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    1   /*
    2    * Copyright (c) 1994, 2011, Oracle and/or its affiliates. All rights reserved.
    3    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
    4    *
    5    * This code is free software; you can redistribute it and/or modify it
    6    * under the terms of the GNU General Public License version 2 only, as
    7    * published by the Free Software Foundation.  Oracle designates this
    8    * particular file as subject to the "Classpath" exception as provided
    9    * by Oracle in the LICENSE file that accompanied this code.
   10    *
   11    * This code is distributed in the hope that it will be useful, but WITHOUT
   12    * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   13    * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   14    * version 2 for more details (a copy is included in the LICENSE file that
   15    * accompanied this code).
   16    *
   17    * You should have received a copy of the GNU General Public License version
   18    * 2 along with this work; if not, write to the Free Software Foundation,
   19    * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   20    *
   21    * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   22    * or visit www.oracle.com if you need additional information or have any
   23    * questions.
   24    */
   25   package java.lang;
   26   
   27   import java.io.InputStream;
   28   import java.io.IOException;
   29   import java.io.File;
   30   import java.lang.reflect.Constructor;
   31   import java.lang.reflect.InvocationTargetException;
   32   import java.net.MalformedURLException;
   33   import java.net.URL;
   34   import java.security.AccessController;
   35   import java.security.AccessControlContext;
   36   import java.security.CodeSource;
   37   import java.security.Policy;
   38   import java.security.PrivilegedAction;
   39   import java.security.PrivilegedActionException;
   40   import java.security.PrivilegedExceptionAction;
   41   import java.security.ProtectionDomain;
   42   import java.security.cert.Certificate;
   43   import java.util.Collections;
   44   import java.util.Enumeration;
   45   import java.util.HashMap;
   46   import java.util.HashSet;
   47   import java.util.Set;
   48   import java.util.Stack;
   49   import java.util.Map;
   50   import java.util.Vector;
   51   import java.util.Hashtable;
   52   import java.util.WeakHashMap;
   53   import java.util.concurrent.ConcurrentHashMap;
   54   import sun.misc.ClassFileTransformer;
   55   import sun.misc.CompoundEnumeration;
   56   import sun.misc.Resource;
   57   import sun.misc.URLClassPath;
   58   import sun.misc.VM;
   59   import sun.reflect.Reflection;
   60   import sun.security.util.SecurityConstants;
   61   
   62   /**
   63    * A class loader is an object that is responsible for loading classes. The
   64    * class <tt>ClassLoader</tt> is an abstract class.  Given the <a
   65    * href="#name">binary name</a> of a class, a class loader should attempt to
   66    * locate or generate data that constitutes a definition for the class.  A
   67    * typical strategy is to transform the name into a file name and then read a
   68    * "class file" of that name from a file system.
   69    *
   70    * <p> Every {@link Class <tt>Class</tt>} object contains a {@link
   71    * Class#getClassLoader() reference} to the <tt>ClassLoader</tt> that defined
   72    * it.
   73    *
   74    * <p> <tt>Class</tt> objects for array classes are not created by class
   75    * loaders, but are created automatically as required by the Java runtime.
   76    * The class loader for an array class, as returned by {@link
   77    * Class#getClassLoader()} is the same as the class loader for its element
   78    * type; if the element type is a primitive type, then the array class has no
   79    * class loader.
   80    *
   81    * <p> Applications implement subclasses of <tt>ClassLoader</tt> in order to
   82    * extend the manner in which the Java virtual machine dynamically loads
   83    * classes.
   84    *
   85    * <p> Class loaders may typically be used by security managers to indicate
   86    * security domains.
   87    *
   88    * <p> The <tt>ClassLoader</tt> class uses a delegation model to search for
   89    * classes and resources.  Each instance of <tt>ClassLoader</tt> has an
   90    * associated parent class loader.  When requested to find a class or
   91    * resource, a <tt>ClassLoader</tt> instance will delegate the search for the
   92    * class or resource to its parent class loader before attempting to find the
   93    * class or resource itself.  The virtual machine's built-in class loader,
   94    * called the "bootstrap class loader", does not itself have a parent but may
   95    * serve as the parent of a <tt>ClassLoader</tt> instance.
   96    *
   97    * <p> Class loaders that support concurrent loading of classes are known as
   98    * <em>parallel capable</em> class loaders and are required to register
   99    * themselves at their class initialization time by invoking the
  100    * {@link
  101    * #registerAsParallelCapable <tt>ClassLoader.registerAsParallelCapable</tt>}
  102    * method. Note that the <tt>ClassLoader</tt> class is registered as parallel
  103    * capable by default. However, its subclasses still need to register themselves
  104    * if they are parallel capable. <br>
  105    * In environments in which the delegation model is not strictly
  106    * hierarchical, class loaders need to be parallel capable, otherwise class
  107    * loading can lead to deadlocks because the loader lock is held for the
  108    * duration of the class loading process (see {@link #loadClass
  109    * <tt>loadClass</tt>} methods).
  110    *
  111    * <p> Normally, the Java virtual machine loads classes from the local file
  112    * system in a platform-dependent manner.  For example, on UNIX systems, the
  113    * virtual machine loads classes from the directory defined by the
  114    * <tt>CLASSPATH</tt> environment variable.
  115    *
  116    * <p> However, some classes may not originate from a file; they may originate
  117    * from other sources, such as the network, or they could be constructed by an
  118    * application.  The method {@link #defineClass(String, byte[], int, int)
  119    * <tt>defineClass</tt>} converts an array of bytes into an instance of class
  120    * <tt>Class</tt>. Instances of this newly defined class can be created using
  121    * {@link Class#newInstance <tt>Class.newInstance</tt>}.
  122    *
  123    * <p> The methods and constructors of objects created by a class loader may
  124    * reference other classes.  To determine the class(es) referred to, the Java
  125    * virtual machine invokes the {@link #loadClass <tt>loadClass</tt>} method of
  126    * the class loader that originally created the class.
  127    *
  128    * <p> For example, an application could create a network class loader to
  129    * download class files from a server.  Sample code might look like:
  130    *
  131    * <blockquote><pre>
  132    *   ClassLoader loader&nbsp;= new NetworkClassLoader(host,&nbsp;port);
  133    *   Object main&nbsp;= loader.loadClass("Main", true).newInstance();
  134    *       &nbsp;.&nbsp;.&nbsp;.
  135    * </pre></blockquote>
  136    *
  137    * <p> The network class loader subclass must define the methods {@link
  138    * #findClass <tt>findClass</tt>} and <tt>loadClassData</tt> to load a class
  139    * from the network.  Once it has downloaded the bytes that make up the class,
  140    * it should use the method {@link #defineClass <tt>defineClass</tt>} to
  141    * create a class instance.  A sample implementation is:
  142    *
  143    * <blockquote><pre>
  144    *     class NetworkClassLoader extends ClassLoader {
  145    *         String host;
  146    *         int port;
  147    *
  148    *         public Class findClass(String name) {
  149    *             byte[] b = loadClassData(name);
  150    *             return defineClass(name, b, 0, b.length);
  151    *         }
  152    *
  153    *         private byte[] loadClassData(String name) {
  154    *             // load the class data from the connection
  155    *             &nbsp;.&nbsp;.&nbsp;.
  156    *         }
  157    *     }
  158    * </pre></blockquote>
  159    *
  160    * <h4> <a name="name">Binary names</a> </h4>
  161    *
  162    * <p> Any class name provided as a {@link String} parameter to methods in
  163    * <tt>ClassLoader</tt> must be a binary name as defined by
  164    * <cite>The Java&trade; Language Specification</cite>.
  165    *
  166    * <p> Examples of valid class names include:
  167    * <blockquote><pre>
  168    *   "java.lang.String"
  169    *   "javax.swing.JSpinner$DefaultEditor"
  170    *   "java.security.KeyStore$Builder$FileBuilder$1"
  171    *   "java.net.URLClassLoader$3$1"
  172    * </pre></blockquote>
  173    *
  174    * @see      #resolveClass(Class)
  175    * @since 1.0
  176    */
  177   public abstract class ClassLoader {
  178   
  179       private static native void registerNatives();
  180       static {
  181           registerNatives();
  182       }
  183   
  184       // The parent class loader for delegation
  185       // Note: VM hardcoded the offset of this field, thus all new fields
  186       // must be added *after* it.
  187       private final ClassLoader parent;
  188   
  189       /**
  190        * Encapsulates the set of parallel capable loader types.
  191        */
  192       private static class ParallelLoaders {
  193           private ParallelLoaders() {}
  194   
  195           // the set of parallel capable loader types
  196           private static final Set<Class<? extends ClassLoader>> loaderTypes =
  197               Collections.newSetFromMap(
  198                   new WeakHashMap<Class<? extends ClassLoader>, Boolean>());
  199           static {
  200               synchronized (loaderTypes) { loaderTypes.add(ClassLoader.class); }
  201           }
  202   
  203           /**
  204            * Registers the given class loader type as parallel capabale.
  205            * Returns {@code true} is successfully registered; {@code false} if
  206            * loader's super class is not registered.
  207            */
  208           static boolean register(Class<? extends ClassLoader> c) {
  209               synchronized (loaderTypes) {
  210                   if (loaderTypes.contains(c.getSuperclass())) {
  211                       // register the class loader as parallel capable
  212                       // if and only if all of its super classes are.
  213                       // Note: given current classloading sequence, if
  214                       // the immediate super class is parallel capable,
  215                       // all the super classes higher up must be too.
  216                       loaderTypes.add(c);
  217                       return true;
  218                   } else {
  219                       return false;
  220                   }
  221               }
  222           }
  223   
  224           /**
  225            * Returns {@code true} if the given class loader type is
  226            * registered as parallel capable.
  227            */
  228           static boolean isRegistered(Class<? extends ClassLoader> c) {
  229               synchronized (loaderTypes) {
  230                   return loaderTypes.contains(c);
  231               }
  232           }
  233       }
  234   
  235       // Maps class name to the corresponding lock object when the current
  236       // class loader is parallel capable.
  237       // Note: VM also uses this field to decide if the current class loader
  238       // is parallel capable and the appropriate lock object for class loading.
  239       private final ConcurrentHashMap<String, Object> parallelLockMap;
  240   
  241       // Hashtable that maps packages to certs
  242       private final Map <String, Certificate[]> package2certs;
  243   
  244       // Shared among all packages with unsigned classes
  245       private static final Certificate[] nocerts = new Certificate[0];
  246   
  247       // The classes loaded by this class loader. The only purpose of this table
  248       // is to keep the classes from being GC'ed until the loader is GC'ed.
  249       private final Vector<Class<?>> classes = new Vector<>();
  250   
  251       // The "default" domain. Set as the default ProtectionDomain on newly
  252       // created classes.
  253       private final ProtectionDomain defaultDomain =
  254           new ProtectionDomain(new CodeSource(null, (Certificate[]) null),
  255                                null, this, null);
  256   
  257       // The initiating protection domains for all classes loaded by this loader
  258       private final Set<ProtectionDomain> domains;
  259   
  260       // Invoked by the VM to record every loaded class with this loader.
  261       void addClass(Class c) {
  262           classes.addElement(c);
  263       }
  264   
  265       // The packages defined in this class loader.  Each package name is mapped
  266       // to its corresponding Package object.
  267       // @GuardedBy("itself")
  268       private final HashMap<String, Package> packages = new HashMap<>();
  269   
  270       private static Void checkCreateClassLoader() {
  271           SecurityManager security = System.getSecurityManager();
  272           if (security != null) {
  273               security.checkCreateClassLoader();
  274           }
  275           return null;
  276       }
  277   
  278       private ClassLoader(Void unused, ClassLoader parent) {
  279           this.parent = parent;
  280           if (ParallelLoaders.isRegistered(this.getClass())) {
  281               parallelLockMap = new ConcurrentHashMap<>();
  282               package2certs = new ConcurrentHashMap<>();
  283               domains =
  284                   Collections.synchronizedSet(new HashSet<ProtectionDomain>());
  285               assertionLock = new Object();
  286           } else {
  287               // no finer-grained lock; lock on the classloader instance
  288               parallelLockMap = null;
  289               package2certs = new Hashtable<>();
  290               domains = new HashSet<>();
  291               assertionLock = this;
  292           }
  293       }
  294   
  295       /**
  296        * Creates a new class loader using the specified parent class loader for
  297        * delegation.
  298        *
  299        * <p> If there is a security manager, its {@link
  300        * SecurityManager#checkCreateClassLoader()
  301        * <tt>checkCreateClassLoader</tt>} method is invoked.  This may result in
  302        * a security exception.  </p>
  303        *
  304        * @param  parent
  305        *         The parent class loader
  306        *
  307        * @throws  SecurityException
  308        *          If a security manager exists and its
  309        *          <tt>checkCreateClassLoader</tt> method doesn't allow creation
  310        *          of a new class loader.
  311        *
  312        * @since  1.2
  313        */
  314       protected ClassLoader(ClassLoader parent) {
  315           this(checkCreateClassLoader(), parent);
  316       }
  317   
  318       /**
  319        * Creates a new class loader using the <tt>ClassLoader</tt> returned by
  320        * the method {@link #getSystemClassLoader()
  321        * <tt>getSystemClassLoader()</tt>} as the parent class loader.
  322        *
  323        * <p> If there is a security manager, its {@link
  324        * SecurityManager#checkCreateClassLoader()
  325        * <tt>checkCreateClassLoader</tt>} method is invoked.  This may result in
  326        * a security exception.  </p>
  327        *
  328        * @throws  SecurityException
  329        *          If a security manager exists and its
  330        *          <tt>checkCreateClassLoader</tt> method doesn't allow creation
  331        *          of a new class loader.
  332        */
  333       protected ClassLoader() {
  334           this(checkCreateClassLoader(), getSystemClassLoader());
  335       }
  336   
  337       // -- Class --
  338   
  339       /**
  340        * Loads the class with the specified <a href="#name">binary name</a>.
  341        * This method searches for classes in the same manner as the {@link
  342        * #loadClass(String, boolean)} method.  It is invoked by the Java virtual
  343        * machine to resolve class references.  Invoking this method is equivalent
  344        * to invoking {@link #loadClass(String, boolean) <tt>loadClass(name,
  345        * false)</tt>}.  </p>
  346        *
  347        * @param  name
  348        *         The <a href="#name">binary name</a> of the class
  349        *
  350        * @return  The resulting <tt>Class</tt> object
  351        *
  352        * @throws  ClassNotFoundException
  353        *          If the class was not found
  354        */
  355       public Class<?> loadClass(String name) throws ClassNotFoundException {
  356           return loadClass(name, false);
  357       }
  358   
  359       /**
  360        * Loads the class with the specified <a href="#name">binary name</a>.  The
  361        * default implementation of this method searches for classes in the
  362        * following order:
  363        *
  364        * <p><ol>
  365        *
  366        *   <li><p> Invoke {@link #findLoadedClass(String)} to check if the class
  367        *   has already been loaded.  </p></li>
  368        *
  369        *   <li><p> Invoke the {@link #loadClass(String) <tt>loadClass</tt>} method
  370        *   on the parent class loader.  If the parent is <tt>null</tt> the class
  371        *   loader built-in to the virtual machine is used, instead.  </p></li>
  372        *
  373        *   <li><p> Invoke the {@link #findClass(String)} method to find the
  374        *   class.  </p></li>
  375        *
  376        * </ol>
  377        *
  378        * <p> If the class was found using the above steps, and the
  379        * <tt>resolve</tt> flag is true, this method will then invoke the {@link
  380        * #resolveClass(Class)} method on the resulting <tt>Class</tt> object.
  381        *
  382        * <p> Subclasses of <tt>ClassLoader</tt> are encouraged to override {@link
  383        * #findClass(String)}, rather than this method.  </p>
  384        *
  385        * <p> Unless overridden, this method synchronizes on the result of
  386        * {@link #getClassLoadingLock <tt>getClassLoadingLock</tt>} method
  387        * during the entire class loading process.
  388        *
  389        * @param  name
  390        *         The <a href="#name">binary name</a> of the class
  391        *
  392        * @param  resolve
  393        *         If <tt>true</tt> then resolve the class
  394        *
  395        * @return  The resulting <tt>Class</tt> object
  396        *
  397        * @throws  ClassNotFoundException
  398        *          If the class could not be found
  399        */
  400       protected Class<?> loadClass(String name, boolean resolve)
  401           throws ClassNotFoundException
  402       {
  403           synchronized (getClassLoadingLock(name)) {
  404               // First, check if the class has already been loaded
  405               Class c = findLoadedClass(name);
  406               if (c == null) {
  407                   long t0 = System.nanoTime();
  408                   try {
  409                       if (parent != null) {
  410                           c = parent.loadClass(name, false);
  411                       } else {
  412                           c = findBootstrapClassOrNull(name);
  413                       }
  414                   } catch (ClassNotFoundException e) {
  415                       // ClassNotFoundException thrown if class not found
  416                       // from the non-null parent class loader
  417                   }
  418   
  419                   if (c == null) {
  420                       // If still not found, then invoke findClass in order
  421                       // to find the class.
  422                       long t1 = System.nanoTime();
  423                       c = findClass(name);
  424   
  425                       // this is the defining class loader; record the stats
  426                       sun.misc.PerfCounter.getParentDelegationTime().addTime(t1 - t0);
  427                       sun.misc.PerfCounter.getFindClassTime().addElapsedTimeFrom(t1);
  428                       sun.misc.PerfCounter.getFindClasses().increment();
  429                   }
  430               }
  431               if (resolve) {
  432                   resolveClass(c);
  433               }
  434               return c;
  435           }
  436       }
  437   
  438       /**
  439        * Returns the lock object for class loading operations.
  440        * For backward compatibility, the default implementation of this method
  441        * behaves as follows. If this ClassLoader object is registered as
  442        * parallel capable, the method returns a dedicated object associated
  443        * with the specified class name. Otherwise, the method returns this
  444        * ClassLoader object. </p>
  445        *
  446        * @param  className
  447        *         The name of the to-be-loaded class
  448        *
  449        * @return the lock for class loading operations
  450        *
  451        * @throws NullPointerException
  452        *         If registered as parallel capable and <tt>className</tt> is null
  453        *
  454        * @see #loadClass(String, boolean)
  455        *
  456        * @since  1.7
  457        */
  458       protected Object getClassLoadingLock(String className) {
  459           Object lock = this;
  460           if (parallelLockMap != null) {
  461               Object newLock = new Object();
  462               lock = parallelLockMap.putIfAbsent(className, newLock);
  463               if (lock == null) {
  464                   lock = newLock;
  465               }
  466           }
  467           return lock;
  468       }
  469   
  470       // This method is invoked by the virtual machine to load a class.
  471       private Class loadClassInternal(String name)
  472           throws ClassNotFoundException
  473       {
  474           // For backward compatibility, explicitly lock on 'this' when
  475           // the current class loader is not parallel capable.
  476           if (parallelLockMap == null) {
  477               synchronized (this) {
  478                    return loadClass(name);
  479               }
  480           } else {
  481               return loadClass(name);
  482           }
  483       }
  484   
  485       // Invoked by the VM after loading class with this loader.
  486       private void checkPackageAccess(Class cls, ProtectionDomain pd) {
  487           final SecurityManager sm = System.getSecurityManager();
  488           if (sm != null) {
  489               final String name = cls.getName();
  490               final int i = name.lastIndexOf('.');
  491               if (i != -1) {
  492                   AccessController.doPrivileged(new PrivilegedAction<Void>() {
  493                       public Void run() {
  494                           sm.checkPackageAccess(name.substring(0, i));
  495                           return null;
  496                       }
  497                   }, new AccessControlContext(new ProtectionDomain[] {pd}));
  498               }
  499           }
  500           domains.add(pd);
  501       }
  502   
  503       /**
  504        * Finds the class with the specified <a href="#name">binary name</a>.
  505        * This method should be overridden by class loader implementations that
  506        * follow the delegation model for loading classes, and will be invoked by
  507        * the {@link #loadClass <tt>loadClass</tt>} method after checking the
  508        * parent class loader for the requested class.  The default implementation
  509        * throws a <tt>ClassNotFoundException</tt>.  </p>
  510        *
  511        * @param  name
  512        *         The <a href="#name">binary name</a> of the class
  513        *
  514        * @return  The resulting <tt>Class</tt> object
  515        *
  516        * @throws  ClassNotFoundException
  517        *          If the class could not be found
  518        *
  519        * @since  1.2
  520        */
  521       protected Class<?> findClass(String name) throws ClassNotFoundException {
  522           throw new ClassNotFoundException(name);
  523       }
  524   
  525       /**
  526        * Converts an array of bytes into an instance of class <tt>Class</tt>.
  527        * Before the <tt>Class</tt> can be used it must be resolved.  This method
  528        * is deprecated in favor of the version that takes a <a
  529        * href="#name">binary name</a> as its first argument, and is more secure.
  530        *
  531        * @param  b
  532        *         The bytes that make up the class data.  The bytes in positions
  533        *         <tt>off</tt> through <tt>off+len-1</tt> should have the format
  534        *         of a valid class file as defined by
  535        *         <cite>The Java&trade; Virtual Machine Specification</cite>.
  536        *
  537        * @param  off
  538        *         The start offset in <tt>b</tt> of the class data
  539        *
  540        * @param  len
  541        *         The length of the class data
  542        *
  543        * @return  The <tt>Class</tt> object that was created from the specified
  544        *          class data
  545        *
  546        * @throws  ClassFormatError
  547        *          If the data did not contain a valid class
  548        *
  549        * @throws  IndexOutOfBoundsException
  550        *          If either <tt>off</tt> or <tt>len</tt> is negative, or if
  551        *          <tt>off+len</tt> is greater than <tt>b.length</tt>.
  552        *
  553        * @throws  SecurityException
  554        *          If an attempt is made to add this class to a package that
  555        *          contains classes that were signed by a different set of
  556        *          certificates than this class, or if an attempt is made
  557        *          to define a class in a package with a fully-qualified name
  558        *          that starts with "{@code java.}".
  559        *
  560        * @see  #loadClass(String, boolean)
  561        * @see  #resolveClass(Class)
  562        *
  563        * @deprecated  Replaced by {@link #defineClass(String, byte[], int, int)
  564        * defineClass(String, byte[], int, int)}
  565        */
  566       @Deprecated
  567       protected final Class<?> defineClass(byte[] b, int off, int len)
  568           throws ClassFormatError
  569       {
  570           return defineClass(null, b, off, len, null);
  571       }
  572   
  573       /**
  574        * Converts an array of bytes into an instance of class <tt>Class</tt>.
  575        * Before the <tt>Class</tt> can be used it must be resolved.
  576        *
  577        * <p> This method assigns a default {@link java.security.ProtectionDomain
  578        * <tt>ProtectionDomain</tt>} to the newly defined class.  The
  579        * <tt>ProtectionDomain</tt> is effectively granted the same set of
  580        * permissions returned when {@link
  581        * java.security.Policy#getPermissions(java.security.CodeSource)
  582        * <tt>Policy.getPolicy().getPermissions(new CodeSource(null, null))</tt>}
  583        * is invoked.  The default domain is created on the first invocation of
  584        * {@link #defineClass(String, byte[], int, int) <tt>defineClass</tt>},
  585        * and re-used on subsequent invocations.
  586        *
  587        * <p> To assign a specific <tt>ProtectionDomain</tt> to the class, use
  588        * the {@link #defineClass(String, byte[], int, int,
  589        * java.security.ProtectionDomain) <tt>defineClass</tt>} method that takes a
  590        * <tt>ProtectionDomain</tt> as one of its arguments.  </p>
  591        *
  592        * @param  name
  593        *         The expected <a href="#name">binary name</a> of the class, or
  594        *         <tt>null</tt> if not known
  595        *
  596        * @param  b
  597        *         The bytes that make up the class data.  The bytes in positions
  598        *         <tt>off</tt> through <tt>off+len-1</tt> should have the format
  599        *         of a valid class file as defined by
  600        *         <cite>The Java&trade; Virtual Machine Specification</cite>.
  601        *
  602        * @param  off
  603        *         The start offset in <tt>b</tt> of the class data
  604        *
  605        * @param  len
  606        *         The length of the class data
  607        *
  608        * @return  The <tt>Class</tt> object that was created from the specified
  609        *          class data.
  610        *
  611        * @throws  ClassFormatError
  612        *          If the data did not contain a valid class
  613        *
  614        * @throws  IndexOutOfBoundsException
  615        *          If either <tt>off</tt> or <tt>len</tt> is negative, or if
  616        *          <tt>off+len</tt> is greater than <tt>b.length</tt>.
  617        *
  618        * @throws  SecurityException
  619        *          If an attempt is made to add this class to a package that
  620        *          contains classes that were signed by a different set of
  621        *          certificates than this class (which is unsigned), or if
  622        *          <tt>name</tt> begins with "<tt>java.</tt>".
  623        *
  624        * @see  #loadClass(String, boolean)
  625        * @see  #resolveClass(Class)
  626        * @see  java.security.CodeSource
  627        * @see  java.security.SecureClassLoader
  628        *
  629        * @since  1.1
  630        */
  631       protected final Class<?> defineClass(String name, byte[] b, int off, int len)
  632           throws ClassFormatError
  633       {
  634           return defineClass(name, b, off, len, null);
  635       }
  636   
  637       /* Determine protection domain, and check that:
  638           - not define java.* class,
  639           - signer of this class matches signers for the rest of the classes in
  640             package.
  641       */
  642       private ProtectionDomain preDefineClass(String name,
  643                                               ProtectionDomain pd)
  644       {
  645           if (!checkName(name))
  646               throw new NoClassDefFoundError("IllegalName: " + name);
  647   
  648           if ((name != null) && name.startsWith("java.")) {
  649               throw new SecurityException
  650                   ("Prohibited package name: " +
  651                    name.substring(0, name.lastIndexOf('.')));
  652           }
  653           if (pd == null) {
  654               pd = defaultDomain;
  655           }
  656   
  657           if (name != null) checkCerts(name, pd.getCodeSource());
  658   
  659           return pd;
  660       }
  661   
  662       private String defineClassSourceLocation(ProtectionDomain pd)
  663       {
  664           CodeSource cs = pd.getCodeSource();
  665           String source = null;
  666           if (cs != null && cs.getLocation() != null) {
  667               source = cs.getLocation().toString();
  668           }
  669           return source;
  670       }
  671   
  672       private Class defineTransformedClass(String name, byte[] b, int off, int len,
  673                                            ProtectionDomain pd,
  674                                            ClassFormatError cfe, String source)
  675         throws ClassFormatError
  676       {
  677           // Class format error - try to transform the bytecode and
  678           // define the class again
  679           //
  680           ClassFileTransformer[] transformers =
  681               ClassFileTransformer.getTransformers();
  682           Class c = null;
  683   
  684           if (transformers != null) {
  685               for (ClassFileTransformer transformer : transformers) {
  686                   try {
  687                       // Transform byte code using transformer
  688                       byte[] tb = transformer.transform(b, off, len);
  689                       c = defineClass1(name, tb, 0, tb.length,
  690                                        pd, source);
  691                       break;
  692                   } catch (ClassFormatError cfe2)     {
  693                       // If ClassFormatError occurs, try next transformer
  694                   }
  695               }
  696           }
  697   
  698           // Rethrow original ClassFormatError if unable to transform
  699           // bytecode to well-formed
  700           //
  701           if (c == null)
  702               throw cfe;
  703   
  704           return c;
  705       }
  706   
  707       private void postDefineClass(Class c, ProtectionDomain pd)
  708       {
  709           if (pd.getCodeSource() != null) {
  710               Certificate certs[] = pd.getCodeSource().getCertificates();
  711               if (certs != null)
  712                   setSigners(c, certs);
  713           }
  714       }
  715   
  716       /**
  717        * Converts an array of bytes into an instance of class <tt>Class</tt>,
  718        * with an optional <tt>ProtectionDomain</tt>.  If the domain is
  719        * <tt>null</tt>, then a default domain will be assigned to the class as
  720        * specified in the documentation for {@link #defineClass(String, byte[],
  721        * int, int)}.  Before the class can be used it must be resolved.
  722        *
  723        * <p> The first class defined in a package determines the exact set of
  724        * certificates that all subsequent classes defined in that package must
  725        * contain.  The set of certificates for a class is obtained from the
  726        * {@link java.security.CodeSource <tt>CodeSource</tt>} within the
  727        * <tt>ProtectionDomain</tt> of the class.  Any classes added to that
  728        * package must contain the same set of certificates or a
  729        * <tt>SecurityException</tt> will be thrown.  Note that if
  730        * <tt>name</tt> is <tt>null</tt>, this check is not performed.
  731        * You should always pass in the <a href="#name">binary name</a> of the
  732        * class you are defining as well as the bytes.  This ensures that the
  733        * class you are defining is indeed the class you think it is.
  734        *
  735        * <p> The specified <tt>name</tt> cannot begin with "<tt>java.</tt>", since
  736        * all classes in the "<tt>java.*</tt> packages can only be defined by the
  737        * bootstrap class loader.  If <tt>name</tt> is not <tt>null</tt>, it
  738        * must be equal to the <a href="#name">binary name</a> of the class
  739        * specified by the byte array "<tt>b</tt>", otherwise a {@link
  740        * <tt>NoClassDefFoundError</tt>} will be thrown.  </p>
  741        *
  742        * @param  name
  743        *         The expected <a href="#name">binary name</a> of the class, or
  744        *         <tt>null</tt> if not known
  745        *
  746        * @param  b
  747        *         The bytes that make up the class data. The bytes in positions
  748        *         <tt>off</tt> through <tt>off+len-1</tt> should have the format
  749        *         of a valid class file as defined by
  750        *         <cite>The Java&trade; Virtual Machine Specification</cite>.
  751        *
  752        * @param  off
  753        *         The start offset in <tt>b</tt> of the class data
  754        *
  755        * @param  len
  756        *         The length of the class data
  757        *
  758        * @param  protectionDomain
  759        *         The ProtectionDomain of the class
  760        *
  761        * @return  The <tt>Class</tt> object created from the data,
  762        *          and optional <tt>ProtectionDomain</tt>.
  763        *
  764        * @throws  ClassFormatError
  765        *          If the data did not contain a valid class
  766        *
  767        * @throws  NoClassDefFoundError
  768        *          If <tt>name</tt> is not equal to the <a href="#name">binary
  769        *          name</a> of the class specified by <tt>b</tt>
  770        *
  771        * @throws  IndexOutOfBoundsException
  772        *          If either <tt>off</tt> or <tt>len</tt> is negative, or if
  773        *          <tt>off+len</tt> is greater than <tt>b.length</tt>.
  774        *
  775        * @throws  SecurityException
  776        *          If an attempt is made to add this class to a package that
  777        *          contains classes that were signed by a different set of
  778        *          certificates than this class, or if <tt>name</tt> begins with
  779        *          "<tt>java.</tt>".
  780        */
  781       protected final Class<?> defineClass(String name, byte[] b, int off, int len,
  782                                            ProtectionDomain protectionDomain)
  783           throws ClassFormatError
  784       {
  785           protectionDomain = preDefineClass(name, protectionDomain);
  786   
  787           Class c = null;
  788           String source = defineClassSourceLocation(protectionDomain);
  789   
  790           try {
  791               c = defineClass1(name, b, off, len, protectionDomain, source);
  792           } catch (ClassFormatError cfe) {
  793               c = defineTransformedClass(name, b, off, len, protectionDomain, cfe,
  794                                          source);
  795           }
  796   
  797           postDefineClass(c, protectionDomain);
  798           return c;
  799       }
  800   
  801       /**
  802        * Converts a {@link java.nio.ByteBuffer <tt>ByteBuffer</tt>}
  803        * into an instance of class <tt>Class</tt>,
  804        * with an optional <tt>ProtectionDomain</tt>.  If the domain is
  805        * <tt>null</tt>, then a default domain will be assigned to the class as
  806        * specified in the documentation for {@link #defineClass(String, byte[],
  807        * int, int)}.  Before the class can be used it must be resolved.
  808        *
  809        * <p>The rules about the first class defined in a package determining the
  810        * set of certificates for the package, and the restrictions on class names
  811        * are identical to those specified in the documentation for {@link
  812        * #defineClass(String, byte[], int, int, ProtectionDomain)}.
  813        *
  814        * <p> An invocation of this method of the form
  815        * <i>cl</i><tt>.defineClass(</tt><i>name</i><tt>,</tt>
  816        * <i>bBuffer</i><tt>,</tt> <i>pd</i><tt>)</tt> yields exactly the same
  817        * result as the statements
  818        *
  819        * <blockquote><tt>
  820        * ...<br>
  821        * byte[] temp = new byte[</tt><i>bBuffer</i><tt>.{@link
  822        * java.nio.ByteBuffer#remaining remaining}()];<br>
  823        *     </tt><i>bBuffer</i><tt>.{@link java.nio.ByteBuffer#get(byte[])
  824        * get}(temp);<br>
  825        *     return {@link #defineClass(String, byte[], int, int, ProtectionDomain)
  826        * </tt><i>cl</i><tt>.defineClass}(</tt><i>name</i><tt>, temp, 0,
  827        * temp.length, </tt><i>pd</i><tt>);<br>
  828        * </tt></blockquote>
  829        *
  830        * @param  name
  831        *         The expected <a href="#name">binary name</a>. of the class, or
  832        *         <tt>null</tt> if not known
  833        *
  834        * @param  b
  835        *         The bytes that make up the class data. The bytes from positions
  836        *         <tt>b.position()</tt> through <tt>b.position() + b.limit() -1
  837        *         </tt> should have the format of a valid class file as defined by
  838        *         <cite>The Java&trade; Virtual Machine Specification</cite>.
  839        *
  840        * @param  protectionDomain
  841        *         The ProtectionDomain of the class, or <tt>null</tt>.
  842        *
  843        * @return  The <tt>Class</tt> object created from the data,
  844        *          and optional <tt>ProtectionDomain</tt>.
  845        *
  846        * @throws  ClassFormatError
  847        *          If the data did not contain a valid class.
  848        *
  849        * @throws  NoClassDefFoundError
  850        *          If <tt>name</tt> is not equal to the <a href="#name">binary
  851        *          name</a> of the class specified by <tt>b</tt>
  852        *
  853        * @throws  SecurityException
  854        *          If an attempt is made to add this class to a package that
  855        *          contains classes that were signed by a different set of
  856        *          certificates than this class, or if <tt>name</tt> begins with
  857        *          "<tt>java.</tt>".
  858        *
  859        * @see      #defineClass(String, byte[], int, int, ProtectionDomain)
  860        *
  861        * @since  1.5
  862        */
  863       protected final Class<?> defineClass(String name, java.nio.ByteBuffer b,
  864                                            ProtectionDomain protectionDomain)
  865           throws ClassFormatError
  866       {
  867           int len = b.remaining();
  868   
  869           // Use byte[] if not a direct ByteBufer:
  870           if (!b.isDirect()) {
  871               if (b.hasArray()) {
  872                   return defineClass(name, b.array(),
  873                                      b.position() + b.arrayOffset(), len,
  874                                      protectionDomain);
  875               } else {
  876                   // no array, or read-only array
  877                   byte[] tb = new byte[len];
  878                   b.get(tb);  // get bytes out of byte buffer.
  879                   return defineClass(name, tb, 0, len, protectionDomain);
  880               }
  881           }
  882   
  883           protectionDomain = preDefineClass(name, protectionDomain);
  884   
  885           Class c = null;
  886           String source = defineClassSourceLocation(protectionDomain);
  887   
  888           try {
  889               c = defineClass2(name, b, b.position(), len, protectionDomain,
  890                                source);
  891           } catch (ClassFormatError cfe) {
  892               byte[] tb = new byte[len];
  893               b.get(tb);  // get bytes out of byte buffer.
  894               c = defineTransformedClass(name, tb, 0, len, protectionDomain, cfe,
  895                                          source);
  896           }
  897   
  898           postDefineClass(c, protectionDomain);
  899           return c;
  900       }
  901   
  902       private native Class defineClass0(String name, byte[] b, int off, int len,
  903                                         ProtectionDomain pd);
  904   
  905       private native Class defineClass1(String name, byte[] b, int off, int len,
  906                                         ProtectionDomain pd, String source);
  907   
  908       private native Class defineClass2(String name, java.nio.ByteBuffer b,
  909                                         int off, int len, ProtectionDomain pd,
  910                                         String source);
  911   
  912       // true if the name is null or has the potential to be a valid binary name
  913       private boolean checkName(String name) {
  914           if ((name == null) || (name.length() == 0))
  915               return true;
  916           if ((name.indexOf('/') != -1)
  917               || (!VM.allowArraySyntax() && (name.charAt(0) == '[')))
  918               return false;
  919           return true;
  920       }
  921   
  922       private void checkCerts(String name, CodeSource cs) {
  923           int i = name.lastIndexOf('.');
  924           String pname = (i == -1) ? "" : name.substring(0, i);
  925   
  926           Certificate[] certs = null;
  927           if (cs != null) {
  928               certs = cs.getCertificates();
  929           }
  930           Certificate[] pcerts = null;
  931           if (parallelLockMap == null) {
  932               synchronized (this) {
  933                   pcerts = package2certs.get(pname);
  934                   if (pcerts == null) {
  935                       package2certs.put(pname, (certs == null? nocerts:certs));
  936                   }
  937               }
  938           } else {
  939               pcerts = ((ConcurrentHashMap<String, Certificate[]>)package2certs).
  940                   putIfAbsent(pname, (certs == null? nocerts:certs));
  941           }
  942           if (pcerts != null && !compareCerts(pcerts, certs)) {
  943               throw new SecurityException("class \""+ name +
  944                    "\"'s signer information does not match signer information of other classes in the same package");
  945           }
  946       }
  947   
  948       /**
  949        * check to make sure the certs for the new class (certs) are the same as
  950        * the certs for the first class inserted in the package (pcerts)
  951        */
  952       private boolean compareCerts(Certificate[] pcerts,
  953                                    Certificate[] certs)
  954       {
  955           // certs can be null, indicating no certs.
  956           if ((certs == null) || (certs.length == 0)) {
  957               return pcerts.length == 0;
  958           }
  959   
  960           // the length must be the same at this point
  961           if (certs.length != pcerts.length)
  962               return false;
  963   
  964           // go through and make sure all the certs in one array
  965           // are in the other and vice-versa.
  966           boolean match;
  967           for (int i = 0; i < certs.length; i++) {
  968               match = false;
  969               for (int j = 0; j < pcerts.length; j++) {
  970                   if (certs[i].equals(pcerts[j])) {
  971                       match = true;
  972                       break;
  973                   }
  974               }
  975               if (!match) return false;
  976           }
  977   
  978           // now do the same for pcerts
  979           for (int i = 0; i < pcerts.length; i++) {
  980               match = false;
  981               for (int j = 0; j < certs.length; j++) {
  982                   if (pcerts[i].equals(certs[j])) {
  983                       match = true;
  984                       break;
  985                   }
  986               }
  987               if (!match) return false;
  988           }
  989   
  990           return true;
  991       }
  992   
  993       /**
  994        * Links the specified class.  This (misleadingly named) method may be
  995        * used by a class loader to link a class.  If the class <tt>c</tt> has
  996        * already been linked, then this method simply returns. Otherwise, the
  997        * class is linked as described in the "Execution" chapter of
  998        * <cite>The Java&trade; Language Specification</cite>.
  999        * </p>
 1000        *
 1001        * @param  c
 1002        *         The class to link
 1003        *
 1004        * @throws  NullPointerException
 1005        *          If <tt>c</tt> is <tt>null</tt>.
 1006        *
 1007        * @see  #defineClass(String, byte[], int, int)
 1008        */
 1009       protected final void resolveClass(Class<?> c) {
 1010           resolveClass0(c);
 1011       }
 1012   
 1013       private native void resolveClass0(Class c);
 1014   
 1015       /**
 1016        * Finds a class with the specified <a href="#name">binary name</a>,
 1017        * loading it if necessary.
 1018        *
 1019        * <p> This method loads the class through the system class loader (see
 1020        * {@link #getSystemClassLoader()}).  The <tt>Class</tt> object returned
 1021        * might have more than one <tt>ClassLoader</tt> associated with it.
 1022        * Subclasses of <tt>ClassLoader</tt> need not usually invoke this method,
 1023        * because most class loaders need to override just {@link
 1024        * #findClass(String)}.  </p>
 1025        *
 1026        * @param  name
 1027        *         The <a href="#name">binary name</a> of the class
 1028        *
 1029        * @return  The <tt>Class</tt> object for the specified <tt>name</tt>
 1030        *
 1031        * @throws  ClassNotFoundException
 1032        *          If the class could not be found
 1033        *
 1034        * @see  #ClassLoader(ClassLoader)
 1035        * @see  #getParent()
 1036        */
 1037       protected final Class<?> findSystemClass(String name)
 1038           throws ClassNotFoundException
 1039       {
 1040           ClassLoader system = getSystemClassLoader();
 1041           if (system == null) {
 1042               if (!checkName(name))
 1043                   throw new ClassNotFoundException(name);
 1044               Class cls = findBootstrapClass(name);
 1045               if (cls == null) {
 1046                   throw new ClassNotFoundException(name);
 1047               }
 1048               return cls;
 1049           }
 1050           return system.loadClass(name);
 1051       }
 1052   
 1053       /**
 1054        * Returns a class loaded by the bootstrap class loader;
 1055        * or return null if not found.
 1056        */
 1057       private Class findBootstrapClassOrNull(String name)
 1058       {
 1059           if (!checkName(name)) return null;
 1060   
 1061           return findBootstrapClass(name);
 1062       }
 1063   
 1064       // return null if not found
 1065       private native Class findBootstrapClass(String name);
 1066   
 1067       /**
 1068        * Returns the class with the given <a href="#name">binary name</a> if this
 1069        * loader has been recorded by the Java virtual machine as an initiating
 1070        * loader of a class with that <a href="#name">binary name</a>.  Otherwise
 1071        * <tt>null</tt> is returned.  </p>
 1072        *
 1073        * @param  name
 1074        *         The <a href="#name">binary name</a> of the class
 1075        *
 1076        * @return  The <tt>Class</tt> object, or <tt>null</tt> if the class has
 1077        *          not been loaded
 1078        *
 1079        * @since  1.1
 1080        */
 1081       protected final Class<?> findLoadedClass(String name) {
 1082           if (!checkName(name))
 1083               return null;
 1084           return findLoadedClass0(name);
 1085       }
 1086   
 1087       private native final Class findLoadedClass0(String name);
 1088   
 1089       /**
 1090        * Sets the signers of a class.  This should be invoked after defining a
 1091        * class.  </p>
 1092        *
 1093        * @param  c
 1094        *         The <tt>Class</tt> object
 1095        *
 1096        * @param  signers
 1097        *         The signers for the class
 1098        *
 1099        * @since  1.1
 1100        */
 1101       protected final void setSigners(Class<?> c, Object[] signers) {
 1102           c.setSigners(signers);
 1103       }
 1104   
 1105   
 1106       // -- Resource --
 1107   
 1108       /**
 1109        * Finds the resource with the given name.  A resource is some data
 1110        * (images, audio, text, etc) that can be accessed by class code in a way
 1111        * that is independent of the location of the code.
 1112        *
 1113        * <p> The name of a resource is a '<tt>/</tt>'-separated path name that
 1114        * identifies the resource.
 1115        *
 1116        * <p> This method will first search the parent class loader for the
 1117        * resource; if the parent is <tt>null</tt> the path of the class loader
 1118        * built-in to the virtual machine is searched.  That failing, this method
 1119        * will invoke {@link #findResource(String)} to find the resource.  </p>
 1120        *
 1121        * @param  name
 1122        *         The resource name
 1123        *
 1124        * @return  A <tt>URL</tt> object for reading the resource, or
 1125        *          <tt>null</tt> if the resource could not be found or the invoker
 1126        *          doesn't have adequate  privileges to get the resource.
 1127        *
 1128        * @since  1.1
 1129        */
 1130       public URL getResource(String name) {
 1131           URL url;
 1132           if (parent != null) {
 1133               url = parent.getResource(name);
 1134           } else {
 1135               url = getBootstrapResource(name);
 1136           }
 1137           if (url == null) {
 1138               url = findResource(name);
 1139           }
 1140           return url;
 1141       }
 1142   
 1143       /**
 1144        * Finds all the resources with the given name. A resource is some data
 1145        * (images, audio, text, etc) that can be accessed by class code in a way
 1146        * that is independent of the location of the code.
 1147        *
 1148        * <p>The name of a resource is a <tt>/</tt>-separated path name that
 1149        * identifies the resource.
 1150        *
 1151        * <p> The search order is described in the documentation for {@link
 1152        * #getResource(String)}.  </p>
 1153        *
 1154        * @param  name
 1155        *         The resource name
 1156        *
 1157        * @return  An enumeration of {@link java.net.URL <tt>URL</tt>} objects for
 1158        *          the resource.  If no resources could  be found, the enumeration
 1159        *          will be empty.  Resources that the class loader doesn't have
 1160        *          access to will not be in the enumeration.
 1161        *
 1162        * @throws  IOException
 1163        *          If I/O errors occur
 1164        *
 1165        * @see  #findResources(String)
 1166        *
 1167        * @since  1.2
 1168        */
 1169       public Enumeration<URL> getResources(String name) throws IOException {
 1170           Enumeration[] tmp = new Enumeration[2];
 1171           if (parent != null) {
 1172               tmp[0] = parent.getResources(name);
 1173           } else {
 1174               tmp[0] = getBootstrapResources(name);
 1175           }
 1176           tmp[1] = findResources(name);
 1177   
 1178           return new CompoundEnumeration<>(tmp);
 1179       }
 1180   
 1181       /**
 1182        * Finds the resource with the given name. Class loader implementations
 1183        * should override this method to specify where to find resources.  </p>
 1184        *
 1185        * @param  name
 1186        *         The resource name
 1187        *
 1188        * @return  A <tt>URL</tt> object for reading the resource, or
 1189        *          <tt>null</tt> if the resource could not be found
 1190        *
 1191        * @since  1.2
 1192        */
 1193       protected URL findResource(String name) {
 1194           return null;
 1195       }
 1196   
 1197       /**
 1198        * Returns an enumeration of {@link java.net.URL <tt>URL</tt>} objects
 1199        * representing all the resources with the given name. Class loader
 1200        * implementations should override this method to specify where to load
 1201        * resources from.  </p>
 1202        *
 1203        * @param  name
 1204        *         The resource name
 1205        *
 1206        * @return  An enumeration of {@link java.net.URL <tt>URL</tt>} objects for
 1207        *          the resources
 1208        *
 1209        * @throws  IOException
 1210        *          If I/O errors occur
 1211        *
 1212        * @since  1.2
 1213        */
 1214       protected Enumeration<URL> findResources(String name) throws IOException {
 1215           return java.util.Collections.emptyEnumeration();
 1216       }
 1217   
 1218       // index 0: java.lang.ClassLoader.class
 1219       // index 1: the immediate caller of index 0.
 1220       // index 2: the immediate caller of index 1.
 1221       private static native Class<? extends ClassLoader> getCaller(int index);
 1222   
 1223       /**
 1224        * Registers the caller as parallel capable.</p>
 1225        * The registration succeeds if and only if all of the following
 1226        * conditions are met: <br>
 1227        * 1. no instance of the caller has been created</p>
 1228        * 2. all of the super classes (except class Object) of the caller are
 1229        * registered as parallel capable</p>
 1230        * Note that once a class loader is registered as parallel capable, there
 1231        * is no way to change it back. </p>
 1232        *
 1233        * @return  true if the caller is successfully registered as
 1234        *          parallel capable and false if otherwise.
 1235        *
 1236        * @since   1.7
 1237        */
 1238       protected static boolean registerAsParallelCapable() {
 1239           return ParallelLoaders.register(getCaller(1));
 1240       }
 1241   
 1242       /**
 1243        * Find a resource of the specified name from the search path used to load
 1244        * classes.  This method locates the resource through the system class
 1245        * loader (see {@link #getSystemClassLoader()}).  </p>
 1246        *
 1247        * @param  name
 1248        *         The resource name
 1249        *
 1250        * @return  A {@link java.net.URL <tt>URL</tt>} object for reading the
 1251        *          resource, or <tt>null</tt> if the resource could not be found
 1252        *
 1253        * @since  1.1
 1254        */
 1255       public static URL getSystemResource(String name) {
 1256           ClassLoader system = getSystemClassLoader();
 1257           if (system == null) {
 1258               return getBootstrapResource(name);
 1259           }
 1260           return system.getResource(name);
 1261       }
 1262   
 1263       /**
 1264        * Finds all resources of the specified name from the search path used to
 1265        * load classes.  The resources thus found are returned as an
 1266        * {@link java.util.Enumeration <tt>Enumeration</tt>} of {@link
 1267        * java.net.URL <tt>URL</tt>} objects.
 1268        *
 1269        * <p> The search order is described in the documentation for {@link
 1270        * #getSystemResource(String)}.  </p>
 1271        *
 1272        * @param  name
 1273        *         The resource name
 1274        *
 1275        * @return  An enumeration of resource {@link java.net.URL <tt>URL</tt>}
 1276        *          objects
 1277        *
 1278        * @throws  IOException
 1279        *          If I/O errors occur
 1280   
 1281        * @since  1.2
 1282        */
 1283       public static Enumeration<URL> getSystemResources(String name)
 1284           throws IOException
 1285       {
 1286           ClassLoader system = getSystemClassLoader();
 1287           if (system == null) {
 1288               return getBootstrapResources(name);
 1289           }
 1290           return system.getResources(name);
 1291       }
 1292   
 1293       /**
 1294        * Find resources from the VM's built-in classloader.
 1295        */
 1296       private static URL getBootstrapResource(String name) {
 1297           URLClassPath ucp = getBootstrapClassPath();
 1298           Resource res = ucp.getResource(name);
 1299           return res != null ? res.getURL() : null;
 1300       }
 1301   
 1302       /**
 1303        * Find resources from the VM's built-in classloader.
 1304        */
 1305       private static Enumeration<URL> getBootstrapResources(String name)
 1306           throws IOException
 1307       {
 1308           final Enumeration<Resource> e =
 1309               getBootstrapClassPath().getResources(name);
 1310           return new Enumeration<URL> () {
 1311               public URL nextElement() {
 1312                   return e.nextElement().getURL();
 1313               }
 1314               public boolean hasMoreElements() {
 1315                   return e.hasMoreElements();
 1316               }
 1317           };
 1318       }
 1319   
 1320       // Returns the URLClassPath that is used for finding system resources.
 1321       static URLClassPath getBootstrapClassPath() {
 1322           return sun.misc.Launcher.getBootstrapClassPath();
 1323       }
 1324   
 1325   
 1326       /**
 1327        * Returns an input stream for reading the specified resource.
 1328        *
 1329        * <p> The search order is described in the documentation for {@link
 1330        * #getResource(String)}.  </p>
 1331        *
 1332        * @param  name
 1333        *         The resource name
 1334        *
 1335        * @return  An input stream for reading the resource, or <tt>null</tt>
 1336        *          if the resource could not be found
 1337        *
 1338        * @since  1.1
 1339        */
 1340       public InputStream getResourceAsStream(String name) {
 1341           URL url = getResource(name);
 1342           try {
 1343               return url != null ? url.openStream() : null;
 1344           } catch (IOException e) {
 1345               return null;
 1346           }
 1347       }
 1348   
 1349       /**
 1350        * Open for reading, a resource of the specified name from the search path
 1351        * used to load classes.  This method locates the resource through the
 1352        * system class loader (see {@link #getSystemClassLoader()}).  </p>
 1353        *
 1354        * @param  name
 1355        *         The resource name
 1356        *
 1357        * @return  An input stream for reading the resource, or <tt>null</tt>
 1358        *          if the resource could not be found
 1359        *
 1360        * @since  1.1
 1361        */
 1362       public static InputStream getSystemResourceAsStream(String name) {
 1363           URL url = getSystemResource(name);
 1364           try {
 1365               return url != null ? url.openStream() : null;
 1366           } catch (IOException e) {
 1367               return null;
 1368           }
 1369       }
 1370   
 1371   
 1372       // -- Hierarchy --
 1373   
 1374       /**
 1375        * Returns the parent class loader for delegation. Some implementations may
 1376        * use <tt>null</tt> to represent the bootstrap class loader. This method
 1377        * will return <tt>null</tt> in such implementations if this class loader's
 1378        * parent is the bootstrap class loader.
 1379        *
 1380        * <p> If a security manager is present, and the invoker's class loader is
 1381        * not <tt>null</tt> and is not an ancestor of this class loader, then this
 1382        * method invokes the security manager's {@link
 1383        * SecurityManager#checkPermission(java.security.Permission)
 1384        * <tt>checkPermission</tt>} method with a {@link
 1385        * RuntimePermission#RuntimePermission(String)
 1386        * <tt>RuntimePermission("getClassLoader")</tt>} permission to verify
 1387        * access to the parent class loader is permitted.  If not, a
 1388        * <tt>SecurityException</tt> will be thrown.  </p>
 1389        *
 1390        * @return  The parent <tt>ClassLoader</tt>
 1391        *
 1392        * @throws  SecurityException
 1393        *          If a security manager exists and its <tt>checkPermission</tt>
 1394        *          method doesn't allow access to this class loader's parent class
 1395        *          loader.
 1396        *
 1397        * @since  1.2
 1398        */
 1399       public final ClassLoader getParent() {
 1400           if (parent == null)
 1401               return null;
 1402           SecurityManager sm = System.getSecurityManager();
 1403           if (sm != null) {
 1404               ClassLoader ccl = getCallerClassLoader();
 1405               if (ccl != null && !isAncestor(ccl)) {
 1406                   sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
 1407               }
 1408           }
 1409           return parent;
 1410       }
 1411   
 1412       /**
 1413        * Returns the system class loader for delegation.  This is the default
 1414        * delegation parent for new <tt>ClassLoader</tt> instances, and is
 1415        * typically the class loader used to start the application.
 1416        *
 1417        * <p> This method is first invoked early in the runtime's startup
 1418        * sequence, at which point it creates the system class loader and sets it
 1419        * as the context class loader of the invoking <tt>Thread</tt>.
 1420        *
 1421        * <p> The default system class loader is an implementation-dependent
 1422        * instance of this class.
 1423        *
 1424        * <p> If the system property "<tt>java.system.class.loader</tt>" is defined
 1425        * when this method is first invoked then the value of that property is
 1426        * taken to be the name of a class that will be returned as the system
 1427        * class loader.  The class is loaded using the default system class loader
 1428        * and must define a public constructor that takes a single parameter of
 1429        * type <tt>ClassLoader</tt> which is used as the delegation parent.  An
 1430        * instance is then created using this constructor with the default system
 1431        * class loader as the parameter.  The resulting class loader is defined
 1432        * to be the system class loader.
 1433        *
 1434        * <p> If a security manager is present, and the invoker's class loader is
 1435        * not <tt>null</tt> and the invoker's class loader is not the same as or
 1436        * an ancestor of the system class loader, then this method invokes the
 1437        * security manager's {@link
 1438        * SecurityManager#checkPermission(java.security.Permission)
 1439        * <tt>checkPermission</tt>} method with a {@link
 1440        * RuntimePermission#RuntimePermission(String)
 1441        * <tt>RuntimePermission("getClassLoader")</tt>} permission to verify
 1442        * access to the system class loader.  If not, a
 1443        * <tt>SecurityException</tt> will be thrown.  </p>
 1444        *
 1445        * @return  The system <tt>ClassLoader</tt> for delegation, or
 1446        *          <tt>null</tt> if none
 1447        *
 1448        * @throws  SecurityException
 1449        *          If a security manager exists and its <tt>checkPermission</tt>
 1450        *          method doesn't allow access to the system class loader.
 1451        *
 1452        * @throws  IllegalStateException
 1453        *          If invoked recursively during the construction of the class
 1454        *          loader specified by the "<tt>java.system.class.loader</tt>"
 1455        *          property.
 1456        *
 1457        * @throws  Error
 1458        *          If the system property "<tt>java.system.class.loader</tt>"
 1459        *          is defined but the named class could not be loaded, the
 1460        *          provider class does not define the required constructor, or an
 1461        *          exception is thrown by that constructor when it is invoked. The
 1462        *          underlying cause of the error can be retrieved via the
 1463        *          {@link Throwable#getCause()} method.
 1464        *
 1465        * @revised  1.4
 1466        */
 1467       public static ClassLoader getSystemClassLoader() {
 1468           initSystemClassLoader();
 1469           if (scl == null) {
 1470               return null;
 1471           }
 1472           SecurityManager sm = System.getSecurityManager();
 1473           if (sm != null) {
 1474               ClassLoader ccl = getCallerClassLoader();
 1475               if (ccl != null && ccl != scl && !scl.isAncestor(ccl)) {
 1476                   sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
 1477               }
 1478           }
 1479           return scl;
 1480       }
 1481   
 1482       private static synchronized void initSystemClassLoader() {
 1483           if (!sclSet) {
 1484               if (scl != null)
 1485                   throw new IllegalStateException("recursive invocation");
 1486               sun.misc.Launcher l = sun.misc.Launcher.getLauncher();
 1487               if (l != null) {
 1488                   Throwable oops = null;
 1489                   scl = l.getClassLoader();
 1490                   try {
 1491                       scl = AccessController.doPrivileged(
 1492                           new SystemClassLoaderAction(scl));
 1493                   } catch (PrivilegedActionException pae) {
 1494                       oops = pae.getCause();
 1495                       if (oops instanceof InvocationTargetException) {
 1496                           oops = oops.getCause();
 1497                       }
 1498                   }
 1499                   if (oops != null) {
 1500                       if (oops instanceof Error) {
 1501                           throw (Error) oops;
 1502                       } else {
 1503                           // wrap the exception
 1504                           throw new Error(oops);
 1505                       }
 1506                   }
 1507               }
 1508               sclSet = true;
 1509           }
 1510       }
 1511   
 1512       // Returns true if the specified class loader can be found in this class
 1513       // loader's delegation chain.
 1514       boolean isAncestor(ClassLoader cl) {
 1515           ClassLoader acl = this;
 1516           do {
 1517               acl = acl.parent;
 1518               if (cl == acl) {
 1519                   return true;
 1520               }
 1521           } while (acl != null);
 1522           return false;
 1523       }
 1524   
 1525       // Returns the invoker's class loader, or null if none.
 1526       // NOTE: This must always be invoked when there is exactly one intervening
 1527       // frame from the core libraries on the stack between this method's
 1528       // invocation and the desired invoker.
 1529       static ClassLoader getCallerClassLoader() {
 1530           // NOTE use of more generic Reflection.getCallerClass()
 1531           Class caller = Reflection.getCallerClass(3);
 1532           // This can be null if the VM is requesting it
 1533           if (caller == null) {
 1534               return null;
 1535           }
 1536           // Circumvent security check since this is package-private
 1537           return caller.getClassLoader0();
 1538       }
 1539   
 1540       // The class loader for the system
 1541       // @GuardedBy("ClassLoader.class")
 1542       private static ClassLoader scl;
 1543   
 1544       // Set to true once the system class loader has been set
 1545       // @GuardedBy("ClassLoader.class")
 1546       private static boolean sclSet;
 1547   
 1548   
 1549       // -- Package --
 1550   
 1551       /**
 1552        * Defines a package by name in this <tt>ClassLoader</tt>.  This allows
 1553        * class loaders to define the packages for their classes. Packages must
 1554        * be created before the class is defined, and package names must be
 1555        * unique within a class loader and cannot be redefined or changed once
 1556        * created.  </p>
 1557        *
 1558        * @param  name
 1559        *         The package name
 1560        *
 1561        * @param  specTitle
 1562        *         The specification title
 1563        *
 1564        * @param  specVersion
 1565        *         The specification version
 1566        *
 1567        * @param  specVendor
 1568        *         The specification vendor
 1569        *
 1570        * @param  implTitle
 1571        *         The implementation title
 1572        *
 1573        * @param  implVersion
 1574        *         The implementation version
 1575        *
 1576        * @param  implVendor
 1577        *         The implementation vendor
 1578        *
 1579        * @param  sealBase
 1580        *         If not <tt>null</tt>, then this package is sealed with
 1581        *         respect to the given code source {@link java.net.URL
 1582        *         <tt>URL</tt>}  object.  Otherwise, the package is not sealed.
 1583        *
 1584        * @return  The newly defined <tt>Package</tt> object
 1585        *
 1586        * @throws  IllegalArgumentException
 1587        *          If package name duplicates an existing package either in this
 1588        *          class loader or one of its ancestors
 1589        *
 1590        * @since  1.2
 1591        */
 1592       protected Package definePackage(String name, String specTitle,
 1593                                       String specVersion, String specVendor,
 1594                                       String implTitle, String implVersion,
 1595                                       String implVendor, URL sealBase)
 1596           throws IllegalArgumentException
 1597       {
 1598           synchronized (packages) {
 1599               Package pkg = getPackage(name);
 1600               if (pkg != null) {
 1601                   throw new IllegalArgumentException(name);
 1602               }
 1603               pkg = new Package(name, specTitle, specVersion, specVendor,
 1604                                 implTitle, implVersion, implVendor,
 1605                                 sealBase, this);
 1606               packages.put(name, pkg);
 1607               return pkg;
 1608           }
 1609       }
 1610   
 1611       /**
 1612        * Returns a <tt>Package</tt> that has been defined by this class loader
 1613        * or any of its ancestors.  </p>
 1614        *
 1615        * @param  name
 1616        *         The package name
 1617        *
 1618        * @return  The <tt>Package</tt> corresponding to the given name, or
 1619        *          <tt>null</tt> if not found
 1620        *
 1621        * @since  1.2
 1622        */
 1623       protected Package getPackage(String name) {
 1624           Package pkg;
 1625           synchronized (packages) {
 1626               pkg = packages.get(name);
 1627           }
 1628           if (pkg == null) {
 1629               if (parent != null) {
 1630                   pkg = parent.getPackage(name);
 1631               } else {
 1632                   pkg = Package.getSystemPackage(name);
 1633               }
 1634               if (pkg != null) {
 1635                   synchronized (packages) {
 1636                       Package pkg2 = packages.get(name);
 1637                       if (pkg2 == null) {
 1638                           packages.put(name, pkg);
 1639                       } else {
 1640                           pkg = pkg2;
 1641                       }
 1642                   }
 1643               }
 1644           }
 1645           return pkg;
 1646       }
 1647   
 1648       /**
 1649        * Returns all of the <tt>Packages</tt> defined by this class loader and
 1650        * its ancestors.  </p>
 1651        *
 1652        * @return  The array of <tt>Package</tt> objects defined by this
 1653        *          <tt>ClassLoader</tt>
 1654        *
 1655        * @since  1.2
 1656        */
 1657       protected Package[] getPackages() {
 1658           Map<String, Package> map;
 1659           synchronized (packages) {
 1660               map = new HashMap<>(packages);
 1661           }
 1662           Package[] pkgs;
 1663           if (parent != null) {
 1664               pkgs = parent.getPackages();
 1665           } else {
 1666               pkgs = Package.getSystemPackages();
 1667           }
 1668           if (pkgs != null) {
 1669               for (int i = 0; i < pkgs.length; i++) {
 1670                   String pkgName = pkgs[i].getName();
 1671                   if (map.get(pkgName) == null) {
 1672                       map.put(pkgName, pkgs[i]);
 1673                   }
 1674               }
 1675           }
 1676           return map.values().toArray(new Package[map.size()]);
 1677       }
 1678   
 1679   
 1680       // -- Native library access --
 1681   
 1682       /**
 1683        * Returns the absolute path name of a native library.  The VM invokes this
 1684        * method to locate the native libraries that belong to classes loaded with
 1685        * this class loader. If this method returns <tt>null</tt>, the VM
 1686        * searches the library along the path specified as the
 1687        * "<tt>java.library.path</tt>" property.  </p>
 1688        *
 1689        * @param  libname
 1690        *         The library name
 1691        *
 1692        * @return  The absolute path of the native library
 1693        *
 1694        * @see  System#loadLibrary(String)
 1695        * @see  System#mapLibraryName(String)
 1696        *
 1697        * @since  1.2
 1698        */
 1699       protected String findLibrary(String libname) {
 1700           return null;
 1701       }
 1702   
 1703       /**
 1704        * The inner class NativeLibrary denotes a loaded native library instance.
 1705        * Every classloader contains a vector of loaded native libraries in the
 1706        * private field <tt>nativeLibraries</tt>.  The native libraries loaded
 1707        * into the system are entered into the <tt>systemNativeLibraries</tt>
 1708        * vector.
 1709        *
 1710        * <p> Every native library requires a particular version of JNI. This is
 1711        * denoted by the private <tt>jniVersion</tt> field.  This field is set by
 1712        * the VM when it loads the library, and used by the VM to pass the correct
 1713        * version of JNI to the native methods.  </p>
 1714        *
 1715        * @see      ClassLoader
 1716        * @since    1.2
 1717        */
 1718       static class NativeLibrary {
 1719           // opaque handle to native library, used in native code.
 1720           long handle;
 1721           // the version of JNI environment the native library requires.
 1722           private int jniVersion;
 1723           // the class from which the library is loaded, also indicates
 1724           // the loader this native library belongs.
 1725           private Class fromClass;
 1726           // the canonicalized name of the native library.
 1727           String name;
 1728   
 1729           native void load(String name);
 1730           native long find(String name);
 1731           native void unload();
 1732   
 1733           public NativeLibrary(Class fromClass, String name) {
 1734               this.name = name;
 1735               this.fromClass = fromClass;
 1736           }
 1737   
 1738           protected void finalize() {
 1739               synchronized (loadedLibraryNames) {
 1740                   if (fromClass.getClassLoader() != null && handle != 0) {
 1741                       /* remove the native library name */
 1742                       int size = loadedLibraryNames.size();
 1743                       for (int i = 0; i < size; i++) {
 1744                           if (name.equals(loadedLibraryNames.elementAt(i))) {
 1745                               loadedLibraryNames.removeElementAt(i);
 1746                               break;
 1747                           }
 1748                       }
 1749                       /* unload the library. */
 1750                       ClassLoader.nativeLibraryContext.push(this);
 1751                       try {
 1752                           unload();
 1753                       } finally {
 1754                           ClassLoader.nativeLibraryContext.pop();
 1755                       }
 1756                   }
 1757               }
 1758           }
 1759           // Invoked in the VM to determine the context class in
 1760           // JNI_Load/JNI_Unload
 1761           static Class getFromClass() {
 1762               return ClassLoader.nativeLibraryContext.peek().fromClass;
 1763           }
 1764       }
 1765   
 1766       // All native library names we've loaded.
 1767       private static Vector<String> loadedLibraryNames = new Vector<>();
 1768   
 1769       // Native libraries belonging to system classes.
 1770       private static Vector<NativeLibrary> systemNativeLibraries
 1771           = new Vector<>();
 1772   
 1773       // Native libraries associated with the class loader.
 1774       private Vector<NativeLibrary> nativeLibraries = new Vector<>();
 1775   
 1776       // native libraries being loaded/unloaded.
 1777       private static Stack<NativeLibrary> nativeLibraryContext = new Stack<>();
 1778   
 1779       // The paths searched for libraries
 1780       private static String usr_paths[];
 1781       private static String sys_paths[];
 1782   
 1783       private static String[] initializePath(String propname) {
 1784           String ldpath = System.getProperty(propname, "");
 1785           String ps = File.pathSeparator;
 1786           int ldlen = ldpath.length();
 1787           int i, j, n;
 1788           // Count the separators in the path
 1789           i = ldpath.indexOf(ps);
 1790           n = 0;
 1791           while (i >= 0) {
 1792               n++;
 1793               i = ldpath.indexOf(ps, i + 1);
 1794           }
 1795   
 1796           // allocate the array of paths - n :'s = n + 1 path elements
 1797           String[] paths = new String[n + 1];
 1798   
 1799           // Fill the array with paths from the ldpath
 1800           n = i = 0;
 1801           j = ldpath.indexOf(ps);
 1802           while (j >= 0) {
 1803               if (j - i > 0) {
 1804                   paths[n++] = ldpath.substring(i, j);
 1805               } else if (j - i == 0) {
 1806                   paths[n++] = ".";
 1807               }
 1808               i = j + 1;
 1809               j = ldpath.indexOf(ps, i);
 1810           }
 1811           paths[n] = ldpath.substring(i, ldlen);
 1812           return paths;
 1813       }
 1814   
 1815       // Invoked in the java.lang.Runtime class to implement load and loadLibrary.
 1816       static void loadLibrary(Class fromClass, String name,
 1817                               boolean isAbsolute) {
 1818           ClassLoader loader =
 1819               (fromClass == null) ? null : fromClass.getClassLoader();
 1820           if (sys_paths == null) {
 1821               usr_paths = initializePath("java.library.path");
 1822               sys_paths = initializePath("sun.boot.library.path");
 1823           }
 1824           if (isAbsolute) {
 1825               if (loadLibrary0(fromClass, new File(name))) {
 1826                   return;
 1827               }
 1828               throw new UnsatisfiedLinkError("Can't load library: " + name);
 1829           }
 1830           if (loader != null) {
 1831               String libfilename = loader.findLibrary(name);
 1832               if (libfilename != null) {
 1833                   File libfile = new File(libfilename);
 1834                   if (!libfile.isAbsolute()) {
 1835                       throw new UnsatisfiedLinkError(
 1836       "ClassLoader.findLibrary failed to return an absolute path: " + libfilename);
 1837                   }
 1838                   if (loadLibrary0(fromClass, libfile)) {
 1839                       return;
 1840                   }
 1841                   throw new UnsatisfiedLinkError("Can't load " + libfilename);
 1842               }
 1843           }
 1844           for (int i = 0 ; i < sys_paths.length ; i++) {
 1845               File libfile = new File(sys_paths[i], System.mapLibraryName(name));
 1846               if (loadLibrary0(fromClass, libfile)) {
 1847                   return;
 1848               }
 1849           }
 1850           if (loader != null) {
 1851               for (int i = 0 ; i < usr_paths.length ; i++) {
 1852                   File libfile = new File(usr_paths[i],
 1853                                           System.mapLibraryName(name));
 1854                   if (loadLibrary0(fromClass, libfile)) {
 1855                       return;
 1856                   }
 1857               }
 1858           }
 1859           // Oops, it failed
 1860           throw new UnsatisfiedLinkError("no " + name + " in java.library.path");
 1861       }
 1862   
 1863       private static boolean loadLibrary0(Class fromClass, final File file) {
 1864           boolean exists = AccessController.doPrivileged(
 1865               new PrivilegedAction<Object>() {
 1866                   public Object run() {
 1867                       return file.exists() ? Boolean.TRUE : null;
 1868                   }})
 1869               != null;
 1870           if (!exists) {
 1871               return false;
 1872           }
 1873           String name;
 1874           try {
 1875               name = file.getCanonicalPath();
 1876           } catch (IOException e) {
 1877               return false;
 1878           }
 1879           ClassLoader loader =
 1880               (fromClass == null) ? null : fromClass.getClassLoader();
 1881           Vector<NativeLibrary> libs =
 1882               loader != null ? loader.nativeLibraries : systemNativeLibraries;
 1883           synchronized (libs) {
 1884               int size = libs.size();
 1885               for (int i = 0; i < size; i++) {
 1886                   NativeLibrary lib = libs.elementAt(i);
 1887                   if (name.equals(lib.name)) {
 1888                       return true;
 1889                   }
 1890               }
 1891   
 1892               synchronized (loadedLibraryNames) {
 1893                   if (loadedLibraryNames.contains(name)) {
 1894                       throw new UnsatisfiedLinkError
 1895                           ("Native Library " +
 1896                            name +
 1897                            " already loaded in another classloader");
 1898                   }
 1899                   /* If the library is being loaded (must be by the same thread,
 1900                    * because Runtime.load and Runtime.loadLibrary are
 1901                    * synchronous). The reason is can occur is that the JNI_OnLoad
 1902                    * function can cause another loadLibrary invocation.
 1903                    *
 1904                    * Thus we can use a static stack to hold the list of libraries
 1905                    * we are loading.
 1906                    *
 1907                    * If there is a pending load operation for the library, we
 1908                    * immediately return success; otherwise, we raise
 1909                    * UnsatisfiedLinkError.
 1910                    */
 1911                   int n = nativeLibraryContext.size();
 1912                   for (int i = 0; i < n; i++) {
 1913                       NativeLibrary lib = nativeLibraryContext.elementAt(i);
 1914                       if (name.equals(lib.name)) {
 1915                           if (loader == lib.fromClass.getClassLoader()) {
 1916                               return true;
 1917                           } else {
 1918                               throw new UnsatisfiedLinkError
 1919                                   ("Native Library " +
 1920                                    name +
 1921                                    " is being loaded in another classloader");
 1922                           }
 1923                       }
 1924                   }
 1925                   NativeLibrary lib = new NativeLibrary(fromClass, name);
 1926                   nativeLibraryContext.push(lib);
 1927                   try {
 1928                       lib.load(name);
 1929                   } finally {
 1930                       nativeLibraryContext.pop();
 1931                   }
 1932                   if (lib.handle != 0) {
 1933                       loadedLibraryNames.addElement(name);
 1934                       libs.addElement(lib);
 1935                       return true;
 1936                   }
 1937                   return false;
 1938               }
 1939           }
 1940       }
 1941   
 1942       // Invoked in the VM class linking code.
 1943       static long findNative(ClassLoader loader, String name) {
 1944           Vector<NativeLibrary> libs =
 1945               loader != null ? loader.nativeLibraries : systemNativeLibraries;
 1946           synchronized (libs) {
 1947               int size = libs.size();
 1948               for (int i = 0; i < size; i++) {
 1949                   NativeLibrary lib = libs.elementAt(i);
 1950                   long entry = lib.find(name);
 1951                   if (entry != 0)
 1952                       return entry;
 1953               }
 1954           }
 1955           return 0;
 1956       }
 1957   
 1958   
 1959       // -- Assertion management --
 1960   
 1961       final Object assertionLock;
 1962   
 1963       // The default toggle for assertion checking.
 1964       // @GuardedBy("assertionLock")
 1965       private boolean defaultAssertionStatus = false;
 1966   
 1967       // Maps String packageName to Boolean package default assertion status Note
 1968       // that the default package is placed under a null map key.  If this field
 1969       // is null then we are delegating assertion status queries to the VM, i.e.,
 1970       // none of this ClassLoader's assertion status modification methods have
 1971       // been invoked.
 1972       // @GuardedBy("assertionLock")
 1973       private Map<String, Boolean> packageAssertionStatus = null;
 1974   
 1975       // Maps String fullyQualifiedClassName to Boolean assertionStatus If this
 1976       // field is null then we are delegating assertion status queries to the VM,
 1977       // i.e., none of this ClassLoader's assertion status modification methods
 1978       // have been invoked.
 1979       // @GuardedBy("assertionLock")
 1980       Map<String, Boolean> classAssertionStatus = null;
 1981   
 1982       /**
 1983        * Sets the default assertion status for this class loader.  This setting
 1984        * determines whether classes loaded by this class loader and initialized
 1985        * in the future will have assertions enabled or disabled by default.
 1986        * This setting may be overridden on a per-package or per-class basis by
 1987        * invoking {@link #setPackageAssertionStatus(String, boolean)} or {@link
 1988        * #setClassAssertionStatus(String, boolean)}.  </p>
 1989        *
 1990        * @param  enabled
 1991        *         <tt>true</tt> if classes loaded by this class loader will
 1992        *         henceforth have assertions enabled by default, <tt>false</tt>
 1993        *         if they will have assertions disabled by default.
 1994        *
 1995        * @since  1.4
 1996        */
 1997       public void setDefaultAssertionStatus(boolean enabled) {
 1998           synchronized (assertionLock) {
 1999               if (classAssertionStatus == null)
 2000                   initializeJavaAssertionMaps();
 2001   
 2002               defaultAssertionStatus = enabled;
 2003           }
 2004       }
 2005   
 2006       /**
 2007        * Sets the package default assertion status for the named package.  The
 2008        * package default assertion status determines the assertion status for
 2009        * classes initialized in the future that belong to the named package or
 2010        * any of its "subpackages".
 2011        *
 2012        * <p> A subpackage of a package named p is any package whose name begins
 2013        * with "<tt>p.</tt>".  For example, <tt>javax.swing.text</tt> is a
 2014        * subpackage of <tt>javax.swing</tt>, and both <tt>java.util</tt> and
 2015        * <tt>java.lang.reflect</tt> are subpackages of <tt>java</tt>.
 2016        *
 2017        * <p> In the event that multiple package defaults apply to a given class,
 2018        * the package default pertaining to the most specific package takes
 2019        * precedence over the others.  For example, if <tt>javax.lang</tt> and
 2020        * <tt>javax.lang.reflect</tt> both have package defaults associated with
 2021        * them, the latter package default applies to classes in
 2022        * <tt>javax.lang.reflect</tt>.
 2023        *
 2024        * <p> Package defaults take precedence over the class loader's default
 2025        * assertion status, and may be overridden on a per-class basis by invoking
 2026        * {@link #setClassAssertionStatus(String, boolean)}.  </p>
 2027        *
 2028        * @param  packageName
 2029        *         The name of the package whose package default assertion status
 2030        *         is to be set. A <tt>null</tt> value indicates the unnamed
 2031        *         package that is "current"
 2032        *         (see section 7.4.2 of
 2033        *         <cite>The Java&trade; Language Specification</cite>.)
 2034        *
 2035        * @param  enabled
 2036        *         <tt>true</tt> if classes loaded by this classloader and
 2037        *         belonging to the named package or any of its subpackages will
 2038        *         have assertions enabled by default, <tt>false</tt> if they will
 2039        *         have assertions disabled by default.
 2040        *
 2041        * @since  1.4
 2042        */
 2043       public void setPackageAssertionStatus(String packageName,
 2044                                             boolean enabled) {
 2045           synchronized (assertionLock) {
 2046               if (packageAssertionStatus == null)
 2047                   initializeJavaAssertionMaps();
 2048   
 2049               packageAssertionStatus.put(packageName, enabled);
 2050           }
 2051       }
 2052   
 2053       /**
 2054        * Sets the desired assertion status for the named top-level class in this
 2055        * class loader and any nested classes contained therein.  This setting
 2056        * takes precedence over the class loader's default assertion status, and
 2057        * over any applicable per-package default.  This method has no effect if
 2058        * the named class has already been initialized.  (Once a class is
 2059        * initialized, its assertion status cannot change.)
 2060        *
 2061        * <p> If the named class is not a top-level class, this invocation will
 2062        * have no effect on the actual assertion status of any class. </p>
 2063        *
 2064        * @param  className
 2065        *         The fully qualified class name of the top-level class whose
 2066        *         assertion status is to be set.
 2067        *
 2068        * @param  enabled
 2069        *         <tt>true</tt> if the named class is to have assertions
 2070        *         enabled when (and if) it is initialized, <tt>false</tt> if the
 2071        *         class is to have assertions disabled.
 2072        *
 2073        * @since  1.4
 2074        */
 2075       public void setClassAssertionStatus(String className, boolean enabled) {
 2076           synchronized (assertionLock) {
 2077               if (classAssertionStatus == null)
 2078                   initializeJavaAssertionMaps();
 2079   
 2080               classAssertionStatus.put(className, enabled);
 2081           }
 2082       }
 2083   
 2084       /**
 2085        * Sets the default assertion status for this class loader to
 2086        * <tt>false</tt> and discards any package defaults or class assertion
 2087        * status settings associated with the class loader.  This method is
 2088        * provided so that class loaders can be made to ignore any command line or
 2089        * persistent assertion status settings and "start with a clean slate."
 2090        * </p>
 2091        *
 2092        * @since  1.4
 2093        */
 2094       public void clearAssertionStatus() {
 2095           /*
 2096            * Whether or not "Java assertion maps" are initialized, set
 2097            * them to empty maps, effectively ignoring any present settings.
 2098            */
 2099           synchronized (assertionLock) {
 2100               classAssertionStatus = new HashMap<>();
 2101               packageAssertionStatus = new HashMap<>();
 2102               defaultAssertionStatus = false;
 2103           }
 2104       }
 2105   
 2106       /**
 2107        * Returns the assertion status that would be assigned to the specified
 2108        * class if it were to be initialized at the time this method is invoked.
 2109        * If the named class has had its assertion status set, the most recent
 2110        * setting will be returned; otherwise, if any package default assertion
 2111        * status pertains to this class, the most recent setting for the most
 2112        * specific pertinent package default assertion status is returned;
 2113        * otherwise, this class loader's default assertion status is returned.
 2114        * </p>
 2115        *
 2116        * @param  className
 2117        *         The fully qualified class name of the class whose desired
 2118        *         assertion status is being queried.
 2119        *
 2120        * @return  The desired assertion status of the specified class.
 2121        *
 2122        * @see  #setClassAssertionStatus(String, boolean)
 2123        * @see  #setPackageAssertionStatus(String, boolean)
 2124        * @see  #setDefaultAssertionStatus(boolean)
 2125        *
 2126        * @since  1.4
 2127        */
 2128       boolean desiredAssertionStatus(String className) {
 2129           synchronized (assertionLock) {
 2130               // assert classAssertionStatus   != null;
 2131               // assert packageAssertionStatus != null;
 2132   
 2133               // Check for a class entry
 2134               Boolean result = classAssertionStatus.get(className);
 2135               if (result != null)
 2136                   return result.booleanValue();
 2137   
 2138               // Check for most specific package entry
 2139               int dotIndex = className.lastIndexOf(".");
 2140               if (dotIndex < 0) { // default package
 2141                   result = packageAssertionStatus.get(null);
 2142                   if (result != null)
 2143                       return result.booleanValue();
 2144               }
 2145               while(dotIndex > 0) {
 2146                   className = className.substring(0, dotIndex);
 2147                   result = packageAssertionStatus.get(className);
 2148                   if (result != null)
 2149                       return result.booleanValue();
 2150                   dotIndex = className.lastIndexOf(".", dotIndex-1);
 2151               }
 2152   
 2153               // Return the classloader default
 2154               return defaultAssertionStatus;
 2155           }
 2156       }
 2157   
 2158       // Set up the assertions with information provided by the VM.
 2159       // Note: Should only be called inside a synchronized block
 2160       private void initializeJavaAssertionMaps() {
 2161           // assert Thread.holdsLock(assertionLock);
 2162   
 2163           classAssertionStatus = new HashMap<>();
 2164           packageAssertionStatus = new HashMap<>();
 2165           AssertionStatusDirectives directives = retrieveDirectives();
 2166   
 2167           for(int i = 0; i < directives.classes.length; i++)
 2168               classAssertionStatus.put(directives.classes[i],
 2169                                        directives.classEnabled[i]);
 2170   
 2171           for(int i = 0; i < directives.packages.length; i++)
 2172               packageAssertionStatus.put(directives.packages[i],
 2173                                          directives.packageEnabled[i]);
 2174   
 2175           defaultAssertionStatus = directives.deflt;
 2176       }
 2177   
 2178       // Retrieves the assertion directives from the VM.
 2179       private static native AssertionStatusDirectives retrieveDirectives();
 2180   }
 2181   
 2182   
 2183   class SystemClassLoaderAction
 2184       implements PrivilegedExceptionAction<ClassLoader> {
 2185       private ClassLoader parent;
 2186   
 2187       SystemClassLoaderAction(ClassLoader parent) {
 2188           this.parent = parent;
 2189       }
 2190   
 2191       public ClassLoader run() throws Exception {
 2192           String cls = System.getProperty("java.system.class.loader");
 2193           if (cls == null) {
 2194               return parent;
 2195           }
 2196   
 2197           Constructor ctor = Class.forName(cls, true, parent)
 2198               .getDeclaredConstructor(new Class[] { ClassLoader.class });
 2199           ClassLoader sys = (ClassLoader) ctor.newInstance(
 2200               new Object[] { parent });
 2201           Thread.currentThread().setContextClassLoader(sys);
 2202           return sys;
 2203       }
 2204   }

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