Showing the changes to java/pkg/java/nio/channels/FileChannel.java (1 of 18352 files). Show all
Unified · Split
| @@ -0,0 +1,1157 @@ | |||
| 1 | /* | ||
| 2 | * Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved. | ||
| 3 | * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. | ||
| 4 | * | ||
| 5 | * This code is free software; you can redistribute it and/or modify it | ||
| 6 | * under the terms of the GNU General Public License version 2 only, as | ||
| 7 | * published by the Free Software Foundation. Oracle designates this | ||
| 8 | * particular file as subject to the "Classpath" exception as provided | ||
| 9 | * by Oracle in the LICENSE file that accompanied this code. | ||
| 10 | * | ||
| 11 | * This code is distributed in the hope that it will be useful, but WITHOUT | ||
| 12 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | ||
| 13 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | ||
| 14 | * version 2 for more details (a copy is included in the LICENSE file that | ||
| 15 | * accompanied this code). | ||
| 16 | * | ||
| 17 | * You should have received a copy of the GNU General Public License version | ||
| 18 | * 2 along with this work; if not, write to the Free Software Foundation, | ||
| 19 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | ||
| 20 | * | ||
| 21 | * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA | ||
| 22 | * or visit www.oracle.com if you need additional information or have any | ||
| 23 | * questions. | ||
| 24 | */ | ||
| 25 | |||
| 26 | package java.nio.channels; | ||
| 27 | |||
| 28 | import java.io.*; | ||
| 29 | import java.nio.ByteBuffer; | ||
| 30 | import java.nio.MappedByteBuffer; | ||
| 31 | import java.nio.channels.spi.AbstractInterruptibleChannel; | ||
| 32 | import java.nio.file.*; | ||
| 33 | import java.nio.file.attribute.FileAttribute; | ||
| 34 | import java.nio.file.spi.*; | ||
| 35 | import java.util.Set; | ||
| 36 | import java.util.HashSet; | ||
| 37 | import java.util.Collections; | ||
| 38 | |||
| 39 | /** | ||
| 40 | * A channel for reading, writing, mapping, and manipulating a file. | ||
| 41 | * | ||
| 42 | * <p> A file channel is a {@link SeekableByteChannel} that is connected to | ||
| 43 | * a file. It has a current <i>position</i> within its file which can | ||
| 44 | * be both {@link #position() <i>queried</i>} and {@link #position(long) | ||
| 45 | * <i>modified</i>}. The file itself contains a variable-length sequence | ||
| 46 | * of bytes that can be read and written and whose current {@link #size | ||
| 47 | * <i>size</i>} can be queried. The size of the file increases | ||
| 48 | * when bytes are written beyond its current size; the size of the file | ||
| 49 | * decreases when it is {@link #truncate </code><i>truncated</i><code>}. The | ||
| 50 | * file may also have some associated <i>metadata</i> such as access | ||
| 51 | * permissions, content type, and last-modification time; this class does not | ||
| 52 | * define methods for metadata access. | ||
| 53 | * | ||
| 54 | * <p> In addition to the familiar read, write, and close operations of byte | ||
| 55 | * channels, this class defines the following file-specific operations: </p> | ||
| 56 | * | ||
| 57 | * <ul> | ||
| 58 | * | ||
| 59 | * <li><p> Bytes may be {@link #read(ByteBuffer, long) read} or | ||
| 60 | * {@link #write(ByteBuffer, long) <i>written</i>} at an absolute | ||
| 61 | * position in a file in a way that does not affect the channel's current | ||
| 62 | * position. </p></li> | ||
| 63 | * | ||
| 64 | * <li><p> A region of a file may be {@link #map <i>mapped</i>} | ||
| 65 | * directly into memory; for large files this is often much more efficient | ||
| 66 | * than invoking the usual <tt>read</tt> or <tt>write</tt> methods. | ||
| 67 | * </p></li> | ||
| 68 | * | ||
| 69 | * <li><p> Updates made to a file may be {@link #force <i>forced | ||
| 70 | * out</i>} to the underlying storage device, ensuring that data are not | ||
| 71 | * lost in the event of a system crash. </p></li> | ||
| 72 | * | ||
| 73 | * <li><p> Bytes can be transferred from a file {@link #transferTo <i>to | ||
| 74 | * some other channel</i>}, and {@link #transferFrom <i>vice | ||
| 75 | * versa</i>}, in a way that can be optimized by many operating systems | ||
| 76 | * into a very fast transfer directly to or from the filesystem cache. | ||
| 77 | * </p></li> | ||
| 78 | * | ||
| 79 | * <li><p> A region of a file may be {@link FileLock <i>locked</i>} | ||
| 80 | * against access by other programs. </p></li> | ||
| 81 | * | ||
| 82 | * </ul> | ||
| 83 | * | ||
| 84 | * <p> File channels are safe for use by multiple concurrent threads. The | ||
| 85 | * {@link Channel#close close} method may be invoked at any time, as specified | ||
| 86 | * by the {@link Channel} interface. Only one operation that involves the | ||
| 87 | * channel's position or can change its file's size may be in progress at any | ||
| 88 | * given time; attempts to initiate a second such operation while the first is | ||
| 89 | * still in progress will block until the first operation completes. Other | ||
| 90 | * operations, in particular those that take an explicit position, may proceed | ||
| 91 | * concurrently; whether they in fact do so is dependent upon the underlying | ||
| 92 | * implementation and is therefore unspecified. | ||
| 93 | * | ||
| 94 | * <p> The view of a file provided by an instance of this class is guaranteed | ||
| 95 | * to be consistent with other views of the same file provided by other | ||
| 96 | * instances in the same program. The view provided by an instance of this | ||
| 97 | * class may or may not, however, be consistent with the views seen by other | ||
| 98 | * concurrently-running programs due to caching performed by the underlying | ||
| 99 | * operating system and delays induced by network-filesystem protocols. This | ||
| 100 | * is true regardless of the language in which these other programs are | ||
| 101 | * written, and whether they are running on the same machine or on some other | ||
| 102 | * machine. The exact nature of any such inconsistencies are system-dependent | ||
| 103 | * and are therefore unspecified. | ||
| 104 | * | ||
| 105 | * <p> A file channel is created by invoking one of the {@link #open open} | ||
| 106 | * methods defined by this class. A file channel can also be obtained from an | ||
| 107 | * existing {@link java.io.FileInputStream#getChannel FileInputStream}, {@link | ||
| 108 | * java.io.FileOutputStream#getChannel FileOutputStream}, or {@link | ||
| 109 | * java.io.RandomAccessFile#getChannel RandomAccessFile} object by invoking | ||
| 110 | * that object's <tt>getChannel</tt> method, which returns a file channel that | ||
| 111 | * is connected to the same underlying file. Where the file channel is obtained | ||
| 112 | * from an existing stream or random access file then the state of the file | ||
| 113 | * channel is intimately connected to that of the object whose <tt>getChannel</tt> | ||
| 114 | * method returned the channel. Changing the channel's position, whether | ||
| 115 | * explicitly or by reading or writing bytes, will change the file position of | ||
| 116 | * the originating object, and vice versa. Changing the file's length via the | ||
| 117 | * file channel will change the length seen via the originating object, and vice | ||
| 118 | * versa. Changing the file's content by writing bytes will change the content | ||
| 119 | * seen by the originating object, and vice versa. | ||
| 120 | * | ||
| 121 | * <a name="open-mode"></a> <p> At various points this class specifies that an | ||
| 122 | * instance that is "open for reading," "open for writing," or "open for | ||
| 123 | * reading and writing" is required. A channel obtained via the {@link | ||
| 124 | * java.io.FileInputStream#getChannel getChannel} method of a {@link | ||
| 125 | * java.io.FileInputStream} instance will be open for reading. A channel | ||
| 126 | * obtained via the {@link java.io.FileOutputStream#getChannel getChannel} | ||
| 127 | * method of a {@link java.io.FileOutputStream} instance will be open for | ||
| 128 | * writing. Finally, a channel obtained via the {@link | ||
| 129 | * java.io.RandomAccessFile#getChannel getChannel} method of a {@link | ||
| 130 | * java.io.RandomAccessFile} instance will be open for reading if the instance | ||
| 131 | * was created with mode <tt>"r"</tt> and will be open for reading and writing | ||
| 132 | * if the instance was created with mode <tt>"rw"</tt>. | ||
| 133 | * | ||
| 134 | * <a name="append-mode"></a><p> A file channel that is open for writing may be in | ||
| 135 | * <i>append mode</i>, for example if it was obtained from a file-output stream | ||
| 136 | * that was created by invoking the {@link | ||
| 137 | * java.io.FileOutputStream#FileOutputStream(java.io.File,boolean) | ||
| 138 | * FileOutputStream(File,boolean)} constructor and passing <tt>true</tt> for | ||
| 139 | * the second parameter. In this mode each invocation of a relative write | ||
| 140 | * operation first advances the position to the end of the file and then writes | ||
| 141 | * the requested data. Whether the advancement of the position and the writing | ||
| 142 | * of the data are done in a single atomic operation is system-dependent and | ||
| 143 | * therefore unspecified. | ||
| 144 | * | ||
| 145 | * @see java.io.FileInputStream#getChannel() | ||
| 146 | * @see java.io.FileOutputStream#getChannel() | ||
| 147 | * @see java.io.RandomAccessFile#getChannel() | ||
| 148 | * | ||
| 149 | * @author Mark Reinhold | ||
| 150 | * @author Mike McCloskey | ||
| 151 | * @author JSR-51 Expert Group | ||
| 152 | * @since 1.4 | ||
| 153 | */ | ||
| 154 | |||
| 155 | public abstract class FileChannel | ||
| 156 | extends AbstractInterruptibleChannel | ||
| 157 | implements SeekableByteChannel, GatheringByteChannel, ScatteringByteChannel | ||
| 158 | { | ||
| 159 | /** | ||
| 160 | * Initializes a new instance of this class. | ||
| 161 | */ | ||
| 162 | protected FileChannel() { } | ||
| 163 | |||
| 164 | /** | ||
| 165 | * Opens or creates a file, returning a file channel to access the file. | ||
| 166 | * | ||
| 167 | * <p> The {@code options} parameter determines how the file is opened. | ||
| 168 | * The {@link StandardOpenOption#READ READ} and {@link StandardOpenOption#WRITE | ||
| 169 | * WRITE} options determine if the file should be opened for reading and/or | ||
| 170 | * writing. If neither option (or the {@link StandardOpenOption#APPEND APPEND} | ||
| 171 | * option) is contained in the array then the file is opened for reading. | ||
| 172 | * By default reading or writing commences at the beginning of the file. | ||
| 173 | * | ||
| 174 | * <p> In the addition to {@code READ} and {@code WRITE}, the following | ||
| 175 | * options may be present: | ||
| 176 | * | ||
| 177 | * <table border=1 cellpadding=5 summary=""> | ||
| 178 | * <tr> <th>Option</th> <th>Description</th> </tr> | ||
| 179 | * <tr> | ||
| 180 | * <td> {@link StandardOpenOption#APPEND APPEND} </td> | ||
| 181 | * <td> If this option is present then the file is opened for writing and | ||
| 182 | * each invocation of the channel's {@code write} method first advances | ||
| 183 | * the position to the end of the file and then writes the requested | ||
| 184 | * data. Whether the advancement of the position and the writing of the | ||
| 185 | * data are done in a single atomic operation is system-dependent and | ||
| 186 | * therefore unspecified. This option may not be used in conjunction | ||
| 187 | * with the {@code READ} or {@code TRUNCATE_EXISTING} options. </td> | ||
| 188 | * </tr> | ||
| 189 | * <tr> | ||
| 190 | * <td> {@link StandardOpenOption#TRUNCATE_EXISTING TRUNCATE_EXISTING} </td> | ||
| 191 | * <td> If this option is present then the existing file is truncated to | ||
| 192 | * a size of 0 bytes. This option is ignored when the file is opened only | ||
| 193 | * for reading. </td> | ||
| 194 | * </tr> | ||
| 195 | * <tr> | ||
| 196 | * <td> {@link StandardOpenOption#CREATE_NEW CREATE_NEW} </td> | ||
| 197 | * <td> If this option is present then a new file is created, failing if | ||
| 198 | * the file already exists. When creating a file the check for the | ||
| 199 | * existence of the file and the creation of the file if it does not exist | ||
| 200 | * is atomic with respect to other file system operations. This option is | ||
| 201 | * ignored when the file is opened only for reading. </td> | ||
| 202 | * </tr> | ||
| 203 | * <tr> | ||
| 204 | * <td > {@link StandardOpenOption#CREATE CREATE} </td> | ||
| 205 | * <td> If this option is present then an existing file is opened if it | ||
| 206 | * exists, otherwise a new file is created. When creating a file the check | ||
| 207 | * for the existence of the file and the creation of the file if it does | ||
| 208 | * not exist is atomic with respect to other file system operations. This | ||
| 209 | * option is ignored if the {@code CREATE_NEW} option is also present or | ||
| 210 | * the file is opened only for reading. </td> | ||
| 211 | * </tr> | ||
| 212 | * <tr> | ||
| 213 | * <td > {@link StandardOpenOption#DELETE_ON_CLOSE DELETE_ON_CLOSE} </td> | ||
| 214 | * <td> When this option is present then the implementation makes a | ||
| 215 | * <em>best effort</em> attempt to delete the file when closed by the | ||
| 216 | * the {@link #close close} method. If the {@code close} method is not | ||
| 217 | * invoked then a <em>best effort</em> attempt is made to delete the file | ||
| 218 | * when the Java virtual machine terminates. </td> | ||
| 219 | * </tr> | ||
| 220 | * <tr> | ||
| 221 | * <td>{@link StandardOpenOption#SPARSE SPARSE} </td> | ||
| 222 | * <td> When creating a new file this option is a <em>hint</em> that the | ||
| 223 | * new file will be sparse. This option is ignored when not creating | ||
| 224 | * a new file. </td> | ||
| 225 | * </tr> | ||
| 226 | * <tr> | ||
| 227 | * <td> {@link StandardOpenOption#SYNC SYNC} </td> | ||
| 228 | * <td> Requires that every update to the file's content or metadata be | ||
| 229 | * written synchronously to the underlying storage device. (see <a | ||
| 230 | * href="../file/package-summary.html#integrity"> Synchronized I/O file | ||
| 231 | * integrity</a>). </td> | ||
| 232 | * <tr> | ||
| 233 | * <tr> | ||
| 234 | * <td> {@link StandardOpenOption#DSYNC DSYNC} </td> | ||
| 235 | * <td> Requires that every update to the file's content be written | ||
| 236 | * synchronously to the underlying storage device. (see <a | ||
| 237 | * href="../file/package-summary.html#integrity"> Synchronized I/O file | ||
| 238 | * integrity</a>). </td> | ||
| 239 | * </tr> | ||
| 240 | * </table> | ||
| 241 | * | ||
| 242 | * <p> An implementation may also support additional options. | ||
| 243 | * | ||
| 244 | * <p> The {@code attrs} parameter is an optional array of file {@link | ||
| 245 | * FileAttribute file-attributes} to set atomically when creating the file. | ||
| 246 | * | ||
| 247 | * <p> The new channel is created by invoking the {@link | ||
| 248 | * FileSystemProvider#newFileChannel newFileChannel} method on the | ||
| 249 | * provider that created the {@code Path}. | ||
| 250 | * | ||
| 251 | * @param path | ||
| 252 | * The path of the file to open or create | ||
| 253 | * @param options | ||
| 254 | * Options specifying how the file is opened | ||
| 255 | * @param attrs | ||
| 256 | * An optional list of file attributes to set atomically when | ||
| 257 | * creating the file | ||
| 258 | * | ||
| 259 | * @return A new file channel | ||
| 260 | * | ||
| 261 | * @throws IllegalArgumentException | ||
| 262 | * If the set contains an invalid combination of options | ||
| 263 | * @throws UnsupportedOperationException | ||
| 264 | * If the {@code path} is associated with a provider that does not | ||
| 265 | * support creating file channels, or an unsupported open option is | ||
| 266 | * specified, or the array contains an attribute that cannot be set | ||
| 267 | * atomically when creating the file | ||
| 268 | * @throws IOException | ||
| 269 | * If an I/O error occurs | ||
| 270 | * @throws SecurityException | ||
| 271 | * If a security manager is installed and it denies an | ||
| 272 | * unspecified permission required by the implementation. | ||
| 273 | * In the case of the default provider, the {@link | ||
| 274 | * SecurityManager#checkRead(String)} method is invoked to check | ||
| 275 | * read access if the file is opened for reading. The {@link | ||
| 276 | * SecurityManager#checkWrite(String)} method is invoked to check | ||
| 277 | * write access if the file is opened for writing | ||
| 278 | * | ||
| 279 | * @since 1.7 | ||
| 280 | */ | ||
| 281 | public static FileChannel open(Path path, | ||
| 282 | Set<? extends OpenOption> options, | ||
| 283 | FileAttribute<?>... attrs) | ||
| 284 | throws IOException | ||
| 285 | { | ||
| 286 | FileSystemProvider provider = path.getFileSystem().provider(); | ||
| 287 | return provider.newFileChannel(path, options, attrs); | ||
| 288 | } | ||
| 289 | |||
| 290 | private static final FileAttribute<?>[] NO_ATTRIBUTES = new FileAttribute[0]; | ||
| 291 | |||
| 292 | /** | ||
| 293 | * Opens or creates a file, returning a file channel to access the file. | ||
| 294 | * | ||
| 295 | * <p> An invocation of this method behaves in exactly the same way as the | ||
| 296 | * invocation | ||
| 297 | * <pre> | ||
| 298 | * fc.{@link #open(Path,Set,FileAttribute[]) open}(file, opts, new FileAttribute<?>[0]); | ||
| 299 | * </pre> | ||
| 300 | * where {@code opts} is a set of the options specified in the {@code | ||
| 301 | * options} array. | ||
| 302 | * | ||
| 303 | * @param path | ||
| 304 | * The path of the file to open or create | ||
| 305 | * @param options | ||
| 306 | * Options specifying how the file is opened | ||
| 307 | * | ||
| 308 | * @return A new file channel | ||
| 309 | * | ||
| 310 | * @throws IllegalArgumentException | ||
| 311 | * If the set contains an invalid combination of options | ||
| 312 | * @throws UnsupportedOperationException | ||
| 313 | * If the {@code path} is associated with a provider that does not | ||
| 314 | * support creating file channels, or an unsupported open option is | ||
| 315 | * specified | ||
| 316 | * @throws IOException | ||
| 317 | * If an I/O error occurs | ||
| 318 | * @throws SecurityException | ||
| 319 | * If a security manager is installed and it denies an | ||
| 320 | * unspecified permission required by the implementation. | ||
| 321 | * In the case of the default provider, the {@link | ||
| 322 | * SecurityManager#checkRead(String)} method is invoked to check | ||
| 323 | * read access if the file is opened for reading. The {@link | ||
| 324 | * SecurityManager#checkWrite(String)} method is invoked to check | ||
| 325 | * write access if the file is opened for writing | ||
| 326 | * | ||
| 327 | * @since 1.7 | ||
| 328 | */ | ||
| 329 | public static FileChannel open(Path path, OpenOption... options) | ||
| 330 | throws IOException | ||
| 331 | { | ||
| 332 | Set<OpenOption> set = new HashSet<OpenOption>(options.length); | ||
| 333 | Collections.addAll(set, options); | ||
| 334 | return open(path, set, NO_ATTRIBUTES); | ||
| 335 | } | ||
| 336 | |||
| 337 | // -- Channel operations -- | ||
| 338 | |||
| 339 | /** | ||
| 340 | * Reads a sequence of bytes from this channel into the given buffer. | ||
| 341 | * | ||
| 342 | * <p> Bytes are read starting at this channel's current file position, and | ||
| 343 | * then the file position is updated with the number of bytes actually | ||
| 344 | * read. Otherwise this method behaves exactly as specified in the {@link | ||
| 345 | * ReadableByteChannel} interface. </p> | ||
| 346 | */ | ||
| 347 | public abstract int read(ByteBuffer dst) throws IOException; | ||
| 348 | |||
| 349 | /** | ||
| 350 | * Reads a sequence of bytes from this channel into a subsequence of the | ||
| 351 | * given buffers. | ||
| 352 | * | ||
| 353 | * <p> Bytes are read starting at this channel's current file position, and | ||
| 354 | * then the file position is updated with the number of bytes actually | ||
| 355 | * read. Otherwise this method behaves exactly as specified in the {@link | ||
| 356 | * ScatteringByteChannel} interface. </p> | ||
| 357 | */ | ||
| 358 | public abstract long read(ByteBuffer[] dsts, int offset, int length) | ||
| 359 | throws IOException; | ||
| 360 | |||
| 361 | /** | ||
| 362 | * Reads a sequence of bytes from this channel into the given buffers. | ||
| 363 | * | ||
| 364 | * <p> Bytes are read starting at this channel's current file position, and | ||
| 365 | * then the file position is updated with the number of bytes actually | ||
| 366 | * read. Otherwise this method behaves exactly as specified in the {@link | ||
| 367 | * ScatteringByteChannel} interface. </p> | ||
| 368 | */ | ||
| 369 | public final long read(ByteBuffer[] dsts) throws IOException { | ||
| 370 | return read(dsts, 0, dsts.length); | ||
| 371 | } | ||
| 372 | |||
| 373 | /** | ||
| 374 | * Writes a sequence of bytes to this channel from the given buffer. | ||
| 375 | * | ||
| 376 | * <p> Bytes are written starting at this channel's current file position | ||
| 377 | * unless the channel is in append mode, in which case the position is | ||
| 378 | * first advanced to the end of the file. The file is grown, if necessary, | ||
| 379 | * to accommodate the written bytes, and then the file position is updated | ||
| 380 | * with the number of bytes actually written. Otherwise this method | ||
| 381 | * behaves exactly as specified by the {@link WritableByteChannel} | ||
| 382 | * interface. </p> | ||
| 383 | */ | ||
| 384 | public abstract int write(ByteBuffer src) throws IOException; | ||
| 385 | |||
| 386 | /** | ||
| 387 | * Writes a sequence of bytes to this channel from a subsequence of the | ||
| 388 | * given buffers. | ||
| 389 | * | ||
| 390 | * <p> Bytes are written starting at this channel's current file position | ||
| 391 | * unless the channel is in append mode, in which case the position is | ||
| 392 | * first advanced to the end of the file. The file is grown, if necessary, | ||
| 393 | * to accommodate the written bytes, and then the file position is updated | ||
| 394 | * with the number of bytes actually written. Otherwise this method | ||
| 395 | * behaves exactly as specified in the {@link GatheringByteChannel} | ||
| 396 | * interface. </p> | ||
| 397 | */ | ||
| 398 | public abstract long write(ByteBuffer[] srcs, int offset, int length) | ||
| 399 | throws IOException; | ||
| 400 | |||
| 401 | /** | ||
| 402 | * Writes a sequence of bytes to this channel from the given buffers. | ||
| 403 | * | ||
| 404 | * <p> Bytes are written starting at this channel's current file position | ||
| 405 | * unless the channel is in append mode, in which case the position is | ||
| 406 | * first advanced to the end of the file. The file is grown, if necessary, | ||
| 407 | * to accommodate the written bytes, and then the file position is updated | ||
| 408 | * with the number of bytes actually written. Otherwise this method | ||
| 409 | * behaves exactly as specified in the {@link GatheringByteChannel} | ||
| 410 | * interface. </p> | ||
| 411 | */ | ||
| 412 | public final long write(ByteBuffer[] srcs) throws IOException { | ||
| 413 | return write(srcs, 0, srcs.length); | ||
| 414 | } | ||
| 415 | |||
| 416 | |||
| 417 | // -- Other operations -- | ||
| 418 | |||
| 419 | /** | ||
| 420 | * Returns this channel's file position. </p> | ||
| 421 | * | ||
| 422 | * @return This channel's file position, | ||
| 423 | * a non-negative integer counting the number of bytes | ||
| 424 | * from the beginning of the file to the current position | ||
| 425 | * | ||
| 426 | * @throws ClosedChannelException | ||
| 427 | * If this channel is closed | ||
| 428 | * | ||
| 429 | * @throws IOException | ||
| 430 | * If some other I/O error occurs | ||
| 431 | */ | ||
| 432 | public abstract long position() throws IOException; | ||
| 433 | |||
| 434 | /** | ||
| 435 | * Sets this channel's file position. | ||
| 436 | * | ||
| 437 | * <p> Setting the position to a value that is greater than the file's | ||
| 438 | * current size is legal but does not change the size of the file. A later | ||
| 439 | * attempt to read bytes at such a position will immediately return an | ||
| 440 | * end-of-file indication. A later attempt to write bytes at such a | ||
| 441 | * position will cause the file to be grown to accommodate the new bytes; | ||
| 442 | * the values of any bytes between the previous end-of-file and the | ||
| 443 | * newly-written bytes are unspecified. </p> | ||
| 444 | * | ||
| 445 | * @param newPosition | ||
| 446 | * The new position, a non-negative integer counting | ||
| 447 | * the number of bytes from the beginning of the file | ||
| 448 | * | ||
| 449 | * @return This file channel | ||
| 450 | * | ||
| 451 | * @throws ClosedChannelException | ||
| 452 | * If this channel is closed | ||
| 453 | * | ||
| 454 | * @throws IllegalArgumentException | ||
| 455 | * If the new position is negative | ||
| 456 | * | ||
| 457 | * @throws IOException | ||
| 458 | * If some other I/O error occurs | ||
| 459 | */ | ||
| 460 | public abstract FileChannel position(long newPosition) throws IOException; | ||
| 461 | |||
| 462 | /** | ||
| 463 | * Returns the current size of this channel's file. </p> | ||
| 464 | * | ||
| 465 | * @return The current size of this channel's file, | ||
| 466 | * measured in bytes | ||
| 467 | * | ||
| 468 | * @throws ClosedChannelException | ||
| 469 | * If this channel is closed | ||
| 470 | * | ||
| 471 | * @throws IOException | ||
| 472 | * If some other I/O error occurs | ||
| 473 | */ | ||
| 474 | public abstract long size() throws IOException; | ||
| 475 | |||
| 476 | /** | ||
| 477 | * Truncates this channel's file to the given size. | ||
| 478 | * | ||
| 479 | * <p> If the given size is less than the file's current size then the file | ||
| 480 | * is truncated, discarding any bytes beyond the new end of the file. If | ||
| 481 | * the given size is greater than or equal to the file's current size then | ||
| 482 | * the file is not modified. In either case, if this channel's file | ||
| 483 | * position is greater than the given size then it is set to that size. | ||
| 484 | * </p> | ||
| 485 | * | ||
| 486 | * @param size | ||
| 487 | * The new size, a non-negative byte count | ||
| 488 | * | ||
| 489 | * @return This file channel | ||
| 490 | * | ||
| 491 | * @throws NonWritableChannelException | ||
| 492 | * If this channel was not opened for writing | ||
| 493 | * | ||
| 494 | * @throws ClosedChannelException | ||
| 495 | * If this channel is closed | ||
| 496 | * | ||
| 497 | * @throws IllegalArgumentException | ||
| 498 | * If the new size is negative | ||
| 499 | * | ||
| 500 | * @throws IOException | ||
| 501 | * If some other I/O error occurs | ||
| 502 | */ | ||
| 503 | public abstract FileChannel truncate(long size) throws IOException; | ||
| 504 | |||
| 505 | /** | ||
| 506 | * Forces any updates to this channel's file to be written to the storage | ||
| 507 | * device that contains it. | ||
| 508 | * | ||
| 509 | * <p> If this channel's file resides on a local storage device then when | ||
| 510 | * this method returns it is guaranteed that all changes made to the file | ||
| 511 | * since this channel was created, or since this method was last invoked, | ||
| 512 | * will have been written to that device. This is useful for ensuring that | ||
| 513 | * critical information is not lost in the event of a system crash. | ||
| 514 | * | ||
| 515 | * <p> If the file does not reside on a local device then no such guarantee | ||
| 516 | * is made. | ||
| 517 | * | ||
| 518 | * <p> The <tt>metaData</tt> parameter can be used to limit the number of | ||
| 519 | * I/O operations that this method is required to perform. Passing | ||
| 520 | * <tt>false</tt> for this parameter indicates that only updates to the | ||
| 521 | * file's content need be written to storage; passing <tt>true</tt> | ||
| 522 | * indicates that updates to both the file's content and metadata must be | ||
| 523 | * written, which generally requires at least one more I/O operation. | ||
| 524 | * Whether this parameter actually has any effect is dependent upon the | ||
| 525 | * underlying operating system and is therefore unspecified. | ||
| 526 | * | ||
| 527 | * <p> Invoking this method may cause an I/O operation to occur even if the | ||
| 528 | * channel was only opened for reading. Some operating systems, for | ||
| 529 | * example, maintain a last-access time as part of a file's metadata, and | ||
| 530 | * this time is updated whenever the file is read. Whether or not this is | ||
| 531 | * actually done is system-dependent and is therefore unspecified. | ||
| 532 | * | ||
| 533 | * <p> This method is only guaranteed to force changes that were made to | ||
| 534 | * this channel's file via the methods defined in this class. It may or | ||
| 535 | * may not force changes that were made by modifying the content of a | ||
| 536 | * {@link MappedByteBuffer <i>mapped byte buffer</i>} obtained by | ||
| 537 | * invoking the {@link #map map} method. Invoking the {@link | ||
| 538 | * MappedByteBuffer#force force} method of the mapped byte buffer will | ||
| 539 | * force changes made to the buffer's content to be written. </p> | ||
| 540 | * | ||
| 541 | * @param metaData | ||
| 542 | * If <tt>true</tt> then this method is required to force changes | ||
| 543 | * to both the file's content and metadata to be written to | ||
| 544 | * storage; otherwise, it need only force content changes to be | ||
| 545 | * written | ||
| 546 | * | ||
| 547 | * @throws ClosedChannelException | ||
| 548 | * If this channel is closed | ||
| 549 | * | ||
| 550 | * @throws IOException | ||
| 551 | * If some other I/O error occurs | ||
| 552 | */ | ||
| 553 | public abstract void force(boolean metaData) throws IOException; | ||
| 554 | |||
| 555 | /** | ||
| 556 | * Transfers bytes from this channel's file to the given writable byte | ||
| 557 | * channel. | ||
| 558 | * | ||
| 559 | * <p> An attempt is made to read up to <tt>count</tt> bytes starting at | ||
| 560 | * the given <tt>position</tt> in this channel's file and write them to the | ||
| 561 | * target channel. An invocation of this method may or may not transfer | ||
| 562 | * all of the requested bytes; whether or not it does so depends upon the | ||
| 563 | * natures and states of the channels. Fewer than the requested number of | ||
| 564 | * bytes are transferred if this channel's file contains fewer than | ||
| 565 | * <tt>count</tt> bytes starting at the given <tt>position</tt>, or if the | ||
| 566 | * target channel is non-blocking and it has fewer than <tt>count</tt> | ||
| 567 | * bytes free in its output buffer. | ||
| 568 | * | ||
| 569 | * <p> This method does not modify this channel's position. If the given | ||
| 570 | * position is greater than the file's current size then no bytes are | ||
| 571 | * transferred. If the target channel has a position then bytes are | ||
| 572 | * written starting at that position and then the position is incremented | ||
| 573 | * by the number of bytes written. | ||
| 574 | * | ||
| 575 | * <p> This method is potentially much more efficient than a simple loop | ||
| 576 | * that reads from this channel and writes to the target channel. Many | ||
| 577 | * operating systems can transfer bytes directly from the filesystem cache | ||
| 578 | * to the target channel without actually copying them. </p> | ||
| 579 | * | ||
| 580 | * @param position | ||
| 581 | * The position within the file at which the transfer is to begin; | ||
| 582 | * must be non-negative | ||
| 583 | * | ||
| 584 | * @param count | ||
| 585 | * The maximum number of bytes to be transferred; must be | ||
| 586 | * non-negative | ||
| 587 | * | ||
| 588 | * @param target | ||
| 589 | * The target channel | ||
| 590 | * | ||
| 591 | * @return The number of bytes, possibly zero, | ||
| 592 | * that were actually transferred | ||
| 593 | * | ||
| 594 | * @throws IllegalArgumentException | ||
| 595 | * If the preconditions on the parameters do not hold | ||
| 596 | * | ||
| 597 | * @throws NonReadableChannelException | ||
| 598 | * If this channel was not opened for reading | ||
| 599 | * | ||
| 600 | * @throws NonWritableChannelException | ||
| 601 | * If the target channel was not opened for writing | ||
| 602 | * | ||
| 603 | * @throws ClosedChannelException | ||
| 604 | * If either this channel or the target channel is closed | ||
| 605 | * | ||
| 606 | * @throws AsynchronousCloseException | ||
| 607 | * If another thread closes either channel | ||
| 608 | * while the transfer is in progress | ||
| 609 | * | ||
| 610 | * @throws ClosedByInterruptException | ||
| 611 | * If another thread interrupts the current thread while the | ||
| 612 | * transfer is in progress, thereby closing both channels and | ||
| 613 | * setting the current thread's interrupt status | ||
| 614 | * | ||
| 615 | * @throws IOException | ||
| 616 | * If some other I/O error occurs | ||
| 617 | */ | ||
| 618 | public abstract long transferTo(long position, long count, | ||
| 619 | WritableByteChannel target) | ||
| 620 | throws IOException; | ||
| 621 | |||
| 622 | /** | ||
| 623 | * Transfers bytes into this channel's file from the given readable byte | ||
| 624 | * channel. | ||
| 625 | * | ||
| 626 | * <p> An attempt is made to read up to <tt>count</tt> bytes from the | ||
| 627 | * source channel and write them to this channel's file starting at the | ||
| 628 | * given <tt>position</tt>. An invocation of this method may or may not | ||
| 629 | * transfer all of the requested bytes; whether or not it does so depends | ||
| 630 | * upon the natures and states of the channels. Fewer than the requested | ||
| 631 | * number of bytes will be transferred if the source channel has fewer than | ||
| 632 | * <tt>count</tt> bytes remaining, or if the source channel is non-blocking | ||
| 633 | * and has fewer than <tt>count</tt> bytes immediately available in its | ||
| 634 | * input buffer. | ||
| 635 | * | ||
| 636 | * <p> This method does not modify this channel's position. If the given | ||
| 637 | * position is greater than the file's current size then no bytes are | ||
| 638 | * transferred. If the source channel has a position then bytes are read | ||
| 639 | * starting at that position and then the position is incremented by the | ||
| 640 | * number of bytes read. | ||
| 641 | * | ||
| 642 | * <p> This method is potentially much more efficient than a simple loop | ||
| 643 | * that reads from the source channel and writes to this channel. Many | ||
| 644 | * operating systems can transfer bytes directly from the source channel | ||
| 645 | * into the filesystem cache without actually copying them. </p> | ||
| 646 | * | ||
| 647 | * @param src | ||
| 648 | * The source channel | ||
| 649 | * | ||
| 650 | * @param position | ||
| 651 | * The position within the file at which the transfer is to begin; | ||
| 652 | * must be non-negative | ||
| 653 | * | ||
| 654 | * @param count | ||
| 655 | * The maximum number of bytes to be transferred; must be | ||
| 656 | * non-negative | ||
| 657 | * | ||
| 658 | * @return The number of bytes, possibly zero, | ||
| 659 | * that were actually transferred | ||
| 660 | * | ||
| 661 | * @throws IllegalArgumentException | ||
| 662 | * If the preconditions on the parameters do not hold | ||
| 663 | * | ||
| 664 | * @throws NonReadableChannelException | ||
| 665 | * If the source channel was not opened for reading | ||
| 666 | * | ||
| 667 | * @throws NonWritableChannelException | ||
| 668 | * If this channel was not opened for writing | ||
| 669 | * | ||
| 670 | * @throws ClosedChannelException | ||
| 671 | * If either this channel or the source channel is closed | ||
| 672 | * | ||
| 673 | * @throws AsynchronousCloseException | ||
| 674 | * If another thread closes either channel | ||
| 675 | * while the transfer is in progress | ||
| 676 | * | ||
| 677 | * @throws ClosedByInterruptException | ||
| 678 | * If another thread interrupts the current thread while the | ||
| 679 | * transfer is in progress, thereby closing both channels and | ||
| 680 | * setting the current thread's interrupt status | ||
| 681 | * | ||
| 682 | * @throws IOException | ||
| 683 | * If some other I/O error occurs | ||
| 684 | */ | ||
| 685 | public abstract long transferFrom(ReadableByteChannel src, | ||
| 686 | long position, long count) | ||
| 687 | throws IOException; | ||
| 688 | |||
| 689 | /** | ||
| 690 | * Reads a sequence of bytes from this channel into the given buffer, | ||
| 691 | * starting at the given file position. | ||
| 692 | * | ||
| 693 | * <p> This method works in the same manner as the {@link | ||
| 694 | * #read(ByteBuffer)} method, except that bytes are read starting at the | ||
| 695 | * given file position rather than at the channel's current position. This | ||
| 696 | * method does not modify this channel's position. If the given position | ||
| 697 | * is greater than the file's current size then no bytes are read. </p> | ||
| 698 | * | ||
| 699 | * @param dst | ||
| 700 | * The buffer into which bytes are to be transferred | ||
| 701 | * | ||
| 702 | * @param position | ||
| 703 | * The file position at which the transfer is to begin; | ||
| 704 | * must be non-negative | ||
| 705 | * | ||
| 706 | * @return The number of bytes read, possibly zero, or <tt>-1</tt> if the | ||
| 707 | * given position is greater than or equal to the file's current | ||
| 708 | * size | ||
| 709 | * | ||
| 710 | * @throws IllegalArgumentException | ||
| 711 | * If the position is negative | ||
| 712 | * | ||
| 713 | * @throws NonReadableChannelException | ||
| 714 | * If this channel was not opened for reading | ||
| 715 | * | ||
| 716 | * @throws ClosedChannelException | ||
| 717 | * If this channel is closed | ||
| 718 | * | ||
| 719 | * @throws AsynchronousCloseException | ||
| 720 | * If another thread closes this channel | ||
| 721 | * while the read operation is in progress | ||
| 722 | * | ||
| 723 | * @throws ClosedByInterruptException | ||
| 724 | * If another thread interrupts the current thread | ||
| 725 | * while the read operation is in progress, thereby | ||
| 726 | * closing the channel and setting the current thread's | ||
| 727 | * interrupt status | ||
| 728 | * | ||
| 729 | * @throws IOException | ||
| 730 | * If some other I/O error occurs | ||
| 731 | */ | ||
| 732 | public abstract int read(ByteBuffer dst, long position) throws IOException; | ||
| 733 | |||
| 734 | /** | ||
| 735 | * Writes a sequence of bytes to this channel from the given buffer, | ||
| 736 | * starting at the given file position. | ||
| 737 | * | ||
| 738 | * <p> This method works in the same manner as the {@link | ||
| 739 | * #write(ByteBuffer)} method, except that bytes are written starting at | ||
| 740 | * the given file position rather than at the channel's current position. | ||
| 741 | * This method does not modify this channel's position. If the given | ||
| 742 | * position is greater than the file's current size then the file will be | ||
| 743 | * grown to accommodate the new bytes; the values of any bytes between the | ||
| 744 | * previous end-of-file and the newly-written bytes are unspecified. </p> | ||
| 745 | * | ||
| 746 | * @param src | ||
| 747 | * The buffer from which bytes are to be transferred | ||
| 748 | * | ||
| 749 | * @param position | ||
| 750 | * The file position at which the transfer is to begin; | ||
| 751 | * must be non-negative | ||
| 752 | * | ||
| 753 | * @return The number of bytes written, possibly zero | ||
| 754 | * | ||
| 755 | * @throws IllegalArgumentException | ||
| 756 | * If the position is negative | ||
| 757 | * | ||
| 758 | * @throws NonWritableChannelException | ||
| 759 | * If this channel was not opened for writing | ||
| 760 | * | ||
| 761 | * @throws ClosedChannelException | ||
| 762 | * If this channel is closed | ||
| 763 | * | ||
| 764 | * @throws AsynchronousCloseException | ||
| 765 | * If another thread closes this channel | ||
| 766 | * while the write operation is in progress | ||
| 767 | * | ||
| 768 | * @throws ClosedByInterruptException | ||
| 769 | * If another thread interrupts the current thread | ||
| 770 | * while the write operation is in progress, thereby | ||
| 771 | * closing the channel and setting the current thread's | ||
| 772 | * interrupt status | ||
| 773 | * | ||
| 774 | * @throws IOException | ||
| 775 | * If some other I/O error occurs | ||
| 776 | */ | ||
| 777 | public abstract int write(ByteBuffer src, long position) throws IOException; | ||
| 778 | |||
| 779 | |||
| 780 | // -- Memory-mapped buffers -- | ||
| 781 | |||
| 782 | /** | ||
| 783 | * A typesafe enumeration for file-mapping modes. | ||
| 784 | * | ||
| 785 | * @since 1.4 | ||
| 786 | * | ||
| 787 | * @see java.nio.channels.FileChannel#map | ||
| 788 | */ | ||
| 789 | public static class MapMode { | ||
| 790 | |||
| 791 | /** | ||
| 792 | * Mode for a read-only mapping. | ||
| 793 | */ | ||
| 794 | public static final MapMode READ_ONLY | ||
| 795 | = new MapMode("READ_ONLY"); | ||
| 796 | |||
| 797 | /** | ||
| 798 | * Mode for a read/write mapping. | ||
| 799 | */ | ||
| 800 | public static final MapMode READ_WRITE | ||
| 801 | = new MapMode("READ_WRITE"); | ||
| 802 | |||
| 803 | /** | ||
| 804 | * Mode for a private (copy-on-write) mapping. | ||
| 805 | */ | ||
| 806 | public static final MapMode PRIVATE | ||
| 807 | = new MapMode("PRIVATE"); | ||
| 808 | |||
| 809 | private final String name; | ||
| 810 | |||
| 811 | private MapMode(String name) { | ||
| 812 | this.name = name; | ||
| 813 | } | ||
| 814 | |||
| 815 | /** | ||
| 816 | * Returns a string describing this file-mapping mode. | ||
| 817 | * | ||
| 818 | * @return A descriptive string | ||
| 819 | */ | ||
| 820 | public String toString() { | ||
| 821 | return name; | ||
| 822 | } | ||
| 823 | |||
| 824 | } | ||
| 825 | |||
| 826 | /** | ||
| 827 | * Maps a region of this channel's file directly into memory. | ||
| 828 | * | ||
| 829 | * <p> A region of a file may be mapped into memory in one of three modes: | ||
| 830 | * </p> | ||
| 831 | * | ||
| 832 | * <ul type=disc> | ||
| 833 | * | ||
| 834 | * <li><p> <i>Read-only:</i> Any attempt to modify the resulting buffer | ||
| 835 | * will cause a {@link java.nio.ReadOnlyBufferException} to be thrown. | ||
| 836 | * ({@link MapMode#READ_ONLY MapMode.READ_ONLY}) </p></li> | ||
| 837 | * | ||
| 838 | * <li><p> <i>Read/write:</i> Changes made to the resulting buffer will | ||
| 839 | * eventually be propagated to the file; they may or may not be made | ||
| 840 | * visible to other programs that have mapped the same file. ({@link | ||
| 841 | * MapMode#READ_WRITE MapMode.READ_WRITE}) </p></li> | ||
| 842 | * | ||
| 843 | * <li><p> <i>Private:</i> Changes made to the resulting buffer will not | ||
| 844 | * be propagated to the file and will not be visible to other programs | ||
| 845 | * that have mapped the same file; instead, they will cause private | ||
| 846 | * copies of the modified portions of the buffer to be created. ({@link | ||
| 847 | * MapMode#PRIVATE MapMode.PRIVATE}) </p></li> | ||
| 848 | * | ||
| 849 | * </ul> | ||
| 850 | * | ||
| 851 | * <p> For a read-only mapping, this channel must have been opened for | ||
| 852 | * reading; for a read/write or private mapping, this channel must have | ||
| 853 | * been opened for both reading and writing. | ||
| 854 | * | ||
| 855 | * <p> The {@link MappedByteBuffer <i>mapped byte buffer</i>} | ||
| 856 | * returned by this method will have a position of zero and a limit and | ||
| 857 | * capacity of <tt>size</tt>; its mark will be undefined. The buffer and | ||
| 858 | * the mapping that it represents will remain valid until the buffer itself | ||
| 859 | * is garbage-collected. | ||
| 860 | * | ||
| 861 | * <p> A mapping, once established, is not dependent upon the file channel | ||
| 862 | * that was used to create it. Closing the channel, in particular, has no | ||
| 863 | * effect upon the validity of the mapping. | ||
| 864 | * | ||
| 865 | * <p> Many of the details of memory-mapped files are inherently dependent | ||
| 866 | * upon the underlying operating system and are therefore unspecified. The | ||
| 867 | * behavior of this method when the requested region is not completely | ||
| 868 | * contained within this channel's file is unspecified. Whether changes | ||
| 869 | * made to the content or size of the underlying file, by this program or | ||
| 870 | * another, are propagated to the buffer is unspecified. The rate at which | ||
| 871 | * changes to the buffer are propagated to the file is unspecified. | ||
| 872 | * | ||
| 873 | * <p> For most operating systems, mapping a file into memory is more | ||
| 874 | * expensive than reading or writing a few tens of kilobytes of data via | ||
| 875 | * the usual {@link #read read} and {@link #write write} methods. From the | ||
| 876 | * standpoint of performance it is generally only worth mapping relatively | ||
| 877 | * large files into memory. </p> | ||
| 878 | * | ||
| 879 | * @param mode | ||
| 880 | * One of the constants {@link MapMode#READ_ONLY READ_ONLY}, {@link | ||
| 881 | * MapMode#READ_WRITE READ_WRITE}, or {@link MapMode#PRIVATE | ||
| 882 | * PRIVATE} defined in the {@link MapMode} class, according to | ||
| 883 | * whether the file is to be mapped read-only, read/write, or | ||
| 884 | * privately (copy-on-write), respectively | ||
| 885 | * | ||
| 886 | * @param position | ||
| 887 | * The position within the file at which the mapped region | ||
| 888 | * is to start; must be non-negative | ||
| 889 | * | ||
| 890 | * @param size | ||
| 891 | * The size of the region to be mapped; must be non-negative and | ||
| 892 | * no greater than {@link java.lang.Integer#MAX_VALUE} | ||
| 893 | * | ||
| 894 | * @return The mapped byte buffer | ||
| 895 | * | ||
| 896 | * @throws NonReadableChannelException | ||
| 897 | * If the <tt>mode</tt> is {@link MapMode#READ_ONLY READ_ONLY} but | ||
| 898 | * this channel was not opened for reading | ||
| 899 | * | ||
| 900 | * @throws NonWritableChannelException | ||
| 901 | * If the <tt>mode</tt> is {@link MapMode#READ_WRITE READ_WRITE} or | ||
| 902 | * {@link MapMode#PRIVATE PRIVATE} but this channel was not opened | ||
| 903 | * for both reading and writing | ||
| 904 | * | ||
| 905 | * @throws IllegalArgumentException | ||
| 906 | * If the preconditions on the parameters do not hold | ||
| 907 | * | ||
| 908 | * @throws IOException | ||
| 909 | * If some other I/O error occurs | ||
| 910 | * | ||
| 911 | * @see java.nio.channels.FileChannel.MapMode | ||
| 912 | * @see java.nio.MappedByteBuffer | ||
| 913 | */ | ||
| 914 | public abstract MappedByteBuffer map(MapMode mode, | ||
| 915 | long position, long size) | ||
| 916 | throws IOException; | ||
| 917 | |||
| 918 | |||
| 919 | // -- Locks -- | ||
| 920 | |||
| 921 | /** | ||
| 922 | * Acquires a lock on the given region of this channel's file. | ||
| 923 | * | ||
| 924 | * <p> An invocation of this method will block until the region can be | ||
| 925 | * locked, this channel is closed, or the invoking thread is interrupted, | ||
| 926 | * whichever comes first. | ||
| 927 | * | ||
| 928 | * <p> If this channel is closed by another thread during an invocation of | ||
| 929 | * this method then an {@link AsynchronousCloseException} will be thrown. | ||
| 930 | * | ||
| 931 | * <p> If the invoking thread is interrupted while waiting to acquire the | ||
| 932 | * lock then its interrupt status will be set and a {@link | ||
| 933 | * FileLockInterruptionException} will be thrown. If the invoker's | ||
| 934 | * interrupt status is set when this method is invoked then that exception | ||
| 935 | * will be thrown immediately; the thread's interrupt status will not be | ||
| 936 | * changed. | ||
| 937 | * | ||
| 938 | * <p> The region specified by the <tt>position</tt> and <tt>size</tt> | ||
| 939 | * parameters need not be contained within, or even overlap, the actual | ||
| 940 | * underlying file. Lock regions are fixed in size; if a locked region | ||
| 941 | * initially contains the end of the file and the file grows beyond the | ||
| 942 | * region then the new portion of the file will not be covered by the lock. | ||
| 943 | * If a file is expected to grow in size and a lock on the entire file is | ||
| 944 | * required then a region starting at zero, and no smaller than the | ||
| 945 | * expected maximum size of the file, should be locked. The zero-argument | ||
| 946 | * {@link #lock()} method simply locks a region of size {@link | ||
| 947 | * Long#MAX_VALUE}. | ||
| 948 | * | ||
| 949 | * <p> Some operating systems do not support shared locks, in which case a | ||
| 950 | * request for a shared lock is automatically converted into a request for | ||
| 951 | * an exclusive lock. Whether the newly-acquired lock is shared or | ||
| 952 | * exclusive may be tested by invoking the resulting lock object's {@link | ||
| 953 | * FileLock#isShared() isShared} method. | ||
| 954 | * | ||
| 955 | * <p> File locks are held on behalf of the entire Java virtual machine. | ||
| 956 | * They are not suitable for controlling access to a file by multiple | ||
| 957 | * threads within the same virtual machine. </p> | ||
| 958 | * | ||
| 959 | * @param position | ||
| 960 | * The position at which the locked region is to start; must be | ||
| 961 | * non-negative | ||
| 962 | * | ||
| 963 | * @param size | ||
| 964 | * The size of the locked region; must be non-negative, and the sum | ||
| 965 | * <tt>position</tt> + <tt>size</tt> must be non-negative | ||
| 966 | * | ||
| 967 | * @param shared | ||
| 968 | * <tt>true</tt> to request a shared lock, in which case this | ||
| 969 | * channel must be open for reading (and possibly writing); | ||
| 970 | * <tt>false</tt> to request an exclusive lock, in which case this | ||
| 971 | * channel must be open for writing (and possibly reading) | ||
| 972 | * | ||
| 973 | * @return A lock object representing the newly-acquired lock | ||
| 974 | * | ||
| 975 | * @throws IllegalArgumentException | ||
| 976 | * If the preconditions on the parameters do not hold | ||
| 977 | * | ||
| 978 | * @throws ClosedChannelException | ||
| 979 | * If this channel is closed | ||
| 980 | * | ||
| 981 | * @throws AsynchronousCloseException | ||
| 982 | * If another thread closes this channel while the invoking | ||
| 983 | * thread is blocked in this method | ||
| 984 | * | ||
| 985 | * @throws FileLockInterruptionException | ||
| 986 | * If the invoking thread is interrupted while blocked in this | ||
| 987 | * method | ||
| 988 | * | ||
| 989 | * @throws OverlappingFileLockException | ||
| 990 | * If a lock that overlaps the requested region is already held by | ||
| 991 | * this Java virtual machine, or if another thread is already | ||
| 992 | * blocked in this method and is attempting to lock an overlapping | ||
| 993 | * region | ||
| 994 | * | ||
| 995 | * @throws NonReadableChannelException | ||
| 996 | * If <tt>shared</tt> is <tt>true</tt> this channel was not | ||
| 997 | * opened for reading | ||
| 998 | * | ||
| 999 | * @throws NonWritableChannelException | ||
| 1000 | * If <tt>shared</tt> is <tt>false</tt> but this channel was not | ||
| 1001 | * opened for writing | ||
| 1002 | * | ||
| 1003 | * @throws IOException | ||
| 1004 | * If some other I/O error occurs | ||
| 1005 | * | ||
| 1006 | * @see #lock() | ||
| 1007 | * @see #tryLock() | ||
| 1008 | * @see #tryLock(long,long,boolean) | ||
| 1009 | */ | ||
| 1010 | public abstract FileLock lock(long position, long size, boolean shared) | ||
| 1011 | throws IOException; | ||
| 1012 | |||
| 1013 | /** | ||
| 1014 | * Acquires an exclusive lock on this channel's file. | ||
| 1015 | * | ||
| 1016 | * <p> An invocation of this method of the form <tt>fc.lock()</tt> behaves | ||
| 1017 | * in exactly the same way as the invocation | ||
| 1018 | * | ||
| 1019 | * <pre> | ||
| 1020 | * fc.{@link #lock(long,long,boolean) lock}(0L, Long.MAX_VALUE, false) </pre> | ||
| 1021 | * | ||
| 1022 | * @return A lock object representing the newly-acquired lock | ||
| 1023 | * | ||
| 1024 | * @throws ClosedChannelException | ||
| 1025 | * If this channel is closed | ||
| 1026 | * | ||
| 1027 | * @throws AsynchronousCloseException | ||
| 1028 | * If another thread closes this channel while the invoking | ||
| 1029 | * thread is blocked in this method | ||
| 1030 | * | ||
| 1031 | * @throws FileLockInterruptionException | ||
| 1032 | * If the invoking thread is interrupted while blocked in this | ||
| 1033 | * method | ||
| 1034 | * | ||
| 1035 | * @throws OverlappingFileLockException | ||
| 1036 | * If a lock that overlaps the requested region is already held by | ||
| 1037 | * this Java virtual machine, or if another thread is already | ||
| 1038 | * blocked in this method and is attempting to lock an overlapping | ||
| 1039 | * region of the same file | ||
| 1040 | * | ||
| 1041 | * @throws NonWritableChannelException | ||
| 1042 | * If this channel was not opened for writing | ||
| 1043 | * | ||
| 1044 | * @throws IOException | ||
| 1045 | * If some other I/O error occurs | ||
| 1046 | * | ||
| 1047 | * @see #lock(long,long,boolean) | ||
| 1048 | * @see #tryLock() | ||
| 1049 | * @see #tryLock(long,long,boolean) | ||
| 1050 | */ | ||
| 1051 | public final FileLock lock() throws IOException { | ||
| 1052 | return lock(0L, Long.MAX_VALUE, false); | ||
| 1053 | } | ||
| 1054 | |||
| 1055 | /** | ||
| 1056 | * Attempts to acquire a lock on the given region of this channel's file. | ||
| 1057 | * | ||
| 1058 | * <p> This method does not block. An invocation always returns | ||
| 1059 | * immediately, either having acquired a lock on the requested region or | ||
| 1060 | * having failed to do so. If it fails to acquire a lock because an | ||
| 1061 | * overlapping lock is held by another program then it returns | ||
| 1062 | * <tt>null</tt>. If it fails to acquire a lock for any other reason then | ||
| 1063 | * an appropriate exception is thrown. | ||
| 1064 | * | ||
| 1065 | * <p> The region specified by the <tt>position</tt> and <tt>size</tt> | ||
| 1066 | * parameters need not be contained within, or even overlap, the actual | ||
| 1067 | * underlying file. Lock regions are fixed in size; if a locked region | ||
| 1068 | * initially contains the end of the file and the file grows beyond the | ||
| 1069 | * region then the new portion of the file will not be covered by the lock. | ||
| 1070 | * If a file is expected to grow in size and a lock on the entire file is | ||
| 1071 | * required then a region starting at zero, and no smaller than the | ||
| 1072 | * expected maximum size of the file, should be locked. The zero-argument | ||
| 1073 | * {@link #tryLock()} method simply locks a region of size {@link | ||
| 1074 | * Long#MAX_VALUE}. | ||
| 1075 | * | ||
| 1076 | * <p> Some operating systems do not support shared locks, in which case a | ||
| 1077 | * request for a shared lock is automatically converted into a request for | ||
| 1078 | * an exclusive lock. Whether the newly-acquired lock is shared or | ||
| 1079 | * exclusive may be tested by invoking the resulting lock object's {@link | ||
| 1080 | * FileLock#isShared() isShared} method. | ||
| 1081 | * | ||
| 1082 | * <p> File locks are held on behalf of the entire Java virtual machine. | ||
| 1083 | * They are not suitable for controlling access to a file by multiple | ||
| 1084 | * threads within the same virtual machine. </p> | ||
| 1085 | * | ||
| 1086 | * @param position | ||
| 1087 | * The position at which the locked region is to start; must be | ||
| 1088 | * non-negative | ||
| 1089 | * | ||
| 1090 | * @param size | ||
| 1091 | * The size of the locked region; must be non-negative, and the sum | ||
| 1092 | * <tt>position</tt> + <tt>size</tt> must be non-negative | ||
| 1093 | * | ||
| 1094 | * @param shared | ||
| 1095 | * <tt>true</tt> to request a shared lock, | ||
| 1096 | * <tt>false</tt> to request an exclusive lock | ||
| 1097 | * | ||
| 1098 | * @return A lock object representing the newly-acquired lock, | ||
| 1099 | * or <tt>null</tt> if the lock could not be acquired | ||
| 1100 | * because another program holds an overlapping lock | ||
| 1101 | * | ||
| 1102 | * @throws IllegalArgumentException | ||
| 1103 | * If the preconditions on the parameters do not hold | ||
| 1104 | * | ||
| 1105 | * @throws ClosedChannelException | ||
| 1106 | * If this channel is closed | ||
| 1107 | * | ||
| 1108 | * @throws OverlappingFileLockException | ||
| 1109 | * If a lock that overlaps the requested region is already held by | ||
| 1110 | * this Java virtual machine, or if another thread is already | ||
| 1111 | * blocked in this method and is attempting to lock an overlapping | ||
| 1112 | * region of the same file | ||
| 1113 | * | ||
| 1114 | * @throws IOException | ||
| 1115 | * If some other I/O error occurs | ||
| 1116 | * | ||
| 1117 | * @see #lock() | ||
| 1118 | * @see #lock(long,long,boolean) | ||
| 1119 | * @see #tryLock() | ||
| 1120 | */ | ||
| 1121 | public abstract FileLock tryLock(long position, long size, boolean shared) | ||
| 1122 | throws IOException; | ||
| 1123 | |||
| 1124 | /** | ||
| 1125 | * Attempts to acquire an exclusive lock on this channel's file. | ||
| 1126 | * | ||
| 1127 | * <p> An invocation of this method of the form <tt>fc.tryLock()</tt> | ||
| 1128 | * behaves in exactly the same way as the invocation | ||
| 1129 | * | ||
| 1130 | * <pre> | ||
| 1131 | * fc.{@link #tryLock(long,long,boolean) tryLock}(0L, Long.MAX_VALUE, false) </pre> | ||
| 1132 | * | ||
| 1133 | * @return A lock object representing the newly-acquired lock, | ||
| 1134 | * or <tt>null</tt> if the lock could not be acquired | ||
| 1135 | * because another program holds an overlapping lock | ||
| 1136 | * | ||
| 1137 | * @throws ClosedChannelException | ||
| 1138 | * If this channel is closed | ||
| 1139 | * | ||
| 1140 | * @throws OverlappingFileLockException | ||
| 1141 | * If a lock that overlaps the requested region is already held by | ||
| 1142 | * this Java virtual machine, or if another thread is already | ||
| 1143 | * blocked in this method and is attempting to lock an overlapping | ||
| 1144 | * region | ||
| 1145 | * | ||
| 1146 | * @throws IOException | ||
| 1147 | * If some other I/O error occurs | ||
| 1148 | * | ||
| 1149 | * @see #lock() | ||
| 1150 | * @see #lock(long,long,boolean) | ||
| 1151 | * @see #tryLock(long,long,boolean) | ||
| 1152 | */ | ||
| 1153 | public final FileLock tryLock() throws IOException { | ||
| 1154 | return tryLock(0L, Long.MAX_VALUE, false); | ||
| 1155 | } | ||
| 1156 | |||
| 1157 | } | ||