Safely trims a String to a max length of bytes in a desired encoding without cutting multi-byte characters in half.

trimbytes.groovy

static String trimBytes(String input, int lengthBytes, Charset charset) {
  if (input == null) return null
  if (input.getBytes(charset).length <= lengthBytes) return input

  def bytes = charset.encode(input)
  bytes.limit(Math.min(lengthBytes, bytes.limit()))
  def chars = charset.newDecoder()
          .onMalformedInput(CodingErrorAction.IGNORE)
          .onUnmappableCharacter(CodingErrorAction.IGNORE)
          .decode(bytes)
  return new StringBuffer(chars).toString()
}