Project Euler/20
From charlesreid1
Sum of Factorial Digits
For this problem, you're asked to sum the digits of 100!. This is a very quick task using a library like BigInteger - the Go programming language also has the facilities built-in to handle numbers as large as 800!.
https://charlesreid1.com:3000/charlesreid1/hello-world/src/master/go/factorial.go
To do this in Java, you can use the BigInteger class, convert it to a String, and then turn the characters in the string into digits one at a time to sum them up.