Spring中基于注解@AspectJ的AOP实现

@AspectJ 作为通过 Java 5 注释注释的普通的 Java 类，它指的是声明aspects 的一种风格。通过在基于架构的 XML 配置文件中包含以下元素，@AspectJ 支持是可用的。

aop:aspectj-autoproxy/

大致流程如下：

(1) 首先利用注解声明一个Aspect：

import org.aspectj.lang.annotation.Aspect;
@Aspect
public class AspectModule {
}

该aspect在Beans.xml中需要进行如下配置：

Beans.xml：

<bean id="myAspect" class="org.xyz.AspectModule">
   <!-- configure properties of aspect here as normal -->
</bean>

(2) 声明一个切入点PointCut. 切入点表达式定义了我们感兴趣的哪个方法会真正被执行。

一个例子：该切入点将与 com.tutorialspoint 包下的 Student 类中的 getName() 方法相匹配：

import org.aspectj.lang.annotation.Pointcut;
@Pointcut("execution(* com.tutorialspoint.Student.getName(..))") 
private void getname() {}

(3) 声明Advice：

@Before("businessService()")
public void doBeforeTask(){
 ...
}
@After("businessService()")
public void doAfterTask(){
 ...
}
@AfterReturning(pointcut = "businessService()", returning="retVal")
public void doAfterReturnningTask(Object retVal){
  // you can intercept retVal here.
  ...
}
@AfterThrowing(pointcut = "businessService()", throwing="ex")
public void doAfterThrowingTask(Exception ex){
  // you can intercept thrown exception here.
  ...
}
@Around("businessService()")
public void doAroundTask(){
 ...
}

看个具体的例子。

Logging.java:

import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Pointcut;
import org.aspectj.lang.annotation.Before;
import org.aspectj.lang.annotation.After;
import org.aspectj.lang.annotation.AfterThrowing;
import org.aspectj.lang.annotation.AfterReturning;
import org.aspectj.lang.annotation.Around;
@Aspect
public class Logging {
   /** Following is the definition for a pointcut to select
    *  all the methods available. So advice will be called
    *  for all the methods.
    */
   @Pointcut("execution(* com.sap.*.*(..))")
   private void selectAll(){}
   /** 
    * This is the method which I would like to execute
    * before a selected method execution.
    */
   @Before("selectAll()")
   public void beforeAdvice(){
      System.out.println("Going to setup student profile.");
   }
   /** 
    * This is the method which I would like to execute
    * after a selected method execution.
    */
   @After("selectAll()")
   public void afterAdvice(){
      System.out.println("Student profile has been setup.");
   }
   /** 
    * This is the method which I would like to execute
    * when any method returns.
    */
   @AfterReturning(pointcut = "selectAll()", returning="retVal")
   public void afterReturningAdvice(Object retVal){
      System.out.println("Returning:" + retVal.toString() );
   }
   /**
    * This is the method which I would like to execute
    * if there is an exception raised by any method.
    */
   @AfterThrowing(pointcut = "selectAll()", throwing = "ex")
   public void AfterThrowingAdvice(IllegalArgumentException ex){
      System.out.println("There has been an exception: " + ex.toString());   
   }  
}

定义一个名叫selectAll的Pointcut，execution表达式的值为：execution(* com.sap. . (…))

意思是选中package com.sap下的所有Java类方法来动态调用advice.

Beans.xml的内容：

<?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-3.0.xsd 
    http://www.springframework.org/schema/aop 
    http://www.springframework.org/schema/aop/spring-aop-3.0.xsd ">

    <aop:aspectj-autoproxy/>

   <!-- Definition for student bean -->
   <bean id="student" class="com.sap.Student">
      <property name="name"  value="Zara" />
      <property name="age"  value="11"/>      
   </bean>

   <!-- Definition for logging aspect -->
   <bean id="logging" class="com.sap.Logging"/> 

</beans>

如果不使用@AspectJ和@pointcut注解，我们需要在Beans.xml里进行冗长的定义aspect和pointcut定义：

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