Java Networking step by step Tutorial
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Java Networking is a concept of connecting two or more
computing devices together so that we can share resources.
Java socket programming provides facility to share
data between different computing devices.
Advantage of Java Networking
1.
sharing
resources
2.
centralize
software management
Java
Networking Terminology
The widely used java networking terminologies are
given below:
1.
IP
Address
2.
Protocol
3.
Port
Number
4.
MAC
Address
5.
Connection-oriented
and connection-less protocol
6.
Socket
1) IP Address
IP address is a unique number assigned to a node of a
network e.g. 192.168.0.1 . It is composed of octets that range from 0 to 255.
It is a logical address that can be changed.
2) Protocol
A protocol is a set of rules basically that is
followed for communication. For example:
- TCP
- FTP
- Telnet
- SMTP
- POP
etc.
3) Port Number
The port number is used to uniquely identify different
applications. It acts as a communication endpoint between applications.
The port number is associated with the IP address for
communication between two applications.
4) MAC Address
MAC (Media Access Control) Address is a unique
identifier of NIC (Network Interface Controller). A network node can have
multiple NIC but each with unique MAC.
5) Connection-oriented and connection-less
protocol
In connection-oriented protocol, acknowledgement is
sent by the receiver. So it is reliable but slow. The example of
connection-oriented protocol is TCP.
But, in connection-less protocol, acknowledgement is
not sent by the receiver. So it is not reliable but fast. The example of
connection-less protocol is UDP.
6) Socket
A socket is an endpoint between two way communication.
Visit next page for java socket programming.
Some Important Classes
CLASSES
|
|
CacheRequest
|
CookieHandler
|
CookieManager
|
Datagrampacket
|
Inet
Address
|
ServerSocket
|
Socket
|
DatagramSocket
|
Proxy
|
URL
|
URLConnection
|
Some Important Interfaces
INTERFACES
|
|
CookiePolicy
|
CookieStore
|
FileNameMap
|
SocketOption
|
InetAddress
|
ServerSocket
|
SocketImplFactory
|
ProtocolFamily
|
InetAddress
Inet Address
encapsulates both numerical IP address and the domain name for that address.
Inet address can handle both IPv4 and Ipv6 addresses. Inet Address class has no
visible constructor. To create an inet Address object, you have to use Factory methods.
Three commonly
used Inet Address factory methods are.
1. static InetAddress getLocalHost() throws UnknownHostException
2. static InetAddress getByName (String hostname) throws UnknownHostException
3. static InetAddress[ ] getAllByName (String hostname) throws UnknownHostException
Java TCP
Networking Basics
Typically a client
opens a TCP/IP connection to a server. The client then starts to communicate
with the server. When the client is finished it closes the connection again.
Here is an illustration of that:
A client
may send more than one request through an open connection. In fact, a client
can send as much data as the server is ready to receive. The server can also
close the connection if it wants to.
Java Socket's and ServerSocket's
When a client
wants to open a TCP/IP connection to a server, it does so using a Java Socket. The socket is told what IP address
and TCP port to connect to and the rest is done by Java.
If you want to
start a server that listens for incoming connections from clients on some TCP
port, you have to use a Java ServerSocket. When a client connects via a
client socket to a server's ServerSocket, a Socket is assigned on the server to
that connection. The client and server now communicates Socket-to-Socket.
Socket's and
ServerSocket's are covered in more detail in later texts.
Java UDP Networking Basics
UDP works a bit
differently from TCP. Using UDP there is no connection between the client and
server. A client may send data to the server, and the server may (or may not)
receive this data. The client will never know if the data was received at the
other end. The same is true for the data sent the other way from the server to
the client.
Because there is
no guarantee of data delivery, the UDP protocol has less protocol overhead.
Socket Programming in Java
Networking is a concept of connecting two or more
computing devices together so that we can share resources like printer,
scanner, memory.
In Networking
application mainly two programs are running one is Client program and another is Server program. In
Core java Client program can be design using Socket class and Server program can be design using ServerSocket class.
Both Socket and
ServerSocket classes are predefined in java.net package
Advantage
of Network Programming
The main advantage
of network Programming is sharing of data and resources, some more advantages
are;
·
Sharing resources like printer, Scanner.
·
Centralize software management, Software install on only one
system and used in multiple system.
·
Sharing of data due to this reduce redundancy of application.
·
Burden on the developer can be reduced.
·
Wastage of memory can be reduced because no need to install same
application on every system.
·
Time consuming process to develop application is reduced.
Terms used
in Socket Programming
Port
number: It is unique identification value
represents residing position of a server in the computer. It is four digit +ve
number.
Port Name: It is a valid user defined name to know
about client system, the default port name for any local computer is localhost.. Port name
should be the some value which is given at Server programming.
Socket
class
Socket class are
used for design a client program, it have some constructor and methods which
are used in designing client program.
Constructor: Socket class is having a constructor
through this Client program can request to server to get connection.
Syntax to call Socket() Constructor
Socket s=new Socket("localhost", 8080);
// localhost -- port name and 8080 -- port number
Note: If given port name is invalid then
UnknownHostException will be raised.
Method of
Socket class
·
public InputStream getInputStream()
·
public OutputStream getOutputStream()
·
public synchronized void close()
getInputStream()
This method take
the permission to write the data from client program to server program and
server program to client program which returns OutputStream class object.
Syntax
Socket s=new Socket("localhost", 8080);
OutputStream os=new s.getOutputStream();
DataOutputStream dos=new DataOutputStream(os);
getOutputStream()
This method is
used to take the permission to read data from client system by the server or
from the server system by the client which returns InputStream class object.
Syntax
Socket s=new Socket("localhost", 8080);
InputStream is=new s.getInputStream();
DataInputStream dis=new DataInputStream(is);
close()
This method is
used to request for closing or terminating an object of socket class or it is
used to close client request.
Syntax
Socket s=new Socket("localhost", 8080);
s.close();
ServerSocket
class
The ServerSocket
class can be used to create a server socket. ServerSocket object is used to
establish the communication with clients.
ServerSocket class
are used for design a server program, it have some constructor and methods
which are used in designing server program.
Constructor: ServerSocket class contain a constructor
used to create a separate port number to run the server program.
Syntax to call ServerSocket()
Constructor
ServerSocket ss=new ServerSocket(8080);
// 8080 -- port number
Method of
ServerSocket class
·
public Socket accept()
·
public InputStream getInputStream()
·
public OutputStream getOutputStream()
·
public synchronized void close()
accept(): Used to accept the client request it
returns class reference.
Syntax
Socket s=new Socket("localhost", 8080);
ServerSocket ss=new ServerSocket(8080);
Socket s=ss.accept();
Rules to
design server program
·
Every server program should run accepted port number (any 4 digit
+ve numeric value) It can set by relating an object for server socket class (In
any used defined java program).
Syntax
ServerSocket ss=new ServerSocket(8080);
·
Accept client request.
·
Read input data from client using InputStream class.
·
Perform valid business logic operation
·
Send response (writing output data) back to client using
OutputStream class.
·
close or terminate client request.
Rules to
design client program
·
Obtain connection to the server from the client program (any user
defined class) by passing port number and port name in the socket class.
Syntax
Socket s=new Socket(8080, "localhost");
// 8080 is port number and localhost is port name
·
Send request (writing input data) to the server using OutputStream
class.
·
Read output data from the server using InputStream class.
·
Display output data
Note: close the connection is optional.
Server Code
// Saved by Server.java
import java.net.*;
import java.io.*;
class Server
{
public static void main(String[] args)
{
try
{
int pno=Integer.parseInt(args[0]);
ServerSocket ss=new ServerSocket(pno);
System.out.println("server is ready to accept clint request");
Socket s1=ss.accept();
InputStream is=s1.getInputStream();
DataInputStream dis=new DataInputStream(is);
int n=dis.readInt();
System.out.println("Value from client : "+n);
int res=n*n;
OutputStream os=s1.getOutputStream();
DataOutputStream dos=new DataOutputStream(os);
dos.writeInt(res);
s1.close();
}
catch (Exception e)
{
System.out.println(e);
}
}
}
Client Code
// Saved by Client.java
import java.net.*;
import java.io.*;
import java.util.*;
class Client
{
public static void main(String[] args)
{
try
{
String pname=args[0];
int pno=Integer.parseInt(args[1]);
Socket s=new Socket(pname,pno);
System.out.println("clint obtailed connection from server");
System.out.println("Enter a number ");
Scanner sn=new Scanner(System.in);
int data=sn.nextInt();
OutputStream os=s.getOutputStream();
DataOutputStream dos=new DataOutputStream(os);
dos.writeInt(data);
InputStream is=s.getInputStream();
DataInputStream dis=new DataInputStream(is);
int res=dis.readInt();
System.out.println("Result from server : "+res);
}
catch (Exception e)
{
System.out.println(e);
}
}
}
Download Code Client Server code
Steps to
run above program
·
First open two command prompt window separately.
·
Compile Client program on one command prompt and compile server
program on other command prompt.
·
First run Server program and pass valid port number.
·
Second run client program and pass valid port name and post number
(which is already passed at server).
·
Finally give the request to server from client (from client
command prompt).
·
Now you can get response from server.
Compile and
run server program
Compile and run client
program
Limitation of J2SE network
programming
·
Using this concept you can share resource locally but not
globally.
·
Using this concept you can not develop internet based application.
·
Using this concept you can develop only half-duplex application.
·
Using this concept you can not get service from universal
protocols like http, ftp etc...
·
Using this concept you can not get services from universal server
software like tomcat, weblogic etc..
To overcome all
these limitation use Servlet and JSP technology.
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