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java.net
Class DatagramSocket

java.lang.Object
  |
  +--java.net.DatagramSocket

Direct Known Subclasses:

MulticastSocket

public class DatagramSocket

extends Object

This class represents a socket for sending and receiving datagram packets.

A datagram socket is the sending or receiving point for a packet delivery service. Each packet sent or received on a datagram socket is individually addressed and routed. Multiple packets sent from one machine to another may be routed differently, and may arrive in any order.

UDP broadcasts sends and receives are always enabled on a DatagramSocket.

Since:

JDK1.0

See Also:

DatagramPacket

Constructor Summary

DatagramSocket()
Constructs a datagram socket and binds it to any available port on the local host machine.

DatagramSocket(int port)
Constructs a datagram socket and binds it to the specified port on the local host machine.

DatagramSocket(int port, InetAddress laddr)
Creates a datagram socket, bound to the specified local address.

Method Summary

void	close() Closes this datagram socket.
void	connect(InetAddress address, int port) Connects the socket to a remote address for this socket.
void	disconnect() Disconnects the socket.
InetAddress	getInetAddress() Returns the address to which this socket is connected.
InetAddress	getLocalAddress() Gets the local address to which the socket is bound.
int	getLocalPort() Returns the port number on the local host to which this socket is bound.
int	getPort() Returns the port for this socket.
int	getReceiveBufferSize() Get value of the SO_RCVBUF option for this socket, that is the buffer size used by the platform for input on the this Socket.
int	getSendBufferSize() Get value of the SO_SNDBUF option for this socket, that is the buffer size used by the platform for output on the this Socket.
int	getSoTimeout() Retrive setting for SO_TIMEOUT.
void	receive(DatagramPacket p) Receives a datagram packet from this socket.
void	send(DatagramPacket p) Sends a datagram packet from this socket.
void	setReceiveBufferSize(int size) Sets the SO_RCVBUF option to the specified value for this DatagramSocket.
void	setSendBufferSize(int size) Sets the SO_SNDBUF option to the specified value for this DatagramSocket.
void	setSoTimeout(int timeout) Enable/disable SO_TIMEOUT with the specified timeout, in milliseconds.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

DatagramSocket

public DatagramSocket()
               throws SocketException

Constructs a datagram socket and binds it to any available port on the local host machine.

If there is a security manager, its checkListen method is first called with 0 as its argument to ensure the operation is allowed. This could result in a SecurityException.

Throws:

SocketException - if the socket could not be opened, or the socket could not bind to the specified local port.

SecurityException - if a security manager exists and its checkListen method doesn't allow the operation.

See Also:

SecurityManager.checkListen(int)

DatagramSocket

public DatagramSocket(int port)
               throws SocketException

Constructs a datagram socket and binds it to the specified port on the local host machine.

If there is a security manager, its checkListen method is first called with the port argument as its argument to ensure the operation is allowed. This could result in a SecurityException.

Parameters:

port - port to use.

Throws:

SocketException - if the socket could not be opened, or the socket could not bind to the specified local port.

SecurityException - if a security manager exists and its checkListen method doesn't allow the operation.

See Also:

SecurityManager.checkListen(int)

DatagramSocket

public DatagramSocket(int port,
                      InetAddress laddr)
               throws SocketException

Creates a datagram socket, bound to the specified local address. The local port must be between 0 and 65535 inclusive.

If there is a security manager, its checkListen method is first called with the port argument as its argument to ensure the operation is allowed. This could result in a SecurityException.

Parameters:

port - local port to use

laddr - local address to bind

Throws:

SocketException - if the socket could not be opened, or the socket could not bind to the specified local port.

SecurityException - if a security manager exists and its checkListen method doesn't allow the operation.

Since:

JDK1.1

See Also:

SecurityManager.checkListen(int)

Method Detail

connect

public void connect(InetAddress address,
                    int port)

Connects the socket to a remote address for this socket. When a socket is connected to a remote address, packets may only be sent to or received from that address. By default a datagram socket is not connected.

A caller's permission to send and receive datagrams to a given host and port are checked at connect time. When a socket is connected, receive and send will not perform any security checks on incoming and outgoing packets, other than matching the packet's and the socket's address and port. On a send operation, if the packet's address is set and the packet's address and the socket's address do not match, an IllegalArgumentException will be thrown. A socket connected to a multicast address may only be used to send packets.

Parameters:

address - the remote address for the socket

port - the remote port for the socket.

Throws:

IllegalArgumentException - if the address is invalid or the port is out of range.

SecurityException - if the caller is not allowed to send datagrams to and receive datagrams from the address and port.

See Also:

disconnect(), send(java.net.DatagramPacket), receive(java.net.DatagramPacket)

disconnect

public void disconnect()

Disconnects the socket. This does nothing if the socket is not connected.

See Also:

connect(java.net.InetAddress, int)

getInetAddress

public InetAddress getInetAddress()

Returns the address to which this socket is connected. Returns null if the socket is not connected.

Returns:

the address to which this socket is connected.

getPort

public int getPort()

Returns the port for this socket. Returns -1 if the socket is not connected.

Returns:

the port to which this socket is connected.

send

public void send(DatagramPacket p)
          throws IOException

Sends a datagram packet from this socket. The DatagramPacket includes information indicating the data to be sent, its length, the IP address of the remote host, and the port number on the remote host.

If there is a security manager, and the socket is not currently connected to a remote address, this method first performs some security checks. First, if p.getAddress().isMulticastAddress() is true, this method calls the security manager's checkMulticast method with p.getAddress() as its argument. If the evaluation of that expression is false, this method instead calls the security manager's checkConnect method with arguments p.getAddress().getHostAddress() and p.getPort(). Each call to a security manager method could result in a SecurityException if the operation is not allowed.

Parameters:

p - the DatagramPacket to be sent.

Throws:

IOException - if an I/O error occurs.

SecurityException - if a security manager exists and its checkMulticast or checkConnect method doesn't allow the send.

See Also:

DatagramPacket, SecurityManager.checkMulticast(InetAddress), SecurityManager.checkConnect(java.lang.String, int)

receive

public void receive(DatagramPacket p)
             throws IOException

Receives a datagram packet from this socket. When this method returns, the DatagramPacket's buffer is filled with the data received. The datagram packet also contains the sender's IP address, and the port number on the sender's machine.

This method blocks until a datagram is received. The length field of the datagram packet object contains the length of the received message. If the message is longer than the packet's length, the message is truncated.

If there is a security manager, a packet cannot be received if the security manager's checkAccept method does not allow it.

Parameters:

p - the DatagramPacket into which to place the incoming data.

Throws:

IOException - if an I/O error occurs.

See Also:

DatagramPacket, DatagramSocket

getLocalAddress

public InetAddress getLocalAddress()

Gets the local address to which the socket is bound.

If there is a security manager, its checkConnect method is first called with the host address and -1 as its arguments to see if the operation is allowed.

Throws:

SecurityException - if a security manager exists and its checkConnect method doesn't allow the operation.

Since:

1.1

See Also:

SecurityManager.checkConnect(java.lang.String, int)

getLocalPort

public int getLocalPort()

Returns the port number on the local host to which this socket is bound.

Returns:

the port number on the local host to which this socket is bound.

setSoTimeout

public void setSoTimeout(int timeout)
                  throws SocketException

Enable/disable SO_TIMEOUT with the specified timeout, in milliseconds. With this option set to a non-zero timeout, a call to receive() for this DatagramSocket will block for only this amount of time. If the timeout expires, a java.io.InterruptedIOException is raised, though the ServerSocket is still valid. The option must be enabled prior to entering the blocking operation to have effect. The timeout must be > 0. A timeout of zero is interpreted as an infinite timeout.

Since:

JDK1.1

getSoTimeout

public int getSoTimeout()
                 throws SocketException

Retrive setting for SO_TIMEOUT. 0 returns implies that the option is disabled (i.e., timeout of infinity).

Since:

JDK1.1

setSendBufferSize

public void setSendBufferSize(int size)
                       throws SocketException

Sets the SO_SNDBUF option to the specified value for this DatagramSocket. The SO_SNDBUF option is used by the platform's networking code as a hint for the size to use to allocate set the underlying network I/O buffers.

Increasing buffer size can increase the performance of network I/O for high-volume connection, while decreasing it can help reduce the backlog of incoming data. For UDP, this sets the maximum size of a packet that may be sent on this socket.

Because SO_SNDBUF is a hint, applications that want to verify what size the buffers were set to should call getSendBufferSize.

Parameters:

size - the size to which to set the send buffer size. This value must be greater than 0.

Throws:

IllegalArgumentException - if the value is 0 or is negative.

getSendBufferSize

public int getSendBufferSize()
                      throws SocketException

Get value of the SO_SNDBUF option for this socket, that is the buffer size used by the platform for output on the this Socket.

See Also:

setSendBufferSize(int)

setReceiveBufferSize

public void setReceiveBufferSize(int size)
                          throws SocketException

Sets the SO_RCVBUF option to the specified value for this DatagramSocket. The SO_RCVBUF option is used by the platform's networking code as a hint for the size to use to allocate set the underlying network I/O buffers.

Increasing buffer size can increase the performance of network I/O for high-volume connection, while decreasing it can help reduce the backlog of incoming data. For UDP, this sets the maximum size of a packet that may be sent on this socket.

Because SO_RCVBUF is a hint, applications that want to verify what size the buffers were set to should call getReceiveBufferSize.

Parameters:

size - the size to which to set the receive buffer size. This value must be greater than 0.

Throws:

IllegalArgumentException - if the value is 0 or is negative.

getReceiveBufferSize

public int getReceiveBufferSize()
                         throws SocketException

Get value of the SO_RCVBUF option for this socket, that is the buffer size used by the platform for input on the this Socket.

See Also:

setReceiveBufferSize(int)

close

public void close()

Closes this datagram socket.