java.lang.ClassCastException: $Proxy17 cannot be cast to *.*.*.service.impl.DeviceService

报错：

java.lang.ClassCastException: $Proxy17 cannot be cast to *.*.*.service.impl.DeviceServiceat *.*.*.service.impl.DeviceServiceTest.testDeviceIsOnline(DeviceServiceTest.java:436)at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)at java.lang.reflect.Method.invoke(Method.java:597)at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:74)at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:83)at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:72)at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:231)at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:71)at org.junit.runners.ParentRunner.run(ParentRunner.java:309)at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:174)at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)

原因：

        Spring的文档中这么写的：Spring AOP部分使用JDK动态代理或者CGLIB来为目标对象创建代理。如果被代理的目标实现了至少一个接口，则会使用JDK动态代理。所有该目标类型实现的接口都将被代理。若该目标对象没有实现任何接口，则创建一个CGLIB代理。

        所以，解决办法是，如果用JDK动态代理，就必须为被代理的目标实现一个接口（要注意的地方是：需要将ctx.getBean()方法的返回值用接口类型接收）；如果使用CGLIB强制代理，就必选事先将CGLIB包导入项目，设置beanNameAutoProxyCreator的proxyTargetClass属性为true。

这里DeviceService实现了接口IDeviceService，所以会使用JDK动态代理，从而使(DeviceService) deviceService强制转换的时候报错（因为实现IDeviceService接口的代理类是属于DeviceService子类）。因此需要使用CGLIB强制代理。需要在springContext.xml中增加如下配置：

<aop:aspectj-autoproxy proxy-target-class="true"/>