JDK动态代理步骤详解(源码分析)

 ProxyObject proxyObject = new ProxyObject(); InvocationHandler invocationHandler = new DynamicProxy(proxyObject); ClassLoader classLoader = proxyObject.getClass().getClassLoader(); ProxyObjectInterface proxy = (IRoom) Proxy.newProxyInstance(classLoader,new Class[] {ProxyObjectInterface.class},invocationHandler); proxy.execute(); public class DynamicProxy implements InvocationHandler { private Object object; public DynamicProxy(Object object){ this.object = object; } @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { Object result = method.invoke(object,args); return result; } }

 public static Object newProxyInstance(ClassLoader loader, Class[] interfaces, InvocationHandler h) throws IllegalArgumentException { //检验h不为空，h为空抛异常 Objects.requireNonNull(h); //接口的类对象拷贝一份 final Class[] intfs = interfaces.clone(); //进行一些安全性检查 final SecurityManager sm = System.getSecurityManager(); if (sm != null) { checkProxyAccess(Reflection.getCallerClass(), loader, intfs); } /* * Look up or generate the designated proxy class. *  查询（在缓存中已经有）或生成指定的代理类的class对象。 */ Class cl = getProxyClass0(loader, intfs); /* * Invoke its constructor with the designated invocation handler. */ try { if (sm != null) { checkNewProxyPermission(Reflection.getCallerClass(), cl); } //得到代理类对象的构造函数，这个构造函数的参数由constructorParams指定 //参数constructorParames为常量值： private static final Class[] constructorParams = { InvocationHandler.class }; final Constructor cons = cl.getConstructor(constructorParams); final InvocationHandler ih = h; if (!Modifier.isPublic(cl.getModifiers())) { AccessController.doPrivileged(new PrivilegedAction() { public Void run() { cons.setAccessible(true); return null; } }); } //这里生成代理对象，传入的参数new Object[]{h}后面讲 return cons.newInstance(new Object[]{h}); } catch (IllegalAccessException|InstantiationException e) { throw new InternalError(e.toString(), e); } catch (InvocationTargetException e) { Throwable t = e.getCause(); if (t instanceof RuntimeException) { throw (RuntimeException) t; } else { throw new InternalError(t.toString(), t); } } catch (NoSuchMethodException e) { throw new InternalError(e.toString(), e); } }

 //此方法也是Proxy类下的方法 private static Class getProxyClass0(ClassLoader loader, Class... interfaces) { if (interfaces.length > 65535) { throw new IllegalArgumentException("interface limit exceeded"); } // If the proxy class defined by the given loader implementing // the given interfaces exists, this will simply return the cached copy; // otherwise, it will create the proxy class via the ProxyClassFactory //意思是：如果代理类被指定的类加载器loader定义了，并实现了给定的接口interfaces， //那么就返回缓存的代理类对象，否则使用ProxyClassFactory创建代理类。 return proxyClassCache.get(loader, interfaces); } 

 private static final WeakCache[], Class> proxyClassCache = new WeakCache<>(new KeyFactory(), new ProxyClassFactory()); //K代表key的类型，P代表参数的类型，V代表value的类型。 // WeakCache[], Class>  proxyClassCache  说明proxyClassCache存的值是Class对象，正是我们需要的代理类对象。 final class WeakCache { private final ReferenceQueue refQueue = new ReferenceQueue<>(); // the key type is Object for supporting null key private final ConcurrentMap>> map = new ConcurrentHashMap<>(); private final ConcurrentMap, Boolean> reverseMap = new ConcurrentHashMap<>(); private final BiFunction subKeyFactory; private final BiFunction valueFactory; public WeakCache(BiFunction subKeyFactory, BiFunction valueFactory) { this.subKeyFactory = Objects.requireNonNull(subKeyFactory); this.valueFactory = Objects.requireNonNull(valueFactory); } 

 //K和P就是WeakCache定义中的泛型，key是类加载器，parameter是接口类数组 public V get(K key, P parameter) { //检查parameter不为空 Objects.requireNonNull(parameter); //清除无效的缓存 expungeStaleEntries(); // cacheKey就是(key, sub-key) -> value里的一级key， Object cacheKey = CacheKey.valueOf(key, refQueue); // lazily install the 2nd level valuesMap for the particular cacheKey //根据一级key得到 ConcurrentMap>对象。如果之前不存在，则新建一个ConcurrentMap>和cacheKey（一级key）一起放到map中。 ConcurrentMap> valuesMap = map.get(cacheKey); if (valuesMap == null) { ConcurrentMap> oldValuesMap = map.putIfAbsent(cacheKey, valuesMap = new ConcurrentHashMap<>()); if (oldValuesMap != null) { valuesMap = oldValuesMap; } } // create subKey and retrieve the possible Supplier stored by that // subKey from valuesMap //这部分就是调用生成sub-key的代码，上面我们已经看过怎么生成的了 Object subKey = Objects.requireNonNull(subKeyFactory.apply(key, parameter)); //通过sub-key得到supplier Supplier supplier = valuesMap.get(subKey); //supplier实际上就是这个factory Factory factory = null; while (true) { //如果缓存里有supplier ，那就直接通过get方法，得到代理类对象，返回，就结束了，一会儿分析get方法。 if (supplier != null) { // supplier might be a Factory or a CacheValue instance V value = supplier.get(); if (value != null) { return value; } } // else no supplier in cache // or a supplier that returned null (could be a cleared CacheValue // or a Factory that wasn't successful in installing the CacheValue) // lazily construct a Factory //下面的所有代码目的就是：如果缓存中没有supplier，则创建一个Factory对象，把factory对象在多线程的环境下安全的赋给supplier。 //因为是在while（true）中，赋值成功后又回到上面去调get方法，返回才结束。 if (factory == null) { factory = new Factory(key, parameter, subKey, valuesMap); } if (supplier == null) { supplier = valuesMap.putIfAbsent(subKey, factory); if (supplier == null) { // successfully installed Factory supplier = factory; } // else retry with winning supplier } else { if (valuesMap.replace(subKey, supplier, factory)) { // successfully replaced // cleared CacheEntry / unsuccessful Factory // with our Factory supplier = factory; } else { // retry with current supplier supplier = valuesMap.get(subKey); } } } }

 public synchronized V get() { // serialize access // re-check Supplier supplier = valuesMap.get(subKey); //重新检查得到的supplier是不是当前对象 if (supplier != this) { // something changed while we were waiting: // might be that we were replaced by a CacheValue // or were removed because of failure -> // return null to signal WeakCache.get() to retry // the loop return null; } // else still us (supplier == this) // create new value V value = null; try { //代理类就是在这个位置调用valueFactory生成的 //valueFactory就是我们传入的 new ProxyClassFactory() //一会我们分析ProxyClassFactory()的apply方法 value = Objects.requireNonNull(valueFactory.apply(key, parameter)); } finally { if (value == null) { // remove us on failure valuesMap.remove(subKey, this); } } // the only path to reach here is with non-null value assert value != null; // wrap value with CacheValue (WeakReference) //把value包装成弱引用 CacheValue cacheValue = new CacheValue<>(value); // put into reverseMap // reverseMap是用来实现缓存的有效性 reverseMap.put(cacheValue, Boolean.TRUE); // try replacing us with CacheValue (this should always succeed) if (!valuesMap.replace(subKey, this, cacheValue)) { throw new AssertionError("Should not reach here"); } // successfully replaced us with new CacheValue -> return the value // wrapped by it return value; } }

 //这里的BiFunction是个函数式接口，可以理解为用T，U两种类型做参数，得到R类型的返回值 private static final class ProxyClassFactory implements BiFunction[], Class> { // prefix for all proxy class names //所有代理类名字的前缀 private static final String proxyClassNamePrefix = "$Proxy"; // next number to use for generation of unique proxy class names //用于生成代理类名字的计数器 private static final AtomicLong nextUniqueNumber = new AtomicLong(); @Override public Class apply(ClassLoader loader, Class[] interfaces) { Map

 private static List getMethods(Class[] interfaces) { List result = new ArrayList(); try { result.add(Object.class.getMethod("equals", Object.class)); result.add(Object.class.getMethod("hashCode", EmptyArray.CLASS)); result.add(Object.class.getMethod("toString", EmptyArray.CLASS)); } catch (NoSuchMethodException e) { throw new AssertionError(); } getMethodsRecursive(interfaces, result); return result; } private static void getMethodsRecursive(Class[] interfaces, List methods) { for (Class i : interfaces) { getMethodsRecursive(i.getInterfaces(), methods); Collections.addAll(methods, i.getDeclaredMethods()); } }

 package com.zhb.jdk.proxy; import java.io.FileOutputStream; import java.io.IOException; import java.lang.reflect.Proxy; import com.zhb.jdk.dynamicProxy.HelloworldImpl; import sun.misc.ProxyGenerator; /** * @author ZHB * @date 2018年8月31日下午11:35:07 * @todo TODO */ public class DynamicProxyTest { public static void main(String[] args) { IUserService target = new UserServiceImpl(); MyInvocationHandler handler = new MyInvocationHandler(target); //第一个参数是指定代理类的类加载器（我们传入当前测试类的类加载器） //第二个参数是代理类需要实现的接口（我们传入被代理类实现的接口，这样生成的代理类和被代理类就实现了相同的接口） //第三个参数是invocation handler，用来处理方法的调用。这里传入我们自己实现的handler IUserService proxyObject = (IUserService) Proxy.newProxyInstance(DynamicProxyTest.class.getClassLoader(), target.getClass().getInterfaces(), handler); proxyObject.add("陈粒"); String path = "D:/$Proxy0.class"; byte[] classFile = ProxyGenerator.generateProxyClass("$Proxy0", HelloworldImpl.class.getInterfaces()); FileOutputStream out = null; try { out = new FileOutputStream(path); out.write(classFile); out.flush(); } catch (Exception e) { e.printStackTrace(); } finally { try { out.close(); } catch (IOException e) { e.printStackTrace(); } } } } // Decompiled by Jad v1.5.8e2. Copyright 2001 Pavel Kouznetsov. // Jad home page: http://kpdus.tripod.com/jad.html // Decompiler options: packimports(3) fieldsfirst ansi space import com.zhb.jdk.proxy.IUserService; import java.lang.reflect.*; public final class $Proxy0 extends Proxy implements IUserService { private static Method m1; private static Method m2; private static Method m3; private static Method m0; //代理类的构造函数，其参数正是是InvocationHandler实例， //Proxy.newInstance方法就是通过通过这个构造函数来创建代理实例的 public $Proxy0(InvocationHandler invocationhandler) { super(invocationhandler); } // Object类中的三个方法，equals，toString， hashCode public final boolean equals(Object obj) { try { return ((Boolean)super.h.invoke(this, m1, new Object[] { obj })).booleanValue(); } catch (Error ) { } catch (Throwable throwable) { throw new UndeclaredThrowableException(throwable); } } public final String toString() { try { return (String)super.h.invoke(this, m2, null); } catch (Error ) { } catch (Throwable throwable) { throw new UndeclaredThrowableException(throwable); } } //接口代理方法 public final void add(String s) { try { // invocation handler的 invoke方法在这里被调用 super.h.invoke(this, m3, new Object[] { s }); return; } catch (Error ) { } catch (Throwable throwable) { throw new UndeclaredThrowableException(throwable); } } public final int hashCode() { try { // 在这里调用了invoke方法。 return ((Integer)super.h.invoke(this, m0, null)).intValue(); } catch (Error ) { } catch (Throwable throwable) { throw new UndeclaredThrowableException(throwable); } } // 静态代码块对变量进行一些初始化工作 static { try { m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[] { Class.forName("java.lang.Object") }); m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]); m3 = Class.forName("com.zhb.jdk.proxy.IUserService").getMethod("add", new Class[] { Class.forName("java.lang.String") }); m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]); } catch (NoSuchMethodException nosuchmethodexception) { throw new NoSuchMethodError(nosuchmethodexception.getMessage()); } catch (ClassNotFoundException classnotfoundexception) { throw new NoClassDefFoundError(classnotfoundexception.getMessage()); } } }