java networking basics &sockets

1. B.Kohila
M.Sc(info.tech),
Nadar Saraswathi College of arts and science,
Theni

2.  The Inetaddress class provides you with a limited interface to
DNS for doing both forward and reverse internet address
lookups
- An InetAddress class method corresponds to a DNS request
 Npublic constructoro

3.  Three static methods:
 InetAddress getByName(String)
 Static method used to retrieve the address for the host name passed
as the parameter.
 InetAddress [ ] getAllByName(String)
 Static method used to retrieve all the addresses for the host name
passed as a parameter.
 InetAddress getLocalHost( )
 Static method used to retrieve the address for the current, or local,
host.

4.  Three additional “getter” methods
 String getHostName( )
 Returns the host name.
 byte[ ] getAddress( )
 Returns the IP address.
 String getHostAddress( )
 Returns the IP address as a string.

5. try
{
InetAddress fullname =
netAddress.getByName(“bigyellowcat.cs.binghamton.edu");
InetAddress alias = InetAddress.getByName(“bigyellowcat");
InetAddress octets = InetAddress.getByName(“128.226.121.44");
if (fullname.equals(alias) && fullname.equals(octets))
// All is right with the world!}
catch (UnknownHostException e)
{ // Exception handling here. }

6.  Once a TCP socket connection is made, a virtual
stream is in place. Java’s IO model is that of a stream,
therefore the models are consistent; all you need to do
connect a TCP socket to a stream and read and write
the streams as normal

7.  Socket(String ip, int port)
 Creates a streaming socket and binds it to the host and port specified as
parameters.
 Socket(String ip, int port, boolean TCPorUDP)
 Creates a socket and binds it to the host and port specified as
parameters. The last parameter is used to indicate whether the socket
should be a stream or datagram socket.
 Socket(InetAddress ia, int port)
 Creates a streaming socket connected to the specified host and port.
 Socket(InetAddress ia, int port, boolean TCPorUDP)
 Creates a socket connected to the specified host and port. The last
parameter specifies whether the socket should be a stream or datagram
socket.

8.  InetAddress getInetAddress( )
 Returns an InetAddress object representing the host for this socket.
 Int getPort( )
 . Returns the port number on the remote host for this socket
 Int getLocalPort( )
 Returns the port number on the local host for this socket.
 InputStream getInputStream( )
 Returns an input stream for the socket.
 OutputStream getOutputStream( )
 Returns an output stream for the socket.
 Close( )
 Closes the socket.
 SetSocketImplFactory (SocketImplFactory)
 Sets the socket factory that will be used to create all sockets.

9. try
{
Socket socket = new Socket("somehost.somewhere.com", -1);
// Always a good idea to buffer the stream to mitigate blocking.
PrintStream out = new PrintStream( new BufferedOutputStream(socket.getOutputStream()));
out.println("Are you listening?");
DataInputStream in = new DataInputStream( new BufferedInputStream(socket.getInputStream()));
in.readLine();
// ...
// Don't forget to close the socket!
socket.close()
}
catch (Exception e)
// Exception handling logic.

10.  Since UDP is a connectionless protocol; there is no virtual stream
between the hosts so streams are not used for IO.
 UDP applications are not thought of in terms of clients and servers,
but rather in terms of senders and receivers.
 For conversational applications both ends (sender and receiver) will be
changing states from sender to receiver and back again
 Many UDP based applications are simple send a request then receive the
data (sender’s perspective), like a DNS request. The receiver’s perspective
is to ‘listen’ for a request, send the response, listen for more requests.

11.  UDP sockets send and receive Datagrams
 Constructors: two for receiving, four for sending
 DatagramPacket( byte[ ] buff , int len)
 Constructs a DatagramPacket for receiving packets of length len.
 DatagramPacket(byte[] buf, int off, int len)
 Constructs a DatagramPacket for receiving packets of length len,
specifying an offset of off bytes into the buffer.
 DatagramPacket((byte[] buf, int len, InetAddress addr, int port)
 Constructs a datagram packet for sending packets of length len to the
specified port number on the specified host.
 DatagramPacker(byte[] buf, int off, int len, InetAddress addr, int port)
 Constructs a datagram packet for sending packets of length len with
offset off to the specified port number on the specified host.
 DatagramPacket(byte[] buf, int off, int len, SocketAddress addr)
 Constructs a datagram packet for sending packets of length len with
offset off to the specified port number on the specified host.

12.  Constructors
 DatagramSocket()
 Constructs a datagram socket and binds it to any available port on the
local host.
 DatagramSocket(DatagramSocketImpl impl)
 Creates an unbound datagram socket with the specified
DatagramSocketImpl.
 DatagramSocket(int port)
 Constructs a datagram socket and binds it to the specified port on the
local host.
 DatagramSocket(int port, InetAddress iaddr)
 Creates a datagram socket, bound to the specified local address.
 DatagramSocket(SocketAddress bindaddr)
 Creates a datagram socket, bound to the specified local socket address.