Transcript Slide 1
CHAPTER-3
NETWORKING
PROGRAMMING
Network represents interconnection of computers &
devices either by cable or satellite link where no
cable is needed.
Client- receives service.
Server- provides service.
Reuirement for network:
Hardware
Software
protocol
Networking Basics
TCP/IP suite
UDP
Port & socket
URL
The TCP/IP protocol suite ( Internet Protocol Suite)
is a collection of protocols that collectively provides
the data transport services used on the Internet.
They provide a robust and efficient mechanism for
moving data between machines across computer
networks.
The suite is split into five layers
TCP/IP Five Layer Model
Application Layer - interfaces between application
processes and transport layer services on host
computer.
Transport Layer - determines how to use the network
layer to provide a virtual point-to-point connection
between source and destination.
TCP segments
Network/Internet Layer - layer by which data packets
are routed from source to destination.
Datagrams
Data Link Layer - provides data transfer control across
the physical layer
Physical Layer - the actual physical medium used for
the transfer (e.g. cables, Infra red and microwave)
IP address
It is unique identification number assigned to each
computer.
Contains four integr numbers in range 0 to 255.
Separated by dot.
Address mapped to easy remember site name.
Like, www.yahoo.com -67.195.160.76
Mapping service is called DNS(Domain Name
Service.)
Protocols
HTTP (Hyper Text Transfer Protocol) – transfer web
pages from one computer to another on internet.
FTP (File Transfer Protocol)- download & upload
files from & to the server.
SMTP (Simple Mail Transfer Protocol)- sending
mails on network.
POP (Post Office Protocol)- receives mails into
mailboxes.
UDP
Protocol that transfers data in connection less &
unreliable manner on network.
Does not maintain record of no. Of bits delivered or
received on network.
During transmission data may be lost.
Faster.
Utilizes for images, video,audio files transfer over
network.
Port & Socket
Port is 16 bit number to identify a process on
machine.
Socket is logical connecting point between client &
server that allows communication between two hosts
over network.
Socket contains a port number & IP address.
IP address identifies machine & port number
identifies process on that machine.
A distinct port number is used between 0 to 65535.
80- HTTP
109-POP
21-FTp
25-SMTp
23-Telnet for remote login.
Java.net package
URL
Represents address to access some information or
resource on interent.
Example:
http://www.dreamtech.com:80/index.html
Protocol:http
IP adress or sever name:www.dreamtech.com
Port number:80
File resource: index.html
TCP
UDP
Reliability: TCP is connection-oriented
protocol. When a file or message send it
will get delivered unless connections
fails. If connection lost, the server will
request the lost part. There is no
corruption while transferring a
message.
Ordered: If you send two messages
along a connection, one after the other,
you know the first message will get
there first. You don't have to worry
about data arriving in the wrong order.
Reliability: UDP is connectionless
protocol. When you a send a data or
message, you don't know if it'll get
there, it could get lost on the way. There
may be corruption while transferring a
message.
Ordered: If you send two messages out,
you don't know what order they'll arrive
in i.e. no ordered
TCP VS. UDP
TCP
eavyweight: - when the low level parts
of the TCP "stream" arrive in the wrong
order, resend requests have to be sent,
and all the out of sequence parts have
to be put back together, so requires a
bit of work to piece together.
Streaming: Data is read as a "stream,"
with nothing distinguishing where one
packet ends and another begins. There
may be multiple packets per read call.
UDP
Lightweight: No ordering of messages,
no tracking connections, etc. It's just fire
and forget! This means it's a lot quicker,
and the network card / OS have to do
very little work to translate the data back
from the packets.
Datagrams: Packets are sent individually
and are guaranteed to be whole if they
arrive. One packet per one read call.
Networking Programming
import java.io.*;
import java.net.*;
class Address
{
public static void main(String args[ ]) throws
IOException
{
//accept name of website from keyboard
BufferedReader br = new
BufferedReader(new
InputStreamReader(System.in));
System.out.print("Enter a website name: ");
String site = br.readLine();
try{
//getByName() method accepts site name and
returns its IP
}
//Address
InetAddress ip = InetAddress.getByName(site);
System.out.println("The IP Address is: "+ ip);
}catch(UnknownHostException ue)
{
System.out.println("Website not found");
}
}
URL class
import java.net.*;
class MyURL
{
public static void main(String args[ ]) throws Exception
{
URL obj = new
URL("http://dreamtechpress.com/index.html");
System.out.println("Protocol: "+ obj.getProtocol());
System.out.println("Host: "+ obj.getHost());
System.out.println("File: "+ obj.getFile());
System.out.println("Port: "+ obj.getPort());
System.out.println("Path: "+ obj.getPath());
System.out.println("External form: "+
obj.toExternalForm());
}
}
import java.io.*;
import java.net.*;
import java.util.*;
class Details
{
public static void main(String args[ ]) throws Exception
{
//pass the site url to URL object
URL obj = new URL("http://www.yahoo.com/index.html");
//open a connection with the site on Internet
URLConnection conn = obj.openConnection();
//display the date
System.out.println("Date: "+ new Date(conn.getDate()));
//display the content type whether text or html
System.out.println("Content-type: "+
conn.getContentType());
//display expiry date
System.out.println("Expiry: "+
conn.getExpiration());
//display last modified date
System.out.println("Last modified: "+ new
Date(conn.getLastModified()));
//display how many bytes the index.html
page has
int l = conn.getContentLength();
System.out.println("Length of content: "+ l);
if(l == 0)
{
System.out.println("Content not available");
return;
}
else {
int ch;
InputStream in = conn.getInputStream();
//display the content of the index.html page
while((ch = in.read())!= -1)
System.out.print((char)ch);
}
}
}
Output
Date: Wed Aug 07 11:00:14 IST 2013
Content-type: text/html;charset=utf-8
Expiry: 0
Last modified: Thu Jan 01 05:30:00 IST 1970
Length of content: -1
<!DOCTYPE html>
<html lang="en-IN" class="y-fp-bg y-fp-pg-grad
bkt704" style="">
<!-- m2 template -->
<head>
<meta http-equiv="Content-Type"
content="text/html; charset=utf-8">
<title>Yahoo! India</title>
<meta http-equiv="X-UA-Compatible"
content="chrome=1">
<meta name="description" content="Welcome to Yahoo!,
the world's most visited home page. Quickly find what you're
searching for, get in touch with friends and stay in-the-know
with the latest news and information.">
<meta name="keywords" content="yahoo India, yahoo
india home page, yahoo mail india, yahoo search, yahoo,
yahoo messenger, news, finance, sports, entertainment">
<script type="text/javascript">
//Roundtrip
Creating Network Application
Creates server that delivers information.
Creates client that receives information.
Execute client & server program.
Remember:
Sockets are communication channels, which
facilitate inter-process communication. A socket is
one end of a two-way communications link between
two programs running on the network. When a
computer program needs to connect to a local or
wide area network such as the Internet,
It uses a software component called a socket. The
socket opens the network connection for the
program, allowing data to be read and written over
the network. It is important to note that these
sockets are software, not hardware.
Steps for ServerSocket
Create a ServerSocket object with some port
number at server side.
ServerSocket ss = new ServerSocket(777);
2. Make server to wait till client accept the
connection.
Socket s = ss.accept();
3. Attach output stream to server socket using its
getOutputStream() method. It is used by server
socket to send data to client.
OutputStream obj = s.getOutputStream();
1.
4. Take another stream like PrintStream to send data
to client.
PrintStream ps = new PrintStream(obj);
5. Send data to client using println() method of
PritnStream object.
ps.println(str);
6. Close the connection
ps.close();
ss.close();
s.close();
Steps for Client socket
Create Socket at client side using Socket class.
Socket s = new Socket(“IPaddress", 777);
2. Add InputStream to socket to receive data.
InputStream obj = s.getInputStream();
3. Create BufferedReader object to read data.
BufferedReader br = new BufferedReader(new
InputStreamReader(obj));
4. Read data using read() or readLine() method.
read() can read single character at a time, while
readLine() can read string.
1.
str = br.readLine();
5. Close the connection by closing all streams &
sockets.
br.close();
s.close();
Server1.java
import java.io.*;
import java.net.*;
class Server1
{
public static void main(String args[ ])
throws Exception
{
//Create a server socket with some port number
ServerSocket ss = new ServerSocket(777);
//let the server wait till a client accepts connection
Socket s = ss.accept();
System.out.println("Connection established");
//attach output stream to the server socket
OutputStream obj = s.getOutputStream();
//attach print stream to send data to the socket
PrintStream ps = new PrintStream(obj);
//send 2 strings to the client
String str = "Hello client";
ps.println(str);
ps.println("Bye");
//close connection by closing the streams and sockets
ps.close();
ss.close();
s.close();
}
}
Client1.java
mport java.io.*;
import java.net.*;
class Client1
{
public static void main(String args[ ])
throws Exception
{
//create client socket with same port number
Socket s = new Socket("localhost", 777);
//to read data coming from server, attach InputStream to
the socket
InputStream obj = s.getInputStream();
//to read data from the socket into the client, use
BufferedReader
BufferedReader br = new BufferedReader(new
InputStreamReader(obj));
//receive strings
String str;
while((str = br.readLine()) != null)
System.out.println("From server: "+str);
//close connection by closing the streams and
sockets
br.close();
s.close();
}
}
Two way communication
import java.io.*;
import java.net.*;
class Server2
{
public static void main(String args[ ]) throws Exception
{
//Create server socket
ServerSocket ss = new ServerSocket(888);
//connect it to client socket
Socket s = ss.accept();
System.out.println("Connection established");
//to send data to the client
PrintStream ps = new PrintStream(s.getOutputStream());
//to read data coming from the client
BufferedReader br = new BufferedReader(new
InputStreamReader(s.getInputStream()));
//to read data from the key board
BufferedReader kb = new BufferedReader(new
InputStreamReader(System.in));
while(true) //server executes continuously
{
String str,str1;
//repeat as long as client does not send null
string
while((str = br.readLine()) != null) //read from client
{
System.out.println(str);
str1 = kb.readLine();
ps.println(str1); //send to client
}
//close connection
ps.close();
br.close();
kb.close();
ss.close();
s.close();
System.exit(0); //terminate
application
} //end of while
}
}
Client2.java
import java.io.*;
import java.net.*;
class Client2
{
public static void main(String args[ ])
throws Exception
{
//Create client socket
Socket s = new Socket("localhost", 888);
//to send data to the server
DataOutputStream dos = new
DataOutputStream(s.getOutputStream());
//to read data coming from the server
BufferedReader br = new BufferedReader(new
InputStreamReader(s.getInputStream()));
//to read data from the key board
BufferedReader kb = new BufferedReader(new
InputStreamReader(System.in));
String str,str1;
//repeat as long as exit is not typed at client
while(!(str = kb.readLine()).equals("exit"))
{
dos.writeBytes(str+"\n"); //send to server
str1 = br.readLine(); //receive from server
System.out.println(str1);
}
//close connection.
dos.close();
br.close();
kb.close();
s.close();
}
}
Retrieve file
import java.io.*;
import java.net.*;
class FileServer
{
public static void main(String args[ ]) throws Exception
{
//create server socket
ServerSocket ss = new ServerSocket(8888);
//make the server wait till a client accepts connection
Socket s = ss.accept();
System.out.println("Connection established");
//to accept file name from client
BufferedReader in = new BufferedReader(new
InputStreamReader(s.getInputStream()));
//to send file contents to client
}
DataOutputStream out = new DataOutputStream(s.getOutputStream());
//read the filename from the client
String fname = in.readLine();
FileReader fr = null;
BufferedReader file = null;
boolean flag;
//create File class object with filename
File f = new File(fname);
//test if file exists or not
if(f.exists()) flag = true;
else flag = false;
//if file exists, send "Yes" to client, else send "No"
if(flag == true) out.writeBytes("Yes"+"\n");
else out.writeBytes("No"+"\n");
if(flag == true)
{
//attach file to the FileReader to read data
fr = new FileReader(fname);
//attach FileReader to BufferedReader
file = new BufferedReader(fr);
String str;
//read from BufferedReader and write to
DataOutputStream
while((str = file.readLine()) != null)
{
out.writeBytes(str+"\n");
}
file.close();
out.close();
in.close();
fr.close();
s.close();
ss.close();
}
}
myfile.txt
UDP
UDP transfers datagrams from a process running in
source host to other process running in destination
host.
Each datagram needs destination address.
Datagram communication through java.net package
classes:
DatagramPacket
DatagramSocket
DatagramPacket is used for creating packets or
datagrams.
Different datagrams travel through different route,
may arrive in any order and their delivery is not
guaranteed in UDP.
DatagramSocket is used for sending & receiving
datagram packets over network.
A datagram socket provides an endpoint & methods
to send and receive datagram packets over a
network.
//A server that sends a messages to the client
import java.net.*;
class UDPServerEx
{
public static DatagramSocket mySocket;
public static byte myBuffer[]=new byte[2000];
public static void serverMethod() throws Exception
{
int position=0;
while(true)
{
int charData=System.in.read();
UDP server
switch(charData)
{
case -1: System.out.println("The execution of the
server has been terminated");
return;
case '\r':break;
case '\n':mySocket.send(new
DatagramPacket(myBuffer,position,InetAddress.getLocalHost(),777));
position=0;
break;
default:
myBuffer[position++]=(byte) charData;
}
}
}
UDP client
//UDPClient - receives and displays messages sent from the
server
import java.net.*;
class UDPClient
{
public static DatagramSocket mySocket;
public static byte myBuffer[]=new byte[2000];
public static void clientMethod() throws Exception
{
while(true)
{
DatagramPacket dataPacket=new
DatagramPacket(myBuffer,myBuffer.length);
public static void main(String args[]) throws
Exception
{
System.out.println("Please enter some text here");
mySocket=new DatagramSocket(888);
serverMethod();
}
}
mySocket.receive(dataPacket);
System.out.println("Message Recieved :");
System.out.println(new
String(dataPacket.getData(),0,dataPacket.getLength()));
}
}
public static void main(String args[]) throws Exception
{
System.out.println("You need to press CTRL+C in order to quit");
mySocket=new DatagramSocket(777);
clientMethod();
}
}
Content Handler & Protocol Handler
Content handler is java object for parsing the content
of web page and showing it in web browser window,
at client side.
Every new web page type, such as Portable Network
Graphics (PNG) format, jpg, doc, audio,
is
associated with content handler.
All content handler extends java.net.Content
Handler class.
Content hadler is invoked through getContent()
method of URLConnection class.
The job of content handler to read data provided by
protocol handler.
Protocol handlers are responsible for how data
arrives at host.
Suppose data delivered from network in compressed
form , it is responsibility of protocol handler to
unpack data before providing it to content handler.
try{
URL u= new URL(http://web/Hi.jpg);
Image i= (Image)u.getContent();
}
Catch(Exception e)
{
e.printStackTrace();
}
In code from Url string firsat we find protocol used.
Here it is HTTP, so HTTP protocol handler is
responsible for opening the connection with host &
transmitting requested data.
After connection establishing, protocol handler finds
requested file Multipurpose Internet Mail Extension
(MIME) type.
Protocol handler considers file extension which is
.jpg here.
Then content handler is responsible for MIME type
invocation & then required object I constucted.
Here it returns Image type object, which is returned
by getContent() method.