原文链接：http://www.orlion.ga/205/

一、AOP简介

1、AOP概念

参考文章:http://www.orlion.ml/57

2、AOP的产生

对于如下方法:

    public class UserDAOImpl implements UserDAO{public void saveUser(User user){doSaveUser();}}

想在saveUser方法中执行保存用户之前和之后记录当前时间以求出saveUser花费了多少时间，方法有很多种，最直观的写法就是在doSaveUser()前后加代码取出当前时间:

    public class UserDAOImpl implements UserDAO{public void saveUser(User user){int beginTime = getCurrentTime();doSaveUser();int endTime = getCurrentTime();}}

还有一种方法就是重新写一个类继承自UserDAOImpl然后重写saveUser方法，如下:

    public class UserDAOImpl2 extends UserDAOImpl{@Overridepublic void saveUser(User user){int beginTime = getCurrentTime();super.saveUser();int endTime = getCurrentTime();}}

这种方法耦合性太强，一旦父类改变了子类也会改变，慎用继承

再有一种方法就是在调用saveUser()方法时加代码:

    public class UserService{public void saveUser(User user){UserDAOImpl userDao = new UserDAOImpl();int beginTime = getCurrentTime();userDao.saveUser();int endTime = getCurrentTime();}}

现在如果让我们将项目中所有的对数据库进行CRUD操作的方法都加上获取时间的代码，显然工作量太大，这时候就用动态代理： （可参考http://www.orlion.ml/207/）

UserDAOImpl.java

    package ml.orlion.dao.impl;import ml.orlion.dao.UserDAO;import ml.orlion.model.User;public class UserDAOImpl implements UserDAO{public void saveUser(User user){System.out.println("save usering");}}

TimeInterceptor.java

    package ml.orlion.aop;import java.lang.reflect.InvocationHandler;import java.lang.reflect.Method;public class TimeInterceptor implements InvocationHandler{private Object target;// 被代理的对象public Object getTarget() {return target;}public void setTarget(Object target) {this.target = target;}public void beforeMethod(Method m){System.out.println(m.getName() + "begin start");}@Overridepublic Object invoke(Object proxy, Method m, Object[] args) throws Throwable {this.beforeMethod(m);// 插入方法m.invoke(target, args);return null;}}

测试

    public static void testProxy(){// 首先产生一个被代理对象UserDAO userDao = new UserDAOImpl();// 下一步将被代理对象交给InvocationHandler即TimeInterceptorTimeInterceptor ti = new TimeInterceptor();// 设置被代理对象ti.setTarget(userDao);// 根据被代理对象产生一个代理UserDAO userProxy = (UserDAO)Proxy.newProxyInstance(UserDAO.class.getClassLoader(), new Class[]{UserDAO.class}, ti);userProxy.saveUser(new User());}

运行可以看到控制台打印:saveUserbegin start      save usering

二、使用Spring AOP

UserDAO.java:

package ml.orlion.dao;import ml.orlion.model.User;public interface UserDAO {public void saveUser(User user);
}

UserDAOImpl.java:

package ml.orlion.dao.impl;import ml.orlion.dao.UserDAO;
import ml.orlion.model.User;public class UserDAOImpl implements UserDAO{public void saveUser(User user){System.out.println("save usering");}
}

UserService.java

package ml.orlion.service;import ml.orlion.dao.UserDAO;
import ml.orlion.dao.impl.UserDAOImpl;
import ml.orlion.model.User;public class UserService {private UserDAO userDAO = new UserDAOImpl();public UserDAO getUserDao() {return userDAO;}public void setUserDao(UserDAO userDAO) {this.userDAO = userDAO;}public void saveUser(User user){this.userDAO.saveUser(user);}
}

LogInterceptor.java

package ml.orlion.aop;public class LogInterceptor {public void before(){System.out.println("before");}
}

beans.xml:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xmlns:aop="http://www.springframework.org/schema/aop"xsi:schemaLocation="http://www.springframework.org/schema/beanshttp://www.springframework.org/schema/beans/spring-beans.xsdhttp://www.springframework.org/schema/aophttp://www.springframework.org/schema/aop/spring-aop.xsd"><bean id="logInterceptor" class="ml.orlion.aop.LogInterceptor"></bean><bean id="userDao" class="ml.orlion.dao.impl.UserDAOImpl"></bean><bean id="userService" class="ml.orlion.service.UserService"><property name="userDao" ref="userDao"/></bean><aop:config><aop:pointcut expression="execution(public * ml.orlion.service..*.add(..))"id="servicePointcut" /><aop:aspect id="logAspect" ref="logInterceptor"><aop:before method="before" pointcut-ref="servicePointcut"/></aop:aspect></aop:config>
</beans>

测试：

BeanFactory appContext = new ClassPathXmlApplicationContext("beans.xml");
UserService userService = (UserService) appContext.getBean("userService");
userService.saveUser(new User());