Spring AOP简述

使用面想对象（Object-Oriented Programming,OOP）包含一些弊端，当需要为多个不具有继承关系的对象引入公共行为时，例如日志，安全检测等。我们只有在每个对象中引入公共行为，这样程序中就产生了大量的代码，程序就不便于维护了，所以就有了一个面向对象编程的补充---面向切面编程（Aspect-Oriented Programming, AOP），AOP关注的方向是横向的，OOP关注的时纵向的；OOP中模块的基本单元是class，而AOP中基本的模块单元称作Aspect。

AOP的其主要作用是，在不修改源代码的情况下给某个或者一组操作添加额外的功能。像日志记录，事务处理，权限控制等功能，都可以用AOP来“优雅”地实现，使这些额外功能和真正的业务逻辑分离开来，软件的结构将更加清晰。AOP是OOP的一个强有力的补充。

Key Terms

学习AOP，我们需要关注一些技术名词：

Aspect: 切面，横向贯穿于多个类的某个服务，比如事务处理
Join Point：又叫point cut，是指那些方法需要被执行"AOP"
Advice：join point上特定的时刻执行的操作，Advice有几种不同类型，下文将会讨论（通俗地来讲就是起作用的内容和时间点）。
Introduction: 给对象增加方法或者属性
Target object: Advice起作用的对象
AOP proxy：为实现AOP所实现的代理，在Spring中实现代理的方式有两种，JDK代理和CGLIB代理
Weaving：将Advice织入join point的过程

Advice的类型：

Before advice: 在执行join point之前执行
After returning advice: 执行在join point这个方法返回之后的advice
After throwing advice: 当方法抛出异常之后执行
After (finally) advice: Advice在方法退出之后执行。
Around advice: 包围一个连接点的通知，如方法调用。这是最强大的通知。Aroud通知在方法调用前后完成自定义的行为。它们负责选择继续执行连接点或通过返回它们自己的返回值或抛出异常来短路执行。

Spring AOP的使用

有三种方式使用Spring AOP，分别是：@Aspect-based（Annotation），Schema-based（XML），以及底层的Spring AOP API。其中@Aspect-based是使用最多的一种方式。我们所讲的例子也是基于@Aspect-based(Annotation)这种方式的

Aspect based

配置

Spring AOP Maven依赖

<dependency>
     <groupId>org.springframework</groupId>
     <artifactId>spring-context</artifactId>
     <version>4.2.1.RELEASE</version>
</dependency>   

<dependency>
     <groupId>org.springframework</groupId>
     <artifactId>spring-aop</artifactId>
     <version>4.2.1.RELEASE</version>
</dependency>

<dependency>
     <groupId>org.aspectj</groupId>
     <artifactId>aspectjrt</artifactId>
     <version>1.6.11</version>
</dependency>  

<dependency>
     <groupId>org.aspectj</groupId>
     <artifactId>aspectjweaver</artifactId>
     <version>1.8.7</version>
</dependency>

xml文件配置

 <?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/beans
		http://www.springframework.org/schema/beans/spring-beans-3.1.xsd
		http://www.springframework.org/schema/aop
		http://www.springframework.org/schema/aop/spring-aop-3.1.xsd">
   <!-- 使能AOP-->
   <aop:aspectj-autoproxy/>

   <!-- 声明一个切面-->
   <bean id="myAspect" class="com.mj.spring.aop.MyAspect"></bean>
   <!--声明AOP target-->
   <bean id="userManager" class="com.mj.spring.aop.UserManager"></bean>
</beans>

编码

定义切面类

<!--定义切面类-->
@Aspect 
public class MyAspect {

//定义切点, 这个切点的使用范围是: 定义在com.mj.spring.aop包下的所有方法
@Pointcut("execution(* com.mj.spring.aop.*.*(..))")
public void aPointcut() {
}

//定义Before Advice
@Before("aPointcut()")
public void beforeAdvice() {
    System.out.println("before advice is executed!");
}

//定义AfterReturning Advice
@AfterReturning(pointcut = "aPointcut()", returning = "r")
public void afterReturningAdvice(String r) {
    if (r != null)
        System.out.println("after returning advice is executed! returning String is : " + r);
}

//定义After Advice
@After("aPointcut()")
public void AfterAdvice() {
    System.out.println("after advice is executed!");
}

@After("aPointcut() && args(str)")
public void AfterAdviceWithArg(String str) {
    System.out.println("after advice with arg is executed!arg is : " + str);
}

//定义afterThrowingAdvice Advice
@AfterThrowing(pointcut = "aPointcut()", throwing = "e")
public void afterThrowingAdvice(Exception e) {
    System.out.println("after throwing advice is executed!exception msg is : " + e.getMessage());
}

//定义around advice
@Around(value="execution(public String com.mj.spring.aop.UserManager.getUser(..))")
public void aroundSayHello(ProceedingJoinPoint joinPoint) throws Throwable{
    System.out.println("Around Before !! ");
    joinPoint.proceed();
    System.out.println("Around After !! ");
}

}

定义AOP target类

public class UserManager {
/*这个方法需要一个参数*/
public void addUser(String user) {
    System.out.println("addUser(String str) method is executed!");
}

public void deleteUser() {
    System.out.println("deleteUser() method is executed!");
}

/*这个方法返回一个字符串*/
public String getUser() {
    System.out.println("getUser() method is executed!");
    return "Hello";
}

/*这个方法抛出一个异常*/
public void editUser() throws Exception {
    throw new Exception("something is wrong.");
}
}

测试类

public class UserManagerTest {

private ApplicationContext applicationContext=null;
@Before
public void setUp() throws Exception {
    applicationContext=new ClassPathXmlApplicationContext("ApplicationContext.xml");
}

@Test
public void shoud_get_user_maneger_bean() throws Exception {
    UserManager userManager = (UserManager) applicationContext.getBean("userManager");
    assertThat(userManager!=null,is(true));
}
@Test
public void should_apply_before_advice_and_after_advice_and_after_advice_with_arg() throws Exception{
    UserManager userManager = (UserManager) applicationContext.getBean("userManager");
    userManager.addUser("Jun.Ma");
}
@Test
public void should_apply_before_advice_and_after_advice() throws Exception{
    UserManager userManager = (UserManager) applicationContext.getBean("userManager");
    userManager.deleteUser();
}

@Test
public void should_apply_before_advice_and_after_advice_and_after_throwing_advice() throws Exception{
    UserManager userManager = (UserManager) applicationContext.getBean("userManager");
    userManager.editUser();
}

@Test
public void should_apply_before_advice_and_after_advice_after_return_advice() throws Exception{
    UserManager userManager = (UserManager) applicationContext.getBean("userManager");
    userManager.getUser();
}
@Test
public void should_apply_around_advice_and_before_advice_and_after_advice_after_return_advice() throws Exception{
    UserManager userManager = (UserManager) applicationContext.getBean("userManager");
    userManager.getUser();
}
}

Reference

http://docs.spring.io/spring/docs/current/spring-framework-reference/htmlsingle/#aop-enable-aspectj-java Spring Document Reference

http://blog.psjay.com/posts/summary-of-spring-3-aop/ Spring AOP 3 Summary

源码git路径: git@github.com:jma19/spring.git

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