AOP实现

1. 基于动态代理, 前提是增强的类要基于接口.

package aop.dynamicproxy; import java.lang.reflect.InvocationHandler; import java.lang.reflect.Method; interface GreetingInterface { String sayHello(String name, int age); String sayHi(String name, int age); } class MyGreeting implements GreetingInterface { public String sayHello(String name, int age) { // TODO Auto-generated method stub return "hello, my name is " + name + " and I am " + age; } public String sayHi(String name, int age) { // TODO Auto-generated method stub return "Hi, my name is " + name + " and I am " + age; } } class MyGreetingProxy implements InvocationHandler { private GreetingInterface greeting = null; public MyGreetingProxy(GreetingInterface greeting) { this.greeting = greeting; } public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { // TODO Auto-generated method stub //System.out.println("Hi, before......" + proxy.getClass().getCanonicalName()); String methodName = method.getName(); if ("sayHello".equals(methodName)) { System.out.println("Before invoking sayHello"); Object ret = method.invoke(this.greeting, args); System.out.println("Return value=" + ret); System.out.println("After invoking sayHello"); System.out.println("========================"); return ret; } else if ("sayHi".equals(methodName)) { System.out.println("Before invoking sayHi"); Object ret = method.invoke(this.greeting, args); System.out.println("Return value=" + ret); System.out.println("After invoking sayHi"); System.out.println("========================"); return ret; } else { return method.invoke(this.greeting, args); } } } public class TestDynamicProxy { /** * @param args */ public static void main(String[] args) { MyGreeting greeting = new MyGreeting(); // TODO Auto-generated method stub Object obj = java.lang.reflect.Proxy .newProxyInstance(GreetingInterface.class.getClassLoader(), new Class[] { GreetingInterface.class }, new MyGreetingProxy(greeting)); GreetingInterface in = (GreetingInterface) obj; in.sayHello("vampire", 22); in.sayHi("Terry", 30); } }

我们可以实现before/after/around/return/throwing advice, JNA, resin hession, 前期实现的JBOSS拦截器(甚至RMI实现), 都用到了动态代理, JDK1.3之后引入.

2. 字节码生成, 以CGLIB(objectweb)为例

package aop.cglibproxy; import java.lang.reflect.Method; import net.sf.cglib.proxy.Enhancer; import net.sf.cglib.proxy.MethodInterceptor; import net.sf.cglib.proxy.MethodProxy; class MyGreeting { public String sayHello(String name, int age) { // TODO Auto-generated method stub return "hello, my name is " + name + " and I am " + age; } public String sayHi(String name, int age) { // TODO Auto-generated method stub return "Hi, my name is " + name + " and I am " + age; } } class GreetingInterceptor implements MethodInterceptor { public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable { // TODO Auto-generated method stub String methodName = method.getName(); if ("sayHello".equals(methodName)) { System.out.println("Before invoking sayHello"); Object ret = proxy.invokeSuper(obj, args); System.out.println("Return value=" + ret); System.out.println("After invoking sayHello"); System.out.println("========================"); return ret; } else if ("sayHi".equals(methodName)) { System.out.println("Before invoking sayHi"); Object ret = proxy.invokeSuper(obj, args); System.out.println("Return value=" + ret); System.out.println("After invoking sayHi"); System.out.println("========================"); return ret; } else { return proxy.invokeSuper(obj, args); } } } public class TestCglibProxy { /** * @param args */ public static void main(String[] args) { // TODO Auto-generated method stub GreetingInterceptor interceptor = new GreetingInterceptor(); Enhancer enhancer = new Enhancer(); enhancer.setSuperclass(MyGreeting.class); enhancer.setCallback(interceptor); MyGreeting myGreetingProxy = (MyGreeting) enhancer.create(); myGreetingProxy.sayHello("Vampire", 24); myGreetingProxy.sayHi("Terry", 39); } }

before/after/around/return/throwing advice都可实现.

BTW, CGLIB其实是基于objectweb实现的, 会读取特定.class, 可能是通过继承方式修改生成新的Class, 使用ClassLoader动态生成代理类.

Spring前期版本估计就是使用这两种方式, 2.0支持ASPECTJ POINTCUT解析语法（可能未必是ASPECTJ预编译/特定ClassLoader实现）