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