Networking in Java

By – Gaurav
GOFORELEARNING@GMAIL.COM
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There are 3 requirements to establish a network:
 Hardware: includes the computers, cables, modems,
hubs, etc
 Software: includes program to communicate between
server and clients
 Protocols: represent a way to establish connection
and helps in sending and receiving data in a standard
format.
By – Gaurav

 TCP/IP is a standard protocol model used on any
network.
 TCP/IP model has got the following 5 layers:
1. Application layer
2. TCP
3. IP
4. Data link layer
5. Physical layer
By – Gaurav

1. Application layer
◦ Application layer is the topmost layer.
◦ This layer receives data from the application and formats the
data.
◦ it sends that data to the next layer called TCP in the form of
continuous stream of bytes.
2. TCP
◦ Receives data from Application layer,
◦ TCP will divide it into small segments called ‘packets’. A
packet contains a group of bytes of data.
◦ These packets are then sent to next IP layer
By – Gaurav

3. IP layer
◦ IP layer inserts the packets into envelopes called
‘frames’.
◦ Each frame contains a packet:
 IP address of destination computer,
 IP address of source computer,
 some additional bits useful in error detection and
correction.
◦ These frames are then sent to Data link layer
By – Gaurav

4. Data Link Layer
◦ Receives frames from the IP Layer.
◦ Dispatches them to correct destination computer
on the network.
5. Physical Layer
◦ This layer is used to physically transmit data on
the network using the appropriate hardware.
By – Gaurav

 TCP/IP takes care of number of bits sent and weather
all the bits are received duly by the destination
computer. so it is called ‘connection oriented reliable
protocol’.
 This protocol is highly suitable for transporting data
reliably on a network.
 Almost all the protocol on Internet uses TCP/IP
model internally.
By – Gaurav

IP Address:
 An IP address is a Unique Identification number given
to every computer on the network.
 It contain four integer numbers in the range of 0 to
255 and separated by a dot as 209.191.88.254
DNS (domain naming service)
 DNS is the mapping of IP addresses to human
readable names.
FTP (file transfer protocol)
 Useful to download or upload files from and to the
server.
By – Gaurav

HTTP(Hypertext transfer protocol)
 Most widely used protocol on Internet, which is used
to transfer web pages (.html) from one computer to
anoher computer on Internet.
SMTP (simple mail transfer protocol)
 Useful to send mails on network.
POP(post office protocol)
 Useful to receive mails into the mailboxes.
By – Gaurav

 Protocol that transfer data in a connection less and
unreliable manner.
 It will not check how many bits are sent or received at
the other side during transmission of data.
 UDP is used to send images, audio files and video files.

 Sockets provide the communication mechanism
between two computers using TCP.
 A client program creates a socket on its end of the
communication and attempts to connect that socket to
a server.
 When the connection is made, the server creates a
socket object on its end of the communication.
By – Gaurav

 The client in socket programming must know two
information:
◦ IP Address of Server, and
◦ Port number.
 We should use a new port number for each new
socket.
 A socket, at server side is called ‘server socket’ and
is created using ServerSocket class in Java.
 A socket, at client side is called ‘socket’ and is
created using Socket class in Java.
By – Gaurav

 getByName() method of InetAddress class of java.net
package.
By – Gaurav
getByName()
Host Name / Server
Name
InetAddress/
IP Address

 URL URL(Uniform Resource Locator) represents the
address that is specified to access some information or
resources on world wide web.
 http://www.goforelearning.com:80/index.html
 The URL contains 4 parts
◦ The protocol to use (http://).
◦ The server name or IP address of the server(www.goforelearning.com)
◦ The third part represents ports number, which is optional (:80)
◦ The last part is the file name or directory name that is referred
(index.html).
 URL is represented by a class ‘URL’ in java.net package.
URL obj = new URL(String protocol, String host, int port,
String path);
By – Gaurav

URLConnection Class is useful to actually connect
to a website or resource on a network and get all
the details of the website.
For example,
 To know the details of www.yahoo.com
◦ We should pass the URL to the object of URL class.
◦ Then using openConnection() method, we should
establish a contact with the site on Internet.
◦ This method return URLConnection object.
◦ Then using URLConnection class method, we can
display all the details of the website and also content
of the webpage whose name is given in URL.
By – Gaurav

By – Gaurav
Server
Server
Socket
OutputStreamPrintStream
ServerSocket ss = new ServerSocket (8080);
Socket s = ss.accept();
OutputStream obj = s.getOutputStream();
PrintStream ps = new PrintStream (obj);
ps.println(str);
ss.close();
s.close()
ps.close

By – Gaurav
Socket
BufferedReaderInputStream
Socket s = new Socket (“IPAddress” , port number) ;
InputStream obj = s.get InputStream();
BufferedReader br = new BufferedReader (new InputStreamReader(obj));
Str = br.readLine();
br.close();
s.close()
Client
In case you don’t have your computer in a network, you have to run
both the server and client programs in the same system. In that case,
you can use localhost in place of IPAddress. The work localhost
represents that the server is also locally available in the same system.

We need additional streams both at server and client.
 InputStream obj = s.getInputStream();
 BufferedReader br = new BufferedReader (new
InputStreamReader(obj));
 OutputStream obj = s. getOutputStream();
 DataOutputStream dos = new DataOutputStream(obj);
writeBytes() method of DataOutputStream can be used to
send strings in form of groups of bytes.

Thank You !
Go GrEEN !
Save Environment!
For Any Queries: GOFORELEARNING@GMAIL.COM

Networking in Java

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