@ 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
