001/*
002 * Copyright (C) 2007 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
005 * in compliance with the License. You may obtain a copy of the License at
006 *
007 * http://www.apache.org/licenses/LICENSE-2.0
008 *
009 * Unless required by applicable law or agreed to in writing, software distributed under the License
010 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
011 * or implied. See the License for the specific language governing permissions and limitations under
012 * the License.
013 */
014
015package com.google.common.io;
016
017import static com.google.common.base.Preconditions.checkArgument;
018import static com.google.common.base.Preconditions.checkNotNull;
019import static com.google.common.io.FileWriteMode.APPEND;
020
021import com.google.common.annotations.Beta;
022import com.google.common.annotations.GwtIncompatible;
023import com.google.common.base.Joiner;
024import com.google.common.base.Optional;
025import com.google.common.base.Predicate;
026import com.google.common.base.Splitter;
027import com.google.common.collect.ImmutableList;
028import com.google.common.collect.ImmutableSet;
029import com.google.common.collect.Lists;
030import com.google.common.graph.SuccessorsFunction;
031import com.google.common.graph.Traverser;
032import com.google.common.hash.HashCode;
033import com.google.common.hash.HashFunction;
034import com.google.errorprone.annotations.CanIgnoreReturnValue;
035import java.io.BufferedReader;
036import java.io.BufferedWriter;
037import java.io.File;
038import java.io.FileInputStream;
039import java.io.FileNotFoundException;
040import java.io.FileOutputStream;
041import java.io.IOException;
042import java.io.InputStreamReader;
043import java.io.OutputStream;
044import java.io.OutputStreamWriter;
045import java.io.RandomAccessFile;
046import java.nio.MappedByteBuffer;
047import java.nio.channels.FileChannel;
048import java.nio.channels.FileChannel.MapMode;
049import java.nio.charset.Charset;
050import java.nio.charset.StandardCharsets;
051import java.util.ArrayList;
052import java.util.Arrays;
053import java.util.Collections;
054import java.util.List;
055
056/**
057 * Provides utility methods for working with {@linkplain File files}.
058 *
059 * <p>{@link java.nio.file.Path} users will find similar utilities in {@link MoreFiles} and the
060 * JDK's {@link java.nio.file.Files} class.
061 *
062 * @author Chris Nokleberg
063 * @author Colin Decker
064 * @since 1.0
065 */
066@GwtIncompatible
067public final class Files {
068
069  /** Maximum loop count when creating temp directories. */
070  private static final int TEMP_DIR_ATTEMPTS = 10000;
071
072  private Files() {}
073
074  /**
075   * Returns a buffered reader that reads from a file using the given character set.
076   *
077   * <p><b>{@link java.nio.file.Path} equivalent:</b> {@link
078   * java.nio.file.Files#newBufferedReader(java.nio.file.Path, Charset)}.
079   *
080   * @param file the file to read from
081   * @param charset the charset used to decode the input stream; see {@link StandardCharsets} for
082   *     helpful predefined constants
083   * @return the buffered reader
084   */
085  @Beta
086  public static BufferedReader newReader(File file, Charset charset) throws FileNotFoundException {
087    checkNotNull(file);
088    checkNotNull(charset);
089    return new BufferedReader(new InputStreamReader(new FileInputStream(file), charset));
090  }
091
092  /**
093   * Returns a buffered writer that writes to a file using the given character set.
094   *
095   * <p><b>{@link java.nio.file.Path} equivalent:</b> {@link
096   * java.nio.file.Files#newBufferedWriter(java.nio.file.Path, Charset,
097   * java.nio.file.OpenOption...)}.
098   *
099   * @param file the file to write to
100   * @param charset the charset used to encode the output stream; see {@link StandardCharsets} for
101   *     helpful predefined constants
102   * @return the buffered writer
103   */
104  @Beta
105  public static BufferedWriter newWriter(File file, Charset charset) throws FileNotFoundException {
106    checkNotNull(file);
107    checkNotNull(charset);
108    return new BufferedWriter(new OutputStreamWriter(new FileOutputStream(file), charset));
109  }
110
111  /**
112   * Returns a new {@link ByteSource} for reading bytes from the given file.
113   *
114   * @since 14.0
115   */
116  public static ByteSource asByteSource(File file) {
117    return new FileByteSource(file);
118  }
119
120  private static final class FileByteSource extends ByteSource {
121
122    private final File file;
123
124    private FileByteSource(File file) {
125      this.file = checkNotNull(file);
126    }
127
128    @Override
129    public FileInputStream openStream() throws IOException {
130      return new FileInputStream(file);
131    }
132
133    @Override
134    public Optional<Long> sizeIfKnown() {
135      if (file.isFile()) {
136        return Optional.of(file.length());
137      } else {
138        return Optional.absent();
139      }
140    }
141
142    @Override
143    public long size() throws IOException {
144      if (!file.isFile()) {
145        throw new FileNotFoundException(file.toString());
146      }
147      return file.length();
148    }
149
150    @Override
151    public byte[] read() throws IOException {
152      Closer closer = Closer.create();
153      try {
154        FileInputStream in = closer.register(openStream());
155        return ByteStreams.toByteArray(in, in.getChannel().size());
156      } catch (Throwable e) {
157        throw closer.rethrow(e);
158      } finally {
159        closer.close();
160      }
161    }
162
163    @Override
164    public String toString() {
165      return "Files.asByteSource(" + file + ")";
166    }
167  }
168
169  /**
170   * Returns a new {@link ByteSink} for writing bytes to the given file. The given {@code modes}
171   * control how the file is opened for writing. When no mode is provided, the file will be
172   * truncated before writing. When the {@link FileWriteMode#APPEND APPEND} mode is provided, writes
173   * will append to the end of the file without truncating it.
174   *
175   * @since 14.0
176   */
177  public static ByteSink asByteSink(File file, FileWriteMode... modes) {
178    return new FileByteSink(file, modes);
179  }
180
181  private static final class FileByteSink extends ByteSink {
182
183    private final File file;
184    private final ImmutableSet<FileWriteMode> modes;
185
186    private FileByteSink(File file, FileWriteMode... modes) {
187      this.file = checkNotNull(file);
188      this.modes = ImmutableSet.copyOf(modes);
189    }
190
191    @Override
192    public FileOutputStream openStream() throws IOException {
193      return new FileOutputStream(file, modes.contains(APPEND));
194    }
195
196    @Override
197    public String toString() {
198      return "Files.asByteSink(" + file + ", " + modes + ")";
199    }
200  }
201
202  /**
203   * Returns a new {@link CharSource} for reading character data from the given file using the given
204   * character set.
205   *
206   * @since 14.0
207   */
208  public static CharSource asCharSource(File file, Charset charset) {
209    return asByteSource(file).asCharSource(charset);
210  }
211
212  /**
213   * Returns a new {@link CharSink} for writing character data to the given file using the given
214   * character set. The given {@code modes} control how the file is opened for writing. When no mode
215   * is provided, the file will be truncated before writing. When the {@link FileWriteMode#APPEND
216   * APPEND} mode is provided, writes will append to the end of the file without truncating it.
217   *
218   * @since 14.0
219   */
220  public static CharSink asCharSink(File file, Charset charset, FileWriteMode... modes) {
221    return asByteSink(file, modes).asCharSink(charset);
222  }
223
224  /**
225   * Reads all bytes from a file into a byte array.
226   *
227   * <p><b>{@link java.nio.file.Path} equivalent:</b> {@link java.nio.file.Files#readAllBytes}.
228   *
229   * @param file the file to read from
230   * @return a byte array containing all the bytes from file
231   * @throws IllegalArgumentException if the file is bigger than the largest possible byte array
232   *     (2^31 - 1)
233   * @throws IOException if an I/O error occurs
234   */
235  @Beta
236  public static byte[] toByteArray(File file) throws IOException {
237    return asByteSource(file).read();
238  }
239
240  /**
241   * Reads all characters from a file into a {@link String}, using the given character set.
242   *
243   * @param file the file to read from
244   * @param charset the charset used to decode the input stream; see {@link StandardCharsets} for
245   *     helpful predefined constants
246   * @return a string containing all the characters from the file
247   * @throws IOException if an I/O error occurs
248   * @deprecated Prefer {@code asCharSource(file, charset).read()}. This method is scheduled to be
249   *     removed in October 2019.
250   */
251  @Beta
252  @Deprecated
253  public static String toString(File file, Charset charset) throws IOException {
254    return asCharSource(file, charset).read();
255  }
256
257  /**
258   * Overwrites a file with the contents of a byte array.
259   *
260   * <p><b>{@link java.nio.file.Path} equivalent:</b> {@link
261   * java.nio.file.Files#write(java.nio.file.Path, byte[], java.nio.file.OpenOption...)}.
262   *
263   * @param from the bytes to write
264   * @param to the destination file
265   * @throws IOException if an I/O error occurs
266   */
267  @Beta
268  public static void write(byte[] from, File to) throws IOException {
269    asByteSink(to).write(from);
270  }
271
272  /**
273   * Writes a character sequence (such as a string) to a file using the given character set.
274   *
275   * @param from the character sequence to write
276   * @param to the destination file
277   * @param charset the charset used to encode the output stream; see {@link StandardCharsets} for
278   *     helpful predefined constants
279   * @throws IOException if an I/O error occurs
280   * @deprecated Prefer {@code asCharSink(to, charset).write(from)}. This method is scheduled to be
281   *     removed in October 2019.
282   */
283  @Beta
284  @Deprecated
285  public static void write(CharSequence from, File to, Charset charset) throws IOException {
286    asCharSink(to, charset).write(from);
287  }
288
289  /**
290   * Copies all bytes from a file to an output stream.
291   *
292   * <p><b>{@link java.nio.file.Path} equivalent:</b> {@link
293   * java.nio.file.Files#copy(java.nio.file.Path, OutputStream)}.
294   *
295   * @param from the source file
296   * @param to the output stream
297   * @throws IOException if an I/O error occurs
298   */
299  @Beta
300  public static void copy(File from, OutputStream to) throws IOException {
301    asByteSource(from).copyTo(to);
302  }
303
304  /**
305   * Copies all the bytes from one file to another.
306   *
307   * <p>Copying is not an atomic operation - in the case of an I/O error, power loss, process
308   * termination, or other problems, {@code to} may not be a complete copy of {@code from}. If you
309   * need to guard against those conditions, you should employ other file-level synchronization.
310   *
311   * <p><b>Warning:</b> If {@code to} represents an existing file, that file will be overwritten
312   * with the contents of {@code from}. If {@code to} and {@code from} refer to the <i>same</i>
313   * file, the contents of that file will be deleted.
314   *
315   * <p><b>{@link java.nio.file.Path} equivalent:</b> {@link
316   * java.nio.file.Files#copy(java.nio.file.Path, java.nio.file.Path, java.nio.file.CopyOption...)}.
317   *
318   * @param from the source file
319   * @param to the destination file
320   * @throws IOException if an I/O error occurs
321   * @throws IllegalArgumentException if {@code from.equals(to)}
322   */
323  @Beta
324  public static void copy(File from, File to) throws IOException {
325    checkArgument(!from.equals(to), "Source %s and destination %s must be different", from, to);
326    asByteSource(from).copyTo(asByteSink(to));
327  }
328
329  /**
330   * Copies all characters from a file to an appendable object, using the given character set.
331   *
332   * @param from the source file
333   * @param charset the charset used to decode the input stream; see {@link StandardCharsets} for
334   *     helpful predefined constants
335   * @param to the appendable object
336   * @throws IOException if an I/O error occurs
337   * @deprecated Prefer {@code asCharSource(from, charset).copyTo(to)}. This method is scheduled to
338   *     be removed in October 2019.
339   */
340  @Beta
341  @Deprecated
342  public
343  static void copy(File from, Charset charset, Appendable to) throws IOException {
344    asCharSource(from, charset).copyTo(to);
345  }
346
347  /**
348   * Appends a character sequence (such as a string) to a file using the given character set.
349   *
350   * @param from the character sequence to append
351   * @param to the destination file
352   * @param charset the charset used to encode the output stream; see {@link StandardCharsets} for
353   *     helpful predefined constants
354   * @throws IOException if an I/O error occurs
355   * @deprecated Prefer {@code asCharSink(to, charset, FileWriteMode.APPEND).write(from)}. This
356   *     method is scheduled to be removed in October 2019.
357   */
358  @Beta
359  @Deprecated
360  public
361  static void append(CharSequence from, File to, Charset charset) throws IOException {
362    asCharSink(to, charset, FileWriteMode.APPEND).write(from);
363  }
364
365  /**
366   * Returns true if the given files exist, are not directories, and contain the same bytes.
367   *
368   * @throws IOException if an I/O error occurs
369   */
370  @Beta
371  public static boolean equal(File file1, File file2) throws IOException {
372    checkNotNull(file1);
373    checkNotNull(file2);
374    if (file1 == file2 || file1.equals(file2)) {
375      return true;
376    }
377
378    /*
379     * Some operating systems may return zero as the length for files denoting system-dependent
380     * entities such as devices or pipes, in which case we must fall back on comparing the bytes
381     * directly.
382     */
383    long len1 = file1.length();
384    long len2 = file2.length();
385    if (len1 != 0 && len2 != 0 && len1 != len2) {
386      return false;
387    }
388    return asByteSource(file1).contentEquals(asByteSource(file2));
389  }
390
391  /**
392   * Atomically creates a new directory somewhere beneath the system's temporary directory (as
393   * defined by the {@code java.io.tmpdir} system property), and returns its name.
394   *
395   * <p>Use this method instead of {@link File#createTempFile(String, String)} when you wish to
396   * create a directory, not a regular file. A common pitfall is to call {@code createTempFile},
397   * delete the file and create a directory in its place, but this leads a race condition which can
398   * be exploited to create security vulnerabilities, especially when executable files are to be
399   * written into the directory.
400   *
401   * <p>Depending on the environmment that this code is run in, the system temporary directory (and
402   * thus the directory this method creates) may be more visible that a program would like - files
403   * written to this directory may be read or overwritten by hostile programs running on the same
404   * machine.
405   *
406   * <p>This method assumes that the temporary volume is writable, has free inodes and free blocks,
407   * and that it will not be called thousands of times per second.
408   *
409   * <p><b>{@link java.nio.file.Path} equivalent:</b> {@link
410   * java.nio.file.Files#createTempDirectory}.
411   *
412   * @return the newly-created directory
413   * @throws IllegalStateException if the directory could not be created
414   * @deprecated For Android users, see the <a
415   *     href="https://developer.android.com/training/data-storage" target="_blank">Data and File
416   *     Storage overview</a> to select an appropriate temporary directory (perhaps {@code
417   *     context.getCacheDir()}). For developers on Java 7 or later, use {@link
418   *     java.nio.file.Files#createTempDirectory}, transforming it to a {@link File} using {@link
419   *     java.nio.file.Path#toFile() toFile()} if needed.
420   */
421  @Beta
422  @Deprecated
423  public static File createTempDir() {
424    File baseDir = new File(System.getProperty("java.io.tmpdir"));
425    @SuppressWarnings("GoodTime") // reading system time without TimeSource
426    String baseName = System.currentTimeMillis() + "-";
427
428    for (int counter = 0; counter < TEMP_DIR_ATTEMPTS; counter++) {
429      File tempDir = new File(baseDir, baseName + counter);
430      if (tempDir.mkdir()) {
431        return tempDir;
432      }
433    }
434    throw new IllegalStateException(
435        "Failed to create directory within "
436            + TEMP_DIR_ATTEMPTS
437            + " attempts (tried "
438            + baseName
439            + "0 to "
440            + baseName
441            + (TEMP_DIR_ATTEMPTS - 1)
442            + ')');
443  }
444
445  /**
446   * Creates an empty file or updates the last updated timestamp on the same as the unix command of
447   * the same name.
448   *
449   * @param file the file to create or update
450   * @throws IOException if an I/O error occurs
451   */
452  @Beta
453  @SuppressWarnings("GoodTime") // reading system time without TimeSource
454  public static void touch(File file) throws IOException {
455    checkNotNull(file);
456    if (!file.createNewFile() && !file.setLastModified(System.currentTimeMillis())) {
457      throw new IOException("Unable to update modification time of " + file);
458    }
459  }
460
461  /**
462   * Creates any necessary but nonexistent parent directories of the specified file. Note that if
463   * this operation fails it may have succeeded in creating some (but not all) of the necessary
464   * parent directories.
465   *
466   * @throws IOException if an I/O error occurs, or if any necessary but nonexistent parent
467   *     directories of the specified file could not be created.
468   * @since 4.0
469   */
470  @Beta
471  public static void createParentDirs(File file) throws IOException {
472    checkNotNull(file);
473    File parent = file.getCanonicalFile().getParentFile();
474    if (parent == null) {
475      /*
476       * The given directory is a filesystem root. All zero of its ancestors exist. This doesn't
477       * mean that the root itself exists -- consider x:\ on a Windows machine without such a drive
478       * -- or even that the caller can create it, but this method makes no such guarantees even for
479       * non-root files.
480       */
481      return;
482    }
483    parent.mkdirs();
484    if (!parent.isDirectory()) {
485      throw new IOException("Unable to create parent directories of " + file);
486    }
487  }
488
489  /**
490   * Moves a file from one path to another. This method can rename a file and/or move it to a
491   * different directory. In either case {@code to} must be the target path for the file itself; not
492   * just the new name for the file or the path to the new parent directory.
493   *
494   * <p><b>{@link java.nio.file.Path} equivalent:</b> {@link java.nio.file.Files#move}.
495   *
496   * @param from the source file
497   * @param to the destination file
498   * @throws IOException if an I/O error occurs
499   * @throws IllegalArgumentException if {@code from.equals(to)}
500   */
501  @Beta
502  public static void move(File from, File to) throws IOException {
503    checkNotNull(from);
504    checkNotNull(to);
505    checkArgument(!from.equals(to), "Source %s and destination %s must be different", from, to);
506
507    if (!from.renameTo(to)) {
508      copy(from, to);
509      if (!from.delete()) {
510        if (!to.delete()) {
511          throw new IOException("Unable to delete " + to);
512        }
513        throw new IOException("Unable to delete " + from);
514      }
515    }
516  }
517
518  /**
519   * Reads the first line from a file. The line does not include line-termination characters, but
520   * does include other leading and trailing whitespace.
521   *
522   * @param file the file to read from
523   * @param charset the charset used to decode the input stream; see {@link StandardCharsets} for
524   *     helpful predefined constants
525   * @return the first line, or null if the file is empty
526   * @throws IOException if an I/O error occurs
527   * @deprecated Prefer {@code asCharSource(file, charset).readFirstLine()}. This method is
528   *     scheduled to be removed in October 2019.
529   */
530  @Beta
531  @Deprecated
532  public
533  static String readFirstLine(File file, Charset charset) throws IOException {
534    return asCharSource(file, charset).readFirstLine();
535  }
536
537  /**
538   * Reads all of the lines from a file. The lines do not include line-termination characters, but
539   * do include other leading and trailing whitespace.
540   *
541   * <p>This method returns a mutable {@code List}. For an {@code ImmutableList}, use {@code
542   * Files.asCharSource(file, charset).readLines()}.
543   *
544   * <p><b>{@link java.nio.file.Path} equivalent:</b> {@link
545   * java.nio.file.Files#readAllLines(java.nio.file.Path, Charset)}.
546   *
547   * @param file the file to read from
548   * @param charset the charset used to decode the input stream; see {@link StandardCharsets} for
549   *     helpful predefined constants
550   * @return a mutable {@link List} containing all the lines
551   * @throws IOException if an I/O error occurs
552   */
553  @Beta
554  public static List<String> readLines(File file, Charset charset) throws IOException {
555    // don't use asCharSource(file, charset).readLines() because that returns
556    // an immutable list, which would change the behavior of this method
557    return asCharSource(file, charset)
558        .readLines(
559            new LineProcessor<List<String>>() {
560              final List<String> result = Lists.newArrayList();
561
562              @Override
563              public boolean processLine(String line) {
564                result.add(line);
565                return true;
566              }
567
568              @Override
569              public List<String> getResult() {
570                return result;
571              }
572            });
573  }
574
575  /**
576   * Streams lines from a {@link File}, stopping when our callback returns false, or we have read
577   * all of the lines.
578   *
579   * @param file the file to read from
580   * @param charset the charset used to decode the input stream; see {@link StandardCharsets} for
581   *     helpful predefined constants
582   * @param callback the {@link LineProcessor} to use to handle the lines
583   * @return the output of processing the lines
584   * @throws IOException if an I/O error occurs
585   * @deprecated Prefer {@code asCharSource(file, charset).readLines(callback)}. This method is
586   *     scheduled to be removed in October 2019.
587   */
588  @Beta
589  @Deprecated
590  @CanIgnoreReturnValue // some processors won't return a useful result
591  public
592  static <T> T readLines(File file, Charset charset, LineProcessor<T> callback) throws IOException {
593    return asCharSource(file, charset).readLines(callback);
594  }
595
596  /**
597   * Process the bytes of a file.
598   *
599   * <p>(If this seems too complicated, maybe you're looking for {@link #toByteArray}.)
600   *
601   * @param file the file to read
602   * @param processor the object to which the bytes of the file are passed.
603   * @return the result of the byte processor
604   * @throws IOException if an I/O error occurs
605   * @deprecated Prefer {@code asByteSource(file).read(processor)}. This method is scheduled to be
606   *     removed in October 2019.
607   */
608  @Beta
609  @Deprecated
610  @CanIgnoreReturnValue // some processors won't return a useful result
611  public
612  static <T> T readBytes(File file, ByteProcessor<T> processor) throws IOException {
613    return asByteSource(file).read(processor);
614  }
615
616  /**
617   * Computes the hash code of the {@code file} using {@code hashFunction}.
618   *
619   * @param file the file to read
620   * @param hashFunction the hash function to use to hash the data
621   * @return the {@link HashCode} of all of the bytes in the file
622   * @throws IOException if an I/O error occurs
623   * @since 12.0
624   * @deprecated Prefer {@code asByteSource(file).hash(hashFunction)}. This method is scheduled to
625   *     be removed in October 2019.
626   */
627  @Beta
628  @Deprecated
629  public
630  static HashCode hash(File file, HashFunction hashFunction) throws IOException {
631    return asByteSource(file).hash(hashFunction);
632  }
633
634  /**
635   * Fully maps a file read-only in to memory as per {@link
636   * FileChannel#map(java.nio.channels.FileChannel.MapMode, long, long)}.
637   *
638   * <p>Files are mapped from offset 0 to its length.
639   *
640   * <p>This only works for files ≤ {@link Integer#MAX_VALUE} bytes.
641   *
642   * @param file the file to map
643   * @return a read-only buffer reflecting {@code file}
644   * @throws FileNotFoundException if the {@code file} does not exist
645   * @throws IOException if an I/O error occurs
646   * @see FileChannel#map(MapMode, long, long)
647   * @since 2.0
648   */
649  @Beta
650  public static MappedByteBuffer map(File file) throws IOException {
651    checkNotNull(file);
652    return map(file, MapMode.READ_ONLY);
653  }
654
655  /**
656   * Fully maps a file in to memory as per {@link
657   * FileChannel#map(java.nio.channels.FileChannel.MapMode, long, long)} using the requested {@link
658   * MapMode}.
659   *
660   * <p>Files are mapped from offset 0 to its length.
661   *
662   * <p>This only works for files ≤ {@link Integer#MAX_VALUE} bytes.
663   *
664   * @param file the file to map
665   * @param mode the mode to use when mapping {@code file}
666   * @return a buffer reflecting {@code file}
667   * @throws FileNotFoundException if the {@code file} does not exist
668   * @throws IOException if an I/O error occurs
669   * @see FileChannel#map(MapMode, long, long)
670   * @since 2.0
671   */
672  @Beta
673  public static MappedByteBuffer map(File file, MapMode mode) throws IOException {
674    return mapInternal(file, mode, -1);
675  }
676
677  /**
678   * Maps a file in to memory as per {@link FileChannel#map(java.nio.channels.FileChannel.MapMode,
679   * long, long)} using the requested {@link MapMode}.
680   *
681   * <p>Files are mapped from offset 0 to {@code size}.
682   *
683   * <p>If the mode is {@link MapMode#READ_WRITE} and the file does not exist, it will be created
684   * with the requested {@code size}. Thus this method is useful for creating memory mapped files
685   * which do not yet exist.
686   *
687   * <p>This only works for files ≤ {@link Integer#MAX_VALUE} bytes.
688   *
689   * @param file the file to map
690   * @param mode the mode to use when mapping {@code file}
691   * @return a buffer reflecting {@code file}
692   * @throws IOException if an I/O error occurs
693   * @see FileChannel#map(MapMode, long, long)
694   * @since 2.0
695   */
696  @Beta
697  public static MappedByteBuffer map(File file, MapMode mode, long size) throws IOException {
698    checkArgument(size >= 0, "size (%s) may not be negative", size);
699    return mapInternal(file, mode, size);
700  }
701
702  private static MappedByteBuffer mapInternal(File file, MapMode mode, long size)
703      throws IOException {
704    checkNotNull(file);
705    checkNotNull(mode);
706
707    Closer closer = Closer.create();
708    try {
709      RandomAccessFile raf =
710          closer.register(new RandomAccessFile(file, mode == MapMode.READ_ONLY ? "r" : "rw"));
711      FileChannel channel = closer.register(raf.getChannel());
712      return channel.map(mode, 0, size == -1 ? channel.size() : size);
713    } catch (Throwable e) {
714      throw closer.rethrow(e);
715    } finally {
716      closer.close();
717    }
718  }
719
720  /**
721   * Returns the lexically cleaned form of the path name, <i>usually</i> (but not always) equivalent
722   * to the original. The following heuristics are used:
723   *
724   * <ul>
725   *   <li>empty string becomes .
726   *   <li>. stays as .
727   *   <li>fold out ./
728   *   <li>fold out ../ when possible
729   *   <li>collapse multiple slashes
730   *   <li>delete trailing slashes (unless the path is just "/")
731   * </ul>
732   *
733   * <p>These heuristics do not always match the behavior of the filesystem. In particular, consider
734   * the path {@code a/../b}, which {@code simplifyPath} will change to {@code b}. If {@code a} is a
735   * symlink to {@code x}, {@code a/../b} may refer to a sibling of {@code x}, rather than the
736   * sibling of {@code a} referred to by {@code b}.
737   *
738   * @since 11.0
739   */
740  @Beta
741  public static String simplifyPath(String pathname) {
742    checkNotNull(pathname);
743    if (pathname.length() == 0) {
744      return ".";
745    }
746
747    // split the path apart
748    Iterable<String> components = Splitter.on('/').omitEmptyStrings().split(pathname);
749    List<String> path = new ArrayList<>();
750
751    // resolve ., .., and //
752    for (String component : components) {
753      switch (component) {
754        case ".":
755          continue;
756        case "..":
757          if (path.size() > 0 && !path.get(path.size() - 1).equals("..")) {
758            path.remove(path.size() - 1);
759          } else {
760            path.add("..");
761          }
762          break;
763        default:
764          path.add(component);
765          break;
766      }
767    }
768
769    // put it back together
770    String result = Joiner.on('/').join(path);
771    if (pathname.charAt(0) == '/') {
772      result = "/" + result;
773    }
774
775    while (result.startsWith("/../")) {
776      result = result.substring(3);
777    }
778    if (result.equals("/..")) {
779      result = "/";
780    } else if ("".equals(result)) {
781      result = ".";
782    }
783
784    return result;
785  }
786
787  /**
788   * Returns the <a href="http://en.wikipedia.org/wiki/Filename_extension">file extension</a> for
789   * the given file name, or the empty string if the file has no extension. The result does not
790   * include the '{@code .}'.
791   *
792   * <p><b>Note:</b> This method simply returns everything after the last '{@code .}' in the file's
793   * name as determined by {@link File#getName}. It does not account for any filesystem-specific
794   * behavior that the {@link File} API does not already account for. For example, on NTFS it will
795   * report {@code "txt"} as the extension for the filename {@code "foo.exe:.txt"} even though NTFS
796   * will drop the {@code ":.txt"} part of the name when the file is actually created on the
797   * filesystem due to NTFS's <a href="https://goo.gl/vTpJi4">Alternate Data Streams</a>.
798   *
799   * @since 11.0
800   */
801  @Beta
802  public static String getFileExtension(String fullName) {
803    checkNotNull(fullName);
804    String fileName = new File(fullName).getName();
805    int dotIndex = fileName.lastIndexOf('.');
806    return (dotIndex == -1) ? "" : fileName.substring(dotIndex + 1);
807  }
808
809  /**
810   * Returns the file name without its <a
811   * href="http://en.wikipedia.org/wiki/Filename_extension">file extension</a> or path. This is
812   * similar to the {@code basename} unix command. The result does not include the '{@code .}'.
813   *
814   * @param file The name of the file to trim the extension from. This can be either a fully
815   *     qualified file name (including a path) or just a file name.
816   * @return The file name without its path or extension.
817   * @since 14.0
818   */
819  @Beta
820  public static String getNameWithoutExtension(String file) {
821    checkNotNull(file);
822    String fileName = new File(file).getName();
823    int dotIndex = fileName.lastIndexOf('.');
824    return (dotIndex == -1) ? fileName : fileName.substring(0, dotIndex);
825  }
826
827  /**
828   * Returns a {@link Traverser} instance for the file and directory tree. The returned traverser
829   * starts from a {@link File} and will return all files and directories it encounters.
830   *
831   * <p><b>Warning:</b> {@code File} provides no support for symbolic links, and as such there is no
832   * way to ensure that a symbolic link to a directory is not followed when traversing the tree. In
833   * this case, iterables created by this traverser could contain files that are outside of the
834   * given directory or even be infinite if there is a symbolic link loop.
835   *
836   * <p>If available, consider using {@link MoreFiles#fileTraverser()} instead. It behaves the same
837   * except that it doesn't follow symbolic links and returns {@code Path} instances.
838   *
839   * <p>If the {@link File} passed to one of the {@link Traverser} methods does not exist or is not
840   * a directory, no exception will be thrown and the returned {@link Iterable} will contain a
841   * single element: that file.
842   *
843   * <p>Example: {@code Files.fileTraverser().depthFirstPreOrder(new File("/"))} may return files
844   * with the following paths: {@code ["/", "/etc", "/etc/config.txt", "/etc/fonts", "/home",
845   * "/home/alice", ...]}
846   *
847   * @since 23.5
848   */
849  @Beta
850  public static Traverser<File> fileTraverser() {
851    return Traverser.forTree(FILE_TREE);
852  }
853
854  private static final SuccessorsFunction<File> FILE_TREE =
855      new SuccessorsFunction<File>() {
856        @Override
857        public Iterable<File> successors(File file) {
858          // check isDirectory() just because it may be faster than listFiles() on a non-directory
859          if (file.isDirectory()) {
860            File[] files = file.listFiles();
861            if (files != null) {
862              return Collections.unmodifiableList(Arrays.asList(files));
863            }
864          }
865
866          return ImmutableList.of();
867        }
868      };
869
870  /**
871   * Returns a predicate that returns the result of {@link File#isDirectory} on input files.
872   *
873   * @since 15.0
874   */
875  @Beta
876  public static Predicate<File> isDirectory() {
877    return FilePredicate.IS_DIRECTORY;
878  }
879
880  /**
881   * Returns a predicate that returns the result of {@link File#isFile} on input files.
882   *
883   * @since 15.0
884   */
885  @Beta
886  public static Predicate<File> isFile() {
887    return FilePredicate.IS_FILE;
888  }
889
890  private enum FilePredicate implements Predicate<File> {
891    IS_DIRECTORY {
892      @Override
893      public boolean apply(File file) {
894        return file.isDirectory();
895      }
896
897      @Override
898      public String toString() {
899        return "Files.isDirectory()";
900      }
901    },
902
903    IS_FILE {
904      @Override
905      public boolean apply(File file) {
906        return file.isFile();
907      }
908
909      @Override
910      public String toString() {
911        return "Files.isFile()";
912      }
913    }
914  }
915}