/*

 * Copyright (c) 1999, 2010, 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.reflect;

/**

 * {@code Proxy} provides static methods for creating dynamic proxy

 * classes and instances, and it is also the superclass of all

 * dynamic proxy classes created by those methods.

 *

 * <p>To create a proxy for some interface {@code Foo}:

 * <pre>

 *     InvocationHandler handler = new MyInvocationHandler(...);

 *     Class proxyClass = Proxy.getProxyClass(

 *         Foo.class.getClassLoader(), new Class[] { Foo.class });

 *     Foo f = (Foo) proxyClass.

 *         getConstructor(new Class[] { InvocationHandler.class }).

 *         newInstance(new Object[] { handler });

 * </pre>

 * or more simply:

 * <pre>

 *     Foo f = (Foo) Proxy.newProxyInstance(Foo.class.getClassLoader(),

 *                                          new Class[] { Foo.class },

 *                                          handler);

 * </pre>

 *

 * <p>A <i>dynamic proxy class</i> (simply referred to as a <i>proxy

 * class</i> below) is a class that implements a list of interfaces

 * specified at runtime when the class is created, with behavior as

 * described below.

 *

 * A <i>proxy interface</i> is such an interface that is implemented

 * by a proxy class.

 *

 * A <i>proxy instance</i> is an instance of a proxy class.

 *

 * Each proxy instance has an associated <i>invocation handler</i>

 * object, which implements the interface {@link InvocationHandler}.

 * A method invocation on a proxy instance through one of its proxy

 * interfaces will be dispatched to the {@link InvocationHandler#invoke

 * invoke} method of the instance's invocation handler, passing the proxy

 * instance, a {@code java.lang.reflect.Method} object identifying

 * the method that was invoked, and an array of type {@code Object}

 * containing the arguments.  The invocation handler processes the

 * encoded method invocation as appropriate and the result that it

 * returns will be returned as the result of the method invocation on

 * the proxy instance.

 *

 * <p>A proxy class has the following properties:

 *

 * <ul>

 * <li>Proxy classes are public, final, and not abstract.

 *

 * <li>The unqualified name of a proxy class is unspecified.  The space

 * of class names that begin with the string {@code "$Proxy"}

 * should be, however, reserved for proxy classes.

 *

 * <li>A proxy class extends {@code java.lang.reflect.Proxy}.

 *

 * <li>A proxy class implements exactly the interfaces specified at its

 * creation, in the same order.

 *

 * <li>If a proxy class implements a non-public interface, then it will

 * be defined in the same package as that interface.  Otherwise, the

 * package of a proxy class is also unspecified.  Note that package

 * sealing will not prevent a proxy class from being successfully defined

 * in a particular package at runtime, and neither will classes already

 * defined by the same class loader and the same package with particular

 * signers.

 *

 * <li>Since a proxy class implements all of the interfaces specified at

 * its creation, invoking {@code getInterfaces} on its

 * {@code Class} object will return an array containing the same

 * list of interfaces (in the order specified at its creation), invoking

 * {@code getMethods} on its {@code Class} object will return

 * an array of {@code Method} objects that include all of the

 * methods in those interfaces, and invoking {@code getMethod} will

 * find methods in the proxy interfaces as would be expected.

 *

 * <li>The {@link Proxy#isProxyClass Proxy.isProxyClass} method will

 * return true if it is passed a proxy class-- a class returned by

 * {@code Proxy.getProxyClass} or the class of an object returned by

 * {@code Proxy.newProxyInstance}-- and false otherwise.

 *

 * <li>The {@code java.security.ProtectionDomain} of a proxy class

 * is the same as that of system classes loaded by the bootstrap class

 * loader, such as {@code java.lang.Object}, because the code for a

 * proxy class is generated by trusted system code.  This protection

 * domain will typically be granted

 * {@code java.security.AllPermission}.

 *

 * <li>Each proxy class has one public constructor that takes one argument,

 * an implementation of the interface {@link InvocationHandler}, to set

 * the invocation handler for a proxy instance.  Rather than having to use

 * the reflection API to access the public constructor, a proxy instance

 * can be also be created by calling the {@link Proxy#newProxyInstance

 * Proxy.newProxyInstance} method, which combines the actions of calling

 * {@link Proxy#getProxyClass Proxy.getProxyClass} with invoking the

 * constructor with an invocation handler.

 * </ul>

 *

 * <p>A proxy instance has the following properties:

 *

 * <ul>

 * <li>Given a proxy instance {@code proxy} and one of the

 * interfaces implemented by its proxy class {@code Foo}, the

 * following expression will return true:

 * <pre>

 *     {@code proxy instanceof Foo}

 * </pre>

 * and the following cast operation will succeed (rather than throwing

 * a {@code ClassCastException}):

 * <pre>

 *     {@code (Foo) proxy}

 * </pre>

 *

 * <li>Each proxy instance has an associated invocation handler, the one

 * that was passed to its constructor.  The static

 * {@link Proxy#getInvocationHandler Proxy.getInvocationHandler} method

 * will return the invocation handler associated with the proxy instance

 * passed as its argument.

 *

 * <li>An interface method invocation on a proxy instance will be

 * encoded and dispatched to the invocation handler's {@link

 * InvocationHandler#invoke invoke} method as described in the

 * documentation for that method.

 *

 * <li>An invocation of the {@code hashCode},

 * {@code equals}, or {@code toString} methods declared in

 * {@code java.lang.Object} on a proxy instance will be encoded and

 * dispatched to the invocation handler's {@code invoke} method in

 * the same manner as interface method invocations are encoded and

 * dispatched, as described above.  The declaring class of the

 * {@code Method} object passed to {@code invoke} will be

 * {@code java.lang.Object}.  Other public methods of a proxy

 * instance inherited from {@code java.lang.Object} are not

 * overridden by a proxy class, so invocations of those methods behave

 * like they do for instances of {@code java.lang.Object}.

 * </ul>

 *

 * <h3>Methods Duplicated in Multiple Proxy Interfaces</h3>

 *

 * <p>When two or more interfaces of a proxy class contain a method with

 * the same name and parameter signature, the order of the proxy class's

 * interfaces becomes significant.  When such a <i>duplicate method</i>

 * is invoked on a proxy instance, the {@code Method} object passed

 * to the invocation handler will not necessarily be the one whose

 * declaring class is assignable from the reference type of the interface

 * that the proxy's method was invoked through.  This limitation exists

 * because the corresponding method implementation in the generated proxy

 * class cannot determine which interface it was invoked through.

 * Therefore, when a duplicate method is invoked on a proxy instance,

 * the {@code Method} object for the method in the foremost interface

 * that contains the method (either directly or inherited through a

 * superinterface) in the proxy class's list of interfaces is passed to

 * the invocation handler's {@code invoke} method, regardless of the

 * reference type through which the method invocation occurred.

 *

 * <p>If a proxy interface contains a method with the same name and

 * parameter signature as the {@code hashCode}, {@code equals},

 * or {@code toString} methods of {@code java.lang.Object},

 * when such a method is invoked on a proxy instance, the

 * {@code Method} object passed to the invocation handler will have

 * {@code java.lang.Object} as its declaring class.  In other words,

 * the public, non-final methods of {@code java.lang.Object}

 * logically precede all of the proxy interfaces for the determination of

 * which {@code Method} object to pass to the invocation handler.

 *

 * <p>Note also that when a duplicate method is dispatched to an

 * invocation handler, the {@code invoke} method may only throw

 * checked exception types that are assignable to one of the exception

 * types in the {@code throws} clause of the method in <i>all</i> of

 * the proxy interfaces that it can be invoked through.  If the

 * {@code invoke} method throws a checked exception that is not

 * assignable to any of the exception types declared by the method in one

 * of the proxy interfaces that it can be invoked through, then an

 * unchecked {@code UndeclaredThrowableException} will be thrown by

 * the invocation on the proxy instance.  This restriction means that not

 * all of the exception types returned by invoking

 * {@code getExceptionTypes} on the {@code Method} object

 * passed to the {@code invoke} method can necessarily be thrown

 * successfully by the {@code invoke} method.

 *

 * @author      Peter Jones

 * @see         InvocationHandler

 * @since       1.3

 */

public class Proxy implements java.io.Serializable {

    private static final long serialVersionUID = -2222568056686623797L;

    /**

     * the invocation handler for this proxy instance.

     * @serial

     */

    protected InvocationHandler h;

    /**

     * Prohibits instantiation.

     */

    private Proxy() {

    }

    /**

     * Constructs a new {@code Proxy} instance from a subclass

     * (typically, a dynamic proxy class) with the specified value

     * for its invocation handler.

     *

     * @param   h the invocation handler for this proxy instance

     */

    protected Proxy(InvocationHandler h) {

        this.h = h;

    }

    /**

     * Returns the {@code java.lang.Class} object for a proxy class

     * given a class loader and an array of interfaces.  The proxy class

     * will be defined by the specified class loader and will implement

     * all of the supplied interfaces.  If a proxy class for the same

     * permutation of interfaces has already been defined by the class

     * loader, then the existing proxy class will be returned; otherwise,

     * a proxy class for those interfaces will be generated dynamically

     * and defined by the class loader.

     *

     * <p>There are several restrictions on the parameters that may be

     * passed to {@code Proxy.getProxyClass}:

     *

     * <ul>

     * <li>All of the {@code Class} objects in the

     * {@code interfaces} array must represent interfaces, not

     * classes or primitive types.

     *

     * <li>No two elements in the {@code interfaces} array may

     * refer to identical {@code Class} objects.

     *

     * <li>All of the interface types must be visible by name through the

     * specified class loader.  In other words, for class loader

     * {@code cl} and every interface {@code i}, the following

     * expression must be true:

     * <pre>

     *     Class.forName(i.getName(), false, cl) == i

     * </pre>

     *

     * <li>All non-public interfaces must be in the same package;

     * otherwise, it would not be possible for the proxy class to

     * implement all of the interfaces, regardless of what package it is

     * defined in.

     *

     * <li>For any set of member methods of the specified interfaces

     * that have the same signature:

     * <ul>

     * <li>If the return type of any of the methods is a primitive

     * type or void, then all of the methods must have that same

     * return type.

     * <li>Otherwise, one of the methods must have a return type that

     * is assignable to all of the return types of the rest of the

     * methods.

     * </ul>

     *

     * <li>The resulting proxy class must not exceed any limits imposed

     * on classes by the virtual machine.  For example, the VM may limit

     * the number of interfaces that a class may implement to 65535; in

     * that case, the size of the {@code interfaces} array must not

     * exceed 65535.

     * </ul>

     *

     * <p>If any of these restrictions are violated,

     * {@code Proxy.getProxyClass} will throw an

     * {@code IllegalArgumentException}.  If the {@code interfaces}

     * array argument or any of its elements are {@code null}, a

     * {@code NullPointerException} will be thrown.

     *

     * <p>Note that the order of the specified proxy interfaces is

     * significant: two requests for a proxy class with the same combination

     * of interfaces but in a different order will result in two distinct

     * proxy classes.

     *

     * @param   loader the class loader to define the proxy class

     * @param   interfaces the list of interfaces for the proxy class

     *          to implement

     * @return  a proxy class that is defined in the specified class loader

     *          and that implements the specified interfaces

     * @throws  IllegalArgumentException if any of the restrictions on the

     *          parameters that may be passed to {@code getProxyClass}

     *          are violated

     * @throws  NullPointerException if the {@code interfaces} array

     *          argument or any of its elements are {@code null}

     */

    public static Class<?> getProxyClass(ClassLoader loader,

                                         Class<?>... interfaces)

        throws IllegalArgumentException

    {

        throw new IllegalArgumentException();

    }

    /**

     * Returns an instance of a proxy class for the specified interfaces

     * that dispatches method invocations to the specified invocation

     * handler.  This method is equivalent to:

     * <pre>

     *     Proxy.getProxyClass(loader, interfaces).

     *         getConstructor(new Class[] { InvocationHandler.class }).

     *         newInstance(new Object[] { handler });

     * </pre>

     *

     * <p>{@code Proxy.newProxyInstance} throws

     * {@code IllegalArgumentException} for the same reasons that

     * {@code Proxy.getProxyClass} does.

     *

     * @param   loader the class loader to define the proxy class

     * @param   interfaces the list of interfaces for the proxy class

     *          to implement

     * @param   h the invocation handler to dispatch method invocations to

     * @return  a proxy instance with the specified invocation handler of a

     *          proxy class that is defined by the specified class loader

     *          and that implements the specified interfaces

     * @throws  IllegalArgumentException if any of the restrictions on the

     *          parameters that may be passed to {@code getProxyClass}

     *          are violated

     * @throws  NullPointerException if the {@code interfaces} array

     *          argument or any of its elements are {@code null}, or

     *          if the invocation handler, {@code h}, is

     *          {@code null}

     */

    public static Object newProxyInstance(ClassLoader loader,

                                          Class<?>[] interfaces,

                                          InvocationHandler h)

        throws IllegalArgumentException

    {

        if (h == null) {

            throw new NullPointerException();

        }

        throw new IllegalArgumentException();

    }

    /**

     * Returns true if and only if the specified class was dynamically

     * generated to be a proxy class using the {@code getProxyClass}

     * method or the {@code newProxyInstance} method.

     *

     * <p>The reliability of this method is important for the ability

     * to use it to make security decisions, so its implementation should

     * not just test if the class in question extends {@code Proxy}.

     *

     * @param   cl the class to test

     * @return  {@code true} if the class is a proxy class and

     *          {@code false} otherwise

     * @throws  NullPointerException if {@code cl} is {@code null}

     */

    public static boolean isProxyClass(Class<?> cl) {

        if (cl == null) {

            throw new NullPointerException();

        }

        return false;

    }

    /**

     * Returns the invocation handler for the specified proxy instance.

     *

     * @param   proxy the proxy instance to return the invocation handler for

     * @return  the invocation handler for the proxy instance

     * @throws  IllegalArgumentException if the argument is not a

     *          proxy instance

     */

    public static InvocationHandler getInvocationHandler(Object proxy)

        throws IllegalArgumentException

    {

        /*

         * Verify that the object is actually a proxy instance.

         */

        if (!isProxyClass(proxy.getClass())) {

            throw new IllegalArgumentException("not a proxy instance");

        }

        Proxy p = (Proxy) proxy;

        return p.h;

    }

    private static native Class defineClass0(ClassLoader loader, String name,

                                             byte[] b, int off, int len);

}