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From Jochen Kuhnle <>
Subject Context/Session/Request lifecycle listeners? (Getting rid of synchronized(session))
Date Sat, 14 May 2005 00:36:10 GMT
For many Cocoon applications, there is the need to initialize Context, 
Session and Request (C/R/S) attributes, e.g. with database connections, 
and dispose those attributes after use so there are no leaks. Right now, 
there are several methods for hooking into C/R/S creation and destruction: 
ServletContextListener and HttpSessionListener from the Servlet API for 
Requests and Sessions, using o.a.c.RequestListener for Requests or even 
subclassing the Cocoon Servlet. This has several disadvantages:

1. It's ugly. You use different APIs (Cocoon and Servlet API) to achieve 
similar goals. When you're done, you don't have a Cocoon application, you 
have a Cocoon & Servlet container application. What about an easy switch 
to Cocoon's 'batch mode'?

2. It's not that easy to access the Cocoon API from the servlet API 
functions. For example, ServletContextListener.contextInitialized is 
called before the Cocoon servlet is initialized. This means there's no 
ComponentManager available, so no access to Avalon/Cocoon components if 
you need them to initialize the session.

3. Although the order of calls is well defined (at least I hope so :), it 
still takes more time to figure out than a common API with a well-defined 

4. Lazy initialization of session and context attributes depends on 
synchronization (mainly done on the session and context objects) which 
poses its own problems, as seen in [1]. When there's a defined 
initialization hook before the C/R/S goes to work, you don't need 
synchronization. And when you need lazy initialization, you can use a 
lightweight proxy object. When you create the proxied heavyweight, you can 
synchronize on the proxy instead of the whole session or even context.

How about introducing C/R/S listeners in Cocoon that are notified of 
creation and destruction events? Something like 
Cocoon.addSessionListener(SessionListener)? Since this would make my life 
easier, too, I would gladly help to write it...



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