https://github.com/google/guava/guava: Guava is a suite of core and expanded libraries that include utility classes, google's collections, io classes, and much much more. 
/*
 * Copyright (C) 2007 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.io;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.io.FileWriteMode.APPEND;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.base.Joiner;
import com.google.common.base.Optional;
import com.google.common.base.Predicate;
import com.google.common.base.Splitter;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Lists;
import com.google.common.collect.TreeTraverser;
import com.google.common.graph.SuccessorsFunction;
import com.google.common.graph.Traverser;
import com.google.common.hash.HashCode;
import com.google.common.hash.HashFunction;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.RandomAccessFile;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.FileChannel.MapMode;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;


Provides utility methods for working with files. 
Path users will find similar utilities in MoreFiles and the JDK's Files class. 
Author:Chris Nokleberg, Colin Decker
Since:1.0
/**
 * Provides utility methods for working with {@linkplain File files}.
 *
 * <p>{@link java.nio.file.Path} users will find similar utilities in {@link MoreFiles} and the
 * JDK's {@link java.nio.file.Files} class.
 *
 * @author Chris Nokleberg
 * @author Colin Decker
 * @since 1.0
 */
@Beta
@GwtIncompatible
public final class Files {

  
Maximum loop count when creating temp directories. 
/** Maximum loop count when creating temp directories. */
  private static final int TEMP_DIR_ATTEMPTS = 10000;

  private Files() {}

  
Returns a buffered reader that reads from a file using the given character set.

Path equivalent: Files.newBufferedReader(Path, Charset). 
Params:
  • file – the file to read from
  • charset – the charset used to decode the input stream; see StandardCharsets for helpful predefined constants
Returns:the buffered reader
/**
   * Returns a buffered reader that reads from a file using the given character set.
   *
   * <p><b>{@link java.nio.file.Path} equivalent:</b> {@link
   * java.nio.file.Files#newBufferedReader(java.nio.file.Path, Charset)}.
   *
   * @param file the file to read from
   * @param charset the charset used to decode the input stream; see {@link StandardCharsets} for
   *     helpful predefined constants
   * @return the buffered reader
   */
  public static BufferedReader newReader(File file, Charset charset) throws FileNotFoundException {
    checkNotNull(file);
    checkNotNull(charset);
    return new BufferedReader(new InputStreamReader(new FileInputStream(file), charset));
  }

  
Returns a buffered writer that writes to a file using the given character set.

Path equivalent: Files.newBufferedWriter(Path, Charset, OpenOption...). 
Params:
  • file – the file to write to
  • charset – the charset used to encode the output stream; see StandardCharsets for helpful predefined constants
Returns:the buffered writer
/**
   * Returns a buffered writer that writes to a file using the given character set.
   *
   * <p><b>{@link java.nio.file.Path} equivalent:</b> {@link
   * java.nio.file.Files#newBufferedWriter(java.nio.file.Path, Charset,
   * java.nio.file.OpenOption...)}.
   *
   * @param file the file to write to
   * @param charset the charset used to encode the output stream; see {@link StandardCharsets} for
   *     helpful predefined constants
   * @return the buffered writer
   */
  public static BufferedWriter newWriter(File file, Charset charset) throws FileNotFoundException {
    checkNotNull(file);
    checkNotNull(charset);
    return new BufferedWriter(new OutputStreamWriter(new FileOutputStream(file), charset));
  }

  
Returns a new ByteSource for reading bytes from the given file. 
Since:14.0
/**
   * Returns a new {@link ByteSource} for reading bytes from the given file.
   *
   * @since 14.0
   */
  public static ByteSource asByteSource(File file) {
    return new FileByteSource(file);
  }

  private static final class FileByteSource extends ByteSource {

    private final File file;

    private FileByteSource(File file) {
      this.file = checkNotNull(file);
    }

    @Override
    public FileInputStream openStream() throws IOException {
      return new FileInputStream(file);
    }

    @Override
    public Optional<Long> sizeIfKnown() {
      if (file.isFile()) {
        return Optional.of(file.length());
      } else {
        return Optional.absent();
      }
    }

    @Override
    public long size() throws IOException {
      if (!file.isFile()) {
        throw new FileNotFoundException(file.toString());
      }
      return file.length();
    }

    @Override
    public byte[] read() throws IOException {
      Closer closer = Closer.create();
      try {
        FileInputStream in = closer.register(openStream());
        return ByteStreams.toByteArray(in, in.getChannel().size());
      } catch (Throwable e) {
        throw closer.rethrow(e);
      } finally {
        closer.close();
      }
    }

    @Override
    public String toString() {
      return "Files.asByteSource(" + file + ")";
    }
  }

  
Returns a new ByteSink for writing bytes to the given file. The given modes control how the file is opened for writing. When no mode is provided, the file will be truncated before writing. When the APPEND mode is provided, writes will append to the end of the file without truncating it. 
Since:14.0
/**
   * Returns a new {@link ByteSink} for writing bytes to the given file. The given {@code modes}
   * control how the file is opened for writing. When no mode is provided, the file will be
   * truncated before writing. When the {@link FileWriteMode#APPEND APPEND} mode is provided, writes
   * will append to the end of the file without truncating it.
   *
   * @since 14.0
   */
  public static ByteSink asByteSink(File file, FileWriteMode... modes) {
    return new FileByteSink(file, modes);
  }

  private static final class FileByteSink extends ByteSink {

    private final File file;
    private final ImmutableSet<FileWriteMode> modes;

    private FileByteSink(File file, FileWriteMode... modes) {
      this.file = checkNotNull(file);
      this.modes = ImmutableSet.copyOf(modes);
    }

    @Override
    public FileOutputStream openStream() throws IOException {
      return new FileOutputStream(file, modes.contains(APPEND));
    }

    @Override
    public String toString() {
      return "Files.asByteSink(" + file + ", " + modes + ")";
    }
  }

  
Returns a new CharSource for reading character data from the given file using the given character set. 
Since:14.0
/**
   * Returns a new {@link CharSource} for reading character data from the given file using the given
   * character set.
   *
   * @since 14.0
   */
  public static CharSource asCharSource(File file, Charset charset) {
    return asByteSource(file).asCharSource(charset);
  }

  
Returns a new CharSink for writing character data to the given file using the given character set. The given modes control how the file is opened for writing. When no mode is provided, the file will be truncated before writing. When the 
APPEND mode is provided, writes will append to the end of the file without truncating it. 
Since:14.0
/**
   * Returns a new {@link CharSink} for writing character data to the given file using the given
   * character set. The given {@code modes} control how the file is opened for writing. When no mode
   * is provided, the file will be truncated before writing. When the {@link FileWriteMode#APPEND
   * APPEND} mode is provided, writes will append to the end of the file without truncating it.
   *
   * @since 14.0
   */
  public static CharSink asCharSink(File file, Charset charset, FileWriteMode... modes) {
    return asByteSink(file, modes).asCharSink(charset);
  }

  
Reads all bytes from a file into a byte array.

Path equivalent: Files.readAllBytes. 
Params:
  • file – the file to read from
Throws:
Returns:a byte array containing all the bytes from file
/**
   * Reads all bytes from a file into a byte array.
   *
   * <p><b>{@link java.nio.file.Path} equivalent:</b> {@link java.nio.file.Files#readAllBytes}.
   *
   * @param file the file to read from
   * @return a byte array containing all the bytes from file
   * @throws IllegalArgumentException if the file is bigger than the largest possible byte array
   *     (2^31 - 1)
   * @throws IOException if an I/O error occurs
   */
  public static byte[] toByteArray(File file) throws IOException {
    return asByteSource(file).read();
  }

  
Reads all characters from a file into a String, using the given character set. 
Params:
  • file – the file to read from
  • charset – the charset used to decode the input stream; see StandardCharsets for helpful predefined constants
Throws:
Returns:a string containing all the characters from the file
Deprecated:Prefer asCharSource(file, charset).read(). This method is scheduled to be removed in January 2019.
/**
   * Reads all characters from a file into a {@link String}, using the given character set.
   *
   * @param file the file to read from
   * @param charset the charset used to decode the input stream; see {@link StandardCharsets} for
   *     helpful predefined constants
   * @return a string containing all the characters from the file
   * @throws IOException if an I/O error occurs
   * @deprecated Prefer {@code asCharSource(file, charset).read()}. This method is scheduled to be
   *     removed in January 2019.
   */
  @Deprecated
  public static String toString(File file, Charset charset) throws IOException {
    return asCharSource(file, charset).read();
  }

  
Overwrites a file with the contents of a byte array.

Path equivalent: Files.write(Path, byte[], OpenOption...). 
Params:
  • from – the bytes to write
  • to – the destination file
Throws:
/**
   * Overwrites a file with the contents of a byte array.
   *
   * <p><b>{@link java.nio.file.Path} equivalent:</b> {@link
   * java.nio.file.Files#write(java.nio.file.Path, byte[], java.nio.file.OpenOption...)}.
   *
   * @param from the bytes to write
   * @param to the destination file
   * @throws IOException if an I/O error occurs
   */
  public static void write(byte[] from, File to) throws IOException {
    asByteSink(to).write(from);
  }

  
Writes a character sequence (such as a string) to a file using the given character set.

Params:
  • from – the character sequence to write
  • to – the destination file
  • charset – the charset used to encode the output stream; see StandardCharsets for helpful predefined constants
Throws:
Deprecated:Prefer asCharSink(to, charset).write(from). This method is scheduled to be removed in January 2019.
/**
   * Writes a character sequence (such as a string) to a file using the given character set.
   *
   * @param from the character sequence to write
   * @param to the destination file
   * @param charset the charset used to encode the output stream; see {@link StandardCharsets} for
   *     helpful predefined constants
   * @throws IOException if an I/O error occurs
   * @deprecated Prefer {@code asCharSink(to, charset).write(from)}. This method is scheduled to be
   *     removed in January 2019.
   */
  @Deprecated
  public static void write(CharSequence from, File to, Charset charset) throws IOException {
    asCharSink(to, charset).write(from);
  }

  
Copies all bytes from a file to an output stream.

Path equivalent: Files.copy(Path, OutputStream). 
Params:
  • from – the source file
  • to – the output stream
Throws:
/**
   * Copies all bytes from a file to an output stream.
   *
   * <p><b>{@link java.nio.file.Path} equivalent:</b> {@link
   * java.nio.file.Files#copy(java.nio.file.Path, OutputStream)}.
   *
   * @param from the source file
   * @param to the output stream
   * @throws IOException if an I/O error occurs
   */
  public static void copy(File from, OutputStream to) throws IOException {
    asByteSource(from).copyTo(to);
  }

  
Copies all the bytes from one file to another.

Copying is not an atomic operation - in the case of an I/O error, power loss, process termination, or other problems, to may not be a complete copy of from. If you need to guard against those conditions, you should employ other file-level synchronization. 
Warning: If to represents an existing file, that file will be overwritten with the contents of from. If to and from refer to the same
file, the contents of that file will be deleted.

Path equivalent: Files.copy(Path, Path, CopyOption...). 
Params:
  • from – the source file
  • to – the destination file
Throws:
/**
   * Copies all the bytes from one file to another.
   *
   * <p>Copying is not an atomic operation - in the case of an I/O error, power loss, process
   * termination, or other problems, {@code to} may not be a complete copy of {@code from}. If you
   * need to guard against those conditions, you should employ other file-level synchronization.
   *
   * <p><b>Warning:</b> If {@code to} represents an existing file, that file will be overwritten
   * with the contents of {@code from}. If {@code to} and {@code from} refer to the <i>same</i>
   * file, the contents of that file will be deleted.
   *
   * <p><b>{@link java.nio.file.Path} equivalent:</b> {@link
   * java.nio.file.Files#copy(java.nio.file.Path, java.nio.file.Path, java.nio.file.CopyOption...)}.
   *
   * @param from the source file
   * @param to the destination file
   * @throws IOException if an I/O error occurs
   * @throws IllegalArgumentException if {@code from.equals(to)}
   */
  public static void copy(File from, File to) throws IOException {
    checkArgument(!from.equals(to), "Source %s and destination %s must be different", from, to);
    asByteSource(from).copyTo(asByteSink(to));
  }

  
Copies all characters from a file to an appendable object, using the given character set.

Params:
  • from – the source file
  • charset – the charset used to decode the input stream; see StandardCharsets for helpful predefined constants
  • to – the appendable object
Throws:
Deprecated:Prefer asCharSource(from, charset).copyTo(to). This method is scheduled to be removed in January 2019.
/**
   * Copies all characters from a file to an appendable object, using the given character set.
   *
   * @param from the source file
   * @param charset the charset used to decode the input stream; see {@link StandardCharsets} for
   *     helpful predefined constants
   * @param to the appendable object
   * @throws IOException if an I/O error occurs
   * @deprecated Prefer {@code asCharSource(from, charset).copyTo(to)}. This method is scheduled to
   *     be removed in January 2019.
   */
  @Deprecated
  public static void copy(File from, Charset charset, Appendable to) throws IOException {
    asCharSource(from, charset).copyTo(to);
  }

  
Appends a character sequence (such as a string) to a file using the given character set.

Params:
  • from – the character sequence to append
  • to – the destination file
  • charset – the charset used to encode the output stream; see StandardCharsets for helpful predefined constants
Throws:
Deprecated:Prefer asCharSink(to, charset, FileWriteMode.APPEND).write(from). This method is scheduled to be removed in January 2019.
/**
   * Appends a character sequence (such as a string) to a file using the given character set.
   *
   * @param from the character sequence to append
   * @param to the destination file
   * @param charset the charset used to encode the output stream; see {@link StandardCharsets} for
   *     helpful predefined constants
   * @throws IOException if an I/O error occurs
   * @deprecated Prefer {@code asCharSink(to, charset, FileWriteMode.APPEND).write(from)}. This
   *     method is scheduled to be removed in January 2019.
   */
  @Deprecated
  public static void append(CharSequence from, File to, Charset charset) throws IOException {
    asCharSink(to, charset, FileWriteMode.APPEND).write(from);
  }

  
Returns true if the given files exist, are not directories, and contain the same bytes.

Throws:
  • IOException – if an I/O error occurs
/**
   * Returns true if the given files exist, are not directories, and contain the same bytes.
   *
   * @throws IOException if an I/O error occurs
   */
  public static boolean equal(File file1, File file2) throws IOException {
    checkNotNull(file1);
    checkNotNull(file2);
    if (file1 == file2 || file1.equals(file2)) {
      return true;
    }

    /*
     * Some operating systems may return zero as the length for files denoting system-dependent
     * entities such as devices or pipes, in which case we must fall back on comparing the bytes
     * directly.
     */
    long len1 = file1.length();
    long len2 = file2.length();
    if (len1 != 0 && len2 != 0 && len1 != len2) {
      return false;
    }
    return asByteSource(file1).contentEquals(asByteSource(file2));
  }

  
Atomically creates a new directory somewhere beneath the system's temporary directory (as defined by the java.io.tmpdir system property), and returns its name. 
Use this method instead of File.createTempFile(String, String) when you wish to create a directory, not a regular file. A common pitfall is to call createTempFile, delete the file and create a directory in its place, but this leads a race condition which can be exploited to create security vulnerabilities, especially when executable files are to be written into the directory. 
This method assumes that the temporary volume is writable, has free inodes and free blocks,
and that it will not be called thousands of times per second.

Path equivalent: Files.createTempDirectory. 
Throws:
Returns:the newly-created directory
/**
   * Atomically creates a new directory somewhere beneath the system's temporary directory (as
   * defined by the {@code java.io.tmpdir} system property), and returns its name.
   *
   * <p>Use this method instead of {@link File#createTempFile(String, String)} when you wish to
   * create a directory, not a regular file. A common pitfall is to call {@code createTempFile},
   * delete the file and create a directory in its place, but this leads a race condition which can
   * be exploited to create security vulnerabilities, especially when executable files are to be
   * written into the directory.
   *
   * <p>This method assumes that the temporary volume is writable, has free inodes and free blocks,
   * and that it will not be called thousands of times per second.
   *
   * <p><b>{@link java.nio.file.Path} equivalent:</b> {@link
   * java.nio.file.Files#createTempDirectory}.
   *
   * @return the newly-created directory
   * @throws IllegalStateException if the directory could not be created
   */
  public static File createTempDir() {
    File baseDir = new File(System.getProperty("java.io.tmpdir"));
    String baseName = System.currentTimeMillis() + "-";

    for (int counter = 0; counter < TEMP_DIR_ATTEMPTS; counter++) {
      File tempDir = new File(baseDir, baseName + counter);
      if (tempDir.mkdir()) {
        return tempDir;
      }
    }
    throw new IllegalStateException(
        "Failed to create directory within "
            + TEMP_DIR_ATTEMPTS
            + " attempts (tried "
            + baseName
            + "0 to "
            + baseName
            + (TEMP_DIR_ATTEMPTS - 1)
            + ')');
  }

  
Creates an empty file or updates the last updated timestamp on the same as the unix command of
the same name.

Params:
  • file – the file to create or update
Throws:
/**
   * Creates an empty file or updates the last updated timestamp on the same as the unix command of
   * the same name.
   *
   * @param file the file to create or update
   * @throws IOException if an I/O error occurs
   */
  public static void touch(File file) throws IOException {
    checkNotNull(file);
    if (!file.createNewFile() && !file.setLastModified(System.currentTimeMillis())) {
      throw new IOException("Unable to update modification time of " + file);
    }
  }

  
Creates any necessary but nonexistent parent directories of the specified file. Note that if
this operation fails it may have succeeded in creating some (but not all) of the necessary
parent directories.

Throws:
  • IOException – if an I/O error occurs, or if any necessary but nonexistent parent
    directories of the specified file could not be created.
Since:4.0
/**
   * Creates any necessary but nonexistent parent directories of the specified file. Note that if
   * this operation fails it may have succeeded in creating some (but not all) of the necessary
   * parent directories.
   *
   * @throws IOException if an I/O error occurs, or if any necessary but nonexistent parent
   *     directories of the specified file could not be created.
   * @since 4.0
   */
  public static void createParentDirs(File file) throws IOException {
    checkNotNull(file);
    File parent = file.getCanonicalFile().getParentFile();
    if (parent == null) {
      /*
       * The given directory is a filesystem root. All zero of its ancestors exist. This doesn't
       * mean that the root itself exists -- consider x:\ on a Windows machine without such a drive
       * -- or even that the caller can create it, but this method makes no such guarantees even for
       * non-root files.
       */
      return;
    }
    parent.mkdirs();
    if (!parent.isDirectory()) {
      throw new IOException("Unable to create parent directories of " + file);
    }
  }

  
Moves a file from one path to another. This method can rename a file and/or move it to a different directory. In either case to must be the target path for the file itself; not just the new name for the file or the path to the new parent directory. 
Path equivalent: Files.move. 
Params:
  • from – the source file
  • to – the destination file
Throws:
/**
   * Moves a file from one path to another. This method can rename a file and/or move it to a
   * different directory. In either case {@code to} must be the target path for the file itself; not
   * just the new name for the file or the path to the new parent directory.
   *
   * <p><b>{@link java.nio.file.Path} equivalent:</b> {@link java.nio.file.Files#move}.
   *
   * @param from the source file
   * @param to the destination file
   * @throws IOException if an I/O error occurs
   * @throws IllegalArgumentException if {@code from.equals(to)}
   */
  public static void move(File from, File to) throws IOException {
    checkNotNull(from);
    checkNotNull(to);
    checkArgument(!from.equals(to), "Source %s and destination %s must be different", from, to);

    if (!from.renameTo(to)) {
      copy(from, to);
      if (!from.delete()) {
        if (!to.delete()) {
          throw new IOException("Unable to delete " + to);
        }
        throw new IOException("Unable to delete " + from);
      }
    }
  }

  
Reads the first line from a file. The line does not include line-termination characters, but
does include other leading and trailing whitespace.

Params:
  • file – the file to read from
  • charset – the charset used to decode the input stream; see StandardCharsets for helpful predefined constants
Throws:
Returns:the first line, or null if the file is empty
Deprecated:Prefer asCharSource(file, charset).readFirstLine(). This method is scheduled to be removed in January 2019.
/**
   * Reads the first line from a file. The line does not include line-termination characters, but
   * does include other leading and trailing whitespace.
   *
   * @param file the file to read from
   * @param charset the charset used to decode the input stream; see {@link StandardCharsets} for
   *     helpful predefined constants
   * @return the first line, or null if the file is empty
   * @throws IOException if an I/O error occurs
   * @deprecated Prefer {@code asCharSource(file, charset).readFirstLine()}. This method is
   *     scheduled to be removed in January 2019.
   */
  @Deprecated
  public static String readFirstLine(File file, Charset charset) throws IOException {
    return asCharSource(file, charset).readFirstLine();
  }

  
Reads all of the lines from a file. The lines do not include line-termination characters, but
do include other leading and trailing whitespace.

This method returns a mutable List. For an ImmutableList, use 
Files.asCharSource(file, charset).readLines(). 
Path equivalent: Files.readAllLines(Path, Charset). 
Params:
  • file – the file to read from
  • charset – the charset used to decode the input stream; see StandardCharsets for helpful predefined constants
Throws:
Returns:a mutable List containing all the lines
/**
   * Reads all of the lines from a file. The lines do not include line-termination characters, but
   * do include other leading and trailing whitespace.
   *
   * <p>This method returns a mutable {@code List}. For an {@code ImmutableList}, use {@code
   * Files.asCharSource(file, charset).readLines()}.
   *
   * <p><b>{@link java.nio.file.Path} equivalent:</b> {@link
   * java.nio.file.Files#readAllLines(java.nio.file.Path, Charset)}.
   *
   * @param file the file to read from
   * @param charset the charset used to decode the input stream; see {@link StandardCharsets} for
   *     helpful predefined constants
   * @return a mutable {@link List} containing all the lines
   * @throws IOException if an I/O error occurs
   */
  public static List<String> readLines(File file, Charset charset) throws IOException {
    // don't use asCharSource(file, charset).readLines() because that returns
    // an immutable list, which would change the behavior of this method
    return asCharSource(file, charset)
        .readLines(
            new LineProcessor<List<String>>() {
              final List<String> result = Lists.newArrayList();

              @Override
              public boolean processLine(String line) {
                result.add(line);
                return true;
              }

              @Override
              public List<String> getResult() {
                return result;
              }
            });
  }

  
Streams lines from a File, stopping when our callback returns false, or we have read all of the lines. 
Params:
  • file – the file to read from
  • charset – the charset used to decode the input stream; see StandardCharsets for helpful predefined constants
  • callback – the LineProcessor to use to handle the lines
Throws:
Returns:the output of processing the lines
Deprecated:Prefer asCharSource(file, charset).readLines(callback). This method is scheduled to be removed in January 2019.
/**
   * Streams lines from a {@link File}, stopping when our callback returns false, or we have read
   * all of the lines.
   *
   * @param file the file to read from
   * @param charset the charset used to decode the input stream; see {@link StandardCharsets} for
   *     helpful predefined constants
   * @param callback the {@link LineProcessor} to use to handle the lines
   * @return the output of processing the lines
   * @throws IOException if an I/O error occurs
   * @deprecated Prefer {@code asCharSource(file, charset).readLines(callback)}. This method is
   *     scheduled to be removed in January 2019.
   */
  @Deprecated
  @CanIgnoreReturnValue // some processors won't return a useful result
  public static <T> T readLines(File file, Charset charset, LineProcessor<T> callback)
      throws IOException {
    return asCharSource(file, charset).readLines(callback);
  }

  
Process the bytes of a file.

(If this seems too complicated, maybe you're looking for toByteArray.) 
Params:
  • file – the file to read
  • processor – the object to which the bytes of the file are passed.
Throws:
Returns:the result of the byte processor
Deprecated:Prefer asByteSource(file).read(processor). This method is scheduled to be removed in January 2019.
/**
   * Process the bytes of a file.
   *
   * <p>(If this seems too complicated, maybe you're looking for {@link #toByteArray}.)
   *
   * @param file the file to read
   * @param processor the object to which the bytes of the file are passed.
   * @return the result of the byte processor
   * @throws IOException if an I/O error occurs
   * @deprecated Prefer {@code asByteSource(file).read(processor)}. This method is scheduled to be
   *     removed in January 2019.
   */
  @Deprecated
  @CanIgnoreReturnValue // some processors won't return a useful result
  public static <T> T readBytes(File file, ByteProcessor<T> processor) throws IOException {
    return asByteSource(file).read(processor);
  }

  
Computes the hash code of the file using hashFunction. 
Params:
  • file – the file to read
  • hashFunction – the hash function to use to hash the data
Throws:
Returns:the HashCode of all of the bytes in the file
Since:12.0
Deprecated:Prefer asByteSource(file).hash(hashFunction). This method is scheduled to be removed in January 2019.
/**
   * Computes the hash code of the {@code file} using {@code hashFunction}.
   *
   * @param file the file to read
   * @param hashFunction the hash function to use to hash the data
   * @return the {@link HashCode} of all of the bytes in the file
   * @throws IOException if an I/O error occurs
   * @since 12.0
   * @deprecated Prefer {@code asByteSource(file).hash(hashFunction)}. This method is scheduled to
   *     be removed in January 2019.
   */
  @Deprecated
  public static HashCode hash(File file, HashFunction hashFunction) throws IOException {
    return asByteSource(file).hash(hashFunction);
  }

  
Fully maps a file read-only in to memory as per FileChannel.map(MapMode, long, long). 
Files are mapped from offset 0 to its length.

This only works for files ≤ Integer.MAX_VALUE bytes. 
Params:
  • file – the file to map
Throws:
See Also:
Returns:a read-only buffer reflecting file
Since:2.0
/**
   * Fully maps a file read-only in to memory as per {@link
   * FileChannel#map(java.nio.channels.FileChannel.MapMode, long, long)}.
   *
   * <p>Files are mapped from offset 0 to its length.
   *
   * <p>This only works for files ≤ {@link Integer#MAX_VALUE} bytes.
   *
   * @param file the file to map
   * @return a read-only buffer reflecting {@code file}
   * @throws FileNotFoundException if the {@code file} does not exist
   * @throws IOException if an I/O error occurs
   * @see FileChannel#map(MapMode, long, long)
   * @since 2.0
   */
  public static MappedByteBuffer map(File file) throws IOException {
    checkNotNull(file);
    return map(file, MapMode.READ_ONLY);
  }

  
Fully maps a file in to memory as per FileChannel.map(MapMode, long, long) using the requested MapMode. 
Files are mapped from offset 0 to its length.

This only works for files ≤ Integer.MAX_VALUE bytes. 
Params:
  • file – the file to map
  • mode – the mode to use when mapping file
Throws:
See Also:
Returns:a buffer reflecting file
Since:2.0
/**
   * Fully maps a file in to memory as per {@link
   * FileChannel#map(java.nio.channels.FileChannel.MapMode, long, long)} using the requested {@link
   * MapMode}.
   *
   * <p>Files are mapped from offset 0 to its length.
   *
   * <p>This only works for files ≤ {@link Integer#MAX_VALUE} bytes.
   *
   * @param file the file to map
   * @param mode the mode to use when mapping {@code file}
   * @return a buffer reflecting {@code file}
   * @throws FileNotFoundException if the {@code file} does not exist
   * @throws IOException if an I/O error occurs
   * @see FileChannel#map(MapMode, long, long)
   * @since 2.0
   */
  public static MappedByteBuffer map(File file, MapMode mode) throws IOException {
    checkNotNull(file);
    checkNotNull(mode);
    if (!file.exists()) {
      throw new FileNotFoundException(file.toString());
    }
    return map(file, mode, file.length());
  }

  
Maps a file in to memory as per FileChannel.map(MapMode, long, long) using the requested MapMode. 
Files are mapped from offset 0 to size. 
If the mode is MapMode.READ_WRITE and the file does not exist, it will be created with the requested size. Thus this method is useful for creating memory mapped files which do not yet exist. 
This only works for files ≤ Integer.MAX_VALUE bytes. 
Params:
  • file – the file to map
  • mode – the mode to use when mapping file
Throws:
See Also:
Returns:a buffer reflecting file
Since:2.0
/**
   * Maps a file in to memory as per {@link FileChannel#map(java.nio.channels.FileChannel.MapMode,
   * long, long)} using the requested {@link MapMode}.
   *
   * <p>Files are mapped from offset 0 to {@code size}.
   *
   * <p>If the mode is {@link MapMode#READ_WRITE} and the file does not exist, it will be created
   * with the requested {@code size}. Thus this method is useful for creating memory mapped files
   * which do not yet exist.
   *
   * <p>This only works for files ≤ {@link Integer#MAX_VALUE} bytes.
   *
   * @param file the file to map
   * @param mode the mode to use when mapping {@code file}
   * @return a buffer reflecting {@code file}
   * @throws IOException if an I/O error occurs
   * @see FileChannel#map(MapMode, long, long)
   * @since 2.0
   */
  public static MappedByteBuffer map(File file, MapMode mode, long size)
      throws FileNotFoundException, IOException {
    checkNotNull(file);
    checkNotNull(mode);

    Closer closer = Closer.create();
    try {
      RandomAccessFile raf =
          closer.register(new RandomAccessFile(file, mode == MapMode.READ_ONLY ? "r" : "rw"));
      return map(raf, mode, size);
    } catch (Throwable e) {
      throw closer.rethrow(e);
    } finally {
      closer.close();
    }
  }

  private static MappedByteBuffer map(RandomAccessFile raf, MapMode mode, long size)
      throws IOException {
    Closer closer = Closer.create();
    try {
      FileChannel channel = closer.register(raf.getChannel());
      return channel.map(mode, 0, size);
    } catch (Throwable e) {
      throw closer.rethrow(e);
    } finally {
      closer.close();
    }
  }

  
Returns the lexically cleaned form of the path name, usually (but not always) equivalent
to the original. The following heuristics are used:

    
  
  • empty string becomes .
  
  • . stays as .
  
  • fold out ./
  
  • fold out ../ when possible
  
  • collapse multiple slashes
  
  • delete trailing slashes (unless the path is just "/")



These heuristics do not always match the behavior of the filesystem. In particular, consider the path a/../b, which simplifyPath will change to b. If a is a symlink to x, a/../b may refer to a sibling of x, rather than the sibling of a referred to by b. 
Since:11.0
/**
   * Returns the lexically cleaned form of the path name, <i>usually</i> (but not always) equivalent
   * to the original. The following heuristics are used:
   *
   * <ul>
   *   <li>empty string becomes .
   *   <li>. stays as .
   *   <li>fold out ./
   *   <li>fold out ../ when possible
   *   <li>collapse multiple slashes
   *   <li>delete trailing slashes (unless the path is just "/")
   * </ul>
   *
   * <p>These heuristics do not always match the behavior of the filesystem. In particular, consider
   * the path {@code a/../b}, which {@code simplifyPath} will change to {@code b}. If {@code a} is a
   * symlink to {@code x}, {@code a/../b} may refer to a sibling of {@code x}, rather than the
   * sibling of {@code a} referred to by {@code b}.
   *
   * @since 11.0
   */
  public static String simplifyPath(String pathname) {
    checkNotNull(pathname);
    if (pathname.length() == 0) {
      return ".";
    }

    // split the path apart
    Iterable<String> components = Splitter.on('/').omitEmptyStrings().split(pathname);
    List<String> path = new ArrayList<>();

    // resolve ., .., and //
    for (String component : components) {
      switch (component) {
        case ".":
          continue;
        case "..":
          if (path.size() > 0 && !path.get(path.size() - 1).equals("..")) {
            path.remove(path.size() - 1);
          } else {
            path.add("..");
          }
          break;
        default:
          path.add(component);
          break;
      }
    }

    // put it back together
    String result = Joiner.on('/').join(path);
    if (pathname.charAt(0) == '/') {
      result = "/" + result;
    }

    while (result.startsWith("/../")) {
      result = result.substring(3);
    }
    if (result.equals("/..")) {
      result = "/";
    } else if ("".equals(result)) {
      result = ".";
    }

    return result;
  }

  
Returns the file extension for the given file name, or the empty string if the file has no extension. The result does not include the '.'. 
Note: This method simply returns everything after the last '.' in the file's name as determined by File.getName. It does not account for any filesystem-specific behavior that the File API does not already account for. For example, on NTFS it will report "txt" as the extension for the filename "foo.exe:.txt" even though NTFS will drop the ":.txt" part of the name when the file is actually created on the filesystem due to NTFS's Alternate Data Streams.

Since:11.0
/**
   * Returns the <a href="http://en.wikipedia.org/wiki/Filename_extension">file extension</a> for
   * the given file name, or the empty string if the file has no extension. The result does not
   * include the '{@code .}'.
   *
   * <p><b>Note:</b> This method simply returns everything after the last '{@code .}' in the file's
   * name as determined by {@link File#getName}. It does not account for any filesystem-specific
   * behavior that the {@link File} API does not already account for. For example, on NTFS it will
   * report {@code "txt"} as the extension for the filename {@code "foo.exe:.txt"} even though NTFS
   * will drop the {@code ":.txt"} part of the name when the file is actually created on the
   * filesystem due to NTFS's <a href="https://goo.gl/vTpJi4">Alternate Data Streams</a>.
   *
   * @since 11.0
   */
  public static String getFileExtension(String fullName) {
    checkNotNull(fullName);
    String fileName = new File(fullName).getName();
    int dotIndex = fileName.lastIndexOf('.');
    return (dotIndex == -1) ? "" : fileName.substring(dotIndex + 1);
  }

  
Returns the file name without its file extension or path. This is similar to the basename unix command. The result does not include the '.'. 
Params:
  • file – The name of the file to trim the extension from. This can be either a fully
    qualified file name (including a path) or just a file name.
Returns:The file name without its path or extension.
Since:14.0
/**
   * Returns the file name without its <a
   * href="http://en.wikipedia.org/wiki/Filename_extension">file extension</a> or path. This is
   * similar to the {@code basename} unix command. The result does not include the '{@code .}'.
   *
   * @param file The name of the file to trim the extension from. This can be either a fully
   *     qualified file name (including a path) or just a file name.
   * @return The file name without its path or extension.
   * @since 14.0
   */
  public static String getNameWithoutExtension(String file) {
    checkNotNull(file);
    String fileName = new File(file).getName();
    int dotIndex = fileName.lastIndexOf('.');
    return (dotIndex == -1) ? fileName : fileName.substring(0, dotIndex);
  }

  
Returns a TreeTraverser instance for File trees. 
Warning: File provides no support for symbolic links, and as such there is no way to ensure that a symbolic link to a directory is not followed when traversing the tree. In this case, iterables created by this traverser could contain files that are outside of the given directory or even be infinite if there is a symbolic link loop. 
Since:15.0
Deprecated:The returned TreeTraverser type is deprecated. Use the replacement method fileTraverser() instead with the same semantics as this method.
/**
   * Returns a {@link TreeTraverser} instance for {@link File} trees.
   *
   * <p><b>Warning:</b> {@code File} provides no support for symbolic links, and as such there is no
   * way to ensure that a symbolic link to a directory is not followed when traversing the tree. In
   * this case, iterables created by this traverser could contain files that are outside of the
   * given directory or even be infinite if there is a symbolic link loop.
   *
   * @since 15.0
   * @deprecated The returned {@link TreeTraverser} type is deprecated. Use the replacement method
   *     {@link #fileTraverser()} instead with the same semantics as this method.
   */
  @Deprecated
  static TreeTraverser<File> fileTreeTraverser() {
    return FILE_TREE_TRAVERSER;
  }

  private static final TreeTraverser<File> FILE_TREE_TRAVERSER =
      new TreeTraverser<File>() {
        @Override
        public Iterable<File> children(File file) {
          return fileTreeChildren(file);
        }

        @Override
        public String toString() {
          return "Files.fileTreeTraverser()";
        }
      };

  
Returns a Traverser instance for the file and directory tree. The returned traverser starts from a File and will return all files and directories it encounters. 
Warning: File provides no support for symbolic links, and as such there is no way to ensure that a symbolic link to a directory is not followed when traversing the tree. In this case, iterables created by this traverser could contain files that are outside of the given directory or even be infinite if there is a symbolic link loop. 
If available, consider using MoreFiles.fileTraverser() instead. It behaves the same except that it doesn't follow symbolic links and returns Path instances. 
If the File passed to one of the Traverser methods does not exist or is not a directory, no exception will be thrown and the returned Iterable will contain a single element: that file. 
Example: Files.fileTraverser().breadthFirst("/") may return files with the following paths: ["/", "/etc", "/home", "/usr", "/etc/config.txt", "/etc/fonts", ...] 
Since:23.5
/**
   * Returns a {@link Traverser} instance for the file and directory tree. The returned traverser
   * starts from a {@link File} and will return all files and directories it encounters.
   *
   * <p><b>Warning:</b> {@code File} provides no support for symbolic links, and as such there is no
   * way to ensure that a symbolic link to a directory is not followed when traversing the tree. In
   * this case, iterables created by this traverser could contain files that are outside of the
   * given directory or even be infinite if there is a symbolic link loop.
   *
   * <p>If available, consider using {@link MoreFiles#fileTraverser()} instead. It behaves the same
   * except that it doesn't follow symbolic links and returns {@code Path} instances.
   *
   * <p>If the {@link File} passed to one of the {@link Traverser} methods does not exist or is not
   * a directory, no exception will be thrown and the returned {@link Iterable} will contain a
   * single element: that file.
   *
   * <p>Example: {@code Files.fileTraverser().breadthFirst("/")} may return files with the following
   * paths: {@code ["/", "/etc", "/home", "/usr", "/etc/config.txt", "/etc/fonts", ...]}
   *
   * @since 23.5
   */
  public static Traverser<File> fileTraverser() {
    return Traverser.forTree(FILE_TREE);
  }

  private static final SuccessorsFunction<File> FILE_TREE =
      new SuccessorsFunction<File>() {
        @Override
        public Iterable<File> successors(File file) {
          return fileTreeChildren(file);
        }
      };

  private static Iterable<File> fileTreeChildren(File file) {
    // check isDirectory() just because it may be faster than listFiles() on a non-directory
    if (file.isDirectory()) {
      File[] files = file.listFiles();
      if (files != null) {
        return Collections.unmodifiableList(Arrays.asList(files));
      }
    }

    return Collections.emptyList();
  }

  
Returns a predicate that returns the result of File.isDirectory on input files. 
Since:15.0
/**
   * Returns a predicate that returns the result of {@link File#isDirectory} on input files.
   *
   * @since 15.0
   */
  public static Predicate<File> isDirectory() {
    return FilePredicate.IS_DIRECTORY;
  }

  
Returns a predicate that returns the result of File.isFile on input files. 
Since:15.0
/**
   * Returns a predicate that returns the result of {@link File#isFile} on input files.
   *
   * @since 15.0
   */
  public static Predicate<File> isFile() {
    return FilePredicate.IS_FILE;
  }

  private enum FilePredicate implements Predicate<File> {
    IS_DIRECTORY {
      @Override
      public boolean apply(File file) {
        return file.isDirectory();
      }

      @Override
      public String toString() {
        return "Files.isDirectory()";
      }
    },

    IS_FILE {
      @Override
      public boolean apply(File file) {
        return file.isFile();
      }

      @Override
      public String toString() {
        return "Files.isFile()";
      }
    }
  }
}