Thread: Multithreading / Multiple Connections

The server should have a loop that contains the call to the accept() method. When the accept method returns with a socket connection to a client, it should create a new thread and pass that socket to the thread to process, and then loop back to the accept statement. The server would only use one port.

Hi again,

I've managed to get it to handle multiple connections however its not responding to the clients until all open clients have entered their command to the server.

ServerHandler

import java.net.*;
 
public class ServerHandler
{
    int listeningPort = 6789;
    int socketPort = 7000;
    int maxConnections = 5;
    ServerSocket welcomeSocket;
 
    public ServerHandler()
    {
        while (true) {
            checkForConnections();
        }
    }
 
    public int checkForConnections() {
        try {
            welcomeSocket = new ServerSocket(listeningPort);
            new Thread(new Server(socketPort, welcomeSocket)).start();
            socketPort++;
            return 1;
        } catch (Exception e) {
 
        }
        return 0;
    }
}

Server

import java.net.*;
import java.io.*;
 
 
public class Server implements Runnable
{
    String clientMessage;
    int serverPort;
    ServerSocket welcomeSocket;
    public Server(int port, ServerSocket socket)
    {
        this.serverPort = port;
        welcomeSocket = socket;
    }
 
    public void run() {
        try {
 
            System.out.println("Server has been started on port: " + serverPort);
        while(true)
        {
            Socket connectionSocket = welcomeSocket.accept();
            BufferedReader inFromClient =
                new BufferedReader(new InputStreamReader(connectionSocket.getInputStream()));
            DataOutputStream outToClient = new DataOutputStream(connectionSocket.getOutputStream());
            clientMessage = inFromClient.readLine();
            String response = checkCommand(clientMessage);
            outToClient.writeBytes(response);
        }
    } catch (Exception e) {
    }
    }
 
    public String checkCommand(String command) {
 
 if (command.equals("hellothere")) {
            return "hello" + "\n";
        }
 
         if (command.equals("CLOSE")) {
            System.out.println(serverPort+": Server received the terminate command, shutting down.");
            System.exit(0);
        }
        return "Command not found" + "\n";
    }
 
}

You should add a call to printStackTrace() to all of the catch blocks to show any errors that occur.
You should not ignore errors.

BTW Please use CODE tags not QUOTE tags around your code.

Try it with the printStackTrace calls to see if there are errors.

Re-read post#2

Your forever while loop is calling a method that is causing the exception.

Re-read post#2

I explained in post#2. What part of that is a problem for you?

Your code did not put the call to accept() in the loop. Your loop called checkForConnections()

When accept() returned with a socket, your code does not create a new thread to handle the connection with that socket. It started processing the connection which would mean that no connections could be made to that socket until it finished.

Make a list of the steps the server should do in pseudo code and get the design down before writing the code.

Have you worked out the logic in pseudo code yet? List the steps the code should do before writing the code.

You need more details. For example where is the looping?

while true
wait for a connection
connection found
create a thread
wait for a connection
....

That's what I expect it to do? I've never written pseudo code, I actually just Googled it and figured this is what you meant.

Is the problem not in here:

public void run() {
        try {
            System.out.println("Server has been started on port: " + serverPort);
        while(true)
        {
            Socket connectionSocket = welcomeSocket.accept();
            BufferedReader inFromClient =
                new BufferedReader(new InputStreamReader(connectionSocket.getInputStream()));
            DataOutputStream outToClient = new DataOutputStream(connectionSocket.getOutputStream());
            clientMessage = inFromClient.readLine();
            String response = checkCommand(clientMessage);
            outToClient.writeBytes(response);
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
    }

This is the run() from my Server. Its still using the socket as its called the accept() so its still on that port.

while true
wait for a connection
connection found
create a thread
wait for a connection <<<<<<<<<<< Not needed already have at top of loop

Your steps are wrong. There should only be one waiting for connection in the loop.

define server socket
begin loop
wait for connection
get socket with connection
create thread and pass it the socket
end loop

Your code is wrong and needs a new design before writing any more code.