1 /*
   2  * Copyright (c) 2013, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 package java.lang;
  26 
  27 import java.io.InputStream;
  28 import java.io.IOException;
  29 import java.io.File;
  30 import java.lang.reflect.Constructor;
  31 import java.lang.reflect.InvocationTargetException;
  32 import java.net.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.CompoundEnumeration;
  55 import sun.misc.Resource;
  56 import sun.misc.URLClassPath;
  57 import sun.misc.VM;
  58 import sun.reflect.CallerSensitive;
  59 import sun.reflect.Reflection;
  60 import sun.reflect.misc.ReflectUtil;
  61 import sun.security.util.SecurityConstants;
  62 
  63 /**
  64  * A class loader is an object that is responsible for loading classes. The
  65  * class <tt>ClassLoader</tt> is an abstract class.  Given the <a
  66  * href="#name">binary name</a> of a class, a class loader should attempt to
  67  * locate or generate data that constitutes a definition for the class.  A
  68  * typical strategy is to transform the name into a file name and then read a
  69  * "class file" of that name from a file system.
  70  *
  71  * <p> Every {@link Class <tt>Class</tt>} object contains a {@link
  72  * Class#getClassLoader() reference} to the <tt>ClassLoader</tt> that defined
  73  * it.
  74  *
  75  * <p> <tt>Class</tt> objects for array classes are not created by class
  76  * loaders, but are created automatically as required by the Java runtime.
  77  * The class loader for an array class, as returned by {@link
  78  * Class#getClassLoader()} is the same as the class loader for its element
  79  * type; if the element type is a primitive type, then the array class has no
  80  * class loader.
  81  *
  82  * <p> Applications implement subclasses of <tt>ClassLoader</tt> in order to
  83  * extend the manner in which the Java virtual machine dynamically loads
  84  * classes.
  85  *
  86  * <p> Class loaders may typically be used by security managers to indicate
  87  * security domains.
  88  *
  89  * <p> The <tt>ClassLoader</tt> class uses a delegation model to search for
  90  * classes and resources.  Each instance of <tt>ClassLoader</tt> has an
  91  * associated parent class loader.  When requested to find a class or
  92  * resource, a <tt>ClassLoader</tt> instance will delegate the search for the
  93  * class or resource to its parent class loader before attempting to find the
  94  * class or resource itself.  The virtual machine's built-in class loader,
  95  * called the "bootstrap class loader", does not itself have a parent but may
  96  * serve as the parent of a <tt>ClassLoader</tt> instance.
  97  *
  98  * <p> Class loaders that support concurrent loading of classes are known as
  99  * <em>parallel capable</em> class loaders and are required to register
 100  * themselves at their class initialization time by invoking the
 101  * {@link
 102  * #registerAsParallelCapable <tt>ClassLoader.registerAsParallelCapable</tt>}
 103  * method. Note that the <tt>ClassLoader</tt> class is registered as parallel
 104  * capable by default. However, its subclasses still need to register themselves
 105  * if they are parallel capable. <br>
 106  * In environments in which the delegation model is not strictly
 107  * hierarchical, class loaders need to be parallel capable, otherwise class
 108  * loading can lead to deadlocks because the loader lock is held for the
 109  * duration of the class loading process (see {@link #loadClass
 110  * <tt>loadClass</tt>} methods).
 111  *
 112  * <p> Normally, the Java virtual machine loads classes from the local file
 113  * system in a platform-dependent manner.  For example, on UNIX systems, the
 114  * virtual machine loads classes from the directory defined by the
 115  * <tt>CLASSPATH</tt> environment variable.
 116  *
 117  * <p> However, some classes may not originate from a file; they may originate
 118  * from other sources, such as the network, or they could be constructed by an
 119  * application.  The method {@link #defineClass(String, byte[], int, int)
 120  * <tt>defineClass</tt>} converts an array of bytes into an instance of class
 121  * <tt>Class</tt>. Instances of this newly defined class can be created using
 122  * {@link Class#newInstance <tt>Class.newInstance</tt>}.
 123  *
 124  * <p> The methods and constructors of objects created by a class loader may
 125  * reference other classes.  To determine the class(es) referred to, the Java
 126  * virtual machine invokes the {@link #loadClass <tt>loadClass</tt>} method of
 127  * the class loader that originally created the class.
 128  *
 129  * <p> For example, an application could create a network class loader to
 130  * download class files from a server.  Sample code might look like:
 131  *
 132  * <blockquote><pre>
 133  *   ClassLoader loader&nbsp;= new NetworkClassLoader(host,&nbsp;port);
 134  *   Object main&nbsp;= loader.loadClass("Main", true).newInstance();
 135  *       &nbsp;.&nbsp;.&nbsp;.
 136  * </pre></blockquote>
 137  *
 138  * <p> The network class loader subclass must define the methods {@link
 139  * #findClass <tt>findClass</tt>} and <tt>loadClassData</tt> to load a class
 140  * from the network.  Once it has downloaded the bytes that make up the class,
 141  * it should use the method {@link #defineClass <tt>defineClass</tt>} to
 142  * create a class instance.  A sample implementation is:
 143  *
 144  * <blockquote><pre>
 145  *     class NetworkClassLoader extends ClassLoader {
 146  *         String host;
 147  *         int port;
 148  *
 149  *         public Class findClass(String name) {
 150  *             byte[] b = loadClassData(name);
 151  *             return defineClass(name, b, 0, b.length);
 152  *         }
 153  *
 154  *         private byte[] loadClassData(String name) {
 155  *             // load the class data from the connection
 156  *             &nbsp;.&nbsp;.&nbsp;.
 157  *         }
 158  *     }
 159  * </pre></blockquote>
 160  *
 161  * <h3> <a name="name">Binary names</a> </h3>
 162  *
 163  * <p> Any class name provided as a {@link String} parameter to methods in
 164  * <tt>ClassLoader</tt> must be a binary name as defined by
 165  * <cite>The Java&trade; Language Specification</cite>.
 166  *
 167  * <p> Examples of valid class names include:
 168  * <blockquote><pre>
 169  *   "java.lang.String"
 170  *   "javax.swing.JSpinner$DefaultEditor"
 171  *   "java.security.KeyStore$Builder$FileBuilder$1"
 172  *   "java.net.URLClassLoader$3$1"
 173  * </pre></blockquote>
 174  *
 175  * @see      #resolveClass(Class)
 176  * @since 1.0
 177  */
 178 public abstract class ClassLoader {
 179 
 180     private static native void registerNatives();
 181     static {
 182         registerNatives();
 183     }
 184 
 185     // The parent class loader for delegation
 186     // Note: VM hardcoded the offset of this field, thus all new fields
 187     // must be added *after* it.
 188     private final ClassLoader parent;
 189 
 190     /**
 191      * Encapsulates the set of parallel capable loader types.
 192      */
 193     private static class ParallelLoaders {
 194         private ParallelLoaders() {}
 195 
 196         // the set of parallel capable loader types
 197         private static final Set<Class<? extends ClassLoader>> loaderTypes =
 198             Collections.newSetFromMap(
 199                 new WeakHashMap<Class<? extends ClassLoader>, Boolean>());
 200         static {
 201             synchronized (loaderTypes) { loaderTypes.add(ClassLoader.class); }
 202         }
 203 
 204         /**
 205          * Registers the given class loader type as parallel capabale.
 206          * Returns {@code true} is successfully registered; {@code false} if
 207          * loader's super class is not registered.
 208          */
 209         static boolean register(Class<? extends ClassLoader> c) {
 210             synchronized (loaderTypes) {
 211                 if (loaderTypes.contains(c.getSuperclass())) {
 212                     // register the class loader as parallel capable
 213                     // if and only if all of its super classes are.
 214                     // Note: given current classloading sequence, if
 215                     // the immediate super class is parallel capable,
 216                     // all the super classes higher up must be too.
 217                     loaderTypes.add(c);
 218                     return true;
 219                 } else {
 220                     return false;
 221                 }
 222             }
 223         }
 224 
 225         /**
 226          * Returns {@code true} if the given class loader type is
 227          * registered as parallel capable.
 228          */
 229         static boolean isRegistered(Class<? extends ClassLoader> c) {
 230             synchronized (loaderTypes) {
 231                 return loaderTypes.contains(c);
 232             }
 233         }
 234     }
 235 
 236     // Maps class name to the corresponding lock object when the current
 237     // class loader is parallel capable.
 238     // Note: VM also uses this field to decide if the current class loader
 239     // is parallel capable and the appropriate lock object for class loading.
 240     private final ConcurrentHashMap<String, Object> parallelLockMap;
 241 
 242     // Hashtable that maps packages to certs
 243     private final Map <String, Certificate[]> package2certs;
 244 
 245     // Shared among all packages with unsigned classes
 246     private static final Certificate[] nocerts = new Certificate[0];
 247 
 248     // The classes loaded by this class loader. The only purpose of this table
 249     // is to keep the classes from being GC'ed until the loader is GC'ed.
 250     private final Vector<Class<?>> classes = new Vector<>();
 251 
 252     // The "default" domain. Set as the default ProtectionDomain on newly
 253     // created classes.
 254     private final ProtectionDomain defaultDomain =
 255         new ProtectionDomain(new CodeSource(null, (Certificate[]) null),
 256                              null, this, null);
 257 
 258     // The initiating protection domains for all classes loaded by this loader
 259     private final Set<ProtectionDomain> domains;
 260 
 261     // Invoked by the VM to record every loaded class with this loader.
 262     void addClass(Class<?> c) {
 263         classes.addElement(c);
 264     }
 265 
 266     // The packages defined in this class loader.  Each package name is mapped
 267     // to its corresponding Package object.
 268     // @GuardedBy("itself")
 269     private final HashMap<String, Package> packages = new HashMap<>();
 270 
 271     private static Void checkCreateClassLoader() {
 272         SecurityManager security = System.getSecurityManager();
 273         if (security != null) {
 274             security.checkCreateClassLoader();
 275         }
 276         return null;
 277     }
 278 
 279     private ClassLoader(Void unused, ClassLoader parent) {
 280         this.parent = parent;
 281         if (ParallelLoaders.isRegistered(this.getClass())) {
 282             parallelLockMap = new ConcurrentHashMap<>();
 283             package2certs = new ConcurrentHashMap<>();
 284             domains =
 285                 Collections.synchronizedSet(new HashSet<ProtectionDomain>());
 286             assertionLock = new Object();
 287         } else {
 288             // no finer-grained lock; lock on the classloader instance
 289             parallelLockMap = null;
 290             package2certs = new Hashtable<>();
 291             domains = new HashSet<>();
 292             assertionLock = this;
 293         }
 294     }
 295 
 296     /**
 297      * Creates a new class loader using the specified parent class loader for
 298      * delegation.
 299      *
 300      * <p> If there is a security manager, its {@link
 301      * SecurityManager#checkCreateClassLoader()
 302      * <tt>checkCreateClassLoader</tt>} method is invoked.  This may result in
 303      * a security exception.  </p>
 304      *
 305      * @param  parent
 306      *         The parent class loader
 307      *
 308      * @throws  SecurityException
 309      *          If a security manager exists and its
 310      *          <tt>checkCreateClassLoader</tt> method doesn't allow creation
 311      *          of a new class loader.
 312      *
 313      * @since  1.2
 314      */
 315     protected ClassLoader(ClassLoader parent) {
 316         this(checkCreateClassLoader(), parent);
 317     }
 318 
 319     /**
 320      * Creates a new class loader using the <tt>ClassLoader</tt> returned by
 321      * the method {@link #getSystemClassLoader()
 322      * <tt>getSystemClassLoader()</tt>} as the parent class loader.
 323      *
 324      * <p> If there is a security manager, its {@link
 325      * SecurityManager#checkCreateClassLoader()
 326      * <tt>checkCreateClassLoader</tt>} method is invoked.  This may result in
 327      * a security exception.  </p>
 328      *
 329      * @throws  SecurityException
 330      *          If a security manager exists and its
 331      *          <tt>checkCreateClassLoader</tt> method doesn't allow creation
 332      *          of a new class loader.
 333      */
 334     protected ClassLoader() {
 335         this(checkCreateClassLoader(), getSystemClassLoader());
 336     }
 337 
 338     // -- Class --
 339 
 340     /**
 341      * Loads the class with the specified <a href="#name">binary name</a>.
 342      * This method searches for classes in the same manner as the {@link
 343      * #loadClass(String, boolean)} method.  It is invoked by the Java virtual
 344      * machine to resolve class references.  Invoking this method is equivalent
 345      * to invoking {@link #loadClass(String, boolean) <tt>loadClass(name,
 346      * false)</tt>}.
 347      *
 348      * @param  name
 349      *         The <a href="#name">binary name</a> of the class
 350      *
 351      * @return  The resulting <tt>Class</tt> object
 352      *
 353      * @throws  ClassNotFoundException
 354      *          If the class was not found
 355      */
 356     public Class<?> loadClass(String name) throws ClassNotFoundException {
 357         return loadClass(name, false);
 358     }
 359 
 360     /**
 361      * Loads the class with the specified <a href="#name">binary name</a>.  The
 362      * default implementation of this method searches for classes in the
 363      * following order:
 364      *
 365      * <ol>
 366      *
 367      *   <li><p> Invoke {@link #findLoadedClass(String)} to check if the class
 368      *   has already been loaded.  </p></li>
 369      *
 370      *   <li><p> Invoke the {@link #loadClass(String) <tt>loadClass</tt>} method
 371      *   on the parent class loader.  If the parent is <tt>null</tt> the class
 372      *   loader built-in to the virtual machine is used, instead.  </p></li>
 373      *
 374      *   <li><p> Invoke the {@link #findClass(String)} method to find the
 375      *   class.  </p></li>
 376      *
 377      * </ol>
 378      *
 379      * <p> If the class was found using the above steps, and the
 380      * <tt>resolve</tt> flag is true, this method will then invoke the {@link
 381      * #resolveClass(Class)} method on the resulting <tt>Class</tt> object.
 382      *
 383      * <p> Subclasses of <tt>ClassLoader</tt> are encouraged to override {@link
 384      * #findClass(String)}, rather than this method.  </p>
 385      *
 386      * <p> Unless overridden, this method synchronizes on the result of
 387      * {@link #getClassLoadingLock <tt>getClassLoadingLock</tt>} method
 388      * during the entire class loading process.
 389      *
 390      * @param  name
 391      *         The <a href="#name">binary name</a> of the class
 392      *
 393      * @param  resolve
 394      *         If <tt>true</tt> then resolve the class
 395      *
 396      * @return  The resulting <tt>Class</tt> object
 397      *
 398      * @throws  ClassNotFoundException
 399      *          If the class could not be found
 400      */
 401     protected Class<?> loadClass(String name, boolean resolve)
 402         throws ClassNotFoundException
 403     {
 404         synchronized (getClassLoadingLock(name)) {
 405             // First, check if the class has already been loaded
 406             Class<?> c = findLoadedClass(name);
 407             if (c == null) {
 408                 long t0 = System.nanoTime();
 409                 try {
 410                     if (parent != null) {
 411                         c = parent.loadClass(name, false);
 412                     } else {
 413                         c = findBootstrapClassOrNull(name);
 414                     }
 415                 } catch (ClassNotFoundException e) {
 416                     // ClassNotFoundException thrown if class not found
 417                     // from the non-null parent class loader
 418                 }
 419 
 420                 if (c == null) {
 421                     // If still not found, then invoke findClass in order
 422                     // to find the class.
 423                     long t1 = System.nanoTime();
 424                     c = findClass(name);
 425 
 426                     // this is the defining class loader; record the stats
 427                     sun.misc.PerfCounter.getParentDelegationTime().addTime(t1 - t0);
 428                     sun.misc.PerfCounter.getFindClassTime().addElapsedTimeFrom(t1);
 429                     sun.misc.PerfCounter.getFindClasses().increment();
 430                 }
 431             }
 432             if (resolve) {
 433                 resolveClass(c);
 434             }
 435             return c;
 436         }
 437     }
 438 
 439     /**
 440      * Returns the lock object for class loading operations.
 441      * For backward compatibility, the default implementation of this method
 442      * behaves as follows. If this ClassLoader object is registered as
 443      * parallel capable, the method returns a dedicated object associated
 444      * with the specified class name. Otherwise, the method returns this
 445      * ClassLoader object.
 446      *
 447      * @param  className
 448      *         The name of the to-be-loaded class
 449      *
 450      * @return the lock for class loading operations
 451      *
 452      * @throws NullPointerException
 453      *         If registered as parallel capable and <tt>className</tt> is null
 454      *
 455      * @see #loadClass(String, boolean)
 456      *
 457      * @since  1.7
 458      */
 459     protected Object getClassLoadingLock(String className) {
 460         Object lock = this;
 461         if (parallelLockMap != null) {
 462             Object newLock = new Object();
 463             lock = parallelLockMap.putIfAbsent(className, newLock);
 464             if (lock == null) {
 465                 lock = newLock;
 466             }
 467         }
 468         return lock;
 469     }
 470 
 471     // This method is invoked by the virtual machine to load a class.
 472     private Class<?> loadClassInternal(String name)
 473         throws ClassNotFoundException
 474     {
 475         // For backward compatibility, explicitly lock on 'this' when
 476         // the current class loader is not parallel capable.
 477         if (parallelLockMap == null) {
 478             synchronized (this) {
 479                  return loadClass(name);
 480             }
 481         } else {
 482             return loadClass(name);
 483         }
 484     }
 485 
 486     // Invoked by the VM after loading class with this loader.
 487     private void checkPackageAccess(Class<?> cls, ProtectionDomain pd) {
 488         final SecurityManager sm = System.getSecurityManager();
 489         if (sm != null) {
 490             if (ReflectUtil.isNonPublicProxyClass(cls)) {
 491                 for (Class<?> intf: cls.getInterfaces()) {
 492                     checkPackageAccess(intf, pd);
 493                 }
 494                 return;
 495             }
 496 
 497             final String name = cls.getName();
 498             final int i = name.lastIndexOf('.');
 499             if (i != -1) {
 500                 AccessController.doPrivileged(new PrivilegedAction<Void>() {
 501                     public Void run() {
 502                         sm.checkPackageAccess(name.substring(0, i));
 503                         return null;
 504                     }
 505                 }, new AccessControlContext(new ProtectionDomain[] {pd}));
 506             }
 507         }
 508         domains.add(pd);
 509     }
 510 
 511     /**
 512      * Finds the class with the specified <a href="#name">binary name</a>.
 513      * This method should be overridden by class loader implementations that
 514      * follow the delegation model for loading classes, and will be invoked by
 515      * the {@link #loadClass <tt>loadClass</tt>} method after checking the
 516      * parent class loader for the requested class.  The default implementation
 517      * throws a <tt>ClassNotFoundException</tt>.
 518      *
 519      * @param  name
 520      *         The <a href="#name">binary name</a> of the class
 521      *
 522      * @return  The resulting <tt>Class</tt> object
 523      *
 524      * @throws  ClassNotFoundException
 525      *          If the class could not be found
 526      *
 527      * @since  1.2
 528      */
 529     protected Class<?> findClass(String name) throws ClassNotFoundException {
 530         throw new ClassNotFoundException(name);
 531     }
 532 
 533     /**
 534      * Converts an array of bytes into an instance of class <tt>Class</tt>.
 535      * Before the <tt>Class</tt> can be used it must be resolved.  This method
 536      * is deprecated in favor of the version that takes a <a
 537      * href="#name">binary name</a> as its first argument, and is more secure.
 538      *
 539      * @param  b
 540      *         The bytes that make up the class data.  The bytes in positions
 541      *         <tt>off</tt> through <tt>off+len-1</tt> should have the format
 542      *         of a valid class file as defined by
 543      *         <cite>The Java&trade; Virtual Machine Specification</cite>.
 544      *
 545      * @param  off
 546      *         The start offset in <tt>b</tt> of the class data
 547      *
 548      * @param  len
 549      *         The length of the class data
 550      *
 551      * @return  The <tt>Class</tt> object that was created from the specified
 552      *          class data
 553      *
 554      * @throws  ClassFormatError
 555      *          If the data did not contain a valid class
 556      *
 557      * @throws  IndexOutOfBoundsException
 558      *          If either <tt>off</tt> or <tt>len</tt> is negative, or if
 559      *          <tt>off+len</tt> is greater than <tt>b.length</tt>.
 560      *
 561      * @throws  SecurityException
 562      *          If an attempt is made to add this class to a package that
 563      *          contains classes that were signed by a different set of
 564      *          certificates than this class, or if an attempt is made
 565      *          to define a class in a package with a fully-qualified name
 566      *          that starts with "{@code java.}".
 567      *
 568      * @see  #loadClass(String, boolean)
 569      * @see  #resolveClass(Class)
 570      *
 571      * @deprecated  Replaced by {@link #defineClass(String, byte[], int, int)
 572      * defineClass(String, byte[], int, int)}
 573      */
 574     @Deprecated
 575     protected final Class<?> defineClass(byte[] b, int off, int len)
 576         throws ClassFormatError
 577     {
 578         return defineClass(null, b, off, len, null);
 579     }
 580 
 581     /**
 582      * Converts an array of bytes into an instance of class <tt>Class</tt>.
 583      * Before the <tt>Class</tt> can be used it must be resolved.
 584      *
 585      * <p> This method assigns a default {@link java.security.ProtectionDomain
 586      * <tt>ProtectionDomain</tt>} to the newly defined class.  The
 587      * <tt>ProtectionDomain</tt> is effectively granted the same set of
 588      * permissions returned when {@link
 589      * java.security.Policy#getPermissions(java.security.CodeSource)
 590      * <tt>Policy.getPolicy().getPermissions(new CodeSource(null, null))</tt>}
 591      * is invoked.  The default domain is created on the first invocation of
 592      * {@link #defineClass(String, byte[], int, int) <tt>defineClass</tt>},
 593      * and re-used on subsequent invocations.
 594      *
 595      * <p> To assign a specific <tt>ProtectionDomain</tt> to the class, use
 596      * the {@link #defineClass(String, byte[], int, int,
 597      * java.security.ProtectionDomain) <tt>defineClass</tt>} method that takes a
 598      * <tt>ProtectionDomain</tt> as one of its arguments.  </p>
 599      *
 600      * @param  name
 601      *         The expected <a href="#name">binary name</a> of the class, or
 602      *         <tt>null</tt> if not known
 603      *
 604      * @param  b
 605      *         The bytes that make up the class data.  The bytes in positions
 606      *         <tt>off</tt> through <tt>off+len-1</tt> should have the format
 607      *         of a valid class file as defined by
 608      *         <cite>The Java&trade; Virtual Machine Specification</cite>.
 609      *
 610      * @param  off
 611      *         The start offset in <tt>b</tt> of the class data
 612      *
 613      * @param  len
 614      *         The length of the class data
 615      *
 616      * @return  The <tt>Class</tt> object that was created from the specified
 617      *          class data.
 618      *
 619      * @throws  ClassFormatError
 620      *          If the data did not contain a valid class
 621      *
 622      * @throws  IndexOutOfBoundsException
 623      *          If either <tt>off</tt> or <tt>len</tt> is negative, or if
 624      *          <tt>off+len</tt> is greater than <tt>b.length</tt>.
 625      *
 626      * @throws  SecurityException
 627      *          If an attempt is made to add this class to a package that
 628      *          contains classes that were signed by a different set of
 629      *          certificates than this class (which is unsigned), or if
 630      *          <tt>name</tt> begins with "<tt>java.</tt>".
 631      *
 632      * @see  #loadClass(String, boolean)
 633      * @see  #resolveClass(Class)
 634      * @see  java.security.CodeSource
 635      * @see  java.security.SecureClassLoader
 636      *
 637      * @since  1.1
 638      */
 639     protected final Class<?> defineClass(String name, byte[] b, int off, int len)
 640         throws ClassFormatError
 641     {
 642         return defineClass(name, b, off, len, null);
 643     }
 644 
 645     /* Determine protection domain, and check that:
 646         - not define java.* class,
 647         - signer of this class matches signers for the rest of the classes in
 648           package.
 649     */
 650     private ProtectionDomain preDefineClass(String name,
 651                                             ProtectionDomain pd)
 652     {
 653         if (!checkName(name))
 654             throw new NoClassDefFoundError("IllegalName: " + name);
 655 
 656         if ((name != null) && name.startsWith("java.")) {
 657             throw new SecurityException
 658                 ("Prohibited package name: " +
 659                  name.substring(0, name.lastIndexOf('.')));
 660         }
 661         if (pd == null) {
 662             pd = defaultDomain;
 663         }
 664 
 665         if (name != null) checkCerts(name, pd.getCodeSource());
 666 
 667         return pd;
 668     }
 669 
 670     private String defineClassSourceLocation(ProtectionDomain pd)
 671     {
 672         CodeSource cs = pd.getCodeSource();
 673         String source = null;
 674         if (cs != null && cs.getLocation() != null) {
 675             source = cs.getLocation().toString();
 676         }
 677         return source;
 678     }
 679 
 680     private void postDefineClass(Class<?> c, ProtectionDomain pd)
 681     {
 682         if (pd.getCodeSource() != null) {
 683             Certificate certs[] = pd.getCodeSource().getCertificates();
 684             if (certs != null)
 685                 setSigners(c, certs);
 686         }
 687     }
 688 
 689     /**
 690      * Converts an array of bytes into an instance of class <tt>Class</tt>,
 691      * with an optional <tt>ProtectionDomain</tt>.  If the domain is
 692      * <tt>null</tt>, then a default domain will be assigned to the class as
 693      * specified in the documentation for {@link #defineClass(String, byte[],
 694      * int, int)}.  Before the class can be used it must be resolved.
 695      *
 696      * <p> The first class defined in a package determines the exact set of
 697      * certificates that all subsequent classes defined in that package must
 698      * contain.  The set of certificates for a class is obtained from the
 699      * {@link java.security.CodeSource <tt>CodeSource</tt>} within the
 700      * <tt>ProtectionDomain</tt> of the class.  Any classes added to that
 701      * package must contain the same set of certificates or a
 702      * <tt>SecurityException</tt> will be thrown.  Note that if
 703      * <tt>name</tt> is <tt>null</tt>, this check is not performed.
 704      * You should always pass in the <a href="#name">binary name</a> of the
 705      * class you are defining as well as the bytes.  This ensures that the
 706      * class you are defining is indeed the class you think it is.
 707      *
 708      * <p> The specified <tt>name</tt> cannot begin with "<tt>java.</tt>", since
 709      * all classes in the "<tt>java.*</tt> packages can only be defined by the
 710      * bootstrap class loader.  If <tt>name</tt> is not <tt>null</tt>, it
 711      * must be equal to the <a href="#name">binary name</a> of the class
 712      * specified by the byte array "<tt>b</tt>", otherwise a {@link
 713      * NoClassDefFoundError <tt>NoClassDefFoundError</tt>} will be thrown. </p>
 714      *
 715      * @param  name
 716      *         The expected <a href="#name">binary name</a> of the class, or
 717      *         <tt>null</tt> if not known
 718      *
 719      * @param  b
 720      *         The bytes that make up the class data. The bytes in positions
 721      *         <tt>off</tt> through <tt>off+len-1</tt> should have the format
 722      *         of a valid class file as defined by
 723      *         <cite>The Java&trade; Virtual Machine Specification</cite>.
 724      *
 725      * @param  off
 726      *         The start offset in <tt>b</tt> of the class data
 727      *
 728      * @param  len
 729      *         The length of the class data
 730      *
 731      * @param  protectionDomain
 732      *         The ProtectionDomain of the class
 733      *
 734      * @return  The <tt>Class</tt> object created from the data,
 735      *          and optional <tt>ProtectionDomain</tt>.
 736      *
 737      * @throws  ClassFormatError
 738      *          If the data did not contain a valid class
 739      *
 740      * @throws  NoClassDefFoundError
 741      *          If <tt>name</tt> is not equal to the <a href="#name">binary
 742      *          name</a> of the class specified by <tt>b</tt>
 743      *
 744      * @throws  IndexOutOfBoundsException
 745      *          If either <tt>off</tt> or <tt>len</tt> is negative, or if
 746      *          <tt>off+len</tt> is greater than <tt>b.length</tt>.
 747      *
 748      * @throws  SecurityException
 749      *          If an attempt is made to add this class to a package that
 750      *          contains classes that were signed by a different set of
 751      *          certificates than this class, or if <tt>name</tt> begins with
 752      *          "<tt>java.</tt>".
 753      */
 754     protected final Class<?> defineClass(String name, byte[] b, int off, int len,
 755                                          ProtectionDomain protectionDomain)
 756         throws ClassFormatError
 757     {
 758         protectionDomain = preDefineClass(name, protectionDomain);
 759         String source = defineClassSourceLocation(protectionDomain);
 760         Class<?> c = defineClass1(name, b, off, len, protectionDomain, source);
 761         postDefineClass(c, protectionDomain);
 762         return c;
 763     }
 764 
 765     /**
 766      * Converts a {@link java.nio.ByteBuffer <tt>ByteBuffer</tt>}
 767      * into an instance of class <tt>Class</tt>,
 768      * with an optional <tt>ProtectionDomain</tt>.  If the domain is
 769      * <tt>null</tt>, then a default domain will be assigned to the class as
 770      * specified in the documentation for {@link #defineClass(String, byte[],
 771      * int, int)}.  Before the class can be used it must be resolved.
 772      *
 773      * <p>The rules about the first class defined in a package determining the
 774      * set of certificates for the package, and the restrictions on class names
 775      * are identical to those specified in the documentation for {@link
 776      * #defineClass(String, byte[], int, int, ProtectionDomain)}.
 777      *
 778      * <p> An invocation of this method of the form
 779      * <i>cl</i><tt>.defineClass(</tt><i>name</i><tt>,</tt>
 780      * <i>bBuffer</i><tt>,</tt> <i>pd</i><tt>)</tt> yields exactly the same
 781      * result as the statements
 782      *
 783      *<p> <tt>
 784      * ...<br>
 785      * byte[] temp = new byte[bBuffer.{@link
 786      * java.nio.ByteBuffer#remaining remaining}()];<br>
 787      *     bBuffer.{@link java.nio.ByteBuffer#get(byte[])
 788      * get}(temp);<br>
 789      *     return {@link #defineClass(String, byte[], int, int, ProtectionDomain)
 790      * cl.defineClass}(name, temp, 0,
 791      * temp.length, pd);<br>
 792      * </tt></p>
 793      *
 794      * @param  name
 795      *         The expected <a href="#name">binary name</a>. of the class, or
 796      *         <tt>null</tt> if not known
 797      *
 798      * @param  b
 799      *         The bytes that make up the class data. The bytes from positions
 800      *         <tt>b.position()</tt> through <tt>b.position() + b.limit() -1
 801      *         </tt> should have the format of a valid class file as defined by
 802      *         <cite>The Java&trade; Virtual Machine Specification</cite>.
 803      *
 804      * @param  protectionDomain
 805      *         The ProtectionDomain of the class, or <tt>null</tt>.
 806      *
 807      * @return  The <tt>Class</tt> object created from the data,
 808      *          and optional <tt>ProtectionDomain</tt>.
 809      *
 810      * @throws  ClassFormatError
 811      *          If the data did not contain a valid class.
 812      *
 813      * @throws  NoClassDefFoundError
 814      *          If <tt>name</tt> is not equal to the <a href="#name">binary
 815      *          name</a> of the class specified by <tt>b</tt>
 816      *
 817      * @throws  SecurityException
 818      *          If an attempt is made to add this class to a package that
 819      *          contains classes that were signed by a different set of
 820      *          certificates than this class, or if <tt>name</tt> begins with
 821      *          "<tt>java.</tt>".
 822      *
 823      * @see      #defineClass(String, byte[], int, int, ProtectionDomain)
 824      *
 825      * @since  1.5
 826      */
 827     protected final Class<?> defineClass(String name, java.nio.ByteBuffer b,
 828                                          ProtectionDomain protectionDomain)
 829         throws ClassFormatError
 830     {
 831         int len = b.remaining();
 832 
 833         // Use byte[] if not a direct ByteBufer:
 834         if (!b.isDirect()) {
 835             if (b.hasArray()) {
 836                 return defineClass(name, b.array(),
 837                                    b.position() + b.arrayOffset(), len,
 838                                    protectionDomain);
 839             } else {
 840                 // no array, or read-only array
 841                 byte[] tb = new byte[len];
 842                 b.get(tb);  // get bytes out of byte buffer.
 843                 return defineClass(name, tb, 0, len, protectionDomain);
 844             }
 845         }
 846 
 847         protectionDomain = preDefineClass(name, protectionDomain);
 848         String source = defineClassSourceLocation(protectionDomain);
 849         Class<?> c = defineClass2(name, b, b.position(), len, protectionDomain, source);
 850         postDefineClass(c, protectionDomain);
 851         return c;
 852     }
 853 
 854     private native Class<?> defineClass0(String name, byte[] b, int off, int len,
 855                                          ProtectionDomain pd);
 856 
 857     private native Class<?> defineClass1(String name, byte[] b, int off, int len,
 858                                          ProtectionDomain pd, String source);
 859 
 860     private native Class<?> defineClass2(String name, java.nio.ByteBuffer b,
 861                                          int off, int len, ProtectionDomain pd,
 862                                          String source);
 863 
 864     // true if the name is null or has the potential to be a valid binary name
 865     private boolean checkName(String name) {
 866         if ((name == null) || (name.length() == 0))
 867             return true;
 868         if ((name.indexOf('/') != -1)
 869             || (!VM.allowArraySyntax() && (name.charAt(0) == '[')))
 870             return false;
 871         return true;
 872     }
 873 
 874     private void checkCerts(String name, CodeSource cs) {
 875         int i = name.lastIndexOf('.');
 876         String pname = (i == -1) ? "" : name.substring(0, i);
 877 
 878         Certificate[] certs = null;
 879         if (cs != null) {
 880             certs = cs.getCertificates();
 881         }
 882         Certificate[] pcerts = null;
 883         if (parallelLockMap == null) {
 884             synchronized (this) {
 885                 pcerts = package2certs.get(pname);
 886                 if (pcerts == null) {
 887                     package2certs.put(pname, (certs == null? nocerts:certs));
 888                 }
 889             }
 890         } else {
 891             pcerts = ((ConcurrentHashMap<String, Certificate[]>)package2certs).
 892                 putIfAbsent(pname, (certs == null? nocerts:certs));
 893         }
 894         if (pcerts != null && !compareCerts(pcerts, certs)) {
 895             throw new SecurityException("class \""+ name +
 896                  "\"'s signer information does not match signer information of other classes in the same package");
 897         }
 898     }
 899 
 900     /**
 901      * check to make sure the certs for the new class (certs) are the same as
 902      * the certs for the first class inserted in the package (pcerts)
 903      */
 904     private boolean compareCerts(Certificate[] pcerts,
 905                                  Certificate[] certs)
 906     {
 907         // certs can be null, indicating no certs.
 908         if ((certs == null) || (certs.length == 0)) {
 909             return pcerts.length == 0;
 910         }
 911 
 912         // the length must be the same at this point
 913         if (certs.length != pcerts.length)
 914             return false;
 915 
 916         // go through and make sure all the certs in one array
 917         // are in the other and vice-versa.
 918         boolean match;
 919         for (int i = 0; i < certs.length; i++) {
 920             match = false;
 921             for (int j = 0; j < pcerts.length; j++) {
 922                 if (certs[i].equals(pcerts[j])) {
 923                     match = true;
 924                     break;
 925                 }
 926             }
 927             if (!match) return false;
 928         }
 929 
 930         // now do the same for pcerts
 931         for (int i = 0; i < pcerts.length; i++) {
 932             match = false;
 933             for (int j = 0; j < certs.length; j++) {
 934                 if (pcerts[i].equals(certs[j])) {
 935                     match = true;
 936                     break;
 937                 }
 938             }
 939             if (!match) return false;
 940         }
 941 
 942         return true;
 943     }
 944 
 945     /**
 946      * Links the specified class.  This (misleadingly named) method may be
 947      * used by a class loader to link a class.  If the class <tt>c</tt> has
 948      * already been linked, then this method simply returns. Otherwise, the
 949      * class is linked as described in the "Execution" chapter of
 950      * <cite>The Java&trade; Language Specification</cite>.
 951      *
 952      * @param  c
 953      *         The class to link
 954      *
 955      * @throws  NullPointerException
 956      *          If <tt>c</tt> is <tt>null</tt>.
 957      *
 958      * @see  #defineClass(String, byte[], int, int)
 959      */
 960     protected final void resolveClass(Class<?> c) {
 961         resolveClass0(c);
 962     }
 963 
 964     private native void resolveClass0(Class<?> c);
 965 
 966     /**
 967      * Finds a class with the specified <a href="#name">binary name</a>,
 968      * loading it if necessary.
 969      *
 970      * <p> This method loads the class through the system class loader (see
 971      * {@link #getSystemClassLoader()}).  The <tt>Class</tt> object returned
 972      * might have more than one <tt>ClassLoader</tt> associated with it.
 973      * Subclasses of <tt>ClassLoader</tt> need not usually invoke this method,
 974      * because most class loaders need to override just {@link
 975      * #findClass(String)}.  </p>
 976      *
 977      * @param  name
 978      *         The <a href="#name">binary name</a> of the class
 979      *
 980      * @return  The <tt>Class</tt> object for the specified <tt>name</tt>
 981      *
 982      * @throws  ClassNotFoundException
 983      *          If the class could not be found
 984      *
 985      * @see  #ClassLoader(ClassLoader)
 986      * @see  #getParent()
 987      */
 988     protected final Class<?> findSystemClass(String name)
 989         throws ClassNotFoundException
 990     {
 991         ClassLoader system = getSystemClassLoader();
 992         if (system == null) {
 993             if (!checkName(name))
 994                 throw new ClassNotFoundException(name);
 995             Class<?> cls = findBootstrapClass(name);
 996             if (cls == null) {
 997                 throw new ClassNotFoundException(name);
 998             }
 999             return cls;
1000         }
1001         return system.loadClass(name);
1002     }
1003 
1004     /**
1005      * Returns a class loaded by the bootstrap class loader;
1006      * or return null if not found.
1007      */
1008     private Class<?> findBootstrapClassOrNull(String name)
1009     {
1010         if (!checkName(name)) return null;
1011 
1012         return findBootstrapClass(name);
1013     }
1014 
1015     // return null if not found
1016     private native Class<?> findBootstrapClass(String name);
1017 
1018     /**
1019      * Returns the class with the given <a href="#name">binary name</a> if this
1020      * loader has been recorded by the Java virtual machine as an initiating
1021      * loader of a class with that <a href="#name">binary name</a>.  Otherwise
1022      * <tt>null</tt> is returned.
1023      *
1024      * @param  name
1025      *         The <a href="#name">binary name</a> of the class
1026      *
1027      * @return  The <tt>Class</tt> object, or <tt>null</tt> if the class has
1028      *          not been loaded
1029      *
1030      * @since  1.1
1031      */
1032     protected final Class<?> findLoadedClass(String name) {
1033         if (!checkName(name))
1034             return null;
1035         return findLoadedClass0(name);
1036     }
1037 
1038     private native final Class<?> findLoadedClass0(String name);
1039 
1040     /**
1041      * Sets the signers of a class.  This should be invoked after defining a
1042      * class.
1043      *
1044      * @param  c
1045      *         The <tt>Class</tt> object
1046      *
1047      * @param  signers
1048      *         The signers for the class
1049      *
1050      * @since  1.1
1051      */
1052     protected final void setSigners(Class<?> c, Object[] signers) {
1053         c.setSigners(signers);
1054     }
1055 
1056 
1057     // -- Resource --
1058 
1059     /**
1060      * Finds the resource with the given name.  A resource is some data
1061      * (images, audio, text, etc) that can be accessed by class code in a way
1062      * that is independent of the location of the code.
1063      *
1064      * <p> The name of a resource is a '<tt>/</tt>'-separated path name that
1065      * identifies the resource.
1066      *
1067      * <p> This method will first search the parent class loader for the
1068      * resource; if the parent is <tt>null</tt> the path of the class loader
1069      * built-in to the virtual machine is searched.  That failing, this method
1070      * will invoke {@link #findResource(String)} to find the resource.  </p>
1071      *
1072      * @apiNote When overriding this method it is recommended that an
1073      * implementation ensures that any delegation is consistent with the {@link
1074      * #getResources(java.lang.String) getResources(String)} method.
1075      *
1076      * @param  name
1077      *         The resource name
1078      *
1079      * @return  A <tt>URL</tt> object for reading the resource, or
1080      *          <tt>null</tt> if the resource could not be found or the invoker
1081      *          doesn't have adequate  privileges to get the resource.
1082      *
1083      * @since  1.1
1084      */
1085     public URL getResource(String name) {
1086         URL url;
1087         if (parent != null) {
1088             url = parent.getResource(name);
1089         } else {
1090             url = getBootstrapResource(name);
1091         }
1092         if (url == null) {
1093             url = findResource(name);
1094         }
1095         return url;
1096     }
1097 
1098     /**
1099      * Finds all the resources with the given name. A resource is some data
1100      * (images, audio, text, etc) that can be accessed by class code in a way
1101      * that is independent of the location of the code.
1102      *
1103      * <p>The name of a resource is a <tt>/</tt>-separated path name that
1104      * identifies the resource.
1105      *
1106      * <p> The search order is described in the documentation for {@link
1107      * #getResource(String)}.  </p>
1108      *
1109      * @apiNote When overriding this method it is recommended that an
1110      * implementation ensures that any delegation is consistent with the {@link
1111      * #getResource(java.lang.String) getResource(String)} method. This should
1112      * ensure that the first element returned by the Enumeration's
1113      * {@code nextElement} method is the same resource that the
1114      * {@code getResource(String)} method would return.
1115      *
1116      * @param  name
1117      *         The resource name
1118      *
1119      * @return  An enumeration of {@link java.net.URL <tt>URL</tt>} objects for
1120      *          the resource.  If no resources could  be found, the enumeration
1121      *          will be empty.  Resources that the class loader doesn't have
1122      *          access to will not be in the enumeration.
1123      *
1124      * @throws  IOException
1125      *          If I/O errors occur
1126      *
1127      * @see  #findResources(String)
1128      *
1129      * @since  1.2
1130      */
1131     public Enumeration<URL> getResources(String name) throws IOException {
1132         @SuppressWarnings("unchecked")
1133         Enumeration<URL>[] tmp = (Enumeration<URL>[]) new Enumeration<?>[2];
1134         if (parent != null) {
1135             tmp[0] = parent.getResources(name);
1136         } else {
1137             tmp[0] = getBootstrapResources(name);
1138         }
1139         tmp[1] = findResources(name);
1140 
1141         return new CompoundEnumeration<>(tmp);
1142     }
1143 
1144     /**
1145      * Finds the resource with the given name. Class loader implementations
1146      * should override this method to specify where to find resources.
1147      *
1148      * @param  name
1149      *         The resource name
1150      *
1151      * @return  A <tt>URL</tt> object for reading the resource, or
1152      *          <tt>null</tt> if the resource could not be found
1153      *
1154      * @since  1.2
1155      */
1156     protected URL findResource(String name) {
1157         return null;
1158     }
1159 
1160     /**
1161      * Returns an enumeration of {@link java.net.URL <tt>URL</tt>} objects
1162      * representing all the resources with the given name. Class loader
1163      * implementations should override this method to specify where to load
1164      * resources from.
1165      *
1166      * @param  name
1167      *         The resource name
1168      *
1169      * @return  An enumeration of {@link java.net.URL <tt>URL</tt>} objects for
1170      *          the resources
1171      *
1172      * @throws  IOException
1173      *          If I/O errors occur
1174      *
1175      * @since  1.2
1176      */
1177     protected Enumeration<URL> findResources(String name) throws IOException {
1178         return java.util.Collections.emptyEnumeration();
1179     }
1180 
1181     /**
1182      * Registers the caller as parallel capable.
1183      * The registration succeeds if and only if all of the following
1184      * conditions are met:
1185      * <ol>
1186      * <li> no instance of the caller has been created</li>
1187      * <li> all of the super classes (except class Object) of the caller are
1188      * registered as parallel capable</li>
1189      * </ol>
1190      * <p>Note that once a class loader is registered as parallel capable, there
1191      * is no way to change it back.</p>
1192      *
1193      * @return  true if the caller is successfully registered as
1194      *          parallel capable and false if otherwise.
1195      *
1196      * @since   1.7
1197      */
1198     @CallerSensitive
1199     protected static boolean registerAsParallelCapable() {
1200         Class<? extends ClassLoader> callerClass =
1201             Reflection.getCallerClass().asSubclass(ClassLoader.class);
1202         return ParallelLoaders.register(callerClass);
1203     }
1204 
1205     /**
1206      * Find a resource of the specified name from the search path used to load
1207      * classes.  This method locates the resource through the system class
1208      * loader (see {@link #getSystemClassLoader()}).
1209      *
1210      * @param  name
1211      *         The resource name
1212      *
1213      * @return  A {@link java.net.URL <tt>URL</tt>} object for reading the
1214      *          resource, or <tt>null</tt> if the resource could not be found
1215      *
1216      * @since  1.1
1217      */
1218     public static URL getSystemResource(String name) {
1219         ClassLoader system = getSystemClassLoader();
1220         if (system == null) {
1221             return getBootstrapResource(name);
1222         }
1223         return system.getResource(name);
1224     }
1225 
1226     /**
1227      * Finds all resources of the specified name from the search path used to
1228      * load classes.  The resources thus found are returned as an
1229      * {@link java.util.Enumeration <tt>Enumeration</tt>} of {@link
1230      * java.net.URL <tt>URL</tt>} objects.
1231      *
1232      * <p> The search order is described in the documentation for {@link
1233      * #getSystemResource(String)}.  </p>
1234      *
1235      * @param  name
1236      *         The resource name
1237      *
1238      * @return  An enumeration of resource {@link java.net.URL <tt>URL</tt>}
1239      *          objects
1240      *
1241      * @throws  IOException
1242      *          If I/O errors occur
1243 
1244      * @since  1.2
1245      */
1246     public static Enumeration<URL> getSystemResources(String name)
1247         throws IOException
1248     {
1249         ClassLoader system = getSystemClassLoader();
1250         if (system == null) {
1251             return getBootstrapResources(name);
1252         }
1253         return system.getResources(name);
1254     }
1255 
1256     /**
1257      * Find resources from the VM's built-in classloader.
1258      */
1259     private static URL getBootstrapResource(String name) {
1260         URLClassPath ucp = getBootstrapClassPath();
1261         Resource res = ucp.getResource(name);
1262         return res != null ? res.getURL() : null;
1263     }
1264 
1265     /**
1266      * Find resources from the VM's built-in classloader.
1267      */
1268     private static Enumeration<URL> getBootstrapResources(String name)
1269         throws IOException
1270     {
1271         final Enumeration<Resource> e =
1272             getBootstrapClassPath().getResources(name);
1273         return new Enumeration<URL> () {
1274             public URL nextElement() {
1275                 return e.nextElement().getURL();
1276             }
1277             public boolean hasMoreElements() {
1278                 return e.hasMoreElements();
1279             }
1280         };
1281     }
1282 
1283     // Returns the URLClassPath that is used for finding system resources.
1284     static URLClassPath getBootstrapClassPath() {
1285         return sun.misc.Launcher.getBootstrapClassPath();
1286     }
1287 
1288 
1289     /**
1290      * Returns an input stream for reading the specified resource.
1291      *
1292      * <p> The search order is described in the documentation for {@link
1293      * #getResource(String)}.  </p>
1294      *
1295      * @param  name
1296      *         The resource name
1297      *
1298      * @return  An input stream for reading the resource, or <tt>null</tt>
1299      *          if the resource could not be found
1300      *
1301      * @since  1.1
1302      */
1303     public InputStream getResourceAsStream(String name) {
1304         URL url = getResource(name);
1305         try {
1306             return url != null ? url.openStream() : null;
1307         } catch (IOException e) {
1308             return null;
1309         }
1310     }
1311 
1312     /**
1313      * Open for reading, a resource of the specified name from the search path
1314      * used to load classes.  This method locates the resource through the
1315      * system class loader (see {@link #getSystemClassLoader()}).
1316      *
1317      * @param  name
1318      *         The resource name
1319      *
1320      * @return  An input stream for reading the resource, or <tt>null</tt>
1321      *          if the resource could not be found
1322      *
1323      * @since  1.1
1324      */
1325     public static InputStream getSystemResourceAsStream(String name) {
1326         URL url = getSystemResource(name);
1327         try {
1328             return url != null ? url.openStream() : null;
1329         } catch (IOException e) {
1330             return null;
1331         }
1332     }
1333 
1334 
1335     // -- Hierarchy --
1336 
1337     /**
1338      * Returns the parent class loader for delegation. Some implementations may
1339      * use <tt>null</tt> to represent the bootstrap class loader. This method
1340      * will return <tt>null</tt> in such implementations if this class loader's
1341      * parent is the bootstrap class loader.
1342      *
1343      * <p> If a security manager is present, and the invoker's class loader is
1344      * not <tt>null</tt> and is not an ancestor of this class loader, then this
1345      * method invokes the security manager's {@link
1346      * SecurityManager#checkPermission(java.security.Permission)
1347      * <tt>checkPermission</tt>} method with a {@link
1348      * RuntimePermission#RuntimePermission(String)
1349      * <tt>RuntimePermission("getClassLoader")</tt>} permission to verify
1350      * access to the parent class loader is permitted.  If not, a
1351      * <tt>SecurityException</tt> will be thrown.  </p>
1352      *
1353      * @return  The parent <tt>ClassLoader</tt>
1354      *
1355      * @throws  SecurityException
1356      *          If a security manager exists and its <tt>checkPermission</tt>
1357      *          method doesn't allow access to this class loader's parent class
1358      *          loader.
1359      *
1360      * @since  1.2
1361      */
1362     @CallerSensitive
1363     public final ClassLoader getParent() {
1364         if (parent == null)
1365             return null;
1366         SecurityManager sm = System.getSecurityManager();
1367         if (sm != null) {
1368             // Check access to the parent class loader
1369             // If the caller's class loader is same as this class loader,
1370             // permission check is performed.
1371             checkClassLoaderPermission(parent, Reflection.getCallerClass());
1372         }
1373         return parent;
1374     }
1375 
1376     /**
1377      * Returns the system class loader for delegation.  This is the default
1378      * delegation parent for new <tt>ClassLoader</tt> instances, and is
1379      * typically the class loader used to start the application.
1380      *
1381      * <p> This method is first invoked early in the runtime's startup
1382      * sequence, at which point it creates the system class loader and sets it
1383      * as the context class loader of the invoking <tt>Thread</tt>.
1384      *
1385      * <p> The default system class loader is an implementation-dependent
1386      * instance of this class.
1387      *
1388      * <p> If the system property "<tt>java.system.class.loader</tt>" is defined
1389      * when this method is first invoked then the value of that property is
1390      * taken to be the name of a class that will be returned as the system
1391      * class loader.  The class is loaded using the default system class loader
1392      * and must define a public constructor that takes a single parameter of
1393      * type <tt>ClassLoader</tt> which is used as the delegation parent.  An
1394      * instance is then created using this constructor with the default system
1395      * class loader as the parameter.  The resulting class loader is defined
1396      * to be the system class loader.
1397      *
1398      * <p> If a security manager is present, and the invoker's class loader is
1399      * not <tt>null</tt> and the invoker's class loader is not the same as or
1400      * an ancestor of the system class loader, then this method invokes the
1401      * security manager's {@link
1402      * SecurityManager#checkPermission(java.security.Permission)
1403      * <tt>checkPermission</tt>} method with a {@link
1404      * RuntimePermission#RuntimePermission(String)
1405      * <tt>RuntimePermission("getClassLoader")</tt>} permission to verify
1406      * access to the system class loader.  If not, a
1407      * <tt>SecurityException</tt> will be thrown.  </p>
1408      *
1409      * @return  The system <tt>ClassLoader</tt> for delegation, or
1410      *          <tt>null</tt> if none
1411      *
1412      * @throws  SecurityException
1413      *          If a security manager exists and its <tt>checkPermission</tt>
1414      *          method doesn't allow access to the system class loader.
1415      *
1416      * @throws  IllegalStateException
1417      *          If invoked recursively during the construction of the class
1418      *          loader specified by the "<tt>java.system.class.loader</tt>"
1419      *          property.
1420      *
1421      * @throws  Error
1422      *          If the system property "<tt>java.system.class.loader</tt>"
1423      *          is defined but the named class could not be loaded, the
1424      *          provider class does not define the required constructor, or an
1425      *          exception is thrown by that constructor when it is invoked. The
1426      *          underlying cause of the error can be retrieved via the
1427      *          {@link Throwable#getCause()} method.
1428      *
1429      * @revised  1.4
1430      */
1431     @CallerSensitive
1432     public static ClassLoader getSystemClassLoader() {
1433         initSystemClassLoader();
1434         if (scl == null) {
1435             return null;
1436         }
1437         SecurityManager sm = System.getSecurityManager();
1438         if (sm != null) {
1439             checkClassLoaderPermission(scl, Reflection.getCallerClass());
1440         }
1441         return scl;
1442     }
1443 
1444     private static synchronized void initSystemClassLoader() {
1445         if (!sclSet) {
1446             if (scl != null)
1447                 throw new IllegalStateException("recursive invocation");
1448             sun.misc.Launcher l = sun.misc.Launcher.getLauncher();
1449             if (l != null) {
1450                 Throwable oops = null;
1451                 scl = l.getClassLoader();
1452                 try {
1453                     scl = AccessController.doPrivileged(
1454                         new SystemClassLoaderAction(scl));
1455                 } catch (PrivilegedActionException pae) {
1456                     oops = pae.getCause();
1457                     if (oops instanceof InvocationTargetException) {
1458                         oops = oops.getCause();
1459                     }
1460                 }
1461                 if (oops != null) {
1462                     if (oops instanceof Error) {
1463                         throw (Error) oops;
1464                     } else {
1465                         // wrap the exception
1466                         throw new Error(oops);
1467                     }
1468                 }
1469             }
1470             sclSet = true;
1471         }
1472     }
1473 
1474     // Returns true if the specified class loader can be found in this class
1475     // loader's delegation chain.
1476     boolean isAncestor(ClassLoader cl) {
1477         ClassLoader acl = this;
1478         do {
1479             acl = acl.parent;
1480             if (cl == acl) {
1481                 return true;
1482             }
1483         } while (acl != null);
1484         return false;
1485     }
1486 
1487     // Tests if class loader access requires "getClassLoader" permission
1488     // check.  A class loader 'from' can access class loader 'to' if
1489     // class loader 'from' is same as class loader 'to' or an ancestor
1490     // of 'to'.  The class loader in a system domain can access
1491     // any class loader.
1492     private static boolean needsClassLoaderPermissionCheck(ClassLoader from,
1493                                                            ClassLoader to)
1494     {
1495         if (from == to)
1496             return false;
1497 
1498         if (from == null)
1499             return false;
1500 
1501         return !to.isAncestor(from);
1502     }
1503 
1504     // Returns the class's class loader, or null if none.
1505     static ClassLoader getClassLoader(Class<?> caller) {
1506         // This can be null if the VM is requesting it
1507         if (caller == null) {
1508             return null;
1509         }
1510         // Circumvent security check since this is package-private
1511         return caller.getClassLoader0();
1512     }
1513 
1514     /*
1515      * Checks RuntimePermission("getClassLoader") permission
1516      * if caller's class loader is not null and caller's class loader
1517      * is not the same as or an ancestor of the given cl argument.
1518      */
1519     static void checkClassLoaderPermission(ClassLoader cl, Class<?> caller) {
1520         SecurityManager sm = System.getSecurityManager();
1521         if (sm != null) {
1522             // caller can be null if the VM is requesting it
1523             ClassLoader ccl = getClassLoader(caller);
1524             if (needsClassLoaderPermissionCheck(ccl, cl)) {
1525                 sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
1526             }
1527         }
1528     }
1529 
1530     // The class loader for the system
1531     // @GuardedBy("ClassLoader.class")
1532     private static ClassLoader scl;
1533 
1534     // Set to true once the system class loader has been set
1535     // @GuardedBy("ClassLoader.class")
1536     private static boolean sclSet;
1537 
1538 
1539     // -- Package --
1540 
1541     /**
1542      * Defines a package by name in this <tt>ClassLoader</tt>.  This allows
1543      * class loaders to define the packages for their classes. Packages must
1544      * be created before the class is defined, and package names must be
1545      * unique within a class loader and cannot be redefined or changed once
1546      * created.
1547      *
1548      * @param  name
1549      *         The package name
1550      *
1551      * @param  specTitle
1552      *         The specification title
1553      *
1554      * @param  specVersion
1555      *         The specification version
1556      *
1557      * @param  specVendor
1558      *         The specification vendor
1559      *
1560      * @param  implTitle
1561      *         The implementation title
1562      *
1563      * @param  implVersion
1564      *         The implementation version
1565      *
1566      * @param  implVendor
1567      *         The implementation vendor
1568      *
1569      * @param  sealBase
1570      *         If not <tt>null</tt>, then this package is sealed with
1571      *         respect to the given code source {@link java.net.URL
1572      *         <tt>URL</tt>}  object.  Otherwise, the package is not sealed.
1573      *
1574      * @return  The newly defined <tt>Package</tt> object
1575      *
1576      * @throws  IllegalArgumentException
1577      *          If package name duplicates an existing package either in this
1578      *          class loader or one of its ancestors
1579      *
1580      * @since  1.2
1581      */
1582     protected Package definePackage(String name, String specTitle,
1583                                     String specVersion, String specVendor,
1584                                     String implTitle, String implVersion,
1585                                     String implVendor, URL sealBase)
1586         throws IllegalArgumentException
1587     {
1588         synchronized (packages) {
1589             Package pkg = getPackage(name);
1590             if (pkg != null) {
1591                 throw new IllegalArgumentException(name);
1592             }
1593             pkg = new Package(name, specTitle, specVersion, specVendor,
1594                               implTitle, implVersion, implVendor,
1595                               sealBase, this);
1596             packages.put(name, pkg);
1597             return pkg;
1598         }
1599     }
1600 
1601     /**
1602      * Returns a <tt>Package</tt> that has been defined by this class loader
1603      * or any of its ancestors.
1604      *
1605      * @param  name
1606      *         The package name
1607      *
1608      * @return  The <tt>Package</tt> corresponding to the given name, or
1609      *          <tt>null</tt> if not found
1610      *
1611      * @since  1.2
1612      */
1613     protected Package getPackage(String name) {
1614         Package pkg;
1615         synchronized (packages) {
1616             pkg = packages.get(name);
1617         }
1618         if (pkg == null) {
1619             if (parent != null) {
1620                 pkg = parent.getPackage(name);
1621             } else {
1622                 pkg = Package.getSystemPackage(name);
1623             }
1624             if (pkg != null) {
1625                 synchronized (packages) {
1626                     Package pkg2 = packages.get(name);
1627                     if (pkg2 == null) {
1628                         packages.put(name, pkg);
1629                     } else {
1630                         pkg = pkg2;
1631                     }
1632                 }
1633             }
1634         }
1635         return pkg;
1636     }
1637 
1638     /**
1639      * Returns all of the <tt>Packages</tt> defined by this class loader and
1640      * its ancestors.
1641      *
1642      * @return  The array of <tt>Package</tt> objects defined by this
1643      *          <tt>ClassLoader</tt>
1644      *
1645      * @since  1.2
1646      */
1647     protected Package[] getPackages() {
1648         Map<String, Package> map;
1649         synchronized (packages) {
1650             map = new HashMap<>(packages);
1651         }
1652         Package[] pkgs;
1653         if (parent != null) {
1654             pkgs = parent.getPackages();
1655         } else {
1656             pkgs = Package.getSystemPackages();
1657         }
1658         if (pkgs != null) {
1659             for (int i = 0; i < pkgs.length; i++) {
1660                 String pkgName = pkgs[i].getName();
1661                 if (map.get(pkgName) == null) {
1662                     map.put(pkgName, pkgs[i]);
1663                 }
1664             }
1665         }
1666         return map.values().toArray(new Package[map.size()]);
1667     }
1668 
1669 
1670     // -- Native library access --
1671 
1672     /**
1673      * Returns the absolute path name of a native library.  The VM invokes this
1674      * method to locate the native libraries that belong to classes loaded with
1675      * this class loader. If this method returns <tt>null</tt>, the VM
1676      * searches the library along the path specified as the
1677      * "<tt>java.library.path</tt>" property.
1678      *
1679      * @param  libname
1680      *         The library name
1681      *
1682      * @return  The absolute path of the native library
1683      *
1684      * @see  System#loadLibrary(String)
1685      * @see  System#mapLibraryName(String)
1686      *
1687      * @since  1.2
1688      */
1689     protected String findLibrary(String libname) {
1690         return null;
1691     }
1692 
1693     /**
1694      * The inner class NativeLibrary denotes a loaded native library instance.
1695      * Every classloader contains a vector of loaded native libraries in the
1696      * private field <tt>nativeLibraries</tt>.  The native libraries loaded
1697      * into the system are entered into the <tt>systemNativeLibraries</tt>
1698      * vector.
1699      *
1700      * <p> Every native library requires a particular version of JNI. This is
1701      * denoted by the private <tt>jniVersion</tt> field.  This field is set by
1702      * the VM when it loads the library, and used by the VM to pass the correct
1703      * version of JNI to the native methods.  </p>
1704      *
1705      * @see      ClassLoader
1706      * @since    1.2
1707      */
1708     static class NativeLibrary {
1709         // opaque handle to native library, used in native code.
1710         long handle;
1711         // the version of JNI environment the native library requires.
1712         private int jniVersion;
1713         // the class from which the library is loaded, also indicates
1714         // the loader this native library belongs.
1715         private final Class<?> fromClass;
1716         // the canonicalized name of the native library.
1717         // or static library name
1718         String name;
1719         // Indicates if the native library is linked into the VM
1720         boolean isBuiltin;
1721         // Indicates if the native library is loaded
1722         boolean loaded;
1723         native void load(String name, boolean isBuiltin);
1724 
1725         native long find(String name);
1726         native void unload(String name, boolean isBuiltin);
1727         static native String findBuiltinLib(String name);
1728 
1729         public NativeLibrary(Class<?> fromClass, String name, boolean isBuiltin) {
1730             this.name = name;
1731             this.fromClass = fromClass;
1732             this.isBuiltin = isBuiltin;
1733         }
1734 
1735         protected void finalize() {
1736             synchronized (loadedLibraryNames) {
1737                 if (fromClass.getClassLoader() != null && loaded) {
1738                     /* remove the native library name */
1739                     int size = loadedLibraryNames.size();
1740                     for (int i = 0; i < size; i++) {
1741                         if (name.equals(loadedLibraryNames.elementAt(i))) {
1742                             loadedLibraryNames.removeElementAt(i);
1743                             break;
1744                         }
1745                     }
1746                     /* unload the library. */
1747                     ClassLoader.nativeLibraryContext.push(this);
1748                     try {
1749                         unload(name, isBuiltin);
1750                     } finally {
1751                         ClassLoader.nativeLibraryContext.pop();
1752                     }
1753                 }
1754             }
1755         }
1756         // Invoked in the VM to determine the context class in
1757         // JNI_Load/JNI_Unload
1758         static Class<?> getFromClass() {
1759             return ClassLoader.nativeLibraryContext.peek().fromClass;
1760         }
1761     }
1762 
1763     // All native library names we've loaded.
1764     private static Vector<String> loadedLibraryNames = new Vector<>();
1765 
1766     // Native libraries belonging to system classes.
1767     private static Vector<NativeLibrary> systemNativeLibraries
1768         = new Vector<>();
1769 
1770     // Native libraries associated with the class loader.
1771     private Vector<NativeLibrary> nativeLibraries = new Vector<>();
1772 
1773     // native libraries being loaded/unloaded.
1774     private static Stack<NativeLibrary> nativeLibraryContext = new Stack<>();
1775 
1776     // The paths searched for libraries
1777     private static String usr_paths[];
1778     private static String sys_paths[];
1779 
1780     private static String[] initializePath(String propname) {
1781         String ldpath = System.getProperty(propname, "");
1782         String ps = File.pathSeparator;
1783         int ldlen = ldpath.length();
1784         int i, j, n;
1785         // Count the separators in the path
1786         i = ldpath.indexOf(ps);
1787         n = 0;
1788         while (i >= 0) {
1789             n++;
1790             i = ldpath.indexOf(ps, i + 1);
1791         }
1792 
1793         // allocate the array of paths - n :'s = n + 1 path elements
1794         String[] paths = new String[n + 1];
1795 
1796         // Fill the array with paths from the ldpath
1797         n = i = 0;
1798         j = ldpath.indexOf(ps);
1799         while (j >= 0) {
1800             if (j - i > 0) {
1801                 paths[n++] = ldpath.substring(i, j);
1802             } else if (j - i == 0) {
1803                 paths[n++] = ".";
1804             }
1805             i = j + 1;
1806             j = ldpath.indexOf(ps, i);
1807         }
1808         paths[n] = ldpath.substring(i, ldlen);
1809         return paths;
1810     }
1811 
1812     // Invoked in the java.lang.Runtime class to implement load and loadLibrary.
1813     static void loadLibrary(Class<?> fromClass, String name,
1814                             boolean isAbsolute) {
1815         ClassLoader loader =
1816             (fromClass == null) ? null : fromClass.getClassLoader();
1817         if (sys_paths == null) {
1818             usr_paths = initializePath("java.library.path");
1819             sys_paths = initializePath("sun.boot.library.path");
1820         }
1821         if (isAbsolute) {
1822             if (loadLibrary0(fromClass, new File(name))) {
1823                 return;
1824             }
1825             throw new UnsatisfiedLinkError("Can't load library: " + name);
1826         }
1827         if (loader != null) {
1828             String libfilename = loader.findLibrary(name);
1829             if (libfilename != null) {
1830                 File libfile = new File(libfilename);
1831                 if (!libfile.isAbsolute()) {
1832                     throw new UnsatisfiedLinkError(
1833     "ClassLoader.findLibrary failed to return an absolute path: " + libfilename);
1834                 }
1835                 if (loadLibrary0(fromClass, libfile)) {
1836                     return;
1837                 }
1838                 throw new UnsatisfiedLinkError("Can't load " + libfilename);
1839             }
1840         }
1841         for (int i = 0 ; i < sys_paths.length ; i++) {
1842             File libfile = new File(sys_paths[i], System.mapLibraryName(name));
1843             if (loadLibrary0(fromClass, libfile)) {
1844                 return;
1845             }
1846             libfile = ClassLoaderHelper.mapAlternativeName(libfile);
1847             if (libfile != null && loadLibrary0(fromClass, libfile)) {
1848                 return;
1849             }
1850         }
1851         if (loader != null) {
1852             for (int i = 0 ; i < usr_paths.length ; i++) {
1853                 File libfile = new File(usr_paths[i],
1854                                         System.mapLibraryName(name));
1855                 if (loadLibrary0(fromClass, libfile)) {
1856                     return;
1857                 }
1858                 libfile = ClassLoaderHelper.mapAlternativeName(libfile);
1859                 if (libfile != null && loadLibrary0(fromClass, libfile)) {
1860                     return;
1861                 }
1862             }
1863         }
1864         // Oops, it failed
1865         throw new UnsatisfiedLinkError("no " + name + " in java.library.path");
1866     }
1867 
1868     private static boolean loadLibrary0(Class<?> fromClass, final File file) {
1869         // Check to see if we're attempting to access a static library
1870         String name = NativeLibrary.findBuiltinLib(file.getName());
1871         boolean isBuiltin = (name != null);
1872         if (!isBuiltin) {
1873             boolean exists = AccessController.doPrivileged(
1874                 new PrivilegedAction<Object>() {
1875                     public Object run() {
1876                         return file.exists() ? Boolean.TRUE : null;
1877                     }})
1878                 != null;
1879             if (!exists) {
1880                 return false;
1881             }
1882             try {
1883                 name = file.getCanonicalPath();
1884             } catch (IOException e) {
1885                 return false;
1886             }
1887         }
1888         ClassLoader loader =
1889             (fromClass == null) ? null : fromClass.getClassLoader();
1890         Vector<NativeLibrary> libs =
1891             loader != null ? loader.nativeLibraries : systemNativeLibraries;
1892         synchronized (libs) {
1893             int size = libs.size();
1894             for (int i = 0; i < size; i++) {
1895                 NativeLibrary lib = libs.elementAt(i);
1896                 if (name.equals(lib.name)) {
1897                     return true;
1898                 }
1899             }
1900 
1901             synchronized (loadedLibraryNames) {
1902                 if (loadedLibraryNames.contains(name)) {
1903                     throw new UnsatisfiedLinkError
1904                         ("Native Library " +
1905                          name +
1906                          " already loaded in another classloader");
1907                 }
1908                 /* If the library is being loaded (must be by the same thread,
1909                  * because Runtime.load and Runtime.loadLibrary are
1910                  * synchronous). The reason is can occur is that the JNI_OnLoad
1911                  * function can cause another loadLibrary invocation.
1912                  *
1913                  * Thus we can use a static stack to hold the list of libraries
1914                  * we are loading.
1915                  *
1916                  * If there is a pending load operation for the library, we
1917                  * immediately return success; otherwise, we raise
1918                  * UnsatisfiedLinkError.
1919                  */
1920                 int n = nativeLibraryContext.size();
1921                 for (int i = 0; i < n; i++) {
1922                     NativeLibrary lib = nativeLibraryContext.elementAt(i);
1923                     if (name.equals(lib.name)) {
1924                         if (loader == lib.fromClass.getClassLoader()) {
1925                             return true;
1926                         } else {
1927                             throw new UnsatisfiedLinkError
1928                                 ("Native Library " +
1929                                  name +
1930                                  " is being loaded in another classloader");
1931                         }
1932                     }
1933                 }
1934                 NativeLibrary lib = new NativeLibrary(fromClass, name, isBuiltin);
1935                 nativeLibraryContext.push(lib);
1936                 try {
1937                     lib.load(name, isBuiltin);
1938                 } finally {
1939                     nativeLibraryContext.pop();
1940                 }
1941                 if (lib.loaded) {
1942                     loadedLibraryNames.addElement(name);
1943                     libs.addElement(lib);
1944                     return true;
1945                 }
1946                 return false;
1947             }
1948         }
1949     }
1950 
1951     // Invoked in the VM class linking code.
1952     static long findNative(ClassLoader loader, String name) {
1953         Vector<NativeLibrary> libs =
1954             loader != null ? loader.nativeLibraries : systemNativeLibraries;
1955         synchronized (libs) {
1956             int size = libs.size();
1957             for (int i = 0; i < size; i++) {
1958                 NativeLibrary lib = libs.elementAt(i);
1959                 long entry = lib.find(name);
1960                 if (entry != 0)
1961                     return entry;
1962             }
1963         }
1964         return 0;
1965     }
1966 
1967 
1968     // -- Assertion management --
1969 
1970     final Object assertionLock;
1971 
1972     // The default toggle for assertion checking.
1973     // @GuardedBy("assertionLock")
1974     private boolean defaultAssertionStatus = false;
1975 
1976     // Maps String packageName to Boolean package default assertion status Note
1977     // that the default package is placed under a null map key.  If this field
1978     // is null then we are delegating assertion status queries to the VM, i.e.,
1979     // none of this ClassLoader's assertion status modification methods have
1980     // been invoked.
1981     // @GuardedBy("assertionLock")
1982     private Map<String, Boolean> packageAssertionStatus = null;
1983 
1984     // Maps String fullyQualifiedClassName to Boolean assertionStatus If this
1985     // field is null then we are delegating assertion status queries to the VM,
1986     // i.e., none of this ClassLoader's assertion status modification methods
1987     // have been invoked.
1988     // @GuardedBy("assertionLock")
1989     Map<String, Boolean> classAssertionStatus = null;
1990 
1991     /**
1992      * Sets the default assertion status for this class loader.  This setting
1993      * determines whether classes loaded by this class loader and initialized
1994      * in the future will have assertions enabled or disabled by default.
1995      * This setting may be overridden on a per-package or per-class basis by
1996      * invoking {@link #setPackageAssertionStatus(String, boolean)} or {@link
1997      * #setClassAssertionStatus(String, boolean)}.
1998      *
1999      * @param  enabled
2000      *         <tt>true</tt> if classes loaded by this class loader will
2001      *         henceforth have assertions enabled by default, <tt>false</tt>
2002      *         if they will have assertions disabled by default.
2003      *
2004      * @since  1.4
2005      */
2006     public void setDefaultAssertionStatus(boolean enabled) {
2007         synchronized (assertionLock) {
2008             if (classAssertionStatus == null)
2009                 initializeJavaAssertionMaps();
2010 
2011             defaultAssertionStatus = enabled;
2012         }
2013     }
2014 
2015     /**
2016      * Sets the package default assertion status for the named package.  The
2017      * package default assertion status determines the assertion status for
2018      * classes initialized in the future that belong to the named package or
2019      * any of its "subpackages".
2020      *
2021      * <p> A subpackage of a package named p is any package whose name begins
2022      * with "<tt>p.</tt>".  For example, <tt>javax.swing.text</tt> is a
2023      * subpackage of <tt>javax.swing</tt>, and both <tt>java.util</tt> and
2024      * <tt>java.lang.reflect</tt> are subpackages of <tt>java</tt>.
2025      *
2026      * <p> In the event that multiple package defaults apply to a given class,
2027      * the package default pertaining to the most specific package takes
2028      * precedence over the others.  For example, if <tt>javax.lang</tt> and
2029      * <tt>javax.lang.reflect</tt> both have package defaults associated with
2030      * them, the latter package default applies to classes in
2031      * <tt>javax.lang.reflect</tt>.
2032      *
2033      * <p> Package defaults take precedence over the class loader's default
2034      * assertion status, and may be overridden on a per-class basis by invoking
2035      * {@link #setClassAssertionStatus(String, boolean)}.  </p>
2036      *
2037      * @param  packageName
2038      *         The name of the package whose package default assertion status
2039      *         is to be set. A <tt>null</tt> value indicates the unnamed
2040      *         package that is "current"
2041      *         (see section 7.4.2 of
2042      *         <cite>The Java&trade; Language Specification</cite>.)
2043      *
2044      * @param  enabled
2045      *         <tt>true</tt> if classes loaded by this classloader and
2046      *         belonging to the named package or any of its subpackages will
2047      *         have assertions enabled by default, <tt>false</tt> if they will
2048      *         have assertions disabled by default.
2049      *
2050      * @since  1.4
2051      */
2052     public void setPackageAssertionStatus(String packageName,
2053                                           boolean enabled) {
2054         synchronized (assertionLock) {
2055             if (packageAssertionStatus == null)
2056                 initializeJavaAssertionMaps();
2057 
2058             packageAssertionStatus.put(packageName, enabled);
2059         }
2060     }
2061 
2062     /**
2063      * Sets the desired assertion status for the named top-level class in this
2064      * class loader and any nested classes contained therein.  This setting
2065      * takes precedence over the class loader's default assertion status, and
2066      * over any applicable per-package default.  This method has no effect if
2067      * the named class has already been initialized.  (Once a class is
2068      * initialized, its assertion status cannot change.)
2069      *
2070      * <p> If the named class is not a top-level class, this invocation will
2071      * have no effect on the actual assertion status of any class. </p>
2072      *
2073      * @param  className
2074      *         The fully qualified class name of the top-level class whose
2075      *         assertion status is to be set.
2076      *
2077      * @param  enabled
2078      *         <tt>true</tt> if the named class is to have assertions
2079      *         enabled when (and if) it is initialized, <tt>false</tt> if the
2080      *         class is to have assertions disabled.
2081      *
2082      * @since  1.4
2083      */
2084     public void setClassAssertionStatus(String className, boolean enabled) {
2085         synchronized (assertionLock) {
2086             if (classAssertionStatus == null)
2087                 initializeJavaAssertionMaps();
2088 
2089             classAssertionStatus.put(className, enabled);
2090         }
2091     }
2092 
2093     /**
2094      * Sets the default assertion status for this class loader to
2095      * <tt>false</tt> and discards any package defaults or class assertion
2096      * status settings associated with the class loader.  This method is
2097      * provided so that class loaders can be made to ignore any command line or
2098      * persistent assertion status settings and "start with a clean slate."
2099      *
2100      * @since  1.4
2101      */
2102     public void clearAssertionStatus() {
2103         /*
2104          * Whether or not "Java assertion maps" are initialized, set
2105          * them to empty maps, effectively ignoring any present settings.
2106          */
2107         synchronized (assertionLock) {
2108             classAssertionStatus = new HashMap<>();
2109             packageAssertionStatus = new HashMap<>();
2110             defaultAssertionStatus = false;
2111         }
2112     }
2113 
2114     /**
2115      * Returns the assertion status that would be assigned to the specified
2116      * class if it were to be initialized at the time this method is invoked.
2117      * If the named class has had its assertion status set, the most recent
2118      * setting will be returned; otherwise, if any package default assertion
2119      * status pertains to this class, the most recent setting for the most
2120      * specific pertinent package default assertion status is returned;
2121      * otherwise, this class loader's default assertion status is returned.
2122      * </p>
2123      *
2124      * @param  className
2125      *         The fully qualified class name of the class whose desired
2126      *         assertion status is being queried.
2127      *
2128      * @return  The desired assertion status of the specified class.
2129      *
2130      * @see  #setClassAssertionStatus(String, boolean)
2131      * @see  #setPackageAssertionStatus(String, boolean)
2132      * @see  #setDefaultAssertionStatus(boolean)
2133      *
2134      * @since  1.4
2135      */
2136     boolean desiredAssertionStatus(String className) {
2137         synchronized (assertionLock) {
2138             // assert classAssertionStatus   != null;
2139             // assert packageAssertionStatus != null;
2140 
2141             // Check for a class entry
2142             Boolean result = classAssertionStatus.get(className);
2143             if (result != null)
2144                 return result.booleanValue();
2145 
2146             // Check for most specific package entry
2147             int dotIndex = className.lastIndexOf(".");
2148             if (dotIndex < 0) { // default package
2149                 result = packageAssertionStatus.get(null);
2150                 if (result != null)
2151                     return result.booleanValue();
2152             }
2153             while(dotIndex > 0) {
2154                 className = className.substring(0, dotIndex);
2155                 result = packageAssertionStatus.get(className);
2156                 if (result != null)
2157                     return result.booleanValue();
2158                 dotIndex = className.lastIndexOf(".", dotIndex-1);
2159             }
2160 
2161             // Return the classloader default
2162             return defaultAssertionStatus;
2163         }
2164     }
2165 
2166     // Set up the assertions with information provided by the VM.
2167     // Note: Should only be called inside a synchronized block
2168     private void initializeJavaAssertionMaps() {
2169         // assert Thread.holdsLock(assertionLock);
2170 
2171         classAssertionStatus = new HashMap<>();
2172         packageAssertionStatus = new HashMap<>();
2173         AssertionStatusDirectives directives = retrieveDirectives();
2174 
2175         for(int i = 0; i < directives.classes.length; i++)
2176             classAssertionStatus.put(directives.classes[i],
2177                                      directives.classEnabled[i]);
2178 
2179         for(int i = 0; i < directives.packages.length; i++)
2180             packageAssertionStatus.put(directives.packages[i],
2181                                        directives.packageEnabled[i]);
2182 
2183         defaultAssertionStatus = directives.deflt;
2184     }
2185 
2186     // Retrieves the assertion directives from the VM.
2187     private static native AssertionStatusDirectives retrieveDirectives();
2188 }
2189 
2190 
2191 class SystemClassLoaderAction
2192     implements PrivilegedExceptionAction<ClassLoader> {
2193     private ClassLoader parent;
2194 
2195     SystemClassLoaderAction(ClassLoader parent) {
2196         this.parent = parent;
2197     }
2198 
2199     public ClassLoader run() throws Exception {
2200         String cls = System.getProperty("java.system.class.loader");
2201         if (cls == null) {
2202             return parent;
2203         }
2204 
2205         Constructor<?> ctor = Class.forName(cls, true, parent)
2206             .getDeclaredConstructor(new Class<?>[] { ClassLoader.class });
2207         ClassLoader sys = (ClassLoader) ctor.newInstance(
2208             new Object[] { parent });
2209         Thread.currentThread().setContextClassLoader(sys);
2210         return sys;
2211     }
2212 }