java jdk动态代理（proxy）

1. 涉及主要jdk api

java.lang.reflect.InvocationHandler；

public interface InvocationHandler {

    /**
     * Processes a method invocation on a proxy instance and returns
     * the result.  This method will be invoked on an invocation handler
     * when a method is invoked on a proxy instance that it is
     * associated with.
     *
     * @param    proxy the proxy instance that the method was invoked on
     *
     * @param    method the <code>Method</code> instance corresponding to
     * the interface method invoked on the proxy instance.  The declaring
     * class of the <code>Method</code> object will be the interface that
     * the method was declared in, which may be a superinterface of the
     * proxy interface that the proxy class inherits the method through.
     *
     * @param    args an array of objects containing the values of the
     * arguments passed in the method invocation on the proxy instance,
     * or <code>null</code> if interface method takes no arguments.
     * Arguments of primitive types are wrapped in instances of the
     * appropriate primitive wrapper class, such as
     * <code>java.lang.Integer</code> or <code>java.lang.Boolean</code>.
     *
     * @return    the value to return from the method invocation on the
     * proxy instance.  If the declared return type of the interface
     * method is a primitive type, then the value returned by
     * this method must be an instance of the corresponding primitive
     * wrapper class; otherwise, it must be a type assignable to the
     * declared return type.  If the value returned by this method is
     * <code>null</code> and the interface method's return type is
     * primitive, then a <code>NullPointerException</code> will be
     * thrown by the method invocation on the proxy instance.  If the
     * value returned by this method is otherwise not compatible with
     * the interface method's declared return type as described above,
     * a <code>ClassCastException</code> will be thrown by the method
     * invocation on the proxy instance.
     *
     * @throws    Throwable the exception to throw from the method
     * invocation on the proxy instance.  The exception's type must be
     * assignable either to any of the exception types declared in the
     * <code>throws</code> clause of the interface method or to the
     * unchecked exception types <code>java.lang.RuntimeException</code>
     * or <code>java.lang.Error</code>.  If a checked exception is
     * thrown by this method that is not assignable to any of the
     * exception types declared in the <code>throws</code> clause of
     * the interface method, then an
     * {@link UndeclaredThrowableException} containing the
     * exception that was thrown by this method will be thrown by the
     * method invocation on the proxy instance.
     *
     * @see    UndeclaredThrowableException
     */
    public Object invoke(Object proxy, Method method, Object[] args)
    throws Throwable;
}

java.lang.reflect.Proxy；

/*
 * Copyright (c) 2006, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.lang.reflect;

import java.lang.ref.Reference;
import java.lang.ref.WeakReference;
import java.security.AccessController;
import java.security.Permission;
import java.security.PrivilegedAction;
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.WeakHashMap;
import sun.misc.ProxyGenerator;
import sun.reflect.Reflection;
import sun.reflect.misc.ReflectUtil;
import sun.security.util.SecurityConstants;

/**
 * <code>Proxy</code> 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</code>:
 * <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</code> object identifying
 * the method that was invoked, and an array of type <code>Object</code>
 * 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"</code>
 * should be, however, reserved for proxy classes.
 *
 * <li>A proxy class extends <code>java.lang.reflect.Proxy</code>.
 *
 * <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</code> on its
 * <code>Class</code> object will return an array containing the same
 * list of interfaces (in the order specified at its creation), invoking
 * <code>getMethods</code> on its <code>Class</code> object will return
 * an array of <code>Method</code> objects that include all of the
 * methods in those interfaces, and invoking <code>getMethod</code> 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</code> or the class of an object returned by
 * <code>Proxy.newProxyInstance</code>-- and false otherwise.
 *
 * <li>The <code>java.security.ProtectionDomain</code> of a proxy class
 * is the same as that of system classes loaded by the bootstrap class
 * loader, such as <code>java.lang.Object</code>, because the code for a
 * proxy class is generated by trusted system code.  This protection
 * domain will typically be granted
 * <code>java.security.AllPermission</code>.
 *
 * <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.newInstance} 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</code> and one of the
 * interfaces implemented by its proxy class <code>Foo</code>, the
 * following expression will return true:
 * <pre>
 *     <code>proxy instanceof Foo</code>
 * </pre>
 * and the following cast operation will succeed (rather than throwing
 * a <code>ClassCastException</code>):
 * <pre>
 *     <code>(Foo) proxy</code>
 * </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>,
 * <code>equals</code>, or <code>toString</code> methods declared in
 * <code>java.lang.Object</code> on a proxy instance will be encoded and
 * dispatched to the invocation handler's <code>invoke</code> method in
 * the same manner as interface method invocations are encoded and
 * dispatched, as described above.  The declaring class of the
 * <code>Method</code> object passed to <code>invoke</code> will be
 * <code>java.lang.Object</code>.  Other public methods of a proxy
 * instance inherited from <code>java.lang.Object</code> are not
 * overridden by a proxy class, so invocations of those methods behave
 * like they do for instances of <code>java.lang.Object</code>.
 * </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</code> 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</code> 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</code> 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>, <code>equals</code>,
 * or <code>toString</code> methods of <code>java.lang.Object</code>,
 * when such a method is invoked on a proxy instance, the
 * <code>Method</code> object passed to the invocation handler will have
 * <code>java.lang.Object</code> as its declaring class.  In other words,
 * the public, non-final methods of <code>java.lang.Object</code>
 * logically precede all of the proxy interfaces for the determination of
 * which <code>Method</code> object to pass to the invocation handler.
 *
 * <p>Note also that when a duplicate method is dispatched to an
 * invocation handler, the <code>invoke</code> method may only throw
 * checked exception types that are assignable to one of the exception
 * types in the <code>throws</code> clause of the method in <i>all</i> of
 * the proxy interfaces that it can be invoked through.  If the
 * <code>invoke</code> 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</code> 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</code> on the <code>Method</code> object
 * passed to the <code>invoke</code> method can necessarily be thrown
 * successfully by the <code>invoke</code> method.
 *
 * @author    Peter Jones
 * @version    %I%, %E%
 * @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 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 proxyClasses =
    Collections.synchronizedMap(new WeakHashMap());

    /**
     * the invocation handler for this proxy instance.
     * @serial
     */
    protected InvocationHandler h;

    /**
     * Prohibits instantiation.
     */
    private Proxy() {
    }

    /**
     * Constructs a new <code>Proxy</code> 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) {
        doNewInstanceCheck();
    this.h = h;
    }

    private static class ProxyAccessHelper {
        // The permission is implementation specific.
        static final Permission PROXY_PERMISSION =
            new ReflectPermission("proxyConstructorNewInstance");
        // These system properties are defined to provide a short-term
        // workaround if customers need to disable the new security checks.
        static final boolean allowNewInstance;
        static final boolean allowNullLoader;
        static {
            allowNewInstance = getBooleanProperty("sun.reflect.proxy.allowsNewInstance");
            allowNullLoader = getBooleanProperty("sun.reflect.proxy.allowsNullLoader");
        }

        private static boolean getBooleanProperty(final String key) {
            String s = AccessController.doPrivileged(new PrivilegedAction<String>() {
                public String run() {
                    return System.getProperty(key);
                }
            });
            return Boolean.valueOf(s);
        }

        static boolean needsNewInstanceCheck(Class<?> proxyClass) {
            if (!Proxy.isProxyClass(proxyClass) || allowNewInstance) {
                return false;
            }

            if (proxyClass.getName().startsWith(ReflectUtil.PROXY_PACKAGE + ".")) {
                // all proxy interfaces are public
                return false;
            }
            for (Class<?> intf : proxyClass.getInterfaces()) {
                if (!Modifier.isPublic(intf.getModifiers())) {
                    return true;
                }
            }
            return false;
        }
    }

    /*
     * Access check on a proxy class that implements any non-public interface.
     *
     * @throws  SecurityException if a security manager exists, and
     *          the caller does not have the permission.
     */
    private void doNewInstanceCheck() {
        SecurityManager sm = System.getSecurityManager();
        Class<?> proxyClass = this.getClass();
        if (sm != null && ProxyAccessHelper.needsNewInstanceCheck(proxyClass)) {
            try {
                sm.checkPermission(ProxyAccessHelper.PROXY_PERMISSION);
            } catch (SecurityException e) {
                throw new SecurityException("Not allowed to construct a Proxy "
                        + "instance that implements a non-public interface", e);
            }
        }
    }

    /**
     * Returns the <code>java.lang.Class</code> 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</code>:
     *
     * <ul>
     * <li>All of the <code>Class</code> objects in the
     * <code>interfaces</code> array must represent interfaces, not
     * classes or primitive types.
     *
     * <li>No two elements in the <code>interfaces</code> array may
     * refer to identical <code>Class</code> 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</code> and every interface <code>i</code>, 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</code> array must not
     * exceed 65535.
     * </ul>
     *
     * <p>If any of these restrictions are violated,
     * <code>Proxy.getProxyClass</code> will throw an
     * <code>IllegalArgumentException</code>.  If the <code>interfaces</code>
     * array argument or any of its elements are <code>null</code>, a
     * <code>NullPointerException</code> 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</code>
     *        are violated
     * @throws    NullPointerException if the <code>interfaces</code> array
     *        argument or any of its elements are <code>null</code>
     */
    public static Class<?> getProxyClass(ClassLoader loader,
                                         Class<?>... interfaces)
    throws IllegalArgumentException
    {
        return getProxyClass0(loader, interfaces); // stack walk magic: do not refactor
    }

    private static void checkProxyLoader(ClassLoader ccl,
                                         ClassLoader loader)
    {
        SecurityManager sm = System.getSecurityManager();
        if (sm != null) {
            if (loader == null && ccl != null) {
                if (!ProxyAccessHelper.allowNullLoader) {
                    sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
                }
            }
        }
    }

    /*
     * Generate a proxy class (caller-sensitive).
     *
     * To define a proxy class, it performs the access checks as in
     * Class.forName (VM will invoke ClassLoader.checkPackageAccess):
     * 1. "getClassLoader" permission check if loader == null
     * 2. checkPackageAccess on the interfaces it implements
     *
     * To get a constructor and new instance of a proxy class, it performs
     * the package access check on the interfaces it implements
     * as in Class.getConstructor.
     *
     * If an interface is non-public, the proxy class must be defined by
     * the defining loader of the interface.  If the caller's class loader
     * is not the same as the defining loader of the interface, the VM
     * will throw IllegalAccessError when the generated proxy class is
     * being defined via the defineClass0 method.
     */
    private static Class<?> getProxyClass0(ClassLoader loader,
                                           Class<?>... interfaces) {
        SecurityManager sm = System.getSecurityManager();
        if (sm != null) {
            final int CALLER_FRAME = 3; // 0: Reflection, 1: getProxyClass0 2: Proxy 3: caller
            final Class<?> caller = Reflection.getCallerClass(CALLER_FRAME);
            final ClassLoader ccl = caller.getClassLoader();
            checkProxyLoader(ccl, loader);
            ReflectUtil.checkProxyPackageAccess(ccl, interfaces);
        }
        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];

    Set interfaceSet = new HashSet();    // for detecting duplicates

    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.
     */
    Object key = Arrays.asList(interfaceNames);

    /*
     * Find or create the proxy class cache for the class loader.
     */
    Map cache;
    synchronized (loaderToCache) {
        cache = (Map) 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, use com.sun.proxy package
                proxyPkg = ReflectUtil.PROXY_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(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</code> throws
     * <code>IllegalArgumentException</code> for the same reasons that
     * <code>Proxy.getProxyClass</code> 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</code>
     *        are violated
     * @throws    NullPointerException if the <code>interfaces</code> array
     *        argument or any of its elements are <code>null</code>, or
     *        if the invocation handler, <code>h</code>, is
     *        <code>null</code>
     */
    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 = getProxyClass0(loader, interfaces); // stack walk magic: do not refactor

    /*
     * Invoke its constructor with the designated invocation handler.
     */
    try {
            final Constructor<?> cons = cl.getConstructor(constructorParams);
            final InvocationHandler ih = h;
            SecurityManager sm = System.getSecurityManager();
            if (sm != null && ProxyAccessHelper.needsNewInstanceCheck(cl)) {
                // create proxy instance with doPrivilege as the proxy class may
                // implement non-public interfaces that requires a special permission
                return AccessController.doPrivileged(new PrivilegedAction<Object>() {
                    public Object run() {
                        return newInstance(cons, ih);
                    }
                });
            } else {
                return newInstance(cons, ih);
            }
    } catch (NoSuchMethodException e) {
        throw new InternalError(e.toString());
    }
    }

    private static Object newInstance(Constructor<?> cons, InvocationHandler h) {
        try {
            return cons.newInstance(new Object[] {h} );
        } catch (IllegalAccessException e) {
            throw new InternalError(e.toString());
        } catch (InstantiationException e) {
            throw new InternalError(e.toString());
        } catch (InvocationTargetException e) {
            Throwable t = e.getCause();
            if (t instanceof RuntimeException) {
                throw (RuntimeException) t;
            } else {
                throw new InternalError(t.toString());
            }
        }
    }

    /**
     * Returns true if and only if the specified class was dynamically
     * generated to be a proxy class using the <code>getProxyClass</code>
     * method or the <code>newProxyInstance</code> 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</code>.
     *
     * @param    cl the class to test
     * @return  <code>true</code> if the class is a proxy class and
     *        <code>false</code> otherwise
     * @throws    NullPointerException if <code>cl</code> is <code>null</code>
     */
    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);
}

2. 例子package test;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.ArrayList;
import java.util.LinkedList;

public class AmbiguousTest {         
//实现 InvocationHandler接口方法invoke
    class SubInvocationHandler implements InvocationHandler{
　　　　　private SubProxyInterface 

subProxyImpl;//被代理接口
　　　　　public SubInvocationHandler(SubInvocationHandler subProxyImpl){
　　　　　　　this.subProxyImpl = subProxyImpl;
　　　　　}

　　　　　// proxy 代理类，method：被调用的方法，args：method方法参数 @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { System.out.println(method.getName()); return method.invoke(subProxyImpl, args); } } interface SubProxyInterface{ void getValue(); void get0(); } class SubProxyImpl implements SubProxyInterface{ @Override public void getValue() { System.out.println("-----------------"); } @Override public void get0() {  } } public static void main(String[] args) {
　　　　　SubInvocationHandler subInvocationHandler = new AmbiguousTest().
		new SubInvocationHandler(new AmbiguousTest().new SubProxyImpl());
        Class[] interfaces = new Class[]{SubProxyInterface.class};
　　　　　//newProxyInstance(加载器,接口数组（被代理接口）,invocationhandler对象)
        Object obj = Proxy.newProxyInstance(SubInvocationHandler.class.getClassLoader()
                , interfaces,subInvocationHandler);
　　　　　/* 间接写法，是对

Proxy.newProxyInstance的详细调用

　　　　　　　　try {
			Object obj0 = Proxy.getProxyClass(SubInvocationHandler.class.getClassLoader()
					, interfaces).getConstructor(new Class[]{InvocationHandler.class}).newInstance(subInvocationHandler);
			((SubProxyInterface)obj0).getValue();
		} catch (IllegalArgumentException e) {
			e.printStackTrace();
		} catch (SecurityException e) {
			e.printStackTrace();
		} catch (InstantiationException e) {
			e.printStackTrace();
		} catch (IllegalAccessException e) {
			e.printStackTrace();
		} catch (InvocationTargetException e) {
			e.printStackTrace();
		} catch (NoSuchMethodException e) {
			e.printStackTrace();
		}
　　　　　*/
        ((SubProxyInterface)obj).getValue();
        ((SubProxyInterface)obj).get0();
    }
 }

3.利用反射实现代理，适时利用反射（经典案例：spring aop，ioc）

参考：https://blog.csdn.net/u012721013/article/details/51833626

https://www.cnblogs.com/techyc/p/3455950.html

public interface InvocationHandler {
    /**     * Processes a method invocation on a proxy instance and returns     * the result.  This method will be invoked on an invocation handler     * when a method is invoked on a proxy instance that it is     * associated with.     *     * @paramproxy the proxy instance that the method was invoked on     *     * @parammethod the <code>Method</code> instance corresponding to     * the interface method invoked on the proxy instance.  The declaring     * class of the <code>Method</code> object will be the interface that     * the method was declared in, which may be a superinterface of the     * proxy interface that the proxy class inherits the method through.     *     * @paramargs an array of objects containing the values of the     * arguments passed in the method invocation on the proxy instance,     * or <code>null</code> if interface method takes no arguments.     * Arguments of primitive types are wrapped in instances of the     * appropriate primitive wrapper class, such as     * <code>java.lang.Integer</code> or <code>java.lang.Boolean</code>.     *     * @returnthe value to return from the method invocation on the     * proxy instance.  If the declared return type of the interface     * method is a primitive type, then the value returned by     * this method must be an instance of the corresponding primitive     * wrapper class; otherwise, it must be a type assignable to the     * declared return type.  If the value returned by this method is     * <code>null</code> and the interface method's return type is     * primitive, then a <code>NullPointerException</code> will be     * thrown by the method invocation on the proxy instance.  If the     * value returned by this method is otherwise not compatible with     * the interface method's declared return type as described above,     * a <code>ClassCastException</code> will be thrown by the method     * invocation on the proxy instance.     *     * @throwsThrowable the exception to throw from the method     * invocation on the proxy instance.  The exception's type must be     * assignable either to any of the exception types declared in the     * <code>throws</code> clause of the interface method or to the     * unchecked exception types <code>java.lang.RuntimeException</code>     * or <code>java.lang.Error</code>.  If a checked exception is     * thrown by this method that is not assignable to any of the     * exception types declared in the <code>throws</code> clause of     * the interface method, then an     * {@link UndeclaredThrowableException} containing the     * exception that was thrown by this method will be thrown by the     * method invocation on the proxy instance.     *     * @seeUndeclaredThrowableException     */    public Object invoke(Object proxy, Method method, Object[] args)throws Throwable;}