Java Code House

Today I will tell you how you can send a HTTP request from your simple Java program and then read the data(HTML) sent from the server. This is actually the process which is carried out by browsers when you type the url in its address bar. The browser receives the data and then parses and displays it. Here we will omit the parsing and only print the data received from server on the console. The request to the url here is a HTTP GET request. The following classes are used
java.net.URL : This class represents the Uniform Resource Locator and points to a resource. Here we will use openConnection() method to connect to the url and get a URLConnection reference.
java.ney.URLConnection : The abstract class URLConnection is the superclass of all classes that represent a communications link between the application and a URL. We will call getInputStream() to get a stream to that url which is used for reading data from url or server.
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import java.net.URL;
import java.net.URLConnection;
import java.io.*;

public class URLConnectionReader {
  public static void main(String[] args) throws Exception {
    URL url = new URL(args[0]);  //url read from command line
    URLConnection c = url.openConnection();  //connecting to url
    BufferedReader in = new BufferedReader(new InputStreamReader(c.getInputStream()));  //stream to resource
    String str;
    while ((str = in.readLine()) != null)   //reading data
       System.out.println(str);  //printing data read from url to console
    in.close();  //closing stream
  }
}

Today I am going to post programs related with networking. Actually today I am going to implement a connectionless packet delivery service using datagram packets. Each machine will be routed from one machine to another solely on the information contained in the packet. But to deliver this datagrams we will have to open a datagram socket programatically. This socket can be used for both sending and receiving datagrams. But to deliver packets we must know the IP address and port number. The following classes will be used for this -->
java.net.InetAddress : This class is used to get the IP address based on the host name using its static method getByName() .
java.net.DatagramSocket : This class represents a socket for sending and receiving datagram packets. Where possible, a newly constructed DatagramSocket has the SO_BROADCAST socket option enabled so as to allow the transmission of broadcast datagrams. In order to receive broadcast packets a DatagramSocket should be bound to the wildcard address.
java.net.DatagramPacket : Each message is routed from one machine to another based solely on information contained within that packet. Multiple packets sent from one machine to another might be routed differently, and might arrive in any order. Packet delivery is not guaranteed.
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/* THE RECEIVER CODE */

import java.net.DatagramSocket;
import java.net.DatagramPacket;
import java.util.Scanner;

public class Receiver{
   public static void main(String[] args)throws Exception{
     String str="";
     Scanner sc=new Scanner(System.in);
     System.out.print("Enter port : ");
     int PORT=sc.nextInt(); //receiver port
     DatagramSocket rsock=new DatagramSocket(PORT); //creating socket
     do{
       byte buf[]=new byte[512];
       DatagramPacket packet=new DatagramPacket(buf,512);
       rsock.receive(packet); //receiving packets
       str=new String(buf); //converting to string
       System.out.println("Received : "+str);
     }while(!str.contains("bye")); //goes on till bye is sent

     rsock.close();  //closing socket
   }
}

/* THE SENDER CODE */

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.DatagramSocket;
import java.net.DatagramPacket;
import java.net.InetAddress;

public class Sender{
   public static void main(String[] args)throws Exception{
     BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
     DatagramSocket ssock=new DatagramSocket(); //binding socket to any 
available port
     System.out.print("Enter host name : ");
     String str=br.readLine();  //getting host-name
     System.out.print("Enter receiver's port : ");
     int PORT=Integer.parseInt(br.readLine()); //getting receiver port
     InetAddress addr=InetAddress.getByName(str); //getting IP of receiver

     do{
       System.out.print("Sending : ");
       str=br.readLine(); //getting data to be sent
       byte buf[]=str.getBytes();
       //creating packet with receiver info inside packet
       DatagramPacket packet=new DatagramPacket(buf,buf.length,addr,PORT);
       ssock.send(packet);  //sending packet
     }while(!str.equals("bye"));
     
     ssock.close();  //closing socket
   }
}
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Screenshots of output

Receiver

Sender

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