Spring AOP CGLIB代理的字段为空

Question

描述

使用vlcj组件时,自定义组件将作为AOP代理对象null的结果出现.

MediaList类

public class MediaList {
    private libvlc_media_list_t mediaListInstance;
    public MediaList(LibVlc libvlc, libvlc_instance_t instance, libvlc_media_list_t mediaListInstance) {
        this.libvlc = libvlc;
        this.instance = instance;
        createInstance(mediaListInstance);
    }
    private void createInstance(libvlc_media_list_t mediaListInstance) {
        logger.debug("createInstance()");
        if(mediaListInstance == null) {
            mediaListInstance = libvlc.libvlc_media_list_new(instance);
        }
        else {
            libvlc.libvlc_media_list_retain(mediaListInstance);
        }

        this.mediaListInstance = mediaListInstance; // <- assignment
        logger.debug("mediaListInstance={}", mediaListInstance);

        mediaListEventManager = libvlc.libvlc_media_list_event_manager(mediaListInstance);
        logger.debug("mediaListEventManager={}", mediaListEventManager);

        registerEventListener();
    }
    public final libvlc_media_list_t mediaListInstance() {
        return mediaListInstance; // <- proxy object return null, if use aop
    }
}

自定义MediaList类

public class TestMediaList extends MediaList {

    public TestMediaList(LibVlc libvlc, libvlc_instance_t instance) {
        super(libvlc, instance);
    }

    public void xTest(String test){
        System.out.println(test);
    }
}

Spring配置类

@Configuration
public class PlayerBeanConfig {

    @Bean
    @Scope(ConfigurableBeanFactory.SCOPE_PROTOTYPE)
    @Resource
    public TestMediaList testMediaList(LibVlc libvlc, libvlc_instance_t instance) {
        return new TestMediaList(libvlc, instance);
    }
}

AOP配置类

@Aspect
public class MediaListAspect {
    @Pointcut("execution(* TestMediaList.xTest(..))")
    private void anyMethod() {
    }

    @Around("anyMethod()")
    public Object lockAndUnlock(ProceedingJoinPoint joinPoint) throws Throwable {
        Object object = joinPoint.proceed();
        return object;
    }
}

测试代码

public static void main(String[] args) {
    boolean b = new NativeDiscovery().discover();

    if (b) {
        springContext = new AnnotationConfigApplicationContext(PlayerBeanConfig.class);

        String[] kkk = new String[]{};
        TestMediaList list = springContext.
                getBean(TestMediaList.class, LibVlc.INSTANCE, LibVlc.INSTANCE.libvlc_new(kkk.length, kkk));

        System.out.println(list.mediaListInstance()); // <- proxy object return null
    } else {
        logger.error("Cannot find vlc lib, exit application");
    }
}

当TestMediaList构建完成时,我尝试单步跟踪.方法的MediaListInstance()返回正常值,但是当spring返回到代理对象时,返回null.同时,如果您不使用AOP,我也会尝试正确返回值.因此,我确定了AOP动态代理的基本问题,但我不知道为什么,之前没有遇到过这样的情况.

---

最小的例子

所有课程包: vod.demo

TargetClass

public class TargetClass {
    private String returnValue;

    public TargetClass() {
        this.returnValue = "Hello World";
    }

    public final String test() {
        System.out.println("TargetClass.test();");
        return returnValue;
    }
}

Aspect Class

@Aspect
public class AspectClass {
    @Pointcut("execution(* vod.demo.TargetClass.*(..))")
    private void targetMethod() {
    }

    @Around("targetMethod()")
    public Object aroundTarget(ProceedingJoinPoint joinPoint) throws Throwable {
        System.out.println("AspectClass.aroundTarget();");
        return joinPoint.proceed();
    }
}

Spring Config类

@Configuration
@EnableAspectJAutoProxy
@Import(AspectClass.class)
public class SpringConfig {
    @Bean
    public TargetClass target() {
        return new TargetClass();
    }
}

客户类

public class Client {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(SpringConfig.class);
        TargetClass target = context.getBean(TargetClass.class);
        System.out.println("Client invoke:" + target.test()); // <- output null
    }
}

Answer 1

这是潜在的意外行为的组合.首先,Spring使用CGLIB为AOP代理您的bean.CGLIB代理是类的动态子类型的实例,它将所有方法调用委托给类的实际实例.但是,即使代理是子类型,其字段也不会被初始化(即,TargetClass不会调用您的超级构造函数).可以在这里找到更长的解释.

另外,你的方法

public final libvlc_media_list_t mediaListInstance() {
    return mediaListInstance; // <- proxy object return null, if use aop
}

要么

public final String test() {
    System.out.println("TargetClass.test();");
    return returnValue;
}

是的final.因此CGLIB不能覆盖它们以委托给实例.这将在Spring日志中暗示.例如,你会看到

22:35:31.773 [main] INFO  o.s.aop.framework.CglibAopProxy - Unable to proxy method [public final java.lang.String com.example.root.TargetClass.test()] because it is final: All calls to this method via a proxy will NOT be routed to the target instance.

将上述所有内容放在一起,您将获得一个代理实例,其中字段位于null代理实例的方法所在的代理实例.所以你的代码实际上会调用

public final String test() {
    System.out.println("TargetClass.test();");
    return returnValue;
}

对于该returnValue字段的实例null.

如果可以,请更改方法,删除final修改器.如果你不能,你将不得不重新考虑你的设计.