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;}
