更新aop
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java/spring aop.md
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java/spring aop.md
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## spring aop 面向切面编程
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**连接点**
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泛指类中的方法
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**切入点**
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被抽取了共同代码的逻辑方法
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切入点一定是连接点 连接点不一定是切入点
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**通知**
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被抽取出来的 共同代码 可以认定为是一个方法
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通知 按照被抽取的代码位置 分为
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1. 前置通知(Before advice) 在逻辑代码前面执行
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2. 后置通知(After (finally) advice) 在逻辑代码后面执行,不管逻辑代码是否正常执行
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3. 返回通知(After returning advice) 在逻辑代码，正常完成后执行的通知
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4. 异常通知(After throwing advice) 抛出异常后通知
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5. 环绕通知(Around Advice) 在逻辑代码前后都执行(执行两次)
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**引入**
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泛指 类中的共同的成员变量 多个通知要使用
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引入 机制可以增加额外的变量
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引入机制是在类的编译器 或者类加载期完成
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**目标对象**
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原始的对象抽离出共同代码后的对象
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缺少完整逻辑代码的对象
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**代理对象**
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Spring 为目标对象注入通知 成为一个可以正常执行的对象
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**织入**
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将目标对象代理并注入通知的过程
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**切面**
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切面是一个设计概念，指切入点与通知的匹配模式
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程序设计视可以设置多个切面，用来描述切入点与通知之间的关系。
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## 代码
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### pom 文件
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~~~xml
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<properties>
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<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
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<maven.compiler.source>1.8</maven.compiler.source>
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<maven.compiler.target>1.8</maven.compiler.target>
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<spring.version>5.2.8.RELEASE</spring.version>
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</properties>
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<dependencies>
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<dependency>
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<groupId>junit</groupId>
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<artifactId>junit</artifactId>
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<version>4.11</version>
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<scope>test</scope>
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</dependency>
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<!-- https://mvnrepository.com/artifact/org.springframework/spring-context -->
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<dependency>
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<groupId>org.springframework</groupId>
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<artifactId>spring-context</artifactId>
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<version>${spring.version}</version>
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</dependency>
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<!-- https://mvnrepository.com/artifact/org.springframework/spring-aop -->
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<dependency>
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<groupId>org.springframework</groupId>
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<artifactId>spring-aop</artifactId>
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<version>${spring.version}</version>
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</dependency>
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<dependency>
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<groupId>org.springframework</groupId>
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<artifactId>spring-aspects</artifactId>
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<version>${spring.version}</version>
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</dependency>
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<dependency>
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<groupId>org.aspectj</groupId>
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<artifactId>aspectjrt</artifactId>
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<version>1.6.11</version>
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</dependency>
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<dependency>
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<groupId>org.aspectj</groupId>
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<artifactId>aspectjweaver</artifactId>
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<version>1.6.11</version>
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</dependency>
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</dependencies>
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~~~
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### applicationContext.xml
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~~~xml
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<?xml version="1.0" encoding="UTF-8"?>
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<beans xmlns="http://www.springframework.org/schema/beans"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop"
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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">
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<aop:config>
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<aop:aspect ref="advice">
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<aop:before method="printOne" pointcut="execution(public void org.example.TargetObject.print2())"/>
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</aop:aspect>
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</aop:config>
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<bean id="target" class="org.example.TargetObject"></bean>
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<bean id="advice" class="org.example.Advice"></bean>
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</beans>
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~~~
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### 目标对象
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~~~java
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package org.example;
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/**
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* @author by xKing
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* @create on 2020/10/30 21:21
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*/
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public class TargetObject {
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public void print2() {
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System.out.println("我是目标对象");
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System.out.println("3");
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}
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public void print3() {
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System.out.println("2");
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System.out.println("3");
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}
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}
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~~~
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### 通知对象
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~~~java
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package org.example;
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/**
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* @author by xKing
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* @create on 2020/10/30 21:22
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*/
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public class Advice {
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public void printOne() {
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System.out.println("我是通知");
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}
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}
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~~~
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### 测试类
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~~~java
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package org.example;
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import org.springframework.context.support.ClassPathXmlApplicationContext;
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/**
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* Hello world!
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*/
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public class App {
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public static void main(String[] args) {
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ClassPathXmlApplicationContext cat = new ClassPathXmlApplicationContext("applicationContext.xml");
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Object target = cat.getBean("target");
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((TargetObject) target).print2();
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System.out.println("Hello World!");
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}
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}
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~~~
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### 输出结果
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~~~sh
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1
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2
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3
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Hello World!
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Process finished with exit code 0
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~~~
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