1 /*
2 * Copyright (c) 2000, 2013, 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
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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
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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 <i>truncated</i>}. 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 {@code read} or {@code write} 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 {@code getChannel} 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 {@code getChannel}
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 id="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 {@code "r"} and will be open for reading and writing
132 * if the instance was created with mode {@code "rw"}.
133 *
134 * <a id="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 {@code true} 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 class="altrows">
178 * <caption style="display:none">additional options</caption>
179 * <thead>
180 * <tr> <th>Option</th> <th>Description</th> </tr>
181 * </thead>
182 * <tbody>
183 * <tr>
184 * <td> {@link StandardOpenOption#APPEND APPEND} </td>
185 * <td> If this option is present then the file is opened for writing and
186 * each invocation of the channel's {@code write} method first advances
187 * the position to the end of the file and then writes the requested
188 * data. Whether the advancement of the position and the writing of the
189 * data are done in a single atomic operation is system-dependent and
190 * therefore unspecified. This option may not be used in conjunction
191 * with the {@code READ} or {@code TRUNCATE_EXISTING} options. </td>
192 * </tr>
193 * <tr>
194 * <td> {@link StandardOpenOption#TRUNCATE_EXISTING TRUNCATE_EXISTING} </td>
195 * <td> If this option is present then the existing file is truncated to
196 * a size of 0 bytes. This option is ignored when the file is opened only
197 * for reading. </td>
198 * </tr>
199 * <tr>
200 * <td> {@link StandardOpenOption#CREATE_NEW CREATE_NEW} </td>
201 * <td> If this option is present then a new file is created, failing if
202 * the file already exists. When creating a file the check for the
203 * existence of the file and the creation of the file if it does not exist
204 * is atomic with respect to other file system operations. This option is
205 * ignored when the file is opened only for reading. </td>
206 * </tr>
207 * <tr>
208 * <td > {@link StandardOpenOption#CREATE CREATE} </td>
209 * <td> If this option is present then an existing file is opened if it
210 * exists, otherwise a new file is created. When creating a file the check
211 * for the existence of the file and the creation of the file if it does
212 * not exist is atomic with respect to other file system operations. This
213 * option is ignored if the {@code CREATE_NEW} option is also present or
214 * the file is opened only for reading. </td>
215 * </tr>
216 * <tr>
217 * <td > {@link StandardOpenOption#DELETE_ON_CLOSE DELETE_ON_CLOSE} </td>
218 * <td> When this option is present then the implementation makes a
219 * <em>best effort</em> attempt to delete the file when closed by the
220 * the {@link #close close} method. If the {@code close} method is not
221 * invoked then a <em>best effort</em> attempt is made to delete the file
222 * when the Java virtual machine terminates. </td>
223 * </tr>
224 * <tr>
225 * <td>{@link StandardOpenOption#SPARSE SPARSE} </td>
226 * <td> When creating a new file this option is a <em>hint</em> that the
227 * new file will be sparse. This option is ignored when not creating
228 * a new file. </td>
229 * </tr>
230 * <tr>
231 * <td> {@link StandardOpenOption#SYNC SYNC} </td>
232 * <td> Requires that every update to the file's content or metadata be
233 * written synchronously to the underlying storage device. (see <a
234 * href="../file/package-summary.html#integrity"> Synchronized I/O file
235 * integrity</a>). </td>
236 * </tr>
237 * <tr>
238 * <td> {@link StandardOpenOption#DSYNC DSYNC} </td>
239 * <td> Requires that every update to the file's content be written
240 * synchronously to the underlying storage device. (see <a
241 * href="../file/package-summary.html#integrity"> Synchronized I/O file
242 * integrity</a>). </td>
243 * </tr>
244 * </tbody>
245 * </table>
246 *
247 * <p> An implementation may also support additional options.
248 *
249 * <p> The {@code attrs} parameter is an optional array of file {@link
250 * FileAttribute file-attributes} to set atomically when creating the file.
251 *
252 * <p> The new channel is created by invoking the {@link
253 * FileSystemProvider#newFileChannel newFileChannel} method on the
254 * provider that created the {@code Path}.
255 *
256 * @param path
257 * The path of the file to open or create
258 * @param options
259 * Options specifying how the file is opened
260 * @param attrs
261 * An optional list of file attributes to set atomically when
262 * creating the file
263 *
264 * @return A new file channel
265 *
266 * @throws IllegalArgumentException
267 * If the set contains an invalid combination of options
268 * @throws UnsupportedOperationException
269 * If the {@code path} is associated with a provider that does not
270 * support creating file channels, or an unsupported open option is
271 * specified, or the array contains an attribute that cannot be set
272 * atomically when creating the file
273 * @throws IOException
274 * If an I/O error occurs
275 * @throws SecurityException
276 * If a security manager is installed and it denies an
277 * unspecified permission required by the implementation.
278 * In the case of the default provider, the {@link
279 * SecurityManager#checkRead(String)} method is invoked to check
280 * read access if the file is opened for reading. The {@link
281 * SecurityManager#checkWrite(String)} method is invoked to check
282 * write access if the file is opened for writing
283 *
284 * @since 1.7
285 */
286 public static FileChannel open(Path path,
287 Set<? extends OpenOption> options,
288 FileAttribute<?>... attrs)
289 throws IOException
290 {
291 FileSystemProvider provider = path.getFileSystem().provider();
292 return provider.newFileChannel(path, options, attrs);
293 }
294
295 @SuppressWarnings({"unchecked", "rawtypes"}) // generic array construction
296 private static final FileAttribute<?>[] NO_ATTRIBUTES = new FileAttribute[0];
297
298 /**
299 * Opens or creates a file, returning a file channel to access the file.
300 *
301 * <p> An invocation of this method behaves in exactly the same way as the
302 * invocation
303 * <pre>
304 * fc.{@link #open(Path,Set,FileAttribute[]) open}(file, opts, new FileAttribute<?>[0]);
305 * </pre>
306 * where {@code opts} is a set of the options specified in the {@code
307 * options} array.
308 *
309 * @param path
310 * The path of the file to open or create
311 * @param options
312 * Options specifying how the file is opened
313 *
314 * @return A new file channel
315 *
316 * @throws IllegalArgumentException
317 * If the set contains an invalid combination of options
318 * @throws UnsupportedOperationException
319 * If the {@code path} is associated with a provider that does not
320 * support creating file channels, or an unsupported open option is
321 * specified
322 * @throws IOException
323 * If an I/O error occurs
324 * @throws SecurityException
325 * If a security manager is installed and it denies an
326 * unspecified permission required by the implementation.
327 * In the case of the default provider, the {@link
328 * SecurityManager#checkRead(String)} method is invoked to check
329 * read access if the file is opened for reading. The {@link
330 * SecurityManager#checkWrite(String)} method is invoked to check
331 * write access if the file is opened for writing
332 *
333 * @since 1.7
334 */
335 public static FileChannel open(Path path, OpenOption... options)
336 throws IOException
337 {
338 Set<OpenOption> set = new HashSet<>(options.length);
339 Collections.addAll(set, options);
340 return open(path, set, NO_ATTRIBUTES);
341 }
342
343 // -- Channel operations --
344
345 /**
346 * Reads a sequence of bytes from this channel into the given buffer.
347 *
348 * <p> Bytes are read starting at this channel's current file position, and
349 * then the file position is updated with the number of bytes actually
350 * read. Otherwise this method behaves exactly as specified in the {@link
351 * ReadableByteChannel} interface. </p>
352 */
353 public abstract int read(ByteBuffer dst) throws IOException;
354
355 /**
356 * Reads a sequence of bytes from this channel into a subsequence of the
357 * given buffers.
358 *
359 * <p> Bytes are read starting at this channel's current file position, and
360 * then the file position is updated with the number of bytes actually
361 * read. Otherwise this method behaves exactly as specified in the {@link
362 * ScatteringByteChannel} interface. </p>
363 */
364 public abstract long read(ByteBuffer[] dsts, int offset, int length)
365 throws IOException;
366
367 /**
368 * Reads a sequence of bytes from this channel into the given buffers.
369 *
370 * <p> Bytes are read starting at this channel's current file position, and
371 * then the file position is updated with the number of bytes actually
372 * read. Otherwise this method behaves exactly as specified in the {@link
373 * ScatteringByteChannel} interface. </p>
374 */
375 public final long read(ByteBuffer[] dsts) throws IOException {
376 return read(dsts, 0, dsts.length);
377 }
378
379 /**
380 * Writes a sequence of bytes to this channel from the given buffer.
381 *
382 * <p> Bytes are written starting at this channel's current file position
383 * unless the channel is in append mode, in which case the position is
384 * first advanced to the end of the file. The file is grown, if necessary,
385 * to accommodate the written bytes, and then the file position is updated
386 * with the number of bytes actually written. Otherwise this method
387 * behaves exactly as specified by the {@link WritableByteChannel}
388 * interface. </p>
389 */
390 public abstract int write(ByteBuffer src) throws IOException;
391
392 /**
393 * Writes a sequence of bytes to this channel from a subsequence of the
394 * given buffers.
395 *
396 * <p> Bytes are written starting at this channel's current file position
397 * unless the channel is in append mode, in which case the position is
398 * first advanced to the end of the file. The file is grown, if necessary,
399 * to accommodate the written bytes, and then the file position is updated
400 * with the number of bytes actually written. Otherwise this method
401 * behaves exactly as specified in the {@link GatheringByteChannel}
402 * interface. </p>
403 */
404 public abstract long write(ByteBuffer[] srcs, int offset, int length)
405 throws IOException;
406
407 /**
408 * Writes a sequence of bytes to this channel from the given buffers.
409 *
410 * <p> Bytes are written starting at this channel's current file position
411 * unless the channel is in append mode, in which case the position is
412 * first advanced to the end of the file. The file is grown, if necessary,
413 * to accommodate the written bytes, and then the file position is updated
414 * with the number of bytes actually written. Otherwise this method
415 * behaves exactly as specified in the {@link GatheringByteChannel}
416 * interface. </p>
417 */
418 public final long write(ByteBuffer[] srcs) throws IOException {
419 return write(srcs, 0, srcs.length);
420 }
421
422
423 // -- Other operations --
424
425 /**
426 * Returns this channel's file position.
427 *
428 * @return This channel's file position,
429 * a non-negative integer counting the number of bytes
430 * from the beginning of the file to the current position
431 *
432 * @throws ClosedChannelException
433 * If this channel is closed
434 *
435 * @throws IOException
436 * If some other I/O error occurs
437 */
438 public abstract long position() throws IOException;
439
440 /**
441 * Sets this channel's file position.
442 *
443 * <p> Setting the position to a value that is greater than the file's
444 * current size is legal but does not change the size of the file. A later
445 * attempt to read bytes at such a position will immediately return an
446 * end-of-file indication. A later attempt to write bytes at such a
447 * position will cause the file to be grown to accommodate the new bytes;
448 * the values of any bytes between the previous end-of-file and the
449 * newly-written bytes are unspecified. </p>
450 *
451 * @param newPosition
452 * The new position, a non-negative integer counting
453 * the number of bytes from the beginning of the file
454 *
455 * @return This file channel
456 *
457 * @throws ClosedChannelException
458 * If this channel is closed
459 *
460 * @throws IllegalArgumentException
461 * If the new position is negative
462 *
463 * @throws IOException
464 * If some other I/O error occurs
465 */
466 public abstract FileChannel position(long newPosition) throws IOException;
467
468 /**
469 * Returns the current size of this channel's file.
470 *
471 * @return The current size of this channel's file,
472 * measured in bytes
473 *
474 * @throws ClosedChannelException
475 * If this channel is closed
476 *
477 * @throws IOException
478 * If some other I/O error occurs
479 */
480 public abstract long size() throws IOException;
481
482 /**
483 * Truncates this channel's file to the given size.
484 *
485 * <p> If the given size is less than the file's current size then the file
486 * is truncated, discarding any bytes beyond the new end of the file. If
487 * the given size is greater than or equal to the file's current size then
488 * the file is not modified. In either case, if this channel's file
489 * position is greater than the given size then it is set to that size.
490 * </p>
491 *
492 * @param size
493 * The new size, a non-negative byte count
494 *
495 * @return This file channel
496 *
497 * @throws NonWritableChannelException
498 * If this channel was not opened for writing
499 *
500 * @throws ClosedChannelException
501 * If this channel is closed
502 *
503 * @throws IllegalArgumentException
504 * If the new size is negative
505 *
506 * @throws IOException
507 * If some other I/O error occurs
508 */
509 public abstract FileChannel truncate(long size) throws IOException;
510
511 /**
512 * Forces any updates to this channel's file to be written to the storage
513 * device that contains it.
514 *
515 * <p> If this channel's file resides on a local storage device then when
516 * this method returns it is guaranteed that all changes made to the file
517 * since this channel was created, or since this method was last invoked,
518 * will have been written to that device. This is useful for ensuring that
519 * critical information is not lost in the event of a system crash.
520 *
521 * <p> If the file does not reside on a local device then no such guarantee
522 * is made.
523 *
524 * <p> The {@code metaData} parameter can be used to limit the number of
525 * I/O operations that this method is required to perform. Passing
526 * {@code false} for this parameter indicates that only updates to the
527 * file's content need be written to storage; passing {@code true}
528 * indicates that updates to both the file's content and metadata must be
529 * written, which generally requires at least one more I/O operation.
530 * Whether this parameter actually has any effect is dependent upon the
531 * underlying operating system and is therefore unspecified.
532 *
533 * <p> Invoking this method may cause an I/O operation to occur even if the
534 * channel was only opened for reading. Some operating systems, for
535 * example, maintain a last-access time as part of a file's metadata, and
536 * this time is updated whenever the file is read. Whether or not this is
537 * actually done is system-dependent and is therefore unspecified.
538 *
539 * <p> This method is only guaranteed to force changes that were made to
540 * this channel's file via the methods defined in this class. It may or
541 * may not force changes that were made by modifying the content of a
542 * {@link MappedByteBuffer <i>mapped byte buffer</i>} obtained by
543 * invoking the {@link #map map} method. Invoking the {@link
544 * MappedByteBuffer#force force} method of the mapped byte buffer will
545 * force changes made to the buffer's content to be written. </p>
546 *
547 * @param metaData
548 * If {@code true} then this method is required to force changes
549 * to both the file's content and metadata to be written to
550 * storage; otherwise, it need only force content changes to be
551 * written
552 *
553 * @throws ClosedChannelException
554 * If this channel is closed
555 *
556 * @throws IOException
557 * If some other I/O error occurs
558 */
559 public abstract void force(boolean metaData) throws IOException;
560
561 /**
562 * Transfers bytes from this channel's file to the given writable byte
563 * channel.
564 *
565 * <p> An attempt is made to read up to {@code count} bytes starting at
566 * the given {@code position} in this channel's file and write them to the
567 * target channel. An invocation of this method may or may not transfer
568 * all of the requested bytes; whether or not it does so depends upon the
569 * natures and states of the channels. Fewer than the requested number of
570 * bytes are transferred if this channel's file contains fewer than
571 * {@code count} bytes starting at the given {@code position}, or if the
572 * target channel is non-blocking and it has fewer than {@code count}
573 * bytes free in its output buffer.
574 *
575 * <p> This method does not modify this channel's position. If the given
576 * position is greater than the file's current size then no bytes are
577 * transferred. If the target channel has a position then bytes are
578 * written starting at that position and then the position is incremented
579 * by the number of bytes written.
580 *
581 * <p> This method is potentially much more efficient than a simple loop
582 * that reads from this channel and writes to the target channel. Many
583 * operating systems can transfer bytes directly from the filesystem cache
584 * to the target channel without actually copying them. </p>
585 *
586 * @param position
587 * The position within the file at which the transfer is to begin;
588 * must be non-negative
589 *
590 * @param count
591 * The maximum number of bytes to be transferred; must be
592 * non-negative
593 *
594 * @param target
595 * The target channel
596 *
597 * @return The number of bytes, possibly zero,
598 * that were actually transferred
599 *
600 * @throws IllegalArgumentException
601 * If the preconditions on the parameters do not hold
602 *
603 * @throws NonReadableChannelException
604 * If this channel was not opened for reading
605 *
606 * @throws NonWritableChannelException
607 * If the target channel was not opened for writing
608 *
609 * @throws ClosedChannelException
610 * If either this channel or the target channel is closed
611 *
612 * @throws AsynchronousCloseException
613 * If another thread closes either channel
614 * while the transfer is in progress
615 *
616 * @throws ClosedByInterruptException
617 * If another thread interrupts the current thread while the
618 * transfer is in progress, thereby closing both channels and
619 * setting the current thread's interrupt status
620 *
621 * @throws IOException
622 * If some other I/O error occurs
623 */
624 public abstract long transferTo(long position, long count,
625 WritableByteChannel target)
626 throws IOException;
627
628 /**
629 * Transfers bytes into this channel's file from the given readable byte
630 * channel.
631 *
632 * <p> An attempt is made to read up to {@code count} bytes from the
633 * source channel and write them to this channel's file starting at the
634 * given {@code position}. An invocation of this method may or may not
635 * transfer all of the requested bytes; whether or not it does so depends
636 * upon the natures and states of the channels. Fewer than the requested
637 * number of bytes will be transferred if the source channel has fewer than
638 * {@code count} bytes remaining, or if the source channel is non-blocking
639 * and has fewer than {@code count} bytes immediately available in its
640 * input buffer.
641 *
642 * <p> This method does not modify this channel's position. If the given
643 * position is greater than the file's current size then no bytes are
644 * transferred. If the source channel has a position then bytes are read
645 * starting at that position and then the position is incremented by the
646 * number of bytes read.
647 *
648 * <p> This method is potentially much more efficient than a simple loop
649 * that reads from the source channel and writes to this channel. Many
650 * operating systems can transfer bytes directly from the source channel
651 * into the filesystem cache without actually copying them. </p>
652 *
653 * @param src
654 * The source channel
655 *
656 * @param position
657 * The position within the file at which the transfer is to begin;
658 * must be non-negative
659 *
660 * @param count
661 * The maximum number of bytes to be transferred; must be
662 * non-negative
663 *
664 * @return The number of bytes, possibly zero,
665 * that were actually transferred
666 *
667 * @throws IllegalArgumentException
668 * If the preconditions on the parameters do not hold
669 *
670 * @throws NonReadableChannelException
671 * If the source channel was not opened for reading
672 *
673 * @throws NonWritableChannelException
674 * If this channel was not opened for writing
675 *
676 * @throws ClosedChannelException
677 * If either this channel or the source channel is closed
678 *
679 * @throws AsynchronousCloseException
680 * If another thread closes either channel
681 * while the transfer is in progress
682 *
683 * @throws ClosedByInterruptException
684 * If another thread interrupts the current thread while the
685 * transfer is in progress, thereby closing both channels and
686 * setting the current thread's interrupt status
687 *
688 * @throws IOException
689 * If some other I/O error occurs
690 */
691 public abstract long transferFrom(ReadableByteChannel src,
692 long position, long count)
693 throws IOException;
694
695 /**
696 * Reads a sequence of bytes from this channel into the given buffer,
697 * starting at the given file position.
698 *
699 * <p> This method works in the same manner as the {@link
700 * #read(ByteBuffer)} method, except that bytes are read starting at the
701 * given file position rather than at the channel's current position. This
702 * method does not modify this channel's position. If the given position
703 * is greater than the file's current size then no bytes are read. </p>
704 *
705 * @param dst
706 * The buffer into which bytes are to be transferred
707 *
708 * @param position
709 * The file position at which the transfer is to begin;
710 * must be non-negative
711 *
712 * @return The number of bytes read, possibly zero, or {@code -1} if the
713 * given position is greater than or equal to the file's current
714 * size
715 *
716 * @throws IllegalArgumentException
717 * If the position is negative
718 *
719 * @throws NonReadableChannelException
720 * If this channel was not opened for reading
721 *
722 * @throws ClosedChannelException
723 * If this channel is closed
724 *
725 * @throws AsynchronousCloseException
726 * If another thread closes this channel
727 * while the read operation is in progress
728 *
729 * @throws ClosedByInterruptException
730 * If another thread interrupts the current thread
731 * while the read operation is in progress, thereby
732 * closing the channel and setting the current thread's
733 * interrupt status
734 *
735 * @throws IOException
736 * If some other I/O error occurs
737 */
738 public abstract int read(ByteBuffer dst, long position) throws IOException;
739
740 /**
741 * Writes a sequence of bytes to this channel from the given buffer,
742 * starting at the given file position.
743 *
744 * <p> This method works in the same manner as the {@link
745 * #write(ByteBuffer)} method, except that bytes are written starting at
746 * the given file position rather than at the channel's current position.
747 * This method does not modify this channel's position. If the given
748 * position is greater than the file's current size then the file will be
749 * grown to accommodate the new bytes; the values of any bytes between the
750 * previous end-of-file and the newly-written bytes are unspecified. </p>
751 *
752 * @param src
753 * The buffer from which bytes are to be transferred
754 *
755 * @param position
756 * The file position at which the transfer is to begin;
757 * must be non-negative
758 *
759 * @return The number of bytes written, possibly zero
760 *
761 * @throws IllegalArgumentException
762 * If the position is negative
763 *
764 * @throws NonWritableChannelException
765 * If this channel was not opened for writing
766 *
767 * @throws ClosedChannelException
768 * If this channel is closed
769 *
770 * @throws AsynchronousCloseException
771 * If another thread closes this channel
772 * while the write operation is in progress
773 *
774 * @throws ClosedByInterruptException
775 * If another thread interrupts the current thread
776 * while the write operation is in progress, thereby
777 * closing the channel and setting the current thread's
778 * interrupt status
779 *
780 * @throws IOException
781 * If some other I/O error occurs
782 */
783 public abstract int write(ByteBuffer src, long position) throws IOException;
784
785
786 // -- Memory-mapped buffers --
787
788 /**
789 * A typesafe enumeration for file-mapping modes.
790 *
791 * @since 1.4
792 *
793 * @see java.nio.channels.FileChannel#map
794 */
795 public static class MapMode {
796
797 /**
798 * Mode for a read-only mapping.
799 */
800 public static final MapMode READ_ONLY
801 = new MapMode("READ_ONLY");
802
803 /**
804 * Mode for a read/write mapping.
805 */
806 public static final MapMode READ_WRITE
807 = new MapMode("READ_WRITE");
808
809 /**
810 * Mode for a private (copy-on-write) mapping.
811 */
812 public static final MapMode PRIVATE
813 = new MapMode("PRIVATE");
814
815 private final String name;
816
817 private MapMode(String name) {
818 this.name = name;
819 }
820
821 /**
822 * Returns a string describing this file-mapping mode.
823 *
824 * @return A descriptive string
825 */
826 public String toString() {
827 return name;
828 }
829
830 }
831
832 /**
833 * Maps a region of this channel's file directly into memory.
834 *
835 * <p> A region of a file may be mapped into memory in one of three modes:
836 * </p>
837 *
838 * <ul>
839 *
840 * <li><p> <i>Read-only:</i> Any attempt to modify the resulting buffer
841 * will cause a {@link java.nio.ReadOnlyBufferException} to be thrown.
842 * ({@link MapMode#READ_ONLY MapMode.READ_ONLY}) </p></li>
843 *
844 * <li><p> <i>Read/write:</i> Changes made to the resulting buffer will
845 * eventually be propagated to the file; they may or may not be made
846 * visible to other programs that have mapped the same file. ({@link
847 * MapMode#READ_WRITE MapMode.READ_WRITE}) </p></li>
848 *
849 * <li><p> <i>Private:</i> Changes made to the resulting buffer will not
850 * be propagated to the file and will not be visible to other programs
851 * that have mapped the same file; instead, they will cause private
852 * copies of the modified portions of the buffer to be created. ({@link
853 * MapMode#PRIVATE MapMode.PRIVATE}) </p></li>
854 *
855 * </ul>
856 *
857 * <p> For a read-only mapping, this channel must have been opened for
858 * reading; for a read/write or private mapping, this channel must have
859 * been opened for both reading and writing.
860 *
861 * <p> The {@link MappedByteBuffer <i>mapped byte buffer</i>}
862 * returned by this method will have a position of zero and a limit and
863 * capacity of {@code size}; its mark will be undefined. The buffer and
864 * the mapping that it represents will remain valid until the buffer itself
865 * is garbage-collected.
866 *
867 * <p> A mapping, once established, is not dependent upon the file channel
868 * that was used to create it. Closing the channel, in particular, has no
869 * effect upon the validity of the mapping.
870 *
871 * <p> Many of the details of memory-mapped files are inherently dependent
872 * upon the underlying operating system and are therefore unspecified. The
873 * behavior of this method when the requested region is not completely
874 * contained within this channel's file is unspecified. Whether changes
875 * made to the content or size of the underlying file, by this program or
876 * another, are propagated to the buffer is unspecified. The rate at which
877 * changes to the buffer are propagated to the file is unspecified.
878 *
879 * <p> For most operating systems, mapping a file into memory is more
880 * expensive than reading or writing a few tens of kilobytes of data via
881 * the usual {@link #read read} and {@link #write write} methods. From the
882 * standpoint of performance it is generally only worth mapping relatively
883 * large files into memory. </p>
884 *
885 * @param mode
886 * One of the constants {@link MapMode#READ_ONLY READ_ONLY}, {@link
887 * MapMode#READ_WRITE READ_WRITE}, or {@link MapMode#PRIVATE
888 * PRIVATE} defined in the {@link MapMode} class, according to
889 * whether the file is to be mapped read-only, read/write, or
890 * privately (copy-on-write), respectively
891 *
892 * @param position
893 * The position within the file at which the mapped region
894 * is to start; must be non-negative
895 *
896 * @param size
897 * The size of the region to be mapped; must be non-negative and
898 * no greater than {@link java.lang.Integer#MAX_VALUE}
899 *
900 * @return The mapped byte buffer
901 *
902 * @throws NonReadableChannelException
903 * If the {@code mode} is {@link MapMode#READ_ONLY READ_ONLY} but
904 * this channel was not opened for reading
905 *
906 * @throws NonWritableChannelException
907 * If the {@code mode} is {@link MapMode#READ_WRITE READ_WRITE} or
908 * {@link MapMode#PRIVATE PRIVATE} but this channel was not opened
909 * for both reading and writing
910 *
911 * @throws IllegalArgumentException
912 * If the preconditions on the parameters do not hold
913 *
914 * @throws IOException
915 * If some other I/O error occurs
916 *
917 * @see java.nio.channels.FileChannel.MapMode
918 * @see java.nio.MappedByteBuffer
919 */
920 public abstract MappedByteBuffer map(MapMode mode,
921 long position, long size)
922 throws IOException;
923
924
925 // -- Locks --
926
927 /**
928 * Acquires a lock on the given region of this channel's file.
929 *
930 * <p> An invocation of this method will block until the region can be
931 * locked, this channel is closed, or the invoking thread is interrupted,
932 * whichever comes first.
933 *
934 * <p> If this channel is closed by another thread during an invocation of
935 * this method then an {@link AsynchronousCloseException} will be thrown.
936 *
937 * <p> If the invoking thread is interrupted while waiting to acquire the
938 * lock then its interrupt status will be set and a {@link
939 * FileLockInterruptionException} will be thrown. If the invoker's
940 * interrupt status is set when this method is invoked then that exception
941 * will be thrown immediately; the thread's interrupt status will not be
942 * changed.
943 *
944 * <p> The region specified by the {@code position} and {@code size}
945 * parameters need not be contained within, or even overlap, the actual
946 * underlying file. Lock regions are fixed in size; if a locked region
947 * initially contains the end of the file and the file grows beyond the
948 * region then the new portion of the file will not be covered by the lock.
949 * If a file is expected to grow in size and a lock on the entire file is
950 * required then a region starting at zero, and no smaller than the
951 * expected maximum size of the file, should be locked. The zero-argument
952 * {@link #lock()} method simply locks a region of size {@link
953 * Long#MAX_VALUE}.
954 *
955 * <p> Some operating systems do not support shared locks, in which case a
956 * request for a shared lock is automatically converted into a request for
957 * an exclusive lock. Whether the newly-acquired lock is shared or
958 * exclusive may be tested by invoking the resulting lock object's {@link
959 * FileLock#isShared() isShared} method.
960 *
961 * <p> File locks are held on behalf of the entire Java virtual machine.
962 * They are not suitable for controlling access to a file by multiple
963 * threads within the same virtual machine. </p>
964 *
965 * @param position
966 * The position at which the locked region is to start; must be
967 * non-negative
968 *
969 * @param size
970 * The size of the locked region; must be non-negative, and the sum
971 * {@code position} + {@code size} must be non-negative
972 *
973 * @param shared
974 * {@code true} to request a shared lock, in which case this
975 * channel must be open for reading (and possibly writing);
976 * {@code false} to request an exclusive lock, in which case this
977 * channel must be open for writing (and possibly reading)
978 *
979 * @return A lock object representing the newly-acquired lock
980 *
981 * @throws IllegalArgumentException
982 * If the preconditions on the parameters do not hold
983 *
984 * @throws ClosedChannelException
985 * If this channel is closed
986 *
987 * @throws AsynchronousCloseException
988 * If another thread closes this channel while the invoking
989 * thread is blocked in this method
990 *
991 * @throws FileLockInterruptionException
992 * If the invoking thread is interrupted while blocked in this
993 * method
994 *
995 * @throws OverlappingFileLockException
996 * If a lock that overlaps the requested region is already held by
997 * this Java virtual machine, or if another thread is already
998 * blocked in this method and is attempting to lock an overlapping
999 * region
1000 *
1001 * @throws NonReadableChannelException
1002 * If {@code shared} is {@code true} this channel was not
1003 * opened for reading
1004 *
1005 * @throws NonWritableChannelException
1006 * If {@code shared} is {@code false} but this channel was not
1007 * opened for writing
1008 *
1009 * @throws IOException
1010 * If some other I/O error occurs
1011 *
1012 * @see #lock()
1013 * @see #tryLock()
1014 * @see #tryLock(long,long,boolean)
1015 */
1016 public abstract FileLock lock(long position, long size, boolean shared)
1017 throws IOException;
1018
1019 /**
1020 * Acquires an exclusive lock on this channel's file.
1021 *
1022 * <p> An invocation of this method of the form {@code fc.lock()} behaves
1023 * in exactly the same way as the invocation
1024 *
1025 * <pre>
1026 * fc.{@link #lock(long,long,boolean) lock}(0L, Long.MAX_VALUE, false) </pre>
1027 *
1028 * @return A lock object representing the newly-acquired lock
1029 *
1030 * @throws ClosedChannelException
1031 * If this channel is closed
1032 *
1033 * @throws AsynchronousCloseException
1034 * If another thread closes this channel while the invoking
1035 * thread is blocked in this method
1036 *
1037 * @throws FileLockInterruptionException
1038 * If the invoking thread is interrupted while blocked in this
1039 * method
1040 *
1041 * @throws OverlappingFileLockException
1042 * If a lock that overlaps the requested region is already held by
1043 * this Java virtual machine, or if another thread is already
1044 * blocked in this method and is attempting to lock an overlapping
1045 * region of the same file
1046 *
1047 * @throws NonWritableChannelException
1048 * If this channel was not opened for writing
1049 *
1050 * @throws IOException
1051 * If some other I/O error occurs
1052 *
1053 * @see #lock(long,long,boolean)
1054 * @see #tryLock()
1055 * @see #tryLock(long,long,boolean)
1056 */
1057 public final FileLock lock() throws IOException {
1058 return lock(0L, Long.MAX_VALUE, false);
1059 }
1060
1061 /**
1062 * Attempts to acquire a lock on the given region of this channel's file.
1063 *
1064 * <p> This method does not block. An invocation always returns
1065 * immediately, either having acquired a lock on the requested region or
1066 * having failed to do so. If it fails to acquire a lock because an
1067 * overlapping lock is held by another program then it returns
1068 * {@code null}. If it fails to acquire a lock for any other reason then
1069 * an appropriate exception is thrown.
1070 *
1071 * <p> The region specified by the {@code position} and {@code size}
1072 * parameters need not be contained within, or even overlap, the actual
1073 * underlying file. Lock regions are fixed in size; if a locked region
1074 * initially contains the end of the file and the file grows beyond the
1075 * region then the new portion of the file will not be covered by the lock.
1076 * If a file is expected to grow in size and a lock on the entire file is
1077 * required then a region starting at zero, and no smaller than the
1078 * expected maximum size of the file, should be locked. The zero-argument
1079 * {@link #tryLock()} method simply locks a region of size {@link
1080 * Long#MAX_VALUE}.
1081 *
1082 * <p> Some operating systems do not support shared locks, in which case a
1083 * request for a shared lock is automatically converted into a request for
1084 * an exclusive lock. Whether the newly-acquired lock is shared or
1085 * exclusive may be tested by invoking the resulting lock object's {@link
1086 * FileLock#isShared() isShared} method.
1087 *
1088 * <p> File locks are held on behalf of the entire Java virtual machine.
1089 * They are not suitable for controlling access to a file by multiple
1090 * threads within the same virtual machine. </p>
1091 *
1092 * @param position
1093 * The position at which the locked region is to start; must be
1094 * non-negative
1095 *
1096 * @param size
1097 * The size of the locked region; must be non-negative, and the sum
1098 * {@code position} + {@code size} must be non-negative
1099 *
1100 * @param shared
1101 * {@code true} to request a shared lock,
1102 * {@code false} to request an exclusive lock
1103 *
1104 * @return A lock object representing the newly-acquired lock,
1105 * or {@code null} if the lock could not be acquired
1106 * because another program holds an overlapping lock
1107 *
1108 * @throws IllegalArgumentException
1109 * If the preconditions on the parameters do not hold
1110 *
1111 * @throws ClosedChannelException
1112 * If this channel is closed
1113 *
1114 * @throws OverlappingFileLockException
1115 * If a lock that overlaps the requested region is already held by
1116 * this Java virtual machine, or if another thread is already
1117 * blocked in this method and is attempting to lock an overlapping
1118 * region of the same file
1119 *
1120 * @throws IOException
1121 * If some other I/O error occurs
1122 *
1123 * @see #lock()
1124 * @see #lock(long,long,boolean)
1125 * @see #tryLock()
1126 */
1127 public abstract FileLock tryLock(long position, long size, boolean shared)
1128 throws IOException;
1129
1130 /**
1131 * Attempts to acquire an exclusive lock on this channel's file.
1132 *
1133 * <p> An invocation of this method of the form {@code fc.tryLock()}
1134 * behaves in exactly the same way as the invocation
1135 *
1136 * <pre>
1137 * fc.{@link #tryLock(long,long,boolean) tryLock}(0L, Long.MAX_VALUE, false) </pre>
1138 *
1139 * @return A lock object representing the newly-acquired lock,
1140 * or {@code null} if the lock could not be acquired
1141 * because another program holds an overlapping lock
1142 *
1143 * @throws ClosedChannelException
1144 * If this channel is closed
1145 *
1146 * @throws OverlappingFileLockException
1147 * If a lock that overlaps the requested region is already held by
1148 * this Java virtual machine, or if another thread is already
1149 * blocked in this method and is attempting to lock an overlapping
1150 * region
1151 *
1152 * @throws IOException
1153 * If some other I/O error occurs
1154 *
1155 * @see #lock()
1156 * @see #lock(long,long,boolean)
1157 * @see #tryLock(long,long,boolean)
1158 */
1159 public final FileLock tryLock() throws IOException {
1160 return tryLock(0L, Long.MAX_VALUE, false);
1161 }
1162
1163 }