Spring Aop：一、四种advice

本文参考实验楼教程：https://www.shiyanlou.com/courses/578/learning/?id=1940

Spring Aop即 Aspect-Oriented Programming，面向切面编程。是用于处理系统中各个模块（不同方法）之间的交叉关注的问题。
简单地说，就是一个拦截器，拦截一些处理过程。
例如：当一个method被执行，Spring AOP能够劫持正在运行的method，在method执行前后加入一些额外的功能。（日志记录、性能统计、权限控制等）

实验环境：
JDK1.8
idea 开发环境

一、Spring AOP 支持4种类型的通知（advice）

Before advice --- method 执行前通知
After returning advice --- method 执行完毕或者返回一个结果后通知
After throwing advice --- method 抛出异常后通知
Around advice --- 环绕通知，结合了以上三种

下面来学习如何使用这四种通知。
以下是整个实验项目结构：

project.png

1、准备环境，创建一个maven工程SpringAop

1)、添加maven依赖，对应的pom.xml文件如下：

<?xml version="1.0" encoding="UTF-8"?>

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>com.shiyanlou.spring</groupId>
  <artifactId>SpringAopTest</artifactId>
  <version>1.0-SNAPSHOT</version>

  <name>SpringAopTest</name>
  <!-- FIXME change it to the project's website -->
  <url>http://www.example.com</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <maven.compiler.source>1.7</maven.compiler.source>
    <maven.compiler.target>1.7</maven.compiler.target>
    <spring.version>5.1.1.RELEASE</spring.version>
  </properties>

  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.11</version>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-core</artifactId>
      <version>${spring.version}</version>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-context</artifactId>
      <version>${spring.version}</version>
    </dependency>
    <dependency>
      <groupId>org.aspectj</groupId>
      <artifactId>aspectjweaver</artifactId>
      <version>1.9.2</version>
    </dependency>
    <dependency>
      <groupId>org.aspectj</groupId>
      <artifactId>aspectjtools</artifactId>
      <version>1.9.2</version>
    </dependency>
    <dependency>
      <groupId>org.aspectj</groupId>
      <artifactId>aspectjrt</artifactId>
      <version>1.9.2</version>
    </dependency>
    <dependency>
      <groupId>cglib</groupId>
      <artifactId>cglib</artifactId>
      <version>3.2.9</version>
    </dependency>
  </dependencies>

</project>

2)、创建类 CustomerService.java 如下：

package com.shiyanlou.spring.aop.advice;

import org.springframework.stereotype.Service;

/**
 * Created by Administrator on 2019/10/30.
 */

public class CustomerService {
    private String name;
    private String url;

    public CustomerService() {
    }

    public CustomerService(String name, String url) {
        this.name = name;
        this.url = url;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getUrl() {
        return url;
    }

    public void setUrl(String url) {
        this.url = url;
    }

    public void printName(){
        System.out.println("Customer name: " + name);
    }

    public void printURL(){
        System.out.println("Customer URL: " + url);
    }

    public void printThrowException(){
        throw new IllegalArgumentException();
    }
}

3)、在src/main/resources/下新建 Xml 配置文件 SpringAopAdvice.xml 如下：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="
                            http://www.springframework.org/schema/beans
                            http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="customerService" class="com.shiyanlou.spring.aop.advice.CustomerService">
        <property name="name" value="weihouye"/>
        <property name="url" value="www.weihouyeaiyangzhan.com"/>
    </bean>

</beans>

4)、在com.shiyanlou.spring包下的App.java中编写如下：

package com.shiyanlou.spring;

import com.shiyanlou.spring.aop.advice.CustomerService;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class App
{
    private static ApplicationContext context;

    public static void main( String[] args ) {

        context = new ClassPathXmlApplicationContext("SpringAopAdvice.xml");

        CustomerService cust = (CustomerService) context.getBean("customerService");

        System.out.println("*************************");
        cust.printName();
        System.out.println("*************************");
        cust.printURL();
        System.out.println("*************************");
        try {
            cust.printThrowException();
        } catch (IllegalArgumentException e){
        }

    }
}

5)、运行App.java文件，结果如下：


*************************
Customer name: weihouye
*************************
Customer URL: www.weihouyeaiyangzhan.com
*************************

2、Before advice

1)、定义org.springframework.aop.MethodBeforeAdvice的实现类WeiBeforeMethod，重写before方法，该方法将在被代理的类的方法之前运行。代码如下：

package com.shiyanlou.spring.aop.advice;

import org.springframework.aop.MethodBeforeAdvice;

import java.lang.reflect.Method;

/**
 * Created by Administrator on 2019/10/30.
 */
public class WeiBeforeMethod implements MethodBeforeAdvice {
    @Override
    public void before(Method method, Object[] args, Object target) throws Throwable {
        System.out.println("WeiBeforeMethod: Before method hi wei!!!");
    }
}

2)、在SpringAopAdvice.xml配置文件中加入新的bean配置weiBeforeMethod，然后创建一个代理bean（Proxy），命名为customerServiceProxy。
代理bean中target定义了被代理（被劫持）的类，拦截器interceptorNames则定义了想要用哪个类（advice）劫持target，拦截器可以有多个，所以写在<list>中。配置如下：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="
                            http://www.springframework.org/schema/beans
                            http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="customerService" class="com.shiyanlou.spring.aop.advice.CustomerService">
        <property name="name" value="weihouye"/>
        <property name="url" value="www.weihouyeaiyangzhan.com"/>
    </bean>

    <bean id="weiBeforeMethod" class="com.shiyanlou.spring.aop.advice.WeiBeforeMethod"/>

    <bean id="customerServiceProxy" class="org.springframework.aop.framework.ProxyFactoryBean">
        <property name="target" ref="customerService"/>
        <property name="interceptorNames">
            <list>
                <value>weiBeforeMethod</value>
            </list>
        </property>
    </bean>
</beans>

用 Spring proxy 之前，必须添加 CGLIB 类库，在之前的 pom.xml 文件中，已经添加到了其中，以下是 pom.xml 依赖：

        <dependency>
            <groupId>cglib</groupId>
            <artifactId>cglib</artifactId>
            <version>3.2.9</version>
        </dependency>

3)、App.java如下

package com.shiyanlou.spring;

import com.shiyanlou.spring.aop.advice.CustomerService;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

/**
 * Hello world!
 *
 */
public class App
{
    private static ApplicationContext context;

    public static void main( String[] args ) {

        context = new ClassPathXmlApplicationContext("SpringAopAdvice.xml");

        CustomerService cust = (CustomerService) context.getBean("customerServiceProxy");

        System.out.println("*************************");
        cust.printName();
        System.out.println("*************************");
        cust.printURL();
        System.out.println("*************************");
        try {
            cust.printThrowException();
        } catch (IllegalArgumentException e){
        }
    }
}

ps:注意 App.java中获取的是代理bean，即customerServiceProxy，由代理bean去执行原来的功能。

4)、运行结果如下：


*************************
WeiBeforeMethod: Before method hi wei!!!
Customer name: weihouye
*************************
WeiBeforeMethod: Before method hi wei!!!
Customer URL: www.weihouyeaiyangzhan.com
*************************
WeiBeforeMethod: Before method hi wei!!!

可以看到，被代理类CustomerService被WeiBeforeMethod劫持，被代理类中的方法被执行前，均先执行WeiBeforeMethod中的before方法。

3、After Returning Advice

1)、创建一个org.springframework.aop.AfterReturningAdvice接口的实现类WeiAfterMethod.java，重写afterReturning方法，用于劫持被代理类；被代理类中的方法执行完毕或者返回结果后，将执行WeiAfterMethod中的afterReturning方法，若中途异常退出，则不会执行该方法。
WeiAfterMethod.java代码如下：

package com.shiyanlou.spring.aop.advice;

import org.springframework.aop.AfterReturningAdvice;

import java.lang.reflect.Method;

/**
 * Created by Administrator on 2019/10/30.
 */
public class WeiAfterMethod implements AfterReturningAdvice {
    @Override
    public void afterReturning(Object returnValue, Method method, Object[] args, Object target) throws Throwable {
        System.out.println("WeiAfterMethod: After Method hi wei!!");
    }
}

2)、修改bean配置xml文件 SpringAopAdvice.xml，加入weiAfterMethod配置，如下：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="
                            http://www.springframework.org/schema/beans
                            http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="customerService" class="com.shiyanlou.spring.aop.advice.CustomerService">
        <property name="name" value="weihouye"/>
        <property name="url" value="www.weihouyeaiyangzhan.com"/>
    </bean>

    <bean id="weiBeforeMethod" class="com.shiyanlou.spring.aop.advice.WeiBeforeMethod"/>
    <bean id="weiAfterMethod" class="com.shiyanlou.spring.aop.advice.WeiAfterMethod"/>

    <bean id="customerServiceProxy" class="org.springframework.aop.framework.ProxyFactoryBean">
        <property name="target" ref="customerService"/>
        <property name="interceptorNames">
            <list>
                <!--<value>weiBeforeMethod</value>-->
                <value>weiAfterMethod</value>
            </list>
        </property>
    </bean>
</beans>

3)、同样在App.java中获取并运行代理bean，结果如下：


*************************
Customer name: weihouye
WeiAfterMethod: After Method hi wei!!
*************************
Customer URL: www.weihouyeaiyangzhan.com
WeiAfterMethod: After Method hi wei!!
*************************

&emps;可以看到，在CustomerService.java中的每个方法执行完毕后，均会执行WeiAfterMethod.java的afterReturning方法，抛出异常除外。

4、Afetr Throwing Advice

1)、创建一个实现org.springframework.aop.ThrowsAdvice接口的实现类WeiThrowExceptionMethod.java，劫持IllegalArgumentException异常，当被劫持的类抛出该异常时，将会执行afterThrowing方法；代码如下：

package com.shiyanlou.spring.aop.advice;

import org.springframework.aop.ThrowsAdvice;

/**
 * Created by Administrator on 2019/10/30.
 */
public class WeiThrowExceptionMethod implements ThrowsAdvice {

    public void afterThrowing(Exception ex){
        System.out.println("WeiThrowException : Throw exception hi wei!!");
    }
}

2)、修改bean配置xml文件 SpringAopAdvice.xml，加入weiThrowExceptionMethod配置，如下：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="
                            http://www.springframework.org/schema/beans
                            http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="customerService" class="com.shiyanlou.spring.aop.advice.CustomerService">
        <property name="name" value="weihouye"/>
        <property name="url" value="www.weihouyeaiyangzhan.com"/>
    </bean>

    <bean id="weiBeforeMethod" class="com.shiyanlou.spring.aop.advice.WeiBeforeMethod"/>
    <bean id="weiAfterMethod" class="com.shiyanlou.spring.aop.advice.WeiAfterMethod"/>
    <bean id="weiThrowExceptionMethod" class="com.shiyanlou.spring.aop.advice.WeiThrowExceptionMethod"/>
    <bean id="weiAroundMethod" class="com.shiyanlou.spring.aop.advice.WeiAroundMethod"/>

    <bean id="customerServiceProxy" class="org.springframework.aop.framework.ProxyFactoryBean">
        <property name="target" ref="customerService"/>
        <property name="interceptorNames">
            <list>
                <!--<value>weiBeforeMethod</value>-->
                <!--<value>weiAfterMethod</value>-->
                <value>weiThrowExceptionMethod</value>
            </list>
        </property>
    </bean>
</beans>

3)、同样在App.java中获取并运行代理bean，结果如下：


*************************
Customer name: weihouye
*************************
Customer URL: www.weihouyeaiyangzhan.com
*************************
WeiThrowException : Throw exception hi wei!!

可以看到当执行到CustomerService.java的printThrowException方法时，我们抛出了IllegalArgumentException异常，异常抛出后执行了拦截器WeiThrowExceptionMethod.java的afterThrowing方法。

5、Around advice

1)、结合上面3种形式的advice，创建一个org.aopalliance.intercept.MethodInterceptor接口的实现类WeiAroundMethod.java，重写public Object invoke(MethodInvocation invocation) throws Throwable方法；
必须通过方法调用对象invocation.proceed()来调用原来的被代理的方法，当然也可以不调用；代码如下，注意注释中包含十分重要的信息。

package com.shiyanlou.spring.aop.advice;


import org.aopalliance.intercept.MethodInterceptor;
import org.aopalliance.intercept.MethodInvocation;

import java.util.Arrays;

/**
 * Created by Administrator on 2019/10/30.
 */
public class WeiAroundMethod implements MethodInterceptor {
    @Override
    public Object invoke(MethodInvocation invocation) throws Throwable {

        //Method调用的处理
        System.out.println("Method Name: " + invocation.getMethod().getName());
        System.out.println("Method Arguments: " + Arrays.toString(invocation.getArguments()));
        //相当于MethodBeforeAdvice
        System.out.println("WeiBeforeMethod: Before method hi wei!!!");

        try {
            //调用原方法，即调用CustomerService中的方法
            Object result = invocation.proceed();

            //相当于AfterReturningAdvice
            System.out.println("WeiAfterMethod: After Method hi wei!!");

            return result;
        } catch (IllegalArgumentException e) {
            //相当于ThrowsAdvice
            System.out.println("WeiThrowException : Throw exception hi wei!!");

            throw e; //将异常抛出
        }
    }
}

2)、修改bean配置xml文件 SpringAopAdvice.xml，加入weiAroundMethod配置，如下：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="
                            http://www.springframework.org/schema/beans
                            http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="customerService" class="com.shiyanlou.spring.aop.advice.CustomerService">
        <property name="name" value="weihouye"/>
        <property name="url" value="www.weihouyeaiyangzhan.com"/>
    </bean>

    <bean id="weiBeforeMethod" class="com.shiyanlou.spring.aop.advice.WeiBeforeMethod"/>
    <bean id="weiAfterMethod" class="com.shiyanlou.spring.aop.advice.WeiAfterMethod"/>
    <bean id="weiThrowExceptionMethod" class="com.shiyanlou.spring.aop.advice.WeiThrowExceptionMethod"/>
    <bean id="weiAroundMethod" class="com.shiyanlou.spring.aop.advice.WeiAroundMethod"/>

    <bean id="customerServiceProxy" class="org.springframework.aop.framework.ProxyFactoryBean">
        <property name="target" ref="customerService"/>
        <property name="interceptorNames">
            <list>
                <!--<value>weiBeforeMethod</value>-->
                <!--<value>weiAfterMethod</value>-->
                <!--<value>weiThrowExceptionMethod</value>-->
                <value>weiAroundMethod</value>
            </list>
        </property>
    </bean>
</beans>

3)、运行App.java结果如下：


*************************
Method Name: printName
Method Arguments: []
WeiBeforeMethod: Before method hi wei!!!
Customer name: weihouye
WeiAfterMethod: After Method hi wei!!
*************************
Method Name: printURL
Method Arguments: []
WeiBeforeMethod: Before method hi wei!!!
Customer URL: www.weihouyeaiyangzhan.com
WeiAfterMethod: After Method hi wei!!
*************************
Method Name: printThrowException
Method Arguments: []
WeiBeforeMethod: Before method hi wei!!!
WeiThrowException : Throw exception hi wei!!

可以看出Around advice 结合了前面三种advice。

6、改进

在上边的结果中，CustomerService.java的全部方法均被拦截，下面展示如何使用Pointcuts只拦截printName()。
在Spring AOP中，有3个常用的名词，Advices、Pointcuts、Advisor，解释如下：

Advices：表示一个方法执行前或者执行后的动作；
Pointcuts：表示根据一个方法的名字或者正则表达式去拦截一个方法；
Advisor：Advices和Pointcuts组成的独立的单元，且可以传给proxy factory对象。

我们可以用名字匹配法或者正则表达式去匹配要拦截的方法。

1)、Pointcuts ——Name match example （根据方法名匹配）

SpringAopAdvice.xml中，创建一个NameMatchMethodPointcut的 Bean，并将想要拦截的方法名printName注入到属性mappedName中。配置如下：

    <bean id="customerPointcut" class="org.springframework.aop.support.NameMatchMethodPointcut">
        <property name="mappedName" value="printName"/>
    </bean>

创建一个DefaultPointcutAdvisor的 Advisor bean，将 Pointcut 和 Advice 注入到 Advisor中。如下：

    <bean id="customerAdvisor" class="org.springframework.aop.support.DefaultPointcutAdvisor">
        <property name="pointcut" ref="customerPointcut"/>
        <property name="advice" ref="weiAroundMethod"/>
    </bean>

更改代理customerServiceProxy的interceptorNames中的值，将上面的Advisor代替原来的weiAroundMethod，所有的配置如下：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="
                            http://www.springframework.org/schema/beans
                            http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="customerService" class="com.shiyanlou.spring.aop.advice.CustomerService">
        <property name="name" value="weihouye"/>
        <property name="url" value="www.weihouyeaiyangzhan.com"/>
    </bean>

    <!--<bean id="weiBeforeMethod" class="com.shiyanlou.spring.aop.advice.WeiBeforeMethod"/>-->
    <!--<bean id="weiAfterMethod" class="com.shiyanlou.spring.aop.advice.WeiAfterMethod"/>-->
    <!--<bean id="weiThrowExceptionMethod" class="com.shiyanlou.spring.aop.advice.WeiThrowExceptionMethod"/>-->
    <bean id="weiAroundMethod" class="com.shiyanlou.spring.aop.advice.WeiAroundMethod"/>

    <bean id="customerPointcut" class="org.springframework.aop.support.NameMatchMethodPointcut">
        <property name="mappedName" value="printName"/>
    </bean>

    <bean id="customerAdvisor" class="org.springframework.aop.support.DefaultPointcutAdvisor">
        <property name="pointcut" ref="customerPointcut"/>
        <property name="advice" ref="weiAroundMethod"/>
    </bean>

    <bean id="customerServiceProxy" class="org.springframework.aop.framework.ProxyFactoryBean">
        <property name="target" ref="customerService"/>
        <property name="interceptorNames">
            <list>
                <!--<value>weiBeforeMethod</value>-->
                <!--<value>weiAfterMethod</value>-->
                <!--<value>weiThrowExceptionMethod</value>-->
                <value>customerAdvisor</value>
            </list>
        </property>
    </bean>
</beans>

运行一下App.java，发现只有个printName方法被拦截了。结果输出如下：

*************************
Method Name: printName
Method Arguments: []
WeiBeforeMethod: Before method hi wei!!!
Customer name: weihouye
WeiAfterMethod: After Method hi wei!!
*************************
Customer URL: www.weihouyeaiyangzhan.com
*************************

以上 Poincut 和 Advisor可以一起配置，即不用单独配置 customerPointcut 和 customerAdvisor，只要在配置 customerAdvisor 时选择 NameMatchMethodPointcutAdvisor，如下：

    <!--pointcut和advisor可以一起配置，只要在配置customerAdvisor时，选择NameMatchMethodPointcutAdvisor-->
    <bean id="customerAdvisor" class="org.springframework.aop.support.NameMatchMethodPointcutAdvisor">
        <property name="mappedName" value="printName"/>
        <property name="advice" ref="weiAroundMethod"/>
    </bean>

2)、Pointcuts ——Regular expression match example （根据正则表达式匹配）

可以使用正则表达式匹配拦截方法，Advisor 配置如下：

    <bean id="customerAdvisor" class="org.springframework.aop.support.RegexpMethodPointcutAdvisor">
        <property name="patterns">
            <list>
                <value>.*URL.*</value>
            </list>
        </property>
        <property name="advice" ref="weiAroundMethod"/>
    </bean>

运行结果：只有个printURL方法被拦截

*************************
Customer name: weihouye
*************************
Method Name: printURL
Method Arguments: []
WeiBeforeMethod: Before method hi wei!!!
Customer URL: www.weihouyeaiyangzhan.com
WeiAfterMethod: After Method hi wei!!
*************************