java使用动态代理来实现AOP（日志记录）

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AOP（面向方面）的思想，就是把项目共同的那部分功能分离开来，比如日志记录，避免在业务逻辑里面夹杂着跟业务逻辑无关的代码。

下面是一个AOP实现的简单例子：

首先定义一些业务方法：

 /**
  * Created with IntelliJ IDEA.
  * Author: wangjie  email:tiantian.china.2@gmail.com
  * Date: 13-9-23
  * Time: 下午3:49
  */
 public interface BussinessService {
     public String login(String username, String password);
     public String find();
 }
 
 public class BussinessServiceImpl implements BussinessService {
     private Logger logger = Logger.getLogger(this.getClass().getSimpleName());
 
     @Override
     public String login(String username, String password) {
         return "login success";
     }
 
     @Override
     public String find() {
         return "find success";
     }
 
 }

 /**
  * Created with IntelliJ IDEA.
  * Author: wangjie  email:tiantian.china.2@gmail.com
  * Date: 13-9-24
  * Time: 上午10:27
  */
 public interface WorkService {
     public String work();
     public String sleep();
 }
 
 public class WorkServiceImpl implements WorkService{
     @Override
     public String work() {
         return "work success";
     }
 
     @Override
     public String sleep() {
         return "sleep success";
     }
 }

实现InvocationHandler接口，使用map来存储不同的InvocationHandler对象，避免生成过多。

 package com.wangjie.aoptest2.invohandler;
 
 import java.lang.reflect.InvocationHandler;
 import java.lang.reflect.Method;
 import java.lang.reflect.Proxy;
 import java.util.Arrays;
 import java.util.HashMap;
 import java.util.logging.Logger;
 
 /**
  * Created with IntelliJ IDEA.
  * Author: wangjie  email:tiantian.china.2@gmail.com
  * Date: 13-9-23
  * Time: 下午3:47
  */
 public class LogInvoHandler implements InvocationHandler{
     private Logger logger = Logger.getLogger(this.getClass().getSimpleName());
 
     private Object target; // 代理目标
     private Object proxy; // 代理对象
 
     private static HashMap<Class<?>, LogInvoHandler> invoHandlers = new HashMap<Class<?>, LogInvoHandler>();
 
     private LogInvoHandler() {
     }
 
     /**
      * 通过Class来生成动态代理对象Proxy
      * @param clazz
      * @return
      */
     public synchronized static<T> T getProxyInstance(Class<T> clazz){
         LogInvoHandler invoHandler = invoHandlers.get(clazz);
 
         if(null == invoHandler){
             invoHandler = new LogInvoHandler();
             try {
                 T tar = clazz.newInstance();
                 invoHandler.setTarget(tar);
                 invoHandler.setProxy(Proxy.newProxyInstance(tar.getClass().getClassLoader(),
                         tar.getClass().getInterfaces(), invoHandler));
             } catch (Exception e) {
                 e.printStackTrace();
             }
             invoHandlers.put(clazz, invoHandler);
 
         }
 
         return (T)invoHandler.getProxy();
     }
 
     @Override
     public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
 
         Object result = method.invoke(target, args); // 执行业务处理
 
         // 打印日志
         logger.info("____invoke method: " + method.getName()
                     + "; args: " + (null == args ? "null" : Arrays.asList(args).toString())
                     + "; return: " + result);
 
         return result;
     }
 
     public Object getTarget() {
         return target;
     }
 
     public void setTarget(Object target) {
         this.target = target;
     }
 
     public Object getProxy() {
         return proxy;
     }
 
     public void setProxy(Object proxy) {
         this.proxy = proxy;
     }
 }

然后编写一个Test类测试：

 /**
  * Created with IntelliJ IDEA.
  * Author: wangjie  email:tiantian.china.2@gmail.com
  * Date: 13-9-24
  * Time: 上午9:54
  */
 public class Test {
     public static Logger logger = Logger.getLogger(Test.class.getSimpleName());
     public static void main(String[] args) {
 
         BussinessService bs = LogInvoHandler.getProxyInstance(BussinessServiceImpl.class);
         bs.login("zhangsan", "123456");
         bs.find();
 
         logger.info("--------------------------------------");
 
         WorkService ws = LogInvoHandler.getProxyInstance(WorkServiceImpl.class);
         ws.work();
         ws.sleep();
 
         logger.info("--------------------------------------");
 
         BussinessService bss = LogInvoHandler.getProxyInstance(BussinessServiceImpl.class);
         bss.login("lisi", "654321");
         bss.find();
 
     }
 }

以后需要添加新的业务逻辑XXXService，只需要调用

XXXService xs = LogInvoHandler.getProxyInstance(XXXServiceImpl.class);

即可。

也可以模仿Spring等框架的配置，把bean的类名配置在xml文件中，如：

<bean id="bussinessService" class="com.wangjie.aoptest2.service.impl.BussinessServiceImpl">

然后在java代码中解析xml，通过Class.forName("com.wangjie.aoptest2.service.impl.BussinessServiceImpl");获得Class对象

然后通过LogInvoHandler.getProxyInstance(Class.forName("com.wangjie.aoptest2.service.impl.BussinessServiceImpl"));获得代理对象Proxy

再使用反射去调用代理对象的方法。

运行结果如下：

九月 24, 2013 11:08:03 上午 com.wangjie.aoptest2.invohandler.LogInvoHandler invoke
INFO: ____invoke method: login; args: [zhangsan, 123456]; return: login success
九月 24, 2013 11:08:03 上午 com.wangjie.aoptest2.invohandler.LogInvoHandler invoke
INFO: ____invoke method: find; args: null; return: find success
九月 24, 2013 11:08:03 上午 com.wangjie.aoptest2.Test main
INFO: --------------------------------------
九月 24, 2013 11:08:03 上午 com.wangjie.aoptest2.invohandler.LogInvoHandler invoke
INFO: ____invoke method: work; args: null; return: work success
九月 24, 2013 11:08:03 上午 com.wangjie.aoptest2.invohandler.LogInvoHandler invoke
INFO: ____invoke method: sleep; args: null; return: sleep success
九月 24, 2013 11:08:03 上午 com.wangjie.aoptest2.Test main
INFO: --------------------------------------
九月 24, 2013 11:08:03 上午 com.wangjie.aoptest2.invohandler.LogInvoHandler invoke
INFO: ____invoke method: login; args: [lisi, 654321]; return: login success
九月 24, 2013 11:08:03 上午 com.wangjie.aoptest2.invohandler.LogInvoHandler invoke
INFO: ____invoke method: find; args: null; return: find success