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) 2013 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.checkNotNull;
import static java.nio.file.LinkOption.NOFOLLOW_LINKS;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.base.Optional;
import com.google.common.base.Predicate;
import com.google.common.collect.ImmutableList;
import com.google.common.graph.SuccessorsFunction;
import com.google.common.graph.Traverser;
import com.google.j2objc.annotations.J2ObjCIncompatible;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.nio.channels.Channels;
import java.nio.channels.SeekableByteChannel;
import java.nio.charset.Charset;
import java.nio.file.DirectoryIteratorException;
import java.nio.file.DirectoryStream;
import java.nio.file.FileAlreadyExistsException;
import java.nio.file.FileSystemException;
import java.nio.file.Files;
import java.nio.file.LinkOption;
import java.nio.file.NoSuchFileException;
import java.nio.file.NotDirectoryException;
import java.nio.file.OpenOption;
import java.nio.file.Path;
import java.nio.file.SecureDirectoryStream;
import java.nio.file.StandardOpenOption;
import java.nio.file.attribute.BasicFileAttributeView;
import java.nio.file.attribute.BasicFileAttributes;
import java.nio.file.attribute.FileAttribute;
import java.nio.file.attribute.FileTime;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.stream.Stream;
import org.checkerframework.checker.nullness.qual.Nullable;


Static utilities for use with Path instances, intended to complement Files. 
Many methods provided by Guava's Files class for File instances are now available via the JDK's Files class for Path - check the JDK's class if a sibling method from Files appears to be missing from this class. 
Author:Colin Decker
Since:21.0
/**
 * Static utilities for use with {@link Path} instances, intended to complement {@link Files}.
 *
 * <p>Many methods provided by Guava's {@code Files} class for {@link java.io.File} instances are
 * now available via the JDK's {@link java.nio.file.Files} class for {@code Path} - check the JDK's
 * class if a sibling method from {@code Files} appears to be missing from this class.
 *
 * @since 21.0
 * @author Colin Decker
 */
@Beta
@GwtIncompatible
@J2ObjCIncompatible // java.nio.file
public final class MoreFiles {

  private MoreFiles() {}

  
Returns a view of the given path as a ByteSource. 
Any open options provided are used when opening streams to the file and may affect the behavior of the returned source and the streams it provides. See StandardOpenOption for the standard options that may be provided. Providing no options is equivalent to providing the READ option. 
/**
   * Returns a view of the given {@code path} as a {@link ByteSource}.
   *
   * <p>Any {@linkplain OpenOption open options} provided are used when opening streams to the file
   * and may affect the behavior of the returned source and the streams it provides. See {@link
   * StandardOpenOption} for the standard options that may be provided. Providing no options is
   * equivalent to providing the {@link StandardOpenOption#READ READ} option.
   */
  public static ByteSource asByteSource(Path path, OpenOption... options) {
    return new PathByteSource(path, options);
  }

  private static final class PathByteSource extends ByteSource {

    private static final LinkOption[] FOLLOW_LINKS = {};

    private final Path path;
    private final OpenOption[] options;
    private final boolean followLinks;

    private PathByteSource(Path path, OpenOption... options) {
      this.path = checkNotNull(path);
      this.options = options.clone();
      this.followLinks = followLinks(this.options);
      // TODO(cgdecker): validate the provided options... for example, just WRITE seems wrong
    }

    private static boolean followLinks(OpenOption[] options) {
      for (OpenOption option : options) {
        if (option == NOFOLLOW_LINKS) {
          return false;
        }
      }
      return true;
    }

    @Override
    public InputStream openStream() throws IOException {
      return Files.newInputStream(path, options);
    }

    private BasicFileAttributes readAttributes() throws IOException {
      return Files.readAttributes(
          path,
          BasicFileAttributes.class,
          followLinks ? FOLLOW_LINKS : new LinkOption[] {NOFOLLOW_LINKS});
    }

    @Override
    public Optional<Long> sizeIfKnown() {
      BasicFileAttributes attrs;
      try {
        attrs = readAttributes();
      } catch (IOException e) {
        // Failed to get attributes; we don't know the size.
        return Optional.absent();
      }

      // Don't return a size for directories or symbolic links; their sizes are implementation
      // specific and they can't be read as bytes using the read methods anyway.
      if (attrs.isDirectory() || attrs.isSymbolicLink()) {
        return Optional.absent();
      }

      return Optional.of(attrs.size());
    }

    @Override
    public long size() throws IOException {
      BasicFileAttributes attrs = readAttributes();

      // Don't return a size for directories or symbolic links; their sizes are implementation
      // specific and they can't be read as bytes using the read methods anyway.
      if (attrs.isDirectory()) {
        throw new IOException("can't read: is a directory");
      } else if (attrs.isSymbolicLink()) {
        throw new IOException("can't read: is a symbolic link");
      }

      return attrs.size();
    }

    @Override
    public byte[] read() throws IOException {
      try (SeekableByteChannel channel = Files.newByteChannel(path, options)) {
        return ByteStreams.toByteArray(Channels.newInputStream(channel), channel.size());
      }
    }

    @Override
    public CharSource asCharSource(Charset charset) {
      if (options.length == 0) {
        // If no OpenOptions were passed, delegate to Files.lines, which could have performance
        // advantages. (If OpenOptions were passed we can't, because Files.lines doesn't have an
        // overload taking OpenOptions, meaning we can't guarantee the same behavior w.r.t. things
        // like following/not following symlinks.
        return new AsCharSource(charset) {
          @SuppressWarnings("FilesLinesLeak") // the user needs to close it in this case
          @Override
          public Stream<String> lines() throws IOException {
            return Files.lines(path, charset);
          }
        };
      }

      return super.asCharSource(charset);
    }

    @Override
    public String toString() {
      return "MoreFiles.asByteSource(" + path + ", " + Arrays.toString(options) + ")";
    }
  }

  
Returns a view of the given path as a ByteSink. 
Any open options provided are used when opening streams to the file and may affect the behavior of the returned sink and the streams it provides. See StandardOpenOption for the standard options that may be provided. Providing no options is equivalent to providing the CREATE, TRUNCATE_EXISTING and 
WRITE options. 
/**
   * Returns a view of the given {@code path} as a {@link ByteSink}.
   *
   * <p>Any {@linkplain OpenOption open options} provided are used when opening streams to the file
   * and may affect the behavior of the returned sink and the streams it provides. See {@link
   * StandardOpenOption} for the standard options that may be provided. Providing no options is
   * equivalent to providing the {@link StandardOpenOption#CREATE CREATE}, {@link
   * StandardOpenOption#TRUNCATE_EXISTING TRUNCATE_EXISTING} and {@link StandardOpenOption#WRITE
   * WRITE} options.
   */
  public static ByteSink asByteSink(Path path, OpenOption... options) {
    return new PathByteSink(path, options);
  }

  private static final class PathByteSink extends ByteSink {

    private final Path path;
    private final OpenOption[] options;

    private PathByteSink(Path path, OpenOption... options) {
      this.path = checkNotNull(path);
      this.options = options.clone();
      // TODO(cgdecker): validate the provided options... for example, just READ seems wrong
    }

    @Override
    public OutputStream openStream() throws IOException {
      return Files.newOutputStream(path, options);
    }

    @Override
    public String toString() {
      return "MoreFiles.asByteSink(" + path + ", " + Arrays.toString(options) + ")";
    }
  }

  
Returns a view of the given path as a CharSource using the given 
charset. 
Any open options provided are used when opening streams to the file and may affect the behavior of the returned source and the streams it provides. See StandardOpenOption for the standard options that may be provided. Providing no options is equivalent to providing the READ option. 
/**
   * Returns a view of the given {@code path} as a {@link CharSource} using the given {@code
   * charset}.
   *
   * <p>Any {@linkplain OpenOption open options} provided are used when opening streams to the file
   * and may affect the behavior of the returned source and the streams it provides. See {@link
   * StandardOpenOption} for the standard options that may be provided. Providing no options is
   * equivalent to providing the {@link StandardOpenOption#READ READ} option.
   */
  public static CharSource asCharSource(Path path, Charset charset, OpenOption... options) {
    return asByteSource(path, options).asCharSource(charset);
  }

  
Returns a view of the given path as a CharSink using the given charset. 
Any open options provided are used when opening streams to the file and may affect the behavior of the returned sink and the streams it provides. See StandardOpenOption for the standard options that may be provided. Providing no options is equivalent to providing the CREATE, TRUNCATE_EXISTING and 
WRITE options. 
/**
   * Returns a view of the given {@code path} as a {@link CharSink} using the given {@code charset}.
   *
   * <p>Any {@linkplain OpenOption open options} provided are used when opening streams to the file
   * and may affect the behavior of the returned sink and the streams it provides. See {@link
   * StandardOpenOption} for the standard options that may be provided. Providing no options is
   * equivalent to providing the {@link StandardOpenOption#CREATE CREATE}, {@link
   * StandardOpenOption#TRUNCATE_EXISTING TRUNCATE_EXISTING} and {@link StandardOpenOption#WRITE
   * WRITE} options.
   */
  public static CharSink asCharSink(Path path, Charset charset, OpenOption... options) {
    return asByteSink(path, options).asCharSink(charset);
  }

  
Returns an immutable list of paths to the files contained in the given directory.

Throws:
  • NoSuchFileException – if the file does not exist (optional specific exception)
  • NotDirectoryException – if the file could not be opened because it is not a directory
    (optional specific exception)
  • IOException – if an I/O error occurs
/**
   * Returns an immutable list of paths to the files contained in the given directory.
   *
   * @throws NoSuchFileException if the file does not exist <i>(optional specific exception)</i>
   * @throws NotDirectoryException if the file could not be opened because it is not a directory
   *     <i>(optional specific exception)</i>
   * @throws IOException if an I/O error occurs
   */
  public static ImmutableList<Path> listFiles(Path dir) throws IOException {
    try (DirectoryStream<Path> stream = Files.newDirectoryStream(dir)) {
      return ImmutableList.copyOf(stream);
    } catch (DirectoryIteratorException e) {
      throw e.getCause();
    }
  }

  
Returns a Traverser instance for the file and directory tree. The returned traverser starts from a Path and will return all files and directories it encounters. 
The returned traverser attempts to avoid following symbolic links to directories. However,
the traverser cannot guarantee that it will not follow symbolic links to directories as it is
possible for a directory to be replaced with a symbolic link between checking if the file is a
directory and actually reading the contents of that directory.

If the Path passed to one of the traversal methods does not exist or is not a directory, no exception will be thrown and the returned Iterable will contain a single element: that path. 
DirectoryIteratorException may be thrown when iterating Iterable instances created by this traverser if an IOException is thrown by a call to listFiles(Path). 
Example: MoreFiles.fileTraverser().depthFirstPreOrder(Paths.get("/")) may return the following paths: ["/", "/etc", "/etc/config.txt", "/etc/fonts", "/home", "/home/alice",
...] 
Since:23.5
/**
   * Returns a {@link Traverser} instance for the file and directory tree. The returned traverser
   * starts from a {@link Path} and will return all files and directories it encounters.
   *
   * <p>The returned traverser attempts to avoid following symbolic links to directories. However,
   * the traverser cannot guarantee that it will not follow symbolic links to directories as it is
   * possible for a directory to be replaced with a symbolic link between checking if the file is a
   * directory and actually reading the contents of that directory.
   *
   * <p>If the {@link Path} passed to one of the traversal 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 path.
   *
   * <p>{@link DirectoryIteratorException} may be thrown when iterating {@link Iterable} instances
   * created by this traverser if an {@link IOException} is thrown by a call to {@link
   * #listFiles(Path)}.
   *
   * <p>Example: {@code MoreFiles.fileTraverser().depthFirstPreOrder(Paths.get("/"))} may return the
   * following paths: {@code ["/", "/etc", "/etc/config.txt", "/etc/fonts", "/home", "/home/alice",
   * ...]}
   *
   * @since 23.5
   */
  public static Traverser<Path> fileTraverser() {
    return Traverser.forTree(FILE_TREE);
  }

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

  private static Iterable<Path> fileTreeChildren(Path dir) {
    if (Files.isDirectory(dir, NOFOLLOW_LINKS)) {
      try {
        return listFiles(dir);
      } catch (IOException e) {
        // the exception thrown when iterating a DirectoryStream if an I/O exception occurs
        throw new DirectoryIteratorException(e);
      }
    }
    return ImmutableList.of();
  }

  
Returns a predicate that returns the result of Files.isDirectory(Path, LinkOption...) on input paths with the given link options. 
/**
   * Returns a predicate that returns the result of {@link java.nio.file.Files#isDirectory(Path,
   * LinkOption...)} on input paths with the given link options.
   */
  public static Predicate<Path> isDirectory(LinkOption... options) {
    final LinkOption[] optionsCopy = options.clone();
    return new Predicate<Path>() {
      @Override
      public boolean apply(Path input) {
        return Files.isDirectory(input, optionsCopy);
      }

      @Override
      public String toString() {
        return "MoreFiles.isDirectory(" + Arrays.toString(optionsCopy) + ")";
      }
    };
  }

  
Returns whether or not the file with the given name in the given dir is a directory. 
/** Returns whether or not the file with the given name in the given dir is a directory. */
  private static boolean isDirectory(
      SecureDirectoryStream<Path> dir, Path name, LinkOption... options) throws IOException {
    return dir.getFileAttributeView(name, BasicFileAttributeView.class, options)
        .readAttributes()
        .isDirectory();
  }

  
Returns a predicate that returns the result of Files.isRegularFile(Path, LinkOption...) on input paths with the given link options. 
/**
   * Returns a predicate that returns the result of {@link java.nio.file.Files#isRegularFile(Path,
   * LinkOption...)} on input paths with the given link options.
   */
  public static Predicate<Path> isRegularFile(LinkOption... options) {
    final LinkOption[] optionsCopy = options.clone();
    return new Predicate<Path>() {
      @Override
      public boolean apply(Path input) {
        return Files.isRegularFile(input, optionsCopy);
      }

      @Override
      public String toString() {
        return "MoreFiles.isRegularFile(" + Arrays.toString(optionsCopy) + ")";
      }
    };
  }

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

Throws:
  • IOException – if an I/O error occurs
Since:22.0
/**
   * Returns true if the files located by the given paths exist, are not directories, and contain
   * the same bytes.
   *
   * @throws IOException if an I/O error occurs
   * @since 22.0
   */
  public static boolean equal(Path path1, Path path2) throws IOException {
    checkNotNull(path1);
    checkNotNull(path2);
    if (Files.isSameFile(path1, path2)) {
      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.
     */
    ByteSource source1 = asByteSource(path1);
    ByteSource source2 = asByteSource(path2);
    long len1 = source1.sizeIfKnown().or(0L);
    long len2 = source2.sizeIfKnown().or(0L);
    if (len1 != 0 && len2 != 0 && len1 != len2) {
      return false;
    }
    return source1.contentEquals(source2);
  }

  
Like the unix command of the same name, creates an empty file or updates the last modified
timestamp of the existing file at the given path to the current system time.

/**
   * Like the unix command of the same name, creates an empty file or updates the last modified
   * timestamp of the existing file at the given path to the current system time.
   */
  @SuppressWarnings("GoodTime") // reading system time without TimeSource
  public static void touch(Path path) throws IOException {
    checkNotNull(path);

    try {
      Files.setLastModifiedTime(path, FileTime.fromMillis(System.currentTimeMillis()));
    } catch (NoSuchFileException e) {
      try {
        Files.createFile(path);
      } catch (FileAlreadyExistsException ignore) {
        // The file didn't exist when we called setLastModifiedTime, but it did when we called
        // createFile, so something else created the file in between. The end result is
        // what we wanted: a new file that probably has its last modified time set to approximately
        // now. Or it could have an arbitrary last modified time set by the creator, but that's no
        // different than if another process set its last modified time to something else after we
        // created it here.
      }
    }
  }

  
Creates any necessary but nonexistent parent directories of the specified path. Note that if this operation fails, it may have succeeded in creating some (but not all) of the necessary parent directories. The parent directory is created with the given attrs. 
Throws:
  • IOException – if an I/O error occurs, or if any necessary but nonexistent parent
    directories of the specified file could not be created.
/**
   * Creates any necessary but nonexistent parent directories of the specified path. Note that if
   * this operation fails, it may have succeeded in creating some (but not all) of the necessary
   * parent directories. The parent directory is created with the given {@code attrs}.
   *
   * @throws IOException if an I/O error occurs, or if any necessary but nonexistent parent
   *     directories of the specified file could not be created.
   */
  public static void createParentDirectories(Path path, FileAttribute<?>... attrs)
      throws IOException {
    // Interestingly, unlike File.getCanonicalFile(), Path/Files provides no way of getting the
    // canonical (absolute, normalized, symlinks resolved, etc.) form of a path to a nonexistent
    // file. getCanonicalFile() can at least get the canonical form of the part of the path which
    // actually exists and then append the normalized remainder of the path to that.
    Path normalizedAbsolutePath = path.toAbsolutePath().normalize();
    Path parent = normalizedAbsolutePath.getParent();
    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;
    }

    // Check if the parent is a directory first because createDirectories will fail if the parent
    // exists and is a symlink to a directory... we'd like for this to succeed in that case.
    // (I'm kind of surprised that createDirectories would fail in that case; doesn't seem like
    // what you'd want to happen.)
    if (!Files.isDirectory(parent)) {
      Files.createDirectories(parent, attrs);
      if (!Files.isDirectory(parent)) {
        throw new IOException("Unable to create parent directories of " + path);
      }
    }
  }

  
Returns the file extension for the file at the given path, 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 Path.getFileName. It does not account for any filesystem-specific behavior that the Path 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.

/**
   * Returns the <a href="http://en.wikipedia.org/wiki/Filename_extension">file extension</a> for
   * the file at the given path, 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 Path#getFileName}. It does not account for any filesystem-specific
   * behavior that the {@link Path} 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>.
   */
  public static String getFileExtension(Path path) {
    Path name = path.getFileName();

    // null for empty paths and root-only paths
    if (name == null) {
      return "";
    }

    String fileName = name.toString();
    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 '.'. 
/**
   * 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 .}'.
   */
  public static String getNameWithoutExtension(Path path) {
    Path name = path.getFileName();

    // null for empty paths and root-only paths
    if (name == null) {
      return "";
    }

    String fileName = name.toString();
    int dotIndex = fileName.lastIndexOf('.');
    return dotIndex == -1 ? fileName : fileName.substring(0, dotIndex);
  }

  
Deletes the file or directory at the given path recursively. Deletes symbolic links, not their targets (subject to the caveat below). 
If an I/O exception occurs attempting to read, open or delete any file under the given directory, this method skips that file and continues. All such exceptions are collected and, after attempting to delete all files, an IOException is thrown containing those exceptions as suppressed exceptions. 
Warning: Security of recursive deletes


On a file system that supports symbolic links and does not support SecureDirectoryStream, it is possible for a recursive delete to delete files and directories that are outside the directory being deleted. This can happen if, after checking that a
file is a directory (and not a symbolic link), that directory is replaced by a symbolic link to
an outside directory before the call that opens the directory to read its entries.

By default, this method throws InsecureRecursiveDeleteException if it can't guarantee the security of recursive deletes. If you wish to allow the recursive deletes anyway, pass RecursiveDeleteOption.ALLOW_INSECURE to this method to override that behavior. 
Throws:
/**
   * Deletes the file or directory at the given {@code path} recursively. Deletes symbolic links,
   * not their targets (subject to the caveat below).
   *
   * <p>If an I/O exception occurs attempting to read, open or delete any file under the given
   * directory, this method skips that file and continues. All such exceptions are collected and,
   * after attempting to delete all files, an {@code IOException} is thrown containing those
   * exceptions as {@linkplain Throwable#getSuppressed() suppressed exceptions}.
   *
   * <h2>Warning: Security of recursive deletes</h2>
   *
   * <p>On a file system that supports symbolic links and does <i>not</i> support {@link
   * SecureDirectoryStream}, it is possible for a recursive delete to delete files and directories
   * that are <i>outside</i> the directory being deleted. This can happen if, after checking that a
   * file is a directory (and not a symbolic link), that directory is replaced by a symbolic link to
   * an outside directory before the call that opens the directory to read its entries.
   *
   * <p>By default, this method throws {@link InsecureRecursiveDeleteException} if it can't
   * guarantee the security of recursive deletes. If you wish to allow the recursive deletes anyway,
   * pass {@link RecursiveDeleteOption#ALLOW_INSECURE} to this method to override that behavior.
   *
   * @throws NoSuchFileException if {@code path} does not exist <i>(optional specific exception)</i>
   * @throws InsecureRecursiveDeleteException if the security of recursive deletes can't be
   *     guaranteed for the file system and {@link RecursiveDeleteOption#ALLOW_INSECURE} was not
   *     specified
   * @throws IOException if {@code path} or any file in the subtree rooted at it can't be deleted
   *     for any reason
   */
  public static void deleteRecursively(Path path, RecursiveDeleteOption... options)
      throws IOException {
    Path parentPath = getParentPath(path);
    if (parentPath == null) {
      throw new FileSystemException(path.toString(), null, "can't delete recursively");
    }

    Collection<IOException> exceptions = null; // created lazily if needed
    try {
      boolean sdsSupported = false;
      try (DirectoryStream<Path> parent = Files.newDirectoryStream(parentPath)) {
        if (parent instanceof SecureDirectoryStream) {
          sdsSupported = true;
          exceptions =
              deleteRecursivelySecure((SecureDirectoryStream<Path>) parent, path.getFileName());
        }
      }

      if (!sdsSupported) {
        checkAllowsInsecure(path, options);
        exceptions = deleteRecursivelyInsecure(path);
      }
    } catch (IOException e) {
      if (exceptions == null) {
        throw e;
      } else {
        exceptions.add(e);
      }
    }

    if (exceptions != null) {
      throwDeleteFailed(path, exceptions);
    }
  }

  
Deletes all files within the directory at the given path 
recursively. Does not delete the directory itself. Deletes symbolic links, not their targets (subject to the caveat below). If path itself is a symbolic link to a directory, that link is followed and the contents of the directory it targets are deleted. 
If an I/O exception occurs attempting to read, open or delete any file under the given directory, this method skips that file and continues. All such exceptions are collected and, after attempting to delete all files, an IOException is thrown containing those exceptions as suppressed exceptions. 
Warning: Security of recursive deletes


On a file system that supports symbolic links and does not support SecureDirectoryStream, it is possible for a recursive delete to delete files and directories that are outside the directory being deleted. This can happen if, after checking that a
file is a directory (and not a symbolic link), that directory is replaced by a symbolic link to
an outside directory before the call that opens the directory to read its entries.

By default, this method throws InsecureRecursiveDeleteException if it can't guarantee the security of recursive deletes. If you wish to allow the recursive deletes anyway, pass RecursiveDeleteOption.ALLOW_INSECURE to this method to override that behavior. 
Throws:
/**
   * Deletes all files within the directory at the given {@code path} {@linkplain #deleteRecursively
   * recursively}. Does not delete the directory itself. Deletes symbolic links, not their targets
   * (subject to the caveat below). If {@code path} itself is a symbolic link to a directory, that
   * link is followed and the contents of the directory it targets are deleted.
   *
   * <p>If an I/O exception occurs attempting to read, open or delete any file under the given
   * directory, this method skips that file and continues. All such exceptions are collected and,
   * after attempting to delete all files, an {@code IOException} is thrown containing those
   * exceptions as {@linkplain Throwable#getSuppressed() suppressed exceptions}.
   *
   * <h2>Warning: Security of recursive deletes</h2>
   *
   * <p>On a file system that supports symbolic links and does <i>not</i> support {@link
   * SecureDirectoryStream}, it is possible for a recursive delete to delete files and directories
   * that are <i>outside</i> the directory being deleted. This can happen if, after checking that a
   * file is a directory (and not a symbolic link), that directory is replaced by a symbolic link to
   * an outside directory before the call that opens the directory to read its entries.
   *
   * <p>By default, this method throws {@link InsecureRecursiveDeleteException} if it can't
   * guarantee the security of recursive deletes. If you wish to allow the recursive deletes anyway,
   * pass {@link RecursiveDeleteOption#ALLOW_INSECURE} to this method to override that behavior.
   *
   * @throws NoSuchFileException if {@code path} does not exist <i>(optional specific exception)</i>
   * @throws NotDirectoryException if the file at {@code path} is not a directory <i>(optional
   *     specific exception)</i>
   * @throws InsecureRecursiveDeleteException if the security of recursive deletes can't be
   *     guaranteed for the file system and {@link RecursiveDeleteOption#ALLOW_INSECURE} was not
   *     specified
   * @throws IOException if one or more files can't be deleted for any reason
   */
  public static void deleteDirectoryContents(Path path, RecursiveDeleteOption... options)
      throws IOException {
    Collection<IOException> exceptions = null; // created lazily if needed
    try (DirectoryStream<Path> stream = Files.newDirectoryStream(path)) {
      if (stream instanceof SecureDirectoryStream) {
        SecureDirectoryStream<Path> sds = (SecureDirectoryStream<Path>) stream;
        exceptions = deleteDirectoryContentsSecure(sds);
      } else {
        checkAllowsInsecure(path, options);
        exceptions = deleteDirectoryContentsInsecure(stream);
      }
    } catch (IOException e) {
      if (exceptions == null) {
        throw e;
      } else {
        exceptions.add(e);
      }
    }

    if (exceptions != null) {
      throwDeleteFailed(path, exceptions);
    }
  }

  
Secure recursive delete using SecureDirectoryStream. Returns a collection of exceptions that occurred or null if no exceptions were thrown. 
/**
   * Secure recursive delete using {@code SecureDirectoryStream}. Returns a collection of exceptions
   * that occurred or null if no exceptions were thrown.
   */
  private static @Nullable Collection<IOException> deleteRecursivelySecure(
      SecureDirectoryStream<Path> dir, Path path) {
    Collection<IOException> exceptions = null;
    try {
      if (isDirectory(dir, path, NOFOLLOW_LINKS)) {
        try (SecureDirectoryStream<Path> childDir = dir.newDirectoryStream(path, NOFOLLOW_LINKS)) {
          exceptions = deleteDirectoryContentsSecure(childDir);
        }

        // If exceptions is not null, something went wrong trying to delete the contents of the
        // directory, so we shouldn't try to delete the directory as it will probably fail.
        if (exceptions == null) {
          dir.deleteDirectory(path);
        }
      } else {
        dir.deleteFile(path);
      }

      return exceptions;
    } catch (IOException e) {
      return addException(exceptions, e);
    }
  }

  
Secure method for deleting the contents of a directory using SecureDirectoryStream. Returns a collection of exceptions that occurred or null if no exceptions were thrown. 
/**
   * Secure method for deleting the contents of a directory using {@code SecureDirectoryStream}.
   * Returns a collection of exceptions that occurred or null if no exceptions were thrown.
   */
  private static @Nullable Collection<IOException> deleteDirectoryContentsSecure(
      SecureDirectoryStream<Path> dir) {
    Collection<IOException> exceptions = null;
    try {
      for (Path path : dir) {
        exceptions = concat(exceptions, deleteRecursivelySecure(dir, path.getFileName()));
      }

      return exceptions;
    } catch (DirectoryIteratorException e) {
      return addException(exceptions, e.getCause());
    }
  }

  
Insecure recursive delete for file systems that don't support SecureDirectoryStream. Returns a collection of exceptions that occurred or null if no exceptions were thrown. 
/**
   * Insecure recursive delete for file systems that don't support {@code SecureDirectoryStream}.
   * Returns a collection of exceptions that occurred or null if no exceptions were thrown.
   */
  private static @Nullable Collection<IOException> deleteRecursivelyInsecure(Path path) {
    Collection<IOException> exceptions = null;
    try {
      if (Files.isDirectory(path, NOFOLLOW_LINKS)) {
        try (DirectoryStream<Path> stream = Files.newDirectoryStream(path)) {
          exceptions = deleteDirectoryContentsInsecure(stream);
        }
      }

      // If exceptions is not null, something went wrong trying to delete the contents of the
      // directory, so we shouldn't try to delete the directory as it will probably fail.
      if (exceptions == null) {
        Files.delete(path);
      }

      return exceptions;
    } catch (IOException e) {
      return addException(exceptions, e);
    }
  }

  
Simple, insecure method for deleting the contents of a directory for file systems that don't support SecureDirectoryStream. Returns a collection of exceptions that occurred or null if no exceptions were thrown. 
/**
   * Simple, insecure method for deleting the contents of a directory for file systems that don't
   * support {@code SecureDirectoryStream}. Returns a collection of exceptions that occurred or null
   * if no exceptions were thrown.
   */
  private static @Nullable Collection<IOException> deleteDirectoryContentsInsecure(
      DirectoryStream<Path> dir) {
    Collection<IOException> exceptions = null;
    try {
      for (Path entry : dir) {
        exceptions = concat(exceptions, deleteRecursivelyInsecure(entry));
      }

      return exceptions;
    } catch (DirectoryIteratorException e) {
      return addException(exceptions, e.getCause());
    }
  }

  
Returns a path to the parent directory of the given path. If the path actually has a parent
path, this is simple. Otherwise, we need to do some trickier things. Returns null if the path
is a root or is the empty path.

/**
   * Returns a path to the parent directory of the given path. If the path actually has a parent
   * path, this is simple. Otherwise, we need to do some trickier things. Returns null if the path
   * is a root or is the empty path.
   */
  private static @Nullable Path getParentPath(Path path) {
    Path parent = path.getParent();

    // Paths that have a parent:
    if (parent != null) {
      // "/foo" ("/")
      // "foo/bar" ("foo")
      // "C:\foo" ("C:\")
      // "\foo" ("\" - current drive for process on Windows)
      // "C:foo" ("C:" - working dir of drive C on Windows)
      return parent;
    }

    // Paths that don't have a parent:
    if (path.getNameCount() == 0) {
      // "/", "C:\", "\" (no parent)
      // "" (undefined, though typically parent of working dir)
      // "C:" (parent of working dir of drive C on Windows)
      //
      // For working dir paths ("" and "C:"), return null because:
      //   A) it's not specified that "" is the path to the working directory.
      //   B) if we're getting this path for recursive delete, it's typically not possible to
      //      delete the working dir with a relative path anyway, so it's ok to fail.
      //   C) if we're getting it for opening a new SecureDirectoryStream, there's no need to get
      //      the parent path anyway since we can safely open a DirectoryStream to the path without
      //      worrying about a symlink.
      return null;
    } else {
      // "foo" (working dir)
      return path.getFileSystem().getPath(".");
    }
  }

  
Checks that the given options allow an insecure delete, throwing an exception if not. 
/** Checks that the given options allow an insecure delete, throwing an exception if not. */
  private static void checkAllowsInsecure(Path path, RecursiveDeleteOption[] options)
      throws InsecureRecursiveDeleteException {
    if (!Arrays.asList(options).contains(RecursiveDeleteOption.ALLOW_INSECURE)) {
      throw new InsecureRecursiveDeleteException(path.toString());
    }
  }

  
Adds the given exception to the given collection, creating the collection if it's null. Returns
the collection.

/**
   * Adds the given exception to the given collection, creating the collection if it's null. Returns
   * the collection.
   */
  private static Collection<IOException> addException(
      @Nullable Collection<IOException> exceptions, IOException e) {
    if (exceptions == null) {
      exceptions = new ArrayList<>(); // don't need Set semantics
    }
    exceptions.add(e);
    return exceptions;
  }

  
Concatenates the contents of the two given collections of exceptions. If either collection is null, the other collection is returned. Otherwise, the elements of other are added to exceptions and exceptions is returned. 
/**
   * Concatenates the contents of the two given collections of exceptions. If either collection is
   * null, the other collection is returned. Otherwise, the elements of {@code other} are added to
   * {@code exceptions} and {@code exceptions} is returned.
   */
  private static @Nullable Collection<IOException> concat(
      @Nullable Collection<IOException> exceptions, @Nullable Collection<IOException> other) {
    if (exceptions == null) {
      return other;
    } else if (other != null) {
      exceptions.addAll(other);
    }
    return exceptions;
  }

  
Throws an exception indicating that one or more files couldn't be deleted. The thrown exception
contains all the exceptions in the given collection as suppressed exceptions.

/**
   * Throws an exception indicating that one or more files couldn't be deleted. The thrown exception
   * contains all the exceptions in the given collection as suppressed exceptions.
   */
  private static void throwDeleteFailed(Path path, Collection<IOException> exceptions)
      throws FileSystemException {
    // TODO(cgdecker): Should there be a custom exception type for this?
    // Also, should we try to include the Path of each file we may have failed to delete rather
    // than just the exceptions that occurred?
    FileSystemException deleteFailed =
        new FileSystemException(
            path.toString(),
            null,
            "failed to delete one or more files; see suppressed exceptions for details");
    for (IOException e : exceptions) {
      deleteFailed.addSuppressed(e);
    }
    throw deleteFailed;
  }
}