创建简单的RMI应用程序时出现"ClassCastException:$ Proxy0无法转换"错误

Question

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.

这是代码:

接口"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":

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";
    }

}

这是我的服务器"CommunicationServer"的主要类:

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":

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:

1. 我使用终端导航到我的项目的bin目录
2. 我从那里开始执行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,它会抛出异常.

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

到目前为止,我试图通过使用rmic创建一个'CommunicationImpl'对象的存根来修复它,但现在代替'$ Proxy0',错误引用'CommunicationImpl_Stub':

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

此时我不知道是在寻找错误.任何人都可以给我任何建议吗？

Answer 1

更换

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

同

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

CommunicationImpl是服务器的实现ICommunication.客户既不知道也不关心实现,只关心接口.