1169 lines
50 KiB
Java
1169 lines
50 KiB
Java
/*
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* Copyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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package java.nio.channels;
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import java.io.*;
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import java.nio.ByteBuffer;
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import java.nio.MappedByteBuffer;
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import java.nio.channels.spi.AbstractInterruptibleChannel;
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import java.nio.file.*;
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import java.nio.file.attribute.FileAttribute;
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import java.nio.file.spi.*;
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import java.util.Set;
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import java.util.HashSet;
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import java.util.Collections;
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/**
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* A channel for reading, writing, mapping, and manipulating a file.
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*
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* <p> A file channel is a {@link SeekableByteChannel} that is connected to
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* a file. It has a current <i>position</i> within its file which can
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* be both {@link #position() <i>queried</i>} and {@link #position(long)
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* <i>modified</i>}. The file itself contains a variable-length sequence
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* of bytes that can be read and written and whose current {@link #size
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* <i>size</i>} can be queried. The size of the file increases
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* when bytes are written beyond its current size; the size of the file
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* decreases when it is {@link #truncate <i>truncated</i>}. The
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* file may also have some associated <i>metadata</i> such as access
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* permissions, content type, and last-modification time; this class does not
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* define methods for metadata access.
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*
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* <p> In addition to the familiar read, write, and close operations of byte
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* channels, this class defines the following file-specific operations: </p>
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*
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* <ul>
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*
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* <li><p> Bytes may be {@link #read(ByteBuffer, long) read} or
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* {@link #write(ByteBuffer, long) <i>written</i>} at an absolute
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* position in a file in a way that does not affect the channel's current
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* position. </p></li>
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*
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* <li><p> A region of a file may be {@link #map <i>mapped</i>}
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* directly into memory; for large files this is often much more efficient
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* than invoking the usual {@code read} or {@code write} methods.
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* </p></li>
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*
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* <li><p> Updates made to a file may be {@link #force <i>forced
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* out</i>} to the underlying storage device, ensuring that data are not
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* lost in the event of a system crash. </p></li>
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*
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* <li><p> Bytes can be transferred from a file {@link #transferTo <i>to
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* some other channel</i>}, and {@link #transferFrom <i>vice
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* versa</i>}, in a way that can be optimized by many operating systems
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* into a very fast transfer directly to or from the filesystem cache.
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* </p></li>
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*
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* <li><p> A region of a file may be {@link FileLock <i>locked</i>}
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* against access by other programs. </p></li>
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*
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* </ul>
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*
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* <p> File channels are safe for use by multiple concurrent threads. The
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* {@link Channel#close close} method may be invoked at any time, as specified
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* by the {@link Channel} interface. Only one operation that involves the
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* channel's position or can change its file's size may be in progress at any
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* given time; attempts to initiate a second such operation while the first is
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* still in progress will block until the first operation completes. Other
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* operations, in particular those that take an explicit position, may proceed
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* concurrently; whether they in fact do so is dependent upon the underlying
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* implementation and is therefore unspecified.
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*
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* <p> The view of a file provided by an instance of this class is guaranteed
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* to be consistent with other views of the same file provided by other
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* instances in the same program. The view provided by an instance of this
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* class may or may not, however, be consistent with the views seen by other
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* concurrently-running programs due to caching performed by the underlying
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* operating system and delays induced by network-filesystem protocols. This
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* is true regardless of the language in which these other programs are
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* written, and whether they are running on the same machine or on some other
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* machine. The exact nature of any such inconsistencies are system-dependent
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* and are therefore unspecified.
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*
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* <p> A file channel is created by invoking one of the {@link #open open}
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* methods defined by this class. A file channel can also be obtained from an
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* existing {@link java.io.FileInputStream#getChannel FileInputStream}, {@link
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* java.io.FileOutputStream#getChannel FileOutputStream}, or {@link
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* java.io.RandomAccessFile#getChannel RandomAccessFile} object by invoking
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* that object's {@code getChannel} method, which returns a file channel that
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* is connected to the same underlying file. Where the file channel is obtained
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* from an existing stream or random access file then the state of the file
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* channel is intimately connected to that of the object whose {@code getChannel}
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* method returned the channel. Changing the channel's position, whether
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* explicitly or by reading or writing bytes, will change the file position of
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* the originating object, and vice versa. Changing the file's length via the
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* file channel will change the length seen via the originating object, and vice
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* versa. Changing the file's content by writing bytes will change the content
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* seen by the originating object, and vice versa.
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*
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* <a id="open-mode"></a> <p> At various points this class specifies that an
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* instance that is "open for reading," "open for writing," or "open for
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* reading and writing" is required. A channel obtained via the {@link
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* java.io.FileInputStream#getChannel getChannel} method of a {@link
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* java.io.FileInputStream} instance will be open for reading. A channel
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* obtained via the {@link java.io.FileOutputStream#getChannel getChannel}
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* method of a {@link java.io.FileOutputStream} instance will be open for
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* writing. Finally, a channel obtained via the {@link
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* java.io.RandomAccessFile#getChannel getChannel} method of a {@link
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* java.io.RandomAccessFile} instance will be open for reading if the instance
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* was created with mode {@code "r"} and will be open for reading and writing
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* if the instance was created with mode {@code "rw"}.
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*
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* <a id="append-mode"></a><p> A file channel that is open for writing may be in
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* <i>append mode</i>, for example if it was obtained from a file-output stream
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* that was created by invoking the {@link
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* java.io.FileOutputStream#FileOutputStream(java.io.File,boolean)
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* FileOutputStream(File,boolean)} constructor and passing {@code true} for
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* the second parameter. In this mode each invocation of a relative write
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* operation first advances the position to the end of the file and then writes
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* the requested data. Whether the advancement of the position and the writing
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* of the data are done in a single atomic operation is system-dependent and
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* therefore unspecified.
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*
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* @see java.io.FileInputStream#getChannel()
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* @see java.io.FileOutputStream#getChannel()
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* @see java.io.RandomAccessFile#getChannel()
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*
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* @author Mark Reinhold
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* @author Mike McCloskey
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* @author JSR-51 Expert Group
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* @since 1.4
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*/
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public abstract class FileChannel
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extends AbstractInterruptibleChannel
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implements SeekableByteChannel, GatheringByteChannel, ScatteringByteChannel
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{
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/**
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* Initializes a new instance of this class.
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*/
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protected FileChannel() { }
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/**
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* Opens or creates a file, returning a file channel to access the file.
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*
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* <p> The {@code options} parameter determines how the file is opened.
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* The {@link StandardOpenOption#READ READ} and {@link StandardOpenOption#WRITE
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* WRITE} options determine if the file should be opened for reading and/or
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* writing. If neither option (or the {@link StandardOpenOption#APPEND APPEND}
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* option) is contained in the array then the file is opened for reading.
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* By default reading or writing commences at the beginning of the file.
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*
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* <p> In the addition to {@code READ} and {@code WRITE}, the following
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* options may be present:
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*
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* <table class="striped">
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* <caption style="display:none">additional options</caption>
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* <thead>
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* <tr> <th scope="col">Option</th> <th scope="col">Description</th> </tr>
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* </thead>
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* <tbody>
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* <tr>
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* <th scope="row"> {@link StandardOpenOption#APPEND APPEND} </th>
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* <td> If this option is present then the file is opened for writing and
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* each invocation of the channel's {@code write} method first advances
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* the position to the end of the file and then writes the requested
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* data. Whether the advancement of the position and the writing of the
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* data are done in a single atomic operation is system-dependent and
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* therefore unspecified. This option may not be used in conjunction
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* with the {@code READ} or {@code TRUNCATE_EXISTING} options. </td>
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* </tr>
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* <tr>
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* <th scope="row"> {@link StandardOpenOption#TRUNCATE_EXISTING TRUNCATE_EXISTING} </th>
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* <td> If this option is present then the existing file is truncated to
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* a size of 0 bytes. This option is ignored when the file is opened only
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* for reading. </td>
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* </tr>
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* <tr>
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* <th scope="row"> {@link StandardOpenOption#CREATE_NEW CREATE_NEW} </th>
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* <td> If this option is present then a new file is created, failing if
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* the file already exists. When creating a file the check for the
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* existence of the file and the creation of the file if it does not exist
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* is atomic with respect to other file system operations. This option is
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* ignored when the file is opened only for reading. </td>
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* </tr>
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* <tr>
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* <th scope="row" > {@link StandardOpenOption#CREATE CREATE} </th>
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* <td> If this option is present then an existing file is opened if it
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* exists, otherwise a new file is created. When creating a file the check
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* for the existence of the file and the creation of the file if it does
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* not exist is atomic with respect to other file system operations. This
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* option is ignored if the {@code CREATE_NEW} option is also present or
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* the file is opened only for reading. </td>
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* </tr>
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* <tr>
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* <th scope="row" > {@link StandardOpenOption#DELETE_ON_CLOSE DELETE_ON_CLOSE} </th>
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* <td> When this option is present then the implementation makes a
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* <em>best effort</em> attempt to delete the file when closed by
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* the {@link #close close} method. If the {@code close} method is not
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* invoked then a <em>best effort</em> attempt is made to delete the file
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* when the Java virtual machine terminates. </td>
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* </tr>
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* <tr>
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* <th scope="row">{@link StandardOpenOption#SPARSE SPARSE} </th>
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* <td> When creating a new file this option is a <em>hint</em> that the
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* new file will be sparse. This option is ignored when not creating
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* a new file. </td>
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* </tr>
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* <tr>
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* <th scope="row"> {@link StandardOpenOption#SYNC SYNC} </th>
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* <td> Requires that every update to the file's content or metadata be
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* written synchronously to the underlying storage device. (see <a
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* href="../file/package-summary.html#integrity"> Synchronized I/O file
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* integrity</a>). </td>
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* </tr>
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* <tr>
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* <th scope="row"> {@link StandardOpenOption#DSYNC DSYNC} </th>
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* <td> Requires that every update to the file's content be written
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* synchronously to the underlying storage device. (see <a
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* href="../file/package-summary.html#integrity"> Synchronized I/O file
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* integrity</a>). </td>
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* </tr>
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* </tbody>
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* </table>
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*
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* <p> An implementation may also support additional options.
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*
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* <p> The {@code attrs} parameter is an optional array of file {@link
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* FileAttribute file-attributes} to set atomically when creating the file.
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*
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* <p> The new channel is created by invoking the {@link
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* FileSystemProvider#newFileChannel newFileChannel} method on the
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* provider that created the {@code Path}.
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*
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* @param path
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* The path of the file to open or create
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* @param options
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* Options specifying how the file is opened
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* @param attrs
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* An optional list of file attributes to set atomically when
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* creating the file
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*
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* @return A new file channel
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*
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* @throws IllegalArgumentException
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* If the set contains an invalid combination of options
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* @throws UnsupportedOperationException
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* If the {@code path} is associated with a provider that does not
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* support creating file channels, or an unsupported open option is
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* specified, or the array contains an attribute that cannot be set
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* atomically when creating the file
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* @throws IOException
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* If an I/O error occurs
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* @throws SecurityException
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* If a security manager is installed and it denies an
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* unspecified permission required by the implementation.
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* In the case of the default provider, the {@link
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* SecurityManager#checkRead(String)} method is invoked to check
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* read access if the file is opened for reading. The {@link
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* SecurityManager#checkWrite(String)} method is invoked to check
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* write access if the file is opened for writing
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*
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* @since 1.7
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*/
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public static FileChannel open(Path path,
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Set<? extends OpenOption> options,
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FileAttribute<?>... attrs)
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throws IOException
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{
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FileSystemProvider provider = path.getFileSystem().provider();
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return provider.newFileChannel(path, options, attrs);
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}
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@SuppressWarnings({"unchecked", "rawtypes"}) // generic array construction
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private static final FileAttribute<?>[] NO_ATTRIBUTES = new FileAttribute[0];
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/**
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* Opens or creates a file, returning a file channel to access the file.
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*
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* <p> An invocation of this method behaves in exactly the same way as the
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* invocation
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* <pre>
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* fc.{@link #open(Path,Set,FileAttribute[]) open}(file, opts, new FileAttribute<?>[0]);
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* </pre>
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* where {@code opts} is a set of the options specified in the {@code
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* options} array.
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*
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* @param path
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* The path of the file to open or create
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* @param options
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* Options specifying how the file is opened
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*
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* @return A new file channel
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*
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* @throws IllegalArgumentException
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* If the set contains an invalid combination of options
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* @throws UnsupportedOperationException
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* If the {@code path} is associated with a provider that does not
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* support creating file channels, or an unsupported open option is
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* specified
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* @throws IOException
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* If an I/O error occurs
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* @throws SecurityException
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* If a security manager is installed and it denies an
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* unspecified permission required by the implementation.
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* In the case of the default provider, the {@link
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* SecurityManager#checkRead(String)} method is invoked to check
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* read access if the file is opened for reading. The {@link
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* SecurityManager#checkWrite(String)} method is invoked to check
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* write access if the file is opened for writing
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*
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* @since 1.7
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*/
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public static FileChannel open(Path path, OpenOption... options)
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throws IOException
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{
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Set<OpenOption> set;
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if (options.length == 0) {
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set = Collections.emptySet();
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} else {
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set = new HashSet<>();
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Collections.addAll(set, options);
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}
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return open(path, set, NO_ATTRIBUTES);
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}
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// -- Channel operations --
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/**
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* Reads a sequence of bytes from this channel into the given buffer.
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*
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* <p> Bytes are read starting at this channel's current file position, and
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* then the file position is updated with the number of bytes actually
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* read. Otherwise this method behaves exactly as specified in the {@link
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* ReadableByteChannel} interface. </p>
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*/
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public abstract int read(ByteBuffer dst) throws IOException;
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/**
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* Reads a sequence of bytes from this channel into a subsequence of the
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* given buffers.
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*
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* <p> Bytes are read starting at this channel's current file position, and
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* then the file position is updated with the number of bytes actually
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* read. Otherwise this method behaves exactly as specified in the {@link
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* ScatteringByteChannel} interface. </p>
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*/
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public abstract long read(ByteBuffer[] dsts, int offset, int length)
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throws IOException;
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/**
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* Reads a sequence of bytes from this channel into the given buffers.
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*
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* <p> Bytes are read starting at this channel's current file position, and
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* then the file position is updated with the number of bytes actually
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* read. Otherwise this method behaves exactly as specified in the {@link
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* ScatteringByteChannel} interface. </p>
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*/
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public final long read(ByteBuffer[] dsts) throws IOException {
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return read(dsts, 0, dsts.length);
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}
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/**
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* Writes a sequence of bytes to this channel from the given buffer.
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*
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* <p> Bytes are written starting at this channel's current file position
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* unless the channel is in append mode, in which case the position is
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* first advanced to the end of the file. The file is grown, if necessary,
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* to accommodate the written bytes, and then the file position is updated
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* with the number of bytes actually written. Otherwise this method
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* behaves exactly as specified by the {@link WritableByteChannel}
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* interface. </p>
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*/
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public abstract int write(ByteBuffer src) throws IOException;
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/**
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* Writes a sequence of bytes to this channel from a subsequence of the
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* given buffers.
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*
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* <p> Bytes are written starting at this channel's current file position
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* unless the channel is in append mode, in which case the position is
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* first advanced to the end of the file. The file is grown, if necessary,
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* to accommodate the written bytes, and then the file position is updated
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* with the number of bytes actually written. Otherwise this method
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* behaves exactly as specified in the {@link GatheringByteChannel}
|
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* interface. </p>
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*/
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public abstract long write(ByteBuffer[] srcs, int offset, int length)
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throws IOException;
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|
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/**
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* Writes a sequence of bytes to this channel from the given buffers.
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*
|
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* <p> Bytes are written starting at this channel's current file position
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* unless the channel is in append mode, in which case the position is
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* first advanced to the end of the file. The file is grown, if necessary,
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* to accommodate the written bytes, and then the file position is updated
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* with the number of bytes actually written. Otherwise this method
|
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* behaves exactly as specified in the {@link GatheringByteChannel}
|
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* interface. </p>
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*/
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public final long write(ByteBuffer[] srcs) throws IOException {
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return write(srcs, 0, srcs.length);
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}
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|
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// -- Other operations --
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|
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/**
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* Returns this channel's file position.
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*
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* @return This channel's file position,
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* a non-negative integer counting the number of bytes
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* from the beginning of the file to the current position
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*
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* @throws ClosedChannelException
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* If this channel is closed
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*
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* @throws IOException
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* If some other I/O error occurs
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*/
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public abstract long position() throws IOException;
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/**
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* Sets this channel's file position.
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*
|
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* <p> Setting the position to a value that is greater than the file's
|
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* current size is legal but does not change the size of the file. A later
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* attempt to read bytes at such a position will immediately return an
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* end-of-file indication. A later attempt to write bytes at such a
|
|
* position will cause the file to be grown to accommodate the new bytes;
|
|
* the values of any bytes between the previous end-of-file and the
|
|
* newly-written bytes are unspecified. </p>
|
|
*
|
|
* @param newPosition
|
|
* The new position, a non-negative integer counting
|
|
* the number of bytes from the beginning of the file
|
|
*
|
|
* @return This file channel
|
|
*
|
|
* @throws ClosedChannelException
|
|
* If this channel is closed
|
|
*
|
|
* @throws IllegalArgumentException
|
|
* If the new position is negative
|
|
*
|
|
* @throws IOException
|
|
* If some other I/O error occurs
|
|
*/
|
|
public abstract FileChannel position(long newPosition) throws IOException;
|
|
|
|
/**
|
|
* Returns the current size of this channel's file.
|
|
*
|
|
* @return The current size of this channel's file,
|
|
* measured in bytes
|
|
*
|
|
* @throws ClosedChannelException
|
|
* If this channel is closed
|
|
*
|
|
* @throws IOException
|
|
* If some other I/O error occurs
|
|
*/
|
|
public abstract long size() throws IOException;
|
|
|
|
/**
|
|
* Truncates this channel's file to the given size.
|
|
*
|
|
* <p> If the given size is less than the file's current size then the file
|
|
* is truncated, discarding any bytes beyond the new end of the file. If
|
|
* the given size is greater than or equal to the file's current size then
|
|
* the file is not modified. In either case, if this channel's file
|
|
* position is greater than the given size then it is set to that size.
|
|
* </p>
|
|
*
|
|
* @param size
|
|
* The new size, a non-negative byte count
|
|
*
|
|
* @return This file channel
|
|
*
|
|
* @throws NonWritableChannelException
|
|
* If this channel was not opened for writing
|
|
*
|
|
* @throws ClosedChannelException
|
|
* If this channel is closed
|
|
*
|
|
* @throws IllegalArgumentException
|
|
* If the new size is negative
|
|
*
|
|
* @throws IOException
|
|
* If some other I/O error occurs
|
|
*/
|
|
public abstract FileChannel truncate(long size) throws IOException;
|
|
|
|
/**
|
|
* Forces any updates to this channel's file to be written to the storage
|
|
* device that contains it.
|
|
*
|
|
* <p> If this channel's file resides on a local storage device then when
|
|
* this method returns it is guaranteed that all changes made to the file
|
|
* since this channel was created, or since this method was last invoked,
|
|
* will have been written to that device. This is useful for ensuring that
|
|
* critical information is not lost in the event of a system crash.
|
|
*
|
|
* <p> If the file does not reside on a local device then no such guarantee
|
|
* is made.
|
|
*
|
|
* <p> The {@code metaData} parameter can be used to limit the number of
|
|
* I/O operations that this method is required to perform. Passing
|
|
* {@code false} for this parameter indicates that only updates to the
|
|
* file's content need be written to storage; passing {@code true}
|
|
* indicates that updates to both the file's content and metadata must be
|
|
* written, which generally requires at least one more I/O operation.
|
|
* Whether this parameter actually has any effect is dependent upon the
|
|
* underlying operating system and is therefore unspecified.
|
|
*
|
|
* <p> Invoking this method may cause an I/O operation to occur even if the
|
|
* channel was only opened for reading. Some operating systems, for
|
|
* example, maintain a last-access time as part of a file's metadata, and
|
|
* this time is updated whenever the file is read. Whether or not this is
|
|
* actually done is system-dependent and is therefore unspecified.
|
|
*
|
|
* <p> This method is only guaranteed to force changes that were made to
|
|
* this channel's file via the methods defined in this class. It may or
|
|
* may not force changes that were made by modifying the content of a
|
|
* {@link MappedByteBuffer <i>mapped byte buffer</i>} obtained by
|
|
* invoking the {@link #map map} method. Invoking the {@link
|
|
* MappedByteBuffer#force force} method of the mapped byte buffer will
|
|
* force changes made to the buffer's content to be written. </p>
|
|
*
|
|
* @param metaData
|
|
* If {@code true} then this method is required to force changes
|
|
* to both the file's content and metadata to be written to
|
|
* storage; otherwise, it need only force content changes to be
|
|
* written
|
|
*
|
|
* @throws ClosedChannelException
|
|
* If this channel is closed
|
|
*
|
|
* @throws IOException
|
|
* If some other I/O error occurs
|
|
*/
|
|
public abstract void force(boolean metaData) throws IOException;
|
|
|
|
/**
|
|
* Transfers bytes from this channel's file to the given writable byte
|
|
* channel.
|
|
*
|
|
* <p> An attempt is made to read up to {@code count} bytes starting at
|
|
* the given {@code position} in this channel's file and write them to the
|
|
* target channel. An invocation of this method may or may not transfer
|
|
* all of the requested bytes; whether or not it does so depends upon the
|
|
* natures and states of the channels. Fewer than the requested number of
|
|
* bytes are transferred if this channel's file contains fewer than
|
|
* {@code count} bytes starting at the given {@code position}, or if the
|
|
* target channel is non-blocking and it has fewer than {@code count}
|
|
* bytes free in its output buffer.
|
|
*
|
|
* <p> This method does not modify this channel's position. If the given
|
|
* position is greater than the file's current size then no bytes are
|
|
* transferred. If the target channel has a position then bytes are
|
|
* written starting at that position and then the position is incremented
|
|
* by the number of bytes written.
|
|
*
|
|
* <p> This method is potentially much more efficient than a simple loop
|
|
* that reads from this channel and writes to the target channel. Many
|
|
* operating systems can transfer bytes directly from the filesystem cache
|
|
* to the target channel without actually copying them. </p>
|
|
*
|
|
* @param position
|
|
* The position within the file at which the transfer is to begin;
|
|
* must be non-negative
|
|
*
|
|
* @param count
|
|
* The maximum number of bytes to be transferred; must be
|
|
* non-negative
|
|
*
|
|
* @param target
|
|
* The target channel
|
|
*
|
|
* @return The number of bytes, possibly zero,
|
|
* that were actually transferred
|
|
*
|
|
* @throws IllegalArgumentException
|
|
* If the preconditions on the parameters do not hold
|
|
*
|
|
* @throws NonReadableChannelException
|
|
* If this channel was not opened for reading
|
|
*
|
|
* @throws NonWritableChannelException
|
|
* If the target channel was not opened for writing
|
|
*
|
|
* @throws ClosedChannelException
|
|
* If either this channel or the target channel is closed
|
|
*
|
|
* @throws AsynchronousCloseException
|
|
* If another thread closes either channel
|
|
* while the transfer is in progress
|
|
*
|
|
* @throws ClosedByInterruptException
|
|
* If another thread interrupts the current thread while the
|
|
* transfer is in progress, thereby closing both channels and
|
|
* setting the current thread's interrupt status
|
|
*
|
|
* @throws IOException
|
|
* If some other I/O error occurs
|
|
*/
|
|
public abstract long transferTo(long position, long count,
|
|
WritableByteChannel target)
|
|
throws IOException;
|
|
|
|
/**
|
|
* Transfers bytes into this channel's file from the given readable byte
|
|
* channel.
|
|
*
|
|
* <p> An attempt is made to read up to {@code count} bytes from the
|
|
* source channel and write them to this channel's file starting at the
|
|
* given {@code position}. An invocation of this method may or may not
|
|
* transfer all of the requested bytes; whether or not it does so depends
|
|
* upon the natures and states of the channels. Fewer than the requested
|
|
* number of bytes will be transferred if the source channel has fewer than
|
|
* {@code count} bytes remaining, or if the source channel is non-blocking
|
|
* and has fewer than {@code count} bytes immediately available in its
|
|
* input buffer.
|
|
*
|
|
* <p> This method does not modify this channel's position. If the given
|
|
* position is greater than the file's current size then no bytes are
|
|
* transferred. If the source channel has a position then bytes are read
|
|
* starting at that position and then the position is incremented by the
|
|
* number of bytes read.
|
|
*
|
|
* <p> This method is potentially much more efficient than a simple loop
|
|
* that reads from the source channel and writes to this channel. Many
|
|
* operating systems can transfer bytes directly from the source channel
|
|
* into the filesystem cache without actually copying them. </p>
|
|
*
|
|
* @param src
|
|
* The source channel
|
|
*
|
|
* @param position
|
|
* The position within the file at which the transfer is to begin;
|
|
* must be non-negative
|
|
*
|
|
* @param count
|
|
* The maximum number of bytes to be transferred; must be
|
|
* non-negative
|
|
*
|
|
* @return The number of bytes, possibly zero,
|
|
* that were actually transferred
|
|
*
|
|
* @throws IllegalArgumentException
|
|
* If the preconditions on the parameters do not hold
|
|
*
|
|
* @throws NonReadableChannelException
|
|
* If the source channel was not opened for reading
|
|
*
|
|
* @throws NonWritableChannelException
|
|
* If this channel was not opened for writing
|
|
*
|
|
* @throws ClosedChannelException
|
|
* If either this channel or the source channel is closed
|
|
*
|
|
* @throws AsynchronousCloseException
|
|
* If another thread closes either channel
|
|
* while the transfer is in progress
|
|
*
|
|
* @throws ClosedByInterruptException
|
|
* If another thread interrupts the current thread while the
|
|
* transfer is in progress, thereby closing both channels and
|
|
* setting the current thread's interrupt status
|
|
*
|
|
* @throws IOException
|
|
* If some other I/O error occurs
|
|
*/
|
|
public abstract long transferFrom(ReadableByteChannel src,
|
|
long position, long count)
|
|
throws IOException;
|
|
|
|
/**
|
|
* Reads a sequence of bytes from this channel into the given buffer,
|
|
* starting at the given file position.
|
|
*
|
|
* <p> This method works in the same manner as the {@link
|
|
* #read(ByteBuffer)} method, except that bytes are read starting at the
|
|
* given file position rather than at the channel's current position. This
|
|
* method does not modify this channel's position. If the given position
|
|
* is greater than the file's current size then no bytes are read. </p>
|
|
*
|
|
* @param dst
|
|
* The buffer into which bytes are to be transferred
|
|
*
|
|
* @param position
|
|
* The file position at which the transfer is to begin;
|
|
* must be non-negative
|
|
*
|
|
* @return The number of bytes read, possibly zero, or {@code -1} if the
|
|
* given position is greater than or equal to the file's current
|
|
* size
|
|
*
|
|
* @throws IllegalArgumentException
|
|
* If the position is negative
|
|
*
|
|
* @throws NonReadableChannelException
|
|
* If this channel was not opened for reading
|
|
*
|
|
* @throws ClosedChannelException
|
|
* If this channel is closed
|
|
*
|
|
* @throws AsynchronousCloseException
|
|
* If another thread closes this channel
|
|
* while the read operation is in progress
|
|
*
|
|
* @throws ClosedByInterruptException
|
|
* If another thread interrupts the current thread
|
|
* while the read operation is in progress, thereby
|
|
* closing the channel and setting the current thread's
|
|
* interrupt status
|
|
*
|
|
* @throws IOException
|
|
* If some other I/O error occurs
|
|
*/
|
|
public abstract int read(ByteBuffer dst, long position) throws IOException;
|
|
|
|
/**
|
|
* Writes a sequence of bytes to this channel from the given buffer,
|
|
* starting at the given file position.
|
|
*
|
|
* <p> This method works in the same manner as the {@link
|
|
* #write(ByteBuffer)} method, except that bytes are written starting at
|
|
* the given file position rather than at the channel's current position.
|
|
* This method does not modify this channel's position. If the given
|
|
* position is greater than the file's current size then the file will be
|
|
* grown to accommodate the new bytes; the values of any bytes between the
|
|
* previous end-of-file and the newly-written bytes are unspecified. </p>
|
|
*
|
|
* @param src
|
|
* The buffer from which bytes are to be transferred
|
|
*
|
|
* @param position
|
|
* The file position at which the transfer is to begin;
|
|
* must be non-negative
|
|
*
|
|
* @return The number of bytes written, possibly zero
|
|
*
|
|
* @throws IllegalArgumentException
|
|
* If the position is negative
|
|
*
|
|
* @throws NonWritableChannelException
|
|
* If this channel was not opened for writing
|
|
*
|
|
* @throws ClosedChannelException
|
|
* If this channel is closed
|
|
*
|
|
* @throws AsynchronousCloseException
|
|
* If another thread closes this channel
|
|
* while the write operation is in progress
|
|
*
|
|
* @throws ClosedByInterruptException
|
|
* If another thread interrupts the current thread
|
|
* while the write operation is in progress, thereby
|
|
* closing the channel and setting the current thread's
|
|
* interrupt status
|
|
*
|
|
* @throws IOException
|
|
* If some other I/O error occurs
|
|
*/
|
|
public abstract int write(ByteBuffer src, long position) throws IOException;
|
|
|
|
|
|
// -- Memory-mapped buffers --
|
|
|
|
/**
|
|
* A typesafe enumeration for file-mapping modes.
|
|
*
|
|
* @since 1.4
|
|
*
|
|
* @see java.nio.channels.FileChannel#map
|
|
*/
|
|
public static class MapMode {
|
|
|
|
/**
|
|
* Mode for a read-only mapping.
|
|
*/
|
|
public static final MapMode READ_ONLY
|
|
= new MapMode("READ_ONLY");
|
|
|
|
/**
|
|
* Mode for a read/write mapping.
|
|
*/
|
|
public static final MapMode READ_WRITE
|
|
= new MapMode("READ_WRITE");
|
|
|
|
/**
|
|
* Mode for a private (copy-on-write) mapping.
|
|
*/
|
|
public static final MapMode PRIVATE
|
|
= new MapMode("PRIVATE");
|
|
|
|
private final String name;
|
|
|
|
private MapMode(String name) {
|
|
this.name = name;
|
|
}
|
|
|
|
/**
|
|
* Returns a string describing this file-mapping mode.
|
|
*
|
|
* @return A descriptive string
|
|
*/
|
|
public String toString() {
|
|
return name;
|
|
}
|
|
|
|
}
|
|
|
|
/**
|
|
* Maps a region of this channel's file directly into memory.
|
|
*
|
|
* <p> A region of a file may be mapped into memory in one of three modes:
|
|
* </p>
|
|
*
|
|
* <ul>
|
|
*
|
|
* <li><p> <i>Read-only:</i> Any attempt to modify the resulting buffer
|
|
* will cause a {@link java.nio.ReadOnlyBufferException} to be thrown.
|
|
* ({@link MapMode#READ_ONLY MapMode.READ_ONLY}) </p></li>
|
|
*
|
|
* <li><p> <i>Read/write:</i> Changes made to the resulting buffer will
|
|
* eventually be propagated to the file; they may or may not be made
|
|
* visible to other programs that have mapped the same file. ({@link
|
|
* MapMode#READ_WRITE MapMode.READ_WRITE}) </p></li>
|
|
*
|
|
* <li><p> <i>Private:</i> Changes made to the resulting buffer will not
|
|
* be propagated to the file and will not be visible to other programs
|
|
* that have mapped the same file; instead, they will cause private
|
|
* copies of the modified portions of the buffer to be created. ({@link
|
|
* MapMode#PRIVATE MapMode.PRIVATE}) </p></li>
|
|
*
|
|
* </ul>
|
|
*
|
|
* <p> For a read-only mapping, this channel must have been opened for
|
|
* reading; for a read/write or private mapping, this channel must have
|
|
* been opened for both reading and writing.
|
|
*
|
|
* <p> The {@link MappedByteBuffer <i>mapped byte buffer</i>}
|
|
* returned by this method will have a position of zero and a limit and
|
|
* capacity of {@code size}; its mark will be undefined. The buffer and
|
|
* the mapping that it represents will remain valid until the buffer itself
|
|
* is garbage-collected.
|
|
*
|
|
* <p> A mapping, once established, is not dependent upon the file channel
|
|
* that was used to create it. Closing the channel, in particular, has no
|
|
* effect upon the validity of the mapping.
|
|
*
|
|
* <p> Many of the details of memory-mapped files are inherently dependent
|
|
* upon the underlying operating system and are therefore unspecified. The
|
|
* behavior of this method when the requested region is not completely
|
|
* contained within this channel's file is unspecified. Whether changes
|
|
* made to the content or size of the underlying file, by this program or
|
|
* another, are propagated to the buffer is unspecified. The rate at which
|
|
* changes to the buffer are propagated to the file is unspecified.
|
|
*
|
|
* <p> For most operating systems, mapping a file into memory is more
|
|
* expensive than reading or writing a few tens of kilobytes of data via
|
|
* the usual {@link #read read} and {@link #write write} methods. From the
|
|
* standpoint of performance it is generally only worth mapping relatively
|
|
* large files into memory. </p>
|
|
*
|
|
* @param mode
|
|
* One of the constants {@link MapMode#READ_ONLY READ_ONLY}, {@link
|
|
* MapMode#READ_WRITE READ_WRITE}, or {@link MapMode#PRIVATE
|
|
* PRIVATE} defined in the {@link MapMode} class, according to
|
|
* whether the file is to be mapped read-only, read/write, or
|
|
* privately (copy-on-write), respectively
|
|
*
|
|
* @param position
|
|
* The position within the file at which the mapped region
|
|
* is to start; must be non-negative
|
|
*
|
|
* @param size
|
|
* The size of the region to be mapped; must be non-negative and
|
|
* no greater than {@link java.lang.Integer#MAX_VALUE}
|
|
*
|
|
* @return The mapped byte buffer
|
|
*
|
|
* @throws NonReadableChannelException
|
|
* If the {@code mode} is {@link MapMode#READ_ONLY READ_ONLY} but
|
|
* this channel was not opened for reading
|
|
*
|
|
* @throws NonWritableChannelException
|
|
* If the {@code mode} is {@link MapMode#READ_WRITE READ_WRITE} or
|
|
* {@link MapMode#PRIVATE PRIVATE} but this channel was not opened
|
|
* for both reading and writing
|
|
*
|
|
* @throws IllegalArgumentException
|
|
* If the preconditions on the parameters do not hold
|
|
*
|
|
* @throws IOException
|
|
* If some other I/O error occurs
|
|
*
|
|
* @see java.nio.channels.FileChannel.MapMode
|
|
* @see java.nio.MappedByteBuffer
|
|
*/
|
|
public abstract MappedByteBuffer map(MapMode mode,
|
|
long position, long size)
|
|
throws IOException;
|
|
|
|
|
|
// -- Locks --
|
|
|
|
/**
|
|
* Acquires a lock on the given region of this channel's file.
|
|
*
|
|
* <p> An invocation of this method will block until the region can be
|
|
* locked, this channel is closed, or the invoking thread is interrupted,
|
|
* whichever comes first.
|
|
*
|
|
* <p> If this channel is closed by another thread during an invocation of
|
|
* this method then an {@link AsynchronousCloseException} will be thrown.
|
|
*
|
|
* <p> If the invoking thread is interrupted while waiting to acquire the
|
|
* lock then its interrupt status will be set and a {@link
|
|
* FileLockInterruptionException} will be thrown. If the invoker's
|
|
* interrupt status is set when this method is invoked then that exception
|
|
* will be thrown immediately; the thread's interrupt status will not be
|
|
* changed.
|
|
*
|
|
* <p> The region specified by the {@code position} and {@code size}
|
|
* parameters need not be contained within, or even overlap, the actual
|
|
* underlying file. Lock regions are fixed in size; if a locked region
|
|
* initially contains the end of the file and the file grows beyond the
|
|
* region then the new portion of the file will not be covered by the lock.
|
|
* If a file is expected to grow in size and a lock on the entire file is
|
|
* required then a region starting at zero, and no smaller than the
|
|
* expected maximum size of the file, should be locked. The zero-argument
|
|
* {@link #lock()} method simply locks a region of size {@link
|
|
* Long#MAX_VALUE}.
|
|
*
|
|
* <p> Some operating systems do not support shared locks, in which case a
|
|
* request for a shared lock is automatically converted into a request for
|
|
* an exclusive lock. Whether the newly-acquired lock is shared or
|
|
* exclusive may be tested by invoking the resulting lock object's {@link
|
|
* FileLock#isShared() isShared} method.
|
|
*
|
|
* <p> File locks are held on behalf of the entire Java virtual machine.
|
|
* They are not suitable for controlling access to a file by multiple
|
|
* threads within the same virtual machine. </p>
|
|
*
|
|
* @param position
|
|
* The position at which the locked region is to start; must be
|
|
* non-negative
|
|
*
|
|
* @param size
|
|
* The size of the locked region; must be non-negative, and the sum
|
|
* {@code position} + {@code size} must be non-negative
|
|
*
|
|
* @param shared
|
|
* {@code true} to request a shared lock, in which case this
|
|
* channel must be open for reading (and possibly writing);
|
|
* {@code false} to request an exclusive lock, in which case this
|
|
* channel must be open for writing (and possibly reading)
|
|
*
|
|
* @return A lock object representing the newly-acquired lock
|
|
*
|
|
* @throws IllegalArgumentException
|
|
* If the preconditions on the parameters do not hold
|
|
*
|
|
* @throws ClosedChannelException
|
|
* If this channel is closed
|
|
*
|
|
* @throws AsynchronousCloseException
|
|
* If another thread closes this channel while the invoking
|
|
* thread is blocked in this method
|
|
*
|
|
* @throws FileLockInterruptionException
|
|
* If the invoking thread is interrupted while blocked in this
|
|
* method
|
|
*
|
|
* @throws OverlappingFileLockException
|
|
* If a lock that overlaps the requested region is already held by
|
|
* this Java virtual machine, or if another thread is already
|
|
* blocked in this method and is attempting to lock an overlapping
|
|
* region
|
|
*
|
|
* @throws NonReadableChannelException
|
|
* If {@code shared} is {@code true} this channel was not
|
|
* opened for reading
|
|
*
|
|
* @throws NonWritableChannelException
|
|
* If {@code shared} is {@code false} but this channel was not
|
|
* opened for writing
|
|
*
|
|
* @throws IOException
|
|
* If some other I/O error occurs
|
|
*
|
|
* @see #lock()
|
|
* @see #tryLock()
|
|
* @see #tryLock(long,long,boolean)
|
|
*/
|
|
public abstract FileLock lock(long position, long size, boolean shared)
|
|
throws IOException;
|
|
|
|
/**
|
|
* Acquires an exclusive lock on this channel's file.
|
|
*
|
|
* <p> An invocation of this method of the form {@code fc.lock()} behaves
|
|
* in exactly the same way as the invocation
|
|
*
|
|
* <pre>
|
|
* fc.{@link #lock(long,long,boolean) lock}(0L, Long.MAX_VALUE, false) </pre>
|
|
*
|
|
* @return A lock object representing the newly-acquired lock
|
|
*
|
|
* @throws ClosedChannelException
|
|
* If this channel is closed
|
|
*
|
|
* @throws AsynchronousCloseException
|
|
* If another thread closes this channel while the invoking
|
|
* thread is blocked in this method
|
|
*
|
|
* @throws FileLockInterruptionException
|
|
* If the invoking thread is interrupted while blocked in this
|
|
* method
|
|
*
|
|
* @throws OverlappingFileLockException
|
|
* If a lock that overlaps the requested region is already held by
|
|
* this Java virtual machine, or if another thread is already
|
|
* blocked in this method and is attempting to lock an overlapping
|
|
* region of the same file
|
|
*
|
|
* @throws NonWritableChannelException
|
|
* If this channel was not opened for writing
|
|
*
|
|
* @throws IOException
|
|
* If some other I/O error occurs
|
|
*
|
|
* @see #lock(long,long,boolean)
|
|
* @see #tryLock()
|
|
* @see #tryLock(long,long,boolean)
|
|
*/
|
|
public final FileLock lock() throws IOException {
|
|
return lock(0L, Long.MAX_VALUE, false);
|
|
}
|
|
|
|
/**
|
|
* Attempts to acquire a lock on the given region of this channel's file.
|
|
*
|
|
* <p> This method does not block. An invocation always returns
|
|
* immediately, either having acquired a lock on the requested region or
|
|
* having failed to do so. If it fails to acquire a lock because an
|
|
* overlapping lock is held by another program then it returns
|
|
* {@code null}. If it fails to acquire a lock for any other reason then
|
|
* an appropriate exception is thrown.
|
|
*
|
|
* <p> The region specified by the {@code position} and {@code size}
|
|
* parameters need not be contained within, or even overlap, the actual
|
|
* underlying file. Lock regions are fixed in size; if a locked region
|
|
* initially contains the end of the file and the file grows beyond the
|
|
* region then the new portion of the file will not be covered by the lock.
|
|
* If a file is expected to grow in size and a lock on the entire file is
|
|
* required then a region starting at zero, and no smaller than the
|
|
* expected maximum size of the file, should be locked. The zero-argument
|
|
* {@link #tryLock()} method simply locks a region of size {@link
|
|
* Long#MAX_VALUE}.
|
|
*
|
|
* <p> Some operating systems do not support shared locks, in which case a
|
|
* request for a shared lock is automatically converted into a request for
|
|
* an exclusive lock. Whether the newly-acquired lock is shared or
|
|
* exclusive may be tested by invoking the resulting lock object's {@link
|
|
* FileLock#isShared() isShared} method.
|
|
*
|
|
* <p> File locks are held on behalf of the entire Java virtual machine.
|
|
* They are not suitable for controlling access to a file by multiple
|
|
* threads within the same virtual machine. </p>
|
|
*
|
|
* @param position
|
|
* The position at which the locked region is to start; must be
|
|
* non-negative
|
|
*
|
|
* @param size
|
|
* The size of the locked region; must be non-negative, and the sum
|
|
* {@code position} + {@code size} must be non-negative
|
|
*
|
|
* @param shared
|
|
* {@code true} to request a shared lock,
|
|
* {@code false} to request an exclusive lock
|
|
*
|
|
* @return A lock object representing the newly-acquired lock,
|
|
* or {@code null} if the lock could not be acquired
|
|
* because another program holds an overlapping lock
|
|
*
|
|
* @throws IllegalArgumentException
|
|
* If the preconditions on the parameters do not hold
|
|
*
|
|
* @throws ClosedChannelException
|
|
* If this channel is closed
|
|
*
|
|
* @throws OverlappingFileLockException
|
|
* If a lock that overlaps the requested region is already held by
|
|
* this Java virtual machine, or if another thread is already
|
|
* blocked in this method and is attempting to lock an overlapping
|
|
* region of the same file
|
|
*
|
|
* @throws IOException
|
|
* If some other I/O error occurs
|
|
*
|
|
* @see #lock()
|
|
* @see #lock(long,long,boolean)
|
|
* @see #tryLock()
|
|
*/
|
|
public abstract FileLock tryLock(long position, long size, boolean shared)
|
|
throws IOException;
|
|
|
|
/**
|
|
* Attempts to acquire an exclusive lock on this channel's file.
|
|
*
|
|
* <p> An invocation of this method of the form {@code fc.tryLock()}
|
|
* behaves in exactly the same way as the invocation
|
|
*
|
|
* <pre>
|
|
* fc.{@link #tryLock(long,long,boolean) tryLock}(0L, Long.MAX_VALUE, false) </pre>
|
|
*
|
|
* @return A lock object representing the newly-acquired lock,
|
|
* or {@code null} if the lock could not be acquired
|
|
* because another program holds an overlapping lock
|
|
*
|
|
* @throws ClosedChannelException
|
|
* If this channel is closed
|
|
*
|
|
* @throws OverlappingFileLockException
|
|
* If a lock that overlaps the requested region is already held by
|
|
* this Java virtual machine, or if another thread is already
|
|
* blocked in this method and is attempting to lock an overlapping
|
|
* region
|
|
*
|
|
* @throws IOException
|
|
* If some other I/O error occurs
|
|
*
|
|
* @see #lock()
|
|
* @see #lock(long,long,boolean)
|
|
* @see #tryLock(long,long,boolean)
|
|
*/
|
|
public final FileLock tryLock() throws IOException {
|
|
return tryLock(0L, Long.MAX_VALUE, false);
|
|
}
|
|
|
|
}
|