Socket Programming in Java.ppt yeh haii

Socket Programming in Java
-First Step of Network Programming-

2
Network
R
e
q
u
e
s
t
Result
a client, a server, and network
Client
Server
Client machine
Server machine
Elements of C-S Computing

3
Networking Basics
• Applications Layer
– Standard apps
• HTTP
• FTP
• Telnet
– User apps
• Transport Layer
– TCP
– UDP
– Programming Interface:
• Sockets
• Network Layer
– IP
• Link Layer
– Device drivers
• TCP/IP Stack
Application
(http,ftp,telnet,…)
Transport
(TCP, UDP,..)
Network
(IP,..)
Link
(device driver,..)

4
Networking Basics
• TCP (Transport Control
Protocol) is a connection-
oriented protocol that
provides a reliable flow of
data between two
computers.
• Example applications:
– HTTP
– FTP
– Telnet
• TCP/IP Stack
Application
Transport
(TCP, UDP,..)
Network
(IP,..)
Link
(device driver,..)

5
Networking Basics
• UDP (User Datagram
Protocol) is a protocol that
sends independent packets
of data, called datagrams,
from one computer to
another with no guarantees
about arrival.
• Example applications:
– Ping
• TCP/IP Stack
Application
Transport
(TCP, UDP,..)
Network
(IP,..)
Link
(device driver,..)

6
Understanding Ports
• The TCP and UDP
protocols use ports to
map incoming data to a
particular process
running on a computer.
server
P
o
r
t
Client
TCP
TCP or UDP
port port port port
app app app app
port# data
Data
Packet

7
Understanding Ports
• Port is represented by a positive (16-bit) integer
value
• Some ports have been reserved to support
common/well known services:
– ftp 21/tcp
– telnet 23/tcp
– smtp 25/tcp
– login 513/tcp
• User level process/services generally use port
number value >= 1024

8
Socket Communication
• A server (program) runs on a specific
computer and has a socket that is bound to a
specific port. The server waits and listens to
the socket for a client to make a connection
request.
server
Client
Connection request
port

9
Socket Communication
• If everything goes well, the server accepts the connection.
Upon acceptance, the server gets a new socket bounds to a
different port. It needs a new socket (consequently a different
port number) so that it can continue to listen to the original
socket for connection requests while serving the connected
client.
server
Client
Connection
port
port
port

10
Sockets and Java Socket Classes
• A socket is an endpoint of a two-way
communication link between two programs
running on the network.
• A socket is bound to a port number so that the
TCP layer can identify the application that
data destined to be sent.
• Java’s .net package provides two classes:
– Socket – for implementing a client
– ServerSocket – for implementing a server

11
Java Sockets
ServerSocket(1234)
Socket(“128.250.25.158”, 1234)
Output/write stream
Input/read stream
It can be host_name like “iiu.edu.pk”
Client
Server

12
Server
Threads
Server Process
Client 1 Process
Client 2 Process
Multithreaded Server: For Serving
Multiple Clients Concurrently
Internet

How to Open a Socket?
-Client-
Socket MyClient;
MyClient = new Socket("Machine name",
PortNumber);

-Client-
• With exception handling, the code look like
following:
Socket MyClient;
try {
MyClient = new Socket("Machine name", PortNumber);
}
catch (IOException e) {
System.out.println(e);
}

-Server-
ServerSocket MyService;
try {
MyServerice = new ServerSocket(PortNumber);
}
}

How Do I Create an Input Stream?
-Client-
• On the client side, you can use the DataInputStream class to
create an input stream to receive response from the server:
DataInputStream input;
try {
input = new DataInputStream(MyClient.getInputStream());
}
}

-Client-
• The class DataInputStream allows you to read
lines of text and Java primitive data types in a
portable way.
• It has methods such as read, readChar,
readInt, readDouble, and readLine,.
• Use whichever function you think suits your
needs depending on the type of data that you
receive from the server.

-Server-
• On the server side, you can use DataInputStream to receive
input from the client
DataInputStream input;
try {
input = new DataInputStream(serviceSocket.getInputStream());
}
}

How do I Create an Output Stream?
-Client-
• On the client side, you can create an output
stream to send information to the server
socket using the class PrintStream or
DataOutputStream of java.io:

-Client-
PrintStream output;
try {
output = new PrintStream(MyClient.getOutputStream()); }
}

-Client-
• The class PrintStream has methods for
displaying textual representation of Java
primitive data types.
• you may use the DataOutputStream

-Client-
DataOutputStream output;
try {
output = new DataOutputStream(MyClient.getOutputStream());
}
}

-Client-
• The class DataOutputStream allows you to
write Java primitive data types; many of its
methods write a single Java primitive type to
the output stream.
• The method writeBytes is a useful one.

-Server-
• On the server side, you can use the class PrintStream to send
information to the client.
PrintStream output;
try {
output = new
PrintStream(serviceSocket.getOutputStream());
}
}

-Server-
• You can use the class DataOutputStream as
mentioned
DataOutputStream output;
try {
output = new
DataOutputStream(serviceSocket.getOutputStream()
);
}
}

How Do I Close Sockets?
-Client-
• You should always close the output and input stream
before you close the socket.
try {
output.close();
input.close();
MyClient.close();
}
}

How Do I Close Sockets?
-Server-
try {
output.close();
input.close();
serviceSocket.close();
MyService.close();
}
}

28
Implementing a Server
1. Open the Server Socket:
ServerSocket server;
DataOutputStream os;
DataInputStream is;
server = new ServerSocket( PORT );
2. Wait for the Client Request:
Socket client = server.accept();
3. Create I/O streams for communicating to the client
is = new DataInputStream( client.getInputStream() );
os = new DataOutputStream( client.getOutputStream() );
4. Perform communication with client
Receive from client: String line = is.readLine();
Send to client: os.writeBytes("Hellon");
5. Close sockets: client.close();
For multithreaded server:
while(true) {
i. wait for client requests (step 2 above)
ii. create a thread with “client” socket as parameter (the thread creates streams (as in step
(3) and does communication as stated in (4). Remove thread once service is provided.
}

29
Implementing a Client
1. Create a Socket Object:
client = new Socket( server, port_id );
2. Create I/O streams for communicating with the server.
is = new DataInputStream(client.getInputStream() );
os = new DataOutputStream( client.getOutputStream() );
3. Perform I/O or communication with the server:
– Receive data from the server:
String line = is.readLine();
– Send data to the server:
os.writeBytes("Hellon");
4. Close the socket when done:
client.close();

Socket functional calls
• socket (): Create a socket
• bind(): bind a socket to a local IP address and port #
• listen(): passively waiting for connections
• connect(): initiating connection to another socket
• accept(): accept a new connection
• Write(): write data to a socket
• Read(): read data from a socket
• sendto(): send a datagram to another UDP socket
• recvfrom(): read a datagram from a UDP socket
• close(): close a socket (tear down the connection)

Sockets
: Client socket, welcoming socket and connection socket

Socket-programming using TCP
TCP service: reliable byte stream transfer
process
TCP with
buffers,
variables
socket
controlled by
application
developer
controlled by
operating
system
process
TCP with
buffers,
variables
socket
internet
client
server
socket( )
bind( )
connect( )
socket( )
bind( )
listen( )
accept( )
send( )
recv( )
close( ) close( )
recv( )
send( )
TCP conn. request
TCP ACK

Socket programming with
TCP
Example client-server app:
• client reads line from
standard input (inFromUser
stream) , sends to server via
socket (outToServer stream)
• server reads line from socket
• server converts line to
uppercase, sends back to
client
• client reads, prints modified
line from socket
(inFromServer stream)
outT
oServer
to network from network
inFromServer
inFromUser
keyboard monitor
Process
clientSocket
input
stream
input
stream
output
stream
TCP
socket
Input stream:
sequence of bytes
into process
output stream:
sequence of bytes
out of process
Client
process
client TCP
socket

Client/server socket interaction:
TCP
wait for incoming
connection request
connectionSocket =
welcomeSocket.accept()
create socket,
port=x, for
incoming request:
welcomeSocket =
ServerSocket()
create socket,
connect to hostid, port=x
clientSocket =
Socket()
close
connectionSocket
read reply from
clientSocket
close
clientSocket
Server (running on hostid) Client
send request using
clientSocket
read request from
connectionSocket
write reply to
connectionSocket
TCP
connection setup

35
Example: Java client (TCP)
import java.io.*;
import java.net.*;
class TCPClient {
public static void main(String argv[]) throws Exception
{
String sentence;
String modifiedSentence;
BufferedReader inFromUser =
new BufferedReader(new InputStreamReader(System.in));
Socket clientSocket = new Socket("hostname", 6789);
DataOutputStream outToServer =
new DataOutputStream(clientSocket.getOutputStream());
Create
input stream
Create
client socket,
connect to server
Create
output stream
attached to socket

36
Example: Java client (TCP), cont.
BufferedReader inFromServer =
new BufferedReader(new
InputStreamReader(clientSocket.getInputStream()));
sentence = inFromUser.readLine();
outToServer.writeBytes(sentence + 'n');
modifiedSentence = inFromServer.readLine();
System.out.println("FROM SERVER: " + modifiedSentence);
clientSocket.close();
}
}
Create
input stream
attached to socket
Send line
to server
Read line
from server

37
Example: Java server (TCP)
import java.io.*;
import java.net.*;
class TCPServer {
public static void main(String argv[]) throws Exception
{
String clientSentence;
String capitalizedSentence;
ServerSocket welcomeSocket = new ServerSocket(6789);
while(true) {
Socket connectionSocket = welcomeSocket.accept();
BufferedReader inFromClient =
new BufferedReader(new
InputStreamReader(connectionSocket.getInputStream()));
Create
welcoming socket
at port 6789
Wait, on welcoming
socket for contact
by client
Create input
stream, attached
to socket

38
Example: Java server (TCP), cont
DataOutputStream outToClient =
new DataOutputStream(connectionSocket.getOutputStream());
clientSentence = inFromClient.readLine();
capitalizedSentence = clientSentence.toUpperCase() + 'n';
outToClient.writeBytes(capitalizedSentence);
}
}
}
Read in line
from socket
Create output
stream, attached
to socket
Write out line
to socket
End of while loop,
loop back and wait for
another client connection

39
Socket programming with UDP
UDP: no “connection” between
client and server
• no handshaking
• sender explicitly attaches IP
address and port of destination
to each packet
• server must extract IP address,
port of sender from received
packet
UDP: transmitted data may be
received out of order, or lost
application viewpoint
UDP provides unreliable transfer
of groups of bytes (“datagrams”)
between client and server

40
Example: Java client (UDP)
import java.io.*;
import java.net.*;
class UDPClient {
public static void main(String args[]) throws Exception
{
BufferedReader inFromUser =
new BufferedReader(new InputStreamReader(System.in));
DatagramSocket clientSocket = new DatagramSocket();
InetAddress IPAddress = InetAddress.getByName("hostname");
byte[] sendData = new byte[1024];
byte[] receiveData = new byte[1024];
String sentence = inFromUser.readLine();
sendData = sentence.getBytes();
Create
input stream
Create
client socket
Translate
hostname to IP
address using DNS

41
Example: Java client (UDP), cont.
DatagramPacket sendPacket =
new DatagramPacket(sendData, sendData.length, IPAddress, 9876);
clientSocket.send(sendPacket);
DatagramPacket receivePacket =
new DatagramPacket(receiveData, receiveData.length);
clientSocket.receive(receivePacket);
String modifiedSentence =
new String(receivePacket.getData());
System.out.println("FROM SERVER:" + modifiedSentence);
clientSocket.close();
}
}
Create datagram with
data-to-send,
length, IP addr, port
Send datagram
to server
Read datagram
from server

42
Example: Java server (UDP)
import java.io.*;
import java.net.*;
class UDPServer {
public static void main(String args[]) throws Exception
{
DatagramSocket serverSocket = new DatagramSocket(9876);
byte[] receiveData = new byte[1024];
byte[] sendData = new byte[1024];
while(true)
{
DatagramPacket receivePacket =
new DatagramPacket(receiveData, receiveData.length);
serverSocket.receive(receivePacket);
Create
datagram socket
at port 9876
Create space for
received datagram
Receive
datagram

43
Example: Java server (UDP), cont
String sentence = new String(receivePacket.getData());
InetAddress IPAddress = receivePacket.getAddress();
int port = receivePacket.getPort();
String capitalizedSentence = sentence.toUpperCase();
sendData = capitalizedSentence.getBytes();
DatagramPacket sendPacket =
new DatagramPacket(sendData, sendData.length, IPAddress,
port);
serverSocket.send(sendPacket);
}
}
}
Get IP addr
port #, of
sender
Write out
datagram
to socket
End of while loop,
loop back and wait for
another datagram
Create datagram
to send to client

Socket Programming in Java.ppt yeh haii

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