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

/*** @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

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

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

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;@Autowiredpublic 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

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

<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

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