假设有如下需求：
写一个计算器类，里面包含加减乘除四个方法。在每个方法开始前打印出该方法开始的消息，在每个方法结束前打印出该方法结束的消息和计算的结果。
普通方法，先写一个借口，然后在接口里实现四个方法。在每个方法里加上要打印的语句。实现代码如下。
ArithmeticCalculator接口
package com.spring.aop.helloworld;
public interface ArithmeticCalculator {
int add(int i, int j);
int sub(int i, int j);
int mul(int i, int j);
int div(int i, int j);
}ArithmeticCalculatorLoggingImpl.java 实现上面的接口
package com.spring.aop.helloworld;
public class ArithmeticCalculatorLoggingImpl implements ArithmeticCalculator{
@Override
public int add(int i, int j) {
System.out.println("The method add begins with [" + i + ", " + j + "]");
int result = i + j;
System.out.println("The method add end with " + result);
return result;
}
@Override
public int sub(int i, int j) {
System.out.println("The method sub begins with [" + i + ", " + j + "]");
int result = i - j;
System.out.println("The method sub end with " + result);
return result;
}
@Override
public int mul(int i, int j) {
System.out.println("The method mul begins with [" + i + ", " + j + "]");
int result = i * j;
System.out.println("The method mul end with " + result);
return result;
}
@Override
public int div(int i, int j) {
System.out.println("The method div begins with [" + i + ", " + j + "]");
int result = i / j;
System.out.println("The method div end with " + result);
return result;
}
}Main.java
ArithmeticCalculator arithmeticCalculator = new ArithmeticCalculatorLoggingImpl();
arithmeticCalculator.add(1, 5);
System.out.println("----------");
arithmeticCalculator.sub(5, 3);
System.out.println("----------");
arithmeticCalculator.mul(3, 7);
System.out.println("----------");
arithmeticCalculator.div(9, 3);程序运行结果：
The method add begins with [1, 5]
The method add end with 6
----------
The method sub begins with [5, 3]
The method sub end with 2
----------
The method mul begins with [3, 7]
The method mul end with 21
----------
The method div begins with [9, 3]
The method div end with 3
可见，上面的代码中间存在这大量相似的代码。而面向对象编程又不能很好地解决这个问题，下面采用动态代理的方法来解决上面的问题。
接口不变。写一个实现类ArithmeticCalculatorImpl.java 这个实现类只关注业务，没有需要打印的内容
package com.spring.aop.helloworld;
public class ArithmeticCalculatorImpl implements ArithmeticCalculator{
@Override
public int add(int i, int j) {
int result = i + j;
return result;
}
@Override
public int sub(int i, int j) {
int result = i - j;
return result;
}
@Override
public int mul(int i, int j) {
int result = i * j;
return result;
}
@Override
public int div(int i, int j) {
int result = i / j;
return result;
}
}ArithmeticCaculatorLogginProxy.java
package com.spring.aop.helloworld;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.Arrays;
public class ArithmeticCaculatorLogginProxy {
//要代理的对象
private ArithmeticCalculator target;
public ArithmeticCaculatorLogginProxy(ArithmeticCalculator target){
this.target = target;
}
public ArithmeticCalculator getLoggingProxy() {
ArithmeticCalculator proxy = null;
//代理对象由哪一个类加载器负责加载
ClassLoader loader = target.getClass().getClassLoader();
//代理对象的类型，即其中有哪些方法
Class[] interfaces = new Class[]{ArithmeticCalculator.class};
//当调用代理对象其中的方法时，该执行的代码
InvocationHandler h = new InvocationHandler() {
/**
* proxy:正在返回的代理对象，一般情况下，在invoke方法中都不适用该对象
* method：正在被调用的方法
* args：调用方法时，传入的参数
*/
@Override
public Object invoke(Object proxy, Method method, Object[] args)
throws Throwable {
//下面这句执行的时候又会调用invoke方法，所以会出现死循环导致内存溢出
//System.out.println(proxy.toString());
String methodName = method.getName();
//日志
System.out.println("The method " + methodName + " begins with" + Arrays.asList(args));
System.out.println("Invoke...");
//执行方法
Object result = method.invoke(target, args);
//日志
System.out.println("The method" + methodName + " ends with " + result);
return result;
}
};
proxy = (ArithmeticCalculator) Proxy.newProxyInstance(loader, interfaces, h);
return proxy;
}
}main方法
ArithmeticCalculator target = new ArithmeticCalculatorImpl();
ArithmeticCalculator proxy = new ArithmeticCaculatorLogginProxy(target).getLoggingProxy();
proxy.add(1, 5);
System.out.println("----------");
proxy.sub(5, 3);
System.out.println("----------");
proxy.mul(3, 7);
System.out.println("----------");
proxy.div(9, 3);程序运行结果 ：
The method add begins with[1, 5]
Invoke...
The methodadd ends with 6
----------
The method sub begins with[5, 3]
Invoke...
The methodsub ends with 2
----------
The method mul begins with[3, 7]
Invoke...
The methodmul ends with 21
----------
The method div begins with[9, 3]
Invoke...
The methoddiv ends with 3
本文出自 “阿凡达” 博客，请务必保留此出处http://shamrock.blog.51cto.com/2079212/1557431
原文：http://shamrock.blog.51cto.com/2079212/1557431