EXP 5 CN

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Connection Oriented Iterative server

An iterative server iterates through each client, handling it one at a time. 
  
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)
Communication
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.

// 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);
    }
}

·         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.
Server Side Programming
In the iterative server example, a single server job handles all incoming connections and all data flows with the client jobs.  When the accept() API completes, the server handles the entire transaction. 

·         Server application makes a ServerSocket on a specific port which is 5000. This starts our Server listening for client requests coming in for port 5000.
·         Then Server makes a new Socket to communicate with the client.
socket = server.accept()
·         The accept() method blocks(just sits there) until a client connects to the server.
·         Then we take input from the socket using getInputStream() method. Our Server keeps receiving messages until the Client sends “Over”.
·         After we’re done we close the connection by closing the socket and the input stream.
·         To run the Client and Server application on your machine, compile both of them. Then first run the server application and then run the Client application.
  
// 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);
    }
}

Advantages:
Simple
Reduced network overhead
Less CPU intensive
Higher single-threaded transaction throughput
Disadvantages:
Severely limits concurrent access
Server is locked while dealing with one client




Output:
To run on Terminal or Command Prompt
Open two windows one for Server and another for Client
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.
  

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