1 /*
   2  * Copyright (c) 1994, 2011, 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.MalformedURLException;
  33 import java.net.URL;
  34 import java.security.AccessController;
  35 import java.security.AccessControlContext;
  36 import java.security.CodeSource;
  37 import java.security.Policy;
  38 import java.security.PrivilegedAction;
  39 import java.security.PrivilegedActionException;
  40 import java.security.PrivilegedExceptionAction;
  41 import java.security.ProtectionDomain;
  42 import java.security.cert.Certificate;
  43 import java.util.Collections;
  44 import java.util.Enumeration;
  45 import java.util.HashMap;
  46 import java.util.HashSet;
  47 import java.util.Set;
  48 import java.util.Stack;
  49 import java.util.Map;
  50 import java.util.Vector;
  51 import java.util.Hashtable;
  52 import java.util.WeakHashMap;
  53 import java.util.concurrent.ConcurrentHashMap;
  54 import sun.misc.ClassFileTransformer;
  55 import sun.misc.CompoundEnumeration;
  56 import sun.misc.Resource;
  57 import sun.misc.URLClassPath;
  58 import sun.misc.VM;
  59 import sun.reflect.Reflection;
  60 import sun.security.util.SecurityConstants;
  61 
  62 /**
  63  * A class loader is an object that is responsible for loading classes. The
  64  * class <tt>ClassLoader</tt> is an abstract class.  Given the <a
  65  * href="#name">binary name</a> of a class, a class loader should attempt to
  66  * locate or generate data that constitutes a definition for the class.  A
  67  * typical strategy is to transform the name into a file name and then read a
  68  * "class file" of that name from a file system.
  69  *
  70  * <p> Every {@link Class <tt>Class</tt>} object contains a {@link
  71  * Class#getClassLoader() reference} to the <tt>ClassLoader</tt> that defined
  72  * it.
  73  *
  74  * <p> <tt>Class</tt> objects for array classes are not created by class
  75  * loaders, but are created automatically as required by the Java runtime.
  76  * The class loader for an array class, as returned by {@link
  77  * Class#getClassLoader()} is the same as the class loader for its element
  78  * type; if the element type is a primitive type, then the array class has no
  79  * class loader.
  80  *
  81  * <p> Applications implement subclasses of <tt>ClassLoader</tt> in order to
  82  * extend the manner in which the Java virtual machine dynamically loads
  83  * classes.
  84  *
  85  * <p> Class loaders may typically be used by security managers to indicate
  86  * security domains.
  87  *
  88  * <p> The <tt>ClassLoader</tt> class uses a delegation model to search for
  89  * classes and resources.  Each instance of <tt>ClassLoader</tt> has an
  90  * associated parent class loader.  When requested to find a class or
  91  * resource, a <tt>ClassLoader</tt> instance will delegate the search for the
  92  * class or resource to its parent class loader before attempting to find the
  93  * class or resource itself.  The virtual machine's built-in class loader,
  94  * called the "bootstrap class loader", does not itself have a parent but may
  95  * serve as the parent of a <tt>ClassLoader</tt> instance.
  96  *
  97  * <p> Class loaders that support concurrent loading of classes are known as
  98  * <em>parallel capable</em> class loaders and are required to register
  99  * themselves at their class initialization time by invoking the
 100  * {@link
 101  * #registerAsParallelCapable <tt>ClassLoader.registerAsParallelCapable</tt>}
 102  * method. Note that the <tt>ClassLoader</tt> class is registered as parallel
 103  * capable by default. However, its subclasses still need to register themselves
 104  * if they are parallel capable. <br>
 105  * In environments in which the delegation model is not strictly
 106  * hierarchical, class loaders need to be parallel capable, otherwise class
 107  * loading can lead to deadlocks because the loader lock is held for the
 108  * duration of the class loading process (see {@link #loadClass
 109  * <tt>loadClass</tt>} methods).
 110  *
 111  * <p> Normally, the Java virtual machine loads classes from the local file
 112  * system in a platform-dependent manner.  For example, on UNIX systems, the
 113  * virtual machine loads classes from the directory defined by the
 114  * <tt>CLASSPATH</tt> environment variable.
 115  *
 116  * <p> However, some classes may not originate from a file; they may originate
 117  * from other sources, such as the network, or they could be constructed by an
 118  * application.  The method {@link #defineClass(String, byte[], int, int)
 119  * <tt>defineClass</tt>} converts an array of bytes into an instance of class
 120  * <tt>Class</tt>. Instances of this newly defined class can be created using
 121  * {@link Class#newInstance <tt>Class.newInstance</tt>}.
 122  *
 123  * <p> The methods and constructors of objects created by a class loader may
 124  * reference other classes.  To determine the class(es) referred to, the Java
 125  * virtual machine invokes the {@link #loadClass <tt>loadClass</tt>} method of
 126  * the class loader that originally created the class.
 127  *
 128  * <p> For example, an application could create a network class loader to
 129  * download class files from a server.  Sample code might look like:
 130  *
 131  * <blockquote><pre>
 132  *   ClassLoader loader&nbsp;= new NetworkClassLoader(host,&nbsp;port);
 133  *   Object main&nbsp;= loader.loadClass("Main", true).newInstance();
 134  *       &nbsp;.&nbsp;.&nbsp;.
 135  * </pre></blockquote>
 136  *
 137  * <p> The network class loader subclass must define the methods {@link
 138  * #findClass <tt>findClass</tt>} and <tt>loadClassData</tt> to load a class
 139  * from the network.  Once it has downloaded the bytes that make up the class,
 140  * it should use the method {@link #defineClass <tt>defineClass</tt>} to
 141  * create a class instance.  A sample implementation is:
 142  *
 143  * <blockquote><pre>
 144  *     class NetworkClassLoader extends ClassLoader {
 145  *         String host;
 146  *         int port;
 147  *
 148  *         public Class findClass(String name) {
 149  *             byte[] b = loadClassData(name);
 150  *             return defineClass(name, b, 0, b.length);
 151  *         }
 152  *
 153  *         private byte[] loadClassData(String name) {
 154  *             // load the class data from the connection
 155  *             &nbsp;.&nbsp;.&nbsp;.
 156  *         }
 157  *     }
 158  * </pre></blockquote>
 159  *
 160  * <h4> <a name="name">Binary names</a> </h4>
 161  *
 162  * <p> Any class name provided as a {@link String} parameter to methods in
 163  * <tt>ClassLoader</tt> must be a binary name as defined by
 164  * <cite>The Java&trade; Language Specification</cite>.
 165  *
 166  * <p> Examples of valid class names include:
 167  * <blockquote><pre>
 168  *   "java.lang.String"
 169  *   "javax.swing.JSpinner$DefaultEditor"
 170  *   "java.security.KeyStore$Builder$FileBuilder$1"
 171  *   "java.net.URLClassLoader$3$1"
 172  * </pre></blockquote>
 173  *
 174  * @see      #resolveClass(Class)
 175  * @since 1.0
 176  */
 177 public abstract class ClassLoader {
 178 
 179     private static native void registerNatives();
 180     static {
 181         registerNatives();
 182     }
 183 
 184     // The parent class loader for delegation
 185     // Note: VM hardcoded the offset of this field, thus all new fields
 186     // must be added *after* it.
 187     private final ClassLoader parent;
 188 
 189     /**
 190      * Encapsulates the set of parallel capable loader types.
 191      */
 192     private static class ParallelLoaders {
 193         private ParallelLoaders() {}
 194 
 195         // the set of parallel capable loader types
 196         private static final Set<Class<? extends ClassLoader>> loaderTypes =
 197             Collections.newSetFromMap(
 198                 new WeakHashMap<Class<? extends ClassLoader>, Boolean>());
 199         static {
 200             synchronized (loaderTypes) { loaderTypes.add(ClassLoader.class); }
 201         }
 202 
 203         /**
 204          * Registers the given class loader type as parallel capabale.
 205          * Returns {@code true} is successfully registered; {@code false} if
 206          * loader's super class is not registered.
 207          */
 208         static boolean register(Class<? extends ClassLoader> c) {
 209             synchronized (loaderTypes) {
 210                 if (loaderTypes.contains(c.getSuperclass())) {
 211                     // register the class loader as parallel capable
 212                     // if and only if all of its super classes are.
 213                     // Note: given current classloading sequence, if
 214                     // the immediate super class is parallel capable,
 215                     // all the super classes higher up must be too.
 216                     loaderTypes.add(c);
 217                     return true;
 218                 } else {
 219                     return false;
 220                 }
 221             }
 222         }
 223 
 224         /**
 225          * Returns {@code true} if the given class loader type is
 226          * registered as parallel capable.
 227          */
 228         static boolean isRegistered(Class<? extends ClassLoader> c) {
 229             synchronized (loaderTypes) {
 230                 return loaderTypes.contains(c);
 231             }
 232         }
 233     }
 234 
 235     // Maps class name to the corresponding lock object when the current
 236     // class loader is parallel capable.
 237     // Note: VM also uses this field to decide if the current class loader
 238     // is parallel capable and the appropriate lock object for class loading.
 239     private final ConcurrentHashMap<String, Object> parallelLockMap;
 240 
 241     // Hashtable that maps packages to certs
 242     private final Map <String, Certificate[]> package2certs;
 243 
 244     // Shared among all packages with unsigned classes
 245     private static final Certificate[] nocerts = new Certificate[0];
 246 
 247     // The classes loaded by this class loader. The only purpose of this table
 248     // is to keep the classes from being GC'ed until the loader is GC'ed.
 249     private final Vector<Class<?>> classes = new Vector<>();
 250 
 251     // The "default" domain. Set as the default ProtectionDomain on newly
 252     // created classes.
 253     private final ProtectionDomain defaultDomain =
 254         new ProtectionDomain(new CodeSource(null, (Certificate[]) null),
 255                              null, this, null);
 256 
 257     // The initiating protection domains for all classes loaded by this loader
 258     private final Set<ProtectionDomain> domains;
 259 
 260     // Invoked by the VM to record every loaded class with this loader.
 261     void addClass(Class<?> c) {
 262         classes.addElement(c);
 263     }
 264 
 265     // The packages defined in this class loader.  Each package name is mapped
 266     // to its corresponding Package object.
 267     // @GuardedBy("itself")
 268     private final HashMap<String, Package> packages = new HashMap<>();
 269 
 270     private static Void checkCreateClassLoader() {
 271         SecurityManager security = System.getSecurityManager();
 272         if (security != null) {
 273             security.checkCreateClassLoader();
 274         }
 275         return null;
 276     }
 277 
 278     private ClassLoader(Void unused, ClassLoader parent) {
 279         this.parent = parent;
 280         if (ParallelLoaders.isRegistered(this.getClass())) {
 281             parallelLockMap = new ConcurrentHashMap<>();
 282             package2certs = new ConcurrentHashMap<>();
 283             domains =
 284                 Collections.synchronizedSet(new HashSet<ProtectionDomain>());
 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>}.  </p>
 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      * <p><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. </p>
 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             final String name = cls.getName();
 490             final int i = name.lastIndexOf('.');
 491             if (i != -1) {
 492                 AccessController.doPrivileged(new PrivilegedAction<Void>() {
 493                     public Void run() {
 494                         sm.checkPackageAccess(name.substring(0, i));
 495                         return null;
 496                     }
 497                 }, new AccessControlContext(new ProtectionDomain[] {pd}));
 498             }
 499         }
 500         domains.add(pd);
 501     }
 502 
 503     /**
 504      * Finds the class with the specified <a href="#name">binary name</a>.
 505      * This method should be overridden by class loader implementations that
 506      * follow the delegation model for loading classes, and will be invoked by
 507      * the {@link #loadClass <tt>loadClass</tt>} method after checking the
 508      * parent class loader for the requested class.  The default implementation
 509      * throws a <tt>ClassNotFoundException</tt>.  </p>
 510      *
 511      * @param  name
 512      *         The <a href="#name">binary name</a> of the class
 513      *
 514      * @return  The resulting <tt>Class</tt> object
 515      *
 516      * @throws  ClassNotFoundException
 517      *          If the class could not be found
 518      *
 519      * @since  1.2
 520      */
 521     protected Class<?> findClass(String name) throws ClassNotFoundException {
 522         throw new ClassNotFoundException(name);
 523     }
 524 
 525     /**
 526      * Converts an array of bytes into an instance of class <tt>Class</tt>.
 527      * Before the <tt>Class</tt> can be used it must be resolved.  This method
 528      * is deprecated in favor of the version that takes a <a
 529      * href="#name">binary name</a> as its first argument, and is more secure.
 530      *
 531      * @param  b
 532      *         The bytes that make up the class data.  The bytes in positions
 533      *         <tt>off</tt> through <tt>off+len-1</tt> should have the format
 534      *         of a valid class file as defined by
 535      *         <cite>The Java&trade; Virtual Machine Specification</cite>.
 536      *
 537      * @param  off
 538      *         The start offset in <tt>b</tt> of the class data
 539      *
 540      * @param  len
 541      *         The length of the class data
 542      *
 543      * @return  The <tt>Class</tt> object that was created from the specified
 544      *          class data
 545      *
 546      * @throws  ClassFormatError
 547      *          If the data did not contain a valid class
 548      *
 549      * @throws  IndexOutOfBoundsException
 550      *          If either <tt>off</tt> or <tt>len</tt> is negative, or if
 551      *          <tt>off+len</tt> is greater than <tt>b.length</tt>.
 552      *
 553      * @throws  SecurityException
 554      *          If an attempt is made to add this class to a package that
 555      *          contains classes that were signed by a different set of
 556      *          certificates than this class, or if an attempt is made
 557      *          to define a class in a package with a fully-qualified name
 558      *          that starts with "{@code java.}".
 559      *
 560      * @see  #loadClass(String, boolean)
 561      * @see  #resolveClass(Class)
 562      *
 563      * @deprecated  Replaced by {@link #defineClass(String, byte[], int, int)
 564      * defineClass(String, byte[], int, int)}
 565      */
 566     @Deprecated
 567     protected final Class<?> defineClass(byte[] b, int off, int len)
 568         throws ClassFormatError
 569     {
 570         return defineClass(null, b, off, len, null);
 571     }
 572 
 573     /**
 574      * Converts an array of bytes into an instance of class <tt>Class</tt>.
 575      * Before the <tt>Class</tt> can be used it must be resolved.
 576      *
 577      * <p> This method assigns a default {@link java.security.ProtectionDomain
 578      * <tt>ProtectionDomain</tt>} to the newly defined class.  The
 579      * <tt>ProtectionDomain</tt> is effectively granted the same set of
 580      * permissions returned when {@link
 581      * java.security.Policy#getPermissions(java.security.CodeSource)
 582      * <tt>Policy.getPolicy().getPermissions(new CodeSource(null, null))</tt>}
 583      * is invoked.  The default domain is created on the first invocation of
 584      * {@link #defineClass(String, byte[], int, int) <tt>defineClass</tt>},
 585      * and re-used on subsequent invocations.
 586      *
 587      * <p> To assign a specific <tt>ProtectionDomain</tt> to the class, use
 588      * the {@link #defineClass(String, byte[], int, int,
 589      * java.security.ProtectionDomain) <tt>defineClass</tt>} method that takes a
 590      * <tt>ProtectionDomain</tt> as one of its arguments.  </p>
 591      *
 592      * @param  name
 593      *         The expected <a href="#name">binary name</a> of the class, or
 594      *         <tt>null</tt> if not known
 595      *
 596      * @param  b
 597      *         The bytes that make up the class data.  The bytes in positions
 598      *         <tt>off</tt> through <tt>off+len-1</tt> should have the format
 599      *         of a valid class file as defined by
 600      *         <cite>The Java&trade; Virtual Machine Specification</cite>.
 601      *
 602      * @param  off
 603      *         The start offset in <tt>b</tt> of the class data
 604      *
 605      * @param  len
 606      *         The length of the class data
 607      *
 608      * @return  The <tt>Class</tt> object that was created from the specified
 609      *          class data.
 610      *
 611      * @throws  ClassFormatError
 612      *          If the data did not contain a valid class
 613      *
 614      * @throws  IndexOutOfBoundsException
 615      *          If either <tt>off</tt> or <tt>len</tt> is negative, or if
 616      *          <tt>off+len</tt> is greater than <tt>b.length</tt>.
 617      *
 618      * @throws  SecurityException
 619      *          If an attempt is made to add this class to a package that
 620      *          contains classes that were signed by a different set of
 621      *          certificates than this class (which is unsigned), or if
 622      *          <tt>name</tt> begins with "<tt>java.</tt>".
 623      *
 624      * @see  #loadClass(String, boolean)
 625      * @see  #resolveClass(Class)
 626      * @see  java.security.CodeSource
 627      * @see  java.security.SecureClassLoader
 628      *
 629      * @since  1.1
 630      */
 631     protected final Class<?> defineClass(String name, byte[] b, int off, int len)
 632         throws ClassFormatError
 633     {
 634         return defineClass(name, b, off, len, null);
 635     }
 636 
 637     /* Determine protection domain, and check that:
 638         - not define java.* class,
 639         - signer of this class matches signers for the rest of the classes in
 640           package.
 641     */
 642     private ProtectionDomain preDefineClass(String name,
 643                                             ProtectionDomain pd)
 644     {
 645         if (!checkName(name))
 646             throw new NoClassDefFoundError("IllegalName: " + name);
 647 
 648         if ((name != null) && name.startsWith("java.")) {
 649             throw new SecurityException
 650                 ("Prohibited package name: " +
 651                  name.substring(0, name.lastIndexOf('.')));
 652         }
 653         if (pd == null) {
 654             pd = defaultDomain;
 655         }
 656 
 657         if (name != null) checkCerts(name, pd.getCodeSource());
 658 
 659         return pd;
 660     }
 661 
 662     private String defineClassSourceLocation(ProtectionDomain pd)
 663     {
 664         CodeSource cs = pd.getCodeSource();
 665         String source = null;
 666         if (cs != null && cs.getLocation() != null) {
 667             source = cs.getLocation().toString();
 668         }
 669         return source;
 670     }
 671 
 672     private Class<?> defineTransformedClass(String name, byte[] b, int off, int len,
 673                                             ProtectionDomain pd,
 674                                             ClassFormatError cfe, String source)
 675       throws ClassFormatError
 676     {
 677         // Class format error - try to transform the bytecode and
 678         // define the class again
 679         //
 680         ClassFileTransformer[] transformers =
 681             ClassFileTransformer.getTransformers();
 682         Class<?> c = null;
 683 
 684         if (transformers != null) {
 685             for (ClassFileTransformer transformer : transformers) {
 686                 try {
 687                     // Transform byte code using transformer
 688                     byte[] tb = transformer.transform(b, off, len);
 689                     c = defineClass1(name, tb, 0, tb.length,
 690                                      pd, source);
 691                     break;
 692                 } catch (ClassFormatError cfe2)     {
 693                     // If ClassFormatError occurs, try next transformer
 694                 }
 695             }
 696         }
 697 
 698         // Rethrow original ClassFormatError if unable to transform
 699         // bytecode to well-formed
 700         //
 701         if (c == null)
 702             throw cfe;
 703 
 704         return c;
 705     }
 706 
 707     private void postDefineClass(Class<?> c, ProtectionDomain pd)
 708     {
 709         if (pd.getCodeSource() != null) {
 710             Certificate certs[] = pd.getCodeSource().getCertificates();
 711             if (certs != null)
 712                 setSigners(c, certs);
 713         }
 714     }
 715 
 716     /**
 717      * Converts an array of bytes into an instance of class <tt>Class</tt>,
 718      * with an optional <tt>ProtectionDomain</tt>.  If the domain is
 719      * <tt>null</tt>, then a default domain will be assigned to the class as
 720      * specified in the documentation for {@link #defineClass(String, byte[],
 721      * int, int)}.  Before the class can be used it must be resolved.
 722      *
 723      * <p> The first class defined in a package determines the exact set of
 724      * certificates that all subsequent classes defined in that package must
 725      * contain.  The set of certificates for a class is obtained from the
 726      * {@link java.security.CodeSource <tt>CodeSource</tt>} within the
 727      * <tt>ProtectionDomain</tt> of the class.  Any classes added to that
 728      * package must contain the same set of certificates or a
 729      * <tt>SecurityException</tt> will be thrown.  Note that if
 730      * <tt>name</tt> is <tt>null</tt>, this check is not performed.
 731      * You should always pass in the <a href="#name">binary name</a> of the
 732      * class you are defining as well as the bytes.  This ensures that the
 733      * class you are defining is indeed the class you think it is.
 734      *
 735      * <p> The specified <tt>name</tt> cannot begin with "<tt>java.</tt>", since
 736      * all classes in the "<tt>java.*</tt> packages can only be defined by the
 737      * bootstrap class loader.  If <tt>name</tt> is not <tt>null</tt>, it
 738      * must be equal to the <a href="#name">binary name</a> of the class
 739      * specified by the byte array "<tt>b</tt>", otherwise a {@link
 740      * <tt>NoClassDefFoundError</tt>} will be thrown.  </p>
 741      *
 742      * @param  name
 743      *         The expected <a href="#name">binary name</a> of the class, or
 744      *         <tt>null</tt> if not known
 745      *
 746      * @param  b
 747      *         The bytes that make up the class data. The bytes in positions
 748      *         <tt>off</tt> through <tt>off+len-1</tt> should have the format
 749      *         of a valid class file as defined by
 750      *         <cite>The Java&trade; Virtual Machine Specification</cite>.
 751      *
 752      * @param  off
 753      *         The start offset in <tt>b</tt> of the class data
 754      *
 755      * @param  len
 756      *         The length of the class data
 757      *
 758      * @param  protectionDomain
 759      *         The ProtectionDomain of the class
 760      *
 761      * @return  The <tt>Class</tt> object created from the data,
 762      *          and optional <tt>ProtectionDomain</tt>.
 763      *
 764      * @throws  ClassFormatError
 765      *          If the data did not contain a valid class
 766      *
 767      * @throws  NoClassDefFoundError
 768      *          If <tt>name</tt> is not equal to the <a href="#name">binary
 769      *          name</a> of the class specified by <tt>b</tt>
 770      *
 771      * @throws  IndexOutOfBoundsException
 772      *          If either <tt>off</tt> or <tt>len</tt> is negative, or if
 773      *          <tt>off+len</tt> is greater than <tt>b.length</tt>.
 774      *
 775      * @throws  SecurityException
 776      *          If an attempt is made to add this class to a package that
 777      *          contains classes that were signed by a different set of
 778      *          certificates than this class, or if <tt>name</tt> begins with
 779      *          "<tt>java.</tt>".
 780      */
 781     protected final Class<?> defineClass(String name, byte[] b, int off, int len,
 782                                          ProtectionDomain protectionDomain)
 783         throws ClassFormatError
 784     {
 785         protectionDomain = preDefineClass(name, protectionDomain);
 786 
 787         Class<?> c = null;
 788         String source = defineClassSourceLocation(protectionDomain);
 789 
 790         try {
 791             c = defineClass1(name, b, off, len, protectionDomain, source);
 792         } catch (ClassFormatError cfe) {
 793             c = defineTransformedClass(name, b, off, len, protectionDomain, cfe,
 794                                        source);
 795         }
 796 
 797         postDefineClass(c, protectionDomain);
 798         return c;
 799     }
 800 
 801     /**
 802      * Converts a {@link java.nio.ByteBuffer <tt>ByteBuffer</tt>}
 803      * into an instance of class <tt>Class</tt>,
 804      * with an optional <tt>ProtectionDomain</tt>.  If the domain is
 805      * <tt>null</tt>, then a default domain will be assigned to the class as
 806      * specified in the documentation for {@link #defineClass(String, byte[],
 807      * int, int)}.  Before the class can be used it must be resolved.
 808      *
 809      * <p>The rules about the first class defined in a package determining the
 810      * set of certificates for the package, and the restrictions on class names
 811      * are identical to those specified in the documentation for {@link
 812      * #defineClass(String, byte[], int, int, ProtectionDomain)}.
 813      *
 814      * <p> An invocation of this method of the form
 815      * <i>cl</i><tt>.defineClass(</tt><i>name</i><tt>,</tt>
 816      * <i>bBuffer</i><tt>,</tt> <i>pd</i><tt>)</tt> yields exactly the same
 817      * result as the statements
 818      *
 819      * <blockquote><tt>
 820      * ...<br>
 821      * byte[] temp = new byte[</tt><i>bBuffer</i><tt>.{@link
 822      * java.nio.ByteBuffer#remaining remaining}()];<br>
 823      *     </tt><i>bBuffer</i><tt>.{@link java.nio.ByteBuffer#get(byte[])
 824      * get}(temp);<br>
 825      *     return {@link #defineClass(String, byte[], int, int, ProtectionDomain)
 826      * </tt><i>cl</i><tt>.defineClass}(</tt><i>name</i><tt>, temp, 0,
 827      * temp.length, </tt><i>pd</i><tt>);<br>
 828      * </tt></blockquote>
 829      *
 830      * @param  name
 831      *         The expected <a href="#name">binary name</a>. of the class, or
 832      *         <tt>null</tt> if not known
 833      *
 834      * @param  b
 835      *         The bytes that make up the class data. The bytes from positions
 836      *         <tt>b.position()</tt> through <tt>b.position() + b.limit() -1
 837      *         </tt> should have the format of a valid class file as defined by
 838      *         <cite>The Java&trade; Virtual Machine Specification</cite>.
 839      *
 840      * @param  protectionDomain
 841      *         The ProtectionDomain of the class, or <tt>null</tt>.
 842      *
 843      * @return  The <tt>Class</tt> object created from the data,
 844      *          and optional <tt>ProtectionDomain</tt>.
 845      *
 846      * @throws  ClassFormatError
 847      *          If the data did not contain a valid class.
 848      *
 849      * @throws  NoClassDefFoundError
 850      *          If <tt>name</tt> is not equal to the <a href="#name">binary
 851      *          name</a> of the class specified by <tt>b</tt>
 852      *
 853      * @throws  SecurityException
 854      *          If an attempt is made to add this class to a package that
 855      *          contains classes that were signed by a different set of
 856      *          certificates than this class, or if <tt>name</tt> begins with
 857      *          "<tt>java.</tt>".
 858      *
 859      * @see      #defineClass(String, byte[], int, int, ProtectionDomain)
 860      *
 861      * @since  1.5
 862      */
 863     protected final Class<?> defineClass(String name, java.nio.ByteBuffer b,
 864                                          ProtectionDomain protectionDomain)
 865         throws ClassFormatError
 866     {
 867         int len = b.remaining();
 868 
 869         // Use byte[] if not a direct ByteBufer:
 870         if (!b.isDirect()) {
 871             if (b.hasArray()) {
 872                 return defineClass(name, b.array(),
 873                                    b.position() + b.arrayOffset(), len,
 874                                    protectionDomain);
 875             } else {
 876                 // no array, or read-only array
 877                 byte[] tb = new byte[len];
 878                 b.get(tb);  // get bytes out of byte buffer.
 879                 return defineClass(name, tb, 0, len, protectionDomain);
 880             }
 881         }
 882 
 883         protectionDomain = preDefineClass(name, protectionDomain);
 884 
 885         Class<?> c = null;
 886         String source = defineClassSourceLocation(protectionDomain);
 887 
 888         try {
 889             c = defineClass2(name, b, b.position(), len, protectionDomain,
 890                              source);
 891         } catch (ClassFormatError cfe) {
 892             byte[] tb = new byte[len];
 893             b.get(tb);  // get bytes out of byte buffer.
 894             c = defineTransformedClass(name, tb, 0, len, protectionDomain, cfe,
 895                                        source);
 896         }
 897 
 898         postDefineClass(c, protectionDomain);
 899         return c;
 900     }
 901 
 902     private native Class<?> defineClass0(String name, byte[] b, int off, int len,
 903                                          ProtectionDomain pd);
 904 
 905     private native Class<?> defineClass1(String name, byte[] b, int off, int len,
 906                                          ProtectionDomain pd, String source);
 907 
 908     private native Class<?> defineClass2(String name, java.nio.ByteBuffer b,
 909                                          int off, int len, ProtectionDomain pd,
 910                                          String source);
 911 
 912     // true if the name is null or has the potential to be a valid binary name
 913     private boolean checkName(String name) {
 914         if ((name == null) || (name.length() == 0))
 915             return true;
 916         if ((name.indexOf('/') != -1)
 917             || (!VM.allowArraySyntax() && (name.charAt(0) == '[')))
 918             return false;
 919         return true;
 920     }
 921 
 922     private void checkCerts(String name, CodeSource cs) {
 923         int i = name.lastIndexOf('.');
 924         String pname = (i == -1) ? "" : name.substring(0, i);
 925 
 926         Certificate[] certs = null;
 927         if (cs != null) {
 928             certs = cs.getCertificates();
 929         }
 930         Certificate[] pcerts = null;
 931         if (parallelLockMap == null) {
 932             synchronized (this) {
 933                 pcerts = package2certs.get(pname);
 934                 if (pcerts == null) {
 935                     package2certs.put(pname, (certs == null? nocerts:certs));
 936                 }
 937             }
 938         } else {
 939             pcerts = ((ConcurrentHashMap<String, Certificate[]>)package2certs).
 940                 putIfAbsent(pname, (certs == null? nocerts:certs));
 941         }
 942         if (pcerts != null && !compareCerts(pcerts, certs)) {
 943             throw new SecurityException("class \""+ name +
 944                  "\"'s signer information does not match signer information of other classes in the same package");
 945         }
 946     }
 947 
 948     /**
 949      * check to make sure the certs for the new class (certs) are the same as
 950      * the certs for the first class inserted in the package (pcerts)
 951      */
 952     private boolean compareCerts(Certificate[] pcerts,
 953                                  Certificate[] certs)
 954     {
 955         // certs can be null, indicating no certs.
 956         if ((certs == null) || (certs.length == 0)) {
 957             return pcerts.length == 0;
 958         }
 959 
 960         // the length must be the same at this point
 961         if (certs.length != pcerts.length)
 962             return false;
 963 
 964         // go through and make sure all the certs in one array
 965         // are in the other and vice-versa.
 966         boolean match;
 967         for (int i = 0; i < certs.length; i++) {
 968             match = false;
 969             for (int j = 0; j < pcerts.length; j++) {
 970                 if (certs[i].equals(pcerts[j])) {
 971                     match = true;
 972                     break;
 973                 }
 974             }
 975             if (!match) return false;
 976         }
 977 
 978         // now do the same for pcerts
 979         for (int i = 0; i < pcerts.length; i++) {
 980             match = false;
 981             for (int j = 0; j < certs.length; j++) {
 982                 if (pcerts[i].equals(certs[j])) {
 983                     match = true;
 984                     break;
 985                 }
 986             }
 987             if (!match) return false;
 988         }
 989 
 990         return true;
 991     }
 992 
 993     /**
 994      * Links the specified class.  This (misleadingly named) method may be
 995      * used by a class loader to link a class.  If the class <tt>c</tt> has
 996      * already been linked, then this method simply returns. Otherwise, the
 997      * class is linked as described in the "Execution" chapter of
 998      * <cite>The Java&trade; Language Specification</cite>.
 999      * </p>
1000      *
1001      * @param  c
1002      *         The class to link
1003      *
1004      * @throws  NullPointerException
1005      *          If <tt>c</tt> is <tt>null</tt>.
1006      *
1007      * @see  #defineClass(String, byte[], int, int)
1008      */
1009     protected final void resolveClass(Class<?> c) {
1010         resolveClass0(c);
1011     }
1012 
1013     private native void resolveClass0(Class<?> c);
1014 
1015     /**
1016      * Finds a class with the specified <a href="#name">binary name</a>,
1017      * loading it if necessary.
1018      *
1019      * <p> This method loads the class through the system class loader (see
1020      * {@link #getSystemClassLoader()}).  The <tt>Class</tt> object returned
1021      * might have more than one <tt>ClassLoader</tt> associated with it.
1022      * Subclasses of <tt>ClassLoader</tt> need not usually invoke this method,
1023      * because most class loaders need to override just {@link
1024      * #findClass(String)}.  </p>
1025      *
1026      * @param  name
1027      *         The <a href="#name">binary name</a> of the class
1028      *
1029      * @return  The <tt>Class</tt> object for the specified <tt>name</tt>
1030      *
1031      * @throws  ClassNotFoundException
1032      *          If the class could not be found
1033      *
1034      * @see  #ClassLoader(ClassLoader)
1035      * @see  #getParent()
1036      */
1037     protected final Class<?> findSystemClass(String name)
1038         throws ClassNotFoundException
1039     {
1040         ClassLoader system = getSystemClassLoader();
1041         if (system == null) {
1042             if (!checkName(name))
1043                 throw new ClassNotFoundException(name);
1044             Class<?> cls = findBootstrapClass(name);
1045             if (cls == null) {
1046                 throw new ClassNotFoundException(name);
1047             }
1048             return cls;
1049         }
1050         return system.loadClass(name);
1051     }
1052 
1053     /**
1054      * Returns a class loaded by the bootstrap class loader;
1055      * or return null if not found.
1056      */
1057     private Class<?> findBootstrapClassOrNull(String name)
1058     {
1059         if (!checkName(name)) return null;
1060 
1061         return findBootstrapClass(name);
1062     }
1063 
1064     // return null if not found
1065     private native Class<?> findBootstrapClass(String name);
1066 
1067     /**
1068      * Returns the class with the given <a href="#name">binary name</a> if this
1069      * loader has been recorded by the Java virtual machine as an initiating
1070      * loader of a class with that <a href="#name">binary name</a>.  Otherwise
1071      * <tt>null</tt> is returned.  </p>
1072      *
1073      * @param  name
1074      *         The <a href="#name">binary name</a> of the class
1075      *
1076      * @return  The <tt>Class</tt> object, or <tt>null</tt> if the class has
1077      *          not been loaded
1078      *
1079      * @since  1.1
1080      */
1081     protected final Class<?> findLoadedClass(String name) {
1082         if (!checkName(name))
1083             return null;
1084         return findLoadedClass0(name);
1085     }
1086 
1087     private native final Class<?> findLoadedClass0(String name);
1088 
1089     /**
1090      * Sets the signers of a class.  This should be invoked after defining a
1091      * class.  </p>
1092      *
1093      * @param  c
1094      *         The <tt>Class</tt> object
1095      *
1096      * @param  signers
1097      *         The signers for the class
1098      *
1099      * @since  1.1
1100      */
1101     protected final void setSigners(Class<?> c, Object[] signers) {
1102         c.setSigners(signers);
1103     }
1104 
1105 
1106     // -- Resource --
1107 
1108     /**
1109      * Finds the resource with the given name.  A resource is some data
1110      * (images, audio, text, etc) that can be accessed by class code in a way
1111      * that is independent of the location of the code.
1112      *
1113      * <p> The name of a resource is a '<tt>/</tt>'-separated path name that
1114      * identifies the resource.
1115      *
1116      * <p> This method will first search the parent class loader for the
1117      * resource; if the parent is <tt>null</tt> the path of the class loader
1118      * built-in to the virtual machine is searched.  That failing, this method
1119      * will invoke {@link #findResource(String)} to find the resource.  </p>
1120      *
1121      * @param  name
1122      *         The resource name
1123      *
1124      * @return  A <tt>URL</tt> object for reading the resource, or
1125      *          <tt>null</tt> if the resource could not be found or the invoker
1126      *          doesn't have adequate  privileges to get the resource.
1127      *
1128      * @since  1.1
1129      */
1130     public URL getResource(String name) {
1131         URL url;
1132         if (parent != null) {
1133             url = parent.getResource(name);
1134         } else {
1135             url = getBootstrapResource(name);
1136         }
1137         if (url == null) {
1138             url = findResource(name);
1139         }
1140         return url;
1141     }
1142 
1143     /**
1144      * Finds all the resources with the given name. A resource is some data
1145      * (images, audio, text, etc) that can be accessed by class code in a way
1146      * that is independent of the location of the code.
1147      *
1148      * <p>The name of a resource is a <tt>/</tt>-separated path name that
1149      * identifies the resource.
1150      *
1151      * <p> The search order is described in the documentation for {@link
1152      * #getResource(String)}.  </p>
1153      *
1154      * @param  name
1155      *         The resource name
1156      *
1157      * @return  An enumeration of {@link java.net.URL <tt>URL</tt>} objects for
1158      *          the resource.  If no resources could  be found, the enumeration
1159      *          will be empty.  Resources that the class loader doesn't have
1160      *          access to will not be in the enumeration.
1161      *
1162      * @throws  IOException
1163      *          If I/O errors occur
1164      *
1165      * @see  #findResources(String)
1166      *
1167      * @since  1.2
1168      */
1169     public Enumeration<URL> getResources(String name) throws IOException {
1170         Enumeration[] tmp = new Enumeration[2];
1171         if (parent != null) {
1172             tmp[0] = parent.getResources(name);
1173         } else {
1174             tmp[0] = getBootstrapResources(name);
1175         }
1176         tmp[1] = findResources(name);
1177 
1178         return new CompoundEnumeration<>(tmp);
1179     }
1180 
1181     /**
1182      * Finds the resource with the given name. Class loader implementations
1183      * should override this method to specify where to find resources.  </p>
1184      *
1185      * @param  name
1186      *         The resource name
1187      *
1188      * @return  A <tt>URL</tt> object for reading the resource, or
1189      *          <tt>null</tt> if the resource could not be found
1190      *
1191      * @since  1.2
1192      */
1193     protected URL findResource(String name) {
1194         return null;
1195     }
1196 
1197     /**
1198      * Returns an enumeration of {@link java.net.URL <tt>URL</tt>} objects
1199      * representing all the resources with the given name. Class loader
1200      * implementations should override this method to specify where to load
1201      * resources from.  </p>
1202      *
1203      * @param  name
1204      *         The resource name
1205      *
1206      * @return  An enumeration of {@link java.net.URL <tt>URL</tt>} objects for
1207      *          the resources
1208      *
1209      * @throws  IOException
1210      *          If I/O errors occur
1211      *
1212      * @since  1.2
1213      */
1214     protected Enumeration<URL> findResources(String name) throws IOException {
1215         return java.util.Collections.emptyEnumeration();
1216     }
1217 
1218     // index 0: java.lang.ClassLoader.class
1219     // index 1: the immediate caller of index 0.
1220     // index 2: the immediate caller of index 1.
1221     private static native Class<? extends ClassLoader> getCaller(int index);
1222 
1223     /**
1224      * Registers the caller as parallel capable.</p>
1225      * The registration succeeds if and only if all of the following
1226      * conditions are met: <br>
1227      * 1. no instance of the caller has been created</p>
1228      * 2. all of the super classes (except class Object) of the caller are
1229      * registered as parallel capable</p>
1230      * Note that once a class loader is registered as parallel capable, there
1231      * is no way to change it back. </p>
1232      *
1233      * @return  true if the caller is successfully registered as
1234      *          parallel capable and false if otherwise.
1235      *
1236      * @since   1.7
1237      */
1238     protected static boolean registerAsParallelCapable() {
1239         return ParallelLoaders.register(getCaller(1));
1240     }
1241 
1242     /**
1243      * Find a resource of the specified name from the search path used to load
1244      * classes.  This method locates the resource through the system class
1245      * loader (see {@link #getSystemClassLoader()}).  </p>
1246      *
1247      * @param  name
1248      *         The resource name
1249      *
1250      * @return  A {@link java.net.URL <tt>URL</tt>} object for reading the
1251      *          resource, or <tt>null</tt> if the resource could not be found
1252      *
1253      * @since  1.1
1254      */
1255     public static URL getSystemResource(String name) {
1256         ClassLoader system = getSystemClassLoader();
1257         if (system == null) {
1258             return getBootstrapResource(name);
1259         }
1260         return system.getResource(name);
1261     }
1262 
1263     /**
1264      * Finds all resources of the specified name from the search path used to
1265      * load classes.  The resources thus found are returned as an
1266      * {@link java.util.Enumeration <tt>Enumeration</tt>} of {@link
1267      * java.net.URL <tt>URL</tt>} objects.
1268      *
1269      * <p> The search order is described in the documentation for {@link
1270      * #getSystemResource(String)}.  </p>
1271      *
1272      * @param  name
1273      *         The resource name
1274      *
1275      * @return  An enumeration of resource {@link java.net.URL <tt>URL</tt>}
1276      *          objects
1277      *
1278      * @throws  IOException
1279      *          If I/O errors occur
1280 
1281      * @since  1.2
1282      */
1283     public static Enumeration<URL> getSystemResources(String name)
1284         throws IOException
1285     {
1286         ClassLoader system = getSystemClassLoader();
1287         if (system == null) {
1288             return getBootstrapResources(name);
1289         }
1290         return system.getResources(name);
1291     }
1292 
1293     /**
1294      * Find resources from the VM's built-in classloader.
1295      */
1296     private static URL getBootstrapResource(String name) {
1297         URLClassPath ucp = getBootstrapClassPath();
1298         Resource res = ucp.getResource(name);
1299         return res != null ? res.getURL() : null;
1300     }
1301 
1302     /**
1303      * Find resources from the VM's built-in classloader.
1304      */
1305     private static Enumeration<URL> getBootstrapResources(String name)
1306         throws IOException
1307     {
1308         final Enumeration<Resource> e =
1309             getBootstrapClassPath().getResources(name);
1310         return new Enumeration<URL> () {
1311             public URL nextElement() {
1312                 return e.nextElement().getURL();
1313             }
1314             public boolean hasMoreElements() {
1315                 return e.hasMoreElements();
1316             }
1317         };
1318     }
1319 
1320     // Returns the URLClassPath that is used for finding system resources.
1321     static URLClassPath getBootstrapClassPath() {
1322         return sun.misc.Launcher.getBootstrapClassPath();
1323     }
1324 
1325 
1326     /**
1327      * Returns an input stream for reading the specified resource.
1328      *
1329      * <p> The search order is described in the documentation for {@link
1330      * #getResource(String)}.  </p>
1331      *
1332      * @param  name
1333      *         The resource name
1334      *
1335      * @return  An input stream for reading the resource, or <tt>null</tt>
1336      *          if the resource could not be found
1337      *
1338      * @since  1.1
1339      */
1340     public InputStream getResourceAsStream(String name) {
1341         URL url = getResource(name);
1342         try {
1343             return url != null ? url.openStream() : null;
1344         } catch (IOException e) {
1345             return null;
1346         }
1347     }
1348 
1349     /**
1350      * Open for reading, a resource of the specified name from the search path
1351      * used to load classes.  This method locates the resource through the
1352      * system class loader (see {@link #getSystemClassLoader()}).  </p>
1353      *
1354      * @param  name
1355      *         The resource name
1356      *
1357      * @return  An input stream for reading the resource, or <tt>null</tt>
1358      *          if the resource could not be found
1359      *
1360      * @since  1.1
1361      */
1362     public static InputStream getSystemResourceAsStream(String name) {
1363         URL url = getSystemResource(name);
1364         try {
1365             return url != null ? url.openStream() : null;
1366         } catch (IOException e) {
1367             return null;
1368         }
1369     }
1370 
1371 
1372     // -- Hierarchy --
1373 
1374     /**
1375      * Returns the parent class loader for delegation. Some implementations may
1376      * use <tt>null</tt> to represent the bootstrap class loader. This method
1377      * will return <tt>null</tt> in such implementations if this class loader's
1378      * parent is the bootstrap class loader.
1379      *
1380      * <p> If a security manager is present, and the invoker's class loader is
1381      * not <tt>null</tt> and is not an ancestor of this class loader, then this
1382      * method invokes the security manager's {@link
1383      * SecurityManager#checkPermission(java.security.Permission)
1384      * <tt>checkPermission</tt>} method with a {@link
1385      * RuntimePermission#RuntimePermission(String)
1386      * <tt>RuntimePermission("getClassLoader")</tt>} permission to verify
1387      * access to the parent class loader is permitted.  If not, a
1388      * <tt>SecurityException</tt> will be thrown.  </p>
1389      *
1390      * @return  The parent <tt>ClassLoader</tt>
1391      *
1392      * @throws  SecurityException
1393      *          If a security manager exists and its <tt>checkPermission</tt>
1394      *          method doesn't allow access to this class loader's parent class
1395      *          loader.
1396      *
1397      * @since  1.2
1398      */
1399     public final ClassLoader getParent() {
1400         if (parent == null)
1401             return null;
1402         SecurityManager sm = System.getSecurityManager();
1403         if (sm != null) {
1404             ClassLoader ccl = getCallerClassLoader();
1405             if (ccl != null && !isAncestor(ccl)) {
1406                 sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
1407             }
1408         }
1409         return parent;
1410     }
1411 
1412     /**
1413      * Returns the system class loader for delegation.  This is the default
1414      * delegation parent for new <tt>ClassLoader</tt> instances, and is
1415      * typically the class loader used to start the application.
1416      *
1417      * <p> This method is first invoked early in the runtime's startup
1418      * sequence, at which point it creates the system class loader and sets it
1419      * as the context class loader of the invoking <tt>Thread</tt>.
1420      *
1421      * <p> The default system class loader is an implementation-dependent
1422      * instance of this class.
1423      *
1424      * <p> If the system property "<tt>java.system.class.loader</tt>" is defined
1425      * when this method is first invoked then the value of that property is
1426      * taken to be the name of a class that will be returned as the system
1427      * class loader.  The class is loaded using the default system class loader
1428      * and must define a public constructor that takes a single parameter of
1429      * type <tt>ClassLoader</tt> which is used as the delegation parent.  An
1430      * instance is then created using this constructor with the default system
1431      * class loader as the parameter.  The resulting class loader is defined
1432      * to be the system class loader.
1433      *
1434      * <p> If a security manager is present, and the invoker's class loader is
1435      * not <tt>null</tt> and the invoker's class loader is not the same as or
1436      * an ancestor of the system class loader, then this method invokes the
1437      * security manager's {@link
1438      * SecurityManager#checkPermission(java.security.Permission)
1439      * <tt>checkPermission</tt>} method with a {@link
1440      * RuntimePermission#RuntimePermission(String)
1441      * <tt>RuntimePermission("getClassLoader")</tt>} permission to verify
1442      * access to the system class loader.  If not, a
1443      * <tt>SecurityException</tt> will be thrown.  </p>
1444      *
1445      * @return  The system <tt>ClassLoader</tt> for delegation, or
1446      *          <tt>null</tt> if none
1447      *
1448      * @throws  SecurityException
1449      *          If a security manager exists and its <tt>checkPermission</tt>
1450      *          method doesn't allow access to the system class loader.
1451      *
1452      * @throws  IllegalStateException
1453      *          If invoked recursively during the construction of the class
1454      *          loader specified by the "<tt>java.system.class.loader</tt>"
1455      *          property.
1456      *
1457      * @throws  Error
1458      *          If the system property "<tt>java.system.class.loader</tt>"
1459      *          is defined but the named class could not be loaded, the
1460      *          provider class does not define the required constructor, or an
1461      *          exception is thrown by that constructor when it is invoked. The
1462      *          underlying cause of the error can be retrieved via the
1463      *          {@link Throwable#getCause()} method.
1464      *
1465      * @revised  1.4
1466      */
1467     public static ClassLoader getSystemClassLoader() {
1468         initSystemClassLoader();
1469         if (scl == null) {
1470             return null;
1471         }
1472         SecurityManager sm = System.getSecurityManager();
1473         if (sm != null) {
1474             ClassLoader ccl = getCallerClassLoader();
1475             if (ccl != null && ccl != scl && !scl.isAncestor(ccl)) {
1476                 sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
1477             }
1478         }
1479         return scl;
1480     }
1481 
1482     private static synchronized void initSystemClassLoader() {
1483         if (!sclSet) {
1484             if (scl != null)
1485                 throw new IllegalStateException("recursive invocation");
1486             sun.misc.Launcher l = sun.misc.Launcher.getLauncher();
1487             if (l != null) {
1488                 Throwable oops = null;
1489                 scl = l.getClassLoader();
1490                 try {
1491                     scl = AccessController.doPrivileged(
1492                         new SystemClassLoaderAction(scl));
1493                 } catch (PrivilegedActionException pae) {
1494                     oops = pae.getCause();
1495                     if (oops instanceof InvocationTargetException) {
1496                         oops = oops.getCause();
1497                     }
1498                 }
1499                 if (oops != null) {
1500                     if (oops instanceof Error) {
1501                         throw (Error) oops;
1502                     } else {
1503                         // wrap the exception
1504                         throw new Error(oops);
1505                     }
1506                 }
1507             }
1508             sclSet = true;
1509         }
1510     }
1511 
1512     // Returns true if the specified class loader can be found in this class
1513     // loader's delegation chain.
1514     boolean isAncestor(ClassLoader cl) {
1515         ClassLoader acl = this;
1516         do {
1517             acl = acl.parent;
1518             if (cl == acl) {
1519                 return true;
1520             }
1521         } while (acl != null);
1522         return false;
1523     }
1524 
1525     // Returns the invoker's class loader, or null if none.
1526     // NOTE: This must always be invoked when there is exactly one intervening
1527     // frame from the core libraries on the stack between this method's
1528     // invocation and the desired invoker.
1529     static ClassLoader getCallerClassLoader() {
1530         // NOTE use of more generic Reflection.getCallerClass()
1531         Class<?> caller = Reflection.getCallerClass(3);
1532         // This can be null if the VM is requesting it
1533         if (caller == null) {
1534             return null;
1535         }
1536         // Circumvent security check since this is package-private
1537         return caller.getClassLoader0();
1538     }
1539 
1540     // The class loader for the system
1541     // @GuardedBy("ClassLoader.class")
1542     private static ClassLoader scl;
1543 
1544     // Set to true once the system class loader has been set
1545     // @GuardedBy("ClassLoader.class")
1546     private static boolean sclSet;
1547 
1548 
1549     // -- Package --
1550 
1551     /**
1552      * Defines a package by name in this <tt>ClassLoader</tt>.  This allows
1553      * class loaders to define the packages for their classes. Packages must
1554      * be created before the class is defined, and package names must be
1555      * unique within a class loader and cannot be redefined or changed once
1556      * created.  </p>
1557      *
1558      * @param  name
1559      *         The package name
1560      *
1561      * @param  specTitle
1562      *         The specification title
1563      *
1564      * @param  specVersion
1565      *         The specification version
1566      *
1567      * @param  specVendor
1568      *         The specification vendor
1569      *
1570      * @param  implTitle
1571      *         The implementation title
1572      *
1573      * @param  implVersion
1574      *         The implementation version
1575      *
1576      * @param  implVendor
1577      *         The implementation vendor
1578      *
1579      * @param  sealBase
1580      *         If not <tt>null</tt>, then this package is sealed with
1581      *         respect to the given code source {@link java.net.URL
1582      *         <tt>URL</tt>}  object.  Otherwise, the package is not sealed.
1583      *
1584      * @return  The newly defined <tt>Package</tt> object
1585      *
1586      * @throws  IllegalArgumentException
1587      *          If package name duplicates an existing package either in this
1588      *          class loader or one of its ancestors
1589      *
1590      * @since  1.2
1591      */
1592     protected Package definePackage(String name, String specTitle,
1593                                     String specVersion, String specVendor,
1594                                     String implTitle, String implVersion,
1595                                     String implVendor, URL sealBase)
1596         throws IllegalArgumentException
1597     {
1598         synchronized (packages) {
1599             Package pkg = getPackage(name);
1600             if (pkg != null) {
1601                 throw new IllegalArgumentException(name);
1602             }
1603             pkg = new Package(name, specTitle, specVersion, specVendor,
1604                               implTitle, implVersion, implVendor,
1605                               sealBase, this);
1606             packages.put(name, pkg);
1607             return pkg;
1608         }
1609     }
1610 
1611     /**
1612      * Returns a <tt>Package</tt> that has been defined by this class loader
1613      * or any of its ancestors.  </p>
1614      *
1615      * @param  name
1616      *         The package name
1617      *
1618      * @return  The <tt>Package</tt> corresponding to the given name, or
1619      *          <tt>null</tt> if not found
1620      *
1621      * @since  1.2
1622      */
1623     protected Package getPackage(String name) {
1624         Package pkg;
1625         synchronized (packages) {
1626             pkg = packages.get(name);
1627         }
1628         if (pkg == null) {
1629             if (parent != null) {
1630                 pkg = parent.getPackage(name);
1631             } else {
1632                 pkg = Package.getSystemPackage(name);
1633             }
1634             if (pkg != null) {
1635                 synchronized (packages) {
1636                     Package pkg2 = packages.get(name);
1637                     if (pkg2 == null) {
1638                         packages.put(name, pkg);
1639                     } else {
1640                         pkg = pkg2;
1641                     }
1642                 }
1643             }
1644         }
1645         return pkg;
1646     }
1647 
1648     /**
1649      * Returns all of the <tt>Packages</tt> defined by this class loader and
1650      * its ancestors.  </p>
1651      *
1652      * @return  The array of <tt>Package</tt> objects defined by this
1653      *          <tt>ClassLoader</tt>
1654      *
1655      * @since  1.2
1656      */
1657     protected Package[] getPackages() {
1658         Map<String, Package> map;
1659         synchronized (packages) {
1660             map = new HashMap<>(packages);
1661         }
1662         Package[] pkgs;
1663         if (parent != null) {
1664             pkgs = parent.getPackages();
1665         } else {
1666             pkgs = Package.getSystemPackages();
1667         }
1668         if (pkgs != null) {
1669             for (int i = 0; i < pkgs.length; i++) {
1670                 String pkgName = pkgs[i].getName();
1671                 if (map.get(pkgName) == null) {
1672                     map.put(pkgName, pkgs[i]);
1673                 }
1674             }
1675         }
1676         return map.values().toArray(new Package[map.size()]);
1677     }
1678 
1679 
1680     // -- Native library access --
1681 
1682     /**
1683      * Returns the absolute path name of a native library.  The VM invokes this
1684      * method to locate the native libraries that belong to classes loaded with
1685      * this class loader. If this method returns <tt>null</tt>, the VM
1686      * searches the library along the path specified as the
1687      * "<tt>java.library.path</tt>" property.  </p>
1688      *
1689      * @param  libname
1690      *         The library name
1691      *
1692      * @return  The absolute path of the native library
1693      *
1694      * @see  System#loadLibrary(String)
1695      * @see  System#mapLibraryName(String)
1696      *
1697      * @since  1.2
1698      */
1699     protected String findLibrary(String libname) {
1700         return null;
1701     }
1702 
1703     /**
1704      * The inner class NativeLibrary denotes a loaded native library instance.
1705      * Every classloader contains a vector of loaded native libraries in the
1706      * private field <tt>nativeLibraries</tt>.  The native libraries loaded
1707      * into the system are entered into the <tt>systemNativeLibraries</tt>
1708      * vector.
1709      *
1710      * <p> Every native library requires a particular version of JNI. This is
1711      * denoted by the private <tt>jniVersion</tt> field.  This field is set by
1712      * the VM when it loads the library, and used by the VM to pass the correct
1713      * version of JNI to the native methods.  </p>
1714      *
1715      * @see      ClassLoader
1716      * @since    1.2
1717      */
1718     static class NativeLibrary {
1719         // opaque handle to native library, used in native code.
1720         long handle;
1721         // the version of JNI environment the native library requires.
1722         private int jniVersion;
1723         // the class from which the library is loaded, also indicates
1724         // the loader this native library belongs.
1725         private Class<?> fromClass;
1726         // the canonicalized name of the native library.
1727         String name;
1728 
1729         native void load(String name);
1730         native long find(String name);
1731         native void unload();
1732 
1733         public NativeLibrary(Class<?> fromClass, String name) {
1734             this.name = name;
1735             this.fromClass = fromClass;
1736         }
1737 
1738         protected void finalize() {
1739             synchronized (loadedLibraryNames) {
1740                 if (fromClass.getClassLoader() != null && handle != 0) {
1741                     /* remove the native library name */
1742                     int size = loadedLibraryNames.size();
1743                     for (int i = 0; i < size; i++) {
1744                         if (name.equals(loadedLibraryNames.elementAt(i))) {
1745                             loadedLibraryNames.removeElementAt(i);
1746                             break;
1747                         }
1748                     }
1749                     /* unload the library. */
1750                     ClassLoader.nativeLibraryContext.push(this);
1751                     try {
1752                         unload();
1753                     } finally {
1754                         ClassLoader.nativeLibraryContext.pop();
1755                     }
1756                 }
1757             }
1758         }
1759         // Invoked in the VM to determine the context class in
1760         // JNI_Load/JNI_Unload
1761         static Class<?> getFromClass() {
1762             return ClassLoader.nativeLibraryContext.peek().fromClass;
1763         }
1764     }
1765 
1766     // All native library names we've loaded.
1767     private static Vector<String> loadedLibraryNames = new Vector<>();
1768 
1769     // Native libraries belonging to system classes.
1770     private static Vector<NativeLibrary> systemNativeLibraries
1771         = new Vector<>();
1772 
1773     // Native libraries associated with the class loader.
1774     private Vector<NativeLibrary> nativeLibraries = new Vector<>();
1775 
1776     // native libraries being loaded/unloaded.
1777     private static Stack<NativeLibrary> nativeLibraryContext = new Stack<>();
1778 
1779     // The paths searched for libraries
1780     private static String usr_paths[];
1781     private static String sys_paths[];
1782 
1783     private static String[] initializePath(String propname) {
1784         String ldpath = System.getProperty(propname, "");
1785         String ps = File.pathSeparator;
1786         int ldlen = ldpath.length();
1787         int i, j, n;
1788         // Count the separators in the path
1789         i = ldpath.indexOf(ps);
1790         n = 0;
1791         while (i >= 0) {
1792             n++;
1793             i = ldpath.indexOf(ps, i + 1);
1794         }
1795 
1796         // allocate the array of paths - n :'s = n + 1 path elements
1797         String[] paths = new String[n + 1];
1798 
1799         // Fill the array with paths from the ldpath
1800         n = i = 0;
1801         j = ldpath.indexOf(ps);
1802         while (j >= 0) {
1803             if (j - i > 0) {
1804                 paths[n++] = ldpath.substring(i, j);
1805             } else if (j - i == 0) {
1806                 paths[n++] = ".";
1807             }
1808             i = j + 1;
1809             j = ldpath.indexOf(ps, i);
1810         }
1811         paths[n] = ldpath.substring(i, ldlen);
1812         return paths;
1813     }
1814 
1815     // Invoked in the java.lang.Runtime class to implement load and loadLibrary.
1816     static void loadLibrary(Class<?> fromClass, String name,
1817                             boolean isAbsolute) {
1818         ClassLoader loader =
1819             (fromClass == null) ? null : fromClass.getClassLoader();
1820         if (sys_paths == null) {
1821             usr_paths = initializePath("java.library.path");
1822             sys_paths = initializePath("sun.boot.library.path");
1823         }
1824         if (isAbsolute) {
1825             if (loadLibrary0(fromClass, new File(name))) {
1826                 return;
1827             }
1828             throw new UnsatisfiedLinkError("Can't load library: " + name);
1829         }
1830         if (loader != null) {
1831             String libfilename = loader.findLibrary(name);
1832             if (libfilename != null) {
1833                 File libfile = new File(libfilename);
1834                 if (!libfile.isAbsolute()) {
1835                     throw new UnsatisfiedLinkError(
1836     "ClassLoader.findLibrary failed to return an absolute path: " + libfilename);
1837                 }
1838                 if (loadLibrary0(fromClass, libfile)) {
1839                     return;
1840                 }
1841                 throw new UnsatisfiedLinkError("Can't load " + libfilename);
1842             }
1843         }
1844         for (int i = 0 ; i < sys_paths.length ; i++) {
1845             File libfile = new File(sys_paths[i], System.mapLibraryName(name));
1846             if (loadLibrary0(fromClass, libfile)) {
1847                 return;
1848             }
1849         }
1850         if (loader != null) {
1851             for (int i = 0 ; i < usr_paths.length ; i++) {
1852                 File libfile = new File(usr_paths[i],
1853                                         System.mapLibraryName(name));
1854                 if (loadLibrary0(fromClass, libfile)) {
1855                     return;
1856                 }
1857             }
1858         }
1859         // Oops, it failed
1860         throw new UnsatisfiedLinkError("no " + name + " in java.library.path");
1861     }
1862 
1863     private static boolean loadLibrary0(Class<?> fromClass, final File file) {
1864         boolean exists = AccessController.doPrivileged(
1865             new PrivilegedAction<Object>() {
1866                 public Object run() {
1867                     return file.exists() ? Boolean.TRUE : null;
1868                 }})
1869             != null;
1870         if (!exists) {
1871             return false;
1872         }
1873         String name;
1874         try {
1875             name = file.getCanonicalPath();
1876         } catch (IOException e) {
1877             return false;
1878         }
1879         ClassLoader loader =
1880             (fromClass == null) ? null : fromClass.getClassLoader();
1881         Vector<NativeLibrary> libs =
1882             loader != null ? loader.nativeLibraries : systemNativeLibraries;
1883         synchronized (libs) {
1884             int size = libs.size();
1885             for (int i = 0; i < size; i++) {
1886                 NativeLibrary lib = libs.elementAt(i);
1887                 if (name.equals(lib.name)) {
1888                     return true;
1889                 }
1890             }
1891 
1892             synchronized (loadedLibraryNames) {
1893                 if (loadedLibraryNames.contains(name)) {
1894                     throw new UnsatisfiedLinkError
1895                         ("Native Library " +
1896                          name +
1897                          " already loaded in another classloader");
1898                 }
1899                 /* If the library is being loaded (must be by the same thread,
1900                  * because Runtime.load and Runtime.loadLibrary are
1901                  * synchronous). The reason is can occur is that the JNI_OnLoad
1902                  * function can cause another loadLibrary invocation.
1903                  *
1904                  * Thus we can use a static stack to hold the list of libraries
1905                  * we are loading.
1906                  *
1907                  * If there is a pending load operation for the library, we
1908                  * immediately return success; otherwise, we raise
1909                  * UnsatisfiedLinkError.
1910                  */
1911                 int n = nativeLibraryContext.size();
1912                 for (int i = 0; i < n; i++) {
1913                     NativeLibrary lib = nativeLibraryContext.elementAt(i);
1914                     if (name.equals(lib.name)) {
1915                         if (loader == lib.fromClass.getClassLoader()) {
1916                             return true;
1917                         } else {
1918                             throw new UnsatisfiedLinkError
1919                                 ("Native Library " +
1920                                  name +
1921                                  " is being loaded in another classloader");
1922                         }
1923                     }
1924                 }
1925                 NativeLibrary lib = new NativeLibrary(fromClass, name);
1926                 nativeLibraryContext.push(lib);
1927                 try {
1928                     lib.load(name);
1929                 } finally {
1930                     nativeLibraryContext.pop();
1931                 }
1932                 if (lib.handle != 0) {
1933                     loadedLibraryNames.addElement(name);
1934                     libs.addElement(lib);
1935                     return true;
1936                 }
1937                 return false;
1938             }
1939         }
1940     }
1941 
1942     // Invoked in the VM class linking code.
1943     static long findNative(ClassLoader loader, String name) {
1944         Vector<NativeLibrary> libs =
1945             loader != null ? loader.nativeLibraries : systemNativeLibraries;
1946         synchronized (libs) {
1947             int size = libs.size();
1948             for (int i = 0; i < size; i++) {
1949                 NativeLibrary lib = libs.elementAt(i);
1950                 long entry = lib.find(name);
1951                 if (entry != 0)
1952                     return entry;
1953             }
1954         }
1955         return 0;
1956     }
1957 
1958 
1959     // -- Assertion management --
1960 
1961     final Object assertionLock;
1962 
1963     // The default toggle for assertion checking.
1964     // @GuardedBy("assertionLock")
1965     private boolean defaultAssertionStatus = false;
1966 
1967     // Maps String packageName to Boolean package default assertion status Note
1968     // that the default package is placed under a null map key.  If this field
1969     // is null then we are delegating assertion status queries to the VM, i.e.,
1970     // none of this ClassLoader's assertion status modification methods have
1971     // been invoked.
1972     // @GuardedBy("assertionLock")
1973     private Map<String, Boolean> packageAssertionStatus = null;
1974 
1975     // Maps String fullyQualifiedClassName to Boolean assertionStatus If this
1976     // field is null then we are delegating assertion status queries to the VM,
1977     // i.e., none of this ClassLoader's assertion status modification methods
1978     // have been invoked.
1979     // @GuardedBy("assertionLock")
1980     Map<String, Boolean> classAssertionStatus = null;
1981 
1982     /**
1983      * Sets the default assertion status for this class loader.  This setting
1984      * determines whether classes loaded by this class loader and initialized
1985      * in the future will have assertions enabled or disabled by default.
1986      * This setting may be overridden on a per-package or per-class basis by
1987      * invoking {@link #setPackageAssertionStatus(String, boolean)} or {@link
1988      * #setClassAssertionStatus(String, boolean)}.  </p>
1989      *
1990      * @param  enabled
1991      *         <tt>true</tt> if classes loaded by this class loader will
1992      *         henceforth have assertions enabled by default, <tt>false</tt>
1993      *         if they will have assertions disabled by default.
1994      *
1995      * @since  1.4
1996      */
1997     public void setDefaultAssertionStatus(boolean enabled) {
1998         synchronized (assertionLock) {
1999             if (classAssertionStatus == null)
2000                 initializeJavaAssertionMaps();
2001 
2002             defaultAssertionStatus = enabled;
2003         }
2004     }
2005 
2006     /**
2007      * Sets the package default assertion status for the named package.  The
2008      * package default assertion status determines the assertion status for
2009      * classes initialized in the future that belong to the named package or
2010      * any of its "subpackages".
2011      *
2012      * <p> A subpackage of a package named p is any package whose name begins
2013      * with "<tt>p.</tt>".  For example, <tt>javax.swing.text</tt> is a
2014      * subpackage of <tt>javax.swing</tt>, and both <tt>java.util</tt> and
2015      * <tt>java.lang.reflect</tt> are subpackages of <tt>java</tt>.
2016      *
2017      * <p> In the event that multiple package defaults apply to a given class,
2018      * the package default pertaining to the most specific package takes
2019      * precedence over the others.  For example, if <tt>javax.lang</tt> and
2020      * <tt>javax.lang.reflect</tt> both have package defaults associated with
2021      * them, the latter package default applies to classes in
2022      * <tt>javax.lang.reflect</tt>.
2023      *
2024      * <p> Package defaults take precedence over the class loader's default
2025      * assertion status, and may be overridden on a per-class basis by invoking
2026      * {@link #setClassAssertionStatus(String, boolean)}.  </p>
2027      *
2028      * @param  packageName
2029      *         The name of the package whose package default assertion status
2030      *         is to be set. A <tt>null</tt> value indicates the unnamed
2031      *         package that is "current"
2032      *         (see section 7.4.2 of
2033      *         <cite>The Java&trade; Language Specification</cite>.)
2034      *
2035      * @param  enabled
2036      *         <tt>true</tt> if classes loaded by this classloader and
2037      *         belonging to the named package or any of its subpackages will
2038      *         have assertions enabled by default, <tt>false</tt> if they will
2039      *         have assertions disabled by default.
2040      *
2041      * @since  1.4
2042      */
2043     public void setPackageAssertionStatus(String packageName,
2044                                           boolean enabled) {
2045         synchronized (assertionLock) {
2046             if (packageAssertionStatus == null)
2047                 initializeJavaAssertionMaps();
2048 
2049             packageAssertionStatus.put(packageName, enabled);
2050         }
2051     }
2052 
2053     /**
2054      * Sets the desired assertion status for the named top-level class in this
2055      * class loader and any nested classes contained therein.  This setting
2056      * takes precedence over the class loader's default assertion status, and
2057      * over any applicable per-package default.  This method has no effect if
2058      * the named class has already been initialized.  (Once a class is
2059      * initialized, its assertion status cannot change.)
2060      *
2061      * <p> If the named class is not a top-level class, this invocation will
2062      * have no effect on the actual assertion status of any class. </p>
2063      *
2064      * @param  className
2065      *         The fully qualified class name of the top-level class whose
2066      *         assertion status is to be set.
2067      *
2068      * @param  enabled
2069      *         <tt>true</tt> if the named class is to have assertions
2070      *         enabled when (and if) it is initialized, <tt>false</tt> if the
2071      *         class is to have assertions disabled.
2072      *
2073      * @since  1.4
2074      */
2075     public void setClassAssertionStatus(String className, boolean enabled) {
2076         synchronized (assertionLock) {
2077             if (classAssertionStatus == null)
2078                 initializeJavaAssertionMaps();
2079 
2080             classAssertionStatus.put(className, enabled);
2081         }
2082     }
2083 
2084     /**
2085      * Sets the default assertion status for this class loader to
2086      * <tt>false</tt> and discards any package defaults or class assertion
2087      * status settings associated with the class loader.  This method is
2088      * provided so that class loaders can be made to ignore any command line or
2089      * persistent assertion status settings and "start with a clean slate."
2090      * </p>
2091      *
2092      * @since  1.4
2093      */
2094     public void clearAssertionStatus() {
2095         /*
2096          * Whether or not "Java assertion maps" are initialized, set
2097          * them to empty maps, effectively ignoring any present settings.
2098          */
2099         synchronized (assertionLock) {
2100             classAssertionStatus = new HashMap<>();
2101             packageAssertionStatus = new HashMap<>();
2102             defaultAssertionStatus = false;
2103         }
2104     }
2105 
2106     /**
2107      * Returns the assertion status that would be assigned to the specified
2108      * class if it were to be initialized at the time this method is invoked.
2109      * If the named class has had its assertion status set, the most recent
2110      * setting will be returned; otherwise, if any package default assertion
2111      * status pertains to this class, the most recent setting for the most
2112      * specific pertinent package default assertion status is returned;
2113      * otherwise, this class loader's default assertion status is returned.
2114      * </p>
2115      *
2116      * @param  className
2117      *         The fully qualified class name of the class whose desired
2118      *         assertion status is being queried.
2119      *
2120      * @return  The desired assertion status of the specified class.
2121      *
2122      * @see  #setClassAssertionStatus(String, boolean)
2123      * @see  #setPackageAssertionStatus(String, boolean)
2124      * @see  #setDefaultAssertionStatus(boolean)
2125      *
2126      * @since  1.4
2127      */
2128     boolean desiredAssertionStatus(String className) {
2129         synchronized (assertionLock) {
2130             // assert classAssertionStatus   != null;
2131             // assert packageAssertionStatus != null;
2132 
2133             // Check for a class entry
2134             Boolean result = classAssertionStatus.get(className);
2135             if (result != null)
2136                 return result.booleanValue();
2137 
2138             // Check for most specific package entry
2139             int dotIndex = className.lastIndexOf(".");
2140             if (dotIndex < 0) { // default package
2141                 result = packageAssertionStatus.get(null);
2142                 if (result != null)
2143                     return result.booleanValue();
2144             }
2145             while(dotIndex > 0) {
2146                 className = className.substring(0, dotIndex);
2147                 result = packageAssertionStatus.get(className);
2148                 if (result != null)
2149                     return result.booleanValue();
2150                 dotIndex = className.lastIndexOf(".", dotIndex-1);
2151             }
2152 
2153             // Return the classloader default
2154             return defaultAssertionStatus;
2155         }
2156     }
2157 
2158     // Set up the assertions with information provided by the VM.
2159     // Note: Should only be called inside a synchronized block
2160     private void initializeJavaAssertionMaps() {
2161         // assert Thread.holdsLock(assertionLock);
2162 
2163         classAssertionStatus = new HashMap<>();
2164         packageAssertionStatus = new HashMap<>();
2165         AssertionStatusDirectives directives = retrieveDirectives();
2166 
2167         for(int i = 0; i < directives.classes.length; i++)
2168             classAssertionStatus.put(directives.classes[i],
2169                                      directives.classEnabled[i]);
2170 
2171         for(int i = 0; i < directives.packages.length; i++)
2172             packageAssertionStatus.put(directives.packages[i],
2173                                        directives.packageEnabled[i]);
2174 
2175         defaultAssertionStatus = directives.deflt;
2176     }
2177 
2178     // Retrieves the assertion directives from the VM.
2179     private static native AssertionStatusDirectives retrieveDirectives();
2180 }
2181 
2182 
2183 class SystemClassLoaderAction
2184     implements PrivilegedExceptionAction<ClassLoader> {
2185     private ClassLoader parent;
2186 
2187     SystemClassLoaderAction(ClassLoader parent) {
2188         this.parent = parent;
2189     }
2190 
2191     public ClassLoader run() throws Exception {
2192         String cls = System.getProperty("java.system.class.loader");
2193         if (cls == null) {
2194             return parent;
2195         }
2196 
2197         Constructor<?> ctor = Class.forName(cls, true, parent)
2198             .getDeclaredConstructor(new Class<?>[] { ClassLoader.class });
2199         ClassLoader sys = (ClassLoader) ctor.newInstance(
2200             new Object[] { parent });
2201         Thread.currentThread().setContextClassLoader(sys);
2202         return sys;
2203     }
2204 }