DatagramChannel

public abstract class DatagramChannel extends AbstractSelectableChannel
implements ByteChannel ScatteringByteChannel GatheringByteChannel NetworkChannel

A selectable channel for datagram-oriented sockets.

A datagram channel is created by invoking one of the open methods of this class. It is not possible to create a channel for an arbitrary, pre-existing datagram socket. A newly-created datagram channel is open but not connected. A datagram channel need not be connected in order for the send and receive methods to be used. A datagram channel may be connected, by invoking its connect method, in order to avoid the overhead of the security checks are otherwise performed as part of every send and receive operation. A datagram channel must be connected in order to use the read and write methods, since those methods do not accept or return socket addresses.

Once connected, a datagram channel remains connected until it is disconnected or closed. Whether or not a datagram channel is connected may be determined by invoking its isConnected method.

Socket options are configured using the setOption method. A datagram channel to an Internet Protocol socket supports the following options:

Option Name Description
SO_SNDBUF The size of the socket send buffer
SO_RCVBUF The size of the socket receive buffer
SO_REUSEADDR Re-use address
SO_BROADCAST Allow transmission of broadcast datagrams
IP_TOS The Type of Service (ToS) octet in the Internet Protocol (IP) header
IP_MULTICAST_IF The network interface for Internet Protocol (IP) multicast datagrams
IP_MULTICAST_TTL The time-to-live for Internet Protocol (IP) multicast datagrams
IP_MULTICAST_LOOP Loopback for Internet Protocol (IP) multicast datagrams
Additional (implementation specific) options may also be supported.

Datagram channels are safe for use by multiple concurrent threads. They support concurrent reading and writing, though at most one thread may be reading and at most one thread may be writing at any given time.

Protected Constructor Summary

DatagramChannel(SelectorProvider provider)
Initializes a new instance of this class.

Public Method Summary

abstract DatagramChannel
bind(SocketAddress local)
Binds the channel's socket to a local address.
abstract DatagramChannel
connect(SocketAddress remote)
Connects this channel's socket.
abstract DatagramChannel
disconnect()
Disconnects this channel's socket.
abstract SocketAddress
getRemoteAddress()
Returns the remote address to which this channel's socket is connected.
abstract boolean
isConnected()
Tells whether or not this channel's socket is connected.
static DatagramChannel
open()
Opens a datagram channel.
static DatagramChannel
open(ProtocolFamily family)
Opens a datagram channel.
abstract long
read(ByteBuffer[] dsts, int offset, int length)
Reads a datagram from this channel.
abstract int
read(ByteBuffer dst)
Reads a datagram from this channel.
final long
read(ByteBuffer[] dsts)
Reads a datagram from this channel.
abstract SocketAddress
receive(ByteBuffer dst)
Receives a datagram via this channel.
abstract int
send(ByteBuffer src, SocketAddress target)
Sends a datagram via this channel.
abstract <T> DatagramChannel
setOption(SocketOption<T> name, T value)
Sets the value of a socket option.
abstract DatagramSocket
socket()
Retrieves a datagram socket associated with this channel.
final int
validOps()
Returns an operation set identifying this channel's supported operations.
abstract int
write(ByteBuffer src)
Writes a datagram to this channel.
final long
write(ByteBuffer[] srcs)
Writes a datagram to this channel.
abstract long
write(ByteBuffer[] srcs, int offset, int length)
Writes a datagram to this channel.

Inherited Method Summary

Protected Constructors

protected DatagramChannel (SelectorProvider provider)

Initializes a new instance of this class.

Parameters
provider

Public Methods

public abstract DatagramChannel bind (SocketAddress local)

Binds the channel's socket to a local address.

This method is used to establish an association between the socket and a local address. Once an association is established then the socket remains bound until the channel is closed. If the local parameter has the value null then the socket will be bound to an address that is assigned automatically.

Parameters
local The address to bind the socket, or null to bind the socket to an automatically assigned socket address
Returns
  • This channel
Throws
AlreadyBoundException
UnsupportedAddressTypeException
ClosedChannelException
IOException
SecurityException If a security manager has been installed and its checkListen method denies the operation

public abstract DatagramChannel connect (SocketAddress remote)

Connects this channel's socket.

The channel's socket is configured so that it only receives datagrams from, and sends datagrams to, the given remote peer address. Once connected, datagrams may not be received from or sent to any other address. A datagram socket remains connected until it is explicitly disconnected or until it is closed.

This method performs exactly the same security checks as the connect method of the DatagramSocket class. That is, if a security manager has been installed then this method verifies that its checkAccept and checkConnect methods permit datagrams to be received from and sent to, respectively, the given remote address.

This method may be invoked at any time. It will not have any effect on read or write operations that are already in progress at the moment that it is invoked. If this channel's socket is not bound then this method will first cause the socket to be bound to an address that is assigned automatically, as if invoking the bind method with a parameter of null.

Parameters
remote The remote address to which this channel is to be connected
Returns
  • This datagram channel
Throws
ClosedChannelException If this channel is closed
AsynchronousCloseException If another thread closes this channel while the connect operation is in progress
ClosedByInterruptException If another thread interrupts the current thread while the connect operation is in progress, thereby closing the channel and setting the current thread's interrupt status
SecurityException If a security manager has been installed and it does not permit access to the given remote address
IOException If some other I/O error occurs

public abstract DatagramChannel disconnect ()

Disconnects this channel's socket.

The channel's socket is configured so that it can receive datagrams from, and sends datagrams to, any remote address so long as the security manager, if installed, permits it.

This method may be invoked at any time. It will not have any effect on read or write operations that are already in progress at the moment that it is invoked.

If this channel's socket is not connected, or if the channel is closed, then invoking this method has no effect.

Returns
  • This datagram channel
Throws
IOException If some other I/O error occurs

public abstract SocketAddress getRemoteAddress ()

Returns the remote address to which this channel's socket is connected.

Returns
  • The remote address; null if the channel's socket is not connected
Throws
ClosedChannelException If the channel is closed
IOException If an I/O error occurs

public abstract boolean isConnected ()

Tells whether or not this channel's socket is connected.

Returns
  • true if, and only if, this channel's socket is open and connected

public static DatagramChannel open ()

Opens a datagram channel.

The new channel is created by invoking the openDatagramChannel method of the system-wide default SelectorProvider object. The channel will not be connected.

The ProtocolFamily of the channel's socket is platform (and possibly configuration) dependent and therefore unspecified. The open allows the protocol family to be selected when opening a datagram channel, and should be used to open datagram channels that are intended for Internet Protocol multicasting.

Returns
  • A new datagram channel
Throws
IOException If an I/O error occurs

public static DatagramChannel open (ProtocolFamily family)

Opens a datagram channel.

The family parameter is used to specify the ProtocolFamily. If the datagram channel is to be used for IP multicasing then this should correspond to the address type of the multicast groups that this channel will join.

The new channel is created by invoking the openDatagramChannel method of the system-wide default SelectorProvider object. The channel will not be connected.

Parameters
family The protocol family
Returns
  • A new datagram channel
Throws
UnsupportedOperationException If the specified protocol family is not supported. For example, suppose the parameter is specified as StandardProtocolFamily.INET6 but IPv6 is not enabled on the platform.
IOException If an I/O error occurs

public abstract long read (ByteBuffer[] dsts, int offset, int length)

Reads a datagram from this channel.

This method may only be invoked if this channel's socket is connected, and it only accepts datagrams from the socket's peer. If there are more bytes in the datagram than remain in the given buffers then the remainder of the datagram is silently discarded. Otherwise this method behaves exactly as specified in the ScatteringByteChannel interface.

Parameters
dsts The buffers into which bytes are to be transferred
offset The offset within the buffer array of the first buffer into which bytes are to be transferred; must be non-negative and no larger than dsts.length
length The maximum number of buffers to be accessed; must be non-negative and no larger than dsts.length - offset
Returns
  • The number of bytes read, possibly zero, or -1 if the channel has reached end-of-stream
Throws
NotYetConnectedException If this channel's socket is not connected
IOException

public abstract int read (ByteBuffer dst)

Reads a datagram from this channel.

This method may only be invoked if this channel's socket is connected, and it only accepts datagrams from the socket's peer. If there are more bytes in the datagram than remain in the given buffer then the remainder of the datagram is silently discarded. Otherwise this method behaves exactly as specified in the ReadableByteChannel interface.

Parameters
dst The buffer into which bytes are to be transferred
Returns
  • The number of bytes read, possibly zero, or -1 if the channel has reached end-of-stream
Throws
NotYetConnectedException If this channel's socket is not connected
IOException

public final long read (ByteBuffer[] dsts)

Reads a datagram from this channel.

This method may only be invoked if this channel's socket is connected, and it only accepts datagrams from the socket's peer. If there are more bytes in the datagram than remain in the given buffers then the remainder of the datagram is silently discarded. Otherwise this method behaves exactly as specified in the ScatteringByteChannel interface.

Parameters
dsts The buffers into which bytes are to be transferred
Returns
  • The number of bytes read, possibly zero, or -1 if the channel has reached end-of-stream
Throws
NotYetConnectedException If this channel's socket is not connected
IOException

public abstract SocketAddress receive (ByteBuffer dst)

Receives a datagram via this channel.

If a datagram is immediately available, or if this channel is in blocking mode and one eventually becomes available, then the datagram is copied into the given byte buffer and its source address is returned. If this channel is in non-blocking mode and a datagram is not immediately available then this method immediately returns null.

The datagram is transferred into the given byte buffer starting at its current position, as if by a regular read operation. If there are fewer bytes remaining in the buffer than are required to hold the datagram then the remainder of the datagram is silently discarded.

This method performs exactly the same security checks as the receive method of the DatagramSocket class. That is, if the socket is not connected to a specific remote address and a security manager has been installed then for each datagram received this method verifies that the source's address and port number are permitted by the security manager's checkAccept method. The overhead of this security check can be avoided by first connecting the socket via the connect method.

This method may be invoked at any time. If another thread has already initiated a read operation upon this channel, however, then an invocation of this method will block until the first operation is complete. If this channel's socket is not bound then this method will first cause the socket to be bound to an address that is assigned automatically, as if invoking the bind method with a parameter of null.

Parameters
dst The buffer into which the datagram is to be transferred
Returns
  • The datagram's source address, or null if this channel is in non-blocking mode and no datagram was immediately available
Throws
ClosedChannelException If this channel is closed
AsynchronousCloseException If another thread closes this channel while the read operation is in progress
ClosedByInterruptException If another thread interrupts the current thread while the read operation is in progress, thereby closing the channel and setting the current thread's interrupt status
SecurityException If a security manager has been installed and it does not permit datagrams to be accepted from the datagram's sender
IOException If some other I/O error occurs

public abstract int send (ByteBuffer src, SocketAddress target)

Sends a datagram via this channel.

If this channel is in non-blocking mode and there is sufficient room in the underlying output buffer, or if this channel is in blocking mode and sufficient room becomes available, then the remaining bytes in the given buffer are transmitted as a single datagram to the given target address.

The datagram is transferred from the byte buffer as if by a regular write operation.

This method performs exactly the same security checks as the send method of the DatagramSocket class. That is, if the socket is not connected to a specific remote address and a security manager has been installed then for each datagram sent this method verifies that the target address and port number are permitted by the security manager's checkConnect method. The overhead of this security check can be avoided by first connecting the socket via the connect method.

This method may be invoked at any time. If another thread has already initiated a write operation upon this channel, however, then an invocation of this method will block until the first operation is complete. If this channel's socket is not bound then this method will first cause the socket to be bound to an address that is assigned automatically, as if by invoking the bind method with a parameter of null.

Parameters
src The buffer containing the datagram to be sent
target The address to which the datagram is to be sent
Returns
  • The number of bytes sent, which will be either the number of bytes that were remaining in the source buffer when this method was invoked or, if this channel is non-blocking, may be zero if there was insufficient room for the datagram in the underlying output buffer
Throws
ClosedChannelException If this channel is closed
AsynchronousCloseException If another thread closes this channel while the read operation is in progress
ClosedByInterruptException If another thread interrupts the current thread while the read operation is in progress, thereby closing the channel and setting the current thread's interrupt status
SecurityException If a security manager has been installed and it does not permit datagrams to be sent to the given address
IOException If some other I/O error occurs

public abstract DatagramChannel setOption (SocketOption<T> name, T value)

Sets the value of a socket option.

Parameters
name The socket option
value The value of the socket option. A value of null may be a valid value for some socket options.
Returns
  • This channel

public abstract DatagramSocket socket ()

Retrieves a datagram socket associated with this channel.

The returned object will not declare any public methods that are not declared in the DatagramSocket class.

Returns
  • A datagram socket associated with this channel

public final int validOps ()

Returns an operation set identifying this channel's supported operations.

Datagram channels support reading and writing, so this method returns (OP_READ | OP_WRITE).

Returns
  • The valid-operation set

public abstract int write (ByteBuffer src)

Writes a datagram to this channel.

This method may only be invoked if this channel's socket is connected, in which case it sends datagrams directly to the socket's peer. Otherwise it behaves exactly as specified in the WritableByteChannel interface.

Parameters
src The buffer from which bytes are to be retrieved
Returns
  • The number of bytes written, possibly zero
Throws
NotYetConnectedException If this channel's socket is not connected
IOException

public final long write (ByteBuffer[] srcs)

Writes a datagram to this channel.

This method may only be invoked if this channel's socket is connected, in which case it sends datagrams directly to the socket's peer. Otherwise it behaves exactly as specified in the GatheringByteChannel interface.

Parameters
srcs The buffers from which bytes are to be retrieved
Returns
  • The number of bytes sent, which will be either the number of bytes that were remaining in the source buffer when this method was invoked or, if this channel is non-blocking, may be zero if there was insufficient room for the datagram in the underlying output buffer
Throws
NotYetConnectedException If this channel's socket is not connected
IOException

public abstract long write (ByteBuffer[] srcs, int offset, int length)

Writes a datagram to this channel.

This method may only be invoked if this channel's socket is connected, in which case it sends datagrams directly to the socket's peer. Otherwise it behaves exactly as specified in the GatheringByteChannel interface.

Parameters
srcs The buffers from which bytes are to be retrieved
offset The offset within the buffer array of the first buffer from which bytes are to be retrieved; must be non-negative and no larger than srcs.length
length The maximum number of buffers to be accessed; must be non-negative and no larger than srcs.length - offset
Returns
  • The number of bytes sent, which will be either the number of bytes that were remaining in the source buffer when this method was invoked or, if this channel is non-blocking, may be zero if there was insufficient room for the datagram in the underlying output buffer
Throws
NotYetConnectedException If this channel's socket is not connected
IOException