Socket identifies endpoints in a network and allows a single computer to serve multiple clients simultaneously through port numbers. There are two main network protocols: TCP ensures reliable delivery of data across packets while UDP is used for fast but unreliable delivery. The URL class provides an API to access internet resources identified by URLs following the protocol://host:port/path format.

2. Networking Basic
0 Java networking supports the concept of Socket.
0 Socket
0 Identifies an endpoint in a n/w.
0 Allows a single computer to serve many different type of
information to many different client as well as server at
once.
0 This is accomplished through port(numbered socket on
a particular machine).

3. Networking Basic
0 Socket
0 Socket communication takes place via protocol
0IP
0 Low-level routing protocol
0 Breaks data into small packets and send them to an address across n/w
0 No guarantee to delivered.
0TCP
0 Higher level protocol
0 Manage packet robustly
0 Sort and retransmit them as necessary
0 Reliably transmit data
0UDP
0 Used directly to support fast ,connectionless , unreliable transport
packets.

4. InetAddress
0 Encapsulate both the numerical IP Address and the
domain name for the address.
0 Can handle IPv4 and IPv6
0 Factory Method
0 InetAddress class does not have visible constructor
0 To create an InetAddress object, you have to use one of
the available factory methods.

5. InetAddress
0 Factory Methods
0 static InetAddress getLocalHost( )throws
UnknownHostException
0 static InetAddress getByName(String hostName) throws
UnknownHostException
0 static InetAddress[ ] getAllByName(String hostName)
throws UnknownHostException

6. TCP/IP Sockets
0 Used to implement reliable, bidirectional, persistent,
point-to-point stream based connection between
hosts on the Internet.
0 There are two types of TCP sockets in Java; one is for
servers and other is for clients.
0 The ServerSocket class is for server and Socket is for
client.
0 The ServetSocket class is designed to be a “listener”,
which waits for clients to connect before do anything.

7. TCP/IP Sockets
0 The Socket class is designed to connect to server
sockets.
0 The creation of a Socket object implicitly established
connection between client and server.
0 Note: There are no methods or constructors that
explicitly expose the details of establishing that
connection.

8. TCP/IP Sockets
0 There are two constructor used to create client
socket:
0 Socket(String hostName, int port) throws
UnknownHostException, IOException
Creates a socket connected to the named host and
port.
0 Socket(InetAddress ipAddress, int port) throws
IOException
Creates a socket using a pre existing InetAddress
object and a port.

9. 0 There are three constructor used to create server
socket:
0 ServerSocket(int port) throws IOException
0 Creates server socket on the specified port with a queue
length of 50.
0 ServerSocket(int port, int maxQueue) throws
IOException
0 Creates a server socket on the specified port with a
maximum queue length of maxQueue.
0 ServerSocket(int port, int maxQueue, InetAddress
localAddress) throws IOException
0 Creates a server socket on the specified port with a
maximum queue length of maxQueue. On a multihomed
host, localAddress specifies the IP address to which this
socket binds.

10. URL
0 Uniform Resource Locator
0 Provide reasonably intelligible form to uniquely
identify or address information on the Internet.
0 URLs are being every where at once every browser
uses them to identify information on the Web.
0 Within Java’s network class library, the URL class
provides a simple, concise (brief important
information) API to access information across the
Internet using URLs.

11. URL
0 A URL specification format is based on four
components.
0 Here are two examples: http://www.osborne.com/
and http://www.osborne.com:80/index.htm.
0 The first is the protocol to use, separated from the rest
of the locator by a colon (:).
0 Common protocols are HTTP, FTP, gopher.
0 The second component is the host name or IP address
of the host to use.
0 The third component, the port number, is an optional
parameter.

12. URL
0 The fourth part is the actual file path.
0Most HTTP servers will append a file named index.html or
index.htm to URLs that refer directly to a directory resource.
0 Constructor:
0 URL(String urlSpecifier) throws
MalformedURLException
0 URL(String protocolName, String hostName, int port,
String path) throws MalformedURLException
0 URL(String protocolName, String hostName, String path)
throws MalformedURLException
0 URL(URL urlObj, String urlSpecifier) throws
MalformedURLException

13. URLConnection
0 URLConnection is a general-purpose class for
accessing the attributes of a remote resource.
0 Once you make a connection to a remote server, you
can use URLConnection to inspect the properties of
the remote object before actually transporting it
locally

14. HttpURLConnection
0 Java provides a subclass of URLConnection that
provides support for HTTP connections.
0 We obtain an HttpURLConnection by calling
openConnection( ) on a URL object, but we must cast
the result to HttpURLConnection.

15. Datagrams
0 Datagram is basically an information but there is no
guarantee of packet delivery.
0 Java implements datagrams on top of the UDP
protocol by using two classes:
0 DatagramPacket
0 Is a message that can be sent or received.
0 If you send multiple packet, it may arrive in any order.
0 DatagramSocket
0 is the mechanism used to send or receive the
DatagramPackets.

16. DatagramSocket
0 Represents a connection-less socket for sending and
receiving datagram packet.
0 DatagramSocket defines four public constructors:
0 DatagramSocket( ) throws SocketException
0 DatagramSocket(int port) throws SocketException
0 DatagramSocket(int port, InetAddress ipAddress) throws
SocketException
0 DatagramSocket(SocketAddress address) throws
SocketException

17. DatagramSocket
0 Methods
0 void send(DatagramPacket packet) throws IOException
0 void receive(DatagramPacket packet) throws
IOException

18. DatagramPacket
0 Constructor:
0 DatagramPacket(byte data[ ], int size)
0 DatagramPacket(byte data[ ], int size, InetAddress
ipAddress, int port)