Java Socket Command Line Argument

Question

I have created a simple server and client in java that sends and receives messages from one another. At the moment I have the port number hard coded into the code but i would like to change that to user input from the command line. In the code below I am using args[0] for the port number but when I compile it fails, can anyone help? I am new to both java and sockets so sorry if this is a trivial question

import java.io.*;
import java.net.*;

class SimpleServer
{
 public static void main(String args[]) throws Exception
    {

      //declaring string variables
       String fromclient;
       String toclient;

       //new socket object, listening on port 3000
       ServerSocket Server = new ServerSocket (args[0]);

       //prints when started and no client connected
       System.out.println ("TCPServer Waiting for client on port 3000");

       //infinate loop
       while(true) 
       {

          //listens for connection
          Socket connected = Server.accept();

          //prints clients adddress and port
          System.out.println( " THE CLIENT"+" "+ connected.getInetAddress() +":"+connected.getPort()+" IS CONNECTED ");

          //reads in message form user
          BufferedReader inFromUser = new BufferedReader(new InputStreamReader(System.in));    

          //reads in message from clinet
          BufferedReader inFromClient = new BufferedReader(new InputStreamReader (connected.getInputStream()));

          //prints message to client 
          PrintWriter outToClient = new PrintWriter(connected.getOutputStream(),true);


          //infinate loop
          while ( true )
          {

              //printing instructions for killing connection
                System.out.println("SEND(Type Q or q to Quit):");

              //reading in user input
                toclient = inFromUser.readLine();

              //if user enters q or Q kill connection
                if ( toclient.equals ("q") || toclient.equals("Q") )
                {
                    outToClient.println(toclient);
                    connected.close();
                    break;
                }
                else
                {
                   outToClient.println(toclient);
              }

              //reading from client
                fromclient = inFromClient.readLine();

              //if user enter q or Q kill connection
              if ( fromclient.equals("q") || fromclient.equals("Q") )
              {
                    connected.close();
                    break;
              }

            //printing out the message from client
                else
                {
                  System.out.println( "RECIEVED:" + fromclient );
                } 

               }  

        }
    }
  }

This is the error that is coming up

SimpleServer.java:14: error: no suitable constructor found for ServerSocket(String)
     ServerSocket Server = new ServerSocket (args[0]);

Try to replace with this code ServerSocket Server = new ServerSocket (Integer.parseInt(args[0])); ServerSocket doesn't have constructor which takes string as parameter. — Eugene
– Eugene, Commented Mar 2, 2015 at 13:26

AJ. · Accepted Answer · 2015-03-02 13:25:22Z

2

ServerSocket Server = new ServerSocket (Integer.parseInt(args[0]));

args[0] is string, needs to be parsed in int

answered Mar 2, 2015 at 13:25

AJ.

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Manuel Spigolon · Accepted Answer · 2015-03-02 13:25:47Z

2

You must convert the arg[0] (String) to int with: Integer.parseInt(arg[0]) ServerSocket doesn't have constructor with ServerSocket(String)

answered Mar 2, 2015 at 13:25

Manuel Spigolon

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Michael Heß · Accepted Answer · 2015-03-02 13:25:20Z

1

The constructor parameter is of type int, while the arguments given to main are of type String. Solution is simply to use Integer.valueOf(args[0]) to parse the argument into an integer. You might want to add more robustness checks, etc - but for a quick fix this should work.

answered Mar 2, 2015 at 13:25

Michael Heß

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