guava/src/com/google/common/io/MoreFiles.java
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);
      }
    }
  }
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);
      }
    }
  }
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.