java.nio.channels
Class DatagramChannel

java.lang.Object
  java.nio.channels.spi.AbstractInterruptibleChannel
      java.nio.channels.SelectableChannel
          java.nio.channels.spi.AbstractSelectableChannel
              java.nio.channels.DatagramChannel

All Implemented Interfaces:

ByteChannel, Channel, GatheringByteChannel, InterruptibleChannel, ReadableByteChannel, ScatteringByteChannel, WritableByteChannel

public abstract class DatagramChannel

extends AbstractSelectableChannel

implements ByteChannel, ScatteringByteChannel, GatheringByteChannel

A selectable channel for datagram-oriented sockets.

Datagram channels are not a complete abstraction of network datagram sockets. Binding and the manipulation of socket options must be done through an associated DatagramSocket object obtained by invoking the socket method. It is not possible to create a channel for an arbitrary, pre-existing datagram socket, nor is it possible to specify the DatagramSocketImpl object to be used by a datagram socket associated with a datagram channel.

A datagram channel is created by invoking the open method of this class. 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.

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.

Since:

1.4

Constructor Summary

protected

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

Method Summary

abstract DatagramChannel	connect(SocketAddress remote) Connects this channel's socket.
abstract DatagramChannel	disconnect() Disconnects this channel's socket.
abstract boolean	isConnected() Tells whether or not this channel's socket is connected.
static DatagramChannel	open() Opens a datagram channel.
abstract int	read(ByteBuffer dst) Reads a datagram from this channel.
long	read(ByteBuffer[] dsts) Reads a datagram from this channel.
abstract long	read(ByteBuffer[] dsts, int offset, int length) 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 DatagramSocket	socket() Retrieves a datagram socket associated with this channel.
int	validOps() Returns an operation set identifying this channel's supported operations.
abstract int	write(ByteBuffer src) Writes a datagram to this channel.
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.

Methods inherited from class java.nio.channels.spi.AbstractSelectableChannel

blockingLock, configureBlocking, implCloseChannel, implCloseSelectableChannel, implConfigureBlocking, isBlocking, isRegistered, keyFor, provider, register

Methods inherited from class java.nio.channels.SelectableChannel

register

Methods inherited from class java.nio.channels.spi.AbstractInterruptibleChannel

begin, close, end, isOpen

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.nio.channels.Channel

close, isOpen

Constructor Detail

DatagramChannel

protected DatagramChannel(SelectorProvider provider)

Initializes a new instance of this class.

Method Detail

open

public static DatagramChannel open()
                            throws IOException

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.

Returns:

A new datagram channel

Throws:

IOException - If an I/O error occurs

validOps

public final int validOps()

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

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

Specified by:

validOps in class SelectableChannel

Returns:

The valid-operation set

socket

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

isConnected

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 connected

connect

public abstract DatagramChannel connect(SocketAddress remote)
                                 throws IOException

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.

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

disconnect

public abstract DatagramChannel disconnect()
                                    throws IOException

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

receive

public abstract SocketAddress receive(ByteBuffer dst)
                               throws IOException

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.

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

send

public abstract int send(ByteBuffer src,
                         SocketAddress target)
                  throws IOException

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.

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

read

public abstract int read(ByteBuffer dst)
                  throws IOException

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.

Specified by:

read in interface ReadableByteChannel

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 - If some other I/O error occurs

read

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

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.

Specified by:

read in interface ScatteringByteChannel

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 - If some other I/O error occurs

read

public final long read(ByteBuffer[] dsts)
                throws IOException

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.

Specified by:

read in interface ScatteringByteChannel

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 - If some other I/O error occurs

write

public abstract int write(ByteBuffer src)
                   throws IOException

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.

Specified by:

write in interface WritableByteChannel

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 - If some other I/O error occurs

write

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

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.

Specified by:

write in interface GatheringByteChannel

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 - If some other I/O error occurs

write

public final long write(ByteBuffer[] srcs)
                 throws IOException

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.

Specified by:

write in interface GatheringByteChannel

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 - If some other I/O error occurs