Spring学习笔记_27——@EnableLoadTimeWeaving

@EnableLoadTimeWeaving

1. 介绍

在Spring框架中，@EnableLoadTimeWeaving 是一个注解，它用于启用加载时织入（Load-Time Weaving, LTW）

LWT[Spring学习笔记_26------LWT-CSDN博客]

2. 场景

AOP：在Spring框架中，LTW通常与Spring AOP结合使用，以提供更强大的AOP功能。例如，可以定义切面来拦截特定的方法调用，并在这些方法调用前后执行额外的操作。

ORM：在一些对象关系映射（ORM）框架中，如Hibernate，LTW可以用来延迟加载实体属性或集合，而无需在运行时显式地配置代理。

3. 源码

java 复制代码

/**
 * @author Chris Beams
 * @since 3.1
 * @see LoadTimeWeaver
 * @see DefaultContextLoadTimeWeaver
 * @see org.aspectj.weaver.loadtime.ClassPreProcessorAgentAdapter
 */
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(LoadTimeWeavingConfiguration.class)
public @interface EnableLoadTimeWeaving {
	AspectJWeaving aspectjWeaving() default AspectJWeaving.AUTODETECT;
	enum AspectJWeaving {
		ENABLED,    // 开启LTW支持
		DISABLED,   // 不开启LTW支持
		AUTODETECT; // 检测类路径下的META-INF目录下是否存在aop.xml文件，如果存在，则开启LTW支持，否则不开启LTW支持
	}
}

4. Demo

配置类

java 复制代码

package com.example.config;

import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.EnableLoadTimeWeaving;
import org.springframework.context.annotation.EnableLoadTimeWeaving.AspectJWeaving;

@Configuration
@EnableLoadTimeWeaving(aspectjWeaving = AspectJWeaving.ENABLED)
public class AppConfig {
}

切面类

java 复制代码

package com.example.aspect;

import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.annotation.After;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.springframework.stereotype.Component;

@Aspect
@Component
public class LoggingAspect {

    @Before("execution(* com.example.service.UserService.login(..))")
    public void logBeforeLogin(JoinPoint joinPoint) {
        System.out.println("User is logging in: " + joinPoint.getSignature());
    }

    @After("execution(* com.example.service.UserService.logout(..))")
    public void logAfterLogout(JoinPoint joinPoint) {
        System.out.println("User has logged out: " + joinPoint.getSignature());
    }
}

控制器类

java 复制代码

package com.example.controller;

import com.example.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@RequestMapping("/users")
public class UserController {

    private final UserService userService;

    @Autowired
    public UserController(UserService userService) {
        this.userService = userService;
    }

    @GetMapping("/login")
    public String login() {
        userService.login();
        return "Logged in";
    }

    @GetMapping("/logout")
    public String logout() {
        userService.logout();
        return "Logged out";
    }
}

service 类

java 复制代码

package com.example.service;

public class UserService {

    public void login() {
        System.out.println("User is logging in...");
    }

    public void logout() {
        System.out.println("User is logging out...");
    }
}

AOP配置文件aop.xml

XML 复制代码

<aspectj>
    <weaver>
        <!-- Specify which packages to weave -->
        <include within="com.example..*"/>
    </weaver>
    <aspects>
        <!-- Specify which aspects to use -->
        <aspect name="com.example.aspect.LoggingAspect"/>
    </aspects>
</aspectj>

启动

bash 复制代码

java -javaagent:/path/to/spring-instrument.jar -jar example.jar