Java Networking

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JAVA Networking
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Agenda
Elements of Client Server Computing
Network Basics
Understanding Ports and Sockets
Java Sockets
o Implementing a Server
o Implementing a Client
Sample Examples
Conclusion
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What is Networking?
When two processes, lying on same or
different machines are communicating
over the network is called networking.
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Client Server

Server & Client
Process providing
services is called
Server.
Process consuming
services is called Client
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Elements of Client-Server computing
Network
Request
Response
There are three elements in networking
 Client : sends request for services
 Server : sends response
 Network : media of communication
Client
Server
Client Machine Server Machine

Single Machine Multiple Clients
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Yahoo
Server
Google
Server
Hotmail
Server
Client’s Machine
One Machine can execute multiple clients’ processes concurrently

Client is a Process
 One machine may run multiple clients (processes) at a time.
 Client is not a machine, it is a process.
o Browser opens google.com is a Client.
o Yahoo Messenger connected to chat server is a client.
o CuteFTP uploading a file to FTP Server is a Client.
 All above mentioned clients (CuteFTP, Messenger,
Browser) run together on a single Machine concurrently.
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Client Machine
Crome Browser
Yahoo Messenger
CuteFTP
Process 4

Server is a Process
 One machine may run multiple servers (processes) at a
time.
 Server is not a machine, it is a process.
o Tomcat Web Server is a process.
o WAMP PHP Server is a process.
o Filezilla FTP Server is a process.
 All above mentioned servers run together on a single
Machine concurrently.
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Single Machine Multiple Servers
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Server Machine
Tomcat Web
Server (Port : 8080)
FileZilla FTP
Server (Port : 21)
WAMP PHP
Server (Port : 80)

Server & Client
 Since Operating Systems can execute multiple processes
concurrently using preemptive scheduling. Thus, one
Machine may run multiple Servers and Clients together.
 Client and Server processes communicate over the network
to exchange data in form of request and response.
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Machine
Crome Browser
Yahoo Messenger
Tomcat
WAMP

How Clients and Servers are identified?
Clients and Servers are uniquely identified on a
single machine by unique Port Numbers.
Unique Port Number is assigned by OS.
Process can ask desired port number from OS, or
OS will assign next available port number to a
process.
Port number is a two bytes unsigned number
ranging from 0-65535.
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Ports
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Server Machine
Tomcat Web
Server
FileZilla FTP
Server
WAMP PHP
Server
8080
21
80
Client Machine
Browser
FTP Client
Browser
1111
2222
3333

Communication Rules (Protocols)
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Hello, I am Vijay, May
I talk to Tisha
Yes, I m Tisha
Blah, Blah, Blah .....
………………………
….
Bye
Have a Good Day
Certain rules are followed when you communicate over the network,
are called Protocols

Protocol over Phone
When you call someone over phone and start
conversation, you follow protocol.
First you greet and say “Hello” , then you tell your
name “I am Vijay”, then you ask with whom you
want to talk “May I talk to Tisha?” .
Likewise when conversation is over you say “Bye”
and other would respond “Have a Good Day”.
This is Protocol
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Protocol Responsibilities
Applies a set of Rules.
Converts your application data into byte stream
and vice versa.
Breaks data into packets and sends over network.
Receives acknowledgements of sent packets.
Decides network route to send data packets.
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Protocol Stack
 A group of network protocols that work together to send and
receive your data over the network, is called a Protocol
Stack.
 The TCP/IP protocol stack uses four layers that map to the
OSI model:
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Application
(http,ftp,telnet,…)
Transport
(TCP, UDP,..)
Network
(IP,..)
Link
(device driver,..)

Protocol Stack Communication
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Application
Transport
(TCP, UDP,..)
Network
(IP,..)
Link
(device driver,..)
Application
Transport
(TCP, UDP,..)
Network
(IP,..)
Link
(device driver,..)

TCP/IP Protocol Stack
Applications Layer:
o contains user custom and high level application protocols
like HTTP, FTP, SMTP, Telnet etc.
Transport Layer:
o Contains TCP or UDP protocols, responsible for making
data packets and send or receive across network.
o Your custom application will communicate to this layer.
Network Layer:
o contains IP Protocol that uses routing information to
decide route of data packet to send it to the destination.
Link Layer:
o converts data into signals.
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TCP Protocols
TCP (Transport Control Protocol) is a connection-
oriented protocol that provides a reliable flow of
data between two computers.
Example applications:
o HTTP
o FTP
o Telnet
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UDP Protocols
UDP (User Datagram Protocol): It is a protocol that
sends independent packets of data (called
datagrams ) from one computer to another with NO
guarantee about arrival.
Example applications:
o Clock server
o Ping
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Network 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
port1 port2 port3 port4
app1 app2 app3 app4
port# data
Data
Packets
Port
port# data
port4 data

Ports
 Port number is a two bytes unsigned number ranging from
0-65535.
 Some ports have been reserved to support common/well
known services:
o ftp 21/tcp
o telnet 23/tcp
o smtp 25/tcp
o http 80/tcp
 Developer defined processes/services are advised to use
port numbers >= 1024 because port numbers <1024 are
reserved for special services.
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Sockets
Server
255.255.192.101
Client
192.168.125.1108080 1234
Socket = IP+ Port
Server Socket = 255.255.192.101:8080
Client Socket = 192.168.125.110:1234
port# data
Server and Client have network end points called sockets. Sockets are
bound to a specific port.

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Java Socket Classes
Java provides socket classes to make
Server and Client.
Package java.net contains socket
classes.
There are separate classes for TCP and
UDP connections.

Make TCP Connection
Following classes are used in Java to make TCP
connection.
o java.net.Socket – for client implementation
o java.net.ServerSocket – for server implementation
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Make UDP Connection
Following classes are used in Java to make UDP
connection.
o java.net.DatagramSocket – for client and server
implementation
o java.net.DatagramPacket – for making data packets
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Create TCP Server
 Class ServerSocket creates a TCP server and waits for
Client request.
o ServerSocket ss = new ServerSocket(4444);
o Socket client = ss.accept() ;
 Server is bound to port number 4444.
 Server is waiting for client request by calling method
ss.accept().
server Client
Connection request
4444
ss

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Create TCP Client
 Class Socket creates a TCP client.
 Server IP and Port number are passed to Socket
parametrized constructor.
Socket client=new Socket(“127.0.0.1”,4444);
 Created socket instance will establish connection with
server.

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Java Sockets
ServerSocket(1234)
Socket(“128.250.25.158”, 1234)
Output/write stream
Input/read stream
It can be host_name like “www.sunilos.com”
Client
Server
128.250.25.158

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Sockets IO
Sockets provide an interface for programming
networks at the transport layer.
Network communication using Sockets is very
much similar to performing file I/O
o The streams used in file I/O operation are also applicable
to socket-based I/O
Socket-based communication is programming
language independent.
o That means, a socket program written in Java language
can also communicate to a program written in Java or
non-Java socket program.

Read and Write from Socket
IO classes are used to read and write byte streams
from the Socket.
 Socket s=new Socket(“127.0.0.1”,4444);//Client Side
 Or
 Socket s=ss.accept();//Server Side
 DataOutputStream os;
 DataInputStream is;
 is=new DataInputStream(s.getInputStream());
 os=new DataOutputStream(s.getOutputStream());
 String line = is.readLine(); //Read from Socket
 os.writeBytes("Hellon"); //Write to Socket
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Network Communication
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Client and Server Communication
 1: ServerSocket server =
new ServerSocket(1234);
 2: Socket client =
server.accept();
 4: in = new DataInputStream(
client.getInputStream())
 5: out=new DataOutputStream(
client.getOutputStream())
 7:String line=in.readLine();
 8:out.writeBytes(
 "Hello Clientn")
 10:client.close()
 3: Socket client = new
Socket(“localhost”,1234);
 4: in = new DataInputStream(
client.getInputStream())
 5: out=new DataOutputStream(
client.getOutputStream())
 6: out.writeBytes("Hello
Servern")
 9:String line=in.readLine();
 10:client.close()
1234
Server
Client
port
Client
in
out
out
in
Hello Server
Hello Client

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Echo Client and Server
Echo Server echoes the text sent by Client.
Uses TCP Protocol.
Server will handle multiple Clients sequentially.
Server will end communication when Client sends
“Bye”.
Server
Client
Hello .. Hello
Hello

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Echo Server
public static void main(String[] args) throws IOException {
ServerSocket ss= new ServerSocket(4444);
System.out.println("Echo Server Started");
Socket client= null;
boolean flag = true;
while (flag) {
client = ss.accept(); //Accept Client
talk(client); //Talk to the client
}
System.out.println("Echo Server Stopped");
ss.close(); //Close server
}

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Echo Server (Cont.)
public static void talk(Socket client) throws IOException {
PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);
BufferedReader in = new BufferedReader(
new InputStreamReader(client.getInputStream()));
String msg =null;
msg = in.readLine();
while (msg != null) {
System.out.println("Server Received " + msg);
out.println(msg + " .. " + msg);
if (msg.equals("Bye")) break;
msg = in.readLine();
}
out.close();
in.close();
client.close();
}

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Multi-Threaded Echo Server
Handles multiple Clients concurrently
public class TalkingThread extends Thread {
private Socket client= null;
public TalkingThread (Socket client) {
this.client = client;
}
public void run() {
//…See next slide

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Multi-Threaded Echo Server (Cont.)
public void run() {
try {
PrintWriter out = new PrintWriter(client.getOutputStream(),true);
BufferedReader in = new BufferedReader(new InputStreamReader(
client.getInputStream()));
String inputLine = in.readLine();
while (inputLine != null) {
System.out.println("Server Recived " + inputLine);
out.println(inputLine + " .. " + inputLine);
if (inputLine.equals("Bye"))
break;
inputLine = in.readLine();
}
out.close(); in.close(); client.close();
} catch (IOException e) { //…}
}

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Multi-Threaded Echo Server (Cont.)
 Starts Multithreaded Server
ServerSocket server = new ServerSocket(4444);
Socket clientSocket = null;
boolean flag = true;
while (flag) {
client = server.accept();
TalkingThread t = new TalkingThread(client);
t.start();
}
System.out.println("Echo Server Stopped”);
server.close();
}

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Echo Client
Socket echoSocket = new Socket("127.0.0.1", 4444);
PrintWriter out = new PrintWriter(echoSocket.getOutputStream(), true);
BufferedReader in = new BufferedReader(
new InputStreamReader(echoSocket.getInputStream()));
BufferedReader stdIn = new BufferedReader(
new InputStreamReader(System.in)); //Read text from Keyboard
String userInput= stdIn.readLine();
while (userInput != null) {
out.println(userInput);
System.out.println("echo: " + in.readLine());
if ("Bye.".equals(userInput)) {
break;
}
userInput = stdIn.readLine();
} echoSocket.close();

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Socket Exception Handling
try {
Socket client = new Socket(host, port); handleConnection(client);
} catch(UnknownHostException uhe) {
System.out.println(“Server not Found: " + host);
}catch(IOException ioe) {
System.out.println(“Likhana Padna Mushkil hai”);
}

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UDP Communication
Server
DatagramSocket(4445)
Client
DatagramSocket()
Mail
DatagramPacket()
send()
receive()
receive() send()

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Quote Server
Quote UDP Server,
Receives empty packet from Client
Replies to the Client with a random quote of
the day.

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Quote Server
String[] quotes = { "Bura mat Dekho", "Bura Mat kaho", "Bura mat suno" };
DatagramSocket socket = new DatagramSocket(4445);
byte[] buf = new byte[256];
DatagramPacket emptyPkt = new DatagramPacket(buf, buf.length);
while (true) { //Infinite loop
socket.receive(emptyPkt);
InetAddress address = emptyPkt.getAddress();
int port = emptyPkt.getPort();
int ind = Math.random()*2; //get random index
String q= quotes[ind]; // Today’s quote";
byte[] quoteBuf = q.getBytes();
DatagramPacket quotePkt = new DatagramPacket(quoteBuf,
quoteBuf.length, address, port);
socket.send( quotePkt );
}

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Quote Client
 Sends empty packet and receives Quote of the Moment.
DatagramSocket socket = new DatagramSocket();
// send request
byte[] buf = new byte[256];
InetAddress address = InetAddress.getByName("localhost");
DatagramPacket packet = new DatagramPacket(buf, buf.length, address,4445);
socket.send(packet);
// get response
packet = new DatagramPacket(buf, buf.length);
socket.receive(packet);
// display response
String received = new String(packet.getData());
System.out.println("Quote of the Moment: " + received);
socket.close();

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Read From URL
Reads text from URL
InputStream inStream = null; URL u = null;
try {
u = new URL("http://www.yahoo.com");
inStream = u.openStream();
} catch (Exception e) {
System.out.println("Error in URL");
System.exit(0);
}
Scanner in = new Scanner(inStream);
while (in.hasNext()) {
System.out.println(in.nextLine());
}
in.close();
}
import java.util.Scanner;
import java.net.URL;
import java.io.*;

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Read from URL (Cont.)
public static void main(String[] args) throws Exception {
URL yahoo = new URL("http://www.yahoo.com/");
URLConnection yahooConnection = yahoo.openConnection();
yahooConnection.connect();
InputStream inStream = yahooConnection.getInputStream();
}
inStream.close();
}

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Write to URL
URL url = new URL("http://search.yahoo.com/search");
URLConnection connection = url.openConnection();
connection.setDoOutput(true);
OutputStreamWriter out = new OutputStreamWriter(connection.getOutputStream());
String nameParameter = “books” //URLEncoder.encode("books", "UTF-8");
out.write("p=" + nameParameter);
out.write("&param2=abc");
out.close();
InputStream inStream = connection.getInputStream();
}in.close();

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Java.net.URL
 Interesting Methods
 getProtocol
o Returns the protocol identifier component of the URL.
 getAuthority
o Returns the authority component of the URL.
 getHost
o Returns the host name component of the URL.
 getPort
o Returns the port number component of the URL. The getPort method returns an
integer that is the port number. If the port is not set, getPort returns -1.
 getPath
o Returns the path component of this URL.
 getQuery
o Returns the query component of this URL.
 getFile
o Returns the filename component of the URL. The getFile method returns the same as
getPath, plus the concatenation of the value of getQuery, if any.
 getRef
• Returns the reference component of the URL.

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Assigment
Create a chat server and chat client
Data will be sent by UDP protocol
Server will be multithreaded
Client messenger window will be implemented by
Swing.

Disclaimer
This is an educational presentation to enhance the
skill of computer science students.
This presentation is available for free to computer
science students.
Some internet images from different URLs are
used in this presentation to simplify technical
examples and correlate examples with the real
world.
We are grateful to owners of these URLs and
pictures.
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Thank You!
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