code: protected InputStream getInputStream(final File f, final long offset)
      throws IOException {
          FileInputStream fin = new FileInputStream(f); 
          return new BufferedInputStream(fin);
      }
docs: Convenience method for constructors.
  
  @param f File to read.
  @param offset Offset at which to start reading.
  @return InputStream to read from.
  @throws IOException If failed open or fail to get a memory
  mapped byte buffer on file.