Spring学习文档_AOP

AOP: Aspect Oriented Programming -- 织入

工作原理为采用代理对象, 继承InvocationHandler, Struts2的Interceptor也是典型的AOP, 原理的sample:

package com.lohamce.aop;import java.lang.reflect.InvocationHandler;import java.lang.reflect.Method;public class LogInterceptor implements InvocationHandler{private Object target;public void beforeMethod(Method method){System.out.println("["+method.getName()+" begins]");}@Overridepublic Object invoke(Object proxy, Method method, Object[] args) throws Throwable {beforeMethod(method);method.invoke(target, args);return null;}public Object getTarget() {return target;}public void setTarget(Object target) {this.target = target;}}

@Testpublic void testProxy() throws Exception{UserDao userDao = new UserDaoImpl();LogInterceptor li = new LogInterceptor();li.setTarget(userDao);UserDao proxy = (UserDao)Proxy.newProxyInstance(userDao.getClass().getClassLoader(), userDao.getClass().getInterfaces(), li);proxy.save(new User());proxy.remove(new User());}

在Spring中有2种方式配置AOP

1. Annotation, 使用AspectJ实现, AspectJ是AOP的框架, 实现需要加入aspectjweaver.jar和aspectjrt.jar

织入的语法比较麻烦, 使用的话,需要查文档

package com.lohamce.aop;import org.aspectj.lang.annotation.Aspect;import org.aspectj.lang.annotation.Before;import org.springframework.stereotype.Component;@Aspect@Component("logInterceptor")public class LogInterceptor {private Object target;@Before("execution (public * com.lohamce.service.impl.*.*(..))")public void beforeMethod(){System.out.println("[Method begins]");}public Object getTarget() {return target;}public void setTarget(Object target) {this.target = target;}}

2. XML,比annotation更有优势,因为可以插拔,有可能切面类的逻辑是第三方的提供的.

<aop:config><aop:pointcut expression="execution (public * com.lohamce.service.impl.*.*(..))" id="servicePointcut"/><aop:aspect id="logAspect" ref="logInterceptor"><aop:before method="beforeMethod" pointcut-ref="servicePointcut" /></aop:aspect></aop:config>

Spring初始化之后,当执行到com.lohamce.service.impl下面的类方法时,判断是否符合表达式 (servicePointcut), 如果符合, 在执行此方法前调用logIntercetor的beforeMethod方法

<aop: advisor> 声明式的事务管理才处理