public abstract class DatagramChannel extends AbstractSelectableChannel implements ByteChannel, ScatteringByteChannel, GatheringByteChannel, MulticastChannel
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:
Additional (implementation specific) options may also be supported.
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
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.
Modifier | Constructor and Description |
---|---|
protected |
DatagramChannel(SelectorProvider provider)
Initializes a new instance of this class.
|
Modifier and Type | Method and 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.
|
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.
|
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.
|
blockingLock, configureBlocking, implCloseChannel, implCloseSelectableChannel, implConfigureBlocking, isBlocking, isRegistered, keyFor, provider, register
register
begin, close, end, isOpen
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
close, join, join
getOption, supportedOptions
protected DatagramChannel(SelectorProvider provider)
provider
- The provider that created this channelpublic static DatagramChannel open() throws IOException
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.
IOException
- If an I/O error occurspublic static DatagramChannel open(ProtocolFamily family) throws IOException
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.
family
- The protocol familyUnsupportedOperationException
- 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 occurspublic final int validOps()
Datagram channels support reading and writing, so this method
returns (SelectionKey.OP_READ
| SelectionKey.OP_WRITE
).
validOps
in class SelectableChannel
public abstract DatagramChannel bind(SocketAddress local) throws IOException
NetworkChannel
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.
bind
in interface NetworkChannel
local
- The address to bind the socket, or null
to bind the socket
to an automatically assigned socket addressAlreadyBoundException
- If the socket is already boundUnsupportedAddressTypeException
- If the type of the given address is not supportedClosedChannelException
- If the channel is closedIOException
- If some other I/O error occursSecurityException
- If a security manager has been installed and its checkListen
method denies the
operationNetworkChannel.getLocalAddress()
public abstract <T> DatagramChannel setOption(SocketOption<T> name, T value) throws IOException
NetworkChannel
setOption
in interface NetworkChannel
T
- The type of the socket option valuename
- The socket optionvalue
- The value of the socket option. A value of null
may be
a valid value for some socket options.UnsupportedOperationException
- If the socket option is not supported by this channelIllegalArgumentException
- If the value is not a valid value for this socket optionClosedChannelException
- If this channel is closedIOException
- If an I/O error occursStandardSocketOptions
public abstract DatagramSocket socket()
The returned object will not declare any public methods that are not
declared in the DatagramSocket
class.
public abstract boolean isConnected()
true
if, and only if, this channel's socket
is open
and connectedpublic abstract DatagramChannel connect(SocketAddress remote) throws IOException
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
.
remote
- The remote address to which this channel is to be connectedClosedChannelException
- If this channel is closedAsynchronousCloseException
- If another thread closes this channel
while the connect operation is in progressClosedByInterruptException
- 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 statusSecurityException
- If a security manager has been installed
and it does not permit access to the given remote addressIOException
- If some other I/O error occurspublic abstract DatagramChannel disconnect() throws IOException
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.
IOException
- If some other I/O error occurspublic abstract SocketAddress getRemoteAddress() throws IOException
null
if the channel's socket is not
connectedClosedChannelException
- If the channel is closedIOException
- If an I/O error occurspublic abstract SocketAddress receive(ByteBuffer dst) throws IOException
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
.
dst
- The buffer into which the datagram is to be transferredClosedChannelException
- If this channel is closedAsynchronousCloseException
- If another thread closes this channel
while the read operation is in progressClosedByInterruptException
- 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 statusSecurityException
- If a security manager has been installed
and it does not permit datagrams to be accepted
from the datagram's senderIOException
- If some other I/O error occurspublic abstract int send(ByteBuffer src, SocketAddress target) throws IOException
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
.
src
- The buffer containing the datagram to be senttarget
- The address to which the datagram is to be sentClosedChannelException
- If this channel is closedAsynchronousCloseException
- If another thread closes this channel
while the read operation is in progressClosedByInterruptException
- 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 statusSecurityException
- If a security manager has been installed
and it does not permit datagrams to be sent
to the given addressIOException
- If some other I/O error occurspublic abstract int read(ByteBuffer dst) throws IOException
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.
read
in interface ReadableByteChannel
dst
- The buffer into which bytes are to be transferredNotYetConnectedException
- If this channel's socket is not connectedClosedChannelException
- If this channel is closedAsynchronousCloseException
- If another thread closes this channel
while the read operation is in progressClosedByInterruptException
- 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 statusIOException
- If some other I/O error occurspublic abstract long read(ByteBuffer[] dsts, int offset, int length) throws IOException
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.
read
in interface ScatteringByteChannel
dsts
- The buffers into which bytes are to be transferredoffset
- 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.lengthlength
- The maximum number of buffers to be accessed; must be
non-negative and no larger than
dsts.length - offsetNotYetConnectedException
- If this channel's socket is not connectedClosedChannelException
- If this channel is closedAsynchronousCloseException
- If another thread closes this channel
while the read operation is in progressClosedByInterruptException
- 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 statusIOException
- If some other I/O error occurspublic final long read(ByteBuffer[] dsts) throws IOException
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.
read
in interface ScatteringByteChannel
dsts
- The buffers into which bytes are to be transferredNotYetConnectedException
- If this channel's socket is not connectedClosedChannelException
- If this channel is closedAsynchronousCloseException
- If another thread closes this channel
while the read operation is in progressClosedByInterruptException
- 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 statusIOException
- If some other I/O error occurspublic abstract int write(ByteBuffer src) throws IOException
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.
write
in interface WritableByteChannel
src
- The buffer from which bytes are to be retrievedNotYetConnectedException
- If this channel's socket is not connectedClosedChannelException
- If this channel is closedAsynchronousCloseException
- If another thread closes this channel
while the write operation is in progressClosedByInterruptException
- 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 statusIOException
- If some other I/O error occurspublic abstract long write(ByteBuffer[] srcs, int offset, int length) throws IOException
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.
write
in interface GatheringByteChannel
srcs
- The buffers from which bytes are to be retrievedoffset
- 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.lengthlength
- The maximum number of buffers to be accessed; must be
non-negative and no larger than
srcs.length - offsetNotYetConnectedException
- If this channel's socket is not connectedClosedChannelException
- If this channel is closedAsynchronousCloseException
- If another thread closes this channel
while the write operation is in progressClosedByInterruptException
- 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 statusIOException
- If some other I/O error occurspublic final long write(ByteBuffer[] srcs) throws IOException
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.
write
in interface GatheringByteChannel
srcs
- The buffers from which bytes are to be retrievedNotYetConnectedException
- If this channel's socket is not connectedClosedChannelException
- If this channel is closedAsynchronousCloseException
- If another thread closes this channel
while the write operation is in progressClosedByInterruptException
- 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 statusIOException
- If some other I/O error occurspublic abstract SocketAddress getLocalAddress() throws IOException
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.
getLocalAddress
in interface NetworkChannel
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 boundClosedChannelException
- If the channel is closedIOException
- If an I/O error occurs Submit a bug or feature
For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
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