实例:
package com.itgarden.taobao.proxy; /** * TODO 类说明 * * @author <a href="mailto:[email protected]">zhangqi.dzq</a> * @version 1.0 * @since 2015年11月19日 */ public interface DemoFirst { public void saveFirst(); }
package com.itgarden.taobao.proxy; /** * TODO 类说明 * * @author <a href="mailto:[email protected]">zhangqi.dzq</a> * @version 1.0 * @since 2015年11月19日 */ public class DemoFirstImpl implements DemoFirst { public void saveFirst() { System.out.println("调用saveFirst()方法"); } }
package com.itgarden.taobao.proxy; import java.lang.reflect.InvocationHandler; import java.lang.reflect.Method; /** * TODO 类说明 * * @author <a href="mailto:[email protected]">zhangqi.dzq</a> * @version 1.0 * @since 2015年11月19日 */ public class InvocationHandlerImpl implements InvocationHandler { private Object target; public InvocationHandlerImpl(Object target) { this.target = target; } public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { System.out.println("target : " + target.getClass().getName()); System.out.println("proxy : " + proxy.getClass().getName()); System.out.println("method : " + method.getName()); System.out.println("args : " + args); System.out.println("开始记录日志"); Object obj = method.invoke(target, args); System.out.println("结束记录日志"); return obj; } }
package com.itgarden.taobao.proxy; import java.lang.reflect.Proxy; /** * TODO 类说明 * * @author <a href="mailto:[email protected]">zhangqi.dzq</a> * @version 1.0 * @since 2015年11月19日 */ public class Test { public static void main(String[] args) { DemoFirst first = new DemoFirstImpl(); DemoFirst firstProxy = (DemoFirst) Proxy.newProxyInstance(first.getClass().getClassLoader(), first.getClass().getInterfaces(), new InvocationHandlerImpl(first)); firstProxy.saveFirst(); } }
result:
target : com.itgarden.taobao.proxy.DemoFirstImpl
proxy : com.sun.proxy.$Proxy0
method : saveFirst
args : null
开始记录日志
调用saveFirst()方法
结束记录日志
分析:从Proxy.newProxyInstance开始
/** * loader:类加载器 * interfaces:目标对象实现的接口 * h:InvocationHandler的实现类 */ public static Object newProxyInstance(ClassLoader loader, Class<?>[] interfaces, InvocationHandler h) throws IllegalArgumentException { if (h == null) { throw new NullPointerException(); } /* * Look up or generate the designated proxy class. */ Class cl = getProxyClass(loader, interfaces); /* * Invoke its constructor with the designated invocation handler. */ try { // 调用代理对象的构造方法(也就是$Proxy0(InvocationHandler h)) Constructor cons = cl.getConstructor(constructorParams); // 生成代理类的实例并把MyInvocationHandler的实例传给它的构造方法 return (Object) 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()); } }
public static Class<?> getProxyClass(ClassLoader loader, Class<?>... interfaces) throws IllegalArgumentException { // 如果目标类实现的接口数大于65535个则抛出异常(我XX,谁会写这么NB的代码啊?) if (interfaces.length > 65535) { throw new IllegalArgumentException("interface limit exceeded"); } // 声明代理对象所代表的Class对象 Class proxyClass = null; String[] interfaceNames = new String[interfaces.length]; Set interfaceSet = new HashSet(); // for detecting duplicates // 遍历目标类所实现的接口 for (int i = 0; i < interfaces.length; i++) { // 拿到目标类实现的接口的名称 String interfaceName = interfaces[i].getName(); Class interfaceClass = null; try { // 加载目标类实现的接口到内存中 interfaceClass = Class.forName(interfaceName, false, loader); } catch (ClassNotFoundException e) { } if (interfaceClass != interfaces[i]) { throw new IllegalArgumentException( interfaces[i] + " is not visible from class loader"); } // 中间省略了一些无关紧要的代码 ....... // 把目标类实现的接口代表的Class对象放到Set中 interfaceSet.add(interfaceClass); interfaceNames[i] = interfaceName; } // 把目标类实现的接口名称作为缓存(Map)中的key Object key = Arrays.asList(interfaceNames); Map cache; synchronized (loaderToCache) { // 从缓存中获取cache cache = (Map) loaderToCache.get(loader); if (cache == null) { // 如果获取不到,则新建地个HashMap实例 cache = new HashMap(); // 把HashMap实例和当前加载器放到缓存中 loaderToCache.put(loader, cache); } } synchronized (cache) { do { // 根据接口的名称从缓存中获取对象 Object value = cache.get(key); if (value instanceof Reference) { proxyClass = (Class) ((Reference) value).get(); } if (proxyClass != null) { // 如果代理对象的Class实例已经存在,则直接返回 return proxyClass; } else if (value == pendingGenerationMarker) { try { cache.wait(); } catch (InterruptedException e) { } continue; } else { cache.put(key, pendingGenerationMarker); break; } } while (true); } try { // 中间省略了一些代码 ....... // 这里就是动态生成代理对象的最关键的地方 byte[] proxyClassFile = ProxyGenerator.generateProxyClass( proxyName, interfaces); try { // 根据代理类的字节码生成代理类的实例 proxyClass = defineClass0(loader, proxyName, proxyClassFile, 0, proxyClassFile.length); } catch (ClassFormatError e) { throw new IllegalArgumentException(e.toString()); } } // add to set of all generated proxy classes, for isProxyClass proxyClasses.put(proxyClass, null); } // 中间省略了一些代码 ....... return proxyClass; }
进去ProxyGenerator类的静态方法generateProxyClass,这里是真正生成代理类class字节码的地方。
public static byte[] generateProxyClass(final String name, Class[] interfaces) { ProxyGenerator gen = new ProxyGenerator(name, interfaces); // 这里动态生成代理类的字节码,由于比较复杂就不进去看了 final byte[] classFile = gen.generateClassFile(); // 如果saveGeneratedFiles的值为true,则会把所生成的代理类的字节码保存到硬盘上 if (saveGeneratedFiles) { java.security.AccessController.doPrivileged( new java.security.PrivilegedAction<Void>() { public Void run() { try { FileOutputStream file = new FileOutputStream(dotToSlash(name) + ".class"); file.write(classFile); file.close(); return null; } catch (IOException e) { throw new InternalError( "I/O exception saving generated file: " + e); } } }); } // 返回代理类的字节码 return classFile; }
现在,JDK是怎样动态生成代理类的字节的原理已经一目了然了。
好了,再来解决另外一个问题,那就是由谁来调用InvocationHandler的invoke方法的。要解决这个问题就要看一下JDK到底为我们生成了一个什么东西。用以下代码可以获取到JDK为我们生成的字节码并写到硬盘中。
package com.itgarden.taobao.proxy; import java.io.FileOutputStream; import java.io.IOException; import sun.misc.ProxyGenerator; /** * TODO 类说明 * * @author <a href="mailto:[email protected]">zhangqi.dzq</a> * @version 1.0 * @since 2015年11月19日 */ public class ProxyGeneratorUtils { /** * 把代理类的字节码写到硬盘上 * * @param path 保存路径 */ public static void writeProxyClassToHardDisk(String path) { byte[] classFile = ProxyGenerator.generateProxyClass("$Proxy11", DemoFirstImpl.class.getInterfaces()); FileOutputStream out = null; try { out = new FileOutputStream(path); out.write(classFile); out.flush(); } catch (Exception e) { e.printStackTrace(); } finally { try { out.close(); } catch (IOException e) { e.printStackTrace(); } } } public static void main(String[] args) { writeProxyClassToHardDisk("E:/$Proxy11.class"); } }
通过以上代码,就可以在F盘上生成一个$Proxy.class文件了,现在用反编译工具来看一下这个class文件里面的内容。
import com.itgarden.taobao.proxy.DemoFirst; import java.lang.reflect.InvocationHandler; import java.lang.reflect.Method; import java.lang.reflect.Proxy; import java.lang.reflect.UndeclaredThrowableException; public final class $Proxy11 extends Proxy implements DemoFirst { private static Method m1; private static Method m3; private static Method m0; private static Method m2; public $Proxy11(InvocationHandler paramInvocationHandler) throws { super(paramInvocationHandler); } public final boolean equals(Object paramObject) throws { try { return ((Boolean)this.h.invoke(this, m1, new Object[] { paramObject })).booleanValue(); } catch (Error|RuntimeException localError) { throw localError; } catch (Throwable localThrowable) { throw new UndeclaredThrowableException(localThrowable); } } public final void saveFirst() throws { try { this.h.invoke(this, m3, null); return; } catch (Error|RuntimeException localError) { throw localError; } catch (Throwable localThrowable) { throw new UndeclaredThrowableException(localThrowable); } } public final int hashCode() throws { try { return ((Integer)this.h.invoke(this, m0, null)).intValue(); } catch (Error|RuntimeException localError) { throw localError; } catch (Throwable localThrowable) { throw new UndeclaredThrowableException(localThrowable); } } public final String toString() throws { try { return (String)this.h.invoke(this, m2, null); } catch (Error|RuntimeException localError) { throw localError; } catch (Throwable localThrowable) { throw new UndeclaredThrowableException(localThrowable); } } static { try { m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[] { Class.forName("java.lang.Object") }); m3 = Class.forName("com.itgarden.taobao.proxy.DemoFirst").getMethod("saveFirst", new Class[0]); m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]); m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]); return; } catch (NoSuchMethodException localNoSuchMethodException) { throw new NoSuchMethodError(localNoSuchMethodException.getMessage()); } catch (ClassNotFoundException localClassNotFoundException) { throw new NoClassDefFoundError(localClassNotFoundException.getMessage()); } } }
java.lang.reflect.Proxy源码地址:http://my.oschina.net/u/1185936/blog/532766