Implementation of Tcp socket

Client Side Programming

Establish a Socket Connection

To connect to other machine we need a socket connection. A socket connection means the two machines have information about each other’s network location (IP Address) and TCP port.The java.net.Socket class represents a Socket. To open a socket:

Socket socket = new Socket(“127.0.0.1”, 5000)

·         First argument – IP address of Server. ( 127.0.0.1  is the IP address of localhost, where code will run on single stand-alone machine).

·         Second argument – TCP Port. (Just a number representing which application to run on a server. For example, HTTP runs on port 80. Port number can be from 0 to 65535)

To communicate over a socket connection, streams are used to both input and output the data.

Closing the connection

The socket connection is closed explicitly once the message to server is sent.

In the program, Client keeps reading input from user and sends to the server until “Over” is typed.

Java Implementation

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// A Java program for a Client import java.net.*; import java.io.*;    public class Client {     // initialize socket and input output streams     private Socket socket            = null;     private DataInputStream  input   = null;     private DataOutputStream out     = null;        // constructor to put ip address and port     public Client(String address, int port)     {         // establish a connection         try         {             socket = new Socket(address, port);             System.out.println("Connected");                // takes input from terminal             input  = new DataInputStream(System.in);                // sends output to the socket             out    = new DataOutputStream(socket.getOutputStream());         }         catch(UnknownHostException u)         {             System.out.println(u);         }         catch(IOException i)         {             System.out.println(i);         }            // string to read message from input         String line = "";            // keep reading until "Over" is input         while (!line.equals("Over"))         {             try             {                 line = input.readLine();                 out.writeUTF(line);             }             catch(IOException i)             {                 System.out.println(i);             }         }            // close the connection         try         {             input.close();             out.close();             socket.close();         }         catch(IOException i)         {             System.out.println(i);         }     }        public static void main(String args[])     {         Client client = new Client("127.0.0.1", 5000);     } }

Server Programming

Establish a Socket Connection

To write a server application two sockets are needed.

·         A ServerSocket which waits for the client requests (when a client makes a new Socket())

·         A plain old Socket socket to use for communication with the client.

Communication

getOutputStream() method is used to send the output through the socket.

Close the Connection

After finishing,  it is important to close the connection by closing the socket as well as input/output streams.

// A Java program for a Server import java.net.*; import java.io.*;    public class Server {     //initialize socket and input stream     private Socket          socket   = null;     private ServerSocket    server   = null;     private DataInputStream in       =  null;        // constructor with port     public Server(int port)     {         // starts server and waits for a connection         try         {             server = new ServerSocket(port);             System.out.println("Server started");                System.out.println("Waiting for a client ...");                socket = server.accept();             System.out.println("Client accepted");                // takes input from the client socket             in = new DataInputStream(                 new BufferedInputStream(socket.getInputStream()));                String line = "";                // reads message from client until "Over" is sent             while (!line.equals("Over"))             {                 try                 {                     line = in.readUTF();                     System.out.println(line);                    }                 catch(IOException i)                 {                     System.out.println(i);                 }             }             System.out.println("Closing connection");                // close connection             socket.close();             in.close();         }         catch(IOException i)         {             System.out.println(i);         }     }        public static void main(String args[])     {         Server server = new Server(5000);     } }

1. First run the Server application as ,

$ java Server

Server started
Waiting for a client …

2. Then run the Client application on another terminal as,

$ java Client

It will show – Connected and the server accepts the client and shows,

Client accepted

3. Then you can start typing messages in the Client window. Here is a sample input to the Client

Hello

I made my first socket connection

Over

Which the Server simultaneously receives and shows,

Hello

I made my first socket connection

Over

Closing connection

Notice that sending “Over” closes the connection between the Client and the Server just like said before.