code: public static MappedByteBuffer mapExistingFile(
          final File location, final String descriptionLabel, final long offset, final long length)
      {
          return mapExistingFile(location, READ_WRITE, descriptionLabel, offset, length);
      }
docs: Check that file exists, open file, and return MappedByteBuffer for only region specified as
  {@link java.nio.channels.FileChannel.MapMode#READ_WRITE}.
  <p>
  The file itself will be closed, but the mapping will persist.
  
  @param location         of the file to map
  @param descriptionLabel to be associated for an exceptions
  @param offset           offset to start mapping at
  @param length           length to map region
  @return {@link java.nio.MappedByteBuffer} for the file