Spring基于@AspectJ的AOP

@ AspectJ是指声明方面的风格注释的使用Java 5注释普通的Java类。对@ AspectJ支持由包括您基于XML Schema的配置文件里面的下列元素启用。

<aop:aspectj-autoproxy/>

您还需要在以下应用程序的类路径中的AspectJ库。这些库可以在AspectJ的安装的'lib'目录，可以从网上下载他们.

aspectjrt.jar
aspectjweaver.jar
aspectj.jar

声明一个切面

方面类是像任何其他普通的bean，并可能有方法和字段，就像任何其他类，但他们将被标注了@Aspect 如下：

package org.xyz;

import org.aspectj.lang.annotation.Aspect;

@Aspect
public class AspectModule {

}

他们将在XML中进行配置像任何其他的bean，如下所示：

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

声明一个切入点

一个切入点有助于确定与不同意见要执行的连接点的权益（即方法）。同时用@AspectJ的基础配置工作，切入点声明有两个部分：

切入点表达式，决定哪些方法执行我们感兴趣
一个切入点签名的包含名字和任意数量的参数。该方法的实际主体是不相关的，实际上应为空。

下面的示例定义一个名为'businessService“切入点将匹配每个方法的可用包com.xyz.myapp.service下执行中的类：

import org.aspectj.lang.annotation.Pointcut;

@Pointcut("execution(* com.xyz.myapp.service.*.*(..))") // expression 
private void businessService() {}  // signature

下面的示例定义一个名为'getName'切入点将匹配可用的软件包com.yiibai下执行getName()方法在Student类：

import org.aspectj.lang.annotation.Pointcut;

@Pointcut("execution(* com.yiibai.Student.getName(..))") 
private void getname() {}

声明建议

可以声明任何使用 @{ADVICE-NAME} 注释下面给出的五个建议。这假定已经定义了一个切入点签名的方法的businessService()：

@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(){
 ...
}

可以定义内置切入点的任何意见的。下面是一个例子定义内联的切入点之前的建议：

@Before("execution(* com.xyz.myapp.service.*.*(..))")
public doBeforeTask(){
 ...
}

@AspectJ 基于AOP例子

要理解上述关系到@AspectJ的AOP的基础概念提到，让我们写这将实现几个建议的一个例子。写我们的例子中有一些建议，我们按照下面的步骤来创建一个Spring应用程序：

步骤	描述
1	Create a project with a name SpringExample and create a package com.yiibai under the src folder in the created project.
2	Add required Spring libraries using Add External JARs option as explained in the Spring Hello World Example chapter.
3	Add Spring AOP specific libraries aspectjrt.jar, aspectjweaver.jar and aspectj.jar in the project.
4	Create Java classes Logging, Student and MainApp under the com.yiibai package.
5	Create Beans configuration file Beans.xml under the src folder.
6	The final step is to create the content of all the Java files and Bean Configuration file and run the application as explained below.

这里是Logging.java文件的内容。这实际上是方面模块的一个示例，它定义的方法被调用的各个点。

package com.yiibai;

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.yiibai.*.*(..))")
   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());   
   }
   
}

以下是Student.java文件的内容：

package com.yiibai;

public class Student {
   private Integer age;
   private String name;

   public void setAge(Integer age) {
      this.age = age;
   }
   public Integer getAge() {
	  System.out.println("Age : " + age );
      return age;
   }

   public void setName(String name) {
      this.name = name;
   }
   public String getName() {
      System.out.println("Name : " + name );
      return name;
   }
   public void printThrowException(){
      System.out.println("Exception raised");
      throw new IllegalArgumentException();
   }
}

以下是MainApp.java文件的内容：

package com.yiibai;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MainApp {
   public static void main(String[] args) {
      ApplicationContext context = 
             new ClassPathXmlApplicationContext("Beans.xml");

      Student student = (Student) context.getBean("student");

      student.getName();
      student.getAge();
      
      student.printThrowException();
   }
}

以下是配置文件beans.xml文件：

<?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.yiibai.Student">
      <property name="name"  value="Zara" />
      <property name="age"  value="11"/>      
   </bean>

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

创建源程序和bean配置文件完成后，让我们运行应用程序。如果一切顺利，这将打印以下信息：

Going to setup student profile.
Name : Zara
Student profile has been setup.
Returning:Zara
Going to setup student profile.
Age : 11
Student profile has been setup.
Returning:11
Going to setup student profile.
Exception raised
Student profile has been setup.
There has been an exception: java.lang.IllegalArgumentException
.....
other exception content