学习 spring-AOP时发生了一个Bug,耗费了较多时间去整理思路,后面查找博客时,发现是java动态代理的错误。
看Log:
java.lang.ClassCastException: com.sun.proxy.$Proxy7 cannot be cast to com.spring.Helloworld1
at com.spring.HelloworldTest.test(HelloworldTest.java:13)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:675)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)
解决:这里显示的是动态代理生成的类无法转换到我们自定义的实现类。
(1)spring使用的动态代理有两种:JDK Proxy 和CGLIB。使用前者必须实现至少一个接口才能实现对方法的拦截。使用后者需要两个jar包:asm.jar和cglib.jar,并修改spring配置文件。
(2)
不能用接口的实现类(UserServiceImpl01_AOP)来转换Proxy的实现类,它们是同级,应该用共同的接口来转换。了解一下JDK Proxy的工作原理,然后会很容易理解这个错误出现的原因。
原:
Helloworlda bean1 = (Helloworlda)content.getBean("Helloworlda");
Helloworldb bean2 = (Helloworldb)content.getBean("Helloworldb");
改:
Helloworld bean1 = (Helloworld)content.getBean("Helloworlda");
Helloworld bean2 = (Helloworld)content.getBean("Helloworldb");