Learning how to create a simple java server.

smoothdogg00 · 02-20-2006, 03:16 PM

I have an assignment to create a simple TCP/IP based java server to play a simple guessing game. My problem is that I don't know where to find resources to learn how to write the code. Does anyone know of any good places to look at sample code?

Thanks,
Bill

paulsm4 · 02-21-2006, 12:05 AM

Try this:
http://java.sun.com/docs/books/tutor...rking/sockets/

MRMadhav · 02-21-2006, 01:07 AM

There also this one

http://javaalmanac.com/egs/index.html

smoothdogg00 · 02-22-2006, 10:36 AM

So, can someone tell me how this code looks? Its not the "game" that it's supposed to be yet, but its supposed to respond with "Hello, world!" to the user:

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

public class guessingGame{
public static ServerSocket myServerSocket;

public static void main (String argv[]){
try{
myServerSocket = new ServerSocket(Integer.parseInt(argv[0]));
while (true){
Socket communicationSocket = myServerSocket.accept();
OutputStream out = communicationSocket.getOutputStream();

PrintStream prints = new PrintStream(out);
prints.print("Hello world!");

communicationSocket.close();
}
}
catch(IOException e){
System.out.println("IOException");
}
}
}

I am supposed to be able to telnet into the server.

Thanks for any help!

jlliagre · 02-22-2006, 11:29 AM

Your code is working, which is good.

Two minor remarks:
It is poorly indented, but I suppose the reason is you didn't use the forum code tags.
Your class name should conform to the naming convention and be renamed GuessingGame.

paulsm4 · 02-22-2006, 11:33 AM

Basically, it looks fine:

Code:

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

public class GuessingGame {

  public static void main (String argv[]) {
    try {
      myServerSocket = new ServerSocket(Integer.parseInt(argv[0]));
      while (true) {
        Socket communicationSocket = myServerSocket.accept();
        OutputStream out = communicationSocket.getOutputStream();

        PrintStream prints = new PrintStream(out);
        prints.print("Hello world!");

        communicationSocket.close();
      }
    }
    catch(IOException e) {
      System.out.println("IOException" + e.getMessage ());
    }
  }

  private static ServerSocket myServerSocket;

}

I compiled and executed:

Quote:

javac GuessingGame.java
java GuessingGame 999

In another Window, I used "telnet" to talk to the server:

Quote:

telnet 127.0.0.1 999
Hello world!

Connection to host lost.

Minor suggestions:
1. Use "code" blocks when posting code to LQ

2. Name your classes (especially your public classes) in
Pascal case, with a leading "Capital" (an idiom that makes
a class instantly recognizable as a class)

3. Print out the full text of your exception (if you get
an exception, it's definitely useful to capture as much
detail as possible).

4. Everything that *can* be "private" *should* be private.

Good start!

IMHO .. PSM

paulsm4 · 02-22-2006, 11:43 AM

It looks like jlliagre and I were typing responses at exactly the same time. Fortunately, it looks like we're both in complete agreement ;-)

Anyway, smoothdogg00 - a good start!

One other on-line resource you might be interested in is Java Ranch:
http://www.javaranch.com

Your .. PSM

smoothdogg00 · 02-22-2006, 12:12 PM

Thanks a lot, this is all very helpful...

smoothdogg00 · 02-22-2006, 02:30 PM

Ok, I have the game completed, with one problem remaining. When the user is guessing a number via telnet, the server is bringing it in as a string:

Quote:

BufferedReader in = new BufferedReader(new InputStreamReader(communicationSocket.getInputStream()));

String s = (in.readLine()).toString();
guess = Integer.parseInt(s);

the string is also bringing in the "backspace" character, so that it doesn't recognize the number when calling the Integer.parseInt(). Is there any way around this, either so that it doesn't read the delete characters, or formats the string within the program so that it adjusts accordingly?

jlliagre · 02-23-2006, 12:34 AM

Is it a backspace or a delete character ?
Why is this character received ?

smoothdogg00 · 02-23-2006, 09:21 AM

So, telnet is communicating with my server. So if I put in 25 when I meant 26 and then I press backspace and hit 6, the pattern goes to the server as 25<backspace>6. Its minor, but if you know a way to fix it that would be great.

german · 02-23-2006, 10:16 AM

To fix it, what I would to is create a simple program on the side that prints out the character code for the backspace key with in.read(); then you can do some string manipulation so that when you receive that keycode, you know they pressed backspace, and delete the last digit entered if the string length is > 0. This program will tell you what the character code you typed into telnet is:

Code:

import java.io.InputStream;
import java.net.ServerSocket;
import java.net.Socket;

public class SimpleServer {
    public static void main(String[] args) throws Exception {
        ServerSocket serversock = new ServerSocket(12345);
        
        Socket sock = serversock.accept();
        InputStream in = sock.getInputStream();
        int n;
        while((n = in.read()) != '\n') {
            System.err.println(n);
        }
    }
}

HTH

B.

smoothdogg00 · 02-23-2006, 11:08 AM

Sounds great, thanks a lot!