A Simple Java TCP Server and TCP Client

Following up on my previous post, we also had to demonstrate a sample Java TCP Server and TCP Client. The code footprint pretty small and it gives you a good idea about how a TDP Server opens up a port, and then the TCP Client sends or receives data from that port.

This is a good page on the differences between TCP and UDP.

To compile these, install Java JDK to your system. Then compile the program with “javac TCPClient.java” – this will create a TCPClient.class. Execute the file with “java TCPClient” – leave off the .class, or you will get the error: “Exception in thread “main” java.lang.NoClassDefFoundError”.

Here is sample code for a simple Java TCP Server/Client, originally from Computer Networking: A Top Down Approach, by Kurose and Ross:

TCPServer.java

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

class TCPServer
{
   public static void main(String argv[]) throws Exception
      {
         String clientSentence;
         String capitalizedSentence;
         ServerSocket welcomeSocket = new ServerSocket(6789);

         while(true)
         {
            Socket connectionSocket = welcomeSocket.accept();
            BufferedReader inFromClient =
               new BufferedReader(new InputStreamReader(connectionSocket.getInputStream()));
            DataOutputStream outToClient = new DataOutputStream(connectionSocket.getOutputStream());
            clientSentence = inFromClient.readLine();
            System.out.println("Received: " + clientSentence);
            capitalizedSentence = clientSentence.toUpperCase() + '\n';
            outToClient.writeBytes(capitalizedSentence);
         }
      }
}

and the client:

TCPClient.java

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

class TCPClient
{
 public static void main(String argv[]) throws Exception
 {
  String sentence;
  String modifiedSentence;
  BufferedReader inFromUser = new BufferedReader( new InputStreamReader(System.in));
  Socket clientSocket = new Socket("localhost", 6789);
  DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream());
  BufferedReader inFromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
  sentence = inFromUser.readLine();
  outToServer.writeBytes(sentence + '\n');
  modifiedSentence = inFromServer.readLine();
  System.out.println("FROM SERVER: " + modifiedSentence);
  clientSocket.close();
 }
}

If you have any questions, please leave a comment!

Tagged: code, Code Samples, java, networking, tcp

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By Dave Drager on September 18, 2008 at 1:01 pm

New blog post: A Simple Java TCP Server and TCP Client http://tinyurl.com/3vt9x9
By Dave Drager on March 29, 2010 at 2:11 pm

New Post: A Simple Java TCP Server and TCP Client http://bit.ly/5L5Kbt

14 Comments

Michel

Hi

simply what I needed

Is it possible to add persistence to this example (inserting the data into a Firebird db, the data is in binary format)?

Best regards,
Michel

Posted October 15, 2008 at 12:17 pm | Permalink
The Professor

I wrote my first Java socket client/server application in 1993! So this code looks mighty familiar.

However, servers I’ve written subsequently all implement Thread so you can build a pool of connections available and new ones are spawned as traffic arrives. A small point, but one that makes this code scalable.

Posted October 21, 2008 at 2:14 pm | Permalink
Floatrolo

Hi, Congratulations to the site owner for this marvelous work you’ve done. It has lots of useful and interesting data.

Posted June 4, 2009 at 6:58 pm | Permalink
Venessa

you forgot

import java.net.Socket;
and
public static void main(String[] args) throws IOException {

anyway, thanks, exactly what I needed

Posted June 9, 2009 at 8:22 am | Permalink
vince

Hi, there are nice work for a simple and easy understand server client example.
However, I have some question which is:
what is the use of ‘\n’ in
outToServer.writeBytes(sentence + ‘\n’);

i try to remove it and the program won’t work. Can you please do simple explain to me?
Thanks

Vince

Posted July 20, 2009 at 4:44 am | Permalink
Dave

@vince: \n stands for new line. This lets the TCP Server know that your sentence has been sent. Let me know if you have any other questions.

Posted July 20, 2009 at 6:32 am | Permalink
tam

i need java code that display the area of a circle using TCP server and TCPclient

Posted September 10, 2009 at 9:05 am | Permalink
grüner tee

The Java Tutorials are practical guides for programmers who want to use the Java programming language to create applications.

Posted December 5, 2009 at 2:44 pm | Permalink
sara

HI,,,,
I have cpyied the TCPClient code on my pc
and the TCPServer code on another pc but nothing happened
“there is no error”.
please reply

Posted January 10, 2010 at 2:20 pm | Permalink
AbdelAziz

Thanks man…
it really helps…
but I would like to modify this code so that the client sends a request to the server to “add 10 20″ then the server will calculate it and send back 30 I will try to do.. thanks dude

Posted March 20, 2010 at 4:26 pm | Permalink
Mike

I’m trying to figure out how to add a login mechanism to this code. I also want the server to be the one that grants access not the client for obvious reasons. I’m sending the user/pass through the same socket that will be used for communication, yet my program crashes right at the point of asking for the password. User name gets through no problem. I believe it is some kind of connection reset error.

Posted March 28, 2010 at 9:34 am | Permalink
arthika

Hi…
I want chatting program in java as client side and server side
pls help me

Posted July 6, 2010 at 4:50 am | Permalink
arthika

Hi…
i need chatting program in java
pls help me

Posted July 6, 2010 at 4:53 am | Permalink
Dan

I run server than client… nothing happens…………

Posted July 31, 2010 at 7:35 pm | Permalink