* **
* Channels
Description
* {@link java.nio.channels.Channel} *A nexus for I/O operations * {@link java.nio.channels.ReadableByteChannel} *Can read into a buffer * {@link java.nio.channels.ScatteringByteChannel} *Can read into a sequence of buffers * {@link java.nio.channels.WritableByteChannel} *Can write from a buffer * {@link java.nio.channels.GatheringByteChannel} *Can write from a sequence of buffers * {@link java.nio.channels.ByteChannel} *Can read/write to/from a buffer * {@link java.nio.channels.SeekableByteChannel} *A {@code ByteChannel} connected to an entity that contains a variable-length sequence of bytes * {@link java.nio.channels.AsynchronousChannel} *Supports asynchronous I/O operations. * {@link java.nio.channels.AsynchronousByteChannel} *Can read and write bytes asynchronously * {@link java.nio.channels.NetworkChannel} *A channel to a network socket * {@link java.nio.channels.MulticastChannel} *Can join Internet Protocol (IP) multicast groups * {@link java.nio.channels.Channels} *Utility methods for channel/stream interoperation
A channel represents an open connection to an entity such as a * hardware device, a file, a network socket, or a program component that is * capable of performing one or more distinct I/O operations, for example reading * or writing. As specified in the {@link java.nio.channels.Channel} interface, * channels are either open or closed, and they are both asynchronously * closeable and interruptible. * *
The {@link java.nio.channels.Channel} interface is extended by several * other interfaces. * *
The {@link java.nio.channels.ReadableByteChannel} interface specifies a * {@link java.nio.channels.ReadableByteChannel#read read} method that reads bytes * from the channel into a buffer; similarly, the {@link * java.nio.channels.WritableByteChannel} interface specifies a {@link * java.nio.channels.WritableByteChannel#write write} method that writes bytes * from a buffer to the channel. The {@link java.nio.channels.ByteChannel} * interface unifies these two interfaces for the common case of channels that can * both read and write bytes. The {@link java.nio.channels.SeekableByteChannel} * interface extends the {@code ByteChannel} interface with methods to {@link * java.nio.channels.SeekableByteChannel#position() query} and {@link * java.nio.channels.SeekableByteChannel#position(long) modify} the channel's * current position, and its {@link java.nio.channels.SeekableByteChannel#size * size}. * *
The {@link java.nio.channels.ScatteringByteChannel} and {@link * java.nio.channels.GatheringByteChannel} interfaces extend the {@link * java.nio.channels.ReadableByteChannel} and {@link * java.nio.channels.WritableByteChannel} interfaces, respectively, adding {@link * java.nio.channels.ScatteringByteChannel#read read} and {@link * java.nio.channels.GatheringByteChannel#write write} methods that take a * sequence of buffers rather than a single buffer. * *
The {@link java.nio.channels.NetworkChannel} interface specifies methods * to {@link java.nio.channels.NetworkChannel#bind bind} the channel's socket, * obtain the address to which the socket is bound, and methods to {@link * java.nio.channels.NetworkChannel#getOption get} and {@link * java.nio.channels.NetworkChannel#setOption set} socket options. The {@link * java.nio.channels.MulticastChannel} interface specifies methods to join * Internet Protocol (IP) multicast groups. * *
The {@link java.nio.channels.Channels} utility class defines static methods * that support the interoperation of the stream classes of the {@link * java.io} package with the channel classes of this package. An appropriate * channel can be constructed from an {@link java.io.InputStream} or an {@link * java.io.OutputStream}, and conversely an {@link java.io.InputStream} or an * {@link java.io.OutputStream} can be constructed from a channel. A {@link * java.io.Reader} can be constructed that uses a given charset to decode bytes * from a given readable byte channel, and conversely a {@link java.io.Writer} can * be constructed that uses a given charset to encode characters into bytes and * write them to a given writable byte channel. * *
* **
* File channels
Description
* {@link java.nio.channels.FileChannel} *Reads, writes, maps, and manipulates files * {@link java.nio.channels.FileLock} *A lock on a (region of a) file * {@link java.nio.MappedByteBuffer} *A direct byte buffer mapped to a region of a file
The {@link java.nio.channels.FileChannel} class supports the usual * operations of reading bytes from, and writing bytes to, a channel connected to * a file, as well as those of querying and modifying the current file position * and truncating the file to a specific size. It defines methods for acquiring * locks on the whole file or on a specific region of a file; these methods return * instances of the {@link java.nio.channels.FileLock} class. Finally, it defines * methods for forcing updates to the file to be written to the storage device that * contains it, for efficiently transferring bytes between the file and other * channels, and for mapping a region of the file directly into memory. * *
A {@code FileChannel} is created by invoking one of its static {@link * java.nio.channels.FileChannel#open open} methods, or by invoking the {@code * getChannel} method of a {@link java.io.FileInputStream}, {@link * java.io.FileOutputStream}, or {@link java.io.RandomAccessFile} to return a * file channel connected to the same underlying file as the {@link java.io} * class. * * *
* **
* Multiplexed, non-blocking I/O
Description
* {@link java.nio.channels.SelectableChannel} *A channel that can be multiplexed * {@link java.nio.channels.DatagramChannel} *A channel to a datagram-oriented socket * {@link java.nio.channels.Pipe.SinkChannel} *The write end of a pipe * {@link java.nio.channels.Pipe.SourceChannel} *The read end of a pipe * {@link java.nio.channels.ServerSocketChannel} *A channel to a stream-oriented listening socket * {@link java.nio.channels.SocketChannel} *A channel for a stream-oriented connecting socket * {@link java.nio.channels.Selector} *A multiplexor of selectable channels * {@link java.nio.channels.SelectionKey} *A token representing the registration
of a channel * with a selector* {@link java.nio.channels.Pipe} *Two channels that form a unidirectional pipe
Multiplexed, non-blocking I/O, which is much more scalable than * thread-oriented, blocking I/O, is provided by selectors, selectable * channels, and selection keys. * *
A selector is a multiplexor of selectable channels, which in turn are * a special type of channel that can be put into non-blocking mode. To perform * multiplexed I/O operations, one or more selectable channels are first created, * put into non-blocking mode, and {@link * java.nio.channels.SelectableChannel#register registered} * with a selector. Registering a channel specifies the set of I/O operations * that will be tested for readiness by the selector, and returns a selection key that represents the * registration. * *
Once some channels have been registered with a selector, a selection operation can be performed in * order to discover which channels, if any, have become ready to perform one or * more of the operations in which interest was previously declared. If a channel * is ready then the key returned when it was registered will be added to the * selector's selected-key set. The key set, and the keys within it, can * be examined in order to determine the operations for which each channel is * ready. From each key one can retrieve the corresponding channel in order to * perform whatever I/O operations are required. * *
That a selection key indicates that its channel is ready for some operation * is a hint, but not a guarantee, that such an operation can be performed by a * thread without causing the thread to block. It is imperative that code that * performs multiplexed I/O be written so as to ignore these hints when they prove * to be incorrect. * *
This package defines selectable-channel classes corresponding to the {@link * java.net.DatagramSocket}, {@link java.net.ServerSocket}, and {@link * java.net.Socket} classes defined in the {@link java.net} package. * Minor changes to these classes have been made in order to support sockets that * are associated with channels. This package also defines a simple class that * implements unidirectional pipes. In all cases, a new selectable channel is * created by invoking the static open method of the corresponding class. * If a channel needs an associated socket then a socket will be created as a side * effect of this operation. * *
The implementation of selectors, selectable channels, and selection keys * can be replaced by "plugging in" an alternative definition or instance of the * {@link java.nio.channels.spi.SelectorProvider} class defined in the {@link * java.nio.channels.spi} package. It is not expected that many developers * will actually make use of this facility; it is provided primarily so that * sophisticated users can take advantage of operating-system-specific * I/O-multiplexing mechanisms when very high performance is required. * *
Much of the bookkeeping and synchronization required to implement the * multiplexed-I/O abstractions is performed by the {@link * java.nio.channels.spi.AbstractInterruptibleChannel}, {@link * java.nio.channels.spi.AbstractSelectableChannel}, {@link * java.nio.channels.spi.AbstractSelectionKey}, and {@link * java.nio.channels.spi.AbstractSelector} classes in the {@link * java.nio.channels.spi} package. When defining a custom selector provider, * only the {@link java.nio.channels.spi.AbstractSelector} and {@link * java.nio.channels.spi.AbstractSelectionKey} classes should be subclassed * directly; custom channel classes should extend the appropriate {@link * java.nio.channels.SelectableChannel} subclasses defined in this package. * * * *
* **
* Asynchronous I/O
Description
* {@link java.nio.channels.AsynchronousFileChannel} *An asynchronous channel for reading, writing, and manipulating a file * {@link java.nio.channels.AsynchronousSocketChannel} *An asynchronous channel to a stream-oriented connecting socket * {@link java.nio.channels.AsynchronousServerSocketChannel} *An asynchronous channel to a stream-oriented listening socket * {@link java.nio.channels.CompletionHandler} *A handler for consuming the result of an asynchronous operation * {@link java.nio.channels.AsynchronousChannelGroup} *A grouping of asynchronous channels for the purpose of resource sharing
{@link java.nio.channels.AsynchronousChannel Asynchronous channels} are a * special type of channel capable of asynchronous I/O operations. Asynchronous * channels are non-blocking and define methods to initiate asynchronous * operations, returning a {@link java.util.concurrent.Future} representing the * pending result of each operation. The {@code Future} can be used to poll or * wait for the result of the operation. Asynchronous I/O operations can also * specify a {@link java.nio.channels.CompletionHandler} to invoke when the * operation completes. A completion handler is user provided code that is executed * to consume the result of I/O operation. * *
This package defines asynchronous-channel classes that are connected to * a stream-oriented connecting or listening socket, or a datagram-oriented socket. * It also defines the {@link java.nio.channels.AsynchronousFileChannel} class * for asynchronous reading, writing, and manipulating a file. As with the {@link * java.nio.channels.FileChannel} it supports operations to truncate the file * to a specific size, force updates to the file to be written to the storage * device, or acquire locks on the whole file or on a specific region of the file. * Unlike the {@code FileChannel} it does not define methods for mapping a * region of the file directly into memory. Where memory mapped I/O is required, * then a {@code FileChannel} can be used. * *
Asynchronous channels are bound to an asynchronous channel group for the * purpose of resource sharing. A group has an associated {@link * java.util.concurrent.ExecutorService} to which tasks are submitted to handle * I/O events and dispatch to completion handlers that consume the result of * asynchronous operations performed on channels in the group. The group can * optionally be specified when creating the channel or the channel can be bound * to a default group. Sophisticated users may wish to create their * own asynchronous channel groups or configure the {@code ExecutorService} * that will be used for the default group. * *
As with selectors, the implementatin of asynchronous channels can be * replaced by "plugging in" an alternative definition or instance of the {@link * java.nio.channels.spi.AsynchronousChannelProvider} class defined in the * {@link java.nio.channels.spi} package. It is not expected that many * developers will actually make use of this facility; it is provided primarily * so that sophisticated users can take advantage of operating-system-specific * asynchronous I/O mechanisms when very high performance is required. * *
Unless otherwise noted, passing a null argument to a constructor * or method in any class or interface in this package will cause a {@link * java.lang.NullPointerException NullPointerException} to be thrown. * * @since 1.4 * @author Mark Reinhold * @author JSR-51 Expert Group */ package java.nio.channels;