解决Proxy.newProxyInstance创建动态代理导致类型转换错误的问题(xxx cannot be cast to xxx)

以你之姓@ 2022-05-17 22:20 140阅读 0赞

**运行时报错**

Exception in thread "main" java.lang.ClassCastException: com.sun.proxy.$Proxy0 cannot be cast to com.yabadun.mall.test.proxy.ShiXian
    	at com.yabadun.mall.test.proxy.Test.main(Test.java:13)

代码

public class Test {
        public static void main(String[] args) {
            final JieKou jieKou = new ShiXian();
            JieKou jieKouProxy = (ShiXian) Proxy.newProxyInstance(jieKou.getClass().getClassLoader(), JieKou.class.getInterfaces(), new InvocationHandler() {
                public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                    System.out.println("我开始说了");
                    return method.invoke(jieKou, args);
                }
            });
    
            System.out.println(jieKou.say("hello"));
    
        }
    }

要想分析其原因，还需要对Proxy.newProxyInstance方法进行了解，其原型为

java.lang.reflect.Proxy.newProxyInstance(ClassLoader loader,Class<?>[] interfaces, InvocationHandler h) throwsIllegalArgumentException

问题就出现在第二个参数interfaces,api解释：the list of interfaces for the proxy class to implement，就是被代理类所实现的接口。而JieKou.class.getInterfaces()返回的是接口JieKou继承的上一级接口而已(如果有的话)

**因此解决办法：**

第二个传参修改为jieKou.getClass().getInterfaces()，或者改为ShiXian.class.getInterfaces()，再或者改为

new Class<?>\[\]\{JieKou.class\}