/*

 * 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 = new NetworkClassLoader(host, port);

 *   Object main = loader.loadClass("Main", true).newInstance();

 *        . . .

 * </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

 *              . . .

 *         }

 *     }

 * </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;

    }

    /**