Java 变量不能在绑定内使用

我有一个验证函数，返回失败的部分。比如说-

public class DateValidator{
    public String validateDate(startDate, endDate){
        try{
            LocalDate.parse(startDate, formatter);
            LocalDate.parse(endDate, formatter);
        } catch(DateTimeParseException e) {
            return "INVALID_DATE_FORMAT";
        }
        if (startDate.isAfter(endDate)) {
            return "INVALID_START_AND_END_DATES";
        }
    ..... so on
    }
}

我想在Drools中使用this进行验证

rule
    "ValidateDate"
when
    $error: Error();
    $request: Request();
    DateValidator( $dateValidation: validateDate($request.getStartDate(), $request.getEndDate()) != null);
then
    $error.getBadRequest($dateValidation);
end;

我想使用变量的返回类型NOTNULL表示验证没有通过。但我得到下面的DRL文件例外-

text=Variables can not be used inside bindings.
Variable [$request] is being used in binding 
'validateDate($request.getStartDate(), $request.getEndDate())']

---

尝试将函数调用作为来自条件元素的

的一部分执行：

rule
    "ValidateDate"
when
    $error: Error();
    $request: Request(
      $startDate: startDate,
      $endDate: endDate
    );
    $dv: DateValidator()
    $msg: String() from $dv.validateDate($startDate, $endDate)
then
    $error.getBadRequest($msg);
end

希望有帮助