Making a Client Server application (Socket programming) in java

Article by Haneez Haroon    11 Comments  

The programming languages become handier when the user can create a link between two pieces of compiled codes operating from two different locations.

In this example, a simple server that takes a text string from the client and returned in upper case is discussed. Hope this will give an overall picture about how socket programming work in JAVA.

You do not have to be an expert in Java and all you need is a Java compiler.

Let us get started;

1. Create an empty folder in your C: drive with the name “Tutebox”
2. Create 2 empty JAVA files inside the folder and rename them as:
   1. TCPServer.java
   2. TCPClient.java
   3. Then copy/paste the following codes into those files and save them.
   4. Compile the java files.
      • Open command prompt
      • Type “C:” {enter}
      • Type “cd C:\Tutebox” {enter}
      • Type “javac *.java” {enter}
      • If you have returned to the command prompt, you are ready to run your client server application. (If you do have difficulties please write to us, we would be happy to help you)

or you can simply download TCPClient.java and TCPServer.java from here.

Server side code

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());

System.out.println(“Server waiting for data…”);

clientSentence = inFromClient.readLine();

System.out.println(“Recived from client : ” + clientSentence);

capitalizedSentence = clientSentence.toUpperCase() + ‘\n’;

outToClient.writeBytes(capitalizedSentence);

}

}

}

Client Side code

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()));

System.out.print(“SEND TO SERVER: “);

sentence = inFromUser.readLine();

outToServer.writeBytes(sentence + ‘\n’);

modifiedSentence = inFromServer.readLine();

System.out.println(“FROM SERVER: ” + modifiedSentence);

clientSocket.close();

}

}

You have just created a client server application. Now let us see how it works in real time.

1. Open two command prompts;
2. First command prompt
   • Type “C:”
   • Type “cd C:\Tutebox”
   • Type “java TCPServer”
3. Second command prompt
   • Type “C:”
   • Type “cd C:\Tutebox”
   • Type “java TCPClient”

You are ready to go.
Write some text in any case on the client program and press enter.
Your server, which is running on the other command prompt, will convert it to uppercase and send it back to the clients’ command prompt.

TCP Client Server demo

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