Question

So I’m using Spring MVC and in my controller I call several Utility classes. Do the Collections I use in those utility classes need to be synchronized? Similarly, are multiple threads spawned for each user when they access my webpage in the controller meaning I need to ensure thread-safety?

Answer 1

Each request will be handled by some arbitrary thread allocated by the servlet container (from a thread pool), so multiple requests will mean multiple concurrent executions of the controller. There is no direct correlation between users and threads, just requests and threads, but if you have multiple users, then you typically have concurrent requests, and so multiple threads.

Given that controllers should be thread-safe, you will then need to ensure your utility classes and collections used by the controller thread-safe, either by design (e.g. making them or the controller request or possibly session scope if you ensure the same session cannot be served concurrently) or by use of locking on shared resources.