Flying_Think 2017-12-07 04:46 采纳率: 33.3%
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使用代理的时候报ClassCastException错,完全摸不着头脑。

public abstract class Dog implements Eat {

protected String name;
protected int age;

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public int getAge() {
    return age;
}

public void setAge(int age) {
    this.age = age;
}

}

public interface Eat {

void gotoEat();

void gotoEat(String food);

void gotoEat(String food, int num);

}

public class BorderCollie extends Dog {

@Override
public void gotoEat() {
    System.out.println("什么都不喂我,只能吃草...");
}

@Override
public void gotoEat(String food) {
    System.out.println(food + "吃饱了,牧羊so easy!");
}

@Override
public void gotoEat(String food, int num) {
    System.out.println("足足吃了" + num + "份" + food + ",本边牧需要散步消化");
}

}

public class EatHandler implements InvocationHandler {

private Object target = null;

@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    if ("gotoEat".equals(method.getName()) && args != null) {
        if(args.length == 2){
            System.out.println("这里是调用方法名为:" + method.getName() + ";参数个数为:" + args.length);

            Class<?>[] parameterTypes = method.getParameterTypes();

            List<String> argsType = Stream.of(parameterTypes).map(Class::getName).collect(Collectors.toList());
            argsType.stream().forEach(System.out::println);
        }
    }
    System.out.println("先要洗爪...");
    Object result = method.invoke(target, args);
    System.out.println("吃饱后要记得散步...");
    return result;
}

public EatHandler(Object target) {
    this.target = target;
}

public void setTarget(Object target) {
    this.target = target;
}

public Object getTarget() {
    return target;
}

}

@Test
public void dogEat() {
    Dog borderCollie = new BorderCollie();

    ClassLoader classLoader = BorderCollie.class.getClassLoader();
    Class<?>[] interfaces = BorderCollie.class.getInterfaces();
    EatHandler eatHandler = new EatHandler(borderCollie);

    Object proxyInstance = Proxy.newProxyInstance(classLoader, interfaces, eatHandler);
    BorderCollie obj = (BorderCollie) proxyInstance;
    System.out.println(proxyInstance.getClass().getName());
}

错误信息:
java.lang.ClassCastException: com.sun.proxy.$Proxy4 cannot be cast to myproxy.BorderCollie
at myproxy.EatTest.dogEat2(EatTest.java:39)
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.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:678)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)

我估计着是:BorderCollie obj = (BorderCollie) proxyInstance;这句话出错了,但是搞不懂为什么啊?

  • 写回答

1条回答 默认 最新

  • 小優YoU 2017-12-07 04:51
    关注

    就是强制类型转换错误,你看异常堆栈提示:

    com.sun.proxy.$Proxy4 cannot be cast to myproxy.BorderCollie

    这两个类不是父子关系,你代码做了强转(或隐式强转)

    评论

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