Spring底层原理学习笔记--第十讲--(aop之agent增强)

AOP实现之agent类加载

AOP的另一种实现及原理

A11Application.java

package com.lucifer.itheima.a11;import com.lucifer.itheima.a11.service.MyService;
import lombok.extern.slf4j.Slf4j;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;/***  注意几点*  1.版本选择了java 8，因为目前的aspectj-maven-plugin 1.40.0 最高只支持到java 16*  2.运行时需要在VM option里加入 -jaavaagent:C:/Users/manyh/.m2/repository/org/aspectj/aspectjweaver/1.9.7.jar*      把其中C:/Users/manyh/.m2/repository改为自己maven仓库起始地址**  在类加载阶段修改了MyService类的字节码**  目前为止，讲了三种aop的实现，第一种就是代理实现，第二种就是上讲学到的用aspect编译器，在编译阶段修改字节码，这节课讲的是agent，agent就是在java类加载阶段去改动我们待增强的字节码*  但是后面这两种没有流行起来，实际开发过程中开始以代理为主*/
@SpringBootApplication
@Slf4j
public class A11Application {public static void main(String[] args) {ConfigurableApplicationContext context = SpringApplication.run(A11Application.class,args);MyService service = context.getBean(MyService.class);//MyService 并非代理，但foo方法也被增强了，做增强的java agent，在加载类时，修改了class字节码log.info("service class:{}",service.getClass());//输出结果为//before()
//        2023-11-14 10:51:15.898  INFO 18864 --- [           main] c.lucifer.itheima.a11.service.MyService  : foo()//before()
//        2023-11-14 10:51:15.898  INFO 18864 --- [           main] c.lucifer.itheima.a11.service.MyService  : bar()service.foo();}
}

MyService.java

package com.lucifer.itheima.a11.service;import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Service;@Service
@Slf4j
public class MyService {final public void foo(){log.info("foo()");bar();}public void bar(){log.info("bar()");}
}

MyAspect.java

package com.lucifer.itheima.a11.aop;import lombok.extern.slf4j.Slf4j;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;@Aspect     //注意此切面未被Spring管理
@Slf4j
public class MyAspect {@Before("execution(* com.lucifer.itheima.a11.service.MyService.*())")public void before(){log.info("before()");}
}

MyService.class反编译后的代码

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//package com.lucifer.itheima.a11.service;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Service;@Service
public class MyService {private static final Logger log = LoggerFactory.getLogger(MyService.class);public MyService() {}public final void foo() {MyAspect.aspectOf().before();log.info("foo()");this.bar();}public void bar() {MyAspect.aspectOf().before();log.info("bar()");}
}