code: public static String encodeBytes( byte[] source, int off, int len ) {
          byte[] encoded = encodeBytesToBytes(source, off, len);
          try {
              return new String(encoded, PREFERRED_ENCODING);
          } catch( UnsupportedEncodingException uee ) {
              return new String(encoded);
          }
      }
docs: Encodes a byte array into Base64 notation.
  
  @param source The data to convert
  @param off Offset in array where conversion should begin
  @param len Length of data to convert
  @return The Base64-encoded data as a String
  @throws NullPointerException if source array is null
  @throws IllegalArgumentException if source array, offset, or length are invalid
  @since 2.0