What is so bad with threadlocals

Question

Everybody in Django world seems to hate threadlocals(http://code.djangoproject.com/ticket/4280, http://code.djangoproject.com/wiki/CookBookThreadlocalsAndUser). I read Armin

Answer 1

I have found using ThreadLocal is an excellent way to implement Dependency Injection in a HTTP request/response environment (i.e. any webapp). You just set up a servlet filter to 'inject' the object you need into the thread on receiving the request and 'uninject' it on returning the response.

It's a smart man's DI without all the XML ugliness, without the MB of Spring Jars (not to mention its learning curve) and without all the cryptic repetitive @annotation nonsense and because it doesn't individually inject many object instances with the dependencies it's probably a heck of a lot faster and uses less memory.

It worked so well we opened sourced our exPOJO Filter that can inject a Hibernate session or a JDO PersistenceManager using ThreadLocal:

http://www.expojo.com