Java RMI : how to make client stub method called on server print message on client screen?

Question

我正在用 Java 与 rmi 聊天。我有一个服务器对象和至少两个客户端对象。当客户端远程调用recebeMensagem方法向服务器发送消息时，服务器必须在所有客户端的屏幕上打印该消息(发送消息的客户端除外)。

客户端类有一个方法printMenssagem(Mensagem msg)，该方法由服务器远程调用。问题是该方法正在服务器的屏幕上打印。如何在客户端屏幕上打印消息？

服务器.java:

import java.rmi.NotBoundException;
import java.rmi.RemoteException;
import java.rmi.registry.LocateRegistry;
import java.rmi.registry.Registry;
import java.rmi.server.UnicastRemoteObject;
import java.util.ArrayList;
import java.util.function.Predicate;

public class Server implements ChatServer {

    private ArrayList<String> listaClientes = new ArrayList<>();
    private static int port = 5002;

    public static void main(String[] args) {

        try {

            Server obj = new Server();
            ChatServer stub = (ChatServer) 
            UnicastRemoteObject.exportObject(obj, port);

            // Bind the remote object's stub in the registry
            Registry registry = LocateRegistry.createRegistry(port);
            registry.bind("chat", stub);
            System.out.println("Server ready!");

        } catch (Exception e) {
            System.err.println("Server exception: " + e.toString());
            e.printStackTrace();
        }
   }

   @Override
   public void adicionaCliente(String user) {

       this.listaClientes.add(user);

   }

   @Override
   public void retiraCliente(String userName) {
        Predicate<String> clientePredicate = cp -> 
        cp.equals(userName);
        listaClientes.removeIf(clientePredicate);
        try {
           Registry registry = LocateRegistry.getRegistry(port);
           registry.unbind(userName);
       } catch (RemoteException e) {
           e.printStackTrace();
       } catch (NotBoundException e) {
           e.printStackTrace();
       }

   }

   @Override
   public void recebeMensagem(Mensagem msg) {       

      try {
           Registry registry = LocateRegistry.getRegistry(port);
           for(String cliente : listaClientes) {
               if (!cliente.equals(msg.getRemetente())) {
                   Client stub = (Client) registry.lookup(cliente);
                   stub.printMensagem(msg);
               }                    
           }
       } catch (RemoteException e) {
        e.printStackTrace();
    } catch (NotBoundException e) {
        e.printStackTrace();
    }

    }


    public ArrayList<String> getListaClientes() {
        return listaClientes;
   }

   public void setListaClientes(ArrayList<String> listaClientes) {
       this.listaClientes = listaClientes;
   } 



  }

Client.java:

import java.io.Serializable;
import java.rmi.Remote;

public class Client implements Remote, Serializable {

    private static final long serialVersionUID = 6864579049922061838L;
    private static int port = 5002;
    private static String host = "127.0.0.1";

    public static void main(String[] args) {        

        new Thread(new ClientInterface(host, port)).start();            
    }


    public void printMensagem(Mensagem mensagem) {
        System.out.println(mensagem.getRemetente() + ": " + mensagem.getMensagem());
    }



}

Answer 1

how to make client stub method called on server print message on client screen?

客户端没有 stub 。它不是一个远程对象。它是一个可序列化的对象，并且已被传输到注册表 holus bolus，并且它在执行 Registry.lookup() 来获取它的任何 JVM 中运行。这不是你想要的。您希望它是一个带有 stub 的远程对象，因此您必须使其实现远程接口(interface)，并将其导出，并通过对等方的远程接口(interface)使用它。

您还需要注意，您当前的架构无法在多个主机上工作，因为您无法绑定(bind)到远程注册表。您需要向服务器添加客户端注册方法。