Date format method in NiFi Expression Language doesn't support negative timestamp

[YuNing]

Hello，Everyone
       Now i found the date format method in NiFi Expression Language doesn't 
support negative timestamp which means the time before 1970.01.01 . Is there 
any idea on how to achieve this, and can I define my own  NiFi Expression 
Language.

Thanks for your early reply.



Best Regards
YuNing