AsynchronousSocketChannel (Java Platform SE 7 ) (original) (raw)
- java.nio.channels.AsynchronousSocketChannel
All Implemented Interfaces:
Closeable, AutoCloseable, AsynchronousByteChannel, AsynchronousChannel, Channel, NetworkChannel
public abstract class AsynchronousSocketChannel
extends Object
implements AsynchronousByteChannel, NetworkChannel
An asynchronous channel for stream-oriented connecting sockets.
Asynchronous socket channels are created in one of two ways. A newly-createdAsynchronousSocketChannel is created by invoking one of the open methods defined by this class. A newly-created channel is open but not yet connected. A connected AsynchronousSocketChannel is created when a connection is made to the socket of an AsynchronousServerSocketChannel. It is not possible to create an asynchronous socket channel for an arbitrary, pre-existing socket.
A newly-created channel is connected by invoking its connect method; once connected, a channel remains connected until it is closed. Whether or not a socket channel is connected may be determined by invoking its getRemoteAddress method. An attempt to invoke an I/O operation upon an unconnected channel will cause a NotYetConnectedException to be thrown.
Channels of this type are safe for use by multiple concurrent threads. They support concurrent reading and writing, though at most one read operation and one write operation can be outstanding at any time. If a thread initiates a read operation before a previous read operation has completed then a ReadPendingException will be thrown. Similarly, an attempt to initiate a write operation before a previous write has completed will throw a WritePendingException.
Socket options are configured using the setOption method. Asynchronous socket channels support 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_KEEPALIVE Keep connection alive SO_REUSEADDR Re-use address TCP_NODELAY Disable the Nagle algorithm Additional (implementation specific) options may also be supported.
Timeouts
The read and write methods defined by this class allow a timeout to be specified when initiating a read or write operation. If the timeout elapses before an operation completes then the operation completes with the exception InterruptedByTimeoutException. A timeout may leave the channel, or the underlying connection, in an inconsistent state. Where the implementation cannot guarantee that bytes have not been read from the channel then it puts the channel into an implementation specific error state. A subsequent attempt to initiate a read operation causes an unspecified runtime exception to be thrown. Similarly if a write operation times out and the implementation cannot guarantee bytes have not been written to the channel then further attempts to write to the channel cause an unspecified runtime exception to be thrown. When a timeout elapses then the state of the ByteBuffer, or the sequence of buffers, for the I/O operation is not defined. Buffers should be discarded or at least care must be taken to ensure that the buffers are not accessed while the channel remains open. All methods that accept timeout parameters treat values less than or equal to zero to mean that the I/O operation does not timeout.
Since:
1.7
Constructor Summary
Constructors
Modifier Constructor and Description protected AsynchronousSocketChannel(AsynchronousChannelProvider provider) Initializes a new instance of this class. Method Summary
Methods
Modifier and Type Method and Description abstract AsynchronousSocketChannel bind(SocketAddress local) Binds the channel's socket to a local address. abstract Future<Void> connect(SocketAddress remote) Connects this channel. abstract void connect(SocketAddress remote, A attachment,CompletionHandler<Void,? super A> handler) Connects this channel. abstract SocketAddress getRemoteAddress() Returns the remote address to which this channel's socket is connected. static AsynchronousSocketChannel open() Opens an asynchronous socket channel. static AsynchronousSocketChannel open(AsynchronousChannelGroup group) Opens an asynchronous socket channel. AsynchronousChannelProvider provider() Returns the provider that created this channel. abstract Future<Integer> read(ByteBuffer dst) Reads a sequence of bytes from this channel into the given buffer. abstract void read(ByteBuffer[] dsts, int offset, int length, long timeout,TimeUnit unit, A attachment,CompletionHandler<Long,? super A> handler) Reads a sequence of bytes from this channel into a subsequence of the given buffers. void read(ByteBuffer dst, A attachment,CompletionHandler<Integer,? super A> handler) Reads a sequence of bytes from this channel into the given buffer. abstract void read(ByteBuffer dst, long timeout,TimeUnit unit, A attachment,CompletionHandler<Integer,? super A> handler) Reads a sequence of bytes from this channel into the given buffer. abstract AsynchronousSocketChannel setOption(SocketOption name, T value) Sets the value of a socket option. abstract AsynchronousSocketChannel shutdownInput() Shutdown the connection for reading without closing the channel. abstract AsynchronousSocketChannel shutdownOutput() Shutdown the connection for writing without closing the channel. abstract Future<Integer> write(ByteBuffer src) Writes a sequence of bytes to this channel from the given buffer. abstract void write(ByteBuffer[] srcs, int offset, int length, long timeout,TimeUnit unit, A attachment,CompletionHandler<Long,? super A> handler) Writes a sequence of bytes to this channel from a subsequence of the given buffers. void write(ByteBuffer src, A attachment,CompletionHandler<Integer,? super A> handler) Writes a sequence of bytes to this channel from the given buffer. abstract void write(ByteBuffer src, long timeout,TimeUnit unit, A attachment,CompletionHandler<Integer,? super A> handler) Writes a sequence of bytes to this channel from the given buffer. * ### Methods inherited from class java.lang.[Object](../../../java/lang/Object.html "class in java.lang") `[clone](../../../java/lang/Object.html#clone%28%29), [equals](../../../java/lang/Object.html#equals%28java.lang.Object%29), [finalize](../../../java/lang/Object.html#finalize%28%29), [getClass](../../../java/lang/Object.html#getClass%28%29), [hashCode](../../../java/lang/Object.html#hashCode%28%29), [notify](../../../java/lang/Object.html#notify%28%29), [notifyAll](../../../java/lang/Object.html#notifyAll%28%29), [toString](../../../java/lang/Object.html#toString%28%29), [wait](../../../java/lang/Object.html#wait%28%29), [wait](../../../java/lang/Object.html#wait%28long%29), [wait](../../../java/lang/Object.html#wait%28long,%20int%29)` * ### Methods inherited from interface java.nio.channels.[AsynchronousChannel](../../../java/nio/channels/AsynchronousChannel.html "interface in java.nio.channels") `[close](../../../java/nio/channels/AsynchronousChannel.html#close%28%29)` * ### Methods inherited from interface java.nio.channels.[Channel](../../../java/nio/channels/Channel.html "interface in java.nio.channels") `[isOpen](../../../java/nio/channels/Channel.html#isOpen%28%29)` * ### Methods inherited from interface java.nio.channels.[NetworkChannel](../../../java/nio/channels/NetworkChannel.html "interface in java.nio.channels") `[getLocalAddress](../../../java/nio/channels/NetworkChannel.html#getLocalAddress%28%29), [getOption](../../../java/nio/channels/NetworkChannel.html#getOption%28java.net.SocketOption%29), [supportedOptions](../../../java/nio/channels/NetworkChannel.html#supportedOptions%28%29)`Constructor Detail
* #### AsynchronousSocketChannel protected AsynchronousSocketChannel([AsynchronousChannelProvider](../../../java/nio/channels/spi/AsynchronousChannelProvider.html "class in java.nio.channels.spi") provider) Initializes a new instance of this class.Method Detail
* #### provider public final [AsynchronousChannelProvider](../../../java/nio/channels/spi/AsynchronousChannelProvider.html "class in java.nio.channels.spi") provider() Returns the provider that created this channel. * #### open public static [AsynchronousSocketChannel](../../../java/nio/channels/AsynchronousSocketChannel.html "class in java.nio.channels") open([AsynchronousChannelGroup](../../../java/nio/channels/AsynchronousChannelGroup.html "class in java.nio.channels") group) throws [IOException](../../../java/io/IOException.html "class in java.io") Opens an asynchronous socket channel. The new channel is created by invoking the [openAsynchronousSocketChannel](../../../java/nio/channels/spi/AsynchronousChannelProvider.html#openAsynchronousSocketChannel%28java.nio.channels.AsynchronousChannelGroup%29) method on the [AsynchronousChannelProvider](../../../java/nio/channels/spi/AsynchronousChannelProvider.html "class in java.nio.channels.spi") that created the group. If the group parameter is `null` then the resulting channel is created by the system-wide default provider, and bound to the _default group_. Parameters: `group` \- The group to which the newly constructed channel should be bound, or `null` for the default group Returns: A new asynchronous socket channel Throws: `[ShutdownChannelGroupException](../../../java/nio/channels/ShutdownChannelGroupException.html "class in java.nio.channels")` \- If the channel group is shutdown `[IOException](../../../java/io/IOException.html "class in java.io")` \- If an I/O error occurs * #### open public static [AsynchronousSocketChannel](../../../java/nio/channels/AsynchronousSocketChannel.html "class in java.nio.channels") open() throws [IOException](../../../java/io/IOException.html "class in java.io") Opens an asynchronous socket channel. This method returns an asynchronous socket channel that is bound to the _default group_.This method is equivalent to evaluating the expression: > open((AsynchronousChannelGroup)null); > Returns: A new asynchronous socket channel Throws: `[IOException](../../../java/io/IOException.html "class in java.io")` \- If an I/O error occurs * #### bind public abstract [AsynchronousSocketChannel](../../../java/nio/channels/AsynchronousSocketChannel.html "class in java.nio.channels") bind([SocketAddress](../../../java/net/SocketAddress.html "class in java.net") local) throws [IOException](../../../java/io/IOException.html "class in java.io") 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](../../../java/nio/channels/NetworkChannel.html#bind%28java.net.SocketAddress%29)` in interface `[NetworkChannel](../../../java/nio/channels/NetworkChannel.html "interface in java.nio.channels")` Parameters: `local` \- The address to bind the socket, or `null` to bind the socket to an automatically assigned socket address Returns: This channel Throws: `[ConnectionPendingException](../../../java/nio/channels/ConnectionPendingException.html "class in java.nio.channels")` \- If a connection operation is already in progress on this channel `[AlreadyBoundException](../../../java/nio/channels/AlreadyBoundException.html "class in java.nio.channels")` \- If the socket is already bound `[UnsupportedAddressTypeException](../../../java/nio/channels/UnsupportedAddressTypeException.html "class in java.nio.channels")` \- If the type of the given address is not supported `[ClosedChannelException](../../../java/nio/channels/ClosedChannelException.html "class in java.nio.channels")` \- If the channel is closed `[IOException](../../../java/io/IOException.html "class in java.io")` \- If some other I/O error occurs See Also: [NetworkChannel.getLocalAddress()](../../../java/nio/channels/NetworkChannel.html#getLocalAddress%28%29) * #### setOption public abstract <T> [AsynchronousSocketChannel](../../../java/nio/channels/AsynchronousSocketChannel.html "class in java.nio.channels") setOption([SocketOption](../../../java/net/SocketOption.html "interface in java.net")<T> name, T value) throws [IOException](../../../java/io/IOException.html "class in java.io") Sets the value of a socket option. **Specified by:** `[setOption](../../../java/nio/channels/NetworkChannel.html#setOption%28java.net.SocketOption,%20T%29)` in interface `[NetworkChannel](../../../java/nio/channels/NetworkChannel.html "interface in java.nio.channels")` 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: `[IllegalArgumentException](../../../java/lang/IllegalArgumentException.html "class in java.lang")` \- If the value is not a valid value for this socket option `[ClosedChannelException](../../../java/nio/channels/ClosedChannelException.html "class in java.nio.channels")` \- If this channel is closed `[IOException](../../../java/io/IOException.html "class in java.io")` \- If an I/O error occurs See Also: [StandardSocketOptions](../../../java/net/StandardSocketOptions.html "class in java.net") * #### shutdownInput public abstract [AsynchronousSocketChannel](../../../java/nio/channels/AsynchronousSocketChannel.html "class in java.nio.channels") shutdownInput() throws [IOException](../../../java/io/IOException.html "class in java.io") Shutdown the connection for reading without closing the channel. Once shutdown for reading then further reads on the channel will return `-1`, the end-of-stream indication. If the input side of the connection is already shutdown then invoking this method has no effect. The effect on an outstanding read operation is system dependent and therefore not specified. The effect, if any, when there is data in the socket receive buffer that has not been read, or data arrives subsequently, is also system dependent. Returns: The channel Throws: `[NotYetConnectedException](../../../java/nio/channels/NotYetConnectedException.html "class in java.nio.channels")` \- If this channel is not yet connected `[ClosedChannelException](../../../java/nio/channels/ClosedChannelException.html "class in java.nio.channels")` \- If this channel is closed `[IOException](../../../java/io/IOException.html "class in java.io")` \- If some other I/O error occurs * #### shutdownOutput public abstract [AsynchronousSocketChannel](../../../java/nio/channels/AsynchronousSocketChannel.html "class in java.nio.channels") shutdownOutput() throws [IOException](../../../java/io/IOException.html "class in java.io") Shutdown the connection for writing without closing the channel. Once shutdown for writing then further attempts to write to the channel will throw [ClosedChannelException](../../../java/nio/channels/ClosedChannelException.html "class in java.nio.channels"). If the output side of the connection is already shutdown then invoking this method has no effect. The effect on an outstanding write operation is system dependent and therefore not specified. Returns: The channel Throws: `[NotYetConnectedException](../../../java/nio/channels/NotYetConnectedException.html "class in java.nio.channels")` \- If this channel is not yet connected `[ClosedChannelException](../../../java/nio/channels/ClosedChannelException.html "class in java.nio.channels")` \- If this channel is closed `[IOException](../../../java/io/IOException.html "class in java.io")` \- If some other I/O error occurs * #### getRemoteAddress public abstract [SocketAddress](../../../java/net/SocketAddress.html "class in java.net") getRemoteAddress() throws [IOException](../../../java/io/IOException.html "class in java.io") Returns the remote address to which this channel's socket is connected. Where the channel is bound and connected to an Internet Protocol socket address then the return value from this method is of type [InetSocketAddress](../../../java/net/InetSocketAddress.html "class in java.net"). Returns: The remote address; `null` if the channel's socket is not connected Throws: `[ClosedChannelException](../../../java/nio/channels/ClosedChannelException.html "class in java.nio.channels")` \- If the channel is closed `[IOException](../../../java/io/IOException.html "class in java.io")` \- If an I/O error occurs * #### connect public abstract <A> void connect([SocketAddress](../../../java/net/SocketAddress.html "class in java.net") remote, A attachment, [CompletionHandler](../../../java/nio/channels/CompletionHandler.html "interface in java.nio.channels")<[Void](../../../java/lang/Void.html "class in java.lang"),? super A> handler) Connects this channel. This method initiates an operation to connect this channel. The`handler` parameter is a completion handler that is invoked when the connection is successfully established or connection cannot be established. If the connection cannot be established then the channel is closed. This method performs exactly the same security checks as the [Socket](../../../java/net/Socket.html "class in java.net") class. That is, if a security manager has been installed then this method verifies that its [checkConnect](../../../java/lang/SecurityManager.html#checkConnect%28java.lang.String,%20int%29) method permits connecting to the address and port number of the given remote endpoint. Parameters: `remote` \- The remote address to which this channel is to be connected `attachment` \- The object to attach to the I/O operation; can be `null` `handler` \- The handler for consuming the result Throws: `[UnresolvedAddressException](../../../java/nio/channels/UnresolvedAddressException.html "class in java.nio.channels")` \- If the given remote address is not fully resolved `[UnsupportedAddressTypeException](../../../java/nio/channels/UnsupportedAddressTypeException.html "class in java.nio.channels")` \- If the type of the given remote address is not supported `[AlreadyConnectedException](../../../java/nio/channels/AlreadyConnectedException.html "class in java.nio.channels")` \- If this channel is already connected `[ConnectionPendingException](../../../java/nio/channels/ConnectionPendingException.html "class in java.nio.channels")` \- If a connection operation is already in progress on this channel `[ShutdownChannelGroupException](../../../java/nio/channels/ShutdownChannelGroupException.html "class in java.nio.channels")` \- If the channel group has terminated `[SecurityException](../../../java/lang/SecurityException.html "class in java.lang")` \- If a security manager has been installed and it does not permit access to the given remote endpoint See Also: [getRemoteAddress()](../../../java/nio/channels/AsynchronousSocketChannel.html#getRemoteAddress%28%29) * #### connect public abstract [Future](../../../java/util/concurrent/Future.html "interface in java.util.concurrent")<[Void](../../../java/lang/Void.html "class in java.lang")> connect([SocketAddress](../../../java/net/SocketAddress.html "class in java.net") remote) Connects this channel. This method initiates an operation to connect this channel. This method behaves in exactly the same manner as the [connect(SocketAddress, Object, CompletionHandler)](../../../java/nio/channels/AsynchronousSocketChannel.html#connect%28java.net.SocketAddress,%20A,%20java.nio.channels.CompletionHandler%29) method except that instead of specifying a completion handler, this method returns a `Future` representing the pending result. The `Future`'s [get](../../../java/util/concurrent/Future.html#get%28%29) method returns `null` on successful completion. Parameters: `remote` \- The remote address to which this channel is to be connected Returns: A `Future` object representing the pending result Throws: `[UnresolvedAddressException](../../../java/nio/channels/UnresolvedAddressException.html "class in java.nio.channels")` \- If the given remote address is not fully resolved `[UnsupportedAddressTypeException](../../../java/nio/channels/UnsupportedAddressTypeException.html "class in java.nio.channels")` \- If the type of the given remote address is not supported `[AlreadyConnectedException](../../../java/nio/channels/AlreadyConnectedException.html "class in java.nio.channels")` \- If this channel is already connected `[ConnectionPendingException](../../../java/nio/channels/ConnectionPendingException.html "class in java.nio.channels")` \- If a connection operation is already in progress on this channel `[SecurityException](../../../java/lang/SecurityException.html "class in java.lang")` \- If a security manager has been installed and it does not permit access to the given remote endpoint * #### read public abstract <A> void read([ByteBuffer](../../../java/nio/ByteBuffer.html "class in java.nio") dst, long timeout, [TimeUnit](../../../java/util/concurrent/TimeUnit.html "enum in java.util.concurrent") unit, A attachment, [CompletionHandler](../../../java/nio/channels/CompletionHandler.html "interface in java.nio.channels")<[Integer](../../../java/lang/Integer.html "class in java.lang"),? super A> handler) Reads a sequence of bytes from this channel into the given buffer. This method initiates an asynchronous read operation to read a sequence of bytes from this channel into the given buffer. The `handler` parameter is a completion handler that is invoked when the read operation completes (or fails). The result passed to the completion handler is the number of bytes read or `-1` if no bytes could be read because the channel has reached end-of-stream. If a timeout is specified and the timeout elapses before the operation completes then the operation completes with the exception [InterruptedByTimeoutException](../../../java/nio/channels/InterruptedByTimeoutException.html "class in java.nio.channels"). Where a timeout occurs, and the implementation cannot guarantee that bytes have not been read, or will not be read from the channel into the given buffer, then further attempts to read from the channel will cause an unspecific runtime exception to be thrown. Otherwise this method works in the same manner as the [AsynchronousByteChannel.read(ByteBuffer,Object,CompletionHandler)](../../../java/nio/channels/AsynchronousByteChannel.html#read%28java.nio.ByteBuffer,%20A,%20java.nio.channels.CompletionHandler%29) method. Parameters: `dst` \- The buffer into which bytes are to be transferred `timeout` \- The maximum time for the I/O operation to complete `unit` \- The time unit of the `timeout` argument `attachment` \- The object to attach to the I/O operation; can be `null` `handler` \- The handler for consuming the result Throws: `[IllegalArgumentException](../../../java/lang/IllegalArgumentException.html "class in java.lang")` \- If the buffer is read-only `[ReadPendingException](../../../java/nio/channels/ReadPendingException.html "class in java.nio.channels")` \- If a read operation is already in progress on this channel `[NotYetConnectedException](../../../java/nio/channels/NotYetConnectedException.html "class in java.nio.channels")` \- If this channel is not yet connected `[ShutdownChannelGroupException](../../../java/nio/channels/ShutdownChannelGroupException.html "class in java.nio.channels")` \- If the channel group has terminated * #### read public final <A> void read([ByteBuffer](../../../java/nio/ByteBuffer.html "class in java.nio") dst, A attachment, [CompletionHandler](../../../java/nio/channels/CompletionHandler.html "interface in java.nio.channels")<[Integer](../../../java/lang/Integer.html "class in java.lang"),? super A> handler) Reads a sequence of bytes from this channel into the given buffer. This method initiates an asynchronous read operation to read a sequence of bytes from this channel into the given buffer. The `handler` parameter is a completion handler that is invoked when the read operation completes (or fails). The result passed to the completion handler is the number of bytes read or `-1` if no bytes could be read because the channel has reached end-of-stream. The read operation may read up to _r_ bytes from the channel, where _r_ is the number of bytes remaining in the buffer, that is,`dst.remaining()` at the time that the read is attempted. Where_r_ is 0, the read operation completes immediately with a result of`0` without initiating an I/O operation. Suppose that a byte sequence of length _n_ is read, where0 < _n_ <= _r_. This byte sequence will be transferred into the buffer so that the first byte in the sequence is at index _p_ and the last byte is at index_p_ + _n_ \- 1, where _p_ is the buffer's position at the moment the read is performed. Upon completion the buffer's position will be equal to_p_ + _n_; its limit will not have changed. Buffers are not safe for use by multiple concurrent threads so care should be taken to not access the buffer until the operation has completed. This method may be invoked at any time. Some channel types may not allow more than one read to be outstanding at any given time. If a thread initiates a read operation before a previous read operation has completed then a [ReadPendingException](../../../java/nio/channels/ReadPendingException.html "class in java.nio.channels") will be thrown. **Specified by:** `[read](../../../java/nio/channels/AsynchronousByteChannel.html#read%28java.nio.ByteBuffer,%20A,%20java.nio.channels.CompletionHandler%29)` in interface `[AsynchronousByteChannel](../../../java/nio/channels/AsynchronousByteChannel.html "interface in java.nio.channels")` Parameters: `dst` \- The buffer into which bytes are to be transferred `attachment` \- The object to attach to the I/O operation; can be `null` `handler` \- The completion handler Throws: `[IllegalArgumentException](../../../java/lang/IllegalArgumentException.html "class in java.lang")` \- If the buffer is read-only `[ReadPendingException](../../../java/nio/channels/ReadPendingException.html "class in java.nio.channels")` \- If the channel does not allow more than one read to be outstanding and a previous read has not completed `[NotYetConnectedException](../../../java/nio/channels/NotYetConnectedException.html "class in java.nio.channels")` \- If this channel is not yet connected `[ShutdownChannelGroupException](../../../java/nio/channels/ShutdownChannelGroupException.html "class in java.nio.channels")` \- If the channel group has terminated * #### read public abstract [Future](../../../java/util/concurrent/Future.html "interface in java.util.concurrent")<[Integer](../../../java/lang/Integer.html "class in java.lang")> read([ByteBuffer](../../../java/nio/ByteBuffer.html "class in java.nio") dst) Reads a sequence of bytes from this channel into the given buffer. This method initiates an asynchronous read operation to read a sequence of bytes from this channel into the given buffer. The method behaves in exactly the same manner as the [read(ByteBuffer,Object,CompletionHandler)](../../../java/nio/channels/AsynchronousByteChannel.html#read%28java.nio.ByteBuffer,%20A,%20java.nio.channels.CompletionHandler%29) method except that instead of specifying a completion handler, this method returns a `Future` representing the pending result. The `Future`'s [get](../../../java/util/concurrent/Future.html#get%28%29) method returns the number of bytes read or `-1` if no bytes could be read because the channel has reached end-of-stream. **Specified by:** `[read](../../../java/nio/channels/AsynchronousByteChannel.html#read%28java.nio.ByteBuffer%29)` in interface `[AsynchronousByteChannel](../../../java/nio/channels/AsynchronousByteChannel.html "interface in java.nio.channels")` Parameters: `dst` \- The buffer into which bytes are to be transferred Returns: A Future representing the result of the operation Throws: `[IllegalArgumentException](../../../java/lang/IllegalArgumentException.html "class in java.lang")` \- If the buffer is read-only `[ReadPendingException](../../../java/nio/channels/ReadPendingException.html "class in java.nio.channels")` \- If the channel does not allow more than one read to be outstanding and a previous read has not completed `[NotYetConnectedException](../../../java/nio/channels/NotYetConnectedException.html "class in java.nio.channels")` \- If this channel is not yet connected * #### read public abstract <A> void read([ByteBuffer](../../../java/nio/ByteBuffer.html "class in java.nio")[] dsts, int offset, int length, long timeout, [TimeUnit](../../../java/util/concurrent/TimeUnit.html "enum in java.util.concurrent") unit, A attachment, [CompletionHandler](../../../java/nio/channels/CompletionHandler.html "interface in java.nio.channels")<[Long](../../../java/lang/Long.html "class in java.lang"),? super A> handler) Reads a sequence of bytes from this channel into a subsequence of the given buffers. This operation, sometimes called a _scattering read_, is often useful when implementing network protocols that group data into segments consisting of one or more fixed-length headers followed by a variable-length body. The `handler` parameter is a completion handler that is invoked when the read operation completes (or fails). The result passed to the completion handler is the number of bytes read or`-1` if no bytes could be read because the channel has reached end-of-stream. This method initiates a read of up to _r_ bytes from this channel, where _r_ is the total number of bytes remaining in the specified subsequence of the given buffer array, that is, > dsts[offset].remaining() > + dsts[offset+1].remaining() > + ... + dsts[offset+length-1].remaining() at the moment that the read is attempted. Suppose that a byte sequence of length _n_ is read, where0 < _n_ <= _r_. Up to the first dsts\[offset\].remaining() bytes of this sequence are transferred into buffer dsts\[offset\], up to the nextdsts\[offset+1\].remaining() bytes are transferred into bufferdsts\[offset+1\], and so forth, until the entire byte sequence is transferred into the given buffers. As many bytes as possible are transferred into each buffer, hence the final position of each updated buffer, except the last updated buffer, is guaranteed to be equal to that buffer's limit. The underlying operating system may impose a limit on the number of buffers that may be used in an I/O operation. Where the number of buffers (with bytes remaining), exceeds this limit, then the I/O operation is performed with the maximum number of buffers allowed by the operating system. If a timeout is specified and the timeout elapses before the operation completes then it completes with the exception [InterruptedByTimeoutException](../../../java/nio/channels/InterruptedByTimeoutException.html "class in java.nio.channels"). Where a timeout occurs, and the implementation cannot guarantee that bytes have not been read, or will not be read from the channel into the given buffers, then further attempts to read from the channel will cause an unspecific runtime exception to be thrown. 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` `timeout` \- The maximum time for the I/O operation to complete `unit` \- The time unit of the `timeout` argument `attachment` \- The object to attach to the I/O operation; can be `null` `handler` \- The handler for consuming the result Throws: `[IndexOutOfBoundsException](../../../java/lang/IndexOutOfBoundsException.html "class in java.lang")` \- If the pre-conditions for the `offset` and `length` parameter aren't met `[IllegalArgumentException](../../../java/lang/IllegalArgumentException.html "class in java.lang")` \- If the buffer is read-only `[ReadPendingException](../../../java/nio/channels/ReadPendingException.html "class in java.nio.channels")` \- If a read operation is already in progress on this channel `[NotYetConnectedException](../../../java/nio/channels/NotYetConnectedException.html "class in java.nio.channels")` \- If this channel is not yet connected `[ShutdownChannelGroupException](../../../java/nio/channels/ShutdownChannelGroupException.html "class in java.nio.channels")` \- If the channel group has terminated * #### write public abstract <A> void write([ByteBuffer](../../../java/nio/ByteBuffer.html "class in java.nio") src, long timeout, [TimeUnit](../../../java/util/concurrent/TimeUnit.html "enum in java.util.concurrent") unit, A attachment, [CompletionHandler](../../../java/nio/channels/CompletionHandler.html "interface in java.nio.channels")<[Integer](../../../java/lang/Integer.html "class in java.lang"),? super A> handler) Writes a sequence of bytes to this channel from the given buffer. This method initiates an asynchronous write operation to write a sequence of bytes to this channel from the given buffer. The `handler` parameter is a completion handler that is invoked when the write operation completes (or fails). The result passed to the completion handler is the number of bytes written. If a timeout is specified and the timeout elapses before the operation completes then it completes with the exception [InterruptedByTimeoutException](../../../java/nio/channels/InterruptedByTimeoutException.html "class in java.nio.channels"). Where a timeout occurs, and the implementation cannot guarantee that bytes have not been written, or will not be written to the channel from the given buffer, then further attempts to write to the channel will cause an unspecific runtime exception to be thrown. Otherwise this method works in the same manner as the [AsynchronousByteChannel.write(ByteBuffer,Object,CompletionHandler)](../../../java/nio/channels/AsynchronousByteChannel.html#write%28java.nio.ByteBuffer,%20A,%20java.nio.channels.CompletionHandler%29) method. Parameters: `src` \- The buffer from which bytes are to be retrieved `timeout` \- The maximum time for the I/O operation to complete `unit` \- The time unit of the `timeout` argument `attachment` \- The object to attach to the I/O operation; can be `null` `handler` \- The handler for consuming the result Throws: `[WritePendingException](../../../java/nio/channels/WritePendingException.html "class in java.nio.channels")` \- If a write operation is already in progress on this channel `[NotYetConnectedException](../../../java/nio/channels/NotYetConnectedException.html "class in java.nio.channels")` \- If this channel is not yet connected `[ShutdownChannelGroupException](../../../java/nio/channels/ShutdownChannelGroupException.html "class in java.nio.channels")` \- If the channel group has terminated * #### write public final <A> void write([ByteBuffer](../../../java/nio/ByteBuffer.html "class in java.nio") src, A attachment, [CompletionHandler](../../../java/nio/channels/CompletionHandler.html "interface in java.nio.channels")<[Integer](../../../java/lang/Integer.html "class in java.lang"),? super A> handler) Writes a sequence of bytes to this channel from the given buffer. This method initiates an asynchronous write operation to write a sequence of bytes to this channel from the given buffer. The `handler` parameter is a completion handler that is invoked when the write operation completes (or fails). The result passed to the completion handler is the number of bytes written. The write operation may write up to _r_ bytes to the channel, where _r_ is the number of bytes remaining in the buffer, that is,`src.remaining()` at the time that the write is attempted. Where_r_ is 0, the write operation completes immediately with a result of`0` without initiating an I/O operation. Suppose that a byte sequence of length _n_ is written, where0 < _n_ <= _r_. This byte sequence will be transferred from the buffer starting at index_p_, where _p_ is the buffer's position at the moment the write is performed; the index of the last byte written will be_p_ + _n_ \- 1. Upon completion the buffer's position will be equal to_p_ + _n_; its limit will not have changed. Buffers are not safe for use by multiple concurrent threads so care should be taken to not access the buffer until the operation has completed. This method may be invoked at any time. Some channel types may not allow more than one write to be outstanding at any given time. If a thread initiates a write operation before a previous write operation has completed then a [WritePendingException](../../../java/nio/channels/WritePendingException.html "class in java.nio.channels") will be thrown. **Specified by:** `[write](../../../java/nio/channels/AsynchronousByteChannel.html#write%28java.nio.ByteBuffer,%20A,%20java.nio.channels.CompletionHandler%29)` in interface `[AsynchronousByteChannel](../../../java/nio/channels/AsynchronousByteChannel.html "interface in java.nio.channels")` Parameters: `src` \- The buffer from which bytes are to be retrieved `attachment` \- The object to attach to the I/O operation; can be `null` `handler` \- The completion handler object Throws: `[WritePendingException](../../../java/nio/channels/WritePendingException.html "class in java.nio.channels")` \- If the channel does not allow more than one write to be outstanding and a previous write has not completed `[NotYetConnectedException](../../../java/nio/channels/NotYetConnectedException.html "class in java.nio.channels")` \- If this channel is not yet connected `[ShutdownChannelGroupException](../../../java/nio/channels/ShutdownChannelGroupException.html "class in java.nio.channels")` \- If the channel group has terminated * #### write public abstract [Future](../../../java/util/concurrent/Future.html "interface in java.util.concurrent")<[Integer](../../../java/lang/Integer.html "class in java.lang")> write([ByteBuffer](../../../java/nio/ByteBuffer.html "class in java.nio") src) Writes a sequence of bytes to this channel from the given buffer. This method initiates an asynchronous write operation to write a sequence of bytes to this channel from the given buffer. The method behaves in exactly the same manner as the [write(ByteBuffer,Object,CompletionHandler)](../../../java/nio/channels/AsynchronousByteChannel.html#write%28java.nio.ByteBuffer,%20A,%20java.nio.channels.CompletionHandler%29) method except that instead of specifying a completion handler, this method returns a `Future` representing the pending result. The `Future`'s [get](../../../java/util/concurrent/Future.html#get%28%29) method returns the number of bytes written. **Specified by:** `[write](../../../java/nio/channels/AsynchronousByteChannel.html#write%28java.nio.ByteBuffer%29)` in interface `[AsynchronousByteChannel](../../../java/nio/channels/AsynchronousByteChannel.html "interface in java.nio.channels")` Parameters: `src` \- The buffer from which bytes are to be retrieved Returns: A Future representing the result of the operation Throws: `[WritePendingException](../../../java/nio/channels/WritePendingException.html "class in java.nio.channels")` \- If the channel does not allow more than one write to be outstanding and a previous write has not completed `[NotYetConnectedException](../../../java/nio/channels/NotYetConnectedException.html "class in java.nio.channels")` \- If this channel is not yet connected * #### write public abstract <A> void write([ByteBuffer](../../../java/nio/ByteBuffer.html "class in java.nio")[] srcs, int offset, int length, long timeout, [TimeUnit](../../../java/util/concurrent/TimeUnit.html "enum in java.util.concurrent") unit, A attachment, [CompletionHandler](../../../java/nio/channels/CompletionHandler.html "interface in java.nio.channels")<[Long](../../../java/lang/Long.html "class in java.lang"),? super A> handler) Writes a sequence of bytes to this channel from a subsequence of the given buffers. This operation, sometimes called a _gathering write_, is often useful when implementing network protocols that group data into segments consisting of one or more fixed-length headers followed by a variable-length body. The `handler` parameter is a completion handler that is invoked when the write operation completes (or fails). The result passed to the completion handler is the number of bytes written. This method initiates a write of up to _r_ bytes to this channel, where _r_ is the total number of bytes remaining in the specified subsequence of the given buffer array, that is, > srcs[offset].remaining() > + srcs[offset+1].remaining() > + ... + srcs[offset+length-1].remaining() at the moment that the write is attempted. Suppose that a byte sequence of length _n_ is written, where0 < _n_ <= _r_. Up to the first srcs\[offset\].remaining() bytes of this sequence are written from buffer srcs\[offset\], up to the nextsrcs\[offset+1\].remaining() bytes are written from buffersrcs\[offset+1\], and so forth, until the entire byte sequence is written. As many bytes as possible are written from each buffer, hence the final position of each updated buffer, except the last updated buffer, is guaranteed to be equal to that buffer's limit. The underlying operating system may impose a limit on the number of buffers that may be used in an I/O operation. Where the number of buffers (with bytes remaining), exceeds this limit, then the I/O operation is performed with the maximum number of buffers allowed by the operating system. If a timeout is specified and the timeout elapses before the operation completes then it completes with the exception [InterruptedByTimeoutException](../../../java/nio/channels/InterruptedByTimeoutException.html "class in java.nio.channels"). Where a timeout occurs, and the implementation cannot guarantee that bytes have not been written, or will not be written to the channel from the given buffers, then further attempts to write to the channel will cause an unspecific runtime exception to be thrown. 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` `timeout` \- The maximum time for the I/O operation to complete `unit` \- The time unit of the `timeout` argument `attachment` \- The object to attach to the I/O operation; can be `null` `handler` \- The handler for consuming the result Throws: `[IndexOutOfBoundsException](../../../java/lang/IndexOutOfBoundsException.html "class in java.lang")` \- If the pre-conditions for the `offset` and `length` parameter aren't met `[WritePendingException](../../../java/nio/channels/WritePendingException.html "class in java.nio.channels")` \- If a write operation is already in progress on this channel `[NotYetConnectedException](../../../java/nio/channels/NotYetConnectedException.html "class in java.nio.channels")` \- If this channel is not yet connected `[ShutdownChannelGroupException](../../../java/nio/channels/ShutdownChannelGroupException.html "class in java.nio.channels")` \- If the channel group has terminated
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