Network Concept in Java

***NETWORKING***

*Networking: A Network is an inter connection of computers and it is generally a combination of client and server machines.

A client machine is that machine which Receives information from the network.

A server machine is that machine which sends information on to the network.

To make communication between two different machines on a network they follow a 

protocol.

A protocol is a standard or a set of Rules that must be followed to make communication possible between the difference machines of a networks.

Ex: htp, ftp, tcp/ip, smtp, nntp, pop and etc.

Very machine on a network will be Identify by a u-nick number called as ‘IP Address’.

Port number is a u-nick identification given to very program running on a system.

Ex: 1 to 65536 (Range of port numbers)            

Shoket is an end point of communication.

Both the client and server machine Requires of shoket for communication.

To create a shoket in a client machine to use a shoket class.

To create a shoket in a server machine we use a server shoket class.

Both the shoket and server shoket class are available in “java.net package” (network package).

                                                                                                              

Client IP Address port NO            DNS->Domain Naming Service ex: gmail.com

//program Server

import java.net.*;

import java.io.*;

class Server{

public static void main(String[] args) throws IOException{

//creating the server side socket with 222 as the server program port no.

ServerSocket ss = new ServerSocket(222);

//waiting for the client and accepting the client side socket

Socket s = ss.accept();

//getting the client socketoutputstream

OutputStream out = s.getOutputStream();

//connecting the client outputstream to the printstream

printStream ps = new printStream(out);

//sending data to the client

ps.println(“hai”);

ps.println(“hello h r u?”);

ps.close(); //closing the connection

            }

}

//program is a client side

import java.net.*;

import java.io.*;

class Client{

public static void main(String[] args)throws Exception{

//creating a client side socket by specifying the server machine

//ip address and server program port no.

Socket s = new Socket(“localhost”,222);

//getting the inputStream associated clientSocket

InputStream in = s.getInputStream();

//connecting theinputstream to the br to read the data line by line

BufferedReader br = new BufferedReader(new InputStreamReader(in));

//reading the data from server and display the data in the client

while(str! = null){

System.out.println(str);

str = br.readLine();

            }

br.close(); //closing the connection

            }

}

To make networking(communication) we need to write tow programs one for the server and the other for the client machine.

This networking program is called also socket programming.

To execute the network programs we required two commands prompts one for the server and other client.

Always the server program is execute the first and wait for the client request.

Otherwise we get a runtime exception is called “connect exception”.

Default IP address = “127.0.0.1” (standard machine)

//Two way communication between client and server

import java.net.*;

import java.io.*;

class ServerApp{

public static void main(String[] args) throws IOException{

//creating the server side socket with 9999 as the server program port number

ServreSocket ss = new ServerSocket(9999);

//waiting for the client and accessing the client side socket

Socket s = ss.accept();

//stream for reading data from client

InputStream in = s.getInputStream();

BufferedReader br = new BufferedReader(new InputStreamReader(in));

//Stream for reading data from keyboard

BufferedReader br = new BufferedReader

                                                            (new InputStreamReader(System.in));

//stream for sending data to the client

OutputStream out = s.getOutputStream();

printStream ps = new printStream(out);

//sending and receiving data from client

while(true){

String str, msg;

while((str = br.readLine())! = null){

System.out.println(str);

msg = kb.readLine();

ps.println(msg);

            }

//releasing the resources

br.close();

kb.close();

ps.close();

System.exit(0);

                   } //end of while

          } //end of main()

} //end of class

// Client program

import java.net.*;

import java.io.*;

class ClientApp{

public static void main(String[] args) throws IOException{

//creating a socket in client machine by specifying the server machine

//IP address andserver program port no

Socket s = new Socket(“localhost”, 9999);

//Stream for reading data from keyboard

BufferedReadered kb = new BufferedReadered

                                                (new InputStream(System.in));

OutputStream out = s.getOutputStream();

printStream ps = new printStream(out);

//Stream for reading data from the server

InputStream in = s.getInputStream();

BufferedReadered br = new BufferedReadered

                                                          (new InputStreamReader(in));

//reading and sending data into a server

String str, msg;

while(!(str = kb.readLine()), equals(“bye”)){

ps.println(str);

msg = br.readLine();

System.out.println(msg);

          }

//reading the resources

kb.close();

ps.close();

br.close();

                        }

            }

}

Note: Instead of using local hosts we can use 127.0.0.1, which is default IP address of a standalone system.

         Server socket                  Socket

          Receive                                                                                         Keyboard

          Displaying                                                                                    Sending

          Reading data from kb                                                              Receiving

          Sending                                                                                        Displaying