/*

 * Copyright 1994-2005 Sun Microsystems, Inc.  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.  Sun designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

 * CA 95054 USA or visit www.sun.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.util.Enumeration;

import java.util.Hashtable;

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 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> 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 the <a

 * href="http://java.sun.com/docs/books/jls/">Java Language Specification</a>.

 *

 * <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();

    }

    // If initialization succeed this is set to true and security checks will

    // succeed.  Otherwise the object is not initialized and the object is

    // useless.

    private boolean initialized = false;

    // The parent class loader for delegation

    private ClassLoader parent;

    // Hashtable that maps packages to certs

    private Hashtable package2certs = new Hashtable(11);

    // Shared among all packages with unsigned classes

    java.security.cert.Certificate[] nocerts;

    // 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 Vector classes = new Vector();

    // The initiating protection domains for all classes loaded by this loader

    private Set domains = new HashSet();

    // 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.

    private HashMap packages = new HashMap();

    /**

     * 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) {

        SecurityManager security = System.getSecurityManager();

        if (security != null) {

            security.checkCreateClassLoader();

        }

        this.parent = parent;

        initialized = true;

    }

    /**

     * 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() {

        SecurityManager security = System.getSecurityManager();

        if (security != null) {

            security.checkCreateClassLoader();

        }

        this.parent = getSystemClassLoader();

        initialized = true;

    }

    // -- 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>

     *

     * @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 synchronized Class<?> loadClass(String name, boolean resolve)

        throws ClassNotFoundException

    {

        // First, check if the class has already been loaded

        Class c = findLoadedClass(name);

        if (c == null) {

            try {

                if (parent != null) {

                    c = parent.loadClass(name, false);

                } else {

                    c = findBootstrapClass0(name);

                }

            } catch (ClassNotFoundException e) {

                // If still not found, then invoke findClass in order

                // to find the class.

                c = findClass(name);

            }

        }

        if (resolve) {

            resolveClass(c);

        }

        return c;

    }

    // This method is invoked by the virtual machine to load a class.

    private synchronized Class loadClassInternal(String name)

        throws ClassNotFoundException

    {

        return loadClass(name);

    }

    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() {

                    public Object 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 the <a

     *         href="http://java.sun.com/docs/books/vmspec/">Java Virtual

     *         Machine Specification</a>.

     *

     * @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>.

     *

     * @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 the <a

     *         href="http://java.sun.com/docs/books/vmspec/">Java Virtual

     *         Machine Specification</a>.

     *

     * @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 protectionDomain)

    {

        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 (protectionDomain == null) {

            protectionDomain = getDefaultDomain();

        }

        if (name != null)

            checkCerts(name, protectionDomain.getCodeSource());

        return protectionDomain;

    }

    private String defineClassSourceLocation(ProtectionDomain protectionDomain)

    {

        CodeSource cs = protectionDomain.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 protectionDomain,

                                         ClassFormatError cfe, String source)

      throws ClassFormatError

    {

        // Class format error - try to transform the bytecode and

        // define the class again

        //

        Object[] transformers = ClassFileTransformer.getTransformers();

        Class c = null;