code: public static WebValidator length(String propertyName, String propertyValue, int start, int end) {
  		WebValidator valid = new WebValidator(true, "");
  		if (StringUtils.isBlank(propertyValue)) {
  			return valid;
  		}
  
  		int length = ValidatorUtils.length(propertyValue);
  		if (start == 0 && length > end) {
  			valid = new WebValidator(false, propertyName + "长度不能超过" + end + "个字符");
  		} else if (length < start || length > end) {
  			StringBuilder s = new StringBuilder();
  			s.append(propertyName).append("长度必须在 ").append(start).append(" 到 ").append(end).append(" 之间");
  			valid = new WebValidator(false, s.toString());
  		}
  		return valid;
  	}
docs: 如果包含中文字符，中文字符按两个长度计算 e.g. length('name', value, 0, 20);