Prepared By
Prof. Tarannum Bloch
Assistant Professor, IT Dept.
Past
History
Java
Networking
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
✓ sharing resources
✓ centralize software management
Java
Networking
Past
History
Terminology
The widely used java networking terminologies are given below:
✓
✓
✓
✓
✓
✓
IP Address
Protocol
Port Number
MAC Address
Connection-oriented and connection-less protocol
Socket
Networking
Terminology
Past History
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.
Past History
Networking
Terminology
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.
Past History
Stream
What is Stream ?
A stream can be defined
as a sequence of data.
The InputStream is used to read data from a source and the OutputStream is
used for writing data to a destination.
InputStream and OutputStream are the basic stream classes in Java.
Client Server Communication
Client Server Communication
Past History
UTF
What is UTF ?
Unicode is an international standard of character encoding which has the
capability of representing a majority of written languages all over the globe.
Unicode uses hexadecimal to represent a character.
Unicode is a 16-bit character encoding system. The lowest value is \u0000 and
the highest value is \uFFFF.
Past History
writeUTF
The java.io.DataOuputStream is having writeUTF(String str) method writes a
string to the underlying output stream using modified UTF-8 encoding.
Following is the declaration for java.io.DataOutputStream.writeUTF(String str)
method −
public final void writeUTF(String str)
readUTF
The java.io.DataInputStream.readUTF() method reads in a string that has been
encoded using a modified UTF-8 format. The string of character is decoded from
the UTF and returned as String.
Declaration
Following is the declaration for java.io.DataInputStream.readUTF() method −
public final String readUTF()
What we need for Java network
application programming
1.
2.
3.
4.
5.
Server Class ( port number , to accept the connection)
Client Class ( IP, Port number )
Input Stream method to read
Output Stream method to write
Application Login ( what application will do ?)
Past
History
Java
Socket
Programming
Java Socket programming is used for communication between the
applications running on different JRE.
Java Socket programming can be connection-oriented or connection-less.
Socket and ServerSocket classes are used for connection-oriented socket
programming and DatagramSocket and DatagramPacket classes are used
for connection-less socket programming.
The client in socket programming must know two information:
1.
2.
IP Address of Server, and
Port number.
Past Socket
Historyclass
A socket is simply an endpoint for communications between the machines.
The Socket class can be used to create a socket.
Important methods
Past
History Class
ServerSocket
The ServerSocket class can be used to create a server socket. This object is used
to establish communication with the clients.
Important methods
Method
Description
1) public Socket accept()
returns the socket and establish
a connection between server
and client.
2) public synchronized void
close()
closes the server socket.
Check Programs : Unit2 -> Echo Server and Add
Connection
Past
HistoryOriented
Application Examples
Do it By Yourself → Currency Converter
Check Program → Simple chat
Java Datagram
Java DatagramSocket and DatagramPacket
Java DatagramSocket and DatagramPacket classes are used for
connection-less socket programming.
Java DatagramSocket
class
Java DatagramSocket class represents a connection-less socket for sending
and receiving datagram packets. A datagram is basically an information but
there is no guarantee of its content, arrival or arrival time.
Commonly used 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: it creates a datagram
socket and binds it with the given Port Number.
DatagramSocket(int port, InetAddress address) throws SocketException: it
creates a datagram socket and binds it with the specified port number and
host address.
Java DatagramPacket
class
Java DatagramPacket is a message that can be sent or received. If you send
multiple packet, it may arrive in any order. Additionally, packet delivery is not
guaranteed.
Commonly used Constructors of DatagramPacket class
DatagramPacket(byte[] barr, int length): it creates a datagram packet. This
constructor is used to receive the packets.
DatagramPacket(byte[] barr, int length, InetAddress address, int port): it
creates a datagram packet. This constructor is used to send the packets.
Check Program: Datagram
Do it By Yourself → Digit Character Count in received String
URL (Uniform
Resource Locator)
• It represents the address that is specified to access some
Initially
two tier architecture
(client
server applications)
information
or resource
on internet.
Around since the mid-80s.
• An example of URL is
http://www.sciencedirect.com:80/index.html
Client power.
(VB, Developer/2000,
• RAD
Thedevelopment
URL contains
4 parts whichPowerBuilder).
are as follows :-
1)The
to usefor(http://)
Client protocol
is responsible
data access applying business logic and
presentation of data
2)The Server name or IP address
Only service provided by Server was that of database server.
3)Port
number which is optional (by default :80)
4)The file(resource) that is referred.
URL Class
• Initially
It will
create URL object in java application.
two tier architecture (client server applications)
mid-80s.
•Around
It hassince
thethefollowing
constructors :-
Client power.
✓ URL(String urlSpecifier)
development (VB,
Developer/2000,
PowerBuilder).
✓RADURL(String
protocol,
String hostName,
int port, String
path);
Client is responsible for data access applying business logic and
✓presentation
URL (String
of dataprotocol, String hostName, String path);
✓ URL (URL urlObj, String urlSpecifier);
Only service provided by Server was that of database server.
URL Class (cont…)
ItInitially
contains
following instance methods
two tier architecture (client server applications)
Around Method
since the mid-80s.
Method
Description
public
String getProtocol()
it returns the protocol of the URL.
Description
Client power.
public String getHost()
it returns the host name of the URL.
public
getPort() (VB, Developer/2000,
it returns the Port
Number of the URL.
RADString
development
PowerBuilder).
public String getFile()
it returns the file name of the URL.
Client
is responsible forit returns
data the
access
applying
business i.e.
logic and
public
URLConnection
instance
of URLConnection
presentation of data
openConnection()
associated with this URL.
Only service provided by Server was that of database server.
Check Program : URLDemo.java
URLConnection Class
The Java URLConnection class represents a communication link
Initially two
architecture
(client server applications)
between
thetier
URL
and the application.
This class can be used to read
and write data to the specified resource referred by the URL.
Around since the mid-80s.
How
get the object of URLConnection class
Clienttopower.
The openConnection() method of URL class returns the object of
URLConnection
RAD developmentclass.
(VB, Developer/2000, PowerBuilder).
Client is responsible for data access applying business logic and
Syntax:
presentation
of data
public
URLConnection
openConnection()throws IOException{}
Only service provided by Server was that of database server.
URLConnection Class
(cont…)
This class contains the following methods
Initially two tier architecture (client server applications)
• Around
Long since
getDate(
);
the mid-80s.
• Long getLastModified( );
• Client
Longpower.
getContentLength( );
• InputStreamgetInputStream( );
RAD development (VB, Developer/2000, PowerBuilder).
Client is responsible for data access applying business logic and
presentation of data
OnlyProgram
service: provided
by Server was that of database server.
Check
DisplayData.java
Java HttpURLConnection class
The Java HttpURLConnection class is http specific URLConnection. It works for HTTP
protocol only. By the help of HttpURLConnection class, you can information of any
HTTP URL such as header information, status code, response code etc. The
java.net.HttpURLConnection is subclass of URLConnection class.
The openConnection() method of URL class returns the object of URLConnection class.
Syntax:
public URLConnection openConnection()throws IOException{}
You can typecast it to HttpURLConnection type as given below.
URL url=new URL("http://www.marwadiuniversity.ac.in");
HttpURLConnection huc=(HttpURLConnection)url.openConnection();
Check Programs : HttpURLConnectionDemo.java
InetAddress Class
Java InetAddress class represents an IP address.
The java.net.InetAddress class provides methods to get the IP of
any host name for example www.javatpoint.com,
www.google.com, www.facebook.com etc.
InetAddress Class
cont..
Commonly used methods of InetAddress class
Method
Description
public static InetAddress
getByName(String host)
throws UnknownHostException
it returns the instance of InetAddress
containing LocalHost IP and name.
public static InetAddress getLocalHost()
throws UnknownHostException
it returns the instance of InetAdddress
containing local host name and address.
public String getHostName()
it returns the host name of the IP address.
public String getHostAddress()
it returns the IP address in string format.
Check Programs : InetDemo.java
Local vs Remote
method invocation
Remote Method
Invocation (RMI)
RMI uses stub and skeleton
object for communication
with the remote object.
A remote object is an object
whose method can be invoked
from another JVM.
RMI System Architecture
Built in three layers (they are all independent):
✓ Stub/Skeleton layer
✓ Remote reference layer
✓ Transport layer
Remote Method
Invocation (RMI)
The interface between the application layer and the rest of the
system
Stubs and skeletons are generated using the RMIC compiler
This layer transmits data to the remote reference layer via the
abstraction of marshal streams (that use object serialization)
This layer doesn’t deal with the specifics of any transport
Stub
The stub is an object, acts as a gateway for the client side. All the
outgoing requests are routed through it. It resides at the client side
and represents the remote object. When the caller invokes method on
the stub object, it does the following tasks:
1. It initiates a connection with remote Virtual Machine (JVM),
2. It writes and transmits (marshals) the parameters to the remote
Virtual Machine (JVM),
3. It waits for the result
4. It reads (unmarshals) the return value or exception, and
5. It finally, returns the value to the caller.
Skeleton
The skeleton is an object, acts as a gateway for the server side object.
All the incoming requests are routed through it. When the skeleton
receives the incoming request, it does the following tasks:
1. It reads the parameter for the remote method
2. It invokes the method on the actual remote object, and
3. It writes and transmits (marshals) the result to the caller.
In the Java 2 SDK, an stub protocol was introduced that eliminates the
need for skeletons.
The Remote
Reference Layer
The middle layer
Provides the ability to support varying remote reference or invocation
protocols independent of the client stub and server skeleton
Example: the unicast protocol provides point-to-point invocation, and
multicast provides invocation to replicated groups of objects, other
protocols may deal with different strategies…
The Transport Layer
A low-level layer that ships serialized objects between different
address spaces Responsible for:
Setting up connections to remote address spaces
Managing the connections
Listening to incoming calls
Maintaining a table of remote objects that reside in the same
address space
✓ Setting up connections for an incoming call
✓ Locating the dispatcher for the target of the remote call
✓
✓
✓
✓
How does RMI work?
An invocation will pass through the stub/skeleton layer, which will
transfer data to the remote reference layer
The semantics of the invocation are carried to the transport layer
The transport layer is responsible for setting up the connection
The Naming Registry
The remote object must register itself with the RMI naming registry
A reference to the remote object is obtained by the client by looking
up the registry
Java RMI Example
The 6 steps to write the RMI program.
1. Create the remote interface
2. Provide the implementation of the remote interface
3. Compile the implementation class and create the stub and
skeleton objects using the rmic tool
4. Start the registry service by rmiregistry tool
5. Create and start the remote application
6. Create and start the client application
Java RMI Example
Execution Steps
For running rmi example,
1) compile all the java files
javac *.java
2)create stub and skeleton object by rmic tool
rmic AdderRemote
3)start rmi registry in one command prompt
rmiregistry 5000
4)start the server in another command prompt
java MyServer
5)start the client application in another command prompt
java MyClient
Check Program : rmi1
END OF UNIT - 1