AOP（Aspect Oriented Programming，面向切面编程），通过提供另一种思考程序的方式来补充OOP（Object Oriented Programming，面向对象编程）。AOP是横向抽取，OOP是纵向抽象。
切面可以用于事务管理、日志等方面的模块化
AOP核心概念
- Aspect（切面）
- Join Point（连接点）
- Advice（通知/增强）
- Pointcut（切点）
- Introduction（引入）
- Target Object（目标对象）
- AOP Proxy（AOP代理）
- Weaving（织入）
其中，Advice的主要类型有:
- Before Advice（前置通知）
- After Returning Advice(返回后通知）
- After Throwing Advice（抛出异常后通知）
- After （finally）Advice（最后通知）
- Around Advice（环绕通知）
切入点和连接点的匹配，是AOP的关键
Spring AOP
Spring AOP用纯Java实现，目前仅支持方法调用作为连接点。
Spring AOP通常和Spring IoC容器一起使用
Hello的前置增强练习
- pom.xml中添加AOP相关依赖
<?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.spring</groupId>
<artifactId>aop</artifactId>
<version>1.0-SNAPSHOT</version>
<name>aop</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>1.8</maven.compiler.source>
<maven.compiler.target>1.8</maven.compiler.target>
<spring.version>5.1.5.RELEASE</spring.version>
<aspectj.version>1.9.2</aspectj.version>
<junit.version>4.12</junit.version>
<log4j.version>1.2.17</log4j.version>
<slf4j.version>1.7.12</slf4j.version>
</properties>
<dependencies>
<!--spring-context依赖-->
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-context</artifactId>
<version>${spring.version}</version>
</dependency>
<!--spring-aop依赖-->
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-aop</artifactId>
<version>${spring.version}</version>
</dependency>
<!--aspectj依赖-->
<dependency>
<groupId>org.aspectj</groupId>
<artifactId>aspectjrt</artifactId>
<version>${aspectj.version}</version>
</dependency>
<dependency>
<groupId>org.aspectj</groupId>
<artifactId>aspectjweaver</artifactId>
<version>${aspectj.version}</version>
</dependency>
<!--spring-test依赖-->
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-test</artifactId>
<version>${spring.version}</version>
</dependency>
<!--junit依赖-->
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>${junit.version}</version>
<scope>test</scope>
</dependency>
<!-- log4j日志依赖 -->
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>${log4j.version}</version>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
<version>${slf4j.version}</version>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-log4j12</artifactId>
<version>${slf4j.version}</version>
</dependency>
</dependencies>
<build>
<pluginManagement><!-- lock down plugins versions to avoid using Maven defaults (may be moved to parent pom) -->
<plugins>
<!-- clean lifecycle, see https://maven.apache.org/ref/current/maven-core/lifecycles.html#clean_Lifecycle -->
<plugin>
<artifactId>maven-clean-plugin</artifactId>
<version>3.1.0</version>
</plugin>
<!-- default lifecycle, jar packaging: see https://maven.apache.org/ref/current/maven-core/default-bindings.html#Plugin_bindings_for_jar_packaging -->
<plugin>
<artifactId>maven-resources-plugin</artifactId>
<version>3.0.2</version>
</plugin>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.8.0</version>
</plugin>
<plugin>
<artifactId>maven-surefire-plugin</artifactId>
<version>2.22.1</version>
</plugin>
<plugin>
<artifactId>maven-jar-plugin</artifactId>
<version>3.0.2</version>
</plugin>
<plugin>
<artifactId>maven-install-plugin</artifactId>
<version>2.5.2</version>
</plugin>
<plugin>
<artifactId>maven-deploy-plugin</artifactId>
<version>2.8.2</version>
</plugin>
<!-- site lifecycle, see https://maven.apache.org/ref/current/maven-core/lifecycles.html#site_Lifecycle -->
<plugin>
<artifactId>maven-site-plugin</artifactId>
<version>3.7.1</version>
</plugin>
<plugin>
<artifactId>maven-project-info-reports-plugin</artifactId>
<version>3.0.0</version>
</plugin>
</plugins>
</pluginManagement>
</build>
</project>
- Hello接口和实现类
package com.spring.aop;
public interface Hello {
String sayHello();
}
package com.spring.aop;
public class HelloImpl implements Hello {
@Override
public String sayHello() {
return "Spring AOP";
}
}
- MyBefore类
package com.spring.aop;
/**
* 用戶自定义前置增强类
*/
public class MyBefore {
public void beforeMethod() {
System.out.println("This is a before method...");
}
}
- 配置文件
<bean id="hello" class="com.spring.aop.HelloImpl"/>
<bean id="myBefore" class="com.spring.aop.MyBefore"/>
<aop:config>
<aop:aspect id="before" ref="myBefore">
<aop:pointcut id="myPointcut" expression="execution(* com.spring.aop.*.*(..))"/>
<aop:before method="beforeMethod" pointcut-ref="myPointcut"/>
</aop:aspect>
</aop:config>
- 应用主类
package com.spring.aop;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class HelloApp {
public static void main(String[] args) {
ApplicationContext ac = new ClassPathXmlApplicationContext("applicationContext.xml");
Hello hello = (Hello) ac.getBean("hello");
System.out.println(hello.sayHello());
}
}
-
运行结果
运行结果
可以看到：Mybefore的方法被织入到了Hello的调用方法前面，前置增强生效
实战：使用@AspectJ注解的例子
“武松打虎”——武松（Fighter）在山里等着老虎（Tiger）出现，只要发现老虎出来，就打老虎。
- 定义业务模型
Tiger类
package com.spring.aspectj;
public class Tiger {
public void walk() {
System.out.println("Tiger is walking...");
}
}
- 定义切面和配置
前置通知和后置通知
Fighter类
package com.spring.aspectj;
import org.aspectj.lang.annotation.AfterReturning;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.aspectj.lang.annotation.Pointcut;
@Aspect
public class Fighter {
@Pointcut("execution(* com.spring.aspectj.Tiger.walk())")
public void foundTiger() {
}
@Before(value = "foundTiger()")
public void foundBefore() {
System.out.println("Fighter wait for tiger...");
}
@AfterReturning("foundTiger()")
public void foundAfter() {
System.out.println("Fighter fight with tiger...");
}
}
- 配置文件
<!--启动AspectJ支持-->
<aop:aspectj-autoproxy/>
<!--配置bean-->
<bean id="tiger" class="com.spring.aspectj.Tiger"/>
<bean id="fighter" class="com.spring.aspectj.Fighter"/>
- 主程序
package com.spring.aspectj;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class FighterApp {
public static void main(String[] args) {
ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
Tiger tiger = context.getBean(Tiger.class);
tiger.walk();
}
}
-
运行结果
运行结果
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