JAVA八股与代码实践----JDK代理和CGLIB代理的区别

当spring发现该代理的类实现了接口会使用JDK代理，如果该类没有实现接口，会使用CGLIB代理

如果在springboot中要强制使用CGLIB代理，需要加上

@EnableAspectJAutoProxy(proxyTargetClass = true) // 强制使用 CGLIB

@SpringBootApplication
@EnableAspectJAutoProxy(proxyTargetClass = true) // 强制使用 CGLIB
public class Application {
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
}

动态代理的典型应用就是AOP

1、动态代理代码示例（JDK）（非AOP）

1.1、定义bean和代理逻辑

// 目标类（实际的业务逻辑）
public class UserService {
    public void addUser(String username) {
        System.out.println("User " + username + " added.");
    }

    public void deleteUser(String username) {
        System.out.println("User " + username + " deleted.");
    }
}

// 自定义 InvocationHandler 实现
public class LoggingInvocationHandler implements InvocationHandler {
    private Object target; // 被代理对象

    public LoggingInvocationHandler(Object target) {
        this.target = target;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        // 前置逻辑
        System.out.println("[LOG] Method " + method.getName() + " is called with args: " + java.util.Arrays.toString(args));

        // 调用目标方法
        Object result = method.invoke(target, args);

        // 后置逻辑
        System.out.println("[LOG] Method " + method.getName() + " execution completed.");

        return result;
    }
}

1.2、生成动态代理bean

public class ProxyExample {
    public static void main(String[] args) {
        // 创建目标对象（真实的 Bean）
        UserService userService = new UserService();

        // 创建代理对象
        UserService proxy = (UserService) Proxy.newProxyInstance(
            userService.getClass().getClassLoader(), // 类加载器
            userService.getClass().getInterfaces(),  // 目标类实现的接口
            new LoggingInvocationHandler(userService) // 代理逻辑
        );

        // 调用代理方法
        proxy.addUser("Alice");
        proxy.deleteUser("Bob");
    }
}

结果：

[LOG] Method addUser is called with args: [Alice]
User Alice added.
[LOG] Method addUser execution completed.
[LOG] Method deleteUser is called with args: [Bob]
User Bob deleted.
[LOG] Method deleteUser execution completed.

2、动态代理代码示例（JDK）（AOP）

@Service // 标记为 Spring 容器管理的 Bean
public class UserService {

    public void addUser(String username) {
        System.out.println("User " + username + " added.");
    }

    public void deleteUser(String username) {
        System.out.println("User " + username + " deleted.");
    }
}

@Aspect
@Component // 标记为 Spring 管理的 Bean
public class LoggingAspect {

    @Before("execution(* com.example.service.UserService.*(..))")
    public void logBefore(JoinPoint joinPoint) {
        System.out.println("[LOG] Before method: " + joinPoint.getSignature().getName());
    }

    @After("execution(* com.example.service.UserService.*(..))")
    public void logAfter(JoinPoint joinPoint) {
        System.out.println("[LOG] After method: " + joinPoint.getSignature().getName());
    }
}