DatagramSocket
Java implements datagrams on top of the UDP protocol by using two classes:
- DatagramPacket object is the data container
- DatagramSocket is the mechanism used to send or receive the DatagramPackets.
DatagramSocket defines four public constructors.
DatagramSocket( ) throws SocketException- creates a DatagramSocket bound to any unused port on the local computer.
DatagramSocket(int port) throws SocketException- creates a DatagramSocket bound to the port specified by port.
DatagramSocket(int port, InetAddress ipAddress) throws SocketException- constructs a DatagramSocket bound to the specified port and InetAddress.
DatagramSocket(SocketAddress address) throws SocketException- constructs a DatagramSocket bound to the specified SocketAddress.
SocketAddress is an abstract class that is implemented by the concrete class InetSocketAddress. InetSocketAddress encapsulates an IP address with a port number.
Two of the most important methods are send( ) and receive( ), which are shown here:
void send(DatagramPacket packet) throws IOException
void receive(DatagramPacket packet) throws IOException
The send( ) method sends packet to the port specified by packet. The receive method waits for a packet to be received from the port specified by packet and returns the result.
Other methods defined:
InetAddress getInetAddress( )- If the socket is connected, then the address is returned. Otherwise, null is returned.
int getLocalPort( )- Returns the number of the local port.
int getPort( )- Returns the number of the port to which the socket is connected. It returns -1 if the socket is not connected to a port.
boolean isBound( )- Returns true if the socket is bound to an address. Returns false otherwise.
boolean isConnected( )- Returns true if the socket is connected to a server. Returns false otherwise.
void setSoTimeout(int millis) throws SocketException- Sets the time-out period to the number of milliseconds passed in millis.