Networking in JAVA

Introduction

A computer network is an interconnected collection of computers. The node of a network communicates others using a wired/wireless medium. This communication is actually carried between two processes residing in two different machines. The processes on one machine initiates the request and another responds to the request and another responds to the requests. The initiator is the client and the responder is the server.

TCP Protocol Suite

The TCP/IP protocol suite contains a number of protocols. Its a four layer model followed by the network s. The internet also follows the same model. The client and server applications created by the user reside at the Application layer. They interact with the transport layer using the socket API. Java provide a package java.net. The transport layer take the data from takes data from application layer (sender) and breaks up in to segment attached the port number used by application to the data and passes in to the network layer. Depending upon the protocols used.

TCP/IP models figure

Socket Programming in Java

Network programming revolves around the concept of sockets. A socket is one end-point of a two-way communication link between two programs running on the network. In Java sockets are created with the help of Socket classes and these class are found in the java.net package. There are separate classes in the java.net package for creating TCP sockets and UDP sockets. The client socket is created with the help of the Socket class and the server socket is created using the ServerSocket class.

socket figure

Syntax

// for tcp client side

Socket s= new Socket (InetAddress adr, int port);

//for server side

ServerSocket ss= new ServerSocket (InetAddress adr, int port)

Step 1 - Creating a Socket on the client side (code):

// importing the usefull package like net and io
import java.net.*;
import java.io.*;
class MySocket {
public static void main(String[] args) {
try {
// using socket class constructor create socket
Socket s = new Socket(InetAddress.getLocalHost(), 15);
System.out.println("your socket is created");
// using method of socket class find the local address
System.out.println("Local Address :" + s.getLocalAddress());
// using method of socket class find the local host
System.out.println("Local Host :" + InetAddress.getLocalHost());
// using method of socket class find the local port number
System.out.println("Local Port :" + s.getLocalPort());
// using method of socket class find the local address
System.out.println("Inet Address :" + s.getInetAddress());
// creating input stream by help of method getInputStream()
InputStream in = s.getInputStream();
// Buffered reader object is created to read strings from the socket.The Byte Stream is converted to character stream using the
InputStreamReader
BufferedReader br = new BufferedReader(new InputStreamReader( in ));
String str = null;
while ((str = br.readLine()) != null)
System.out.println(str);
in .close();
s.close();
// catch exception is printing
} catch (Exception e)
{
System.out.println(e);
}
}
}

Step 2 - Creating a TCP Server (code):

import java.io.*;
import java.net.*;
import java.util.*;
class MyServerSocket
{
public static void main(String[] args)
{
try {
ServerSocket ss=new ServerSocket(15);
while(true)
{
Socket client =ss.accept();
System.out.println("socket is created");
// using method of ServerSocket class find the client address
System.out.println("client inet Address :"+client.getInetAddres());
// using method of ServerSocket class find the client port number
System.out.println("client Port number :"+client.getPort() );
// getting the out put stream to the client socket
OutputStream out=client.getOutputStream();
//gettimg the date so make the object of callender class
Calendar c=Calendar.getInstance();
System.out.println("server date and time :"+c.getTime());
PrintWriter pw = new PrintWriter(out,true);
pw.close();
}
}
catch (Exception e)
{
System.out.println(e);
}
}
}

Output

First the server is started and waits for a client.

Then a Client is started and the output is as follows:

After the client starts then the server output is:

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