/*

  * 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

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  */

 package java.lang.reflect;

 import java.lang.ref.Reference;

 import java.lang.ref.WeakReference;

 import java.util.Arrays;

 import java.util.Collections;

 import java.util.HashMap;

 import java.util.HashSet;

 import java.util.Map;

 import java.util.Set;

 import java.util.List;

 import java.util.WeakHashMap;

 import sun.misc.ProxyGenerator;

 /**

  * {@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;

     /** prefix for all proxy class names */

     private final static String proxyClassNamePrefix = "$Proxy";

     /** parameter types of a proxy class constructor */

     private final static Class[] constructorParams =

         { InvocationHandler.class };

     /** maps a class loader to the proxy class cache for that loader */

     private static Map<ClassLoader, Map<List<String>, Object>> loaderToCache

         = new WeakHashMap<>();

     /** marks that a particular proxy class is currently being generated */

     private static Object pendingGenerationMarker = new Object();

     /** next number to use for generation of unique proxy class names */

     private static long nextUniqueNumber = 0;

     private static Object nextUniqueNumberLock = new Object();

     /** set of all generated proxy classes, for isProxyClass implementation */

     private static Map<Class<?>, Void> proxyClasses =

         Collections.synchronizedMap(new WeakHashMap<Class<?>, Void>());

     /**

      * 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

     {

         if (interfaces.length > 65535) {

             throw new IllegalArgumentException("interface limit exceeded");

         }

         Class<?> proxyClass = null;

         /* collect interface names to use as key for proxy class cache */

         String[] interfaceNames = new String[interfaces.length];

         // for detecting duplicates

         Set<Class<?>> interfaceSet = new HashSet<>();

         for (int i = 0; i < interfaces.length; i++) {

             /*

              * Verify that the class loader resolves the name of this

              * interface to the same Class object.

              */

             String interfaceName = interfaces[i].getName();

             Class<?> interfaceClass = null;

             try {

                 interfaceClass = Class.forName(interfaceName, false, loader);

             } catch (ClassNotFoundException e) {

             }

             if (interfaceClass != interfaces[i]) {

                 throw new IllegalArgumentException(

                     interfaces[i] + " is not visible from class loader");

             }

             /*

              * Verify that the Class object actually represents an

              * interface.

              */

             if (!interfaceClass.isInterface()) {

                 throw new IllegalArgumentException(

                     interfaceClass.getName() + " is not an interface");

             }

             /*

              * Verify that this interface is not a duplicate.

              */

             if (interfaceSet.contains(interfaceClass)) {

                 throw new IllegalArgumentException(

                     "repeated interface: " + interfaceClass.getName());

             }

             interfaceSet.add(interfaceClass);

             interfaceNames[i] = interfaceName;

         }

         /*

          * Using string representations of the proxy interfaces as

          * keys in the proxy class cache (instead of their Class

          * objects) is sufficient because we require the proxy

          * interfaces to be resolvable by name through the supplied

          * class loader, and it has the advantage that using a string

          * representation of a class makes for an implicit weak

          * reference to the class.

          */

         List<String> key = Arrays.asList(interfaceNames);

         /*

          * Find or create the proxy class cache for the class loader.

          */

         Map<List<String>, Object> cache;

         synchronized (loaderToCache) {

             cache = loaderToCache.get(loader);

             if (cache == null) {

                 cache = new HashMap<>();

                 loaderToCache.put(loader, cache);

             }

             /*

              * This mapping will remain valid for the duration of this

              * method, without further synchronization, because the mapping

              * will only be removed if the class loader becomes unreachable.

              */

         }

         /*

          * Look up the list of interfaces in the proxy class cache using

          * the key.  This lookup will result in one of three possible

          * kinds of values:

          *     null, if there is currently no proxy class for the list of

          *         interfaces in the class loader,

          *     the pendingGenerationMarker object, if a proxy class for the

          *         list of interfaces is currently being generated,

          *     or a weak reference to a Class object, if a proxy class for

          *         the list of interfaces has already been generated.

          */

         synchronized (cache) {

             /*

              * Note that we need not worry about reaping the cache for

              * entries with cleared weak references because if a proxy class

              * has been garbage collected, its class loader will have been

              * garbage collected as well, so the entire cache will be reaped

              * from the loaderToCache map.

              */

             do {

                 Object value = cache.get(key);

                 if (value instanceof Reference) {

                     proxyClass = (Class<?>) ((Reference) value).get();

                 }

                 if (proxyClass != null) {

                     // proxy class already generated: return it

                     return proxyClass;

                 } else if (value == pendingGenerationMarker) {

                     // proxy class being generated: wait for it

                     try {

                         cache.wait();

                     } catch (InterruptedException e) {

                         /*

                          * The class generation that we are waiting for should

                          * take a small, bounded time, so we can safely ignore

                          * thread interrupts here.

                          */

                     }

                     continue;

                 } else {

                     /*

                      * No proxy class for this list of interfaces has been

                      * generated or is being generated, so we will go and

                      * generate it now.  Mark it as pending generation.

                      */

                     cache.put(key, pendingGenerationMarker);

                     break;

                 }

             } while (true);

         }

         try {

             String proxyPkg = null;     // package to define proxy class in

             /*

              * Record the package of a non-public proxy interface so that the

              * proxy class will be defined in the same package.  Verify that

              * all non-public proxy interfaces are in the same package.

              */

             for (int i = 0; i < interfaces.length; i++) {

                 int flags = interfaces[i].getModifiers();

                 if (!Modifier.isPublic(flags)) {

                     String name = interfaces[i].getName();

                     int n = name.lastIndexOf('.');

                     String pkg = ((n == -1) ? "" : name.substring(0, n + 1));

                     if (proxyPkg == null) {

                         proxyPkg = pkg;

                     } else if (!pkg.equals(proxyPkg)) {

                         throw new IllegalArgumentException(

                             "non-public interfaces from different packages");

                     }

                 }

             }

             if (proxyPkg == null) {     // if no non-public proxy interfaces,

                 proxyPkg = "";          // use the unnamed package

             }

             {

                 /*

                  * Choose a name for the proxy class to generate.

                  */

                 long num;

                 synchronized (nextUniqueNumberLock) {

                     num = nextUniqueNumber++;

                 }

                 String proxyName = proxyPkg + proxyClassNamePrefix + num;

                 /*

                  * Verify that the class loader hasn't already

                  * defined a class with the chosen name.

                  */

                 /*

                  * Generate the specified proxy class.

                  */

                 byte[] proxyClassFile = ProxyGenerator.generateProxyClass(

                     proxyName, interfaces);

                 try {

                     proxyClass = defineClass0(loader, proxyName,

                         proxyClassFile, 0, proxyClassFile.length);

                 } catch (ClassFormatError e) {

                     /*

                      * A ClassFormatError here means that (barring bugs in the

                      * proxy class generation code) there was some other

                      * invalid aspect of the arguments supplied to the proxy

                      * class creation (such as virtual machine limitations

                      * exceeded).

                      */

                     throw new IllegalArgumentException(e.toString());

                 }

             }

             // add to set of all generated proxy classes, for isProxyClass

             proxyClasses.put(proxyClass, null);

         } finally {

             /*

              * We must clean up the "pending generation" state of the proxy

              * class cache entry somehow.  If a proxy class was successfully

              * generated, store it in the cache (with a weak reference);

              * otherwise, remove the reserved entry.  In all cases, notify

              * all waiters on reserved entries in this cache.

              */

             synchronized (cache) {

                 if (proxyClass != null) {

                     cache.put(key, new WeakReference<Class<?>>(proxyClass));

                 } else {

                     cache.remove(key);

                 }

                 cache.notifyAll();

             }

         }

         return proxyClass;

     }

     /**

      * 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();

         }

         /*

          * Look up or generate the designated proxy class.

          */

         Class<?> cl = getProxyClass(loader, interfaces);

         /*

          * Invoke its constructor with the designated invocation handler.

          */

         try {

             Constructor cons = cl.getConstructor(constructorParams);

             return cons.newInstance(new Object[] { h });

         } catch (NoSuchMethodException e) {

             throw new InternalError(e.toString());

         } catch (IllegalAccessException e) {

             throw new InternalError(e.toString());

         } catch (InstantiationException e) {

             throw new InternalError(e.toString());

         } catch (InvocationTargetException e) {

             throw new InternalError(e.toString());

         }

     }

     /**

      * 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 proxyClasses.containsKey(cl);

     }

     /**

      * 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);

 }