DatagramSocket | Java In A Nutshell, 5th Edition

DatagramSocket

java.net

Java 1.0

This class defines a socket that can receive and send unreliable datagram packets over the network using the UDP protocol. A datagram is a very low-level networking interface: it is simply an array of bytes sent over the network. A datagram does not implement any kind of stream-based communication protocol, and there is no connection established between the sender and the receiver. Datagram packets are called unreliable because the protocol does not make any attempt to ensure they arrive or to resend them if they don't. Thus, packets sent through a DatagramSocket are not guaranteed to arrive in the order sent or even to arrive at all. On the other hand, this low-overhead protocol makes datagram transmission very fast. See Socket and URL for higher-level interfaces to networking. This class was introduced in Java 1.0, and was enhanced in Java 1.4 to allow local and remote addresses to be specified using the protocol-independent SocketAddress class.

send( ) sends a DatagramPacket tHRough the socket. The packet must contain the destination address to which it should be sent. receive( ) waits for data to arrive at the socket and stores it, along with the address of the sender, in the specified DatagramPacket . close( ) closes the socket and frees the local port for reuse. Once close( ) has been called, the DatagramSocket should not be used again, except to call the isClosed( ) method which returns true if the socket has been closed.

Each time a packet is sent or received, the system must perform a security check to ensure that the calling code has permission to send data to or receive data from the specified host. In Java 1.2 and later, if you are sending multiple packets to or receiving multiple packets from a single host, use connect( ) to specify the host with which you are communicating. This causes the security check to be done a single time, but does not allow the socket to communicate with any other host until disconnect( ) is called. Use geTRemoteSocketAddress( ) or getInetAddress( ) and getPort( ) to obtain the network address, if any, that the socket is connected to. Use isConnected( ) to determine if the socket is currently connected in this way.

By default, a DatagramSocket sends data through a local address assigned by the system. If desired, however, you can bind the socket to a specified local address. Do this by using one of the constructors other than the no-arg constructor. Or, bind the DatagramSocket to a local SocketAddress with the bind( ) method. You can determine whether a DatagramSocket is bound with isBound( ) , and you can obtain the local address of the socket with getLocalSocketAddress( ) or with getLocalAddress( ) and getLocalPort( ) .

This class defines a number of get/set method pairs for setting and querying a variety of "socket options" for datagram transmission. setSoTimeout( ) specifies the number of milliseconds that receive( ) waits for a packet to arrive before throwing an InterruptedIOException . Specify milliseconds to wait forever. setSendBufferSize( ) and setReceiveBufferSize( ) set hints as to the underlying size of the networking buffers. setBroadcast( ) , setReuseAddress( ) , and setTrafficClass( ) set more complex socket options; use of these options requires a sophisticated understanding of low-level network protocols, and an explaination of them is beyond the scope of this reference.

In Java 1.4 and later, getChannel( ) returns a java.nio.channels.DatagramChannel associated with this DatagramSocket . Sockets created with one of the DatagramSocket( ) constructors always return null from this method. getChannel( ) only returns a useful value for sockets that were created by and belong to a DatagramChannel .

 public class  DatagramSocket  {  // Public Constructors  public  DatagramSocket  ( ) throws SocketException;  1.4  public  DatagramSocket  (SocketAddress  bindaddr  ) throws SocketException;        public  DatagramSocket  (int  port  ) throws SocketException;  1.1  public  DatagramSocket  (int  port  , InetAddress  laddr  ) throws SocketException;  // Protected Constructors   1.4  publicprotected  DatagramSocket  (DatagramSocketImpl  impl  );  // Public Class Methods   1.3  public static void  setDatagramSocketImplFactory  (DatagramSocketImplFactory  fac  ) throws java.io.IOException;  synchronized   // Public Instance Methods   1.4  public void  bind  (SocketAddress  addr  ) throws SocketException;  synchronized  public void  close  ( );  1.4  public void  connect  (SocketAddress  addr  ) throws SocketException;  1.2  public void  connect  (InetAddress  address  , int  port  );  1.2  public void  disconnect  ( );  1.4  public boolean  getBroadcast  ( )  throws SocketException;  synchronized default:true   1.4  public java.nio.channels.DatagramChannel  getChannel  ( );  constant default:null   1.2  public InetAddress  getInetAddress  ( );  default:null   1.1  public InetAddress  getLocalAddress  ( );  default:Inet4Address  public int  getLocalPort  ( );  default:32777   1.4  public SocketAddress  getLocalSocketAddress  ( );  default:InetSocketAddress   1.2  public int  getPort  ( );  default:-1   1.2  public int  getReceiveBufferSize  ( )  throws SocketException;  synchronized default:32767   1.4  public SocketAddress  getRemoteSocketAddress  ( );  default:null   1.4  public boolean  getReuseAddress  ( )  throws SocketException;  synchronized default:false   1.2  public int  getSendBufferSize  ( )  throws SocketException;  synchronized default:32767   1.1  public int  getSoTimeout  ( ) throws SocketException;  synchronized default:0   1.4  public int  getTrafficClass  ( ) throws SocketException;  synchronized default:0   1.4  public boolean  isBound  ( );  default:true   1.4  public boolean  isClosed  ( );  default:false   1.4  public boolean  isConnected  ( );  default:false  public void  receive  (DatagramPacket  p  ) throws java.io.IOException;  synchronized  public void  send  (DatagramPacket  p  ) throws java.io.IOException;  1.4  public void  setBroadcast  (boolean  on  ) throws SocketException;  synchronized   1.2  public void  setReceiveBufferSize  (int  size  ) throws SocketException;  synchronized   1.4  public void  setReuseAddress  (boolean  on  ) throws SocketException;  synchronized   1.2  public void  setSendBufferSize  (int  size  ) throws SocketException;  synchronized   1.1  public void  setSoTimeout  (int  timeout  ) throws SocketException;  synchronized   1.4  public void  setTrafficClass  (int  tc  ) throws SocketException;  synchronized  }

Subclasses

MulticastSocket

Returned By

java.nio.channels.DatagramChannel.socket( )