“ClassCastException：$ Proxy0无法强制转换”创建简单的RMI应用程序时出错 [英] "ClassCastException: $Proxy0 cannot be cast" error while creating simple RMI application

问题描述

我正在创建我的第一个非常简单的RMI客户端 - 服务器应用程序。

I am creating my first, very simple RMI client-server application.

以下是代码：

接口ICommunication

Interface "ICommunication"

package itu.exercies.RMI.server;

    import java.rmi.Remote;
    import java.rmi.RemoteException;

public interface ICommunication extends Remote  
{
    public String doCommunicate(String name) throws RemoteException; 

}

接口实现CommunicationImpl：

Interface implementation "CommunicationImpl":

package itu.exercies.RMI.server;

import java.rmi.RemoteException;
import java.rmi.server.UnicastRemoteObject;

public class CommunicationImpl extends UnicastRemoteObject implements ICommunication {

    /**
     * 
     */
    private static final long serialVersionUID = 1L;

    public CommunicationImpl() throws RemoteException {
        super();

    }

    @Override
    public String doCommunicate(String name) throws RemoteException {

        return "Hello this is server , whats up " +name+ " ?!\n";
    }

}

这是我的主要课程服务器CommunicationServer：

Here is my main class of the server "CommunicationServer":

package itu.exercies.RMI.server;

import java.net.MalformedURLException;
import java.rmi.Naming;
import java.rmi.RemoteException;


public class CommunicationServer {
    /**
     * @param args
     * @throws RemoteException 
     * @throws MalformedURLException 
     */
    public static void main(String[] args) throws RemoteException, MalformedURLException {
        CommunicationImpl imp = new CommunicationImpl();
        Naming.rebind("CommunicationImpl", imp);
        System.out.println("Server started...");
        System.out.println("Object successfully registered. It is bound to the name 'CommunicationImpl'.");

    }

}

这是我的客户CommunicationClient：

And this is my client "CommunicationClient":

package itu.exercies.RMI.client;

import java.net.MalformedURLException;
import java.rmi.Naming;
import java.rmi.NotBoundException;
import java.rmi.RemoteException;

import itu.exercies.RMI.server.CommunicationImpl;

public class CommunicationClient {
    public static void main(String[] args) throws MalformedURLException, RemoteException, NotBoundException {

        String url = new String("rmi://localhost/CommunicationImpl");
        CommunicationImpl comm = (CommunicationImpl)Naming.lookup(url);
        String reply = comm.doCommunicate("Wiktor");
        System.out.println(reply);


    }

}

现在当我尝试运行它时：

Now when I try to run it:

1. 我使用终端导航到项目的bin目录


2. 我从那里运行rmiregistry


3. 我从新的终端窗口运行我的CommunicationServer（并打印出消息，因此它似乎工作）


4. 我打开第三个终端窗口，当我尝试运行我的CommunicationClient时会抛出异常。

1. I navigate to bin directory of my project using Terminal
2. I run rmiregistry from there
3. I run my CommunicationServer from new Terminal window (and it prints out the messages so it seems to work)
4. I open third terminal window and when i try to run my CommunicationClient it throws an exception.

java itu线程main中的.exercies.RMI.client.CommunicationClientException java.lang.ClassCastException：$ Proxy0无法在itu.exercies.RMI.client.CommunicationClient.main中强制转换为itu.exercies.RMI.server.CommunicationImpl
（CommunicationClient.java:14）

java itu.exercies.RMI.client.CommunicationClientException in thread "main" java.lang.ClassCastException: $Proxy0 cannot be cast to itu.exercies.RMI.server.CommunicationImpl at itu.exercies.RMI.client.CommunicationClient.main(CommunicationClient.java:14)

到目前为止，我试图通过使用rmic创建CommunicationImpl对象的存根来修复它现在代替'$ Proxy0'错误引用'CommunicationImpl_Stub'：

So far I have tried to fix it by creating a stub of 'CommunicationImpl' object using rmic but now instead of '$Proxy0' the error refers to 'CommunicationImpl_Stub':

线程main中的异常java.lang.ClassCastException：itu.exercies.RMI.server.CommunicationImpl_Stub无法强制转换为itu.exercies.RMI.server.CommunicationImpl
at itu.exercies.RMI.client.CommunicationClient.main（CommunicationClient.java:14）

Exception in thread "main" java.lang.ClassCastException: itu.exercies.RMI.server.CommunicationImpl_Stub cannot be cast to itu.exercies.RMI.server.CommunicationImpl at itu.exercies.RMI.client.CommunicationClient.main(CommunicationClient.java:14)

此时我没有想法是寻找错误。任何人都可以给我任何建议吗？

推荐答案

替换

CommunicationImpl comm = (CommunicationImpl) Naming.lookup(url);

with

ICommunication comm = (ICommunication) Naming.lookup(url);

CommunicationImpl 是<的服务器实现code> ICommunication 。客户既不知道也不关心实现，只关心接口。

CommunicationImpl is the server implementation of the ICommunication. The client neither knows nor cares about the implementation, only the interface.

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