为什么多播不起作用？

Question

我的程序无法正常运行。问题是第二个客户端看不到来自第一个客户端的消息。我认为问题出在while循环中。只是不从 IP 地址读取。你能帮助我吗？ 提前谢谢你。

package multicastchat;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.DatagramPacket;
import java.net.InetAddress;
import java.net.MulticastSocket;

public class MulticastChat {

    int chatRoom = 0;
    int port = 0;
    String ipAdress = "";
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

    public MulticastChat(){

    }

    public void choosingChatRoom() throws IOException{
        while (!(chatRoom > 0 && chatRoom < 5)) {
            System.out.println(
                    "We have four chat rooms, choose one of them (1, 2, 3, 4)");
            chatRoom = Integer.valueOf(br.readLine());
            switch (chatRoom) {
                case 1:
                    port = 4441;
                    ipAdress = "230.0.0.1";
                    break;
                case 2:
                    port = 4442;
                    ipAdress = "230.0.0.2";
                    break;
                case 3:
                    port = 4443;
                    ipAdress = "230.0.0.3";
                    break;
                case 4:
                    port = 4444;
                    ipAdress = "230.0.0.4";            
                    break;
                default:
                    System.out.println("Sorry, but we haven't this room, try another room");
                    this.choosingChatRoom();
                    break;
            }
            System.out.println("Welcome to room " + chatRoom);
        }
    }

    public static void main(String[] args) throws IOException {
        MulticastChat mc = new MulticastChat();
        mc.choosingChatRoom();
        MulticastSocket socket = new MulticastSocket(mc.port);
        InetAddress address = InetAddress.getByName(mc.ipAdress);
        socket.joinGroup(address);

        DatagramPacket outMessage;
        DatagramPacket inMessage;

        String userInput;

        while (true) {
            //Receiving message
            inMessage = new DatagramPacket(new byte[4096], 4096);
            inMessage.setLength(inMessage.getData().length);
            socket.receive(inMessage);
            String received = new String(
                    inMessage.getData(), 0, inMessage.getLength());
            System.out.println(received);   
            //Sending message
            if ((userInput = mc.br.readLine()) != null) {
                if (userInput.equals("quit")) {
                    System.out.println("Bye, see you later ^_^");
                    socket.leaveGroup(address);
                    socket.close();
                    System.exit(0);
                } else {
                    byte[] buff = userInput.getBytes();
                    outMessage =
                            new DatagramPacket(buff, buff.length, address, mc.port);
                    socket.send(outMessage);
                }
            }         
        }
    }
}

Answer 1

假设您在聊天的两端使用相同的程序，则不会发生任何事情。每个实例都是在写入任何内容之前从套接字读取启动的，因此它将永远阻塞。

没有实例可以写入套接字。

请注意，套接字编程通常需要多个线程，因为事情在至少两个“通道”（用户交互和套接字 I/O）上异步发生。对如何编写网络代码的完整解释远远超出了 StackOverflow 的设计目的。