spring aop 实现原理---代理模式

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

public class AopTest {

    public static void main(String[] args) {
        
        Before before = new Before() {
            public void before() {
                System.out.println("...before...");                
            }            
        };
        
        After after = new After() {
            public void after() {
                System.out.println("...after...");                
            }            
        };
        
        Hello hello = null;
        
        // 普通方法执行
        System.out.println("-------------普通执行-------------");
        hello = new HelloEnglish();
        hello.sayHello("bao110908");
        hello.sayHi("bao110908");
        System.out.println();                
        
        // 切入方法执行前（前置增强）
        System.out.println("-------------前置增强-------------");
        hello = HelloAopManager.getHelloProxy(new HelloEnglish(), before);
        hello.sayHello("bao110908");
        hello.sayHi("bao110908");        // sayHi 方法没有标注 @Enhancement 所以不会进行代码切入
        System.out.println();
        
        // 切入方法执行后（后置增强）
        System.out.println("-------------后置增强-------------");
        hello = HelloAopManager.getHelloProxy(new HelloEnglish(), after);
        hello.sayHello("bao110908");
        hello.sayHi("bao110908");
        System.out.println();
        
        // 切入方法执行前和执行后（环绕增强）
        System.out.println("-------------环绕增强-------------");
        hello = HelloAopManager.getHelloProxy(new HelloEnglish(), before, after);
        hello.sayHello("bao110908");
        hello.sayHi("bao110908");
        System.out.println();
    }
}



@Retention(RetentionPolicy.RUNTIME)
@interface Enhancement {    
}

interface Hello {
    @Enhancement
    public void sayHello(String name);
    public void sayHi(String name);
}

class HelloChinese implements Hello {
    public void sayHello(String name) {
        System.out.println(name + "，您好");
    }
    public void sayHi(String name) {
        System.out.println("哈啰，" + name);
    }
}

class HelloEnglish implements Hello {
    public void sayHello(String name) {
        System.out.println("Hello, " + name);
    }
    public void sayHi(String name) {
        System.out.println("hi, " + name);
    }
}

class HelloAopManager {
    private HelloAopManager(){        
    }
    
    public static Hello getHelloProxy(Hello hello, Before before) {
        return getHelloProxy(hello, before, null);
    }
    
    public static Hello getHelloProxy(Hello hello, After after) {
        return getHelloProxy(hello, null, after);
    }
    
    public static Hello getHelloProxy(Hello hello, Before before, After after) {
        HelloHandler handler = new HelloHandler();
        if(before != null) {        
            handler.setBefore(before);
        }
        if(after != null) {
            handler.setAfter(after);
        }
        return handler.bind(hello);
    }       
}

/**
 * 前置增强接口
 */
interface Before {
    public void before();
}

/**
 * 后置增强接口
 */
interface After {
    public void after();
}

class HelloHandler implements InvocationHandler {   
    
    /**
     * 需要进行代理的实例
     */
    private Hello hello = null;
    
    /**
     * 前置增强
     */
    private Before before = null;
    
    /**
     * 后置增强
     */
    private After after = null;

    /**
     * InvocationHandler 接口的实现方法，进行动态代理
     */
    public Object invoke(Object proxy, Method method, Object[] args)
            throws Throwable {
        // 看看接口中方法是否标注了需要 Enhancement
        boolean b = method.isAnnotationPresent(Enhancement.class);
        if(!b){
            // 没有标注的话，按原方法执行
            return method.invoke(hello, args);
        }
        // 有标注的话，进行方法的前置和后置增强
        if(before != null) {
            before.before();
        }
        Object obj = method.invoke(hello, args);
        if(after != null) {
            after.after();
        }
        return obj;
    }
    
    /**
     * 将传入的 Hello 与 InvocationHandler 进行绑定，以获得代理类的实例
     * @param hello
     * @return
     */
    public Hello bind(Hello hello) {
        this.hello = hello;
        Hello helloProxy = (Hello)Proxy.newProxyInstance(
                hello.getClass().getClassLoader(),
                hello.getClass().getInterfaces(),
                this
            );
        return helloProxy;
    }
    
    public void setAfter(After after) {
        this.after = after;
    }

    public void setBefore(Before before) {
        this.before = before;
    }
}