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();
    }
}
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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()");
    }
}

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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()");
    }
}

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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()");
    }
}

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