code: public static int countIgnoreCase(final String source, final String target) {
  
      if (isEmpty(source) || isEmpty(target)) {
        return 0;
      }
      return count(source.toLowerCase(), target.toLowerCase());
    }
docs: Count how much target in souce string.</br>统计target在source中出现的次数。
  
  @param source source string
  @param target target string
  @return the count of target in source string.