DatagramChannel

AI-generated Key Takeaways

• DatagramChannel provides a selectable channel for datagram-based network communication using UDP.

• It allows sending and receiving datagrams to specific or any addresses, with or without a connection.

• connect() establishes a connection to a specific address for efficient communication using read() and write().

• send() and receive() enable communication without a connection, handling addressing and security checks.

• Key methods include bind(), connect(), disconnect(), read(), receive(), send(), setOption(), and socket().

public abstract class DatagramChannel extends AbstractSelectableChannel
implements ByteChannel ScatteringByteChannel GatheringByteChannel MulticastChannel

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	getLocalAddress() Returns the socket address that this channel's socket is bound to. If there is a security manager set, its checkConnect method is called with the local address and -1 as its arguments to see if the operation is allowed.
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

From class java.nio.channels.spi.AbstractSelectableChannel

final Object	blockingLock() Retrieves the object upon which the configureBlocking and register methods synchronize.
final SelectableChannel	configureBlocking(boolean block) Adjusts this channel's blocking mode.
final void	implCloseChannel() Closes this channel.
abstract void	implCloseSelectableChannel() Closes this selectable channel.
abstract void	implConfigureBlocking(boolean block) Adjusts this channel's blocking mode.
final boolean	isBlocking() Tells whether or not every I/O operation on this channel will block until it completes.
final boolean	isRegistered() Tells whether or not this channel is currently registered with any selectors.
final SelectionKey	keyFor(Selector sel) Retrieves the key representing the channel's registration with the given selector.
final SelectorProvider	provider() Returns the provider that created this channel.
final SelectionKey	register(Selector sel, int ops, Object att) Registers this channel with the given selector, returning a selection key.

From class java.nio.channels.SelectableChannel

abstract Object	blockingLock() Retrieves the object upon which the configureBlocking and register methods synchronize.
abstract SelectableChannel	configureBlocking(boolean block) Adjusts this channel's blocking mode.
abstract boolean	isBlocking() Tells whether or not every I/O operation on this channel will block until it completes.
abstract boolean	isRegistered() Tells whether or not this channel is currently registered with any selectors.
abstract SelectionKey	keyFor(Selector sel) Retrieves the key representing the channel's registration with the given selector.
abstract SelectorProvider	provider() Returns the provider that created this channel.
abstract SelectionKey	register(Selector sel, int ops, Object att) Registers this channel with the given selector, returning a selection key.
final SelectionKey	register(Selector sel, int ops) Registers this channel with the given selector, returning a selection key.
abstract int	validOps() Returns an operation set identifying this channel's supported operations.

From class java.nio.channels.spi.AbstractInterruptibleChannel

final void	begin() Marks the beginning of an I/O operation that might block indefinitely.
final void	close() Closes this channel.
final void	end(boolean completed) Marks the end of an I/O operation that might block indefinitely.
abstract void	implCloseChannel() Closes this channel.
final boolean	isOpen() Tells whether or not this channel is open.

From class java.lang.Object

Object	clone() Creates and returns a copy of this Object.
boolean	equals(Object obj) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of Class that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait(long timeout, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait(long timeout) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object.

From interface java.nio.channels.Channel

abstract void	close() Closes this channel.
abstract boolean	isOpen() Tells whether or not this channel is open.

From interface java.nio.channels.InterruptibleChannel

abstract void

close() Closes this channel.

From interface java.nio.channels.ScatteringByteChannel

abstract long	read(ByteBuffer[] dsts, int offset, int length) Reads a sequence of bytes from this channel into a subsequence of the given buffers.
abstract long	read(ByteBuffer[] dsts) Reads a sequence of bytes from this channel into the given buffers.

From interface java.nio.channels.GatheringByteChannel

abstract long	write(ByteBuffer[] srcs) Writes a sequence of bytes to this channel from the given buffers.
abstract long	write(ByteBuffer[] srcs, int offset, int length) Writes a sequence of bytes to this channel from a subsequence of the given buffers.

From interface java.nio.channels.MulticastChannel

abstract void	close() Closes this channel.
abstract MembershipKey	join(InetAddress group, NetworkInterface interf) Joins a multicast group to begin receiving all datagrams sent to the group, returning a membership key.
abstract MembershipKey	join(InetAddress group, NetworkInterface interf, InetAddress source) Joins a multicast group to begin receiving datagrams sent to the group from a given source address.

From interface java.io.Closeable

abstract void

close() Closes this stream and releases any system resources associated with it.

From interface java.nio.channels.ReadableByteChannel

abstract int

read(ByteBuffer dst) Reads a sequence of bytes from this channel into the given buffer.

From interface java.nio.channels.WritableByteChannel

abstract int

write(ByteBuffer src) Writes a sequence of bytes to this channel from the given buffer.

From interface java.nio.channels.NetworkChannel

abstract NetworkChannel	bind(SocketAddress local) Binds the channel's socket to a local address.
abstract SocketAddress	getLocalAddress() Returns the socket address that this channel's socket is bound to.
abstract <T> T	getOption(SocketOption<T> name) Returns the value of a socket option.
abstract <T> NetworkChannel	setOption(SocketOption<T> name, T value) Sets the value of a socket option.
abstract Set<SocketOption<?>>	supportedOptions() Returns a set of the socket options supported by this channel.

From interface java.lang.AutoCloseable

abstract void

close() Closes this resource, relinquishing any underlying resources.

Protected Constructors

protected DatagramChannel (SelectorProvider provider)

Initializes a new instance of this class.

Parameters

provider	The provider that created this channel

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 getLocalAddress ()

Returns the socket address that this channel's socket is bound to.

Where the channel is bound to an Internet Protocol socket address then the return value from this method is of type InetSocketAddress.

If there is a security manager set, its checkConnect method is called with the local address and -1 as its arguments to see if the operation is allowed. If the operation is not allowed, a SocketAddress representing the loopback address and the local port of the channel's socket is returned.

Returns

• The SocketAddress that the socket is bound to, or the SocketAddress representing the loopback address if denied by the security manager, or null if the channel's socket is not bound

Throws

ClosedChannelException
IOException

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 multicasting 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

Throws

UnsupportedOperationException
IllegalArgumentException
ClosedChannelException
IOException

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 (SelectionKey.OP_READ | SelectionKey.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