Hi Sweta. For Spring-specific questions, I'd suggest posting the question on Stack Overflow with the spring or spring-mongodb tags. The Spring project actually has a site,
spring.io/questions, where you can go to post Spring questions on SO, and the Spring engineering team does monitor this source. Also, to help out the Spring folks, I suggest including code excerpts that show how you're using .save() and .upsert(). It will make it much easier for them to help you.
-Will