Java Socket Basics(Socket Programming in Java) Part-1(TCP)

Hi friends,
This post is about the Java Socket Programming. I know there are a lot of article and post are available over the internet about Java Socket Programming but all the content like the perquisite of socket programming, example of TCP and UDP is here at one place.

So first question, what is TCP and UDP and what is the difference between these two. See below-

Perquisite:-
There are several things related to socket programming in java which you must not ignore...

• Do not forget to close the stream or socket connection when the related task is done.
• Recommended to use try with resource whenever it is possible.
• If you are not dealing with try with resource, then it is highly recommended to close all the resources and related sockets in finally block.

java.net.SocketException: Too many open files:: 

This is an usual exception which generally thrown by Socket. So the question is What may be the possible reasons for  this exception. So go through the following listings. Possibly...

• You have forgot to close the resources when their task done.
• You have forgot to close socket connection when you done with it.
• May be Number of open file descriptors per process is less than it required by your application.
• TIME_WAIT state(timeout) of your operating system is more than expected. 

Possible ways to deal with 'java.net.SocketException: Too many open files':-

• Do not forget to close the stream or socket connection when the related task is done.
• Recommended to use try with resource whenever it is possible.
• If you are not dealing with try with resource, then it is highly recommended to close all the resources and related sockets in finally block.
• Reduce TIME_WAIT state of your operating system.
• Increase Number of open file descriptors per process in your operating system. You can check Number of open file descriptors per process(In Linux) using ulimit -a command.

TCP Sample:-
We are going to create an small sample which contains two classes.

1. SocketServer.java:- This is a server class. Means this class will serve the purpose of socket connection. ServerSocket is the class which helps for TCP socket connection. This required a system port number on which client can communicate and send data to server.
2. SocketClient.java:- This is client class. This serves the purpose of client which will communicate to server and send data to server. Socket is the class which helps for TCP client connection. This requires Server's IP(URL) and the Server's port number on which Server has open the socket connection.

SocketServer.java

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;

public class SocketSever {

 public static void main(String[] args) {

  try {
   System.out.println("Starting server...");
   ServerSocket serverSocket = new ServerSocket(8086);
   System.out.println("Server started. Waiting for client connection...");
   Socket socket = serverSocket.accept();
   System.out.println("Client connected. Reading data from client...");
   InputStream inputStream = socket.getInputStream();
   OutputStream outputStream = socket.getOutputStream();
   PrintWriter printWriter = new PrintWriter(outputStream, true);
   BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));

   String receiveMessage;
   if ((receiveMessage = reader.readLine()) != null) {
    System.out.println("Data sent from client : " + receiveMessage);
   }
   System.out.println("Sending data back to client..");
   printWriter.println("Hello Client");
   printWriter.flush();
   socket.close();
   serverSocket.close();
   System.out.println("Shuting down server...");
  } catch (Exception e) {
   e.printStackTrace();
  }
 }
}

SocketClient.java

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.net.Socket;

public class SocketClient {
 public static void main(String... strings) {
  try {
   System.out.println("Connecting to server...");
   final Socket socket = new Socket("localhost", 8086);
   System.out.println("Connected to server");

   final OutputStream outputStream = socket.getOutputStream();
   final PrintWriter printWriter = new PrintWriter(outputStream, true);
   final InputStream inputStream = socket.getInputStream();
   final BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));
   System.out.println("Writting data on server...");
   printWriter.println("Hello Server");
   printWriter.flush();
   String receiveMessage;
   System.out.println("Reading data from server...");
   if ((receiveMessage = reader.readLine()) != null) {
    System.out.println(receiveMessage);
   }
   socket.close();
   System.out.println("Closing client connection");
  } catch (Exception e) {
   System.out.println("Server is unable to reach");
   e.printStackTrace();
  }
 }
}

This example works as Client->Server and Server->Client mechanism. Means this example describes two way communication between Client and Server.

Note:- You can modify these classes little bit and this will start working as Chat Application. Just put the read and write logic inside an infinite while loop and send data to server or client after reading the message from console. Please try this yourself and let me know. You gonna develop a Simple Chat Application :)

So this was all about for TCP. In next post we will see a sample about UDP.

Hope this will help you. Suggestions are most welcome. Keep visiting my blog :)