1 /*
2 * Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
3 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
4 *
5 *
6 *
7 *
8 *
9 *
10 *
11 *
12 *
13 *
14 *
15 *
16 *
17 *
18 *
19 *
20 *
21 *
22 *
23 *
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 <tt>read</tt> or <tt>write</tt> methods.
67 * </p></li>
68 *
69 * <li><p> Updates made to a file may be {@link #force <i>forced
70 * out</i>} to the underlying storage device, ensuring that data are not
71 * lost in the event of a system crash. </p></li>
72 *
73 * <li><p> Bytes can be transferred from a file {@link #transferTo <i>to
74 * some other channel</i>}, and {@link #transferFrom <i>vice
75 * versa</i>}, in a way that can be optimized by many operating systems
76 * into a very fast transfer directly to or from the filesystem cache.
77 * </p></li>
78 *
79 * <li><p> A region of a file may be {@link FileLock <i>locked</i>}
80 * against access by other programs. </p></li>
81 *
82 * </ul>
83 *
84 * <p> File channels are safe for use by multiple concurrent threads. The
85 * {@link Channel#close close} method may be invoked at any time, as specified
86 * by the {@link Channel} interface. Only one operation that involves the
87 * channel's position or can change its file's size may be in progress at any
88 * given time; attempts to initiate a second such operation while the first is
89 * still in progress will block until the first operation completes. Other
90 * operations, in particular those that take an explicit position, may proceed
91 * concurrently; whether they in fact do so is dependent upon the underlying
92 * implementation and is therefore unspecified.
93 *
94 * <p> The view of a file provided by an instance of this class is guaranteed
95 * to be consistent with other views of the same file provided by other
96 * instances in the same program. The view provided by an instance of this
97 * class may or may not, however, be consistent with the views seen by other
98 * concurrently-running programs due to caching performed by the underlying
99 * operating system and delays induced by network-filesystem protocols. This
100 * is true regardless of the language in which these other programs are
101 * written, and whether they are running on the same machine or on some other
102 * machine. The exact nature of any such inconsistencies are system-dependent
103 * and are therefore unspecified.
104 *
105 * <p> A file channel is created by invoking one of the {@link #open open}
106 * methods defined by this class. A file channel can also be obtained from an
107 * existing {@link java.io.FileInputStream#getChannel FileInputStream}, {@link
108 * java.io.FileOutputStream#getChannel FileOutputStream}, or {@link
109 * java.io.RandomAccessFile#getChannel RandomAccessFile} object by invoking
110 * that object's <tt>getChannel</tt> method, which returns a file channel that
111 * is connected to the same underlying file. Where the file channel is obtained
112 * from an existing stream or random access file then the state of the file
113 * channel is intimately connected to that of the object whose <tt>getChannel</tt>
114 * method returned the channel. Changing the channel's position, whether
115 * explicitly or by reading or writing bytes, will change the file position of
116 * the originating object, and vice versa. Changing the file's length via the
117 * file channel will change the length seen via the originating object, and vice
118 * versa. Changing the file's content by writing bytes will change the content
119 * seen by the originating object, and vice versa.
120 *
121 * <a name="open-mode"></a> <p> At various points this class specifies that an
122 * instance that is "open for reading," "open for writing," or "open for
123 * reading and writing" is required. A channel obtained via the {@link
124 * java.io.FileInputStream#getChannel getChannel} method of a {@link
125 * java.io.FileInputStream} instance will be open for reading. A channel
126 * obtained via the {@link java.io.FileOutputStream#getChannel getChannel}
127 * method of a {@link java.io.FileOutputStream} instance will be open for
128 * writing. Finally, a channel obtained via the {@link
129 * java.io.RandomAccessFile#getChannel getChannel} method of a {@link
130 * java.io.RandomAccessFile} instance will be open for reading if the instance
131 * was created with mode <tt>"r"</tt> and will be open for reading and writing
132 * if the instance was created with mode <tt>"rw"</tt>.
133 *
134 * <a name="append-mode"></a><p> A file channel that is open for writing may be in
135 * <i>append mode</i>, for example if it was obtained from a file-output stream
136 * that was created by invoking the {@link
137 * java.io.FileOutputStream#FileOutputStream(java.io.File,boolean)
138 * FileOutputStream(File,boolean)} constructor and passing <tt>true</tt> for
139 * the second parameter. In this mode each invocation of a relative write
140 * operation first advances the position to the end of the file and then writes
141 * the requested data. Whether the advancement of the position and the writing
142 * of the data are done in a single atomic operation is system-dependent and
143 * therefore unspecified.
144 *
145 * @see java.io.FileInputStream#getChannel()
146 * @see java.io.FileOutputStream#getChannel()
147 * @see java.io.RandomAccessFile#getChannel()
148 *
149 * @author Mark Reinhold
150 * @author Mike McCloskey
151 * @author JSR-51 Expert Group
152 * @since 1.4
153 */
154
155 public abstract class FileChannel
156 extends AbstractInterruptibleChannel
157 implements SeekableByteChannel, GatheringByteChannel, ScatteringByteChannel
158 {
159 /**
160 * Initializes a new instance of this class.
161 */
162 protected FileChannel() { }
163
164 /**
165 * Opens or creates a file, returning a file channel to access the file.
166 *
167 * <p> The {@code options} parameter determines how the file is opened.
168 * The {@link StandardOpenOption#READ READ} and {@link StandardOpenOption#WRITE
169 * WRITE} options determine if the file should be opened for reading and/or
170 * writing. If neither option (or the {@link StandardOpenOption#APPEND APPEND}
171 * option) is contained in the array then the file is opened for reading.
172 * By default reading or writing commences at the beginning of the file.
173 *
174 * <p> In the addition to {@code READ} and {@code WRITE}, the following
175 * options may be present:
176 *
177 * <table border=1 cellpadding=5 summary="">
178 * <tr> <th>Option</th> <th>Description</th> </tr>
179 * <tr>
180 * <td> {@link StandardOpenOption#APPEND APPEND} </td>
181 * <td> If this option is present then the file is opened for writing and
182 * each invocation of the channel's {@code write} method first advances
183 * the position to the end of the file and then writes the requested
184 * data. Whether the advancement of the position and the writing of the
185 * data are done in a single atomic operation is system-dependent and
186 * therefore unspecified. This option may not be used in conjunction
187 * with the {@code READ} or {@code TRUNCATE_EXISTING} options. </td>
188 * </tr>
189 * <tr>
190 * <td> {@link StandardOpenOption#TRUNCATE_EXISTING TRUNCATE_EXISTING} </td>
191 * <td> If this option is present then the existing file is truncated to
192 * a size of 0 bytes. This option is ignored when the file is opened only
193 * for reading. </td>
194 * </tr>
195 * <tr>
196 * <td> {@link StandardOpenOption#CREATE_NEW CREATE_NEW} </td>
197 * <td> If this option is present then a new file is created, failing if
198 * the file already exists. When creating a file the check for the
199 * existence of the file and the creation of the file if it does not exist
200 * is atomic with respect to other file system operations. This option is
201 * ignored when the file is opened only for reading. </td>
202 * </tr>
203 * <tr>
204 * <td > {@link StandardOpenOption#CREATE CREATE} </td>
205 * <td> If this option is present then an existing file is opened if it
206 * exists, otherwise a new file is created. When creating a file the check
207 * for the existence of the file and the creation of the file if it does
208 * not exist is atomic with respect to other file system operations. This
209 * option is ignored if the {@code CREATE_NEW} option is also present or
210 * the file is opened only for reading. </td>
211 * </tr>
212 * <tr>
213 * <td > {@link StandardOpenOption#DELETE_ON_CLOSE DELETE_ON_CLOSE} </td>
214 * <td> When this option is present then the implementation makes a
215 * <em>best effort</em> attempt to delete the file when closed by the
216 * the {@link #close close} method. If the {@code close} method is not
217 * invoked then a <em>best effort</em> attempt is made to delete the file
218 * when the Java virtual machine terminates. </td>
219 * </tr>
220 * <tr>
221 * <td>{@link StandardOpenOption#SPARSE SPARSE} </td>
222 * <td> When creating a new file this option is a <em>hint</em> that the
223 * new file will be sparse. This option is ignored when not creating
224 * a new file. </td>
225 * </tr>
226 * <tr>
227 * <td> {@link StandardOpenOption#SYNC SYNC} </td>
228 * <td> Requires that every update to the file's content or metadata be
229 * written synchronously to the underlying storage device. (see <a
230 * href="../file/package-summary.html#integrity"> Synchronized I/O file
231 * integrity</a>). </td>
232 * </tr>
233 * <tr>
234 * <td> {@link StandardOpenOption#DSYNC DSYNC} </td>
235 * <td> Requires that every update to the file's content be written
236 * synchronously to the underlying storage device. (see <a
237 * href="../file/package-summary.html#integrity"> Synchronized I/O file
238 * integrity</a>). </td>
239 * </tr>
240 * </table>
241 *
242 * <p> An implementation may also support additional options.
243 *
244 * <p> The {@code attrs} parameter is an optional array of file {@link
245 * FileAttribute file-attributes} to set atomically when creating the file.
246 *
247 * <p> The new channel is created by invoking the {@link
248 * FileSystemProvider#newFileChannel newFileChannel} method on the
249 * provider that created the {@code Path}.
250 *
251 * @param path
252 * The path of the file to open or create
253 * @param options
254 * Options specifying how the file is opened
255 * @param attrs
256 * An optional list of file attributes to set atomically when
257 * creating the file
258 *
259 * @return A new file channel
260 *
261 * @throws IllegalArgumentException
262 * If the set contains an invalid combination of options
263 * @throws UnsupportedOperationException
264 * If the {@code path} is associated with a provider that does not
265 * support creating file channels, or an unsupported open option is
266 * specified, or the array contains an attribute that cannot be set
267 * atomically when creating the file
268 * @throws IOException
269 * If an I/O error occurs
270 * @throws SecurityException
271 * If a security manager is installed and it denies an
272 * unspecified permission required by the implementation.
273 * In the case of the default provider, the {@link
274 * SecurityManager#checkRead(String)} method is invoked to check
275 * read access if the file is opened for reading. The {@link
276 * SecurityManager#checkWrite(String)} method is invoked to check
277 * write access if the file is opened for writing
278 *
279 * @since 1.7
280 */
281 public static FileChannel open(Path path,
282 Set<? extends OpenOption> options,
283 FileAttribute<?>... attrs)
284 throws IOException
285 {
286 FileSystemProvider provider = path.getFileSystem().provider();
287 return provider.newFileChannel(path, options, attrs);
288 }
289
290 @SuppressWarnings({"unchecked", "rawtypes"}) // generic array construction
291 private static final FileAttribute<?>[] NO_ATTRIBUTES = new FileAttribute[0];
292
293 /**
294 * Opens or creates a file, returning a file channel to access the file.
295 *
296 * <p> An invocation of this method behaves in exactly the same way as the
297 * invocation
298 * <pre>
299 * fc.{@link #open(Path,Set,FileAttribute[]) open}(file, opts, new FileAttribute<?>[0]);
300 * </pre>
301 * where {@code opts} is a set of the options specified in the {@code
302 * options} array.
303 *
304 * @param path
305 * The path of the file to open or create
306 * @param options
307 * Options specifying how the file is opened
308 *
309 * @return A new file channel
310 *
311 * @throws IllegalArgumentException
312 * If the set contains an invalid combination of options
313 * @throws UnsupportedOperationException
314 * If the {@code path} is associated with a provider that does not
315 * support creating file channels, or an unsupported open option is
316 * specified
317 * @throws IOException
318 * If an I/O error occurs
319 * @throws SecurityException
320 * If a security manager is installed and it denies an
321 * unspecified permission required by the implementation.
322 * In the case of the default provider, the {@link
323 * SecurityManager#checkRead(String)} method is invoked to check
324 * read access if the file is opened for reading. The {@link
325 * SecurityManager#checkWrite(String)} method is invoked to check
326 * write access if the file is opened for writing
327 *
328 * @since 1.7
329 */
330 public static FileChannel open(Path path, OpenOption... options)
331 throws IOException
332 {
333 Set<OpenOption> set = new HashSet<OpenOption>(options.length);
334 Collections.addAll(set, options);
335 return open(path, set, NO_ATTRIBUTES);
336 }
337
338 // -- Channel operations --
339
340 /**
341 * Reads a sequence of bytes from this channel into the given buffer.
342 *
343 * <p> Bytes are read starting at this channel's current file position, and
344 * then the file position is updated with the number of bytes actually
345 * read. Otherwise this method behaves exactly as specified in the {@link
346 * ReadableByteChannel} interface. </p>
347 */
348 public abstract int read(ByteBuffer dst) throws IOException;
349
350 /**
351 * Reads a sequence of bytes from this channel into a subsequence of the
352 * given buffers.
353 *
354 * <p> Bytes are read starting at this channel's current file position, and
355 * then the file position is updated with the number of bytes actually
356 * read. Otherwise this method behaves exactly as specified in the {@link
357 * ScatteringByteChannel} interface. </p>
358 */
359 public abstract long read(ByteBuffer[] dsts, int offset, int length)
360 throws IOException;
361
362 /**
363 * Reads a sequence of bytes from this channel into the given buffers.
364 *
365 * <p> Bytes are read starting at this channel's current file position, and
366 * then the file position is updated with the number of bytes actually
367 * read. Otherwise this method behaves exactly as specified in the {@link
368 * ScatteringByteChannel} interface. </p>
369 */
370 public final long read(ByteBuffer[] dsts) throws IOException {
371 return read(dsts, 0, dsts.length);
372 }
373
374 /**
375 * Writes a sequence of bytes to this channel from the given buffer.
376 *
377 * <p> Bytes are written starting at this channel's current file position
378 * unless the channel is in append mode, in which case the position is
379 * first advanced to the end of the file. The file is grown, if necessary,
380 * to accommodate the written bytes, and then the file position is updated
381 * with the number of bytes actually written. Otherwise this method
382 * behaves exactly as specified by the {@link WritableByteChannel}
383 * interface. </p>
384 */
385 public abstract int write(ByteBuffer src) throws IOException;
386
387 /**
388 * Writes a sequence of bytes to this channel from a subsequence of the
389 * given buffers.
390 *
391 * <p> Bytes are written starting at this channel's current file position
392 * unless the channel is in append mode, in which case the position is
393 * first advanced to the end of the file. The file is grown, if necessary,
394 * to accommodate the written bytes, and then the file position is updated
395 * with the number of bytes actually written. Otherwise this method
396 * behaves exactly as specified in the {@link GatheringByteChannel}
397 * interface. </p>
398 */
399 public abstract long write(ByteBuffer[] srcs, int offset, int length)
400 throws IOException;
401
402 /**
403 * Writes a sequence of bytes to this channel from the given buffers.
404 *
405 * <p> Bytes are written starting at this channel's current file position
406 * unless the channel is in append mode, in which case the position is
407 * first advanced to the end of the file. The file is grown, if necessary,
408 * to accommodate the written bytes, and then the file position is updated
409 * with the number of bytes actually written. Otherwise this method
410 * behaves exactly as specified in the {@link GatheringByteChannel}
411 * interface. </p>
412 */
413 public final long write(ByteBuffer[] srcs) throws IOException {
414 return write(srcs, 0, srcs.length);
415 }
416
417
418 // -- Other operations --
419
420 /**
421 * Returns this channel's file position.
422 *
423 * @return This channel's file position,
424 * a non-negative integer counting the number of bytes
425 * from the beginning of the file to the current position
426 *
427 * @throws ClosedChannelException
428 * If this channel is closed
429 *
430 * @throws IOException
431 * If some other I/O error occurs
432 */
433 public abstract long position() throws IOException;
434
435 /**
436 * Sets this channel's file position.
437 *
438 * <p> Setting the position to a value that is greater than the file's
439 * current size is legal but does not change the size of the file. A later
440 * attempt to read bytes at such a position will immediately return an
441 * end-of-file indication. A later attempt to write bytes at such a
442 * position will cause the file to be grown to accommodate the new bytes;
443 * the values of any bytes between the previous end-of-file and the
444 * newly-written bytes are unspecified. </p>
445 *
446 * @param newPosition
447 * The new position, a non-negative integer counting
448 * the number of bytes from the beginning of the file
449 *
450 * @return This file channel
451 *
452 * @throws ClosedChannelException
453 * If this channel is closed
454 *
455 * @throws IllegalArgumentException
456 * If the new position is negative
457 *
458 * @throws IOException
459 * If some other I/O error occurs
460 */
461 public abstract FileChannel position(long newPosition) throws IOException;
462
463 /**
464 * Returns the current size of this channel's file.
465 *
466 * @return The current size of this channel's file,
467 * measured in bytes
468 *
469 * @throws ClosedChannelException
470 * If this channel is closed
471 *
472 * @throws IOException
473 * If some other I/O error occurs
474 */
475 public abstract long size() throws IOException;
476
477 /**
478 * Truncates this channel's file to the given size.
479 *
480 * <p> If the given size is less than the file's current size then the file
481 * is truncated, discarding any bytes beyond the new end of the file. If
482 * the given size is greater than or equal to the file's current size then
483 * the file is not modified. In either case, if this channel's file
484 * position is greater than the given size then it is set to that size.
485 * </p>
486 *
487 * @param size
488 * The new size, a non-negative byte count
489 *
490 * @return This file channel
491 *
492 * @throws NonWritableChannelException
493 * If this channel was not opened for writing
494 *
495 * @throws ClosedChannelException
496 * If this channel is closed
497 *
498 * @throws IllegalArgumentException
499 * If the new size is negative
500 *
501 * @throws IOException
502 * If some other I/O error occurs
503 */
504 public abstract FileChannel truncate(long size) throws IOException;
505
506 /**
507 * Forces any updates to this channel's file to be written to the storage
508 * device that contains it.
509 *
510 * <p> If this channel's file resides on a local storage device then when
511 * this method returns it is guaranteed that all changes made to the file
512 * since this channel was created, or since this method was last invoked,
513 * will have been written to that device. This is useful for ensuring that
514 * critical information is not lost in the event of a system crash.
515 *
516 * <p> If the file does not reside on a local device then no such guarantee
517 * is made.
518 *
519 * <p> The <tt>metaData</tt> parameter can be used to limit the number of
520 * I/O operations that this method is required to perform. Passing
521 * <tt>false</tt> for this parameter indicates that only updates to the
522 * file's content need be written to storage; passing <tt>true</tt>
523 * indicates that updates to both the file's content and metadata must be
524 * written, which generally requires at least one more I/O operation.
525 * Whether this parameter actually has any effect is dependent upon the
526 * underlying operating system and is therefore unspecified.
527 *
528 * <p> Invoking this method may cause an I/O operation to occur even if the
529 * channel was only opened for reading. Some operating systems, for
530 * example, maintain a last-access time as part of a file's metadata, and
531 * this time is updated whenever the file is read. Whether or not this is
532 * actually done is system-dependent and is therefore unspecified.
533 *
534 * <p> This method is only guaranteed to force changes that were made to
535 * this channel's file via the methods defined in this class. It may or
536 * may not force changes that were made by modifying the content of a
537 * {@link MappedByteBuffer <i>mapped byte buffer</i>} obtained by
538 * invoking the {@link #map map} method. Invoking the {@link
539 * MappedByteBuffer#force force} method of the mapped byte buffer will
540 * force changes made to the buffer's content to be written. </p>
541 *
542 * @param metaData
543 * If <tt>true</tt> then this method is required to force changes
544 * to both the file's content and metadata to be written to
545 * storage; otherwise, it need only force content changes to be
546 * written
547 *
548 * @throws ClosedChannelException
549 * If this channel is closed
550 *
551 * @throws IOException
552 * If some other I/O error occurs
553 */
554 public abstract void force(boolean metaData) throws IOException;
555
556 /**
557 * Transfers bytes from this channel's file to the given writable byte
558 * channel.
559 *
560 * <p> An attempt is made to read up to <tt>count</tt> bytes starting at
561 * the given <tt>position</tt> in this channel's file and write them to the
562 * target channel. An invocation of this method may or may not transfer
563 * all of the requested bytes; whether or not it does so depends upon the
564 * natures and states of the channels. Fewer than the requested number of
565 * bytes are transferred if this channel's file contains fewer than
566 * <tt>count</tt> bytes starting at the given <tt>position</tt>, or if the
567 * target channel is non-blocking and it has fewer than <tt>count</tt>
568 * bytes free in its output buffer.
569 *
570 * <p> This method does not modify this channel's position. If the given
571 * position is greater than the file's current size then no bytes are
572 * transferred. If the target channel has a position then bytes are
573 * written starting at that position and then the position is incremented
574 * by the number of bytes written.
575 *
576 * <p> This method is potentially much more efficient than a simple loop
577 * that reads from this channel and writes to the target channel. Many
578 * operating systems can transfer bytes directly from the filesystem cache
579 * to the target channel without actually copying them. </p>
580 *
581 * @param position
582 * The position within the file at which the transfer is to begin;
583 * must be non-negative
584 *
585 * @param count
586 * The maximum number of bytes to be transferred; must be
587 * non-negative
588 *
589 * @param target
590 * The target channel
591 *
592 * @return The number of bytes, possibly zero,
593 * that were actually transferred
594 *
595 * @throws IllegalArgumentException
596 * If the preconditions on the parameters do not hold
597 *
598 * @throws NonReadableChannelException
599 * If this channel was not opened for reading
600 *
601 * @throws NonWritableChannelException
602 * If the target channel was not opened for writing
603 *
604 * @throws ClosedChannelException
605 * If either this channel or the target channel is closed
606 *
607 * @throws AsynchronousCloseException
608 * If another thread closes either channel
609 * while the transfer is in progress
610 *
611 * @throws ClosedByInterruptException
612 * If another thread interrupts the current thread while the
613 * transfer is in progress, thereby closing both channels and
614 * setting the current thread's interrupt status
615 *
616 * @throws IOException
617 * If some other I/O error occurs
618 */
619 public abstract long transferTo(long position, long count,
620 WritableByteChannel target)
621 throws IOException;
622
623 /**
624 * Transfers bytes into this channel's file from the given readable byte
625 * channel.
626 *
627 * <p> An attempt is made to read up to <tt>count</tt> bytes from the
628 * source channel and write them to this channel's file starting at the
629 * given <tt>position</tt>. An invocation of this method may or may not
630 * transfer all of the requested bytes; whether or not it does so depends
631 * upon the natures and states of the channels. Fewer than the requested
632 * number of bytes will be transferred if the source channel has fewer than
633 * <tt>count</tt> bytes remaining, or if the source channel is non-blocking
634 * and has fewer than <tt>count</tt> bytes immediately available in its
635 * input buffer.
636 *
637 * <p> This method does not modify this channel's position. If the given
638 * position is greater than the file's current size then no bytes are
639 * transferred. If the source channel has a position then bytes are read
640 * starting at that position and then the position is incremented by the
641 * number of bytes read.
642 *
643 * <p> This method is potentially much more efficient than a simple loop
644 * that reads from the source channel and writes to this channel. Many
645 * operating systems can transfer bytes directly from the source channel
646 * into the filesystem cache without actually copying them. </p>
647 *
648 * @param src
649 * The source channel
650 *
651 * @param position
652 * The position within the file at which the transfer is to begin;
653 * must be non-negative
654 *
655 * @param count
656 * The maximum number of bytes to be transferred; must be
657 * non-negative
658 *
659 * @return The number of bytes, possibly zero,
660 * that were actually transferred
661 *
662 * @throws IllegalArgumentException
663 * If the preconditions on the parameters do not hold
664 *
665 * @throws NonReadableChannelException
666 * If the source channel was not opened for reading
667 *
668 * @throws NonWritableChannelException
669 * If this channel was not opened for writing
670 *
671 * @throws ClosedChannelException
672 * If either this channel or the source channel is closed
673 *
674 * @throws AsynchronousCloseException
675 * If another thread closes either channel
676 * while the transfer is in progress
677 *
678 * @throws ClosedByInterruptException
679 * If another thread interrupts the current thread while the
680 * transfer is in progress, thereby closing both channels and
681 * setting the current thread's interrupt status
682 *
683 * @throws IOException
684 * If some other I/O error occurs
685 */
686 public abstract long transferFrom(ReadableByteChannel src,
687 long position, long count)
688 throws IOException;
689
690 /**
691 * Reads a sequence of bytes from this channel into the given buffer,
692 * starting at the given file position.
693 *
694 * <p> This method works in the same manner as the {@link
695 * #read(ByteBuffer)} method, except that bytes are read starting at the
696 * given file position rather than at the channel's current position. This
697 * method does not modify this channel's position. If the given position
698 * is greater than the file's current size then no bytes are read. </p>
699 *
700 * @param dst
701 * The buffer into which bytes are to be transferred
702 *
703 * @param position
704 * The file position at which the transfer is to begin;
705 * must be non-negative
706 *
707 * @return The number of bytes read, possibly zero, or <tt>-1</tt> if the
708 * given position is greater than or equal to the file's current
709 * size
710 *
711 * @throws IllegalArgumentException
712 * If the position is negative
713 *
714 * @throws NonReadableChannelException
715 * If this channel was not opened for reading
716 *
717 * @throws ClosedChannelException
718 * If this channel is closed
719 *
720 * @throws AsynchronousCloseException
721 * If another thread closes this channel
722 * while the read operation is in progress
723 *
724 * @throws ClosedByInterruptException
725 * If another thread interrupts the current thread
726 * while the read operation is in progress, thereby
727 * closing the channel and setting the current thread's
728 * interrupt status
729 *
730 * @throws IOException
731 * If some other I/O error occurs
732 */
733 public abstract int read(ByteBuffer dst, long position) throws IOException;
734
735 /**
736 * Writes a sequence of bytes to this channel from the given buffer,
737 * starting at the given file position.
738 *
739 * <p> This method works in the same manner as the {@link
740 * #write(ByteBuffer)} method, except that bytes are written starting at
741 * the given file position rather than at the channel's current position.
742 * This method does not modify this channel's position. If the given
743 * position is greater than the file's current size then the file will be
744 * grown to accommodate the new bytes; the values of any bytes between the
745 * previous end-of-file and the newly-written bytes are unspecified. </p>
746 *
747 * @param src
748 * The buffer from which bytes are to be transferred
749 *
750 * @param position
751 * The file position at which the transfer is to begin;
752 * must be non-negative
753 *
754 * @return The number of bytes written, possibly zero
755 *
756 * @throws IllegalArgumentException
757 * If the position is negative
758 *
759 * @throws NonWritableChannelException
760 * If this channel was not opened for writing
761 *
762 * @throws ClosedChannelException
763 * If this channel is closed
764 *
765 * @throws AsynchronousCloseException
766 * If another thread closes this channel
767 * while the write operation is in progress
768 *
769 * @throws ClosedByInterruptException
770 * If another thread interrupts the current thread
771 * while the write operation is in progress, thereby
772 * closing the channel and setting the current thread's
773 * interrupt status
774 *
775 * @throws IOException
776 * If some other I/O error occurs
777 */
778 public abstract int write(ByteBuffer src, long position) throws IOException;
779
780
781 // -- Memory-mapped buffers --
782
783 /**
784 * A typesafe enumeration for file-mapping modes.
785 *
786 * @since 1.4
787 *
788 * @see java.nio.channels.FileChannel#map
789 */
790 public static class MapMode {
791
792 /**
793 * Mode for a read-only mapping.
794 */
795 public static final MapMode READ_ONLY
796 = new MapMode("READ_ONLY");
797
798 /**
799 * Mode for a read/write mapping.
800 */
801 public static final MapMode READ_WRITE
802 = new MapMode("READ_WRITE");
803
804 /**
805 * Mode for a private (copy-on-write) mapping.
806 */
807 public static final MapMode PRIVATE
808 = new MapMode("PRIVATE");
809
810 private final String name;
811
812 private MapMode(String name) {
813 this.name = name;
814 }
815
816 /**
817 * Returns a string describing this file-mapping mode.
818 *
819 * @return A descriptive string
820 */
821 public String toString() {
822 return name;
823 }
824
825 }
826
827 /**
828 * Maps a region of this channel's file directly into memory.
829 *
830 * <p> A region of a file may be mapped into memory in one of three modes:
831 * </p>
832 *
833 * <ul>
834 *
835 * <li><p> <i>Read-only:</i> Any attempt to modify the resulting buffer
836 * will cause a {@link java.nio.ReadOnlyBufferException} to be thrown.
837 * ({@link MapMode#READ_ONLY MapMode.READ_ONLY}) </p></li>
838 *
839 * <li><p> <i>Read/write:</i> Changes made to the resulting buffer will
840 * eventually be propagated to the file; they may or may not be made
841 * visible to other programs that have mapped the same file. ({@link
842 * MapMode#READ_WRITE MapMode.READ_WRITE}) </p></li>
843 *
844 * <li><p> <i>Private:</i> Changes made to the resulting buffer will not
845 * be propagated to the file and will not be visible to other programs
846 * that have mapped the same file; instead, they will cause private
847 * copies of the modified portions of the buffer to be created. ({@link
848 * MapMode#PRIVATE MapMode.PRIVATE}) </p></li>
849 *
850 * </ul>
851 *
852 * <p> For a read-only mapping, this channel must have been opened for
853 * reading; for a read/write or private mapping, this channel must have
854 * been opened for both reading and writing.
855 *
856 * <p> The {@link MappedByteBuffer <i>mapped byte buffer</i>}
857 * returned by this method will have a position of zero and a limit and
858 * capacity of <tt>size</tt>; its mark will be undefined. The buffer and
859 * the mapping that it represents will remain valid until the buffer itself
860 * is garbage-collected.
861 *
862 * <p> A mapping, once established, is not dependent upon the file channel
863 * that was used to create it. Closing the channel, in particular, has no
864 * effect upon the validity of the mapping.
865 *
866 * <p> Many of the details of memory-mapped files are inherently dependent
867 * upon the underlying operating system and are therefore unspecified. The
868 * behavior of this method when the requested region is not completely
869 * contained within this channel's file is unspecified. Whether changes
870 * made to the content or size of the underlying file, by this program or
871 * another, are propagated to the buffer is unspecified. The rate at which
872 * changes to the buffer are propagated to the file is unspecified.
873 *
874 * <p> For most operating systems, mapping a file into memory is more
875 * expensive than reading or writing a few tens of kilobytes of data via
876 * the usual {@link #read read} and {@link #write write} methods. From the
877 * standpoint of performance it is generally only worth mapping relatively
878 * large files into memory. </p>
879 *
880 * @param mode
881 * One of the constants {@link MapMode#READ_ONLY READ_ONLY}, {@link
882 * MapMode#READ_WRITE READ_WRITE}, or {@link MapMode#PRIVATE
883 * PRIVATE} defined in the {@link MapMode} class, according to
884 * whether the file is to be mapped read-only, read/write, or
885 * privately (copy-on-write), respectively
886 *
887 * @param position
888 * The position within the file at which the mapped region
889 * is to start; must be non-negative
890 *
891 * @param size
892 * The size of the region to be mapped; must be non-negative and
893 * no greater than {@link java.lang.Integer#MAX_VALUE}
894 *
895 * @return The mapped byte buffer
896 *
897 * @throws NonReadableChannelException
898 * If the <tt>mode</tt> is {@link MapMode#READ_ONLY READ_ONLY} but
899 * this channel was not opened for reading
900 *
901 * @throws NonWritableChannelException
902 * If the <tt>mode</tt> is {@link MapMode#READ_WRITE READ_WRITE} or
903 * {@link MapMode#PRIVATE PRIVATE} but this channel was not opened
904 * for both reading and writing
905 *
906 * @throws IllegalArgumentException
907 * If the preconditions on the parameters do not hold
908 *
909 * @throws IOException
910 * If some other I/O error occurs
911 *
912 * @see java.nio.channels.FileChannel.MapMode
913 * @see java.nio.MappedByteBuffer
914 */
915 public abstract MappedByteBuffer map(MapMode mode,
916 long position, long size)
917 throws IOException;
918
919
920 // -- Locks --
921
922 /**
923 * Acquires a lock on the given region of this channel's file.
924 *
925 * <p> An invocation of this method will block until the region can be
926 * locked, this channel is closed, or the invoking thread is interrupted,
927 * whichever comes first.
928 *
929 * <p> If this channel is closed by another thread during an invocation of
930 * this method then an {@link AsynchronousCloseException} will be thrown.
931 *
932 * <p> If the invoking thread is interrupted while waiting to acquire the
933 * lock then its interrupt status will be set and a {@link
934 * FileLockInterruptionException} will be thrown. If the invoker's
935 * interrupt status is set when this method is invoked then that exception
936 * will be thrown immediately; the thread's interrupt status will not be
937 * changed.
938 *
939 * <p> The region specified by the <tt>position</tt> and <tt>size</tt>
940 * parameters need not be contained within, or even overlap, the actual
941 * underlying file. Lock regions are fixed in size; if a locked region
942 * initially contains the end of the file and the file grows beyond the
943 * region then the new portion of the file will not be covered by the lock.
944 * If a file is expected to grow in size and a lock on the entire file is
945 * required then a region starting at zero, and no smaller than the
946 * expected maximum size of the file, should be locked. The zero-argument
947 * {@link #lock()} method simply locks a region of size {@link
948 * Long#MAX_VALUE}.
949 *
950 * <p> Some operating systems do not support shared locks, in which case a
951 * request for a shared lock is automatically converted into a request for
952 * an exclusive lock. Whether the newly-acquired lock is shared or
953 * exclusive may be tested by invoking the resulting lock object's {@link
954 * FileLock#isShared() isShared} method.
955 *
956 * <p> File locks are held on behalf of the entire Java virtual machine.
957 * They are not suitable for controlling access to a file by multiple
958 * threads within the same virtual machine. </p>
959 *
960 * @param position
961 * The position at which the locked region is to start; must be
962 * non-negative
963 *
964 * @param size
965 * The size of the locked region; must be non-negative, and the sum
966 * <tt>position</tt> + <tt>size</tt> must be non-negative
967 *
968 * @param shared
969 * <tt>true</tt> to request a shared lock, in which case this
970 * channel must be open for reading (and possibly writing);
971 * <tt>false</tt> to request an exclusive lock, in which case this
972 * channel must be open for writing (and possibly reading)
973 *
974 * @return A lock object representing the newly-acquired lock
975 *
976 * @throws IllegalArgumentException
977 * If the preconditions on the parameters do not hold
978 *
979 * @throws ClosedChannelException
980 * If this channel is closed
981 *
982 * @throws AsynchronousCloseException
983 * If another thread closes this channel while the invoking
984 * thread is blocked in this method
985 *
986 * @throws FileLockInterruptionException
987 * If the invoking thread is interrupted while blocked in this
988 * method
989 *
990 * @throws OverlappingFileLockException
991 * If a lock that overlaps the requested region is already held by
992 * this Java virtual machine, or if another thread is already
993 * blocked in this method and is attempting to lock an overlapping
994 * region
995 *
996 * @throws NonReadableChannelException
997 * If <tt>shared</tt> is <tt>true</tt> this channel was not
998 * opened for reading
999 *
1000 * @throws NonWritableChannelException
1001 * If <tt>shared</tt> is <tt>false</tt> but this channel was not
1002 * opened for writing
1003 *
1004 * @throws IOException
1005 * If some other I/O error occurs
1006 *
1007 * @see #lock()
1008 * @see #tryLock()
1009 * @see #tryLock(long,long,boolean)
1010 */
1011 public abstract FileLock lock(long position, long size, boolean shared)
1012 throws IOException;
1013
1014 /**
1015 * Acquires an exclusive lock on this channel's file.
1016 *
1017 * <p> An invocation of this method of the form <tt>fc.lock()</tt> behaves
1018 * in exactly the same way as the invocation
1019 *
1020 * <pre>
1021 * fc.{@link #lock(long,long,boolean) lock}(0L, Long.MAX_VALUE, false) </pre>
1022 *
1023 * @return A lock object representing the newly-acquired lock
1024 *
1025 * @throws ClosedChannelException
1026 * If this channel is closed
1027 *
1028 * @throws AsynchronousCloseException
1029 * If another thread closes this channel while the invoking
1030 * thread is blocked in this method
1031 *
1032 * @throws FileLockInterruptionException
1033 * If the invoking thread is interrupted while blocked in this
1034 * method
1035 *
1036 * @throws OverlappingFileLockException
1037 * If a lock that overlaps the requested region is already held by
1038 * this Java virtual machine, or if another thread is already
1039 * blocked in this method and is attempting to lock an overlapping
1040 * region of the same file
1041 *
1042 * @throws NonWritableChannelException
1043 * If this channel was not opened for writing
1044 *
1045 * @throws IOException
1046 * If some other I/O error occurs
1047 *
1048 * @see #lock(long,long,boolean)
1049 * @see #tryLock()
1050 * @see #tryLock(long,long,boolean)
1051 */
1052 public final FileLock lock() throws IOException {
1053 return lock(0L, Long.MAX_VALUE, false);
1054 }
1055
1056 /**
1057 * Attempts to acquire a lock on the given region of this channel's file.
1058 *
1059 * <p> This method does not block. An invocation always returns
1060 * immediately, either having acquired a lock on the requested region or
1061 * having failed to do so. If it fails to acquire a lock because an
1062 * overlapping lock is held by another program then it returns
1063 * <tt>null</tt>. If it fails to acquire a lock for any other reason then
1064 * an appropriate exception is thrown.
1065 *
1066 * <p> The region specified by the <tt>position</tt> and <tt>size</tt>
1067 * parameters need not be contained within, or even overlap, the actual
1068 * underlying file. Lock regions are fixed in size; if a locked region
1069 * initially contains the end of the file and the file grows beyond the
1070 * region then the new portion of the file will not be covered by the lock.
1071 * If a file is expected to grow in size and a lock on the entire file is
1072 * required then a region starting at zero, and no smaller than the
1073 * expected maximum size of the file, should be locked. The zero-argument
1074 * {@link #tryLock()} method simply locks a region of size {@link
1075 * Long#MAX_VALUE}.
1076 *
1077 * <p> Some operating systems do not support shared locks, in which case a
1078 * request for a shared lock is automatically converted into a request for
1079 * an exclusive lock. Whether the newly-acquired lock is shared or
1080 * exclusive may be tested by invoking the resulting lock object's {@link
1081 * FileLock#isShared() isShared} method.
1082 *
1083 * <p> File locks are held on behalf of the entire Java virtual machine.
1084 * They are not suitable for controlling access to a file by multiple
1085 * threads within the same virtual machine. </p>
1086 *
1087 * @param position
1088 * The position at which the locked region is to start; must be
1089 * non-negative
1090 *
1091 * @param size
1092 * The size of the locked region; must be non-negative, and the sum
1093 * <tt>position</tt> + <tt>size</tt> must be non-negative
1094 *
1095 * @param shared
1096 * <tt>true</tt> to request a shared lock,
1097 * <tt>false</tt> to request an exclusive lock
1098 *
1099 * @return A lock object representing the newly-acquired lock,
1100 * or <tt>null</tt> if the lock could not be acquired
1101 * because another program holds an overlapping lock
1102 *
1103 * @throws IllegalArgumentException
1104 * If the preconditions on the parameters do not hold
1105 *
1106 * @throws ClosedChannelException
1107 * If this channel is closed
1108 *
1109 * @throws OverlappingFileLockException
1110 * If a lock that overlaps the requested region is already held by
1111 * this Java virtual machine, or if another thread is already
1112 * blocked in this method and is attempting to lock an overlapping
1113 * region of the same file
1114 *
1115 * @throws IOException
1116 * If some other I/O error occurs
1117 *
1118 * @see #lock()
1119 * @see #lock(long,long,boolean)
1120 * @see #tryLock()
1121 */
1122 public abstract FileLock tryLock(long position, long size, boolean shared)
1123 throws IOException;
1124
1125 /**
1126 * Attempts to acquire an exclusive lock on this channel's file.
1127 *
1128 * <p> An invocation of this method of the form <tt>fc.tryLock()</tt>
1129 * behaves in exactly the same way as the invocation
1130 *
1131 * <pre>
1132 * fc.{@link #tryLock(long,long,boolean) tryLock}(0L, Long.MAX_VALUE, false) </pre>
1133 *
1134 * @return A lock object representing the newly-acquired lock,
1135 * or <tt>null</tt> if the lock could not be acquired
1136 * because another program holds an overlapping lock
1137 *
1138 * @throws ClosedChannelException
1139 * If this channel is closed
1140 *
1141 * @throws OverlappingFileLockException
1142 * If a lock that overlaps the requested region is already held by
1143 * this Java virtual machine, or if another thread is already
1144 * blocked in this method and is attempting to lock an overlapping
1145 * region
1146 *
1147 * @throws IOException
1148 * If some other I/O error occurs
1149 *
1150 * @see #lock()
1151 * @see #lock(long,long,boolean)
1152 * @see #tryLock(long,long,boolean)
1153 */
1154 public final FileLock tryLock() throws IOException {
1155 return tryLock(0L, Long.MAX_VALUE, false);
1156 }
1157
1158 }
1159