CODEWITHSUNDEEP
javatomcatvaadin
Valyrion
Valyrion

Reputation: 2613

Vaadin starts multiple Application instances for single application

I'm looking at my Vaadin app running on a local tomcat server with JProfiler. This shows that every time I start up the server and run my application, there are 3 instances of my main Application class. If I close the application in the browser or even close the browser completely, there are 2 left. I've noticed that the Application's init() method gets called 3 times during startup, even though I never explicitly call it myself. I am using the Threadlocal pattern (but with InheritableThreadlocal).

It doesn't look normal to me, is there anything that can cause this kind of behaviour?

(Copied this question from my post on the vaadin forums)

Upvotes: 0

Views: 1200

Answers (1)

Aaron Digulla
Aaron Digulla

Reputation: 328760

From your description, I gather that Application is a class written by you (and not something supplied by Vaadin) and that you somehow save the instances of this class in a ThreadLocal.

This would explain the behavior that you're seeing: Tomcat will start several threads to handle client requests. For each thread, a new Application instance will be saved in the ThreadLocal.

Try the (evil) Singleton pattern or (better) dependency injection with the singleton scope instead.

If you use the singleton pattern, make sure you use the code under "Construct in multi-threaded applications" or you will get odd errors in Tomcat. This article on JavaWorld explains it in depth: Simply Singleton

EDIT Based on your feedback: The behavior your see is expected and correct. Tomcat uses threads to handle requests and it will pre-spawn a couple to be ready for business (in your case, it spawns three).

Upvotes: 1

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