| /* |
| * Copyright (c) 2000, 2011, 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 |
| * under the terms of the GNU General Public License version 2 only, as |
| * 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 |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| */ |
| |
| package java.nio.channels; |
| |
| import java.io.*; |
| import java.nio.ByteBuffer; |
| import java.nio.MappedByteBuffer; |
| import java.nio.channels.spi.AbstractInterruptibleChannel; |
| import java.nio.file.*; |
| import java.nio.file.attribute.FileAttribute; |
| import java.nio.file.spi.*; |
| import java.util.Set; |
| import java.util.HashSet; |
| import java.util.Collections; |
| |
| /** |
| * A channel for reading, writing, mapping, and manipulating a file. |
| * |
| * <p> A file channel is a {@link SeekableByteChannel} that is connected to |
| * a file. It has a current <i>position</i> within its file which can |
| * be both {@link #position() <i>queried</i>} and {@link #position(long) |
| * <i>modified</i>}. The file itself contains a variable-length sequence |
| * of bytes that can be read and written and whose current {@link #size |
| * <i>size</i>} can be queried. The size of the file increases |
| * when bytes are written beyond its current size; the size of the file |
| * decreases when it is {@link #truncate </code><i>truncated</i><code>}. The |
| * file may also have some associated <i>metadata</i> such as access |
| * permissions, content type, and last-modification time; this class does not |
| * define methods for metadata access. |
| * |
| * <p> In addition to the familiar read, write, and close operations of byte |
| * channels, this class defines the following file-specific operations: </p> |
| * |
| * <ul> |
| * |
| * <li><p> Bytes may be {@link #read(ByteBuffer, long) read} or |
| * {@link #write(ByteBuffer, long) <i>written</i>} at an absolute |
| * position in a file in a way that does not affect the channel's current |
| * position. </p></li> |
| * |
| * <li><p> A region of a file may be {@link #map <i>mapped</i>} |
| * directly into memory; for large files this is often much more efficient |
| * than invoking the usual <tt>read</tt> or <tt>write</tt> methods. |
| * </p></li> |
| * |
| * <li><p> Updates made to a file may be {@link #force <i>forced |
| * out</i>} to the underlying storage device, ensuring that data are not |
| * lost in the event of a system crash. </p></li> |
| * |
| * <li><p> Bytes can be transferred from a file {@link #transferTo <i>to |
| * some other channel</i>}, and {@link #transferFrom <i>vice |
| * versa</i>}, in a way that can be optimized by many operating systems |
| * into a very fast transfer directly to or from the filesystem cache. |
| * </p></li> |
| * |
| * <li><p> A region of a file may be {@link FileLock <i>locked</i>} |
| * against access by other programs. </p></li> |
| * |
| * </ul> |
| * |
| * <p> File channels are safe for use by multiple concurrent threads. The |
| * {@link Channel#close close} method may be invoked at any time, as specified |
| * by the {@link Channel} interface. Only one operation that involves the |
| * channel's position or can change its file's size may be in progress at any |
| * given time; attempts to initiate a second such operation while the first is |
| * still in progress will block until the first operation completes. Other |
| * operations, in particular those that take an explicit position, may proceed |
| * concurrently; whether they in fact do so is dependent upon the underlying |
| * implementation and is therefore unspecified. |
| * |
| * <p> The view of a file provided by an instance of this class is guaranteed |
| * to be consistent with other views of the same file provided by other |
| * instances in the same program. The view provided by an instance of this |
| * class may or may not, however, be consistent with the views seen by other |
| * concurrently-running programs due to caching performed by the underlying |
| * operating system and delays induced by network-filesystem protocols. This |
| * is true regardless of the language in which these other programs are |
| * written, and whether they are running on the same machine or on some other |
| * machine. The exact nature of any such inconsistencies are system-dependent |
| * and are therefore unspecified. |
| * |
| * <p> A file channel is created by invoking one of the {@link #open open} |
| * methods defined by this class. A file channel can also be obtained from an |
| * existing {@link java.io.FileInputStream#getChannel FileInputStream}, {@link |
| * java.io.FileOutputStream#getChannel FileOutputStream}, or {@link |
| * java.io.RandomAccessFile#getChannel RandomAccessFile} object by invoking |
| * that object's <tt>getChannel</tt> method, which returns a file channel that |
| * is connected to the same underlying file. Where the file channel is obtained |
| * from an existing stream or random access file then the state of the file |
| * channel is intimately connected to that of the object whose <tt>getChannel</tt> |
| * method returned the channel. Changing the channel's position, whether |
| * explicitly or by reading or writing bytes, will change the file position of |
| * the originating object, and vice versa. Changing the file's length via the |
| * file channel will change the length seen via the originating object, and vice |
| * versa. Changing the file's content by writing bytes will change the content |
| * seen by the originating object, and vice versa. |
| * |
| * <a name="open-mode"></a> <p> At various points this class specifies that an |
| * instance that is "open for reading," "open for writing," or "open for |
| * reading and writing" is required. A channel obtained via the {@link |
| * java.io.FileInputStream#getChannel getChannel} method of a {@link |
| * java.io.FileInputStream} instance will be open for reading. A channel |
| * obtained via the {@link java.io.FileOutputStream#getChannel getChannel} |
| * method of a {@link java.io.FileOutputStream} instance will be open for |
| * writing. Finally, a channel obtained via the {@link |
| * java.io.RandomAccessFile#getChannel getChannel} method of a {@link |
| * java.io.RandomAccessFile} instance will be open for reading if the instance |
| * was created with mode <tt>"r"</tt> and will be open for reading and writing |
| * if the instance was created with mode <tt>"rw"</tt>. |
| * |
| * <a name="append-mode"></a><p> A file channel that is open for writing may be in |
| * <i>append mode</i>, for example if it was obtained from a file-output stream |
| * that was created by invoking the {@link |
| * java.io.FileOutputStream#FileOutputStream(java.io.File,boolean) |
| * FileOutputStream(File,boolean)} constructor and passing <tt>true</tt> for |
| * the second parameter. In this mode each invocation of a relative write |
| * operation first advances the position to the end of the file and then writes |
| * the requested data. Whether the advancement of the position and the writing |
| * of the data are done in a single atomic operation is system-dependent and |
| * therefore unspecified. |
| * |
| * @see java.io.FileInputStream#getChannel() |
| * @see java.io.FileOutputStream#getChannel() |
| * @see java.io.RandomAccessFile#getChannel() |
| * |
| * @author Mark Reinhold |
| * @author Mike McCloskey |
| * @author JSR-51 Expert Group |
| * @since 1.4 |
| */ |
| |
| public abstract class FileChannel |
| extends AbstractInterruptibleChannel |
| implements SeekableByteChannel, GatheringByteChannel, ScatteringByteChannel |
| { |
| /** |
| * Initializes a new instance of this class. |
| */ |
| protected FileChannel() { } |
| |
| /** |
| * Opens or creates a file, returning a file channel to access the file. |
| * |
| * <p> The {@code options} parameter determines how the file is opened. |
| * The {@link StandardOpenOption#READ READ} and {@link StandardOpenOption#WRITE |
| * WRITE} options determine if the file should be opened for reading and/or |
| * writing. If neither option (or the {@link StandardOpenOption#APPEND APPEND} |
| * option) is contained in the array then the file is opened for reading. |
| * By default reading or writing commences at the beginning of the file. |
| * |
| * <p> In the addition to {@code READ} and {@code WRITE}, the following |
| * options may be present: |
| * |
| * <table border=1 cellpadding=5 summary=""> |
| * <tr> <th>Option</th> <th>Description</th> </tr> |
| * <tr> |
| * <td> {@link StandardOpenOption#APPEND APPEND} </td> |
| * <td> If this option is present then the file is opened for writing and |
| * each invocation of the channel's {@code write} method first advances |
| * the position to the end of the file and then writes the requested |
| * data. Whether the advancement of the position and the writing of the |
| * data are done in a single atomic operation is system-dependent and |
| * therefore unspecified. This option may not be used in conjunction |
| * with the {@code READ} or {@code TRUNCATE_EXISTING} options. </td> |
| * </tr> |
| * <tr> |
| * <td> {@link StandardOpenOption#TRUNCATE_EXISTING TRUNCATE_EXISTING} </td> |
| * <td> If this option is present then the existing file is truncated to |
| * a size of 0 bytes. This option is ignored when the file is opened only |
| * for reading. </td> |
| * </tr> |
| * <tr> |
| * <td> {@link StandardOpenOption#CREATE_NEW CREATE_NEW} </td> |
| * <td> If this option is present then a new file is created, failing if |
| * the file already exists. When creating a file the check for the |
| * existence of the file and the creation of the file if it does not exist |
| * is atomic with respect to other file system operations. This option is |
| * ignored when the file is opened only for reading. </td> |
| * </tr> |
| * <tr> |
| * <td > {@link StandardOpenOption#CREATE CREATE} </td> |
| * <td> If this option is present then an existing file is opened if it |
| * exists, otherwise a new file is created. When creating a file the check |
| * for the existence of the file and the creation of the file if it does |
| * not exist is atomic with respect to other file system operations. This |
| * option is ignored if the {@code CREATE_NEW} option is also present or |
| * the file is opened only for reading. </td> |
| * </tr> |
| * <tr> |
| * <td > {@link StandardOpenOption#DELETE_ON_CLOSE DELETE_ON_CLOSE} </td> |
| * <td> When this option is present then the implementation makes a |
| * <em>best effort</em> attempt to delete the file when closed by the |
| * the {@link #close close} method. If the {@code close} method is not |
| * invoked then a <em>best effort</em> attempt is made to delete the file |
| * when the Java virtual machine terminates. </td> |
| * </tr> |
| * <tr> |
| * <td>{@link StandardOpenOption#SPARSE SPARSE} </td> |
| * <td> When creating a new file this option is a <em>hint</em> that the |
| * new file will be sparse. This option is ignored when not creating |
| * a new file. </td> |
| * </tr> |
| * <tr> |
| * <td> {@link StandardOpenOption#SYNC SYNC} </td> |
| * <td> Requires that every update to the file's content or metadata be |
| * written synchronously to the underlying storage device. (see <a |
| * href="../file/package-summary.html#integrity"> Synchronized I/O file |
| * integrity</a>). </td> |
| * <tr> |
| * <tr> |
| * <td> {@link StandardOpenOption#DSYNC DSYNC} </td> |
| * <td> Requires that every update to the file's content be written |
| * synchronously to the underlying storage device. (see <a |
| * href="../file/package-summary.html#integrity"> Synchronized I/O file |
| * integrity</a>). </td> |
| * </tr> |
| * </table> |
| * |
| * <p> An implementation may also support additional options. |
| * |
| * <p> The {@code attrs} parameter is an optional array of file {@link |
| * FileAttribute file-attributes} to set atomically when creating the file. |
| * |
| * <p> The new channel is created by invoking the {@link |
| * FileSystemProvider#newFileChannel newFileChannel} method on the |
| * provider that created the {@code Path}. |
| * |
| * @param path |
| * The path of the file to open or create |
| * @param options |
| * Options specifying how the file is opened |
| * @param attrs |
| * An optional list of file attributes to set atomically when |
| * creating the file |
| * |
| * @return A new file channel |
| * |
| * @throws IllegalArgumentException |
| * If the set contains an invalid combination of options |
| * @throws UnsupportedOperationException |
| * If the {@code path} is associated with a provider that does not |
| * support creating file channels, or an unsupported open option is |
| * specified, or the array contains an attribute that cannot be set |
| * atomically when creating the file |
| * @throws IOException |
| * If an I/O error occurs |
| * @throws SecurityException |
| * If a security manager is installed and it denies an |
| * unspecified permission required by the implementation. |
| * In the case of the default provider, the {@link |
| * SecurityManager#checkRead(String)} method is invoked to check |
| * read access if the file is opened for reading. The {@link |
| * SecurityManager#checkWrite(String)} method is invoked to check |
| * write access if the file is opened for writing |
| * |
| * @since 1.7 |
| */ |
| public static FileChannel open(Path path, |
| Set<? extends OpenOption> options, |
| FileAttribute<?>... attrs) |
| throws IOException |
| { |
| FileSystemProvider provider = path.getFileSystem().provider(); |
| return provider.newFileChannel(path, options, attrs); |
| } |
| |
| private static final FileAttribute<?>[] NO_ATTRIBUTES = new FileAttribute[0]; |
| |
| /** |
| * Opens or creates a file, returning a file channel to access the file. |
| * |
| * <p> An invocation of this method behaves in exactly the same way as the |
| * invocation |
| * <pre> |
| * fc.{@link #open(Path,Set,FileAttribute[]) open}(file, opts, new FileAttribute<?>[0]); |
| * </pre> |
| * where {@code opts} is a set of the options specified in the {@code |
| * options} array. |
| * |
| * @param path |
| * The path of the file to open or create |
| * @param options |
| * Options specifying how the file is opened |
| * |
| * @return A new file channel |
| * |
| * @throws IllegalArgumentException |
| * If the set contains an invalid combination of options |
| * @throws UnsupportedOperationException |
| * If the {@code path} is associated with a provider that does not |
| * support creating file channels, or an unsupported open option is |
| * specified |
| * @throws IOException |
| * If an I/O error occurs |
| * @throws SecurityException |
| * If a security manager is installed and it denies an |
| * unspecified permission required by the implementation. |
| * In the case of the default provider, the {@link |
| * SecurityManager#checkRead(String)} method is invoked to check |
| * read access if the file is opened for reading. The {@link |
| * SecurityManager#checkWrite(String)} method is invoked to check |
| * write access if the file is opened for writing |
| * |
| * @since 1.7 |
| */ |
| public static FileChannel open(Path path, OpenOption... options) |
| throws IOException |
| { |
| Set<OpenOption> set = new HashSet<OpenOption>(options.length); |
| Collections.addAll(set, options); |
| return open(path, set, NO_ATTRIBUTES); |
| } |
| |
| // -- Channel operations -- |
| |
| /** |
| * Reads a sequence of bytes from this channel into the given buffer. |
| * |
| * <p> Bytes are read starting at this channel's current file position, and |
| * then the file position is updated with the number of bytes actually |
| * read. Otherwise this method behaves exactly as specified in the {@link |
| * ReadableByteChannel} interface. </p> |
| */ |
| public abstract int read(ByteBuffer dst) throws IOException; |
| |
| /** |
| * Reads a sequence of bytes from this channel into a subsequence of the |
| * given buffers. |
| * |
| * <p> Bytes are read starting at this channel's current file position, and |
| * then the file position is updated with the number of bytes actually |
| * read. Otherwise this method behaves exactly as specified in the {@link |
| * ScatteringByteChannel} interface. </p> |
| */ |
| public abstract long read(ByteBuffer[] dsts, int offset, int length) |
| throws IOException; |
| |
| /** |
| * Reads a sequence of bytes from this channel into the given buffers. |
| * |
| * <p> Bytes are read starting at this channel's current file position, and |
| * then the file position is updated with the number of bytes actually |
| * read. Otherwise this method behaves exactly as specified in the {@link |
| * ScatteringByteChannel} interface. </p> |
| */ |
| public final long read(ByteBuffer[] dsts) throws IOException { |
| return read(dsts, 0, dsts.length); |
| } |
| |
| /** |
| * Writes a sequence of bytes to this channel from the given buffer. |
| * |
| * <p> Bytes are written starting at this channel's current file position |
| * unless the channel is in append mode, in which case the position is |
| * first advanced to the end of the file. The file is grown, if necessary, |
| * to accommodate the written bytes, and then the file position is updated |
| * with the number of bytes actually written. Otherwise this method |
| * behaves exactly as specified by the {@link WritableByteChannel} |
| * interface. </p> |
| */ |
| public abstract int write(ByteBuffer src) throws IOException; |
| |
| /** |
| * Writes a sequence of bytes to this channel from a subsequence of the |
| * given buffers. |
| * |
| * <p> Bytes are written starting at this channel's current file position |
| * unless the channel is in append mode, in which case the position is |
| * first advanced to the end of the file. The file is grown, if necessary, |
| * to accommodate the written bytes, and then the file position is updated |
| * with the number of bytes actually written. Otherwise this method |
| * behaves exactly as specified in the {@link GatheringByteChannel} |
| * interface. </p> |
| */ |
| public abstract long write(ByteBuffer[] srcs, int offset, int length) |
| throws IOException; |
| |
| /** |
| * Writes a sequence of bytes to this channel from the given buffers. |
| * |
| * <p> Bytes are written starting at this channel's current file position |
| * unless the channel is in append mode, in which case the position is |
| * first advanced to the end of the file. The file is grown, if necessary, |
| * to accommodate the written bytes, and then the file position is updated |
| * with the number of bytes actually written. Otherwise this method |
| * behaves exactly as specified in the {@link GatheringByteChannel} |
| * interface. </p> |
| */ |
| public final long write(ByteBuffer[] srcs) throws IOException { |
| return write(srcs, 0, srcs.length); |
| } |
| |
| |
| // -- Other operations -- |
| |
| /** |
| * Returns this channel's file position. </p> |
| * |
| * @return This channel's file position, |
| * a non-negative integer counting the number of bytes |
| * from the beginning of the file to the current position |
| * |
| * @throws ClosedChannelException |
| * If this channel is closed |
| * |
| * @throws IOException |
| * If some other I/O error occurs |
| */ |
| public abstract long position() throws IOException; |
| |
| /** |
| * Sets this channel's file position. |
| * |
| * <p> Setting the position to a value that is greater than the file's |
| * current size is legal but does not change the size of the file. A later |
| * attempt to read bytes at such a position will immediately return an |
| * 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. </p> |
| * |
| * @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 <tt>metaData</tt> parameter can be used to limit the number of |
| * I/O operations that this method is required to perform. Passing |
| * <tt>false</tt> for this parameter indicates that only updates to the |
| * file's content need be written to storage; passing <tt>true</tt> |
| * 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 <tt>true</tt> 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 <tt>count</tt> bytes starting at |
| * the given <tt>position</tt> 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 |
| * <tt>count</tt> bytes starting at the given <tt>position</tt>, or if the |
| * target channel is non-blocking and it has fewer than <tt>count</tt> |
| * 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 <tt>count</tt> bytes from the |
| * source channel and write them to this channel's file starting at the |
| * given <tt>position</tt>. 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 |
| * <tt>count</tt> bytes remaining, or if the source channel is non-blocking |
| * and has fewer than <tt>count</tt> 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 <tt>-1</tt> 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 type=disc> |
| * |
| * <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 <tt>size</tt>; 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 <tt>mode</tt> is {@link MapMode#READ_ONLY READ_ONLY} but |
| * this channel was not opened for reading |
| * |
| * @throws NonWritableChannelException |
| * If the <tt>mode</tt> 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 <tt>position</tt> and <tt>size</tt> |
| * 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 |
| * <tt>position</tt> + <tt>size</tt> must be non-negative |
| * |
| * @param shared |
| * <tt>true</tt> to request a shared lock, in which case this |
| * channel must be open for reading (and possibly writing); |
| * <tt>false</tt> 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 <tt>shared</tt> is <tt>true</tt> this channel was not |
| * opened for reading |
| * |
| * @throws NonWritableChannelException |
| * If <tt>shared</tt> is <tt>false</tt> 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 <tt>fc.lock()</tt> 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 |
| * <tt>null</tt>. If it fails to acquire a lock for any other reason then |
| * an appropriate exception is thrown. |
| * |
| * <p> The region specified by the <tt>position</tt> and <tt>size</tt> |
| * 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 |
| * <tt>position</tt> + <tt>size</tt> must be non-negative |
| * |
| * @param shared |
| * <tt>true</tt> to request a shared lock, |
| * <tt>false</tt> to request an exclusive lock |
| * |
| * @return A lock object representing the newly-acquired lock, |
| * or <tt>null</tt> 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 <tt>fc.tryLock()</tt> |
| * 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 <tt>null</tt> 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); |
| } |
| |
| } |
