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 are always enabled on a DatagramSocket. In order to receive broadcast packets a DatagramSocket should be bound to the wildcard address. In some implementations, broadcast packets may also be received when a DatagramSocket is bound to a more specific address.

Example: DatagramSocket s = new DatagramSocket(null); s.bind(new InetSocketAddress(8888)); Which is equivalent to: DatagramSocket s = new DatagramSocket(8888); Both cases will create a DatagramSocket able to receive broadcasts on UDP port 8888.

Since:

JDK1.0

See Also:

DatagramPacket , DatagramChannel

Constructor Summary

	DatagramSocket () Constructs a datagram socket and binds it to any available port on the local host machine.
protected	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 machine.
	DatagramSocket (int port, InetAddress laddr) Creates a datagram socket, bound to the specified local address.
	DatagramSocket (SocketAddress bindaddr) Creates a datagram socket, bound to the specified local socket address.

Method Summary

void	bind (SocketAddress addr) Binds this DatagramSocket to a specific address & port.
void	close () Closes this datagram socket.
void	connect (InetAddress address, int port) Connects the socket to a remote address for this socket.
void	connect (SocketAddress addr) Connects this socket to a remote socket address (IP address + port number).
void	disconnect () Disconnects the socket.
boolean	getBroadcast () Tests if SO_BROADCAST is enabled.
DatagramChannel	getChannel () Returns the unique DatagramChannel object associated with this datagram socket, if any.
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.
SocketAddress	getLocalSocketAddress () Returns the address of the endpoint this socket is bound to, or null if it is not bound yet.
int	getPort () Returns the port for this socket.
int	getReceiveBufferSize () Get value of the SO_RCVBUF option for this DatagramSocket, that is the buffer size used by the platform for input on this DatagramSocket.
SocketAddress	getRemoteSocketAddress () Returns the address of the endpoint this socket is connected to, or null if it is unconnected.
boolean	getReuseAddress () Tests if SO_REUSEADDR is enabled.
int	getSendBufferSize () Get value of the SO_SNDBUF option for this DatagramSocket, that is the buffer size used by the platform for output on this DatagramSocket.
int	getSoTimeout () Retrive setting for SO_TIMEOUT.
int	getTrafficClass () Gets traffic class or type-of-service in the IP datagram header for packets sent from this DatagramSocket.
boolean	isBound () Returns the binding state of the socket.
boolean	isClosed () Returns whether the socket is closed or not.
boolean	isConnected () Returns the connection state of the socket.
void	receive (DatagramPacket p) Receives a datagram packet from this socket.
void	send (DatagramPacket p) Sends a datagram packet from this socket.
void	setBroadcast (boolean on) Enable/disable SO_BROADCAST.
static void	setDatagramSocketImplFactory (DatagramSocketImplFactory fac) Sets the datagram socket implementation factory for the application.
void	setReceiveBufferSize (int size) Sets the SO_RCVBUF option to the specified value for this DatagramSocket.
void	setReuseAddress (boolean on) Enable/disable the SO_REUSEADDR socket option.
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.
void	setTrafficClass (int tc) Sets traffic class or type-of-service octet in the IP datagram header for datagrams sent from this DatagramSocket.

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. The socket will be bound to the wildcard address, an IP address chosen by the kernel.

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

protected DatagramSocket(DatagramSocketImpl    impl)

Creates an unbound datagram socket with the specified DatagramSocketImpl.

Parameters:

impl - an instance of a DatagramSocketImpl the subclass wishes to use on the DatagramSocket.

Since:

1.4

DatagramSocket

public DatagramSocket(SocketAddress    bindaddr)
               throws SocketException   

Creates a datagram socket, bound to the specified local socket address.

If, if the address is null, creates an unbound socket.

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

Parameters:

bindaddr - local socket address to bind, or null for an unbound socket.

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:

1.4

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. The socket will be bound to the wildcard address, an IP address chosen by the kernel.

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 the IP address is 0.0.0.0, the socket will be bound to the wildcard address, an IP address chosen by the kernel.

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

bind

public void bind(SocketAddress    addr)
          throws SocketException   

Binds this DatagramSocket to a specific address & port.

If the address is null, then the system will pick up an ephemeral port and a valid local address to bind the socket.

Parameters:

addr - The address & port to bind to.

Throws:

SocketException - if any error happens during the bind, or if the socket is already bound.

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

IllegalArgumentException - if addr is a SocketAddress subclass not supported by this socket.

Since:

1.4

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.

If the remote destination to which the socket is connected does not exist, or is otherwise unreachable, and if an ICMP destination unreachable packet has been received for that address, then a subsequent call to send or receive may throw a PortUnreachableException. Note, there is no guarantee that the exception will be thrown.

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 null, 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)

connect

public void connect(SocketAddress    addr)
             throws SocketException   

Connects this socket to a remote socket address (IP address + port number).

Parameters:

addr - The remote address.

Throws:

SocketException - if the connect fails

IllegalArgumentException - if addr is null or addr is a SocketAddress subclass not supported by this socket

Since:

1.4

See Also:

connect(java.net.InetAddress, int)

disconnect

public void disconnect()

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

See Also:

connect(java.net.InetAddress, int)

isBound

public boolean isBound()

Returns the binding state of the socket.

Returns:

true if the socket succesfuly bound to an address

Since:

1.4

isConnected

public boolean isConnected()

Returns the connection state of the socket.

Returns:

true if the socket succesfuly connected to a server

Since:

1.4

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.

getRemoteSocketAddress

public SocketAddress    getRemoteSocketAddress()

Returns the address of the endpoint this socket is connected to, or null if it is unconnected.

Returns:

a SocketAddress representing the remote endpoint of this socket, or null if it is not connected yet.

Since:

1.4

See Also:

getInetAddress() , getPort() , connect(SocketAddress)

getLocalSocketAddress

public SocketAddress    getLocalSocketAddress()

Returns the address of the endpoint this socket is bound to, or null if it is not bound yet.

Returns:

a SocketAddress representing the local endpoint of this socket, or null if it is not bound yet.

Since:

1.4

See Also:

getLocalAddress() , getLocalPort() , bind(SocketAddress)

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.

PortUnreachableException - may be thrown if the socket is connected to a currently unreachable destination. Note, there is no guarantee that the exception will be thrown.

IllegalBlockingModeException - if this socket has an associated channel, and the channel is in non-blocking mode.

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.

SocketTimeoutException - if setSoTimeout was previously called and the timeout has expired.

PortUnreachableException - may be thrown if the socket is connected to a currently unreachable destination. Note, there is no guarantee that the exception will be thrown.

IllegalBlockingModeException - if this socket has an associated channel, and the channel is in non-blocking mode.

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.

Returns:

the local address to which the socket is bound, or an InetAddress representing any local address if either the socket is not bound, or the security manager checkConnect method does not 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.net.SocketTimeoutException is raised, though the DatagramSocket 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.

Parameters:

timeout - the specified timeout in milliseconds.

Throws:

SocketException