代理模式,CGLIB 与Spring AOP实现原理

参考资料：http://www.cnblogs.com/jqyp/archive/2010/08/20/1805041.html

AOP 面向接口的编程，JAVA的另一个特性。

其实现原理主要是使用代理模式。

---

 代理模式，就是利用一个对象的代理去执行目标对象的方法，同时可以在执行目标对象方法前后执行其他语句。

代理模式的对象必须实现接口。

目标对象实现的接口

package com.jason.prj;

/**
 * Created by Administrator on 2016/6/19.
 */
public interface BookFacade {
    public void addBook();
    public void deleteBook();
}

目标对象

package com.jason.prj;

/**
 * Created by Administrator on 2016/6/19.
 */
public class BookFacadeImpl implements BookFacade {
    @Override
    public void addBook() {
        System.out.println("Add Book Logic is running ...");
    }

    @Override
    public void deleteBook() {
        System.out.println("Delete Book Logic is running ...");
    }
}

 实现InvocationHandler接口

package com.jason.prj;

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

/**
 * Created by Administrator on 2016/6/19.
 */
public class BookFacadeProxy implements InvocationHandler{
    private Object target;

    public Object bind(Object target){
        this.target = target;
        //生成代理对象
        return Proxy.newProxyInstance(target.getClass().getClassLoader(),target.getClass().getInterfaces(),this);
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        Object result = null;
        System.out.println("Proxy start ...");
        System.out.println("Class Name: "+target.getClass().getName());
        System.out.println("Method Name: "+method.getName());
        //执行目标方法
        result = method.invoke(target, args);
        System.out.println("Proxy end ...");
        return null;
    }
}

测试

package com.jason.prj;

import static org.junit.Assert.*;

public class BookFacadeProxyTest {

    @org.junit.Test
    public void testBind() throws Exception {
        BookFacadeProxy proxy = new BookFacadeProxy();
        //生成代理
        BookFacade bookProxy = (BookFacade) proxy.bind(new BookFacadeImpl());
        //利用代理执行方法
        bookProxy.addBook();
        //利用代理执行方法
        bookProxy.deleteBook();
    }
}

测试结果

Proxy start ... 
Class Name: com.jason.prj.BookFacadeImpl
Method Name: addBook
Add Book Logic is running ... //执行目标方法 addBook()
Proxy end ...
Proxy start ...
Class Name: com.jason.prj.BookFacadeImpl
Method Name: deleteBook
Delete Book Logic is running ... //执行目标方法 deleteBook()
Proxy end ...

---

用CGLIB实现代理

JAVA自身的代理需要目标对象实现接口，使用CGLIB就不需要实现接口。

 首先来创建一个不实现接口的类

package com.jason.prj;

/**
 * Created by Administrator on 2016/6/20.
 */
public class BookFacadeImp1 {
    public void addBook(){
        System.out.println("Add book ...");
    }
    public void deleteBook(){
        System.out.println("Delete book ...");
    }
}

实现MethodInterceptor接口

package com.jason.prj;

import net.sf.cglib.proxy.Enhancer;
import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.MethodProxy;

import java.lang.reflect.Method;

/**
 * Created by Administrator on 2016/6/20.
 */
public class BookFacadeCglib implements MethodInterceptor {
    private Object target;

    public Object getInstance(Object target){
        this.target = target;
        Enhancer enhancer = new Enhancer();
        enhancer.setSuperclass(this.target.getClass());
        enhancer.setCallback(this);
        return enhancer.create();
    }

    @Override
    public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
        System.out.println("Transaction Starts");
        methodProxy.invokeSuper(o, objects);
        System.out.println("Transaction Ends");
        return null;
    }
}

测试代码

package com.jason.prj;

/**
 * Created by Administrator on 2016/6/20.
 */
public class Testlib {
    public static void main(String[] args){
        BookFacadeCglib cglib = new BookFacadeCglib();
        BookFacadeImp1 bookCglib = (BookFacadeImp1) cglib.getInstance(new BookFacadeImp1());
        bookCglib.addBook();
    }
}

测试结果

Transaction Starts
Add book ...
Transaction Ends

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代理模式为Spring AOP的实现原理

可以利用代理模式在执行目标方法前后去加入通知，完成对业务功能的分割，形成切面。