小马哥 你视频里的代码我自己运行了报NPE,你在视频里演示的时候也是一样报了这个异常。我试着把proxyFactory.setTargetClass(DefaultEchoService.class);这行代码注释后，就能正常运行了，这是为什么，spring内部做了什么处理 DefaultEchoService defaultEchoService = new DefaultEchoService(); // 注入目标对象（被代理） ProxyFactory proxyFactory = new ProxyFactory(defaultEchoService); proxyFactory.setTargetClass(DefaultEchoService.class); // 添加 Advice 实现 MethodInterceptor < Interceptor < Advice proxyFactory.addAdvice(new EchoServiceMethodInterceptor()); // 获取代理对象 EchoService echoService = (EchoService) proxyFactory.getProxy(); System.out.println(echoService.echo("Hello,World"));

拦截 EchoService 的方法：public abstract java.lang.String org.geekbang.thinking.in.spring.aop.overview.EchoService.echo(java.lang.String) throws java.lang.NullPointerException Exception in thread "main" java.lang.NullPointerException at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:343) at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:198) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163) at org.geekbang.thinking.in.spring.aop.features.interceptor.EchoServiceMethodInterceptor.invoke(EchoServiceMethodInterceptor.java:34) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:212) at com.sun.proxy.$Proxy0.echo(Unknown Source) at org.geekbang.thinking.in.spring.aop.features.ProxyFactoryDemo.main(ProxyFactoryDemo.java:40)