一个关于IntroductionAdvisor的bug

news2024/11/25 2:34:28

一个关于IntroductionAdvisor的bug

public class TestMain {
    public static void main(String[] args) {
        // 1. 准备被代理的目标对象
        People peo = new People();
        // 2. 准备代理工厂
        ProxyFactory pf = new ProxyFactory();
        // 3. 准备introduction advice,advice 持有需要额外添加的接口Developer和Developer接口的实现类
        DelegatingIntroductionInterceptor dii = new DelegatingIntroductionInterceptor((Developer) () -> System.out.println("编码"));
        // 4. 添加advice和代理对象需要继承的接口
        pf.addAdvice(dii);
        // 5. 设置被代理对象
        pf.setTarget(peo);
        // 6. 这里强制类型转换会失败,因为代理对象采用JDK进行动态代理,只实现了Developer接口和Spring AOP内部接口
        //  这里按理应该采用Cglib代理才对 !!!
        peo = (People) pf.getProxy();
        peo.drink();
        peo.eat();
        // 7. 强制转换为Developer接口,实际方法调用会被introduction advice拦截,调用请求转发给了advice内部持有的Developer接口实现类
        Developer developer = (Developer) peo;
        developer.code();
    }

    public static class People {
        void eat() {
            System.out.println("eat");
        }

        void drink() {
            System.out.println("drink");
        }
    }

    public interface Developer {
        void code();
    }
}

运行结果:

Exception in thread "main" java.lang.ClassCastException: class com.sun.proxy.$Proxy0 cannot be cast to class com.spring.TestMain$People (com.sun.proxy.$Proxy0 and com.spring.TestMain$People are in unnamed module of loader 'app')
	at com.spring.TestMain.main(TestMain.java:20)

Spring AOP 模块版本为: 5.3.9

在这里插入图片描述

原因:

AdvisedSupport 在添加advice的时候会特殊处理IntroductionInfo类型的Advice , 将其额外实现的接口添加到interfaces接口集合中去 :

	@Override
	public void addAdvice(Advice advice) throws AopConfigException {
		int pos = this.advisors.size();
		addAdvice(pos, advice);
	}

	@Override
	public void addAdvice(int pos, Advice advice) throws AopConfigException {
		Assert.notNull(advice, "Advice must not be null");
		if (advice instanceof IntroductionInfo) {
			// We don't need an IntroductionAdvisor for this kind of introduction:
			// It's fully self-describing.
			addAdvisor(pos, new DefaultIntroductionAdvisor(advice, (IntroductionInfo) advice));
		}
		...
	}

	@Override
	public void addAdvisor(int pos, Advisor advisor) throws AopConfigException {
		if (advisor instanceof IntroductionAdvisor) {
			validateIntroductionAdvisor((IntroductionAdvisor) advisor);
		}
		addAdvisorInternal(pos, advisor);
	}

	private void validateIntroductionAdvisor(IntroductionAdvisor advisor) {
		advisor.validateInterfaces();
		// If the advisor passed validation, we can make the change.
		Class<?>[] ifcs = advisor.getInterfaces();
		for (Class<?> ifc : ifcs) {
			addInterface(ifc);
		}
	}

此时即便目标对象没有实现接口,interfaces集合也不会为空:

	private List<Class<?>> interfaces = new ArrayList<>();

这会导致DefaultAopProxyFactory选择是采用jdk还是cglib进行动态代理时,错误的选择JDK而非cglib进行动态代理,因此最终得到的代理对象不能够强制转换为目标对象类型,这与我们预期目标不符合:

	@Override
	public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {
		if (!NativeDetector.inNativeImage() &&
				(config.isOptimize() || config.isProxyTargetClass() || hasNoUserSuppliedProxyInterfaces(config))) {
			Class<?> targetClass = config.getTargetClass();
			if (targetClass == null) {
				throw new AopConfigException("TargetSource cannot determine target class: " +
						"Either an interface or a target is required for proxy creation.");
			}
			if (targetClass.isInterface() || Proxy.isProxyClass(targetClass)) {
				return new JdkDynamicAopProxy(config);
			}
			return new ObjenesisCglibAopProxy(config);
		}
		else {
			return new JdkDynamicAopProxy(config);
		}
	}
    
    // interfaces集合此时不为空,所以会采用jdk进行动态代理
	private boolean hasNoUserSuppliedProxyInterfaces(AdvisedSupport config) {
		Class<?>[] ifcs = config.getProxiedInterfaces();
		return (ifcs.length == 0 || (ifcs.length == 1 && SpringProxy.class.isAssignableFrom(ifcs[0])));
	}