Advance Java Programming( CM5I) 4. Networking Basics

4.Networking Basics (10
Marks)
Miss.P.S.Dungarwal
Lecturer in CM Department.
SHHJB Polytechnic, Chandwad.
Advance Java Programming(22517)

“TheNetwork isComputer”
Interne
t
Server
PCclient
LocalArea Network
PDA
2Miss.P.S.Dungarwal

Increased demand for Internet
applications
 To take advantage of opportunities presented by the
Internet, businesses are continuously seeking new
and innovative ways and means for offering their
services via the Internet.
 This created a huge demand for software designers
with skills to create new Internet-enabled
applications or migrate existing/legacy applications
on the Internet platform.
 Object-oriented Java technologies- Sockets,
threads, RMI, clustering, Web services have
emerged as leading solutions for creating portable,
efficient, and maintainable large and complex
Internet applications.
3Miss.P.S.Dungarwal

Network
a client, a server, and network
Client
Server
Client machine
Server machine
Elements of C-S Computing
4Miss.P.S.Dungarwal

Client/Server
 A server is anything that has some resource
that can be shared.
 There are compute servers, which provide
computing power; print servers, which
manage a collection of printers; disk servers,
which provide networked disk space; and web
servers, which store web pages.
 A client is simply any other entity that wants
to gain access to a particular server.
5Miss.P.S.Dungarwal

Networking Basics
 Computers running on the Internet communicate
with each other using either the Transmission
Control Protocol (TCP) or the User Datagram
Protocol (UDP)
6Miss.P.S.Dungarwal

DNS - Domain name system
 The Domain Name system (DNS) associates various
sorts of information with so-called domain names.
 Most importantly, it serves as the "phone book" for the
Internet by translating human-readable computer
hostnames, e.g. www.example.com, into the IP addresses,
e.g. 208.77.188.166, that networking equipment needs to
deliver information.
 It also stores other information such as the list of mail
exchange servers that accept email for a given domain.
7Miss.P.S.Dungarwal

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# dataData
Packet
8Miss.P.S.Dungarwal

Ports
 Data transmitted over the Internet is
accompanied by addressing information that
identifies the computer and the port for
which it is destined.
 The computer is identified by its 32-bit IP
address, which it uses to deliver data to the
right computer on the network.
 Ports are identified by a 16-bit number,
which TCP and UDP use to deliver the data to
the right application.
9Miss.P.S.Dungarwal

Port
 Port numbers range from 0 to 65,535 (16-
bit)
◦ Ports 0 - 1023 are called well-known ports. They
are reserved for use by well-known services:
 20, 21: FTP
 23: TELNET
 25: SMTP
 110: POP3
 80: HTTP
10Miss.P.S.Dungarwal

Introduction to Sockets

Socket
logical connection
sockets (end points)
• A socket is an endpoint for communication
between two machines.
• The combination of an IP address and a port
number.

SocketCommunication
• Aserver(program) runson aspecific computer
andhasasocketthat isboundtoa specificport.
• Theserverwaits andlistens to the socketfor a
client to makeaconnection request.
server
Client
Connection request
port

• The notion of a socket allows a single computer to
serve many different clients at once.
• This feat is managed by the introduction of a port,
which is a numbered socket on a particular machine.
• A server process is said to listen to a port until a
client connects to it

 Why Sockets?
◦ Used for Interprocess communication.
 The Client-Server model
◦ Client & Server are two processes that wants to
communicate with each other
◦ The Client process connects to the Server process,
to make a request for services own by the Server.
◦ Once the connection is established between Client
process and Server process, they can start sending
/ receiving information.
 What are Sockets?
◦ End-point of inter-process communication.
◦ An interface through which processes can
send / receive information

 What exactly creates a Socket?
◦ <IP address, Port #> tuple
 What makes a connection?
◦ {Source<IP address, Port #> , Destination <IP
address, Port #>} i.e. source socket – destination
socket pair uniquely identifies a connection.
 Example
Server
Client
Client
192.168.0.1
192.168.0.2
192.168.0.2
80
1343
5488
Client
192.168.0.3
1343

 Socket Types
◦ STREAM – uses TCP which is reliable, stream
oriented protocol,
◦ DATAGRAM – uses UDP which is unreliable, message
oriented protocol
◦ RAW – provides RAW data transfer directly over IP
protocol (no transport layer)
 Sockets can use
◦ “unicast” ( for a particular IP address destination)
◦ “multicast” ( a set of destinations – 224.x.x.x)
◦ “broadcast” (direct and limited)
◦ “Loopback” address i.e. 127.x.x.x

Transmission Control Protocol
 A connection-based protocol that provides a reliable
flow of data between two computers.
 Provides a point-to-point channel for applications that
require reliable communications.
◦ The Hypertext Transfer Protocol (HTTP), File Transfer
Protocol (FTP), and Telnet are all examples of applications
that require a reliable communication channel
 Guarantees that data sent from one end of the
connection actually gets to the other end and in the
same order it was sent. Otherwise, an error is
reported.

User Datagram Protocol
 A protocol that sends independent packets of
data, called datagrams, from one computer to
another with no guarantees about arrival. UDP
is not connection-based like TCP and is not
reliable:
◦ Sender does not wait for acknowledgements
◦ Arrival order is not guaranteed
◦ Arrival is not guaranteed
 Used when speed is essential, even in cost of
reliability
◦ e.g. streaming media, games, Internet telephony, etc.

Proxy Server
 A proxy server is a dedicated computer or a
software system running on a computer that acts
as an intermediary between client and server
from which a user or client is requesting a service.
 The proxy server may exist in the same machine as
a firewall server or it may be on a separate server,
which forwards requests through the firewall.

Working of Proxy Server
 When a proxy server receives a request for an
Internet resource (such as a Web page), it looks in its
local cache of previous pages.
 If it finds the page, it returns it to the user without
needing to forward the request to the Internet.
 If the page is not in the cache, the proxy server,
acting as a client on behalf of the user, uses one of its
own IP addresses to request the page from the
server out on the Internet.
 When the page is returned, the proxy server relates
it to the original request and forwards it on to the
user.

Proxy Server
 Proxy servers are related to firewalls. If a
firewall prevents hosts on a network from
making direct connections to the outside world,
a proxy server can act as a go-between.
 Thus, a machine that is prevented from
connecting to the external network by a firewall
would make a request for a web page from the
local proxy server instead of requesting the
web page directly from the remote web server.

 One of the security advantages of using a proxy
server is that external hosts only find out about the
proxy server.
 They do not learn the names and IP addresses of
the internal machines, making it more difficult
to hack into internal systems.

Internet Addressing
 Every computer on the Internet has an address.
 An Internet address is a number that uniquely identifies each
computer on the Net.
 Originally, all Internet addresses consisted of 32-bit values.
 This address type was specified by IPv4 (Internet Protocol,
version 4).
 However, a new addressing scheme, called IPv6 (Internet
Protocol, version 6) has come into play.
 IPv6 uses a 128-bit value to represent an address.
 The main advantage of IPv6 is that it supports a much larger
address space than does IPv4.
 IPv4 is the most widely used scheme, but this situation is likely
to change over time.

Internet Addressing
 There are 32 bits in an IPv4 IP address, and we often refer to
them as a sequence of four numbers between 0 and 255
separated by dots (.).
 The first few bits define which class of network, letter A, B, C,
D, or E, the address represents.
 Most Internet users are on a class C network, since there are
over two million networks in class C.
 The first byte of a class C network is between 192 and 224,
with the last byte actually identifying an individual computer
among the 256 allowed on a single class C network.
 This scheme allows for half a billion devices to live on class C
networks.

Internet Addressing
 Handling internet addresses (domain names,
and IP addresses) is made easy with Java.
 Internet addresses are represented in Java by
the InetAddress class.
 InetAddress provides simple methods to
convert between domain names, and
numbered addresses.

InetAddress
 The InetAddress class is used to encapsulate
both the numerical IP address and the domain
name for that address.
 We interact with this class by using the name
of an IP host, which is more convenient and
understandable than its IP address.
 The InetAddress class hides the number
inside.

InetAddress class
• static methods you can use to create new
InetAddress objects.
–getByName(String host)
–getAllByName(String host)
–getLocalHost()
–getByAddress(Byte[] addr)
–getByAddress(String host, Byte[] addr)
InetAddress x = InetAddress.getByName( “msbte.com”);
throws UnknownHostException

Factory Methods
 static InetAddress getLocalHost( )
• returns the IP address of the localhost machine.
 static InetAddress getByName(String hostName)
• returns an InetAddress instance representing the hostname.
 static InetAddress[ ] getAllByName(String hostName)
• returns an array of InetAddress instances representing the
hostname.
 static InetAddress getByAddress(byte[] addr)
• Returns an InetAddress object given the raw IP address.
 static InetAddress getByAddress(String host, byte[]
addr)
• Creates an InetAddress based on the provided host name
and IP address.*Note each methiod: throws UnknownHostException 30Miss.P.S.Dungarwal

Factory Methods Example
class InetAddressTest {
public static void main(String args[])
throws UnknownHostException {
InetAddress Address =
InetAddress.getLocalHost();
System.out.println(Address);
Address =
InetAddress.getByName("www.javatpont.com");
System.out.println(Address);
InetAddress
SW[]=InetAddress.getAllByName("www.yahoo.com");
for (int i=0; i<SW.length; i++)
System.out.println(SW[i]); }}
D:jdk1.7.0_17bin>java InetAddressTes
DESKTOP-OJIM16I/192.168.0.5
google.com/172.217.166.46
www.yahoo.com/106.10.250.11
www.yahoo.com/106.10.250.10

Instance Methods
 boolean equals(Object obj)
◦ Compares two IP addresses, returns true if there is a match.
 byte[ ] getAddress( )
◦ Returns the IP address in byte format.
 String getHostAddress( )
◦ Returns the IP address in dotted decimal format.
 String getHostName( )
◦ Returns the hostname of the InetAddress.
 boolean isMulticastAddress( )
◦ Returns true if the InetAddress is a multicast address (class
D address).
• String toString()
◦ Converts this IP address to a String.

Instance Methods
import java.net.*;
class InetAddressTest1{
public static void main(String args[])throws
UnknownHostException {
InetAddress Address =
InetAddress.getByName("www.google.com");
System.out.println(Address.getHostAddress());
System.out.println(Address.getHostName());
if(Address.isMulticastAddress())
System.out.println("It is multicast address");
} }
D:jdk1.7.0_17bin>javac InetAddressTest1.java
D:jdk1.7.0_17bin>java InetAddressTest1
216.58.203.164
www.google.com

TCP/IP Sockets
 Server sockets
◦ Wait for requests to come in over the network
◦ Implemented by java.net.ServerSocket class
 Client sockets
◦ Used to send and receive data
◦ Can be thought of as a pair of input and output
streams.
◦ Implemented by java.net.Socket class

Server vs Client Socket
 Server socket: waiting for connection requests
 Client socket: transmission of data
server socket
connection request
client socket

Server socket
The constructors used to create server socket are given below. All of them
throw IOException
 ServerSocket (int port) throws BindException, IOException
creates a server socket bounded to the specified port with a queue
length 50.
 ServerSocket (int port, int maxQueue) throws BindException, IOException
length of maxQueue.
 ServerSocket (int port, int maxQ, InetAddress ip) throws IOException
length of maxQueue. On a multihomed host, ip specifies the IP Address
to which this socket binds.

Client socket
The constructors used to server socket are given below. All of
them throw IO Exception
 public Socket(String host, int port) throws
UnknownHostException, IOException.
Creates a socket connecting to the local host to the named
host and port
 public Socket(InetAddress host, int port) throws
IOException
Creates a socket using a preexisting InetAddress and port

Server socket
 Methods
Some method defined in the Server Socket are:
Methods Description
public Socket accept() throws
IOException
Waits for a connection request and
returns a Socket
public void setSoTimeout(int
timeout)
Sets the time-out value for how long the
server socket waits for a client during the
accept().
public int getLocalPort() Returns the port number on which this
socket is listening

Methods Description
public int getPort() Returns the remote port to which this
socket is bound.
public int getLocalPort() Returns the port the socket is bound to
on the local machine.
public InetAddress getInetAddress() Returns IP address to which socket are
connected.
public SocketAddress getLocalAddress() Returns local address to which socket are
connected.
public SocketAddress
getRemoteSocketAddress()
Returns the address of the remote
socket.
public InputStream getInputStream() throws
IOException
Returns an InputStream for receiving
data.
public OutputStream getOutputStream() throws
IOException
Returns an OutputStream to
send data.
public void close() throws IOException Closes the socket connection.
Methods used by both Server and Client Sockets

Programming TCP Client-Server in Java
 All the classes related to sockets are in the java.net package.
 All the input/output stream classes are in the java.io package.
 How to open a socket?
◦ If you are programming a client, then create object of Socket class.
◦ Machine name is the machine you are trying to open a connection to,
◦ PortNumber is the port (a number) on which the server you are trying
to connect to is running. select one that is greater than 1,023.
Socket MyClient;
try {
MyClient = new Socket("Machine name", PortNumber);
}
catch (IOException e) {
System.out.println(e);
}

 If you are programming a server, then this is how you open a socket:
 When implementing a server you also need to create a socket object from the
ServerSocket in order to listen for and accept connections from clients.
ServerSocket MyService;
try {
MyServerice = new ServerSocket(PortNumber);
}
}
Socket clientSocket = null;
try {
clientSocket = MyService.accept();
}
}

 How to create an input stream?
◦ On the client side, you can use the DataInputStream class to create an
input stream to receive response from the server:
◦ The class DataInputStream allows you to read lines of text and Java
primitive data types. It has methods such as read, readChar, readInt,
readDouble, and readLine,.
◦ On the server side, you can use DataInputStream to receive input from
the client:
DataInputStream input;
try {
input = new DataInputStream(MyClient.getInputStream());
}
}
DataInputStream input;
try {
input = new DataInputStream(clientSocket.getInputStream());
}
}

 How to create an output stream?
◦ 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:
◦ The class PrintStream has methods for displaying textual representation
of Java primitive data types. Its write and println methods are important.
Also, you may want to use the DataOutputStream:
◦ Many of its methods write a single Java primitive type to the output stream.
The method writeBytes is a useful one.
PrintStream output;
try {
output = new PrintStream(MyClient.getOutputStream());
}
}
DataOutputStream output;
try {
output = new DataOutputStream(MyClient.getOutputStream());
}
}

 On the server side
◦ you can use the class PrintStream to send information to the client.
 Note: You can use the class DataOutputStream as mentioned previously.
PrintStream output;
try {
output = new PrintStream(clientSocket.getOutputStream());
}
}

 How to close sockets?
◦ You should always close the output and input stream before you close
the socket.
◦ On the client side:
◦ On the server side:
try {
output.close();
input.close();
MyClient.close();
}
}
try {
output.close();
input.close();
clientSocket.close();
MyService.close();
}
} 45Miss.P.S.Dungarwal

import java.io.*;
import java.net.*;
public class MyServer
{
public static void main(String[] args)
{
try
{
ServerSocket ss=new ServerSocket(6666);
Socket s=ss.accept();//establishes connection
DataInputStream dis=new DataInputStream(s.getInputStream());
String str=(String)dis.readUTF();
System.out.println("message= "+str);
ss.close();
}
catch(Exception e)
{
}
}
}
File: MyServer.java

import java.io.*;
import java.net.*;
public class MyClient
{
public static void main(String[] args)
{
try
{
Socket s=new Socket("localhost",6666);
DataOutputStream dout=new DataOutputStream(s.getOutputStream())
;
dout.writeUTF("Hello Server");
dout.flush();
dout.close();
s.close();
}
catch(Exception e)
{
}
}
MyClient.java

Example of Java Socket
Programming (Read-Write both side)

import java.net.*;
import java.io.*;
class MyServer{
public static void main(String args[])throws Exception{
ServerSocket ss=new ServerSocket(3333);
Socket s=ss.accept();
DataInputStream din=new DataInputStream(s.getInputStream());
DataOutputStream dout=new DataOutputStream(s.getOutputStream());
BufferedReader br=new BufferedReader(new InputStreamReader(System.in)
);
String str="",str2="";
while(!str.equals("stop")){
str=din.readUTF();
System.out.println("client says: "+str);
str2=br.readLine();
dout.writeUTF(str2);
dout.flush();
}
din.close();
s.close();
ss.close();
MyServer.java

import java.net.*;
import java.io.*;
class MyClient{
public static void main(String args[])throws Exception{
Socket s=new Socket("localhost",3333);
DataInputStream din=new DataInputStream(s.getInputStream());
DataOutputStream dout=new DataOutputStream(s.getOutputStream());
BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
String str="",str2="";
while(!str.equals("stop")){
str=br.readLine();
dout.writeUTF(str);
dout.flush();
str2=din.readUTF();
System.out.println("Server says: "+str2);
}
dout.close();
s.close();
}}
MyClient.java

DatagramSocket and
DatagramPacket
• Java DatagramSocket and
DatagramPacket classes are used for
connection-less socket
programming.

Constructors of DatagramSocket class
 DatagramSocket() throws SocketException:
◦ it creates a datagram socket and binds it with the
available Port Number on the localhost machine.
 DatagramSocket(int port) throws
SocketException:
given Port Number.
 DatagramSocket(int port, InetAddress address)
throws SocketException:
specified port number and host address.

Methods
 public void bind(SocketAddress addr)
◦ Binds this socket to specified address and port
number.
 public void connect(InetAddress address, int port)
◦ Connects to the specified address and port.
 public void send(DatagramPacket p)
◦ Sends a datagram packet from this socket.
 public void receive(DatagramPacket p)
◦ It is used to receive the packet from a sender.

DatagramPacket class
 DatagramPacket is a message that can be sent or
received. If you send multiple packet, it may arrive
in any order.
 Constructors
 DatagramPacket(byte[] barr, int length):
◦ This constructor is used to receive the packets.
 DatagramPacket(byte[] barr, int length,
InetAddress address, int port):
◦ This constructor is used to send the packets.

import java.net.*;
public class DSender{
public static void main(String[] args) throws Excepti
on {
DatagramSocket ds = new DatagramSocket();
String str = "Welcome java";
InetAddress ip = InetAddress.getByName("127.0.0.1
");
DatagramPacket dp = new DatagramPacket(str.ge
tBytes(), str.length(), ip, 3000);
ds.send(dp);
ds.close();
}
} 56Miss.P.S.Dungarwal

import java.net.*;
public class DReceiver{
public static void main(String[] args) throws Exception {
DatagramSocket ds = new DatagramSocket(3000);
byte[] buf = new byte[1024];
DatagramPacket dp = new DatagramPacket(buf, 1024);
ds.receive(dp);
String str = new String(dp.getData(), 0, dp.getLength());
System.out.println(str);
ds.close();
}
}

URL Class
Java URL Class present in java.net package,
deals with URL (Uniform Resource Locator)
which uniquely identify or locate resources on
internet.
Format:

Constructors of URL class
 URL (String urlspecifier)
◦ Creates a URL object from the String representation.
 URL (String protocol, String host, int port, String
file)
◦ Creates a URL object from the specified protocol, host,
port number, and file.
 URL (String protocol, String host, String file)
◦ Creates a URL from the specified protocol name, host
name, and file name.
 URL (URL urlObj, String urlspecifier)
◦ Creates a URL by parsing the given spec within a 59Miss.P.S.Dungarwal

Important Methods of URL class
 getProtocol()
◦ Returns protocol of URL
 getHost()
◦ Returns hostname(domain name) of URL
 getPort()
◦ Returns port number of URL
 getFile()
◦ Returns filename of URL
 public URLConnection openConnection() throws IOException
◦ Creates a URLConnection object that contains a connection to the
remote object referred to by the URL.
 public final Object getContent() throws IOException
◦ Gets the contents from this opened connection.

import java.net.*;
public class URLDemo{
public static void main(String[] args){
try{
URL url=new
URL("https://www.google.com/search?q=javatpoint&o
q=javatpoint& sourceid=chrome&ie=UTF-8");
System.out.println("Protocol: "+url.getProtocol());
System.out.println("Host Name: "+url.getHost());
System.out.println("Port Number: "+url.getPort());
System.out.println("Default Port Number:
"+url.getDefaultPort());
System.out.println("Query String: "+url.getQuery());
System.out.println("Path: "+url.getPath());
System.out.println("File: "+url.getFile());
} catch(Exception e){System.out.println(e);}
} }
Protocol: https
Host Name: www.google.com
Port Number: -1
Default Port Number: 443
Query String: q=javatpoint&oq=javatpoint&sourceid=chrome&ie=UTF-8
Path: /search
File: /search?q=javatpoint&oq=javatpoint&sourceid=chrome&ie=UTF-8

URLConnection Class
 URLConnection is an abstract class that represents an active
connection to a resource specified by a URL.
◦ It provides more control over the
interaction with a server (HTTP server) than
the URL class.
◦ With a URLConnection, we can inspect the
header sent by the server.
◦ We can set the header fields used in the
client request.
◦ A URLConnection lets us send data back to a
web server with POST or PUT and use other
HTTP request methods. 62Miss.P.S.Dungarwal

Methods of URLConnection class
 public abstract void connect()throws IOException
◦ Opens a communications link to the resource referenced by this URL.
 public URL getURL()
◦ Returns the value of this URLConnection's URL field.
 public int getContentLength()
◦ Returns the value of the content-length header field.
 public String getContentType()
◦ Returns the value of the content-type header field.
 public long getDate()
◦ Returns the value of the date header field.
 public Object getContent()throws IOException
◦ Retrieves the contents of this URL connection.
 public InputStream getInputStream()throws IOException
◦ Returns an input stream that reads from this open connection.
 public OutputStream getOutputStream()throws

import java.io.*;
import java.net.*;
public class URLConnectionExample {
public static void main(String[] args){
try{
URL url=new URL("http://www.javatpoint.com/java-tutorial");
URLConnection urlcon=url.openConnection();
InputStream stream=urlcon.getInputStream();
int i;
while((i=stream.read())!=-1){
System.out.print((char)i);
} }catch(Exception e){System.out.println(e);}
} }
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<html><head>
<title>302 Found</title>
</head><body>
<h1>Found</h1>
<p>The document has moved <a href="https://www.javatpoint.com/java-
tutorial">here</a>.</p>
</body></html>

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Advance Java Programming( CM5I) 4. Networking Basics