注解AOP

AOP的基本概念

(1)Aspect(切面):通常是一个类，里面可以定义切入点和通知

(2)JointPoint(连接点):程序执行过程中明确的点，一般是方法的调用

(3)Advice(通知):AOP在特定的切入点上执行的增强处理，有before,after,afterReturning,afterThrowing,around

(4)Pointcut(切入点):就是带有通知的连接点，在程序中主要体现为书写切入点表达式

基于注解的AOP配置方式

1.启用@AsjectJ支持

在applicationContext.xml中配置下面一句:

<aop:aspectj-autoproxy />

2.通知类型介绍

(1)Before:在目标方法被调用之前做增强处理,@Before只需要指定切入点表达式即可

(2)AfterReturning:在目标方法正常完成后做增强,@AfterReturning除了指定切入点表达式后，还可以指定一个返回值形参名returning,代表目标方法的返回值

(3)AfterThrowing:主要用来处理程序中未处理的异常,@AfterThrowing除了指定切入点表达式后，还可以指定一个throwing的返回值形参名,可以通过该形参名

来访问目标方法中所抛出的异常对象

(4)After:在目标方法完成之后做增强，无论目标方法时候成功完成。@After可以指定一个切入点表达式

(5)Around:环绕通知,在目标方法完成前后做增强处理,环绕通知是最重要的通知类型,像事务,日志等都是环绕通知,注意编程中核心是一个ProceedingJoinPoint

代理示例

（1）添加依赖文件

<properties>
    <java.version>18</java.version>
  </properties>
  <dependencies>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-context</artifactId>
      <version>4.0.0.RELEASE</version>
    </dependency>
    <!-- https://mvnrepository.com/artifact/org.springframework/spring-core -->
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-core</artifactId>
      <version>4.0.0.RELEASE</version>
    </dependency>
    <!-- https://mvnrepository.com/artifact/org.springframework/spring-beans -->
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-beans</artifactId>
      <version>4.0.0.RELEASE</version>
    </dependency>
    <!-- https://mvnrepository.com/artifact/commons-logging/commons-logging -->
    <dependency>
      <groupId>commons-logging</groupId>
      <artifactId>commons-logging</artifactId>
      <version>1.1.1</version>
    </dependency>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.12</version>
      <scope>compile</scope>
    </dependency>

    <!-- https://mvnrepository.com/artifact/org.springframework/spring-aop -->
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-aop</artifactId>
      <version>4.0.0.RELEASE</version>
    </dependency>
    <!-- https://mvnrepository.com/artifact/cglib/cglib -->
    <dependency>
      <groupId>cglib</groupId>
      <artifactId>cglib</artifactId>
      <version>2.2.2</version>
    </dependency>
    <!-- https://mvnrepository.com/artifact/org.aspectj/aspectjweaver -->
    <dependency>
      <groupId>org.aspectj</groupId>
      <artifactId>aspectjweaver</artifactId>
      <version>1.8.13</version>
    </dependency>
    <!-- https://mvnrepository.com/artifact/aopalliance/aopalliance -->
    <dependency>
      <groupId>aopalliance</groupId>
      <artifactId>aopalliance</artifactId>
      <version>1.0</version>
    </dependency>
  </dependencies>

<build>
  <finalName>AOPTest</finalName>
  <plugins>
    <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-compiler-plugin</artifactId>
      <version>3.8.1</version>
      <configuration>
        <!--根据个人需要自己修改-->
        <source>8</source>
        <target>8</target>
      </configuration>
    </plugin>
  </plugins>
</build>

（2）配置文件开启切面注解（applicationContext.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:context="http://www.springframework.org/schema/context"
       xmlns:tx="http://www.springframework.org/schema/tx"
       xmlns:aop="http://www.springframework.org/schema/aop"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context.xsd
        http://www.springframework.org/schema/aop
        http://www.springframework.org/schema/aop/spring-aop.xsd
        http://www.springframework.org/schema/tx
        http://www.springframework.org/schema/tx/spring-tx.xsd">

    <context:component-scan base-package="com.gqx.anno"/>
    <aop:aspectj-autoproxy />
</beans>

（3）创建目标类

@Component(value = "studentService")
public class StudentService {
    public void eat(){
        System.out.println("我要开始吃午饭了");
    }
}

（4）切面增强

@Component
@Aspect
public class AnnoAspect {
    @Pointcut("execution(* com.gqx.anno.StudentService.*(..))")
    public void pointCut(){}
    @Before("execution(* com.gqx.anno.StudentService.*(..))")
    public void doBefore(JoinPoint joinPoint){
        System.out.println("AOP Before Advice...");
    }
    @After("pointCut()")
    public void doAfter(JoinPoint joinPoint){
        System.out.println("AOP After Advice...");
    }
    @AfterReturning(pointcut="pointCut()",returning="returnVal")
    public void afterReturn(JoinPoint joinPoint,Object returnVal){
        System.out.println("AOP AfterReturning Advice:" + returnVal);
    }
    @AfterThrowing(pointcut="pointCut()",throwing="error")
    public void afterThrowing(JoinPoint joinPoint,Throwable error){
        System.out.println("AOP AfterThrowing Advice..." + error);
        System.out.println("AfterThrowing...");
    }
    @Around("pointCut()")
    public void around(ProceedingJoinPoint pjp){
        System.out.println("AOP Aronud before...");
        try {
            pjp.proceed();
        } catch (Throwable e) {
            e.printStackTrace();
        }
        System.out.println("AOP Aronud after...");
    }
}

（5）主运行类

public class AppMain {
    public static void main(String[] args) {
        //1. 创建IoC容器对象，加载spring核心配置文件
        //初始化Spring容器ApplicationContext，加载配置文件
        ApplicationContext application = new ClassPathXmlApplicationContext("applicationContext.xml");
        //2. 从IOC容器中获取Bean对象
        StudentService studentService = (StudentService) application.getBean("studentService");
        studentService.eat();
    }
}

 若运行出错：

Unable to make protected final java.lang.Class java.lang.ClassLoader.defineClass(java.lang.String,byte[],int,int,java.security.ProtectionDomain) throws java.lang.ClassFormatError accessible: module java.base does not "opens java.lang" to unnamed module @9d5509a

在idea的vm中添加下面的选项

--add-opens java.base/java.lang=ALL-UNNAMED --add-opens java.base/java.lang.reflect=ALL-UNNAMED