Question

我无法弄清楚如何阻止消息在客户端的屏幕上出现两次。

实际输出应该是这样的：

运行代码的步骤：
1.在一个终端上运行服务器
2.在两个不同的终端上运行两个客户端

当我运行服务器时 - main方法创建一个Server对象：

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

服务器构造函数：

Server() throws IOException {
            Date dNow = new Date();
            System.out.println("MultiThreadServer started at " + String.format("%tc", dNow));
            System.out.println();

            ServerSocket server = new ServerSocket(8000);
            ClientSockets = new Vector<Socket>();


            while (true) {
                    Socket client = server.accept();
                    AcceptClient acceptClient = new AcceptClient(client);
                    System.out.println("Connection from Socket " + "[addr = " + client.getLocalAddress() + ",port = "
                                    + client.getPort() + ",localport = " + client.getLocalPort() + "] at "
                                    + String.format("%tc", dNow));
                    System.out.println();
                    //System.out.println(clientCount);

            }
            //server.close();
    }

我正在使用Socket连接到服务器。这是我的服务器代码。

的 Server.java

import java.io.IOException;
import java.net.*;
import java.util.Vector;
import java.io.*;
import java.util.*;
import java.io.DataInputStream;
import java.net.ServerSocket;
import java.net.Socket;
import java.time.LocalDateTime;
import java.util.logging.Level;
import java.util.logging.Logger;
import java.text.*;
import java.util.Scanner;



public class Server {
    static Vector<Socket> ClientSockets;
    int clientCount = 0;
    //int i = 0;


    Server() throws IOException {
            Date dNow = new Date();
            System.out.println("MultiThreadServer started at " + String.format("%tc", dNow));
            System.out.println();

            ServerSocket server = new ServerSocket(8000);
            ClientSockets = new Vector<Socket>();


            while (true) {
                    Socket client = server.accept();
                    AcceptClient acceptClient = new AcceptClient(client);
                    System.out.println("Connection from Socket " + "[addr = " + client.getLocalAddress() + ",port = "
                                    + client.getPort() + ",localport = " + client.getLocalPort() + "] at "
                                    + String.format("%tc", dNow));
                    System.out.println();
                    //System.out.println(clientCount);

            }
            //server.close();
    }

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

    class AcceptClient extends Thread {
            Socket ClientSocket;
            DataInputStream din;
            DataOutputStream dout;

            AcceptClient(Socket client) throws IOException {
                    ClientSocket = client;
                    din = new DataInputStream(ClientSocket.getInputStream());
                    dout = new DataOutputStream(ClientSocket.getOutputStream());

                    //String LoginName = din.readUTF();
                    //i = clientCount;
                    clientCount++;
                    ClientSockets.add(ClientSocket);
                    //System.out.println(ClientSockets.elementAt(i));
                    //System.out.println(ClientSockets.elementAt(1));

                    start();
            }

            public void run() {

                            try {
                                    while (true) {
                                    String msgFromClient = din.readUTF();
                                    System.out.println(msgFromClient);
                                    for (int i = 0; i < ClientSockets.size(); i++) {
                                            Socket pSocket = (Socket) ClientSockets.elementAt(i);
                                            DataOutputStream pOut = new DataOutputStream(pSocket.getOutputStream());
                                            pOut.writeUTF(msgFromClient);
                                            pOut.flush();
                                    }
                            }

                            } catch (IOException e) {
                                    e.printStackTrace();
                            }

            }
    }

}

Client.java

import java.net.Socket;
import java.util.Scanner;
import java.io.*;
import java.net.*;


public class Client implements Runnable{

    Socket socketConnection;
    DataOutputStream outToServer; 
    DataInputStream din;


    Client() throws UnknownHostException, IOException {

            socketConnection = new Socket("127.0.0.1", 8000);
            outToServer = new DataOutputStream(socketConnection.getOutputStream());
            din = new DataInputStream(socketConnection.getInputStream());


            Thread thread;
            thread = new Thread(this);
            thread.start();

            BufferedReader br = null;
            String ClientName = null;
            Scanner input = new Scanner(System.in);
            String SQL = "";
            try {
                    System.out.print("Enter you name: ");
                    ClientName = input.next();
                    ClientName += ": ";
                    //QUERY PASSING

                    br = new BufferedReader(new InputStreamReader(System.in));
                    while (!SQL.equalsIgnoreCase("exit")) {
                            System.out.println();
                            System.out.print(ClientName);

                            SQL = br.readLine();
                            //SQL = input.next();
                            outToServer.writeUTF(ClientName + SQL);
                            //outToServer.flush();
                            //System.out.println(din.readUTF());

                    }

            } catch (Exception e) {
                    System.out.println(e);
            }
    }

    public static void main(String[] arg) throws UnknownHostException, IOException {
            Client client = new Client();
    }


    public void run() {
            while (true) {
                    try {
                            System.out.println("\n" + din.readUTF());

                    } catch (IOException e) {
                            e.printStackTrace();
                    }

            }
    }

}

Answer 1

之所以这样，是因为您正在向服务器发送客户端在控制台中编写的任何内容，服务器会将其发送回所有客户端（包括发件人））。

所以你在控制台中写了一条消息（你看到它），然后你就把它作为一个客户端收回了（你又看到了）。

一个简单的解决方法是不将刚收到的消息发送回客户端（他已在控制台中看到它）。将其添加到Server.AcceptClient#run方法：

for (int i = 0; i < ClientSockets.size(); i++) { Socket pSocket = (Socket) ClientSockets.elementAt(i); if(ClientSocket.equals(pSocket)){ continue; } ...

使用线程

1 个答案: