered.
 208          */
 209         static boolean register(Class<? extends ClassLoader> c) {
 210             synchronized (loaderTypes) {
 211                 if (loaderTypes.contains(c.getSuperclass())) {
 212                     // register the class loader as parallel capable
 213                     // if and only if all of its super classes are.
 214                     // Note: given current classloading sequence, if
 215                     // the immediate super class is parallel capable,
 216                     // all the super classes higher up must be too.
 217                     loaderTypes.add(c);
 218                     return true;
 219                 } else {
 220                     return false;
 221                 }
 222             }
 223         }
 224 
 225         /**
 226          * Returns {@code true} if the given class loader type is
 227          * registered as parallel capable.
 228          */
 229         static boolean isRegistered(Class<? extends ClassLoader> c) {
 230             synchronized (loaderTypes) {
 231                 return loaderTypes.contains(c);
 232             }
 233         }
 234     }
 235 
 236     // Maps class name to the corresponding lock object when the current
 237     // class loader is parallel capable.
 238     // Note: VM also uses this field to decide if the current class loader
 239     // is parallel capable and the appropriate lock object for class loading.
 240     private final ConcurrentHashMap<String, Object> parallelLockMap;
 241 
 242     // Hashtable that maps packages to certs
 243     private final Map <String, Certificate[]> package2certs;
 244 
 245     // Shared among all packages with unsigned classes
 246     private static final Certificate[] nocerts = new Certificate[0];
 247 
 248     // The classes loaded by this class loader. The only purpose of this table
 249     // is to keep the classes from being GC'ed until the loader is GC'ed.
 250     private final Vector<Class<?>> classes = new Vector<>();
 251 
 252     // The "default" domain. Set as the default ProtectionDomain on newly
 253     // created classes.
 254     private final ProtectionDomain defaultDomain =
 255         new ProtectionDomain(new CodeSource(null, (Certificate[]) null),
 256                              null, this, null);
 257 
 258     // The initiating protection domains for all classes loaded by this loader
 259     private final Set<ProtectionDomain> domains;
 260 
 261     // Invoked by the VM to record every loaded class with this loader.
 262     void addClass(Class<?> c) {
 263         classes.addElement(c);
 264     }
 265 
 266     // The packages defined in this class loader.  Each package name is mapped
 267     // to its corresponding Package object.
 268     private final ConcurrentHashMap<String, Package> packages
 269             = new ConcurrentHashMap<>();
 270 
 271     private static Void checkCreateClassLoader() {
 272         SecurityManager security = System.getSecurityManager();
 273         if (security != null) {
 274             security.checkCreateClassLoader();
 275         }
 276         return null;
 277     }
 278 
 279     private ClassLoader(Void unused, ClassLoader parent) {
 280         this.parent = parent;
 281         if (ParallelLoaders.isRegistered(this.getClass())) {
 282             parallelLockMap = new ConcurrentHashMap<>();
 283             package2certs = new ConcurrentHashMap<>();
 284             domains = Collections.synchronizedSet(new HashSet<>());
 285             assertionLock = new Object();
 286         } else {
 287             // no finer-grained lock; lock on the classloader instance
 288             parallelLockMap = null;
 289             package2certs = new Hashtable<>();
 290             domains = new HashSet<>();
 291             assertionLock = this;
 292         }
 293     }
 294 
 295     /**
 296      * Creates a new class loader using the specified parent class loader for
 297      * delegation.
 298      *
 299      * <p> If there is a security manager, its {@link
 300      * SecurityManager#checkCreateClassLoader()
 301      * <tt>checkCreateClassLoader</tt>} method is invoked.  This may result in
 302      * a security exception.  </p>
 303      *
 304      * @param  parent
 305      *         The parent class loader
 306      *
 307      * @throws  SecurityException
 308      *          If a security manager exists and its
 309      *          <tt>checkCreateClassLoader</tt> method doesn't allow creation
 310      *          of a new class loader.
 311      *
 312      * @since  1.2
 313      */
 314     protected ClassLoader(ClassLoader parent) {
 315         this(checkCreateClassLoader(), parent);
 316     }
 317 
 318     /**
 319      * Creates a new class loader using the <tt>ClassLoader</tt> returned by
 320      * the method {@link #getSystemClassLoader()
 321      * <tt>getSystemClassLoader()</tt>} as the parent class loader.
 322      *
 323      * <p> If there is a security manager, its {@link
 324      * SecurityManager#checkCreateClassLoader()
 325      * <tt>checkCreateClassLoader</tt>} method is invoked.  This may result in
 326      * a security exception.  </p>
 327      *
 328      * @throws  SecurityException
 329      *          If a security manager exists and its
 330      *          <tt>checkCreateClassLoader</tt> method doesn't allow creation
 331      *          of a new class loader.
 332      */
 333     protected ClassLoader() {
 334         this(checkCreateClassLoader(), getSystemClassLoader());
 335     }
 336 
 337     // -- Class --
 338 
 339     /**
 340      * Loads the class with the specified <a href="#name">binary name</a>.
 341      * This method searches for classes in the same manner as the {@link
 342      * #loadClass(String, boolean)} method.  It is invoked by the Java virtual
 343      * machine to resolve class references.  Invoking this method is equivalent
 344      * to invoking {@link #loadClass(String, boolean) <tt>loadClass(name,
 345      * false)</tt>}.
 346      *
 347      * @param  name
 348      *         The <a href="#name">binary name</a> of the class
 349      *
 350      * @return  The resulting <tt>Class</tt> object
 351      *
 352      * @throws  ClassNotFoundException
 353      *          If the class was not found
 354      */
 355     public Class<?> loadClass(String name) throws ClassNotFoundException {
 356         return loadClass(name, false);
 357     }
 358 
 359     /**
 360      * Loads the class with the specified <a href="#name">binary name</a>.  The
 361      * default implementation of this method searches for classes in the
 362      * following order:
 363      *
 364      * <ol>
 365      *
 366      *   <li><p> Invoke {@link #findLoadedClass(String)} to check if the class
 367      *   has already been loaded.  </p></li>
 368      *
 369      *   <li><p> Invoke the {@link #loadClass(String) <tt>loadClass</tt>} method
 370      *   on the parent class loader.  If the parent is <tt>null</tt> the class
 371      *   loader built-in to the virtual machine is used, instead.  </p></li>
 372      *
 373      *   <li><p> Invoke the {@link #findClass(String)} method to find the
 374      *   class.  </p></li>
 375      *
 376      * </ol>
 377      *
 378      * <p> If the class was found using the above steps, and the
 379      * <tt>resolve</tt> flag is true, this method will then invoke the {@link
 380      * #resolveClass(Class)} method on the resulting <tt>Class</tt> object.
 381      *
 382      * <p> Subclasses of <tt>ClassLoader</tt> are encouraged to override {@link
 383      * #findClass(String)}, rather than this method.  </p>
 384      *
 385      * <p> Unless overridden, this method synchronizes on the result of
 386      * {@link #getClassLoadingLock <tt>getClassLoadingLock</tt>} method
 387      * during the entire class loading process.
 388      *
 389      * @param  name
 390      *         The <a href="#name">binary name</a> of the class
 391      *
 392      * @param  resolve
 393      *         If <tt>true</tt> then resolve the class
 394      *
 395      * @return  The resulting <tt>Class</tt> object
 396      *
 397      * @throws  ClassNotFoundException
 398      *          If the class could not be found
 399      */
 400     protected Class<?> loadClass(String name, boolean resolve)
 401         throws ClassNotFoundException
 402     {
 403         synchronized (getClassLoadingLock(name)) {
 404             // First, check if the class has already been loaded
 405             Class<?> c = findLoadedClass(name);
 406             if (c == null) {
 407                 long t0 = System.nanoTime();
 408                 try {
 409                     if (parent != null) {
 410                         c = parent.loadClass(name, false);
 411                     } else {
 412                         c = findBootstrapClassOrNull(name);
 413                     }
 414                 } catch (ClassNotFoundException e) {
 415                     // ClassNotFoundException thrown if class not found
 416                     // from the non-null parent class loader
 417                 }
 418 
 419                 if (c == null) {
 420                     // If still not found, then invoke findClass in order
 421                     // to find the class.
 422                     long t1 = System.nanoTime();
 423                     c = findClass(name);
 424 
 425                     // this is the defining class loader; record the stats
 426                     sun.misc.PerfCounter.getParentDelegationTime().addTime(t1 - t0);
 427                     sun.misc.PerfCounter.getFindClassTime().addElapsedTimeFrom(t1);
 428                     sun.misc.PerfCounter.getFindClasses().increment();
 429                 }
 430             }
 431             if (resolve) {
 432                 resolveClass(c);
 433             }
 434             return c;
 435         }
 436     }
 437 
 438     /**
 439      * Returns the lock object for class loading operations.
 440      * For backward compatibility, the default implementation of this method
 441      * behaves as follows. If this ClassLoader object is registered as
 442      * parallel capable, the method returns a dedicated object associated
 443      * with the specified class name. Otherwise, the method returns this
 444      * ClassLoader object.
 445      *
 446      * @param  className
 447      *         The name of the to-be-loaded class
 448      *
 449      * @return the lock for class loading operations
 450      *
 451      * @throws NullPointerException
 452      *         If registered as parallel capable and <tt>className</tt> is null
 453      *
 454      * @see #loadClass(String, boolean)
 455      *
 456      * @since  1.7
 457      */
 458     protected Object getClassLoadingLock(String className) {
 459         Object lock = this;
 460         if (parallelLockMap != null) {
 461             Object newLock = new Object();
 462             lock = parallelLockMap.putIfAbsent(className, newLock);
 463             if (lock == null) {
 464                 lock = newLock;
 465             }
 466         }
 467         return lock;
 468     }
 469 
 470     // This method is invoked by the virtual machine to load a class.
 471     private Class<?> loadClassInternal(String name)
 472         throws ClassNotFoundException
 473     {
 474         // For backward compatibility, explicitly lock on 'this' when
 475         // the current class loader is not parallel capable.
 476         if (parallelLockMap == null) {
 477             synchronized (this) {
 478                  return loadClass(name);
 479             }
 480         } else {
 481             return loadClass(name);
 482         }
 483     }
 484 
 485     // Invoked by the VM after loading class with this loader.
 486     private void checkPackageAccess(Class<?> cls, ProtectionDomain pd) {
 487         final SecurityManager sm = System.getSecurityManager();
 488         if (sm != null) {
 489             if (ReflectUtil.isNonPublicProxyClass(cls)) {
 490                 for (Class<?> intf: cls.getInterfaces()) {
 491                     checkPackageAccess(intf, pd);
 492                 }
 493                 return;
 494             }
 495 
 496             final String name = cls.getName();
 497             final int i = name.lastIndexOf('.');
 498             if (i != -1) {
 499                 AccessController.doPrivileged(new PrivilegedAction<Void>() {
 500                     public Void run() {
 501                         sm.checkPackageAccess(name.substring(0, i));
 502                         return null;
 503                     }
 504                 }, new AccessControlContext(new ProtectionDomain[] {pd}));
 505             }
 506         }
 507         domains.add(pd);
 508     }
 509 
 510     /**
 511      * Finds the class with the specified <a href="#name">binary name</a>.
 512      * This method should be overridden by class loader implementations that
 513      * follow the delegation model for loading classes, and will be invoked by
 514      * the {@link #loadClass <tt>loadClass</tt>} method after checking the
 515      * parent class loader for the requested class.  The default implementation
 516      * throws a <tt>ClassNotFoundException</tt>.
 517      *
 518      * @param  name
 519      *         The <a href="#name">binary name</a> of the class
 520      *
 521      * @return  The resulting <tt>Class</tt> object
 522      *
 523      * @throws  ClassNotFoundException
 524      *          If the class could not be found
 525      *
 526      * @since  1.2
 527      */
 528     protected Class<?> findClass(String name) throws ClassNotFoundException {
 529         throw new ClassNotFoundException(name);
 530     }
 531 
 532     /**
 533      * Converts an array of bytes into an instance of class <tt>Class</tt>.
 534      * Before the <tt>Class</tt> can be used it must be resolved.  This method
 535      * is deprecated in favor of the version that takes a <a
 536      * href="#name">binary name</a> as its first argument, and is more secure.
 537      *
 538      * @param  b
 539      *         The bytes that make up the class data.  The bytes in positions
 540      *         <tt>off</tt> through <tt>off+len-1</tt> should have the format
 541      *         of a valid class file as defined by
 542      *         <cite>The Java&trade; Virtual Machine Specification</cite>.
 543      *
 544      * @param  off
 545      *         The start offset in <tt>b</tt> of the class data
 546      *
 547      * @param  len
 548      *         The length of the class data
 549      *
 550      * @return  The <tt>Class</tt> object that was created from the specified
 551      *          class data
 552      *
 553      * @throws  ClassFormatError
 554      *          If the data did not contain a valid class
 555      *
 556      * @throws  IndexOutOfBoundsException
 557      *          If either <tt>off</tt> or <tt>len</tt> is negative, or if
 558      *          <tt>off+len</tt> is greater than <tt>b.length</tt>.
 559      *
 560      * @throws  SecurityException
 561      *          If an attempt is made to add this class to a package that
 562      *          contains classes that were signed by a different set of
 563      *          certificates than this class, or if an attempt is made
 564      *          to define a class in a package with a fully-qualified name
 565      *          that starts with "{@code java.}".
 566      *
 567      * @see  #loadClass(String, boolean)
 568      * @see  #resolveClass(Class)
 569      *
 570      * @deprecated  Replaced by {@link #defineClass(String, byte[], int, int)
 571      * defineClass(String, byte[], int, int)}
 572      */
 573     @Deprecated
 574     protected final Class<?> defineClass(byte[] b, int off, int len)
 575         throws ClassFormatError
 576     {
 577         return defineClass(null, b, off, len, null);
 578     }
 579 
 580     /**
 581      * Converts an array of bytes into an instance of class <tt>Class</tt>.
 582      * Before the <tt>Class</tt> can be used it must be resolved.
 583      *
 584      * <p> This method assigns a default {@link java.security.ProtectionDomain
 585      * <tt>ProtectionDomain</tt>} to the newly defined class.  The
 586      * <tt>ProtectionDomain</tt> is effectively granted the same set of
 587      * permissions returned when {@link
 588      * java.security.Policy#getPermissions(java.security.CodeSource)
 589      * <tt>Policy.getPolicy().getPermissions(new CodeSource(null, null))</tt>}
 590      * is invoked.  The default domain is created on the first invocation of
 591      * {@link #defineClass(String, byte[], int, int) <tt>defineClass</tt>},
 592      * and re-used on subsequent invocations.
 593      *
 594      * <p> To assign a specific <tt>ProtectionDomain</tt> to the class, use
 595      * the {@link #defineClass(String, byte[], int, int,
 596      * java.security.ProtectionDomain) <tt>defineClass</tt>} method that takes a
 597      * <tt>ProtectionDomain</tt> as one of its arguments.  </p>
 598      *
 599      * @param  name
 600      *         The expected <a href="#name">binary name</a> of the class, or
 601      *         <tt>null</tt> if not known
 602      *
 603      * @param  b
 604      *         The bytes that make up the class data.  The bytes in positions
 605      *         <tt>off</tt> through <tt>off+len-1</tt> should have the format
 606      *         of a valid class file as defined by
 607      *         <cite>The Java&trade; Virtual Machine Specification</cite>.
 608      *
 609      * @param  off
 610      *         The start offset in <tt>b</tt> of the class data
 611      *
 612      * @param  len
 613      *         The length of the class data
 614      *
 615      * @return  The <tt>Class</tt> object that was created from the specified
 616      *          class data.
 617      *
 618      * @throws  ClassFormatError
 619      *          If the data did not contain a valid class
 620      *
 621      * @throws  IndexOutOfBoundsException
 622      *          If either <tt>off</tt> or <tt>len</tt> is negative, or if
 623      *          <tt>off+len</tt> is greater than <tt>b.length</tt>.
 624      *
 625      * @throws  SecurityException
 626      *          If an attempt is made to add this class to a package that
 627      *          contains classes that were signed by a different set of
 628      *          certificates than this class (which is unsigned), or if
 629      *          <tt>name</tt> begins with "<tt>java.</tt>".
 630      *
 631      * @see  #loadClass(String, boolean)
 632      * @see  #resolveClass(Class)
 633      * @see  java.security.CodeSource
 634      * @see  java.security.SecureClassLoader
 635      *
 636      * @since  1.1
 637      */
 638     protected final Class<?> defineClass(String name, byte[] b, int off, int len)
 639         throws ClassFormatError
 640     {
 641         return defineClass(name, b, off, len, null);
 642     }
 643 
 644     /* Determine protection domain, and check that:
 645         - not define java.* class,
 646         - signer of this class matches signers for the rest of the classes in
 647           package.
 648     */
 649     private ProtectionDomain preDefineClass(String name,
 650                                             ProtectionDomain pd)
 651     {
 652         if (!checkName(name))
 653             throw new NoClassDefFoundError("IllegalName: " + name);
 654 
 655         if ((name != null) && name.startsWith("java.")) {
 656             throw new SecurityException
 657                 ("Prohibited package name: " +
 658                  name.substring(0, name.lastIndexOf('.')));
 659         }
 660         if (pd == null) {
 661             pd = defaultDomain;
 662         }
 663 
 664         if (name != null) checkCerts(name, pd.getCodeSource());
 665 
 666         return pd;
 667     }
 668 
 669     private String defineClassSourceLocation(ProtectionDomain pd)
 670     {
 671         CodeSource cs = pd.getCodeSource();
 672         String source = null;
 673         if (cs != null && cs.getLocation() != null) {
 674             source = cs.getLocation().toString();
 675         }
 676         return source;
 677     }
 678 
 679     private void postDefineClass(Class<?> c, ProtectionDomain pd)
 680     {
 681         if (pd.getCodeSource() != null) {
 682             Certificate certs[] = pd.getCodeSource().getCertificates();
 683             if (certs != null)
 684                 setSigners(c, certs);
 685         }
 686     }
 687 
 688     /**
 689      * Converts an array of bytes into an instance of class <tt>Class</tt>,
 690      * with an optional <tt>ProtectionDomain</tt>.  If the domain is
 691      * <tt>null</tt>, then a default domain will be assigned to the class as
 692      * specified in the documentation for {@link #defineClass(String, byte[],
 693      * int, int)}.  Before the class can be used it must be resolved.
 694      *
 695      * <p> The first class defined in a package determines the exact set of
 696      * certificates that all subsequent classes defined in that package must
 697      * contain.  The set of certificates for a class is obtained from the
 698      * {@link java.security.CodeSource <tt>CodeSource</tt>} within the
 699      * <tt>ProtectionDomain</tt> of the class.  Any classes added to that
 700      * package must contain the same set of certificates or a
 701      * <tt>SecurityException</tt> will be thrown.  Note that if
 702      * <tt>name</tt> is <tt>null</tt>, this check is not performed.
 703      * You should always pass in the <a href="#name">binary name</a> of the
 704      * class you are defining as well as the bytes.  This ensures that the
 705      * class you are defining is indeed the class you think it is.
 706      *
 707      * <p> The specified <tt>name</tt> cannot begin with "<tt>java.</tt>", since
 708      * all classes in the "<tt>java.*</tt> packages can only be defined by the
 709      * bootstrap class loader.  If <tt>name</tt> is not <tt>null</tt>, it
 710      * must be equal to the <a href="#name">binary name</a> of the class
 711      * specified by the byte array "<tt>b</tt>", otherwise a {@link
 712      * NoClassDefFoundError <tt>NoClassDefFoundError</tt>} will be thrown. </p>
 713      *
 714      * @param  name
 715      *         The expected <a href="#name">binary name</a> of the class, or
 716      *         <tt>null</tt> if not known
 717      *
 718      * @param  b
 719      *         The bytes that make up the class data. The bytes in positions
 720      *         <tt>off</tt> through <tt>off+len-1</tt> should have the format
 721      *         of a valid class file as defined by
 722      *         <cite>The Java&trade; Virtual Machine Specification</cite>.
 723      *
 724      * @param  off
 725      *         The start offset in <tt>b</tt> of the class data
 726      *
 727      * @param  len
 728      *         The length of the class data
 729      *
 730      * @param  protectionDomain
 731      *         The ProtectionDomain of the class
 732      *
 733      * @return  The <tt>Class</tt> object created from the data,
 734      *          and optional <tt>ProtectionDomain</tt>.
 735      *
 736      * @throws  ClassFormatError
 737      *          If the data did not contain a valid class
 738      *
 739      * @throws  NoClassDefFoundError
 740      *          If <tt>name</tt> is not equal to the <a href="#name">binary
 741      *          name</a> of the class specified by <tt>b</tt>
 742      *
 743      * @throws  IndexOutOfBoundsException
 744      *          If either <tt>off</tt> or <tt>len</tt> is negative, or if
 745      *          <tt>off+len</tt> is greater than <tt>b.length</tt>.
 746      *
 747      * @throws  SecurityException
 748      *          If an attempt is made to add this class to a package that
 749      *          contains classes that were signed by a different set of
 750      *          certificates than this class, or if <tt>name</tt> begins with
 751      *          "<tt>java.</tt>".
 752      */
 753     protected final Class<?> defineClass(String name, byte[] b, int off, int len,
 754                                          ProtectionDomain protectionDomain)
 755         throws ClassFormatError
 756     {
 757         protectionDomain = preDefineClass(name, protectionDomain);
 758         String source = defineClassSourceLocation(protectionDomain);
 759         Class<?> c = defineClass1(name, b, off, len, protectionDomain, source);
 760         postDefineClass(c, protectionDomain);
 761         return c;
 762     }
 763 
 764     /**
 765      * Converts a {@link java.nio.ByteBuffer <tt>ByteBuffer</tt>}
 766      * into an instance of class <tt>Class</tt>,
 767      * with an optional <tt>ProtectionDomain</tt>.  If the domain is
 768      * <tt>null</tt>, then a default domain will be assigned to the class as
 769      * specified in the documentation for {@link #defineClass(String, byte[],
 770      * int, int)}.  Before the class can be used it must be resolved.
 771      *
 772      * <p>The rules about the first class defined in a package determining the
 773      * set of certificates for the package, and the restrictions on class names
 774      * are identical to those specified in the documentation for {@link
 775      * #defineClass(String, byte[], int, int, ProtectionDomain)}.
 776      *
 777      * <p> An invocation of this method of the form
 778      * <i>cl</i><tt>.defineClass(</tt><i>name</i><tt>,</tt>
 779      * <i>bBuffer</i><tt>,</tt> <i>pd</i><tt>)</tt> yields exactly the same
 780      * result as the statements
 781      *
 782      *<p> <tt>
 783      * ...<br>
 784      * byte[] temp = new byte[bBuffer.{@link
 785      * java.nio.ByteBuffer#remaining remaining}()];<br>
 786      *     bBuffer.{@link java.nio.ByteBuffer#get(byte[])
 787      * get}(temp);<br>
 788      *     return {@link #defineClass(String, byte[], int, int, ProtectionDomain)
 789      * cl.defineClass}(name, temp, 0,
 790      * temp.length, pd);<br>
 791      * </tt></p>
 792      *
 793      * @param  name
 794      *         The expected <a href="#name">binary name</a>. of the class, or
 795      *         <tt>null</tt> if not known
 796      *
 797      * @param  b
 798      *         The bytes that make up the class data. The bytes from positions
 799      *         <tt>b.position()</tt> through <tt>b.position() + b.limit() -1
 800      *         </tt> should have the format of a valid class file as defined by
 801      *         <cite>The Java&trade; Virtual Machine Specification</cite>.
 802      *
 803      * @param  protectionDomain
 804      *         The ProtectionDomain of the class, or <tt>null</tt>.
 805      *
 806      * @return  The <tt>Class</tt> object created from the data,
 807      *          and optional <tt>ProtectionDomain</tt>.
 808      *
 809      * @throws  ClassFormatError
 810      *          If the data did not contain a valid class.
 811      *
 812      * @throws  NoClassDefFoundError
 813      *          If <tt>name</tt> is not equal to the <a href="#name">binary
 814      *          name</a> of the class specified by <tt>b</tt>
 815      *
 816      * @throws  SecurityException
 817      *          If an attempt is made to add this class to a package that
 818      *          contains classes that were signed by a different set of
 819      *          certificates than this class, or if <tt>name</tt> begins with
 820      *          "<tt>java.</tt>".
 821      *
 822      * @see      #defineClass(String, byte[], int, int, ProtectionDomain)
 823      *
 824      * @since  1.5
 825      */
 826     protected final Class<?> defineClass(String name, java.nio.ByteBuffer b,
 827                                          ProtectionDomain protectionDomain)
 828         throws ClassFormatError
 829     {
 830         int len = b.remaining();
 831 
 832         // Use byte[] if not a direct ByteBuffer:
 833         if (!b.isDirect()) {
 834             if (b.hasArray()) {
 835                 return defineClass(name, b.array(),
 836                                    b.position() + b.arrayOffset(), len,
 837                                    protectionDomain);
 838             } else {
 839                 // no array, or read-only array
 840                 byte[] tb = new byte[len];
 841                 b.get(tb);  // get bytes out of byte buffer.
 842                 return defineClass(name, tb, 0, len, protectionDomain);
 843             }
 844         }
 845 
 846         protectionDomain = preDefineClass(name, protectionDomain);
 847         String source = defineClassSourceLocation(protectionDomain);
 848         Class<?> c = defineClass2(name, b, b.position(), len, protectionDomain, source);
 849         postDefineClass(c, protectionDomain);
 850         return c;
 851     }
 852 
 853     private native Class<?> defineClass1(String name, byte[] b, int off, int len,
 854                                          ProtectionDomain pd, String source);
 855 
 856     private native Class<?> defineClass2(String name, java.nio.ByteBuffer b,
 857                                          int off, int len, ProtectionDomain pd,
 858                                          String source);
 859 
 860     // true if the name is null or has the potential to be a valid binary name
 861     private boolean checkName(String name) {
 862         if ((name == null) || (name.length() == 0))
 863             return true;
 864         if ((name.indexOf('/') != -1) || (name.charAt(0) == '['))
 865             return false;
 866         return true;
 867     }
 868 
 869     private void checkCerts(String name, CodeSource cs) {
 870         int i = name.lastIndexOf('.');
 871         String pname = (i == -1) ? "" : name.substring(0, i);
 872 
 873         Certificate[] certs = null;
 874         if (cs != null) {
 875             certs = cs.getCertificates();
 876         }
 877         Certificate[] pcerts = null;
 878         if (parallelLockMap == null) {
 879             synchronized (this) {
 880                 pcerts = package2certs.get(pname);
 881                 if (pcerts == null) {
 882                     package2certs.put(pname, (certs == null? nocerts:certs));
 883                 }
 884             }
 885         } else {
 886             pcerts = ((ConcurrentHashMap<String, Certificate[]>)package2certs).
 887                 putIfAbsent(pname, (certs == null? nocerts:certs));
 888         }
 889         if (pcerts != null && !compareCerts(pcerts, certs)) {
 890             throw new SecurityException("class \""+ name +
 891                  "\"'s signer information does not match signer information of other classes in the same package");
 892         }
 893     }
 894 
 895     /**
 896      * check to make sure the certs for the new class (certs) are the same as
 897      * the certs for the first class inserted in the package (pcerts)
 898      */
 899     private boolean compareCerts(Certificate[] pcerts,
 900                                  Certificate[] certs)
 901     {
 902         // certs can be null, indicating no certs.
 903         if ((certs == null) || (certs.length == 0)) {
 904             return pcerts.length == 0;
 905         }
 906 
 907         // the length must be the same at this point
 908         if (certs.length != pcerts.length)
 909             return false;
 910 
 911         // go through and make sure all the certs in one array
 912         // are in the other and vice-versa.
 913         boolean match;
 914         for (Certificate cert : certs) {
 915             match = false;
 916             for (Certificate pcert : pcerts) {
 917                 if (cert.equals(pcert)) {
 918                     match = true;
 919                     break;
 920                 }
 921             }
 922             if (!match) return false;
 923         }
 924 
 925         // now do the same for pcerts
 926         for (Certificate pcert : pcerts) {
 927             match = false;
 928             for (Certificate cert : certs) {
 929                 if (pcert.equals(cert)) {
 930                     match = true;
 931                     break;
 932                 }
 933             }
 934             if (!match) return false;
 935         }
 936 
 937         return true;
 938     }
 939 
 940     /**
 941      * Links the specified class.  This (misleadingly named) method may be
 942      * used by a class loader to link a class.  If the class <tt>c</tt> has
 943      * already been linked, then this method simply returns. Otherwise, the
 944      * class is linked as described in the "Execution" chapter of
 945      * <cite>The Java&trade; Language Specification</cite>.
 946      *
 947      * @param  c
 948      *         The class to link
 949      *
 950      * @throws  NullPointerException
 951      *          If <tt>c</tt> is <tt>null</tt>.
 952      *
 953      * @see  #defineClass(String, byte[], int, int)
 954      */
 955     protected final void resolveClass(Class<?> c) {
 956         resolveClass0(c);
 957     }
 958 
 959     private native void resolveClass0(Class<?> c);
 960 
 961     /**
 962      * Finds a class with the specified <a href="#name">binary name</a>,
 963      * loading it if necessary.
 964      *
 965      * <p> This method loads the class through the system class loader (see
 966      * {@link #getSystemClassLoader()}).  The <tt>Class</tt> object returned
 967      * might have more than one <tt>ClassLoader</tt> associated with it.
 968      * Subclasses of <tt>ClassLoader</tt> need not usually invoke this method,
 969      * because most class loaders need to override just {@link
 970      * #findClass(String)}.  </p>
 971      *
 972      * @param  name
 973      *         The <a href="#name">binary name</a> of the class
 974      *
 975      * @return  The <tt>Class</tt> object for the specified <tt>name</tt>
 976      *
 977      * @throws  ClassNotFoundException
 978      *          If the class could not be found
 979      *
 980      * @see  #ClassLoader(ClassLoader)
 981      * @see  #getParent()
 982      */
 983     protected final Class<?> findSystemClass(String name)
 984         throws ClassNotFoundException
 985     {
 986         ClassLoader system = getSystemClassLoader();
 987         if (system == null) {
 988             if (!checkName(name))
 989                 throw new ClassNotFoundException(name);
 990             Class<?> cls = findBootstrapClass(name);
 991             if (cls == null) {
 992                 throw new ClassNotFoundException(name);
 993             }
 994             return cls;
 995         }
 996         return system.loadClass(name);
 997     }
 998 
 999     /**
1000      * Returns a class loaded by the bootstrap class loader;
1001      * or return null if not found.
1002      */
1003     private Class<?> findBootstrapClassOrNull(String name)
1004     {
1005         if (!checkName(name)) return null;
1006 
1007         return findBootstrapClass(name);
1008     }
1009 
1010     // return null if not found
1011     private native Class<?> findBootstrapClass(String name);
1012 
1013     /**
1014      * Returns the class with the given <a href="#name">binary name</a> if this
1015      * loader has been recorded by the Java virtual machine as an initiating
1016      * loader of a class with that <a href="#name">binary name</a>.  Otherwise
1017      * <tt>null</tt> is returned.
1018      *
1019      * @param  name
1020      *         The <a href="#name">binary name</a> of the class
1021      *
1022      * @return  The <tt>Class</tt> object, or <tt>null</tt> if the class has
1023      *          not been loaded
1024      *
1025      * @since  1.1
1026      */
1027     protected final Class<?> findLoadedClass(String name) {
1028         if (!checkName(name))
1029             return null;
1030         return findLoadedClass0(name);
1031     }
1032 
1033     private native final Class<?> findLoadedClass0(String name);
1034 
1035     /**
1036      * Sets the signers of a class.  This should be invoked after defining a
1037      * class.
1038      *
1039      * @param  c
1040      *         The <tt>Class</tt> object
1041      *
1042      * @param  signers
1043      *         The signers for the class
1044      *
1045      * @since  1.1
1046      */
1047     protected final void setSigners(Class<?> c, Object[] signers) {
1048         c.setSigners(signers);
1049     }
1050 
1051 
1052     // -- Resource --
1053 
1054     /**
1055      * Finds the resource with the given name.  A resource is some data
1056      * (images, audio, text, etc) that can be accessed by class code in a way
1057      * that is independent of the location of the code.
1058      *
1059      * <p> The name of a resource is a '<tt>/</tt>'-separated path name that
1060      * identifies the resource.
1061      *
1062      * <p> This method will first search the parent class loader for the
1063      * resource; if the parent is <tt>null</tt> the path of the class loader
1064      * built-in to the virtual machine is searched.  That failing, this method
1065      * will invoke {@link #findResource(String)} to find the resource.  </p>
1066      *
1067      * @apiNote When overriding this method it is recommended that an
1068      * implementation ensures that any delegation is consistent with the {@link
1069      * #getResources(java.lang.String) getResources(String)} method.
1070      *
1071      * @param  name
1072      *         The resource name
1073      *
1074      * @return  A <tt>URL</tt> object for reading the resource, or
1075      *          <tt>null</tt> if the resource could not be found or the invoker
1076      *          doesn't have adequate  privileges to get the resource.
1077      *
1078      * @since  1.1
1079      */
1080     public URL getResource(String name) {
1081         URL url;
1082         if (parent != null) {
1083             url = parent.getResource(name);
1084         } else {
1085             url = getBootstrapResource(name);
1086         }
1087         if (url == null) {
1088             url = findResource(name);
1089         }
1090         return url;
1091     }
1092 
1093     /**
1094      * Finds all the resources with the given name. A resource is some data
1095      * (images, audio, text, etc) that can be accessed by class code in a way
1096      * that is independent of the location of the code.
1097      *
1098      * <p>The name of a resource is a <tt>/</tt>-separated path name that
1099      * identifies the resource.
1100      *
1101      * <p> The search order is described in the documentation for {@link
1102      * #getResource(String)}.  </p>
1103      *
1104      * @apiNote When overriding this method it is recommended that an
1105      * implementation ensures that any delegation is consistent with the {@link
1106      * #getResource(java.lang.String) getResource(String)} method. This should
1107      * ensure that the first element returned by the Enumeration's
1108      * {@code nextElement} method is the same resource that the
1109      * {@code getResource(String)} method would return.
1110      *
1111      * @param  name
1112      *         The resource name
1113      *
1114      * @return  An enumeration of {@link java.net.URL <tt>URL</tt>} objects for
1115      *          the resource.  If no resources could  be found, the enumeration
1116      *          will be empty.  Resources that the class loader doesn't have
1117      *          access to will not be in the enumeration.
1118      *
1119      * @throws  IOException
1120      *          If I/O errors occur
1121      *
1122      * @see  #findResources(String)
1123      *
1124      * @since  1.2
1125      */
1126     public Enumeration<URL> getResources(String name) throws IOException {
1127         @SuppressWarnings("unchecked")
1128         Enumeration<URL>[] tmp = (Enumeration<URL>[]) new Enumeration<?>[2];
1129         if (parent != null) {
1130             tmp[0] = parent.getResources(name);
1131         } else {
1132             tmp[0] = getBootstrapResources(name);
1133         }
1134         tmp[1] = findResources(name);
1135 
1136         return new CompoundEnumeration<>(tmp);
1137     }
1138 
1139     /**
1140      * Finds the resource with the given name. Class loader implementations
1141      * should override this method to specify where to find resources.
1142      *
1143      * @param  name
1144      *         The resource name
1145      *
1146      * @return  A <tt>URL</tt> object for reading the resource, or
1147      *          <tt>null</tt> if the resource could not be found
1148      *
1149      * @since  1.2
1150      */
1151     protected URL findResource(String name) {
1152         return null;
1153     }
1154 
1155     /**
1156      * Returns an enumeration of {@link java.net.URL <tt>URL</tt>} objects
1157      * representing all the resources with the given name. Class loader
1158      * implementations should override this method to specify where to load
1159      * resources from.
1160      *
1161      * @param  name
1162      *         The resource name
1163      *
1164      * @return  An enumeration of {@link java.net.URL <tt>URL</tt>} objects for
1165      *          the resources
1166      *
1167      * @throws  IOException
1168      *          If I/O errors occur
1169      *
1170      * @since  1.2
1171      */
1172     protected Enumeration<URL> findResources(String name) throws IOException {
1173         return java.util.Collections.emptyEnumeration();
1174     }
1175 
1176     /**
1177      * Registers the caller as parallel capable.
1178      * The registration succeeds if and only if all of the following
1179      * conditions are met:
1180      * <ol>
1181      * <li> no instance of the caller has been created</li>
1182      * <li> all of the super classes (except class Object) of the caller are
1183      * registered as parallel capable</li>
1184      * </ol>
1185      * <p>Note that once a class loader is registered as parallel capable, there
1186      * is no way to change it back.</p>
1187      *
1188      * @return  true if the caller is successfully registered as
1189      *          parallel capable and false if otherwise.
1190      *
1191      * @since   1.7
1192      */
1193     @CallerSensitive
1194     protected static boolean registerAsParallelCapable() {
1195         Class<? extends ClassLoader> callerClass =
1196             Reflection.getCallerClass().asSubclass(ClassLoader.class);
1197         return ParallelLoaders.register(callerClass);
1198     }
1199 
1200     /**
1201      * Find a resource of the specified name from the search path used to load
1202      * classes.  This method locates the resource through the system class
1203      * loader (see {@link #getSystemClassLoader()}).
1204      *
1205      * @param  name
1206      *         The resource name
1207      *
1208      * @return  A {@link java.net.URL <tt>URL</tt>} object for reading the
1209      *          resource, or <tt>null</tt> if the resource could not be found
1210      *
1211      * @since  1.1
1212      */
1213     public static URL getSystemResource(String name) {
1214         ClassLoader system = getSystemClassLoader();
1215         if (system == null) {
1216             return getBootstrapResource(name);
1217         }
1218         return system.getResource(name);
1219     }
1220 
1221     /**
1222      * Finds all resources of the specified name from the search path used to
1223      * load classes.  The resources thus found are returned as an
1224      * {@link java.util.Enumeration <tt>Enumeration</tt>} of {@link
1225      * java.net.URL <tt>URL</tt>} objects.
1226      *
1227      * <p> The search order is described in the documentation for {@link
1228      * #getSystemResource(String)}.  </p>
1229      *
1230      * @param  name
1231      *         The resource name
1232      *
1233      * @return  An enumeration of resource {@link java.net.URL <tt>URL</tt>}
1234      *          objects
1235      *
1236      * @throws  IOException
1237      *          If I/O errors occur
1238 
1239      * @since  1.2
1240      */
1241     public static Enumeration<URL> getSystemResources(String name)
1242         throws IOException
1243     {
1244         ClassLoader system = getSystemClassLoader();
1245         if (system == null) {
1246             return getBootstrapResources(name);
1247         }
1248         return system.getResources(name);
1249     }
1250 
1251     /**
1252      * Find resources from the VM's built-in classloader.
1253      */
1254     private static URL getBootstrapResource(String name) {
1255         URLClassPath ucp = getBootstrapClassPath();
1256         Resource res = ucp.getResource(name);
1257         return res != null ? res.getURL() : null;
1258     }
1259 
1260     /**
1261      * Find resources from the VM's built-in classloader.
1262      */
1263     private static Enumeration<URL> getBootstrapResources(String name)
1264         throws IOException
1265     {
1266         final Enumeration<Resource> e =
1267             getBootstrapClassPath().getResources(name);
1268         return new Enumeration<URL> () {
1269             public URL nextElement() {
1270                 return e.nextElement().getURL();
1271             }
1272             public boolean hasMoreElements() {
1273                 return e.hasMoreElements();
1274             }
1275         };
1276     }
1277 
1278     // Returns the URLClassPath that is used for finding system resources.
1279     static URLClassPath getBootstrapClassPath() {
1280         return sun.misc.Launcher.getBootstrapClassPath();
1281     }
1282 
1283 
1284     /**
1285      * Returns an input stream for reading the specified resource.
1286      *
1287      * <p> The search order is described in the documentation for {@link
1288      * #getResource(String)}.  </p>
1289      *
1290      * @param  name
1291      *         The resource name
1292      *
1293      * @return  An input stream for reading the resource, or <tt>null</tt>
1294      *          if the resource could not be found
1295      *
1296      * @since  1.1
1297      */
1298     public InputStream getResourceAsStream(String name) {
1299         URL url = getResource(name);
1300         try {
1301             return url != null ? url.openStream() : null;
1302         } catch (IOException e) {
1303             return null;
1304         }
1305     }
1306 
1307     /**
1308      * Open for reading, a resource of the specified name from the search path
1309      * used to load classes.  This method locates the resource through the
1310      * system class loader (see {@link #getSystemClassLoader()}).
1311      *
1312      * @param  name
1313      *         The resource name
1314      *
1315      * @return  An input stream for reading the resource, or <tt>null</tt>
1316      *          if the resource could not be found
1317      *
1318      * @since  1.1
1319      */
1320     public static InputStream getSystemResourceAsStream(String name) {
1321         URL url = getSystemResource(name);
1322         try {
1323             return url != null ? url.openStream() : null;
1324         } catch (IOException e) {
1325             return null;
1326         }
1327     }
1328 
1329 
1330     // -- Hierarchy --
1331 
1332     /**
1333      * Returns the parent class loader for delegation. Some implementations may
1334      * use <tt>null</tt> to represent the bootstrap class loader. This method
1335      * will return <tt>null</tt> in such implementations if this class loader's
1336      * parent is the bootstrap class loader.
1337      *
1338      * <p> If a security manager is present, and the invoker's class loader is
1339      * not <tt>null</tt> and is not an ancestor of this class loader, then this
1340      * method invokes the security manager's {@link
1341      * SecurityManager#checkPermission(java.security.Permission)
1342      * <tt>checkPermission</tt>} method with a {@link
1343      * RuntimePermission#RuntimePermission(String)
1344      * <tt>RuntimePermission("getClassLoader")</tt>} permission to verify
1345      * access to the parent class loader is permitted.  If not, a
1346      * <tt>SecurityException</tt> will be thrown.  </p>
1347      *
1348      * @return  The parent <tt>ClassLoader</tt>
1349      *
1350      * @throws  SecurityException
1351      *          If a security manager exists and its <tt>checkPermission</tt>
1352      *          method doesn't allow access to this class loader's parent class
1353      *          loader.
1354      *
1355      * @since  1.2
1356      */
1357     @CallerSensitive
1358     public final ClassLoader getParent() {
1359         if (parent == null)
1360             return null;
1361         SecurityManager sm = System.getSecurityManager();
1362         if (sm != null) {
1363             checkClassLoaderPermission(this, Reflection.getCallerClass());
1364         }
1365         return parent;
1366     }
1367 
1368     /**
1369      * Returns the system class loader for delegation.  This is the default
1370      * delegation parent for new <tt>ClassLoader</tt> instances, and is
1371      * typically the class loader used to start the application.
1372      *
1373      * <p> This method is first invoked early in the runtime's startup
1374      * sequence, at which point it creates the system class loader and sets it
1375      * as the context class loader of the invoking <tt>Thread</tt>.
1376      *
1377      * <p> The default system class loader is an implementation-dependent
1378      * instance of this class.
1379      *
1380      * <p> If the system property "<tt>java.system.class.loader</tt>" is defined
1381      * when this method is first invoked then the value of that property is
1382      * taken to be the name of a class that will be returned as the system
1383      * class loader.  The class is loaded using the default system class loader
1384      * and must define a public constructor that takes a single parameter of
1385      * type <tt>ClassLoader</tt> which is used as the delegation parent.  An
1386      * instance is then created using this constructor with the default system
1387      * class loader as the parameter.  The resulting class loader is defined
1388      * to be the system class loader.
1389      *
1390      * <p> If a security manager is present, and the invoker's class loader is
1391      * not <tt>null</tt> and the invoker's class loader is not the same as or
1392      * an ancestor of the system class loader, then this method invokes the
1393      * security manager's {@link
1394      * SecurityManager#checkPermission(java.security.Permission)
1395      * <tt>checkPermission</tt>} method with a {@link
1396      * RuntimePermission#RuntimePermission(String)
1397      * <tt>RuntimePermission("getClassLoader")</tt>} permission to verify
1398      * access to the system class loader.  If not, a
1399      * <tt>SecurityException</tt> will be thrown.  </p>
1400      *
1401      * @return  The system <tt>ClassLoader</tt> for delegation, or
1402      *          <tt>null</tt> if none
1403      *
1404      * @throws  SecurityException
1405      *          If a security manager exists and its <tt>checkPermission</tt>
1406      *          method doesn't allow access to the system class loader.
1407      *
1408      * @throws  IllegalStateException
1409      *          If invoked recursively during the construction of the class
1410      *          loader specified by the "<tt>java.system.class.loader</tt>"
1411      *          property.
1412      *
1413      * @throws  Error
1414      *          If the system property "<tt>java.system.class.loader</tt>"
1415      *          is defined but the named class could not be loaded, the
1416      *          provider class does not define the required constructor, or an
1417      *          exception is thrown by that constructor when it is invoked. The
1418      *          underlying cause of the error can be retrieved via the
1419      *          {@link Throwable#getCause()} method.
1420      *
1421      * @revised  1.4
1422      */
1423     @CallerSensitive
1424     public static ClassLoader getSystemClassLoader() {
1425         initSystemClassLoader();
1426         if (scl == null) {
1427             return null;
1428         }
1429         SecurityManager sm = System.getSecurityManager();
1430         if (sm != null) {
1431             checkClassLoaderPermission(scl, Reflection.getCallerClass());
1432         }
1433         return scl;
1434     }
1435 
1436     private static synchronized void initSystemClassLoader() {
1437         if (!sclSet) {
1438             if (scl != null)
1439                 throw new IllegalStateException("recursive invocation");
1440             sun.misc.Launcher l = sun.misc.Launcher.getLauncher();
1441             if (l != null) {
1442                 Throwable oops = null;
1443                 scl = l.getClassLoader();
1444                 try {
1445                     scl = AccessController.doPrivileged(
1446                         new SystemClassLoaderAction(scl));
1447                 } catch (PrivilegedActionException pae) {
1448                     oops = pae.getCause();
1449                     if (oops instanceof InvocationTargetException) {
1450                         oops = oops.getCause();
1451                     }
1452                 }
1453                 if (oops != null) {
1454                     if (oops instanceof Error) {
1455                         throw (Error) oops;
1456                     } else {
1457                         // wrap the exception
1458                         throw new Error(oops);
1459                     }
1460                 }
1461             }
1462             sclSet = true;
1463         }
1464     }
1465 
1466     // Returns true if the specified class loader can be found in this class
1467     // loader's delegation chain.
1468     boolean isAncestor(ClassLoader cl) {
1469         ClassLoader acl = this;
1470         do {
1471             acl = acl.parent;
1472             if (cl == acl) {
1473                 return true;
1474             }
1475         } while (acl != null);
1476         return false;
1477     }
1478 
1479     // Tests if class loader access requires "getClassLoader" permission
1480     // check.  A class loader 'from' can access class loader 'to' if
1481     // class loader 'from' is same as class loader 'to' or an ancestor
1482     // of 'to'.  The class loader in a system domain can access
1483     // any class loader.
1484     private static boolean needsClassLoaderPermissionCheck(ClassLoader from,
1485                                                            ClassLoader to)
1486     {
1487         if (from == to)
1488             return false;
1489 
1490         if (from == null)
1491             return false;
1492 
1493         return !to.isAncestor(from);
1494     }
1495 
1496     // Returns the class's class loader, or null if none.
1497     static ClassLoader getClassLoader(Class<?> caller) {
1498         // This can be null if the VM is requesting it
1499         if (caller == null) {
1500             return null;
1501         }
1502         // Circumvent security check since this is package-private
1503         return caller.getClassLoader0();
1504     }
1505 
1506     static void checkClassLoaderPermission(ClassLoader cl, Class<?> caller) {
1507         SecurityManager sm = System.getSecurityManager();
1508         if (sm != null) {
1509             // caller can be null if the VM is requesting it
1510             ClassLoader ccl = getClassLoader(caller);
1511             if (needsClassLoaderPermissionCheck(ccl, cl)) {
1512                 sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
1513             }
1514         }
1515     }
1516 
1517     // The class loader for the system
1518     // @GuardedBy("ClassLoader.class")
1519     private static ClassLoader scl;
1520 
1521     // Set to true once the system class loader has been set
1522     // @GuardedBy("ClassLoader.class")
1523     private static boolean sclSet;
1524 
1525 
1526     // -- Package --
1527 
1528     /**
1529      * Defines a package by name in this <tt>ClassLoader</tt>.  This allows
1530      * class loaders to define the packages for their classes. Packages must
1531      * be created before the class is defined, and package names must be
1532      * unique within a class loader and cannot be redefined or changed once
1533      * created.
1534      *
1535      * @param  name
1536      *         The package name
1537      *
1538      * @param  specTitle
1539      *         The specification title
1540      *
1541      * @param  specVersion
1542      *         The specification version
1543      *
1544      * @param  specVendor
1545      *         The specification vendor
1546      *
1547      * @param  implTitle
1548      *         The implementation title
1549      *
1550      * @param  implVersion
1551      *         The implementation version
1552      *
1553      * @param  implVendor
1554      *         The implementation vendor
1555      *
1556      * @param  sealBase
1557      *         If not <tt>null</tt>, then this package is sealed with
1558      *         respect to the given code source {@link java.net.URL
1559      *         <tt>URL</tt>}  object.  Otherwise, the package is not sealed.
1560      *
1561      * @return  The newly defined <tt>Package</tt> object
1562      *
1563      * @throws  IllegalArgumentException
1564      *          If package name duplicates an existing package either in this
1565      *          class loader or one of its ancestors
1566      *
1567      * @since  1.2
1568      */
1569     protected Package definePackage(String name, String specTitle,
1570                                     String specVersion, String specVendor,
1571                                     String implTitle, String implVersion,
1572                                     String implVendor, URL sealBase)
1573         throws IllegalArgumentException
1574     {
1575         Package pkg = getPackage(name);
1576         if (pkg != null) {
1577             throw new IllegalArgumentException(name);
1578         }
1579         pkg = new Package(name, specTitle, specVersion, specVendor,
1580                           implTitle, implVersion, implVendor,
1581                           sealBase, this);
1582         Package oldPkg = packages.putIfAbsent(name, pkg);
1583         if (oldPkg != null) {
1584             throw new IllegalArgumentException(name);
1585         }
1586         return pkg;
1587     }
1588 
1589     /**
1590      * Returns a <tt>Package</tt> that has been defined by this class loader
1591      * or any of its ancestors.
1592      *
1593      * @param  name
1594      *         The package name
1595      *
1596      * @return  The <tt>Package</tt> corresponding to the given name, or
1597      *          <tt>null</tt> if not found
1598      *
1599      * @since  1.2
1600      */
1601     protected Package getPackage(String name) {
1602         Package pkg = packages.get(name);
1603         if (pkg == null) {
1604             if (parent != null) {
1605                 pkg = parent.getPackage(name);
1606             } else {
1607                 pkg = Package.getSystemPackage(name);
1608             }
1609         }
1610         return pkg;
1611     }
1612 
1613     /**
1614      * Returns all of the <tt>Packages</tt> defined by this class loader and
1615      * its ancestors.
1616      *
1617      * @return  The array of <tt>Package</tt> objects defined by this
1618      *          <tt>ClassLoader</tt>
1619      *
1620      * @since  1.2
1621      */
1622     protected Package[] getPackages() {
1623         Package[] pkgs;
1624         if (parent != null) {
1625             pkgs = parent.getPackages();
1626         } else {
1627             pkgs = Package.getSystemPackages();
1628         }
1629 
1630         Map<String, Package> map = packages;
1631         if (pkgs != null) {
1632             map = new HashMap<>(packages);
1633             for (Package pkg : pkgs) {
1634                 String pkgName = pkg.getName();
1635                 if (!map.containsKey(pkgName)) {
1636                     map.put(pkgName, pkg);
1637                 }
1638             }
1639         }
1640         return map.values().toArray(new Package[map.size()]);
1641     }
1642 
1643 
1644     // -- Native library access --
1645 
1646     /**
1647      * Returns the absolute path name of a native library.  The VM invokes this
1648      * method to locate the native libraries that belong to classes loaded with
1649      * this class loader. If this method returns <tt>null</tt>, the VM
1650      * searches the library along the path specified as the
1651      * "<tt>java.library.path</tt>" property.
1652      *
1653      * @param  libname
1654      *         The library name
1655      *
1656      * @return  The absolute path of the native library
1657      *
1658      * @see  System#loadLibrary(String)
1659      * @see  System#mapLibraryName(String)
1660      *
1661      * @since  1.2
1662      */
1663     protected String findLibrary(String libname) {
1664         return null;
1665     }
1666 
1667     /**
1668      * The inner class NativeLibrary denotes a loaded native library instance.
1669      * Every classloader contains a vector of loaded native libraries in the
1670      * private field <tt>nativeLibraries</tt>.  The native libraries loaded
1671      * into the system are entered into the <tt>systemNativeLibraries</tt>
1672      * vector.
1673      *
1674      * <p> Every native library requires a particular version of JNI. This is
1675      * denoted by the private <tt>jniVersion</tt> field.  This field is set by
1676      * the VM when it loads the library, and used by the VM to pass the correct
1677      * version of JNI to the native methods.  </p>
1678      *
1679      * @see      ClassLoader
1680      * @since    1.2
1681      */
1682     static class NativeLibrary {
1683         // opaque handle to native library, used in native code.
1684         long handle;
1685         // the version of JNI environment the native library requires.
1686         private int jniVersion;
1687         // the class from which the library is loaded, also indicates
1688         // the loader this native library belongs.
1689         private final Class<?> fromClass;
1690         // the canonicalized name of the native library.
1691         // or static library name
1692         String name;
1693         // Indicates if the native library is linked into the VM
1694         boolean isBuiltin;
1695         // Indicates if the native library is loaded
1696         boolean loaded;
1697         native void load(String name, boolean isBuiltin);
1698 
1699         native long find(String name);
1700         native void unload(String name, boolean isBuiltin);
1701         static native String findBuiltinLib(String name);
1702 
1703         public NativeLibrary(Class<?> fromClass, String name, boolean isBuiltin) {
1704             this.name = name;
1705             this.fromClass = fromClass;
1706             this.isBuiltin = isBuiltin;
1707         }
1708 
1709         protected void finalize() {
1710             synchronized (loadedLibraryNames) {
1711                 if (fromClass.getClassLoader() != null && loaded) {
1712                     /* remove the native library name */
1713                     int size = loadedLibraryNames.size();
1714                     for (int i = 0; i < size; i++) {
1715                         if (name.equals(loadedLibraryNames.elementAt(i))) {
1716                             loadedLibraryNames.removeElementAt(i);
1717                             break;
1718                         }
1719                     }
1720                     /* unload the library. */
1721                     ClassLoader.nativeLibraryContext.push(this);
1722                     try {
1723                         unload(name, isBuiltin);
1724                     } finally {
1725                         ClassLoader.nativeLibraryContext.pop();
1726                     }
1727                 }
1728             }
1729         }
1730         // Invoked in the VM to determine the context class in
1731         // JNI_Load/JNI_Unload
1732         static Class<?> getFromClass() {
1733             return ClassLoader.nativeLibraryContext.peek().fromClass;
1734         }
1735     }
1736 
1737     // All native library names we've loaded.
1738     private static Vector<String> loadedLibraryNames = new Vector<>();
1739 
1740     // Native libraries belonging to system classes.
1741     private static Vector<NativeLibrary> systemNativeLibraries
1742         = new Vector<>();
1743 
1744     // Native libraries associated with the class loader.
1745     private Vector<NativeLibrary> nativeLibraries = new Vector<>();
1746 
1747     // native libraries being loaded/unloaded.
1748     private static Stack<NativeLibrary> nativeLibraryContext = new Stack<>();
1749 
1750     // The paths searched for libraries
1751     private static String usr_paths[];
1752     private static String sys_paths[];
1753 
1754     private static String[] initializePath(String propname) {
1755         String ldpath = System.getProperty(propname, "");
1756         String ps = File.pathSeparator;
1757         int ldlen = ldpath.length();
1758         int i, j, n;
1759         // Count the separators in the path
1760         i = ldpath.indexOf(ps);
1761         n = 0;
1762         while (i >= 0) {
1763             n++;
1764             i = ldpath.indexOf(ps, i + 1);
1765         }
1766 
1767         // allocate the array of paths - n :'s = n + 1 path elements
1768         String[] paths = new String[n + 1];
1769 
1770         // Fill the array with paths from the ldpath
1771         n = i = 0;
1772         j = ldpath.indexOf(ps);
1773         while (j >= 0) {
1774             if (j - i > 0) {
1775                 paths[n++] = ldpath.substring(i, j);
1776             } else if (j - i == 0) {
1777                 paths[n++] = ".";
1778             }
1779             i = j + 1;
1780             j = ldpath.indexOf(ps, i);
1781         }
1782         paths[n] = ldpath.substring(i, ldlen);
1783         return paths;
1784     }
1785 
1786     // Invoked in the java.lang.Runtime class to implement load and loadLibrary.
1787     static void loadLibrary(Class<?> fromClass, String name,
1788                             boolean isAbsolute) {
1789         ClassLoader loader =
1790             (fromClass == null) ? null : fromClass.getClassLoader();
1791         if (sys_paths == null) {
1792             usr_paths = initializePath("java.library.path");
1793             sys_paths = initializePath("sun.boot.library.path");
1794         }
1795         if (isAbsolute) {
1796             if (loadLibrary0(fromClass, new File(name))) {
1797                 return;
1798             }
1799             throw new UnsatisfiedLinkError("Can't load library: " + name);
1800         }
1801         if (loader != null) {
1802             String libfilename = loader.findLibrary(name);
1803             if (libfilename != null) {
1804                 File libfile = new File(libfilename);
1805                 if (!libfile.isAbsolute()) {
1806                     throw new UnsatisfiedLinkError(
1807     "ClassLoader.findLibrary failed to return an absolute path: " + libfilename);
1808                 }
1809                 if (loadLibrary0(fromClass, libfile)) {
1810                     return;
1811                 }
1812                 throw new UnsatisfiedLinkError("Can't load " + libfilename);
1813             }
1814         }
1815         for (String sys_path : sys_paths) {
1816             File libfile = new File(sys_path, System.mapLibraryName(name));
1817             if (loadLibrary0(fromClass, libfile)) {
1818                 return;
1819             }
1820             libfile = ClassLoaderHelper.mapAlternativeName(libfile);
1821             if (libfile != null && loadLibrary0(fromClass, libfile)) {
1822                 return;
1823             }
1824         }
1825         if (loader != null) {
1826             for (String usr_path : usr_paths) {
1827                 File libfile = new File(usr_path, System.mapLibraryName(name));
1828                 if (loadLibrary0(fromClass, libfile)) {
1829                     return;
1830                 }
1831                 libfile = ClassLoaderHelper.mapAlternativeName(libfile);
1832                 if (libfile != null && loadLibrary0(fromClass, libfile)) {
1833                     return;
1834                 }
1835             }
1836         }
1837         // Oops, it failed
1838         throw new UnsatisfiedLinkError("no " + name + " in java.library.path");
1839     }
1840 
1841     private static boolean loadLibrary0(Class<?> fromClass, final File file) {
1842         // Check to see if we're attempting to access a static library
1843         String name = NativeLibrary.findBuiltinLib(file.getName());
1844         boolean isBuiltin = (name != null);
1845         if (!isBuiltin) {
1846             name = AccessController.doPrivileged(
1847                 new PrivilegedAction<String>() {
1848                     public String run() {
1849                         try {
1850                             return file.exists() ? file.getCanonicalPath() : null;
1851                         } catch (IOException e) {
1852                             return null;
1853                         }
1854                     }
1855                 });
1856             if (name == null) {
1857                 return false;
1858             }
1859         }
1860         ClassLoader loader =
1861             (fromClass == null) ? null : fromClass.getClassLoader();
1862         Vector<NativeLibrary> libs =
1863             loader != null ? loader.nativeLibraries : systemNativeLibraries;
1864         synchronized (libs) {
1865             int size = libs.size();
1866             for (int i = 0; i < size; i++) {
1867                 NativeLibrary lib = libs.elementAt(i);
1868                 if (name.equals(lib.name)) {
1869                     return true;
1870                 }
1871             }
1872 
1873             synchronized (loadedLibraryNames) {
1874                 if (loadedLibraryNames.contains(name)) {
1875                     throw new UnsatisfiedLinkError
1876                         ("Native Library " +
1877                          name +
1878                          " already loaded in another classloader");
1879                 }
1880                 /* If the library is being loaded (must be by the same thread,
1881                  * because Runtime.load and Runtime.loadLibrary are
1882                  * synchronous). The reason is can occur is that the JNI_OnLoad
1883                  * function can cause another loadLibrary invocation.
1884                  *
1885                  * Thus we can use a static stack to hold the list of libraries
1886                  * we are loading.
1887                  *
1888                  * If there is a pending load operation for the library, we
1889                  * immediately return success; otherwise, we raise
1890                  * UnsatisfiedLinkError.
1891                  */
1892                 int n = nativeLibraryContext.size();
1893                 for (int i = 0; i < n; i++) {
1894                     NativeLibrary lib = nativeLibraryContext.elementAt(i);
1895                     if (name.equals(lib.name)) {
1896                         if (loader == lib.fromClass.getClassLoader()) {
1897                             return true;
1898                         } else {
1899                             throw new UnsatisfiedLinkError
1900                                 ("Native Library " +
1901                                  name +
1902                                  " is being loaded in another classloader");
1903                         }
1904                     }
1905                 }
1906                 NativeLibrary lib = new NativeLibrary(fromClass, name, isBuiltin);
1907                 nativeLibraryContext.push(lib);
1908                 try {
1909                     lib.load(name, isBuiltin);
1910                 } finally {
1911                     nativeLibraryContext.pop();
1912                 }
1913                 if (lib.loaded) {
1914                     loadedLibraryNames.addElement(name);
1915                     libs.addElement(lib);
1916                     return true;
1917                 }
1918                 return false;
1919             }
1920         }
1921     }
1922 
1923     // Invoked in the VM class linking code.
1924     static long findNative(ClassLoader loader, String name) {
1925         Vector<NativeLibrary> libs =
1926             loader != null ? loader.nativeLibraries : systemNativeLibraries;
1927         synchronized (libs) {
1928             int size = libs.size();
1929             for (int i = 0; i < size; i++) {
1930                 NativeLibrary lib = libs.elementAt(i);
1931                 long entry = lib.find(name);
1932                 if (entry != 0)
1933                     return entry;
1934             }
1935         }
1936         return 0;
1937     }
1938 
1939 
1940     // -- Assertion management --
1941 
1942     final Object assertionLock;
1943 
1944     // The default toggle for assertion checking.
1945     // @GuardedBy("assertionLock")
1946     private boolean defaultAssertionStatus = false;
1947 
1948     // Maps String packageName to Boolean package default assertion status Note
1949     // that the default package is placed under a null map key.  If this field
1950     // is null then we are delegating assertion status queries to the VM, i.e.,
1951     // none of this ClassLoader's assertion status modification methods have
1952     // been invoked.
1953     // @GuardedBy("assertionLock")
1954     private Map<String, Boolean> packageAssertionStatus = null;
1955 
1956     // Maps String fullyQualifiedClassName to Boolean assertionStatus If this
1957     // field is null then we are delegating assertion status queries to the VM,
1958     // i.e., none of this ClassLoader's assertion status modification methods
1959     // have been invoked.
1960     // @GuardedBy("assertionLock")
1961     Map<String, Boolean> classAssertionStatus = null;
1962 
1963     /**
1964      * Sets the default assertion status for this class loader.  This setting
1965      * determines whether classes loaded by this class loader and initialized
1966      * in the future will have assertions enabled or disabled by default.
1967      * This setting may be overridden on a per-package or per-class basis by
1968      * invoking {@link #setPackageAssertionStatus(String, boolean)} or {@link
1969      * #setClassAssertionStatus(String, boolean)}.
1970      *
1971      * @param  enabled
1972      *         <tt>true</tt> if classes loaded by this class loader will
1973      *         henceforth have assertions enabled by default, <tt>false</tt>
1974      *         if they will have assertions disabled by default.
1975      *
1976      * @since  1.4
1977      */
1978     public void setDefaultAssertionStatus(boolean enabled) {
1979         synchronized (assertionLock) {
1980             if (classAssertionStatus == null)
1981                 initializeJavaAssertionMaps();
1982 
1983             defaultAssertionStatus = enabled;
1984         }
1985     }
1986 
1987     /**
1988      * Sets the package default assertion status for the named package.  The
1989      * package default assertion status determines the assertion status for
1990      * classes initialized in the future that belong to the named package or
1991      * any of its "subpackages".
1992      *
1993      * <p> A subpackage of a package named p is any package whose name begins
1994      * with "<tt>p.</tt>".  For example, <tt>javax.swing.text</tt> is a
1995      * subpackage of <tt>javax.swing</tt>, and both <tt>java.util</tt> and
1996      * <tt>java.lang.reflect</tt> are subpackages of <tt>java</tt>.
1997      *
1998      * <p> In the event that multiple package defaults apply to a given class,
1999      * the package default pertaining to the most specific package takes
2000      * precedence over the others.  For example, if <tt>javax.lang</tt> and
2001      * <tt>javax.lang.reflect</tt> both have package defaults associated with
2002      * them, the latter package default applies to classes in
2003      * <tt>javax.lang.reflect</tt>.
2004      *
2005      * <p> Package defaults take precedence over the class loader's default
2006      * assertion status, and may be overridden on a per-class basis by invoking
2007      * {@link #setClassAssertionStatus(String, boolean)}.  </p>
2008      *
2009      * @param  packageName
2010      *         The name of the package whose package default assertion status
2011      *         is to be set. A <tt>null</tt> value indicates the unnamed
2012      *         package that is "current"
2013      *         (see section 7.4.2 of
2014      *         <cite>The Java&trade; Language Specification</cite>.)
2015      *
2016      * @param  enabled
2017      *         <tt>true</tt> if classes loaded by this classloader and
2018      *         belonging to the named package or any of its subpackages will
2019      *         have assertions enabled by default, <tt>false</tt> if they will
2020      *         have assertions disabled by default.
2021      *
2022      * @since  1.4
2023      */
2024     public void setPackageAssertionStatus(String packageName,
2025                                           boolean enabled) {
2026         synchronized (assertionLock) {
2027             if (packageAssertionStatus == null)
2028                 initializeJavaAssertionMaps();
2029 
2030             packageAssertionStatus.put(packageName, enabled);
2031         }
2032     }
2033 
2034     /**
2035      * Sets the desired assertion status for the named top-level class in this
2036      * class loader and any nested classes contained therein.  This setting
2037      * takes precedence over the class loader's default assertion status, and
2038      * over any applicable per-package default.  This method has no effect if
2039      * the named class has already been initialized.  (Once a class is
2040      * initialized, its assertion status cannot change.)
2041      *
2042      * <p> If the named class is not a top-level class, this invocation will
2043      * have no effect on the actual assertion status of any class. </p>
2044      *
2045      * @param  className
2046      *         The fully qualified class name of the top-level class whose
2047      *         assertion status is to be set.
2048      *
2049      * @param  enabled
2050      *         <tt>true</tt> if the named class is to have assertions
2051      *         enabled when (and if) it is initialized, <tt>false</tt> if the
2052      *         class is to have assertions disabled.
2053      *
2054      * @since  1.4
2055      */
2056     public void setClassAssertionStatus(String className, boolean enabled) {
2057         synchronized (assertionLock) {
2058             if (classAssertionStatus == null)
2059                 initializeJavaAssertionMaps();
2060 
2061             classAssertionStatus.put(className, enabled);
2062         }
2063     }
2064 
2065     /**
2066      * Sets the default assertion status for this class loader to
2067      * <tt>false</tt> and discards any package defaults or class assertion
2068      * status settings associated with the class loader.  This method is
2069      * provided so that class loaders can be made to ignore any command line or
2070      * persistent assertion status settings and "start with a clean slate."
2071      *
2072      * @since  1.4
2073      */
2074     public void clearAssertionStatus() {
2075         /*
2076          * Whether or not "Java assertion maps" are initialized, set
2077          * them to empty maps, effectively ignoring any present settings.
2078          */
2079         synchronized (assertionLock) {
2080             classAssertionStatus = new HashMap<>();
2081             packageAssertionStatus = new HashMap<>();
2082             defaultAssertionStatus = false;
2083         }
2084     }
2085 
2086     /**
2087      * Returns the assertion status that would be assigned to the specified
2088      * class if it were to be initialized at the time this method is invoked.
2089      * If the named class has had its assertion status set, the most recent
2090      * setting will be returned; otherwise, if any package default assertion
2091      * status pertains to this class, the most recent setting for the most
2092      * specific pertinent package default assertion status is returned;
2093      * otherwise, this class loader's default assertion status is returned.
2094      * </p>
2095      *
2096      * @param  className
2097      *         The fully qualified class name of the class whose desired
2098      *         assertion status is being queried.
2099      *
2100      * @return  The desired assertion status of the specified class.
2101      *
2102      * @see  #setClassAssertionStatus(String, boolean)
2103      * @see  #setPackageAssertionStatus(String, boolean)
2104      * @see  #setDefaultAssertionStatus(boolean)
2105      *
2106      * @since  1.4
2107      */
2108     boolean desiredAssertionStatus(String className) {
2109         synchronized (assertionLock) {
2110             // assert classAssertionStatus   != null;
2111             // assert packageAssertionStatus != null;
2112 
2113             // Check for a class entry
2114             Boolean result = classAssertionStatus.get(className);
2115             if (result != null)
2116                 return result.booleanValue();
2117 
2118             // Check for most specific package entry
2119             int dotIndex = className.lastIndexOf('.');
2120             if (dotIndex < 0) { // default package
2121                 result = packageAssertionStatus.get(null);
2122                 if (result != null)
2123                     return result.booleanValue();
2124             }
2125             while(dotIndex > 0) {
2126                 className = className.substring(0, dotIndex);
2127                 result = packageAssertionStatus.get(className);
2128                 if (result != null)
2129                     return result.booleanValue();
2130                 dotIndex = className.lastIndexOf('.', dotIndex-1);
2131             }
2132 
2133             // Return the classloader default
2134             return defaultAssertionStatus;
2135         }
2136     }
2137 
2138     // Set up the assertions with information provided by the VM.
2139     // Note: Should only be called inside a synchronized block
2140     private void initializeJavaAssertionMaps() {
2141         // assert Thread.holdsLock(assertionLock);
2142 
2143         classAssertionStatus = new HashMap<>();
2144         packageAssertionStatus = new HashMap<>();
2145         AssertionStatusDirectives directives = retrieveDirectives();
2146 
2147         for(int i = 0; i < directives.classes.length; i++)
2148             classAssertionStatus.put(directives.classes[i],
2149                                      directives.classEnabled[i]);
2150 
2151         for(int i = 0; i < directives.packages.length; i++)
2152             packageAssertionStatus.put(directives.packages[i],
2153                                        directives.packageEnabled[i]);
2154 
2155         defaultAssertionStatus = directives.deflt;
2156     }
2157 
2158     // Retrieves the assertion directives from the VM.
2159     private static native AssertionStatusDirectives retrieveDirectives();
2160 }
2161 
2162 
2163 class SystemClassLoaderAction
2164     implements PrivilegedExceptionAction<ClassLoader> {
2165     private ClassLoader parent;
2166 
2167     SystemClassLoaderAction(ClassLoader parent) {
2168         this.parent = parent;
2169     }
2170 
2171     public ClassLoader run() throws Exception {
2172         String cls = System.getProperty("java.system.class.loader");
2173         if (cls == null) {
2174             return parent;
2175         }
2176 
2177         Constructor<?> ctor = Class.forName(cls, true, parent)
2178             .getDeclaredConstructor(new Class<?>[] { ClassLoader.class });
2179         ClassLoader sys = (ClassLoader) ctor.newInstance(
2180             new Object[] { parent });
2181         Thread.currentThread().setContextClassLoader(sys);
2182         return sys;
2183     }
2184 }