Jdk动态代理与Cglib动态代理

　　本文介绍动态代理的两种方式，作为Spring AOP的引入。

一、JDK动态代理实现

package dynamicProxyTest;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

interface Print{
    void print();
}
/**
 * 目标方法
 */
class JdkTarget implements Print{//目标类需要保证有接口定义
    public void print(){
        System.out.println("hello jdkProxy");
    }
}
/**
 * 需要自定义一个处理器，实现InvocationHandler的invoke方法
 */
class MyInvocationHandler implements InvocationHandler{
    Object target ;
    public MyInvocationHandler(Object target) {
        this.target = target;
    }
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        Object obj = null ;
        //jdk动态代理中没有提供类似cglib中的过滤器，所以只能采取这种方式过滤掉对于"toString()"的增强
        if(method.getName().startsWith("print")) {
            System.out.println("before");
            obj = method.invoke(target, args);
            System.out.println("after");
        }else {
            obj = method.invoke(target, args);
        }
        return obj;
    }
    
}
/**
 * 测试类 
 */
public class JdkProxy {
    public static void main(String[] args) {
        MyInvocationHandler myInvocationHandler = new MyInvocationHandler(new JdkTarget());
        Print p = (Print) Proxy.newProxyInstance(JdkTarget.class.getClassLoader(), JdkTarget.class.getInterfaces(), myInvocationHandler);
        p.print();
        System.out.println(p.toString());
    }
}

before
hello jdkProxy
after
dynamicProxyTest.JdkTarget@6bc7c054

二、Cglib动态代理实现

package dynamicProxyTest;

import java.lang.reflect.Method;

import net.sf.cglib.proxy.Callback;
import net.sf.cglib.proxy.CallbackFilter;
import net.sf.cglib.proxy.Enhancer;
import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.MethodProxy;
import net.sf.cglib.proxy.NoOp;
/**
 * 目标类
 */
class CglibTarget{//目标类不需要有实现接口
    void print(){
        System.out.println("hello cglibProxy");
    }
}
/**
 * 拦截器,实现MethodInterceptor的iintercept()方法
 */
class MyMethodInterceptor implements MethodInterceptor{

    @Override
    public Object intercept(Object obj, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
        System.out.println("BeforeInterceptor");
        Object returnValue = methodProxy.invokeSuper(obj, args);
        System.out.println("AfterInterceptor");
        return returnValue;
    }
    
}
/**
 * 过滤器
 */
class MyMethodFilter implements CallbackFilter{

    @Override
    public int accept(Method method) {
        if(method.getName().startsWith("print")) {
            return 0;//使用自定义拦截器MyMethodInterceptor
        }else {
            return 1;//使用空拦截器NoOp.INSTANCE，即什么也进行增强处理
        }
    }
}

/**
 * 测试类
 */
public class CglibProxy {

    public static void main(String[] args) {
        Enhancer enhancer = new Enhancer();
        enhancer.setSuperclass(CglibTarget.class);
        enhancer.setCallbacks(new Callback[] {new MyMethodInterceptor(),NoOp.INSTANCE});
        enhancer.setCallbackFilter(new MyMethodFilter());
        CglibTarget target = (CglibTarget) enhancer.create() ;
        target.print();
        System.out.println(target.toString());
    }

}

BeforeInterceptor
hello cglibProxy
AfterInterceptor
dynamicProxyTest.CglibTarget$$EnhancerByCGLIB$$4318edbe@1b4fb997