Spring 中基于 AOP 的 @AspectJ

@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。

通过在你的基于架构的 XML 配置文件中包含以下元素，@AspectJ 支持是可用的。

<aop:aspectj-autoproxy/>

声明一个 aspect

Aspects 类和其他任何正常的 bean 一样，除了它们将会用 @AspectJ 注释之外，它和其他类一样可能有方法和字段，如下所示：

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

它们将在 XML 中按照如下进行配置，就和其他任何 bean 一样：

<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使用不同建议执行的感兴趣的连接点（即方法）。在处理基于配置的 XML 架构时，切入点的声明有两个部分：

一个切入点表达式决定了我们感兴趣的哪个方法会真正被执行。
一个切入点标签包含一个名称和任意数量的参数。方法的真正内容是不相干的，并且实际上它应该是空的。

下面的示例中定义了一个名为 ‘businessService’ 的切入点，该切入点将与 com.xyz.myapp.service 包下的类中可用的每一个方法相匹配：

import org.aspectj.lang.annotation.Pointcut;
@Pointcut("execution(* com.xyz.myapp.service.*.*(..))") // expression 
private void businessService() {}  // signature

下面的示例中定义了一个名为 ‘getname’ 的切入点，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() {}

声明建议

你可以使用 @{ADVICE-NAME} 注释声明五个建议中的任意一个，如下所示。这假设你已经定义了一个切入点标签方法 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(){
 ...
}

基于 AOP 的 @AspectJ 示例

新建Spring项目
在项目中添加 Spring AOP 指定的库文件 aspectjrt.jar， aspectjweaver.jar 和 aspectj.jar。
保证aspectjweaver.jar的版本在1.8以上，否则会报错。
创建 Java 类 Logging， Student 和 MainApp

这里是 Logging.java 文件的内容。这实际上是 aspect 模块的一个示例，它定义了在各个点调用的方法。

package hello;
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;

//import org.springframework.aop.aspectj.AspectJAfterThrowingAdvice;
@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(* hello.*.*(..))")
    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.
     */
    @AfterThrowing(pointcut = "selectAll()", throwing = "ex")
    public void AfterThrowingAdvice(IllegalArgumentException ex){
        System.out.println("there has been an exception:"+ex.toString());
    }
}

下面是 Student.java 文件的内容：

package hello;
//import org.springframework.beans.factory.annotation.Autowired;

public class Student {
    private int age;
    private String name;
    public void setAge(int age){
        this.age = age;
    }
    public int 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();
    }
}

下面是 MainApp.java 文件的内容：

package hello;
//import org.springframework.context.support.AbstractApplicationContext;
//import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
//import org.springframework.context.annotation.*;

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();
    }
}

下面是配置文件 Beans.xml：

<?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"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans.xsd
       http://www.springframework.org/schema/aop
       http://www.springframework.org/schema/aop/spring-aop.xsd">

    <!--aop:config>
        <aop:aspect id="log" ref="logging">
            <aop:pointcut id="selectAll" expression="execution(* hello.*.*(..))"/>
            <aop:before pointcut-ref="selectAll" method="beforeAdvice"/>
            <aop:after pointcut-ref="selectAll" method="afterAdvice"/>
            <aop:after-returning pointcut-ref="selectAll"
                                 returning="retVal"
                                 method="afterReturningAdvice"/>
            <aop:after-throwing pointcut-ref="selectAll"
                                throwing="ex"
                                method="AfterThrowingAdvice"/>
        </aop:aspect>
    </aop:config-->

    <aop:aspectj-autoproxy/>

    <!-- Definition for student bean -->
    <bean id="student" class="hello.Student">
        <property name="name" value="番茄"/>
        <property name="age" value="10"/>
    </bean>

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

</beans>

运行一下应用程序

Going to setup student profile.
name:番茄
Student profile has been setup
Returning:番茄
Going to setup student profile.
age:10
Student profile has been setup
Returning:10

Process finished with exit code 0

每天学习一点点，每天进步一点点。