标签：耦合度 强制 ann throwable let 重用 info point 代理
在软件业，AOP为Aspect Oriented Programming的缩写，意为：面向切面编程，通过预编译方式和运行期动态代理实现程序功能的统一维护的一种技术。AOP是OOP的延续，是软件开发中的一个热点，也是Spring框架中的一个重要内容，是函数式编程的一种衍生范型。利用AOP可以对业务逻辑的各个部分进行隔离，从而使得业务逻辑各部分之间的耦合度降低，提高程序的可重用性，同时提高了开发的效率。
先来了解一下AOP的相关概念，《Spring参考手册》中定义了以下几个AOP的重要概念，结合以上代码分析如下：
通知（Advice）类型：
注：可以将多个通知应用到一个目标对象上，即可以将多个切面织入到同一目标对象。
使用Spring AOP可以基于两种方式，一种是比较方便和强大的注解方式，另一种则是中规中矩的xml配置方式。
先说注解，使用注解配置Spring AOP总体分为两步：
第一步是在xml文件中声明激活自动扫描组件功能，同时激活自动代理功能（同时在xml中添加一个UserService的普通服务层组件，来测试AOP的注解功能）：
<?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:context="http://www.springframework.org/schema/context" xmlns:aop="http://www.springframework.org/schema/aop" xsi:schemaLocation="http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-3.1.xsd http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.0.xsd"> <!-- 激活组件扫描功能,在包cn.ysh.studio.spring.aop及其子包下面自动扫描通过注解配置的组件 --> <context:component-scan base-package="cn.ysh.studio.spring.aop"/> <!-- 激活自动代理功能 --> <aop:aspectj-autoproxy proxy-target-class="true"/> <!-- 用户服务对象 --> <bean id="userService" class="cn.ysh.studio.spring.aop.service.UserService" /> </beans>
第二步是为Aspect切面类添加注解：
package cn.ysh.studio.spring.aop.aspect; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.aspectj.lang.JoinPoint; import org.aspectj.lang.ProceedingJoinPoint; import org.aspectj.lang.annotation.After; import org.aspectj.lang.annotation.AfterReturning; import org.aspectj.lang.annotation.AfterThrowing; import org.aspectj.lang.annotation.Around; import org.aspectj.lang.annotation.Aspect; import org.aspectj.lang.annotation.Before; import org.aspectj.lang.annotation.Pointcut; import org.springframework.stereotype.Component; /** * 系统服务组件Aspect切面Bean * @author * @date 2017-3-28 */ //声明这是一个组件 @Component //声明这是一个切面Bean @Aspect public class ServiceAspect { private final static Log log = LogFactory.getLog(ServiceAspect.class); //配置切入点,该方法无方法体,主要为方便同类中其他方法使用此处配置的切入点 @Pointcut("execution(* cn.ysh.studio.spring.aop.service..*(..))") public void aspect(){ } /* * 配置前置通知,使用在方法aspect()上注册的切入点 * 同时接受JoinPoint切入点对象,可以没有该参数 */ @Before("aspect()") public void before(JoinPoint joinPoint){ if(log.isInfoEnabled()){ log.info("before " + joinPoint); } } //配置后置通知,使用在方法aspect()上注册的切入点 @After("aspect()") public void after(JoinPoint joinPoint){ if(log.isInfoEnabled()){ log.info("after " + joinPoint); } } //配置环绕通知,使用在方法aspect()上注册的切入点 @Around("aspect()") public void around(JoinPoint joinPoint){ long start = System.currentTimeMillis(); try { ((ProceedingJoinPoint) joinPoint).proceed(); long end = System.currentTimeMillis(); if(log.isInfoEnabled()){ log.info("around " + joinPoint + "\tUse time : " + (end - start) + " ms!"); } } catch (Throwable e) { long end = System.currentTimeMillis(); if(log.isInfoEnabled()){ log.info("around " + joinPoint + "\tUse time : " + (end - start) + " ms with exception : " + e.getMessage()); } } } //配置后置返回通知,使用在方法aspect()上注册的切入点 @AfterReturning("aspect()") public void afterReturn(JoinPoint joinPoint){ if(log.isInfoEnabled()){ log.info("afterReturn " + joinPoint); } } //配置抛出异常后通知,使用在方法aspect()上注册的切入点 @AfterThrowing(pointcut="aspect()", throwing="ex") public void afterThrow(JoinPoint joinPoint, Exception ex){ if(log.isInfoEnabled()){ log.info("afterThrow " + joinPoint + "\t" + ex.getMessage()); } } }
测试代码：
package cn.ysh.studio.spring.aop; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; import cn.ysh.studio.spring.aop.service.UserService; import cn.ysh.studio.spring.mvc.bean.User; /** * Spring AOP测试 * @author * @date 2017-3-28 */ public class Tester { private final static Log log = LogFactory.getLog(Tester.class); public static void main(String[] args) { //启动Spring容器 ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml"); //获取service组件 UserService service = (UserService) context.getBean("userService"); //以普通的方式调用UserService对象的三个方法 User user = service.get(1L); service.save(user); try { service.delete(1L); } catch (Exception e) { if(log.isWarnEnabled()){ log.warn("Delete user : " + e.getMessage()); } } } }
测试结果如下：
INFO [spring.aop.aspect.ServiceAspect:40] before execution(User cn.ysh.studio.spring.aop.service.UserService.get(long)) INFO [spring.aop.service.UserService:19] getUser method . . . INFO [spring.aop.aspect.ServiceAspect:60] around execution(User cn.ysh.studio.spring.aop.service.UserService.get(long)) Use time : 42 ms! INFO [spring.aop.aspect.ServiceAspect:48] after execution(User cn.ysh.studio.spring.aop.service.UserService.get(long)) INFO [spring.aop.aspect.ServiceAspect:74] afterReturn execution(User cn.ysh.studio.spring.aop.service.UserService.get(long)) INFO [spring.aop.aspect.ServiceAspect:40] before execution(void cn.ysh.studio.spring.aop.service.UserService.save(User)) INFO [spring.aop.service.UserService:26] saveUser method . . . INFO [spring.aop.aspect.ServiceAspect:60] around execution(void cn.ysh.studio.spring.aop.service.UserService.save(User)) Use time : 2 ms! INFO [spring.aop.aspect.ServiceAspect:48] after execution(void cn.ysh.studio.spring.aop.service.UserService.save(User)) INFO [spring.aop.aspect.ServiceAspect:74] afterReturn execution(void cn.ysh.studio.spring.aop.service.UserService.save(User)) INFO [spring.aop.aspect.ServiceAspect:40] before execution(boolean cn.ysh.studio.spring.aop.service.UserService.delete(long)) INFO [spring.aop.service.UserService:32] delete method . . . INFO [spring.aop.aspect.ServiceAspect:65] around execution(boolean cn.ysh.studio.spring.aop.service.UserService.delete(long)) Use time : 5 ms with exception : spring aop ThrowAdvice演示 INFO [spring.aop.aspect.ServiceAspect:48] after execution(boolean cn.ysh.studio.spring.aop.service.UserService.delete(long)) INFO [spring.aop.aspect.ServiceAspect:74] afterReturn execution(boolean cn.ysh.studio.spring.aop.service.UserService.delete(long)) WARN [studio.spring.aop.Tester:32] Delete user : Null return value from advice does not match primitive return type for: public boolean cn.ysh.studio.spring.aop.service.UserService.delete(long) throws java.lang.Exception
可以看到，正如我们预期的那样，虽然我们并没有对UserSerivce类包括其调用方式做任何改变，但是Spring仍然拦截到了其中方法的调用，或许这正是AOP的魔力所在。
标签：耦合度 强制 ann throwable let 重用 info point 代理
原文地址：http://www.cnblogs.com/luchangyou/p/6639893.html
