Spring深入浅出（十三），AOP，AspectJ，基于注解开发

一、概述

在 Spring 中，尽管使用 XML 配置文件可以实现 AOP 开发，但是如果所有的相关配置都集中在配置文件中，势必会导致 XML 配置文件过于臃肿，从而给维护和升级带来一定的困难。
为此，AspectJ 框架为 AOP 开发提供了一套注解。AspectJ 允许使用注解定义切面、切入点和增强处理，Spring 框架可以根据这些注解生成 AOP 代理。

名称	说明
@Aspect	用于定义一个切面。
@Pointcut	用于定义一个切入点。
@Before	用于定义前置通知，相当于 BeforeAdvice。
@AfterReturning	用于定义后置通知，相当于 AfterReturningAdvice。
@Around	用于定义环绕通知，相当于MethodInterceptor。
@AfterThrowing	用于定义抛出通知，相当于ThrowAdvice。
@After	用于定义最终final通知，不管是否异常，该通知都会执行。
@DeclareParents	用于定义引介通知，相当于IntroductionInterceptor（不要求掌握）。

启用 @AspectJ 注解有以下两种方法：

1）使用@Configuration和@EnableAspectJAutoProxy注解

@Configuration 
@EnableAspectJAutoProxy
public class Appconfig {
}

2）基于XML配置

<aop:aspectj-autoproxy>

3）相关类库的引用，参考上一篇文章Spring深入浅出（十二），AOP，基于XML开发 

二、基于 AOP 的 @AspectJ 示例

1. 创建aspect 模块 

package com.clzhang.spring.demo;

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;

@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.clzhang.spring.demo.*.*(..))")
    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());
    }
}

 2. 创建Bean类 

package com.clzhang.spring.demo;

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();
    }
}

 3. 创建主程序 

package com.clzhang.spring.demo;

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

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");
      System.out.println("-----Invoke getName begin-----");
      String myName = student.getName();
      System.out.println("-----Invoke getName end. Name is:" + myName + "----");
      student.getAge();     
      student.printThrowException();
   }
}

 4. 创建配置文件 

<?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.clzhang.spring.demo.Student">
      <property name="name"  value="Zara" />
      <property name="age"  value="11"/>      
   </bean>

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

</beans>

 5. 运行输出 

-----Invoke getName begin-----
Going to setup student profile.
Name : Zara
Student profile has been setup.
Returning:Zara
-----Invoke getName end. Name is: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

 本文参考：

https://www.w3cschool.cn/wkspring/k4q21mm8.html