如何在Java Client-Server程序中将消息发送到多个客户端

Question

多个客户端说（A，B，C，D等）通过同一个套接字连接到一个服务器。它们都在需要时向服务器发送消息。客户端消息仅发送到服务器（而不是其他客户端）。但每当服务器发送消息时，它应该被传递给所有客户端。请帮我解决，只能在1个客户端上获取服务器消息

// MultithreadedServer.java

package server;
import java.io.*;

import java.net.*;
import java.util.ArrayList;
import java.util.Vector;
public class MultithreadedServer
{



Vector<ClientHandler> clients = new Vector<ClientHandler>();
    Vector<String> users = new Vector<String>();
    private static ServerSocket servSocket;
    private static final int PORT = 1247;

public MultithreadedServer() throws IOException{
    servSocket = new ServerSocket(PORT);
  while(true) {

                Socket client = servSocket.accept();
                System.out.println("\nNew client accepted.\n");




    ClientHandler handler;
        handler = new ClientHandler(client);
        clients.add(handler);

}
}
public static void main(String[] args) throws IOException
{
    MultithreadedServer ms = new MultithreadedServer();

}
class ClientHandler extends Thread
{

private Socket client;
private BufferedReader in;
private PrintWriter out;
String name,message,response;

public ClientHandler(Socket socket)
{
    //Set up reference to associated socket...
    client = socket;
    try
    {
        in = new BufferedReader(
                new InputStreamReader(
                        client.getInputStream()));
        out = new PrintWriter(
                    client.getOutputStream(),true);
    }
    catch(IOException e)
    {
        e.printStackTrace();
    }
    start();
}
public void sendMessage(String  msg)  {
        System.out.println("is it even coming here?");
    out.println("Server:" + msg);
}
public void boradcast(String message)  {
    // send message to all connected users
    for (ClientHandler c : clients) {

          c.out.println("Server: hello");
}
}
public String getUserName() {  
        return name; 
    }
 public void run()
  {
    try
    {
        String received;
        do
        {   System.out.println("Enter Your Message: ");
            String msg = in.readLine();
            out.println(msg);
            boradcast("testing");
            received = in.readLine();
            out.println("ECHO: " + received);
        //Repeat above until 'QUIT' sent by client...

        }while (!received.equals("QUIT"));
    }
    catch(IOException e)
    {
        e.printStackTrace();
    }
    finally
    {
        try
        {
            if (client!=null)
            {
                System.out.println(
                            "Closing down connection...");
                client.close();
                        }
        }catch(IOException e)
        {
            e.printStackTrace();
        }
      }
   }
}}
//ClientProgram

import java.io.*;
import java.net.*; 
public class Client
 {
private static InetAddress host;
private static final int PORT = 1247;
private static Socket link;
private static BufferedReader in;
private static PrintWriter out;
private static BufferedReader keyboard; 
public static void main(String[] args)  throws IOException
{
    try
  {
        host = InetAddress.getLocalHost();
        link = new Socket(host, PORT);
        in = new BufferedReader(
                new InputStreamReader(
                            link.getInputStream()));
        out = new PrintWriter(
                            link.getOutputStream(),true);
        keyboard = new BufferedReader(
                        new InputStreamReader(System.in));
        String message, response;
        do
        {
            System.out.print(
                  "Enter message ('QUIT' to exit): ");
            message = keyboard.readLine();
           //Send message to server on
            //the socket's output stream...
            out.println(message);
            //Accept response frm server on
            //the socket's input stream...
            response = in.readLine();
            //Display server's response to user...
            System.out.println(response);
        }while (!message.equals("QUIT"));
    }
    catch(UnknownHostException uhEx)
    {
        System.out.println(
                    "\nHost ID not found!\n");
    }
    catch(IOException ioEx)
    {
        ioEx.printStackTrace();
    }
    finally
    {
        try
        {
            if (link!=null)
            {
                System.out.println(
                        "Closing down connection...");
                link.close();
            }
        }
        catch(IOException ioEx)
        {
            ioEx.printStackTrace();
        }
       }
      }
   }

Answer 1

一种显而易见的方法是循环遍历客户端中的所有ClientHandler并将消息发送给每个客户端：

for (ClientHandler ch : clients){
    ch.sendMessage(message); //Or something
}