bugs in client\server program - can't connect to remote server

[Sanjul Jain]

hello!

I have a client/server program in which client lets user input two numbers and the server adds the numbers and returns the sum to client.

the problems I am having are:

1. client is not able to connect to remote server. it is only connecting to local host.

2. if a string seperated by "non-numeric" characters (e.g. 34a2dd) is sent, both client and server throw an uncaught exception. i need to fix the client or server or both and give useful feedback to the user. i need to do the error checking of user i/p so that user enters only integers seperated by whitespace.

I am attaching my code.
I am new to java and probably don't know much.
'shall greatly appreciate your help.

thanks in advance,
sanjul

// usage: java TCPAdditionServer3 <port number>
// default port is 7777
// connection to be closed by client
// this server handles only one connection
 
import java.io.*;
import java.net.*;
import java.lang.*;
import java.util.*;
 
class TCPAdditionServer3{
    public static void main(String[] args)throws Exception{
String clientSentence,capitalizedSentence;
int sum=0;
String sumString = "";
InetAddress serverAddress;
int portNumber = 7777;
Socket connectionSocket = null;

try {
portNumber = Integer.parseInt(args[0]);
}
catch (Exception e) {
System.out.println(" port = 7777 (default)");
portNumber = 7777;
    }     

    // create welcoming socket at port number specified by user or 7777 if no choice is specified by user
ServerSocket welcomeSocket=new ServerSocket(portNumber);

//server infinite loop
while(true){
    try {
        // wait, on welcoming socket for contact by client 
    connectionSocket=welcomeSocket.accept();
     } catch (IOException e) {
       System.out.println("Accept failed:");
       System.exit(-1);     
         }

        // create input stream, attached to socket 
    BufferedReader inFromClient=new BufferedReader(new InputStreamReader(connectionSocket.getInputStream()));
    // create output stream, attached to socket
    DataOutputStream outToClient=new DataOutputStream(connectionSocket.getOutputStream());
    
    // read in line from socket
    clientSentence=inFromClient.readLine();
  
    StringTokenizer st= new StringTokenizer(clientSentence);
    while(st.hasMoreTokens()) {
          sum += Integer.parseInt(st.nextToken());  
    }
   
   System.out.println("Waiting for connections on port " +  connectionSocket.getLocalPort() + " ... ");
   System.out.println("Received connection from " + connectionSocket.getInetAddress() + ":" + connectionSocket.getLocalPort());
              
        sumString = Integer.toString(sum);
        clientSentence = " ";
        capitalizedSentence = clientSentence  + sumString + "\n";
        
        //write out line to socket
        outToClient.writeBytes(capitalizedSentence);
    
        //connection closed by client
        try {
      connectionSocket.close();
      System.out.println("Connection closed by client");
        }
        catch (IOException e) {
      System.out.println(e);
        }
           
}
}
 
}
 

 
 // usage: java TCPAdditionClient3 <server> <port>
// default port is 7777 
 
/**
 * TCPAdditionClient1.java
 *
 *  @author Siddharth Jain 
  * @version 3.0
 */
 
/** Client Code */
 

import java.io.*;
import java.net.*;
  
/** this is the main class */
class TCPAdditionClient3{
    public static void main(String[] args)throws Exception{

String sentence,sentc,portNumberString;
int portNumber= 7777;
String hostName = "localhost";
String modifiedSentence;
InetAddress clientAddress;
/** create input stream */
BufferedReader inFromUser1=new BufferedReader(new InputStreamReader(System.in));

/** read arguments */
if(args.length == 2) {
  hostName = args[0];
     try {
     portNumber = Integer.parseInt(args[1]);
     System.out.println("client user i/p port number " + portNumber);
     } 
     catch (Exception e) {
         System.out.println(" server port = 7777 (default)");
         portNumber = 7777;
     }
 }  

 /** connect to server */
try{ 
   /** create client socket, connect to server */
Socket clientSocket=new Socket(hostName,portNumber);
      
    if (clientSocket.isConnected()== true);
    {
        System.out.println("Connecting to Server " + clientSocket.getInetAddress() + ":" + clientSocket.getPort() + "..." + "Connected");
     }

   /** create output stream attached to socket */       
    DataOutputStream outToServer=new DataOutputStream(clientSocket.getOutputStream());
/** create input stream attached to socket */
    BufferedReader inFromServer=new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
 
System.out.println();
System.out.println("Enter a string of integers seperated by non-numeric characters:");

sentence = inFromUser1.readLine();
/**send line to server */
outToServer.writeBytes(sentence+"\n");
/** read line from server */
modifiedSentence=inFromServer.readLine();
System.out.println("From Server-----> The Sum is:"+modifiedSentence);
 
try {
clientSocket.close();
    }
    catch(IOException e) {
  System.out.println(e);   
    } 

} catch(UnknownHostException e) {
    System.err.println(" Don't know about host: ");
    System.exit(1);
    } catch(IOException e) {
    System.err.println(" Couldn't get I/O for the connection");
    System.exit(1);
    } 

    }
}
 
 

[Alex Wolf]

hello Sanjul,

I have tried your program. Although I have not tried using it over a network, there's no reason it shouldn't. Make sure you are not using a firewall or router between the computers you are testing your program on. I put my own IP instead of "localhost" as default server, but that doesn't mean much.

Check out java.lang.Character, it has a method "isDigit()" and "getType()" which might be usefull for checking the users input.

Another note, if the client is restarted, your "sum" variable needs to be reset, otherwise you will add the new values to the previous sum.

good luck.

[Sanjul Jain]

hello! alex,

i tried connecting two computers on a same network w/o firewall. it is simply not working, and i have no clue why is it so.

i shall really appreciate if you kindly look into it.

regards,
sanjul

[Alex Wolf]

Hello again,
ok i "looked into it", but i can't see a problem. I have tried it using a PC with windows XP running the server, and my macintosh OSX running the client. it works flawlessly. I put the IP address of the Windows XP computer here -> String hostName = "192.168.0.1"; and it worked just fine. I dont know how to fix your problem. It must have something to do with your computer. As far as fixing anything on windows, i'd say delete everything and reinstall - correct me if im wrong . do you have any other computers you could try it on?

[Sanjul Jain]

Hello!,

Thanks for your mail.

can you please show me how to do the second part - if a string seperated by "non-numeric" characters (e.g. 34a2dd) is sent, both client and server throw an uncaught exception. i need to fix the client or server or both and give useful feedback to the user. i need to do the error checking of user i/p so that user enters only integers seperated by whitespace

i tried using isDigit(), but 'am struggling with it.

i probably don't know much about java.

i will be really grateful for your help.

warm regards,
siddharth

[Alex Wolf]

hello again Sanjul,
im guessing your problem with the the Character class is because char and Character are not the same thing. here is some sample code to help you check for integers.

    String number = tokenizer.nextToken();
    char[] test = number.toCharArray();
    for( int i = 0; i < test.length; i++ )   //for each character of "test" check if it is an integer
    {
        if( !Character.isDigit( test[i] ) ) 
        throw new Exception( "\"" + test[i] + "\" of \"" + number + "\" is not an integer" );
    }

then you should put a try catch thing around the whole thing, and make a catch statement similar to this

 
    catch( Exception e )
    {   
        javax.swing.JOptionPane.showMessageDialog( new javax.swing.JFrame(), 
            e.getMessage(), 
            "Exception", 
            javax.swing.JOptionPane.ERROR_MESSAGE );
        //e.printStackTrace(); 
        System.exit( 0 );
    }
 

if you want the server and the client to throw the exception then I would check the user input, and set a boolean if there were errors, send the text to the server and after that, if there were errors throw the exception, because if you throw the exception before you send the data, the server wont throw an exception...

Till next time.

or check the input after you have sent it.
[ December 06, 2004: Message edited by: Alex Wolf ]