Java NetWorking(URL , SOCKET(TCP/IP),DATAGRAMS)- II

 

NetWorking(URL , SOCKET(TCP/IP),DATAGRAMS)- II

 

Datagrams

Datagrams are bundles of information passed between machines.

java implements Datagrams on top of the UDP protocol  by using two classes. The Datagrams Packet object is the data container,while the Datagrams Socket is the mechanism used to send or receive the Datagram Packets.

Datagrampacket

 Datagrampacket defines several constructors.

Datagrampacket(byte data[],int size)

Datagrampacket(byte data[],int offset,int size)

Datagrampacket(byte data[],int size,InetAddress ipAddress,int port)

Datagrampacket(byte data[],int offset,int size,Inet Address ipAddress,int port)

The first constructor specifies a buffer that will receive data,and the size of a packet.it is used for receiving data over a Datagramsocket.The second form allows you to specify an offset into the buffer at which data will be stored.the third form specifies a target address and port,which are used by a Datagramsocket to determine where the data in the packet will be sent.  the fourth form transmit packets beginning at the specified offset into the data.

InetAddress getAddress( )-> Returns the destination InetAddress,typically used for sending.

int getport( )->Returns the port number.

byte[]getdata( )->Return the byte array of data contained in the datagram .mostly used to retrieve data from the datagram after it has been received.

int getLength( )->Return the length of the valid contained inthe byte array that would be returned from the getdata() method.this typically does not equal the length of the whole byte array.

Datagramsocket

The Datagramsocket represents a connectionless datagram socket.this class works with the DatagramPacket class to provide for communication using the UDP protocol . it provides two constructors,the programmer can specify a port to use or allow the system  to randomly   use one.

Methods:The most important methods are -send() and receive().Each takes as an argument an appropriately constructed Datagrampacket.In the case of the send() method,the  data contained in the packet is sent to the specified host and the port.The receive() method will block the execution until a packet is received by the underlying socket,at which time the data will be copied into the packet provided.

Server Program

File name: EchoServer.java

import java.net.*;

import java.io.*;

public class EchoServer{

static final int serverPort=1026;

static final int packetSize=1024;

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

DatagramPacket packet;

DatagramSocket socket;

byte[] data;

int clientPort;

InetAddress address;

String str;

socket=new DatagramSocket(serverPort);

for(;;){

data=new byte[packetSize];

packet=new DatagramPacket(data,packetSize);

System.out.println("Waiting to receive the packets");

try{

socket.receive(packet);

}

catch(IOException ie){

System.out.println("Could not Receive:"+ie.getMessage());

System.exit(0);

}

address=packet.getAddress();

clientPort=packet.getPort();

str=new String(data,0,0,packet.getLength());

System.out.println("Message: "+str.trim());

System.out.println("From: "+address);

packet=new DatagramPacket(data,packetSize,address,clientPort);

try{

socket.send(packet);

}

catch(IOException ex){

System.out.println("Could not Send"+ex.getMessage());

System.exit(0);

}

}

}

}

 

Client Program

File name: EchoClient.java

import java.net.*;

import java.io.*;

public class EchoClient{

static final int serverPort=1026;

static final int packetSize=1024;

public static void main(String args[]) throws UnknownHostException,SocketException{

DatagramSocket socket;

DatagramPacket packet;

InetAddress address;

String messageSend;

String messageReturn;

byte[] data;

if(args.length!=2)

{

System.out.println("Usage Error: Java EchoClient <Server name><Message>");

System.exit(0);

}

address=InetAddress.getByName(args[0]);

socket=new DatagramSocket();

data=new byte[packetSize];

messageSend=new String(args[1]);

messageSend.getBytes(0,messageSend.length(),data,0);

packet=new DatagramPacket(data,data.length,address,serverPort);

System.out.println("Trying to Send the packet");

try{

socket.send(packet);

}

catch(IOException ie){

System.out.println("Could not Send:"+ie.getMessage());

System.exit(0);

}

packet=new DatagramPacket(data,data.length);

try{

socket.receive(packet);

}

catch(IOException iee){

System.out.println("Could not receive: "+iee.getMessage());

System.exit(0);

}

messageReturn=new String(packet.getData(),0);

System.out.println("Message Returned: "+messageReturn.trim());

}

}

Open Two CMD. Run One Cmd Server , and another Cmd Client.First Run Server.After Run Client Program.

Output

Before connecting EchoClient , EchoServer Output

 

After connecting EchoClient , EchoServer and EchoClient Output

 

URL

URL - Uniform resource locator

Urls to access HTML pages from the Web.

Host Name- The name of the machine on which the resources lives.

File Name-The pathname to the file on the machine.

Port Number- The port number to which to connect

Reference- A Reference to a named anchor within a resource that usually identifies a specific location within a file

 

Parsing a URL

The URL class provides several methods that let you query URL objects.

getProtocol - Returns the protocol identifier component of the URL

getHost-Returns the host name component of the URL

getPort-Returns the port number component of the URL.

getFile-Returns the filename component of the URL

getRef-Returns the reference component of the URL

Parsing a URL

File name: ParseURL.java

import java.net.*;

import java.io.*;

public class ParseURL{

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

{

URL aURL=new  URL("http://java.sun.com;80/docs/books/tutorial/intro.html#DOWNLOADING");

System.out.println("protocol="+aURL.getProtocol());

System.out.println("host="+aURL.getHost());

System.out.println("filename="+aURL.getFile());

System.out.println("port="+aURL.getPort());

System.out.println("ref="+aURL.getRef());

}

}

 

Output

 Reading from URLConnection

File name: URLConnectionReader.java

import java.net.*;

import java.io.*;

public class  URLConnectionReader{

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

{

URL yahoo=new URL("http://www.yahoo.com");

URLConnection yc=yahoo.openConnection();

BufferedReader in=new BufferedReader(new InputStreamReader(yc.getInputStream()));

String inputLine;

while((inputLine=in.readLine())!=null)

System.out.println(inputLine);

in.close();

}

}