| /* |
| * Copyright (c) 2001, 2013, Oracle and/or its affiliates. All rights reserved. |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
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| * published by the Free Software Foundation. Oracle designates this |
| * particular file as subject to the "Classpath" exception as provided |
| * by Oracle in the LICENSE file that accompanied this code. |
| * |
| * This code is distributed in the hope that it will be useful, but WITHOUT |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
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| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
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| */ |
| |
| /** |
| * Defines channels, which represent connections to entities that are capable of |
| * performing I/O operations, such as files and sockets; defines selectors, for |
| * multiplexed, non-blocking I/O operations. |
| * |
| * <a name="channels"></a> |
| * |
| * <blockquote><table cellspacing=1 cellpadding=0 summary="Lists channels and their descriptions"> |
| * <tr><th align="left">Channels</th><th align="left">Description</th></tr> |
| * <tr><td valign=top><tt><i>{@link java.nio.channels.Channel}</i></tt></td> |
| * <td>A nexus for I/O operations</td></tr> |
| * <tr><td valign=top><tt> <i>{@link java.nio.channels.ReadableByteChannel}</i></tt></td> |
| * <td>Can read into a buffer</td></tr> |
| * <tr><td valign=top><tt> <i>{@link java.nio.channels.ScatteringByteChannel} </i></tt></td> |
| * <td>Can read into a sequence of buffers</td></tr> |
| * <tr><td valign=top><tt> <i>{@link java.nio.channels.WritableByteChannel}</i></tt></td> |
| * <td>Can write from a buffer</td></tr> |
| * <tr><td valign=top><tt> <i>{@link java.nio.channels.GatheringByteChannel}</i></tt></td> |
| * <td>Can write from a sequence of buffers</td></tr> |
| * <tr><td valign=top><tt> <i>{@link java.nio.channels.ByteChannel}</i></tt></td> |
| * <td>Can read/write to/from a buffer</td></tr> |
| * <tr><td valign=top><tt> <i>{@link java.nio.channels.SeekableByteChannel}</i></tt></td> |
| * <td>A {@code ByteChannel} connected to an entity that contains a variable-length sequence of bytes</td></tr> |
| * <tr><td valign=top><tt> <i>{@link java.nio.channels.AsynchronousChannel}</i></tt></td> |
| * <td>Supports asynchronous I/O operations.</td></tr> |
| * <tr><td valign=top><tt> <i>{@link java.nio.channels.AsynchronousByteChannel}</i></tt></td> |
| * <td>Can read and write bytes asynchronously</td></tr> |
| * <tr><td valign=top><tt> <i>{@link java.nio.channels.NetworkChannel}</i></tt></td> |
| * <td>A channel to a network socket</td></tr> |
| * <tr><td valign=top><tt> <i>{@link java.nio.channels.MulticastChannel}</i></tt></td> |
| * <td>Can join Internet Protocol (IP) multicast groups</td></tr> |
| * <tr><td valign=top><tt>{@link java.nio.channels.Channels}</tt></td> |
| * <td>Utility methods for channel/stream interoperation</td></tr> |
| * </table></blockquote> |
| * |
| * <p> A <i>channel</i> 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 <i>asynchronously |
| * closeable</i> and <i>interruptible</i>. |
| * |
| * <p> The {@link java.nio.channels.Channel} interface is extended by several |
| * other interfaces. |
| * |
| * <p> 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}. |
| * |
| * <p> 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. |
| * |
| * <p> 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. |
| * |
| * <p> The {@link java.nio.channels.Channels} utility class defines static methods |
| * that support the interoperation of the stream classes of the <tt>{@link |
| * java.io}</tt> 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. |
| * |
| * <blockquote><table cellspacing=1 cellpadding=0 summary="Lists file channels and their descriptions"> |
| * <tr><th align="left">File channels</th><th align="left">Description</th></tr> |
| * <tr><td valign=top><tt>{@link java.nio.channels.FileChannel}</tt></td> |
| * <td>Reads, writes, maps, and manipulates files</td></tr> |
| * <tr><td valign=top><tt>{@link java.nio.channels.FileLock}</tt></td> |
| * <td>A lock on a (region of a) file</td></tr> |
| * <tr><td valign=top><tt>{@link java.nio.MappedByteBuffer} </tt></td> |
| * <td>A direct byte buffer mapped to a region of a file</td></tr> |
| * </table></blockquote> |
| * |
| * <p> 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. |
| * |
| * <p> 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 <tt>{@link java.io}</tt> |
| * class. |
| * |
| * <a name="multiplex"></a> |
| * <blockquote><table cellspacing=1 cellpadding=0 summary="Lists multiplexed, non-blocking channels and their descriptions"> |
| * <tr><th align="left">Multiplexed, non-blocking I/O</th><th align="left"><p>Description</th></tr> |
| * <tr><td valign=top><tt>{@link java.nio.channels.SelectableChannel}</tt></td> |
| * <td>A channel that can be multiplexed</td></tr> |
| * <tr><td valign=top><tt> {@link java.nio.channels.DatagramChannel}</tt></td> |
| * <td>A channel to a datagram-oriented socket</td></tr> |
| * <tr><td valign=top><tt> {@link java.nio.channels.Pipe.SinkChannel}</tt></td> |
| * <td>The write end of a pipe</td></tr> |
| * <tr><td valign=top><tt> {@link java.nio.channels.Pipe.SourceChannel}</tt></td> |
| * <td>The read end of a pipe</td></tr> |
| * <tr><td valign=top><tt> {@link java.nio.channels.ServerSocketChannel} </tt></td> |
| * <td>A channel to a stream-oriented listening socket</td></tr> |
| * <tr><td valign=top><tt> {@link java.nio.channels.SocketChannel}</tt></td> |
| * <td>A channel for a stream-oriented connecting socket</td></tr> |
| * <tr><td valign=top><tt>{@link java.nio.channels.Selector}</tt></td> |
| * <td>A multiplexor of selectable channels</td></tr> |
| * <tr><td valign=top><tt>{@link java.nio.channels.SelectionKey}</tt></td> |
| * <td>A token representing the registration <br> of a channel |
| * with a selector</td></tr> |
| * <tr><td valign=top><tt>{@link java.nio.channels.Pipe}</tt></td> |
| * <td>Two channels that form a unidirectional pipe</td></tr> |
| * </table></blockquote> |
| * |
| * <p> Multiplexed, non-blocking I/O, which is much more scalable than |
| * thread-oriented, blocking I/O, is provided by <i>selectors</i>, <i>selectable |
| * channels</i>, and <i>selection keys</i>. |
| * |
| * <p> A <a href="Selector.html"><i>selector</i></a> is a multiplexor of <a |
| * href="SelectableChannel.html"><i>selectable channels</i></a>, which in turn are |
| * a special type of channel that can be put into <a |
| * href="SelectableChannel.html#bm"><i>non-blocking mode</i></a>. 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 <i>registered</i>} |
| * 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 <a |
| * href="SelectionKey.html"><i>selection key</i></a> that represents the |
| * registration. |
| * |
| * <p> Once some channels have been registered with a selector, a <a |
| * href="Selector.html#selop"><i>selection operation</i></a> 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 <i>selected-key set</i>. 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. |
| * |
| * <p> 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. |
| * |
| * <p> 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 <tt>{@link java.net}</tt> 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 <tt>open</tt> 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. |
| * |
| * <p> 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 <tt>{@link |
| * java.nio.channels.spi}</tt> 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. |
| * |
| * <p> 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 <tt>{@link |
| * java.nio.channels.spi}</tt> 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. |
| * |
| * <a name="async"></a> |
| * |
| * <blockquote><table cellspacing=1 cellpadding=0 summary="Lists asynchronous channels and their descriptions"> |
| * <tr><th align="left">Asynchronous I/O</th><th align="left">Description</th></tr> |
| * <tr><td valign=top><tt>{@link java.nio.channels.AsynchronousFileChannel}</tt></td> |
| * <td>An asynchronous channel for reading, writing, and manipulating a file</td></tr> |
| * <tr><td valign=top><tt>{@link java.nio.channels.AsynchronousSocketChannel}</tt></td> |
| * <td>An asynchronous channel to a stream-oriented connecting socket</td></tr> |
| * <tr><td valign=top><tt>{@link java.nio.channels.AsynchronousServerSocketChannel} </tt></td> |
| * <td>An asynchronous channel to a stream-oriented listening socket</td></tr> |
| * <tr><td valign=top><tt>{@link java.nio.channels.CompletionHandler}</tt></td> |
| * <td>A handler for consuming the result of an asynchronous operation</td></tr> |
| * <tr><td valign=top><tt>{@link java.nio.channels.AsynchronousChannelGroup}</tt></td> |
| * <td>A grouping of asynchronous channels for the purpose of resource sharing</td></tr> |
| * </table></blockquote> |
| * |
| * <p> {@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. |
| * |
| * <p> 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. |
| * |
| * <p> 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 <em>default group</em>. Sophisticated users may wish to create their |
| * own asynchronous channel groups or configure the {@code ExecutorService} |
| * that will be used for the default group. |
| * |
| * <p> As with selectors, the implementation 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 |
| * <tt>{@link java.nio.channels.spi}</tt> 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. |
| * |
| * <hr width="80%"> |
| * <p> Unless otherwise noted, passing a <tt>null</tt> 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; |
