public abstract class

DatagramChannel

extends AbstractSelectableChannel
implements ByteChannel GatheringByteChannel ScatteringByteChannel
java.lang.Object
   ↳ java.nio.channels.spi.AbstractInterruptibleChannel
     ↳ java.nio.channels.SelectableChannel
       ↳ java.nio.channels.spi.AbstractSelectableChannel
         ↳ java.nio.channels.DatagramChannel

Class Overview

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.

Summary

Protected Constructors
DatagramChannel(SelectorProvider provider)
Initializes a new instance of this class.
Public Methods
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.
abstract long read(ByteBuffer[] dsts, int offset, int length)
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 DatagramSocket socket()
Retrieves a datagram socket associated with this channel.
final int validOps()
Returns an operation set identifying this channel's supported operations.
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.
abstract int write(ByteBuffer src)
Writes a datagram to this channel.
[Expand]
Inherited Methods
From class java.nio.channels.spi.AbstractSelectableChannel
From class java.nio.channels.SelectableChannel
From class java.nio.channels.spi.AbstractInterruptibleChannel
From class java.lang.Object
From interface java.io.Closeable
From interface java.nio.channels.Channel
From interface java.nio.channels.GatheringByteChannel
From interface java.nio.channels.InterruptibleChannel
From interface java.nio.channels.ReadableByteChannel
From interface java.nio.channels.ScatteringByteChannel
From interface java.nio.channels.WritableByteChannel

Protected Constructors

protected DatagramChannel (SelectorProvider provider)

Initializes a new instance of this class.

Public Methods

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.

Parameters
remote The remote address to which this channel is to be connected
Returns
  • This datagram channel
Throws
If this channel is closed
If another thread closes this channel while the connect operation is in progress
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 boolean isConnected ()

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

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

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

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
If this channel's socket is not connected
IOException

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
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
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.

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
If this channel is closed
If another thread closes this channel while the read operation is in progress
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.

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
If this channel is closed
If another thread closes this channel while the read operation is in progress
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 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 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
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
If this channel's socket is not connected
IOException

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
If this channel's socket is not connected
IOException