Module java.base

Package 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:

Closeable, AutoCloseable, ByteChannel, Channel, GatheringByteChannel, InterruptibleChannel, MulticastChannel, NetworkChannel, ReadableByteChannel, ScatteringByteChannel, WritableByteChannel

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:

Socket 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.

Since:

1.4

Constructor Summary

Constructors

Modifier	Constructor	Description
protected	DatagramChannel(SelectorProvider provider)	Initializes a new instance of this class.

Method Summary

Modifier and Type	Method	Description
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.
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 int	read(ByteBuffer dst)	Reads a datagram from this channel.
final 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 <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.

Methods declared in class java.nio.channels.spi.AbstractSelectableChannel

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

Methods declared in class java.nio.channels.SelectableChannel

register

Methods declared in class java.nio.channels.spi.AbstractInterruptibleChannel

begin, close, end, isOpen

Methods declared in class java.lang.Object

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

Methods declared in interface java.nio.channels.Channel

isOpen

Methods declared in interface java.nio.channels.MulticastChannel

close, join, join

Methods declared in interface java.nio.channels.NetworkChannel

getOption, supportedOptions

Constructor Details

DatagramChannel

protected DatagramChannel(SelectorProvider provider)

Initializes a new instance of this class.

Parameters:

provider - The provider that created this channel

Method Details

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.

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

See Also:

• java.net.preferIPv4Stack system property

open

public static DatagramChannel open(ProtocolFamily family)
                            throws IOException

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.

API Note:

Unix domain sockets are not supported.

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

Since:

1.7

See Also:

• java.net.preferIPv4Stack system property

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

bind

public abstract DatagramChannel bind(SocketAddress local)
                              throws IOException

Description copied from interface: NetworkChannel

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.

Specified by:

bind in interface NetworkChannel

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 - If the socket is already bound

UnsupportedAddressTypeException - If the type of the given address is not supported

ClosedChannelException - If the channel is closed

IOException - If some other I/O error occurs

SecurityException - If a security manager has been installed and its checkListen method denies the operation

Since:

1.7

See Also:

• NetworkChannel.getLocalAddress()

setOption

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

Description copied from interface: NetworkChannel

Sets the value of a socket option.

Specified by:

setOption in interface NetworkChannel

Type Parameters:

T - The type of the socket option value

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 - If the socket option is not supported by this channel

IllegalArgumentException - If the value is not a valid value for this socket option

ClosedChannelException - If this channel is closed

IOException - If an I/O error occurs

Since:

1.7

See Also:

• StandardSocketOptions

socket

public abstract DatagramSocket socket()

Retrieves a datagram socket associated with this channel.

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 open and 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. Datagrams in the channel's socket receive buffer, which have not been received before invoking this method, may be discarded. The channel's 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. Once connected, no further security checks are performed for datagrams received from, or sent to, the given remote address. Care should be taken to ensure that a connected datagram channel is not shared with untrusted code.

This method may be invoked at any time. If another thread has already initiated a read or write operation upon this channel, then an invocation of this method will block until any such 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:

remote - The remote address to which this channel is to be connected

Returns:

This datagram channel

Throws:

AlreadyConnectedException - If this channel is already connected

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

UnresolvedAddressException - If the given remote address is not fully resolved

UnsupportedAddressTypeException - If the type of the given remote address is not supported

SecurityException - If a security manager has been installed and it does not permit access to the given remote address, or if unbound, the security manager checkListen method denies the operation

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. If another thread has already initiated a read or write operation upon this channel, then an invocation of this method will block until any such operation is complete.

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

API Note:

If this method throws an IOException, the channel's socket may be left in an unspecified state. It is strongly recommended that the channel be closed when disconnect fails.

Returns:

This datagram channel

Throws:

IOException - If some other I/O error occurs

getRemoteAddress

public abstract SocketAddress getRemoteAddress()
                                        throws IOException

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

Since:

1.7

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. Datagrams that are not permitted by the security manager are silently discarded. 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:

IllegalArgumentException - If the buffer is read-only

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 unbound, and a security manager has been installed and its checkListen method denies the operation

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. 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:

AlreadyConnectedException - If this channel is connected to a different address from that specified by target

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

UnresolvedAddressException - If the given remote address is not fully resolved

UnsupportedAddressTypeException - If the type of the given remote address is not supported

SecurityException - If a security manager has been installed and it does not permit datagrams to be sent to the given address, or if unbound, and the security manager's checkListen method denies the operation

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

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

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

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

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

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

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

ClosedChannelException - If this channel is closed

AsynchronousCloseException - If another thread closes this channel while the write operation is in progress

ClosedByInterruptException - If another thread interrupts the current thread while the write operation is in progress, thereby closing the channel and setting the current thread's interrupt status

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

ClosedChannelException - If this channel is closed

AsynchronousCloseException - If another thread closes this channel while the write operation is in progress

ClosedByInterruptException - If another thread interrupts the current thread while the write operation is in progress, thereby closing the channel and setting the current thread's interrupt status

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

ClosedChannelException - If this channel is closed

AsynchronousCloseException - If another thread closes this channel while the write operation is in progress

ClosedByInterruptException - If another thread interrupts the current thread while the write operation is in progress, thereby closing the channel and setting the current thread's interrupt status

IOException - If some other I/O error occurs

getLocalAddress

public abstract SocketAddress getLocalAddress()
                                       throws IOException

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 the channel's socket was initially bound to the wildcard address and is now connected, then the address returned may be the local address selected as the source address for datagrams sent via this channel instead of the wildcard address. When disconnect() is called, the bound address reverts to the wildcard address.

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.

Specified by:

getLocalAddress in interface NetworkChannel

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 - If the channel is closed

IOException - If an I/O error occurs