code: public static MappedByteBuffer mapExistingFile(final File location, final String descriptionLabel)
      {
          return mapExistingFile(location, READ_WRITE, descriptionLabel);
      }
docs: Check that file exists, open file, and return MappedByteBuffer for entire file 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 any exceptions
  @return {@link java.nio.MappedByteBuffer} for the file