ServerSocket与客户端Socket的通信

Question

I am trying to make a multi-threaded chat program with a central server and separate chat clients. The server has two roles: read incoming messages from all the chat clients and output the complete lists back to the clients. The server correctly receives input from clients and prints it out. However the clients are do not receive the list. In order to easily see the code segments that affect server to client communication I have marked them with an asterisk.

Server Code:

import java.net.*;
import java.util.*;
import java.io.*;
import java.lang.*;

public class ChatServer {
    public static ArrayList<String> messages =
        new ArrayList<String>();

    public static void main(String[] args) {
        int portNumber = Integer.parseInt(args[0]);
        Scanner cin = new Scanner(System.in);

        ServerSocket serverSocket;
        try {
            serverSocket = new ServerSocket(portNumber); //*
        }catch (IOException ex) {
            System.out.println("Server socket creation failed");
            //ex.printStackTrace();
            return;
        }

        try {
            int maxConnections = 10;
            int curConnections = 0;
            while (curConnections++ < maxConnections) {
                Socket clientSocket = serverSocket.accept();

                ClientConnection clientCon = new ClientConnection(clientSocket);
                Thread clientConT = new Thread(clientCon);
                //clientConT.setPriority(curConnections+1);
                clientConT.start();

                ClientOutputConnection clientOut = new          //*
                    ClientOutputConnection(clientSocket);   
                Thread clientOutT = new Thread(clientOut);      //*
                //clientOutT.setPriority((curConnections+1)*2);
                clientOutT.start();                             //*


                System.out.println("Client "+curConnections+" Connected");
            }
        }catch (IOException ex) {
            System.out.println("Client connection failed");
            ex.printStackTrace();
        }
    }
}

class ClientConnection implements Runnable {
    Socket clientSocket;

    public ClientConnection(Socket clientSocketT) {
        clientSocket = clientSocketT;
    }

    public void run() {
        try {
            System.out.println("ClientConnection server running");
            BufferedReader in = new BufferedReader(
                new InputStreamReader(clientSocket.getInputStream()));

            while (true) {
                String lineIn = null;
                if ((lineIn = in.readLine()) != null) {
                    System.out.println(lineIn);
                    ChatServer.messages.add(lineIn);
                }

                if (lineIn.equalsIgnoreCase("exit") || 
                    lineIn.equalsIgnoreCase("close"))
                    return;
            }
        }catch (Exception ex) {
            ex.printStackTrace();
        }
    } 
}

class ClientOutputConnection implements Runnable {
    private Socket clientSocket;

    public ClientOutputConnection(Socket clientSocketT) {
        clientSocket = clientSocketT;
    }

    public void run() {
        try {
            PrintWriter out = new PrintWriter(
                clientSocket.getOutputStream(), true);

            System.out.println("ClientOutputConnection running");

            int lastMssg = 0;

            while (true) {
                try {
                    //System.out.println(ChatServer.messages);
                    while (lastMssg < ChatServer.messages.size()) {
                        out.println(ChatServer.messages.get(lastMssg)+"\n");
                        //System.out.println(ChatServer.messages.get(lastMssg));
                        lastMssg++;
                    }

                    //Thread.sleep(10);
                }catch (Exception ex){
                    ex.printStackTrace();
                }
            }
        }catch(IOException ex) {
            ex.printStackTrace();
        }
    }
}

Client Code:

import java.net.*;
import java.util.*;
import java.io.*;
import static java.lang.System.*;

public class ChatClient {
    public static void main(String[] args) {
        int portNumber = Integer.parseInt(args[0]);
        Scanner cin = new Scanner(System.in);

        PrintWriter out;
        Socket clientSocket;

        try {
            System.out.println("Break 1");
            clientSocket = new Socket("localhost", portNumber);
            System.out.println("Break 2");
            out = new PrintWriter(clientSocket.getOutputStream(), true);
        }catch (Exception ex) {
            System.out.println("PrintWriter creation failed");
            ex.printStackTrace();
            return;
        }

        //Initializes reader for server
        BufferedReader in = null;  //*
        try {
            in = new BufferedReader(
                new InputStreamReader(clientSocket.getInputStream()));   //*
        }catch (IOException ex) {
            ex.printStackTrace();
        }

        System.out.print("Enter your username: ");
        String username = cin.nextLine();
        out.println();

        ServerListener sl = new ServerListener(in, username);   //*
        Thread slT = new Thread(sl);                            //*
        //slT.setPriority(1);
        slT.start();                                            //*

        ServerOutput so = new ServerOutput(username, out);
        Thread soT = new Thread(so);                        
        //soT.setPriority(2);
        soT.start();                                        
    }
}

class ServerOutput implements Runnable {
    private String username;
    private PrintWriter out;

    public ServerOutput(String usernameT, PrintWriter outT) {
        username = usernameT;
        out = outT;
    }

    public void run() {
        Scanner cin = new Scanner(System.in);
        while (true) {
            String line = cin.nextLine();
            if (line.equalsIgnoreCase("close")) {
                out.close();
                return; 
            }

            out.write("<"+username+"> "+line+"\n");
            out.flush();

            try { Thread.sleep(10); }catch(Exception e){};
        }
    }
}

class ServerListener implements Runnable {
    private BufferedReader in;
    private String username;

    public ServerListener (BufferedReader inT, String usernameT) {
        in = inT;
        username = usernameT;
    }

    public void run() {
        System.out.println("ServerListener running");
        String line = null;
        try {
            while (true){
                //System.out.println(in.readLine());
                while ((line = in.readLine()) != null)
                    //if (line.indexOf(username) != 1)
                        System.out.println(line);
            }
        }catch (IOException ex) {
            //System.out.println("Doesnt work");
            ex.printStackTrace();
        }
    }
}

Could it be an issue with running too many ClientOuputConnection threads at the same time? Or is it an issue that I am running all of these clients on one computer?

Answer 1

Let me give a try. Did you try debugging the code. you are first starting the Clientcon and then ClientOut. when ClientOut is started, it goes to this while loop

while (true) {
                try {
                    //System.out.println(ChatServer.messages);
                    while (lastMssg < ChatServer.messages.size()) {
                        out.println(ChatServer.messages.get(lastMssg)+"\n");
                        //System.out.println(ChatServer.messages.get(lastMssg));
                        lastMssg++;
                    }

                    //Thread.sleep(10);
                }catch (Exception ex){
                    ex.printStackTrace();
                }
            }

There is a chance that your ChatServer does not have anything in the arraylist.and it exits out of the while loop. not sure whether this is right. On looking at the code, I thought this might be an issue.