From simple applications that just need to know what the next working day is in New York, through to rate reset engines that need to generate exact cashflows.
If your primary technology is Java your only options are to write it yourself, buy in a component or integrate with analytics libraries.
Writing it yourself is expensive, and this is a domain that benefits from industry wide testing and validation.
You can't always find a component that will deliver all of the functions you need, or is still good value after you have integrated it with the rest of your infrastructure.
Analytics libraries are often written in C++ with Excel-centric APIs which pose their own challenges.