Truncate a Java string so that its UTF-8 representation will not exceed the specified number of bytes

utf8truncate.java

/**
 * Truncate a Java string so that its UTF-8 representation will not 
 * exceed the specified number of bytes.
 *
 * For discussion of why you might want to do this, see
 * http://lpar.ath0.com/2011/06/07/unicode-alchemy-with-db2/
 */
public static String utf8truncate(String input, int length) {
  StringBuffer result = new StringBuffer(length);
  int resultlen = 0;
  for (int i = 0; i < input.length(); i++) {
    char c = input.charAt(i);
    int charlen = 0;
    if (c <= 0x7f) {
      charlen = 1;
    } else if (c <= 0x7ff) {
      charlen = 2;
    } else if (c <= 0xd7ff) {
      charlen = 3;
    } else if (c <= 0xdbff) {
      charlen = 4;
    } else if (c <= 0xdfff) {
      charlen = 0;
    } else if (c <= 0xffff) {
      charlen = 3;
    }
    if (resultlen + charlen > length) {
      break;
    }
    result.append(c);
    resultlen += charlen;
  }
  return result.toString();
}