Question

Does each HTTP request access the same servlet object but in a different thread? or does it create a new thread and new Servlet Instance ?

Answer 1

The container will use the same servlet instance if your servlet don’t implement SingleThreadModel.
Otherwise there is no guarantee that the same Servlet object is hit. The container is free to create more servlet instances if it considers necessary. But the requests comes on different threads, not necessarily newly created (as Sanjay mentioned).

From the Servlet 3.0 specification:

For a servlet not hosted in a distributed environment (the default), the servlet
container must use only one instance per servlet declaration. However, for a servlet
implementing the SingleThreadModel interface, the servlet container may
instantiate multiple instances to handle a heavy request load and serialize requests
to a particular instance.

…

Generally the Web container handles concurrent requests to the same servlet by
concurrent execution of the service method on different threads.