/*
    * Copyright (c) 1994, 2011, Oracle and/or its affiliates. All rights reserved.
    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
    *
    * This code is free software; you can redistribute it and/or modify it
    * under the terms of the GNU General Public License version 2 only, as
    * published by the Free Software Foundation.  Oracle designates this
    * particular file as subject to the "Classpath" exception as provided
    * by Oracle in the LICENSE file that accompanied this code.
   *
   * This code is distributed in the hope that it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   * version 2 for more details (a copy is included in the LICENSE file that
   * accompanied this code).
   *
   * You should have received a copy of the GNU General Public License version
   * 2 along with this work; if not, write to the Free Software Foundation,
   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   * or visit www.oracle.com if you need additional information or have any
   * questions.
   */
  package java.lang;
  
  import java.io.InputStream;
  import java.io.IOException;
  import java.io.File;
  import java.lang.reflect.Constructor;
  import java.lang.reflect.InvocationTargetException;
  import java.net.MalformedURLException;
  import java.net.URL;
  import java.security.AccessController;
  import java.security.AccessControlContext;
  import java.security.CodeSource;
  import java.security.Policy;
  import java.security.PrivilegedAction;
  import java.security.PrivilegedActionException;
  import java.security.PrivilegedExceptionAction;
  import java.security.ProtectionDomain;
  import java.security.cert.Certificate;
  import java.util.Collections;
  import java.util.Enumeration;
  import java.util.HashMap;
  import java.util.HashSet;
  import java.util.Set;
  import java.util.Stack;
  import java.util.Map;
  import java.util.Vector;
  import java.util.Hashtable;
  import java.util.WeakHashMap;
  import java.util.concurrent.ConcurrentHashMap;
  import sun.misc.ClassFileTransformer;
  import sun.misc.CompoundEnumeration;
  import sun.misc.Resource;
  import sun.misc.URLClassPath;
  import sun.misc.VM;
  import sun.reflect.Reflection;
  import sun.security.util.SecurityConstants;
  
  /**
   * A class loader is an object that is responsible for loading classes. The
   * class <tt>ClassLoader</tt> is an abstract class.  Given the <a
   * href="#name">binary name</a> of a class, a class loader should attempt to
   * locate or generate data that constitutes a definition for the class.  A
   * typical strategy is to transform the name into a file name and then read a
   * "class file" of that name from a file system.
   *
   * <p> Every {@link Class <tt>Class</tt>} object contains a {@link
   * Class#getClassLoader() reference} to the <tt>ClassLoader</tt> that defined
   * it.
   *
   * <p> <tt>Class</tt> objects for array classes are not created by class
   * loaders, but are created automatically as required by the Java runtime.
   * The class loader for an array class, as returned by {@link
   * Class#getClassLoader()} is the same as the class loader for its element
   * type; if the element type is a primitive type, then the array class has no
   * class loader.
   *
   * <p> Applications implement subclasses of <tt>ClassLoader</tt> in order to
   * extend the manner in which the Java virtual machine dynamically loads
   * classes.
   *
   * <p> Class loaders may typically be used by security managers to indicate
   * security domains.
   *
   * <p> The <tt>ClassLoader</tt> class uses a delegation model to search for
   * classes and resources.  Each instance of <tt>ClassLoader</tt> has an
   * associated parent class loader.  When requested to find a class or
   * resource, a <tt>ClassLoader</tt> instance will delegate the search for the
   * class or resource to its parent class loader before attempting to find the
   * class or resource itself.  The virtual machine's built-in class loader,
   * called the "bootstrap class loader", does not itself have a parent but may
   * serve as the parent of a <tt>ClassLoader</tt> instance.
   *
   * <p> Class loaders that support concurrent loading of classes are known as
   * <em>parallel capable</em> class loaders and are required to register
   * themselves at their class initialization time by invoking the
  * {@link
  * #registerAsParallelCapable <tt>ClassLoader.registerAsParallelCapable</tt>}
  * method. Note that the <tt>ClassLoader</tt> class is registered as parallel
  * capable by default. However, its subclasses still need to register themselves
  * if they are parallel capable. <br>
  * In environments in which the delegation model is not strictly
  * hierarchical, class loaders need to be parallel capable, otherwise class
  * loading can lead to deadlocks because the loader lock is held for the
  * duration of the class loading process (see {@link #loadClass
  * <tt>loadClass</tt>} methods).
  *
  * <p> Normally, the Java virtual machine loads classes from the local file
  * system in a platform-dependent manner.  For example, on UNIX systems, the
  * virtual machine loads classes from the directory defined by the
  * <tt>CLASSPATH</tt> environment variable.
  *
  * <p> However, some classes may not originate from a file; they may originate
  * from other sources, such as the network, or they could be constructed by an
  * application.  The method {@link #defineClass(String, byte[], int, int)
  * <tt>defineClass</tt>} converts an array of bytes into an instance of class
  * <tt>Class</tt>. Instances of this newly defined class can be created using
  * {@link Class#newInstance <tt>Class.newInstance</tt>}.
  *
  * <p> The methods and constructors of objects created by a class loader may
  * reference other classes.  To determine the class(es) referred to, the Java
  * virtual machine invokes the {@link #loadClass <tt>loadClass</tt>} method of
  * the class loader that originally created the class.
  *
  * <p> For example, an application could create a network class loader to
  * download class files from a server.  Sample code might look like:
  *
  * <blockquote><pre>
  *   ClassLoader loader&nbsp;= new NetworkClassLoader(host,&nbsp;port);
  *   Object main&nbsp;= loader.loadClass("Main", true).newInstance();
  *       &nbsp;.&nbsp;.&nbsp;.
  * </pre></blockquote>
  *
  * <p> The network class loader subclass must define the methods {@link
  * #findClass <tt>findClass</tt>} and <tt>loadClassData</tt> to load a class
  * from the network.  Once it has downloaded the bytes that make up the class,
  * it should use the method {@link #defineClass <tt>defineClass</tt>} to
  * create a class instance.  A sample implementation is:
  *
  * <blockquote><pre>
  *     class NetworkClassLoader extends ClassLoader {
  *         String host;
  *         int port;
  *
  *         public Class findClass(String name) {
  *             byte[] b = loadClassData(name);
  *             return defineClass(name, b, 0, b.length);
  *         }
  *
  *         private byte[] loadClassData(String name) {
  *             // load the class data from the connection
  *             &nbsp;.&nbsp;.&nbsp;.
  *         }
  *     }
  * </pre></blockquote>
  *
  * <h4> <a name="name">Binary names</a> </h4>
  *
  * <p> Any class name provided as a {@link String} parameter to methods in
  * <tt>ClassLoader</tt> must be a binary name as defined by
  * <cite>The Java&trade; Language Specification</cite>.
  *
  * <p> Examples of valid class names include:
  * <blockquote><pre>
  *   "java.lang.String"
  *   "javax.swing.JSpinner$DefaultEditor"
  *   "java.security.KeyStore$Builder$FileBuilder$1"
  *   "java.net.URLClassLoader$3$1"
  * </pre></blockquote>
  *
  * @see      #resolveClass(Class)
  * @since 1.0
  */
 public abstract class ClassLoader {
 
     private static native void registerNatives();
     static {
         registerNatives();
     }
 
     // The parent class loader for delegation
     // Note: VM hardcoded the offset of this field, thus all new fields
     // must be added *after* it.
     private final ClassLoader parent;
 
     /**
      * Encapsulates the set of parallel capable loader types.
      */
     private static class ParallelLoaders {
         private ParallelLoaders() {}
 
         // the set of parallel capable loader types
         private static final Set<Class<? extends ClassLoader>> loaderTypes =
             Collections.newSetFromMap(
                 new WeakHashMap<Class<? extends ClassLoader>, Boolean>());
         static {
             synchronized (loaderTypes) { loaderTypes.add(ClassLoader.class); }
         }
 
         /**
          * Registers the given class loader type as parallel capabale.
          * Returns {@code true} is successfully registered; {@code false} if
          * loader's super class is not registered.
          */
         static boolean register(Class<? extends ClassLoader> c) {
             synchronized (loaderTypes) {
                 if (loaderTypes.contains(c.getSuperclass())) {
                     // register the class loader as parallel capable
                     // if and only if all of its super classes are.
                     // Note: given current classloading sequence, if
                     // the immediate super class is parallel capable,
                     // all the super classes higher up must be too.
                     loaderTypes.add(c);
                     return true;
                 } else {
                     return false;
                 }
             }
         }
 
         /**
          * Returns {@code true} if the given class loader type is
          * registered as parallel capable.
          */
         static boolean isRegistered(Class<? extends ClassLoader> c) {
             synchronized (loaderTypes) {
                 return loaderTypes.contains(c);
             }
         }
     }
 
     // Maps class name to the corresponding lock object when the current
     // class loader is parallel capable.
     // Note: VM also uses this field to decide if the current class loader
     // is parallel capable and the appropriate lock object for class loading.
     private final ConcurrentHashMap<String, Object> parallelLockMap;
 
     // Hashtable that maps packages to certs
     private final Map <String, Certificate[]> package2certs;
 
     // Shared among all packages with unsigned classes
     private static final Certificate[] nocerts = new Certificate[0];
 
     // The classes loaded by this class loader. The only purpose of this table
     // is to keep the classes from being GC'ed until the loader is GC'ed.
     private final Vector<Class<?>> classes = new Vector<>();
 
     // The "default" domain. Set as the default ProtectionDomain on newly
     // created classes.
     private final ProtectionDomain defaultDomain =
         new ProtectionDomain(new CodeSource(null, (Certificate[]) null),
                              null, this, null);
 
     // The initiating protection domains for all classes loaded by this loader
     private final Set<ProtectionDomain> domains;
 
     // Invoked by the VM to record every loaded class with this loader.
     void addClass(Class c) {
         classes.addElement(c);
     }
 
     // The packages defined in this class loader.  Each package name is mapped
     // to its corresponding Package object.
     // @GuardedBy("itself")
     private final HashMap<String, Package> packages = new HashMap<>();
 
     private static Void checkCreateClassLoader() {
         SecurityManager security = System.getSecurityManager();
         if (security != null) {
             security.checkCreateClassLoader();
         }
         return null;
     }
 
     private ClassLoader(Void unused, ClassLoader parent) {
         this.parent = parent;
         if (ParallelLoaders.isRegistered(this.getClass())) {
             parallelLockMap = new ConcurrentHashMap<>();
             package2certs = new ConcurrentHashMap<>();
             domains =
                 Collections.synchronizedSet(new HashSet<ProtectionDomain>());
             assertionLock = new Object();
         } else {
             // no finer-grained lock; lock on the classloader instance
             parallelLockMap = null;
             package2certs = new Hashtable<>();
             domains = new HashSet<>();
             assertionLock = this;
         }
     }
 
     /**
      * Creates a new class loader using the specified parent class loader for
      * delegation.
      *
      * <p> If there is a security manager, its {@link
      * SecurityManager#checkCreateClassLoader()
      * <tt>checkCreateClassLoader</tt>} method is invoked.  This may result in
      * a security exception.  </p>
      *
      * @param  parent
      *         The parent class loader
      *
      * @throws  SecurityException
      *          If a security manager exists and its
      *          <tt>checkCreateClassLoader</tt> method doesn't allow creation
      *          of a new class loader.
      *
      * @since  1.2
      */
     protected ClassLoader(ClassLoader parent) {
         this(checkCreateClassLoader(), parent);
     }
 
     /**
      * Creates a new class loader using the <tt>ClassLoader</tt> returned by
      * the method {@link #getSystemClassLoader()
      * <tt>getSystemClassLoader()</tt>} as the parent class loader.
      *
      * <p> If there is a security manager, its {@link
      * SecurityManager#checkCreateClassLoader()
      * <tt>checkCreateClassLoader</tt>} method is invoked.  This may result in
      * a security exception.  </p>
      *
      * @throws  SecurityException
      *          If a security manager exists and its
      *          <tt>checkCreateClassLoader</tt> method doesn't allow creation
      *          of a new class loader.
      */
     protected ClassLoader() {
         this(checkCreateClassLoader(), getSystemClassLoader());
     }
 
     // -- Class --
 
     /**
      * Loads the class with the specified <a href="#name">binary name</a>.
      * This method searches for classes in the same manner as the {@link
      * #loadClass(String, boolean)} method.  It is invoked by the Java virtual
      * machine to resolve class references.  Invoking this method is equivalent
      * to invoking {@link #loadClass(String, boolean) <tt>loadClass(name,
      * false)</tt>}.  </p>
      *
      * @param  name
      *         The <a href="#name">binary name</a> of the class
      *
      * @return  The resulting <tt>Class</tt> object
      *
      * @throws  ClassNotFoundException
      *          If the class was not found
      */
     public Class<?> loadClass(String name) throws ClassNotFoundException {
         return loadClass(name, false);
     }
 
     /**
      * Loads the class with the specified <a href="#name">binary name</a>.  The
      * default implementation of this method searches for classes in the
      * following order:
      *
      * <p><ol>
      *
      *   <li><p> Invoke {@link #findLoadedClass(String)} to check if the class
      *   has already been loaded.  </p></li>
      *
      *   <li><p> Invoke the {@link #loadClass(String) <tt>loadClass</tt>} method
      *   on the parent class loader.  If the parent is <tt>null</tt> the class
      *   loader built-in to the virtual machine is used, instead.  </p></li>
      *
      *   <li><p> Invoke the {@link #findClass(String)} method to find the
      *   class.  </p></li>
      *
      * </ol>
      *
      * <p> If the class was found using the above steps, and the
      * <tt>resolve</tt> flag is true, this method will then invoke the {@link
      * #resolveClass(Class)} method on the resulting <tt>Class</tt> object.
      *
      * <p> Subclasses of <tt>ClassLoader</tt> are encouraged to override {@link
      * #findClass(String)}, rather than this method.  </p>
      *
      * <p> Unless overridden, this method synchronizes on the result of
      * {@link #getClassLoadingLock <tt>getClassLoadingLock</tt>} method
      * during the entire class loading process.
      *
      * @param  name
      *         The <a href="#name">binary name</a> of the class
      *
      * @param  resolve
      *         If <tt>true</tt> then resolve the class
      *
      * @return  The resulting <tt>Class</tt> object
      *
      * @throws  ClassNotFoundException
      *          If the class could not be found
      */
     protected Class<?> loadClass(String name, boolean resolve)
         throws ClassNotFoundException
     {
         synchronized (getClassLoadingLock(name)) {
             // First, check if the class has already been loaded
             Class c = findLoadedClass(name);
             if (c == null) {
                 long t0 = System.nanoTime();
                 try {
                     if (parent != null) {
                         c = parent.loadClass(name, false);
                     } else {
                         c = findBootstrapClassOrNull(name);
                     }
                 } catch (ClassNotFoundException e) {
                     // ClassNotFoundException thrown if class not found
                     // from the non-null parent class loader
                 }
 
                 if (c == null) {
                     // If still not found, then invoke findClass in order
                     // to find the class.
                     long t1 = System.nanoTime();
                     c = findClass(name);
 
                     // this is the defining class loader; record the stats
                     sun.misc.PerfCounter.getParentDelegationTime().addTime(t1 - t0);
                     sun.misc.PerfCounter.getFindClassTime().addElapsedTimeFrom(t1);
                     sun.misc.PerfCounter.getFindClasses().increment();
                 }
             }
             if (resolve) {
                 resolveClass(c);
             }
             return c;
         }
     }
 
     /**
      * Returns the lock object for class loading operations.
      * For backward compatibility, the default implementation of this method
      * behaves as follows. If this ClassLoader object is registered as
      * parallel capable, the method returns a dedicated object associated
      * with the specified class name. Otherwise, the method returns this
      * ClassLoader object. </p>
      *
      * @param  className
      *         The name of the to-be-loaded class
      *
      * @return the lock for class loading operations
      *
      * @throws NullPointerException
      *         If registered as parallel capable and <tt>className</tt> is null
      *
      * @see #loadClass(String, boolean)
      *
      * @since  1.7
      */
     protected Object getClassLoadingLock(String className) {
         Object lock = this;
         if (parallelLockMap != null) {
             Object newLock = new Object();
             lock = parallelLockMap.putIfAbsent(className, newLock);
             if (lock == null) {
                 lock = newLock;
             }
         }
         return lock;
     }
 
     // This method is invoked by the virtual machine to load a class.
     private Class loadClassInternal(String name)
         throws ClassNotFoundException
     {
         // For backward compatibility, explicitly lock on 'this' when
         // the current class loader is not parallel capable.
         if (parallelLockMap == null) {
             synchronized (this) {
                  return loadClass(name);
             }
         } else {
             return loadClass(name);
         }
     }
 
     // Invoked by the VM after loading class with this loader.
     private void checkPackageAccess(Class cls, ProtectionDomain pd) {
         final SecurityManager sm = System.getSecurityManager();
         if (sm != null) {
             final String name = cls.getName();
             final int i = name.lastIndexOf('.');
             if (i != -1) {
                 AccessController.doPrivileged(new PrivilegedAction<Void>() {
                     public Void run() {
                         sm.checkPackageAccess(name.substring(0, i));
                         return null;
                     }
                 }, new AccessControlContext(new ProtectionDomain[] {pd}));
             }
         }
         domains.add(pd);
     }
 
     /**
      * Finds the class with the specified <a href="#name">binary name</a>.
      * This method should be overridden by class loader implementations that
      * follow the delegation model for loading classes, and will be invoked by
      * the {@link #loadClass <tt>loadClass</tt>} method after checking the
      * parent class loader for the requested class.  The default implementation
      * throws a <tt>ClassNotFoundException</tt>.  </p>
      *
      * @param  name
      *         The <a href="#name">binary name</a> of the class
      *
      * @return  The resulting <tt>Class</tt> object
      *
      * @throws  ClassNotFoundException
      *          If the class could not be found
      *
      * @since  1.2
      */
     protected Class<?> findClass(String name) throws ClassNotFoundException {
         throw new ClassNotFoundException(name);
     }
 
     /**
      * Converts an array of bytes into an instance of class <tt>Class</tt>.
      * Before the <tt>Class</tt> can be used it must be resolved.  This method
      * is deprecated in favor of the version that takes a <a
      * href="#name">binary name</a> as its first argument, and is more secure.
      *
      * @param  b
      *         The bytes that make up the class data.  The bytes in positions
      *         <tt>off</tt> through <tt>off+len-1</tt> should have the format
      *         of a valid class file as defined by
      *         <cite>The Java&trade; Virtual Machine Specification</cite>.
      *
      * @param  off
      *         The start offset in <tt>b</tt> of the class data
      *
      * @param  len
      *         The length of the class data
      *
      * @return  The <tt>Class</tt> object that was created from the specified
      *          class data
      *
      * @throws  ClassFormatError
      *          If the data did not contain a valid class
      *
      * @throws  IndexOutOfBoundsException
      *          If either <tt>off</tt> or <tt>len</tt> is negative, or if
      *          <tt>off+len</tt> is greater than <tt>b.length</tt>.
      *
      * @throws  SecurityException
      *          If an attempt is made to add this class to a package that
      *          contains classes that were signed by a different set of
      *          certificates than this class, or if an attempt is made
      *          to define a class in a package with a fully-qualified name
      *          that starts with "{@code java.}".
      *
      * @see  #loadClass(String, boolean)
      * @see  #resolveClass(Class)
      *
      * @deprecated  Replaced by {@link #defineClass(String, byte[], int, int)
      * defineClass(String, byte[], int, int)}
      */
     @Deprecated
     protected final Class<?> defineClass(byte[] b, int off, int len)
         throws ClassFormatError
     {
         return defineClass(null, b, off, len, null);
     }
 
     /**
      * Converts an array of bytes into an instance of class <tt>Class</tt>.
      * Before the <tt>Class</tt> can be used it must be resolved.
      *
      * <p> This method assigns a default {@link java.security.ProtectionDomain
      * <tt>ProtectionDomain</tt>} to the newly defined class.  The
      * <tt>ProtectionDomain</tt> is effectively granted the same set of
      * permissions returned when {@link
      * java.security.Policy#getPermissions(java.security.CodeSource)
      * <tt>Policy.getPolicy().getPermissions(new CodeSource(null, null))</tt>}
      * is invoked.  The default domain is created on the first invocation of
      * {@link #defineClass(String, byte[], int, int) <tt>defineClass</tt>},
      * and re-used on subsequent invocations.
      *
      * <p> To assign a specific <tt>ProtectionDomain</tt> to the class, use
      * the {@link #defineClass(String, byte[], int, int,
      * java.security.ProtectionDomain) <tt>defineClass</tt>} method that takes a
      * <tt>ProtectionDomain</tt> as one of its arguments.  </p>
      *
      * @param  name
      *         The expected <a href="#name">binary name</a> of the class, or
      *         <tt>null</tt> if not known
      *
      * @param  b
      *         The bytes that make up the class data.  The bytes in positions
      *         <tt>off</tt> through <tt>off+len-1</tt> should have the format
      *         of a valid class file as defined by
      *         <cite>The Java&trade; Virtual Machine Specification</cite>.
      *
      * @param  off
      *         The start offset in <tt>b</tt> of the class data
      *
      * @param  len
      *         The length of the class data
      *
      * @return  The <tt>Class</tt> object that was created from the specified
      *          class data.
      *
      * @throws  ClassFormatError
      *          If the data did not contain a valid class
      *
      * @throws  IndexOutOfBoundsException
      *          If either <tt>off</tt> or <tt>len</tt> is negative, or if
      *          <tt>off+len</tt> is greater than <tt>b.length</tt>.
      *
      * @throws  SecurityException
      *          If an attempt is made to add this class to a package that
      *          contains classes that were signed by a different set of
      *          certificates than this class (which is unsigned), or if
      *          <tt>name</tt> begins with "<tt>java.</tt>".
      *
      * @see  #loadClass(String, boolean)
      * @see  #resolveClass(Class)
      * @see  java.security.CodeSource
      * @see  java.security.SecureClassLoader
      *
      * @since  1.1
      */
     protected final Class<?> defineClass(String name, byte[] b, int off, int len)
         throws ClassFormatError
     {
         return defineClass(name, b, off, len, null);
     }
 
     /* Determine protection domain, and check that:
         - not define java.* class,
         - signer of this class matches signers for the rest of the classes in
           package.
     */
     private ProtectionDomain preDefineClass(String name,
                                             ProtectionDomain pd)
     {
         if (!checkName(name))
             throw new NoClassDefFoundError("IllegalName: " + name);
 
         if ((name != null) && name.startsWith("java.")) {
             throw new SecurityException
                 ("Prohibited package name: " +
                  name.substring(0, name.lastIndexOf('.')));
         }
         if (pd == null) {
             pd = defaultDomain;
         }
 
         if (name != null) checkCerts(name, pd.getCodeSource());
 
         return pd;
     }
 
     private String defineClassSourceLocation(ProtectionDomain pd)
     {
         CodeSource cs = pd.getCodeSource();
         String source = null;
         if (cs != null && cs.getLocation() != null) {
             source = cs.getLocation().toString();
         }
         return source;
     }
 
     private Class defineTransformedClass(String name, byte[] b, int off, int len,
                                          ProtectionDomain pd,
                                          ClassFormatError cfe, String source)
       throws ClassFormatError
     {
         // Class format error - try to transform the bytecode and
         // define the class again
         //
         ClassFileTransformer[] transformers =
             ClassFileTransformer.getTransformers();
         Class c = null;
 
         if (transformers != null) {
             for (ClassFileTransformer transformer : transformers) {
                 try {
                     // Transform byte code using transformer
                     byte[] tb = transformer.transform(b, off, len);
                     c = defineClass1(name, tb, 0, tb.length,
                                      pd, source);
                     break;
                 } catch (ClassFormatError cfe2)     {
                     // If ClassFormatError occurs, try next transformer
                 }
             }
         }
 
         // Rethrow original ClassFormatError if unable to transform
         // bytecode to well-formed
         //
         if (c == null)
             throw cfe;
 
         return c;
     }
 
     private void postDefineClass(Class c, ProtectionDomain pd)
     {
         if (pd.getCodeSource() != null) {
             Certificate certs[] = pd.getCodeSource().getCertificates();
             if (certs != null)
                 setSigners(c, certs);
         }
     }
 
     /**
      * Converts an array of bytes into an instance of class <tt>Class</tt>,
      * with an optional <tt>ProtectionDomain</tt>.  If the domain is
      * <tt>null</tt>, then a default domain will be assigned to the class as
      * specified in the documentation for {@link #defineClass(String, byte[],
      * int, int)}.  Before the class can be used it must be resolved.
      *
      * <p> The first class defined in a package determines the exact set of
      * certificates that all subsequent classes defined in that package must
      * contain.  The set of certificates for a class is obtained from the
      * {@link java.security.CodeSource <tt>CodeSource</tt>} within the
      * <tt>ProtectionDomain</tt> of the class.  Any classes added to that
      * package must contain the same set of certificates or a
      * <tt>SecurityException</tt> will be thrown.  Note that if
      * <tt>name</tt> is <tt>null</tt>, this check is not performed.
      * You should always pass in the <a href="#name">binary name</a> of the
      * class you are defining as well as the bytes.  This ensures that the
      * class you are defining is indeed the class you think it is.
      *
      * <p> The specified <tt>name</tt> cannot begin with "<tt>java.</tt>", since
      * all classes in the "<tt>java.*</tt> packages can only be defined by the
      * bootstrap class loader.  If <tt>name</tt> is not <tt>null</tt>, it
      * must be equal to the <a href="#name">binary name</a> of the class
      * specified by the byte array "<tt>b</tt>", otherwise a {@link
      * <tt>NoClassDefFoundError</tt>} will be thrown.  </p>
      *
      * @param  name
      *         The expected <a href="#name">binary name</a> of the class, or
      *         <tt>null</tt> if not known
      *
      * @param  b
      *         The bytes that make up the class data. The bytes in positions
      *         <tt>off</tt> through <tt>off+len-1</tt> should have the format
      *         of a valid class file as defined by
      *         <cite>The Java&trade; Virtual Machine Specification</cite>.
      *
      * @param  off
      *         The start offset in <tt>b</tt> of the class data
      *
      * @param  len
      *         The length of the class data
      *
      * @param  protectionDomain
      *         The ProtectionDomain of the class
      *
      * @return  The <tt>Class</tt> object created from the data,
      *          and optional <tt>ProtectionDomain</tt>.
      *
      * @throws  ClassFormatError
      *          If the data did not contain a valid class
      *
      * @throws  NoClassDefFoundError
      *          If <tt>name</tt> is not equal to the <a href="#name">binary
      *          name</a> of the class specified by <tt>b</tt>
      *
      * @throws  IndexOutOfBoundsException
      *          If either <tt>off</tt> or <tt>len</tt> is negative, or if
      *          <tt>off+len</tt> is greater than <tt>b.length</tt>.
      *
      * @throws  SecurityException
      *          If an attempt is made to add this class to a package that
      *          contains classes that were signed by a different set of
      *          certificates than this class, or if <tt>name</tt> begins with
      *          "<tt>java.</tt>".
      */
     protected final Class<?> defineClass(String name, byte[] b, int off, int len,
                                          ProtectionDomain protectionDomain)
         throws ClassFormatError
     {
         protectionDomain = preDefineClass(name, protectionDomain);
 
         Class c = null;
         String source = defineClassSourceLocation(protectionDomain);
 
         try {
             c = defineClass1(name, b, off, len, protectionDomain, source);
         } catch (ClassFormatError cfe) {
             c = defineTransformedClass(name, b, off, len, protectionDomain, cfe,
                                        source);
         }
 
         postDefineClass(c, protectionDomain);
         return c;
     }
 
     /**
      * Converts a {@link java.nio.ByteBuffer <tt>ByteBuffer</tt>}
      * into an instance of class <tt>Class</tt>,
      * with an optional <tt>ProtectionDomain</tt>.  If the domain is
      * <tt>null</tt>, then a default domain will be assigned to the class as
      * specified in the documentation for {@link #defineClass(String, byte[],
      * int, int)}.  Before the class can be used it must be resolved.
      *
      * <p>The rules about the first class defined in a package determining the
      * set of certificates for the package, and the restrictions on class names
      * are identical to those specified in the documentation for {@link
      * #defineClass(String, byte[], int, int, ProtectionDomain)}.
      *
      * <p> An invocation of this method of the form
      * <i>cl</i><tt>.defineClass(</tt><i>name</i><tt>,</tt>
      * <i>bBuffer</i><tt>,</tt> <i>pd</i><tt>)</tt> yields exactly the same
      * result as the statements
      *
      * <blockquote><tt>
      * ...<br>
      * byte[] temp = new byte[</tt><i>bBuffer</i><tt>.{@link
      * java.nio.ByteBuffer#remaining remaining}()];<br>
      *     </tt><i>bBuffer</i><tt>.{@link java.nio.ByteBuffer#get(byte[])
      * get}(temp);<br>
      *     return {@link #defineClass(String, byte[], int, int, ProtectionDomain)
      * </tt><i>cl</i><tt>.defineClass}(</tt><i>name</i><tt>, temp, 0,
      * temp.length, </tt><i>pd</i><tt>);<br>
      * </tt></blockquote>
      *
      * @param  name
      *         The expected <a href="#name">binary name</a>. of the class, or
      *         <tt>null</tt> if not known
      *
      * @param  b
      *         The bytes that make up the class data. The bytes from positions
      *         <tt>b.position()</tt> through <tt>b.position() + b.limit() -1
      *         </tt> should have the format of a valid class file as defined by
      *         <cite>The Java&trade; Virtual Machine Specification</cite>.
      *
      * @param  protectionDomain
      *         The ProtectionDomain of the class, or <tt>null</tt>.
      *
      * @return  The <tt>Class</tt> object created from the data,
      *          and optional <tt>ProtectionDomain</tt>.
      *
      * @throws  ClassFormatError
      *          If the data did not contain a valid class.
      *
      * @throws  NoClassDefFoundError
      *          If <tt>name</tt> is not equal to the <a href="#name">binary
      *          name</a> of the class specified by <tt>b</tt>
      *
      * @throws  SecurityException
      *          If an attempt is made to add this class to a package that
      *          contains classes that were signed by a different set of
      *          certificates than this class, or if <tt>name</tt> begins with
      *          "<tt>java.</tt>".
      *
      * @see      #defineClass(String, byte[], int, int, ProtectionDomain)
      *
      * @since  1.5
      */
     protected final Class<?> defineClass(String name, java.nio.ByteBuffer b,
                                          ProtectionDomain protectionDomain)
         throws ClassFormatError
     {
         int len = b.remaining();
 
         // Use byte[] if not a direct ByteBufer:
         if (!b.isDirect()) {
             if (b.hasArray()) {
                 return defineClass(name, b.array(),
                                    b.position() + b.arrayOffset(), len,
                                    protectionDomain);
             } else {
                 // no array, or read-only array
                 byte[] tb = new byte[len];
                 b.get(tb);  // get bytes out of byte buffer.
                 return defineClass(name, tb, 0, len, protectionDomain);
             }
         }
 
         protectionDomain = preDefineClass(name, protectionDomain);
 
         Class c = null;
         String source = defineClassSourceLocation(protectionDomain);
 
         try {
             c = defineClass2(name, b, b.position(), len, protectionDomain,
                              source);
         } catch (ClassFormatError cfe) {
             byte[] tb = new byte[len];
             b.get(tb);  // get bytes out of byte buffer.
             c = defineTransformedClass(name, tb, 0, len, protectionDomain, cfe,
                                        source);
         }
 
         postDefineClass(c, protectionDomain);
         return c;
     }
 
     private native Class defineClass0(String name, byte[] b, int off, int len,
                                       ProtectionDomain pd);
 
     private native Class defineClass1(String name, byte[] b, int off, int len,
                                       ProtectionDomain pd, String source);
 
     private native Class defineClass2(String name, java.nio.ByteBuffer b,
                                       int off, int len, ProtectionDomain pd,
                                       String source);
 
     // true if the name is null or has the potential to be a valid binary name
     private boolean checkName(String name) {
         if ((name == null) || (name.length() == 0))
             return true;
         if ((name.indexOf('/') != -1)
             || (!VM.allowArraySyntax() && (name.charAt(0) == '[')))
             return false;
         return true;
     }
 
     private void checkCerts(String name, CodeSource cs) {
         int i = name.lastIndexOf('.');
         String pname = (i == -1) ? "" : name.substring(0, i);
 
         Certificate[] certs = null;
         if (cs != null) {
             certs = cs.getCertificates();
         }
         Certificate[] pcerts = null;
         if (parallelLockMap == null) {
             synchronized (this) {
                 pcerts = package2certs.get(pname);
                 if (pcerts == null) {
                     package2certs.put(pname, (certs == null? nocerts:certs));
                 }
             }
         } else {
             pcerts = ((ConcurrentHashMap<String, Certificate[]>)package2certs).
                 putIfAbsent(pname, (certs == null? nocerts:certs));
         }
         if (pcerts != null && !compareCerts(pcerts, certs)) {
             throw new SecurityException("class \""+ name +
                  "\"'s signer information does not match signer information of other classes in the same package");
         }
     }
 
     /**
      * check to make sure the certs for the new class (certs) are the same as
      * the certs for the first class inserted in the package (pcerts)
      */
     private boolean compareCerts(Certificate[] pcerts,
                                  Certificate[] certs)
     {
         // certs can be null, indicating no certs.
         if ((certs == null) || (certs.length == 0)) {
             return pcerts.length == 0;
         }
 
         // the length must be the same at this point
         if (certs.length != pcerts.length)
             return false;
 
         // go through and make sure all the certs in one array
         // are in the other and vice-versa.
         boolean match;
         for (int i = 0; i < certs.length; i++) {
             match = false;
             for (int j = 0; j < pcerts.length; j++) {
                 if (certs[i].equals(pcerts[j])) {
                     match = true;
                     break;
                 }
             }
             if (!match) return false;
         }
 
         // now do the same for pcerts
         for (int i = 0; i < pcerts.length; i++) {
             match = false;
             for (int j = 0; j < certs.length; j++) {
                 if (pcerts[i].equals(certs[j])) {
                     match = true;
                     break;
                 }
             }
             if (!match) return false;
         }
 
         return true;
     }
 
     /**
      * Links the specified class.  This (misleadingly named) method may be
      * used by a class loader to link a class.  If the class <tt>c</tt> has
      * already been linked, then this method simply returns. Otherwise, the
      * class is linked as described in the "Execution" chapter of
      * <cite>The Java&trade; Language Specification</cite>.
      * </p>
      *
      * @param  c
      *         The class to link
      *
      * @throws  NullPointerException
      *          If <tt>c</tt> is <tt>null</tt>.
      *
      * @see  #defineClass(String, byte[], int, int)
      */
     protected final void resolveClass(Class<?> c) {
         resolveClass0(c);
     }
 
     private native void resolveClass0(Class c);
 
     /**
      * Finds a class with the specified <a href="#name">binary name</a>,
      * loading it if necessary.
      *
      * <p> This method loads the class through the system class loader (see
      * {@link #getSystemClassLoader()}).  The <tt>Class</tt> object returned
      * might have more than one <tt>ClassLoader</tt> associated with it.
      * Subclasses of <tt>ClassLoader</tt> need not usually invoke this method,
      * because most class loaders need to override just {@link
      * #findClass(String)}.  </p>
      *
      * @param  name
      *         The <a href="#name">binary name</a> of the class
      *
      * @return  The <tt>Class</tt> object for the specified <tt>name</tt>
      *
      * @throws  ClassNotFoundException
      *          If the class could not be found
      *
      * @see  #ClassLoader(ClassLoader)
      * @see  #getParent()
      */
     protected final Class<?> findSystemClass(String name)
         throws ClassNotFoundException
     {
         ClassLoader system = getSystemClassLoader();
         if (system == null) {
             if (!checkName(name))
                 throw new ClassNotFoundException(name);
             Class cls = findBootstrapClass(name);
             if (cls == null) {
                 throw new ClassNotFoundException(name);
             }
             return cls;
         }
         return system.loadClass(name);
     }
 
     /**
      * Returns a class loaded by the bootstrap class loader;
      * or return null if not found.
      */
     private Class findBootstrapClassOrNull(String name)
     {
         if (!checkName(name)) return null;
 
         return findBootstrapClass(name);
     }
 
     // return null if not found
     private native Class findBootstrapClass(String name);
 
     /**
      * Returns the class with the given <a href="#name">binary name</a> if this
      * loader has been recorded by the Java virtual machine as an initiating
      * loader of a class with that <a href="#name">binary name</a>.  Otherwise
      * <tt>null</tt> is returned.  </p>
      *
      * @param  name
      *         The <a href="#name">binary name</a> of the class
      *
      * @return  The <tt>Class</tt> object, or <tt>null</tt> if the class has
      *          not been loaded
      *
      * @since  1.1
      */
     protected final Class<?> findLoadedClass(String name) {
         if (!checkName(name))
             return null;
         return findLoadedClass0(name);
     }
 
     private native final Class findLoadedClass0(String name);
 
     /**
      * Sets the signers of a class.  This should be invoked after defining a
      * class.  </p>
      *
      * @param  c
      *         The <tt>Class</tt> object
      *
      * @param  signers
      *         The signers for the class
      *
      * @since  1.1
      */
     protected final void setSigners(Class<?> c, Object[] signers) {
         c.setSigners(signers);
     }
 
 
     // -- Resource --
 
     /**
      * Finds the resource with the given name.  A resource is some data
      * (images, audio, text, etc) that can be accessed by class code in a way
      * that is independent of the location of the code.
      *
      * <p> The name of a resource is a '<tt>/</tt>'-separated path name that
      * identifies the resource.
      *
      * <p> This method will first search the parent class loader for the
      * resource; if the parent is <tt>null</tt> the path of the class loader
      * built-in to the virtual machine is searched.  That failing, this method
      * will invoke {@link #findResource(String)} to find the resource.  </p>
      *
      * @param  name
      *         The resource name
      *
      * @return  A <tt>URL</tt> object for reading the resource, or
      *          <tt>null</tt> if the resource could not be found or the invoker
      *          doesn't have adequate  privileges to get the resource.
      *
      * @since  1.1
      */
     public URL getResource(String name) {
         URL url;
         if (parent != null) {
             url = parent.getResource(name);
         } else {
             url = getBootstrapResource(name);
         }
         if (url == null) {
             url = findResource(name);
         }
         return url;
     }
 
     /**
      * Finds all the resources with the given name. A resource is some data
      * (images, audio, text, etc) that can be accessed by class code in a way
      * that is independent of the location of the code.
      *
      * <p>The name of a resource is a <tt>/</tt>-separated path name that
      * identifies the resource.
      *
      * <p> The search order is described in the documentation for {@link
      * #getResource(String)}.  </p>
      *
      * @param  name
      *         The resource name
      *
      * @return  An enumeration of {@link java.net.URL <tt>URL</tt>} objects for
      *          the resource.  If no resources could  be found, the enumeration
      *          will be empty.  Resources that the class loader doesn't have
      *          access to will not be in the enumeration.
      *
      * @throws  IOException
      *          If I/O errors occur
      *
      * @see  #findResources(String)
      *
      * @since  1.2
      */
     public Enumeration<URL> getResources(String name) throws IOException {
         Enumeration[] tmp = new Enumeration[2];
         if (parent != null) {
             tmp[0] = parent.getResources(name);
         } else {
             tmp[0] = getBootstrapResources(name);
         }
         tmp[1] = findResources(name);
 
         return new CompoundEnumeration<>(tmp);
     }
 
     /**
      * Finds the resource with the given name. Class loader implementations
      * should override this method to specify where to find resources.  </p>
      *
      * @param  name
      *         The resource name
      *
      * @return  A <tt>URL</tt> object for reading the resource, or
      *          <tt>null</tt> if the resource could not be found
      *
      * @since  1.2
      */
     protected URL findResource(String name) {
         return null;
     }
 
     /**
      * Returns an enumeration of {@link java.net.URL <tt>URL</tt>} objects
      * representing all the resources with the given name. Class loader
      * implementations should override this method to specify where to load
      * resources from.  </p>
      *
      * @param  name
      *         The resource name
      *
      * @return  An enumeration of {@link java.net.URL <tt>URL</tt>} objects for
      *          the resources
      *
      * @throws  IOException
      *          If I/O errors occur
      *
      * @since  1.2
      */
     protected Enumeration<URL> findResources(String name) throws IOException {
         return java.util.Collections.emptyEnumeration();
     }
 
     // index 0: java.lang.ClassLoader.class
     // index 1: the immediate caller of index 0.
     // index 2: the immediate caller of index 1.
     private static native Class<? extends ClassLoader> getCaller(int index);
 
     /**
      * Registers the caller as parallel capable.</p>
      * The registration succeeds if and only if all of the following
      * conditions are met: <br>
      * 1. no instance of the caller has been created</p>
      * 2. all of the super classes (except class Object) of the caller are
      * registered as parallel capable</p>
      * Note that once a class loader is registered as parallel capable, there
      * is no way to change it back. </p>
      *
      * @return  true if the caller is successfully registered as
      *          parallel capable and false if otherwise.
      *
      * @since   1.7
      */
     protected static boolean registerAsParallelCapable() {
         return ParallelLoaders.register(getCaller(1));
     }
 
     /**
      * Find a resource of the specified name from the search path used to load
      * classes.  This method locates the resource through the system class
      * loader (see {@link #getSystemClassLoader()}).  </p>
      *
      * @param  name
      *         The resource name
      *
      * @return  A {@link java.net.URL <tt>URL</tt>} object for reading the
      *          resource, or <tt>null</tt> if the resource could not be found
      *
      * @since  1.1
      */
     public static URL getSystemResource(String name) {
         ClassLoader system = getSystemClassLoader();
         if (system == null) {
             return getBootstrapResource(name);
         }
         return system.getResource(name);
     }
 
     /**
      * Finds all resources of the specified name from the search path used to
      * load classes.  The resources thus found are returned as an
      * {@link java.util.Enumeration <tt>Enumeration</tt>} of {@link
      * java.net.URL <tt>URL</tt>} objects.
      *
      * <p> The search order is described in the documentation for {@link
      * #getSystemResource(String)}.  </p>
      *
      * @param  name
      *         The resource name
      *
      * @return  An enumeration of resource {@link java.net.URL <tt>URL</tt>}
      *          objects
      *
      * @throws  IOException
      *          If I/O errors occur
 
      * @since  1.2
      */
     public static Enumeration<URL> getSystemResources(String name)
         throws IOException
     {
         ClassLoader system = getSystemClassLoader();
         if (system == null) {
             return getBootstrapResources(name);
         }
         return system.getResources(name);
     }
 
     /**
      * Find resources from the VM's built-in classloader.
      */
     private static URL getBootstrapResource(String name) {
         URLClassPath ucp = getBootstrapClassPath();
         Resource res = ucp.getResource(name);
         return res != null ? res.getURL() : null;
     }
 
     /**
      * Find resources from the VM's built-in classloader.
      */
     private static Enumeration<URL> getBootstrapResources(String name)
         throws IOException
     {
         final Enumeration<Resource> e =
             getBootstrapClassPath().getResources(name);
         return new Enumeration<URL> () {
             public URL nextElement() {
                 return e.nextElement().getURL();
             }
             public boolean hasMoreElements() {
                 return e.hasMoreElements();
             }
         };
     }
 
     // Returns the URLClassPath that is used for finding system resources.
     static URLClassPath getBootstrapClassPath() {
         return sun.misc.Launcher.getBootstrapClassPath();
     }
 
 
     /**
      * Returns an input stream for reading the specified resource.
      *
      * <p> The search order is described in the documentation for {@link
      * #getResource(String)}.  </p>
      *
      * @param  name
      *         The resource name
      *
      * @return  An input stream for reading the resource, or <tt>null</tt>
      *          if the resource could not be found
      *
      * @since  1.1
      */
     public InputStream getResourceAsStream(String name) {
         URL url = getResource(name);
         try {
             return url != null ? url.openStream() : null;
         } catch (IOException e) {
             return null;
         }
     }
 
     /**
      * Open for reading, a resource of the specified name from the search path
      * used to load classes.  This method locates the resource through the
      * system class loader (see {@link #getSystemClassLoader()}).  </p>
      *
      * @param  name
      *         The resource name
      *
      * @return  An input stream for reading the resource, or <tt>null</tt>
      *          if the resource could not be found
      *
      * @since  1.1
      */
     public static InputStream getSystemResourceAsStream(String name) {
         URL url = getSystemResource(name);
         try {
             return url != null ? url.openStream() : null;
         } catch (IOException e) {
             return null;
         }
     }
 
 
     // -- Hierarchy --
 
     /**
      * Returns the parent class loader for delegation. Some implementations may
      * use <tt>null</tt> to represent the bootstrap class loader. This method
      * will return <tt>null</tt> in such implementations if this class loader's
      * parent is the bootstrap class loader.
      *
      * <p> If a security manager is present, and the invoker's class loader is
      * not <tt>null</tt> and is not an ancestor of this class loader, then this
      * method invokes the security manager's {@link
      * SecurityManager#checkPermission(java.security.Permission)
      * <tt>checkPermission</tt>} method with a {@link
      * RuntimePermission#RuntimePermission(String)
      * <tt>RuntimePermission("getClassLoader")</tt>} permission to verify
      * access to the parent class loader is permitted.  If not, a
      * <tt>SecurityException</tt> will be thrown.  </p>
      *
      * @return  The parent <tt>ClassLoader</tt>
      *
      * @throws  SecurityException
      *          If a security manager exists and its <tt>checkPermission</tt>
      *          method doesn't allow access to this class loader's parent class
      *          loader.
      *
      * @since  1.2
      */
     public final ClassLoader getParent() {
         if (parent == null)
             return null;
         SecurityManager sm = System.getSecurityManager();
         if (sm != null) {
             ClassLoader ccl = getCallerClassLoader();
             if (ccl != null && !isAncestor(ccl)) {
                 sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
             }
         }
         return parent;
     }
 
     /**
      * Returns the system class loader for delegation.  This is the default
      * delegation parent for new <tt>ClassLoader</tt> instances, and is
      * typically the class loader used to start the application.
      *
      * <p> This method is first invoked early in the runtime's startup
      * sequence, at which point it creates the system class loader and sets it
      * as the context class loader of the invoking <tt>Thread</tt>.
      *
      * <p> The default system class loader is an implementation-dependent
      * instance of this class.
      *
      * <p> If the system property "<tt>java.system.class.loader</tt>" is defined
      * when this method is first invoked then the value of that property is
      * taken to be the name of a class that will be returned as the system
      * class loader.  The class is loaded using the default system class loader
      * and must define a public constructor that takes a single parameter of
      * type <tt>ClassLoader</tt> which is used as the delegation parent.  An
      * instance is then created using this constructor with the default system
      * class loader as the parameter.  The resulting class loader is defined
      * to be the system class loader.
      *
      * <p> If a security manager is present, and the invoker's class loader is
      * not <tt>null</tt> and the invoker's class loader is not the same as or
      * an ancestor of the system class loader, then this method invokes the
      * security manager's {@link
      * SecurityManager#checkPermission(java.security.Permission)
      * <tt>checkPermission</tt>} method with a {@link
      * RuntimePermission#RuntimePermission(String)
      * <tt>RuntimePermission("getClassLoader")</tt>} permission to verify
      * access to the system class loader.  If not, a
      * <tt>SecurityException</tt> will be thrown.  </p>
      *
      * @return  The system <tt>ClassLoader</tt> for delegation, or
      *          <tt>null</tt> if none
      *
      * @throws  SecurityException
      *          If a security manager exists and its <tt>checkPermission</tt>
      *          method doesn't allow access to the system class loader.
      *
      * @throws  IllegalStateException
      *          If invoked recursively during the construction of the class
      *          loader specified by the "<tt>java.system.class.loader</tt>"
      *          property.
      *
      * @throws  Error
      *          If the system property "<tt>java.system.class.loader</tt>"
      *          is defined but the named class could not be loaded, the
      *          provider class does not define the required constructor, or an
      *          exception is thrown by that constructor when it is invoked. The
      *          underlying cause of the error can be retrieved via the
      *          {@link Throwable#getCause()} method.
      *
      * @revised  1.4
      */
     public static ClassLoader getSystemClassLoader() {
         initSystemClassLoader();
         if (scl == null) {
             return null;
         }
         SecurityManager sm = System.getSecurityManager();
         if (sm != null) {
             ClassLoader ccl = getCallerClassLoader();
             if (ccl != null && ccl != scl && !scl.isAncestor(ccl)) {
                 sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
             }
         }
         return scl;
     }
 
     private static synchronized void initSystemClassLoader() {
         if (!sclSet) {
             if (scl != null)
                 throw new IllegalStateException("recursive invocation");
             sun.misc.Launcher l = sun.misc.Launcher.getLauncher();
             if (l != null) {
                 Throwable oops = null;
                 scl = l.getClassLoader();
                 try {
                     scl = AccessController.doPrivileged(
                         new SystemClassLoaderAction(scl));
                 } catch (PrivilegedActionException pae) {
                     oops = pae.getCause();
                     if (oops instanceof InvocationTargetException) {
                         oops = oops.getCause();
                     }
                 }
                 if (oops != null) {
                     if (oops instanceof Error) {
                         throw (Error) oops;
                     } else {
                         // wrap the exception
                         throw new Error(oops);
                     }
                 }
             }
             sclSet = true;
         }
     }
 
     // Returns true if the specified class loader can be found in this class
     // loader's delegation chain.
     boolean isAncestor(ClassLoader cl) {
         ClassLoader acl = this;
         do {
             acl = acl.parent;
             if (cl == acl) {
                 return true;
             }
         } while (acl != null);
         return false;
     }
 
     // Returns the invoker's class loader, or null if none.
     // NOTE: This must always be invoked when there is exactly one intervening
     // frame from the core libraries on the stack between this method's
     // invocation and the desired invoker.
     static ClassLoader getCallerClassLoader() {
         // NOTE use of more generic Reflection.getCallerClass()
         Class caller = Reflection.getCallerClass(3);
         // This can be null if the VM is requesting it
         if (caller == null) {
             return null;
         }
         // Circumvent security check since this is package-private
         return caller.getClassLoader0();
     }
 
     // The class loader for the system
     // @GuardedBy("ClassLoader.class")
     private static ClassLoader scl;
 
     // Set to true once the system class loader has been set
     // @GuardedBy("ClassLoader.class")
     private static boolean sclSet;
 
 
     // -- Package --
 
     /**
      * Defines a package by name in this <tt>ClassLoader</tt>.  This allows
      * class loaders to define the packages for their classes. Packages must
      * be created before the class is defined, and package names must be
      * unique within a class loader and cannot be redefined or changed once
      * created.  </p>
      *
      * @param  name
      *         The package name
      *
      * @param  specTitle
      *         The specification title
      *
      * @param  specVersion
      *         The specification version
      *
      * @param  specVendor
      *         The specification vendor
      *
      * @param  implTitle
      *         The implementation title
      *
      * @param  implVersion
      *         The implementation version
      *
      * @param  implVendor
      *         The implementation vendor
      *
      * @param  sealBase
      *         If not <tt>null</tt>, then this package is sealed with
      *         respect to the given code source {@link java.net.URL
      *         <tt>URL</tt>}  object.  Otherwise, the package is not sealed.
      *
      * @return  The newly defined <tt>Package</tt> object
      *
      * @throws  IllegalArgumentException
      *          If package name duplicates an existing package either in this
      *          class loader or one of its ancestors
      *
      * @since  1.2
      */
     protected Package definePackage(String name, String specTitle,
                                     String specVersion, String specVendor,
                                     String implTitle, String implVersion,
                                     String implVendor, URL sealBase)
         throws IllegalArgumentException
     {
         synchronized (packages) {
             Package pkg = getPackage(name);
             if (pkg != null) {
                 throw new IllegalArgumentException(name);
             }
             pkg = new Package(name, specTitle, specVersion, specVendor,
                               implTitle, implVersion, implVendor,
                               sealBase, this);
             packages.put(name, pkg);
             return pkg;
         }
     }
 
     /**
      * Returns a <tt>Package</tt> that has been defined by this class loader
      * or any of its ancestors.  </p>
      *
      * @param  name
      *         The package name
      *
      * @return  The <tt>Package</tt> corresponding to the given name, or
      *          <tt>null</tt> if not found
      *
      * @since  1.2
      */
     protected Package getPackage(String name) {
         Package pkg;
         synchronized (packages) {
             pkg = packages.get(name);
         }
         if (pkg == null) {
             if (parent != null) {
                 pkg = parent.getPackage(name);
             } else {
                 pkg = Package.getSystemPackage(name);
             }
             if (pkg != null) {
                 synchronized (packages) {
                     Package pkg2 = packages.get(name);
                     if (pkg2 == null) {
                         packages.put(name, pkg);
                     } else {
                         pkg = pkg2;
                     }
                 }
             }
         }
         return pkg;
     }
 
     /**
      * Returns all of the <tt>Packages</tt> defined by this class loader and
      * its ancestors.  </p>
      *
      * @return  The array of <tt>Package</tt> objects defined by this
      *          <tt>ClassLoader</tt>
      *
      * @since  1.2
      */
     protected Package[] getPackages() {
         Map<String, Package> map;
         synchronized (packages) {
             map = new HashMap<>(packages);
         }
         Package[] pkgs;
         if (parent != null) {
             pkgs = parent.getPackages();
         } else {
             pkgs = Package.getSystemPackages();
         }
         if (pkgs != null) {
             for (int i = 0; i < pkgs.length; i++) {
                 String pkgName = pkgs[i].getName();
                 if (map.get(pkgName) == null) {
                     map.put(pkgName, pkgs[i]);
                 }
             }
         }
         return map.values().toArray(new Package[map.size()]);
     }
 
 
     // -- Native library access --
 
     /**
      * Returns the absolute path name of a native library.  The VM invokes this
      * method to locate the native libraries that belong to classes loaded with
      * this class loader. If this method returns <tt>null</tt>, the VM
      * searches the library along the path specified as the
      * "<tt>java.library.path</tt>" property.  </p>
      *
      * @param  libname
      *         The library name
      *
      * @return  The absolute path of the native library
      *
      * @see  System#loadLibrary(String)
      * @see  System#mapLibraryName(String)
      *
      * @since  1.2
      */
     protected String findLibrary(String libname) {
         return null;
     }
 
     /**
      * The inner class NativeLibrary denotes a loaded native library instance.
      * Every classloader contains a vector of loaded native libraries in the
      * private field <tt>nativeLibraries</tt>.  The native libraries loaded
      * into the system are entered into the <tt>systemNativeLibraries</tt>
      * vector.
      *
      * <p> Every native library requires a particular version of JNI. This is
      * denoted by the private <tt>jniVersion</tt> field.  This field is set by
      * the VM when it loads the library, and used by the VM to pass the correct
      * version of JNI to the native methods.  </p>
      *
      * @see      ClassLoader
      * @since    1.2
      */
     static class NativeLibrary {
         // opaque handle to native library, used in native code.
         long handle;
         // the version of JNI environment the native library requires.
         private int jniVersion;
         // the class from which the library is loaded, also indicates
         // the loader this native library belongs.
         private Class fromClass;
         // the canonicalized name of the native library.
         String name;
 
         native void load(String name);
         native long find(String name);
         native void unload();
 
         public NativeLibrary(Class fromClass, String name) {
             this.name = name;
             this.fromClass = fromClass;
         }
 
         protected void finalize() {
             synchronized (loadedLibraryNames) {
                 if (fromClass.getClassLoader() != null && handle != 0) {
                     /* remove the native library name */
                     int size = loadedLibraryNames.size();
                     for (int i = 0; i < size; i++) {
                         if (name.equals(loadedLibraryNames.elementAt(i))) {
                             loadedLibraryNames.removeElementAt(i);
                             break;
                         }
                     }
                     /* unload the library. */
                     ClassLoader.nativeLibraryContext.push(this);
                     try {
                         unload();
                     } finally {
                         ClassLoader.nativeLibraryContext.pop();
                     }
                 }
             }
         }
         // Invoked in the VM to determine the context class in
         // JNI_Load/JNI_Unload
         static Class getFromClass() {
             return ClassLoader.nativeLibraryContext.peek().fromClass;
         }
     }
 
     // All native library names we've loaded.
     private static Vector<String> loadedLibraryNames = new Vector<>();
 
     // Native libraries belonging to system classes.
     private static Vector<NativeLibrary> systemNativeLibraries
         = new Vector<>();
 
     // Native libraries associated with the class loader.
     private Vector<NativeLibrary> nativeLibraries = new Vector<>();
 
     // native libraries being loaded/unloaded.
     private static Stack<NativeLibrary> nativeLibraryContext = new Stack<>();
 
     // The paths searched for libraries
     private static String usr_paths[];
     private static String sys_paths[];
 
     private static String[] initializePath(String propname) {
         String ldpath = System.getProperty(propname, "");
         String ps = File.pathSeparator;
         int ldlen = ldpath.length();
         int i, j, n;
         // Count the separators in the path
         i = ldpath.indexOf(ps);
         n = 0;
         while (i >= 0) {
             n++;
             i = ldpath.indexOf(ps, i + 1);
         }
 
         // allocate the array of paths - n :'s = n + 1 path elements
         String[] paths = new String[n + 1];
 
         // Fill the array with paths from the ldpath
         n = i = 0;
         j = ldpath.indexOf(ps);
         while (j >= 0) {
             if (j - i > 0) {
                 paths[n++] = ldpath.substring(i, j);
             } else if (j - i == 0) {
                 paths[n++] = ".";
             }
             i = j + 1;
             j = ldpath.indexOf(ps, i);
         }
         paths[n] = ldpath.substring(i, ldlen);
         return paths;
     }
 
     // Invoked in the java.lang.Runtime class to implement load and loadLibrary.
     static void loadLibrary(Class fromClass, String name,
                             boolean isAbsolute) {
         ClassLoader loader =
             (fromClass == null) ? null : fromClass.getClassLoader();
         if (sys_paths == null) {
             usr_paths = initializePath("java.library.path");
             sys_paths = initializePath("sun.boot.library.path");
         }
         if (isAbsolute) {
             if (loadLibrary0(fromClass, new File(name))) {
                 return;
             }
             throw new UnsatisfiedLinkError("Can't load library: " + name);
         }
         if (loader != null) {
             String libfilename = loader.findLibrary(name);
             if (libfilename != null) {
                 File libfile = new File(libfilename);
                 if (!libfile.isAbsolute()) {
                     throw new UnsatisfiedLinkError(
     "ClassLoader.findLibrary failed to return an absolute path: " + libfilename);
                 }
                 if (loadLibrary0(fromClass, libfile)) {
                     return;
                 }
                 throw new UnsatisfiedLinkError("Can't load " + libfilename);
             }
         }
         for (int i = 0 ; i < sys_paths.length ; i++) {
             File libfile = new File(sys_paths[i], System.mapLibraryName(name));
             if (loadLibrary0(fromClass, libfile)) {
                 return;
             }
         }
         if (loader != null) {
             for (int i = 0 ; i < usr_paths.length ; i++) {
                 File libfile = new File(usr_paths[i],
                                         System.mapLibraryName(name));
                 if (loadLibrary0(fromClass, libfile)) {
                     return;
                 }
             }
         }
         // Oops, it failed
         throw new UnsatisfiedLinkError("no " + name + " in java.library.path");
     }
 
     private static boolean loadLibrary0(Class fromClass, final File file) {
         boolean exists = AccessController.doPrivileged(
             new PrivilegedAction<Object>() {
                 public Object run() {
                     return file.exists() ? Boolean.TRUE : null;
                 }})
             != null;
         if (!exists) {
             return false;
         }
         String name;
         try {
             name = file.getCanonicalPath();
         } catch (IOException e) {
             return false;
         }
         ClassLoader loader =
             (fromClass == null) ? null : fromClass.getClassLoader();
         Vector<NativeLibrary> libs =
             loader != null ? loader.nativeLibraries : systemNativeLibraries;
         synchronized (libs) {
             int size = libs.size();
             for (int i = 0; i < size; i++) {
                 NativeLibrary lib = libs.elementAt(i);
                 if (name.equals(lib.name)) {
                     return true;
                 }
             }
 
             synchronized (loadedLibraryNames) {
                 if (loadedLibraryNames.contains(name)) {
                     throw new UnsatisfiedLinkError
                         ("Native Library " +
                          name +
                          " already loaded in another classloader");
                 }
                 /* If the library is being loaded (must be by the same thread,
                  * because Runtime.load and Runtime.loadLibrary are
                  * synchronous). The reason is can occur is that the JNI_OnLoad
                  * function can cause another loadLibrary invocation.
                  *
                  * Thus we can use a static stack to hold the list of libraries
                  * we are loading.
                  *
                  * If there is a pending load operation for the library, we
                  * immediately return success; otherwise, we raise
                  * UnsatisfiedLinkError.
                  */
                 int n = nativeLibraryContext.size();
                 for (int i = 0; i < n; i++) {
                     NativeLibrary lib = nativeLibraryContext.elementAt(i);
                     if (name.equals(lib.name)) {
                         if (loader == lib.fromClass.getClassLoader()) {
                             return true;
                         } else {
                             throw new UnsatisfiedLinkError
                                 ("Native Library " +
                                  name +
                                  " is being loaded in another classloader");
                         }
                     }
                 }
                 NativeLibrary lib = new NativeLibrary(fromClass, name);
                 nativeLibraryContext.push(lib);
                 try {
                     lib.load(name);
                 } finally {
                     nativeLibraryContext.pop();
                 }
                 if (lib.handle != 0) {
                     loadedLibraryNames.addElement(name);
                     libs.addElement(lib);
                     return true;
                 }
                 return false;
             }
         }
     }
 
     // Invoked in the VM class linking code.
     static long findNative(ClassLoader loader, String name) {
         Vector<NativeLibrary> libs =
             loader != null ? loader.nativeLibraries : systemNativeLibraries;
         synchronized (libs) {
             int size = libs.size();
             for (int i = 0; i < size; i++) {
                 NativeLibrary lib = libs.elementAt(i);
                 long entry = lib.find(name);
                 if (entry != 0)
                     return entry;
             }
         }
         return 0;
     }
 
 
     // -- Assertion management --
 
     final Object assertionLock;
 
     // The default toggle for assertion checking.
     // @GuardedBy("assertionLock")
     private boolean defaultAssertionStatus = false;
 
     // Maps String packageName to Boolean package default assertion status Note
     // that the default package is placed under a null map key.  If this field
     // is null then we are delegating assertion status queries to the VM, i.e.,
     // none of this ClassLoader's assertion status modification methods have
     // been invoked.
     // @GuardedBy("assertionLock")
     private Map<String, Boolean> packageAssertionStatus = null;
 
     // Maps String fullyQualifiedClassName to Boolean assertionStatus If this
     // field is null then we are delegating assertion status queries to the VM,
     // i.e., none of this ClassLoader's assertion status modification methods
     // have been invoked.
     // @GuardedBy("assertionLock")
     Map<String, Boolean> classAssertionStatus = null;
 
     /**
      * Sets the default assertion status for this class loader.  This setting
      * determines whether classes loaded by this class loader and initialized
      * in the future will have assertions enabled or disabled by default.
      * This setting may be overridden on a per-package or per-class basis by
      * invoking {@link #setPackageAssertionStatus(String, boolean)} or {@link
      * #setClassAssertionStatus(String, boolean)}.  </p>
      *
      * @param  enabled
      *         <tt>true</tt> if classes loaded by this class loader will
      *         henceforth have assertions enabled by default, <tt>false</tt>
      *         if they will have assertions disabled by default.
      *
      * @since  1.4
      */
     public void setDefaultAssertionStatus(boolean enabled) {
         synchronized (assertionLock) {
             if (classAssertionStatus == null)
                 initializeJavaAssertionMaps();
 
             defaultAssertionStatus = enabled;
         }
     }
 
     /**
      * Sets the package default assertion status for the named package.  The
      * package default assertion status determines the assertion status for
      * classes initialized in the future that belong to the named package or
      * any of its "subpackages".
      *
      * <p> A subpackage of a package named p is any package whose name begins
      * with "<tt>p.</tt>".  For example, <tt>javax.swing.text</tt> is a
      * subpackage of <tt>javax.swing</tt>, and both <tt>java.util</tt> and
      * <tt>java.lang.reflect</tt> are subpackages of <tt>java</tt>.
      *
      * <p> In the event that multiple package defaults apply to a given class,
      * the package default pertaining to the most specific package takes
      * precedence over the others.  For example, if <tt>javax.lang</tt> and
      * <tt>javax.lang.reflect</tt> both have package defaults associated with
      * them, the latter package default applies to classes in
      * <tt>javax.lang.reflect</tt>.
      *
      * <p> Package defaults take precedence over the class loader's default
      * assertion status, and may be overridden on a per-class basis by invoking
      * {@link #setClassAssertionStatus(String, boolean)}.  </p>
      *
      * @param  packageName
      *         The name of the package whose package default assertion status
      *         is to be set. A <tt>null</tt> value indicates the unnamed
      *         package that is "current"
      *         (see section 7.4.2 of
      *         <cite>The Java&trade; Language Specification</cite>.)
      *
      * @param  enabled
      *         <tt>true</tt> if classes loaded by this classloader and
      *         belonging to the named package or any of its subpackages will
      *         have assertions enabled by default, <tt>false</tt> if they will
      *         have assertions disabled by default.
      *
      * @since  1.4
      */
     public void setPackageAssertionStatus(String packageName,
                                           boolean enabled) {
         synchronized (assertionLock) {
             if (packageAssertionStatus == null)
                 initializeJavaAssertionMaps();
 
             packageAssertionStatus.put(packageName, enabled);
         }
     }
 
     /**
      * Sets the desired assertion status for the named top-level class in this
      * class loader and any nested classes contained therein.  This setting
      * takes precedence over the class loader's default assertion status, and
      * over any applicable per-package default.  This method has no effect if
      * the named class has already been initialized.  (Once a class is
      * initialized, its assertion status cannot change.)
      *
      * <p> If the named class is not a top-level class, this invocation will
      * have no effect on the actual assertion status of any class. </p>
      *
      * @param  className
      *         The fully qualified class name of the top-level class whose
      *         assertion status is to be set.
      *
      * @param  enabled
      *         <tt>true</tt> if the named class is to have assertions
      *         enabled when (and if) it is initialized, <tt>false</tt> if the
      *         class is to have assertions disabled.
      *
      * @since  1.4
      */
     public void setClassAssertionStatus(String className, boolean enabled) {
         synchronized (assertionLock) {
             if (classAssertionStatus == null)
                 initializeJavaAssertionMaps();
 
             classAssertionStatus.put(className, enabled);
         }
     }
 
     /**
      * Sets the default assertion status for this class loader to
      * <tt>false</tt> and discards any package defaults or class assertion
      * status settings associated with the class loader.  This method is
      * provided so that class loaders can be made to ignore any command line or
      * persistent assertion status settings and "start with a clean slate."
      * </p>
      *
      * @since  1.4
      */
     public void clearAssertionStatus() {
         /*
          * Whether or not "Java assertion maps" are initialized, set
          * them to empty maps, effectively ignoring any present settings.
          */
         synchronized (assertionLock) {
             classAssertionStatus = new HashMap<>();
             packageAssertionStatus = new HashMap<>();
             defaultAssertionStatus = false;
         }
     }
 
     /**
      * Returns the assertion status that would be assigned to the specified
      * class if it were to be initialized at the time this method is invoked.
      * If the named class has had its assertion status set, the most recent
      * setting will be returned; otherwise, if any package default assertion
      * status pertains to this class, the most recent setting for the most
      * specific pertinent package default assertion status is returned;
      * otherwise, this class loader's default assertion status is returned.
      * </p>
      *
      * @param  className
      *         The fully qualified class name of the class whose desired
      *         assertion status is being queried.
      *
      * @return  The desired assertion status of the specified class.
      *
      * @see  #setClassAssertionStatus(String, boolean)
      * @see  #setPackageAssertionStatus(String, boolean)
      * @see  #setDefaultAssertionStatus(boolean)
      *
      * @since  1.4
      */
     boolean desiredAssertionStatus(String className) {
         synchronized (assertionLock) {
             // assert classAssertionStatus   != null;
             // assert packageAssertionStatus != null;
 
             // Check for a class entry
             Boolean result = classAssertionStatus.get(className);
             if (result != null)
                 return result.booleanValue();
 
             // Check for most specific package entry
             int dotIndex = className.lastIndexOf(".");
             if (dotIndex < 0) { // default package
                 result = packageAssertionStatus.get(null);
                 if (result != null)
                     return result.booleanValue();
             }
             while(dotIndex > 0) {
                 className = className.substring(0, dotIndex);
                 result = packageAssertionStatus.get(className);
                 if (result != null)
                     return result.booleanValue();
                 dotIndex = className.lastIndexOf(".", dotIndex-1);
             }
 
             // Return the classloader default
             return defaultAssertionStatus;
         }
     }
 
     // Set up the assertions with information provided by the VM.
     // Note: Should only be called inside a synchronized block
     private void initializeJavaAssertionMaps() {
         // assert Thread.holdsLock(assertionLock);
 
         classAssertionStatus = new HashMap<>();
         packageAssertionStatus = new HashMap<>();
         AssertionStatusDirectives directives = retrieveDirectives();
 
         for(int i = 0; i < directives.classes.length; i++)
             classAssertionStatus.put(directives.classes[i],
                                      directives.classEnabled[i]);
 
         for(int i = 0; i < directives.packages.length; i++)
             packageAssertionStatus.put(directives.packages[i],
                                        directives.packageEnabled[i]);
 
         defaultAssertionStatus = directives.deflt;
     }
 
     // Retrieves the assertion directives from the VM.
     private static native AssertionStatusDirectives retrieveDirectives();
 }
 
 
 class SystemClassLoaderAction
     implements PrivilegedExceptionAction<ClassLoader> {
     private ClassLoader parent;
 
     SystemClassLoaderAction(ClassLoader parent) {
         this.parent = parent;
     }
 
     public ClassLoader run() throws Exception {
         String cls = System.getProperty("java.system.class.loader");
         if (cls == null) {
             return parent;
         }
 
         Constructor ctor = Class.forName(cls, true, parent)
             .getDeclaredConstructor(new Class[] { ClassLoader.class });
         ClassLoader sys = (ClassLoader) ctor.newInstance(
             new Object[] { parent });
         Thread.currentThread().setContextClassLoader(sys);
         return sys;
     }
 }