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From André Warnier ...@ice-sa.com>
Subject Re: The best place for implementing context specific behavior?
Date Thu, 25 Jun 2009 10:23:19 GMT
Caldarale, Charles R wrote:
>> From: André Warnier [mailto:aw@ice-sa.com]
>> Subject: Re: The best place for implementing context specific behavior?
>>
>> I believe (but we need a real expert here) that having multiple <Host>
>> entries sharing the same appBase is a receipe for problems.
> 
> It seems to work for most usages.  As Mark pointed out, each <Host> or <Context>
should have separate work directories to avoid conflicts with temp files, JSPs, etc.
> 
>> If it is really just to have a single copy of the code on disk however,
>> you may be able to get away with having multiple (differently named)
>> appBase attributes, but all symlinked to the same physical location
> 
> That will make no difference, since the underlying location is the same for all.
> 
>> I must say that I don't really understand the requirement, unless your
>> "fruit" webapp is really big (in disk size), or you have many different
>> "fruit" hosts.
> 
> It's not clear to me that the OP wants separate instances of one webapp (one per host),
or if he wants one instance of one webapp that services all hosts.  We really need that clarified
before any further suggestions can be made.
> 
Agreed.
But was is relatively clear is that, synthetically, he wants to do some 
kind of relatively heavy intialisation that is hostname-dependent, and 
would rather not have to redo it at each new request.

For example - but just as an example - open a connection with a 
database, and read a row of a table, the exact row being accessed being 
dependent on the hostname addressed in the request; then, in a manner 
depending on the data read, initialise some persistent object that could 
be accessed subsequently by all servlets belonging to this webapp in 
this Host, for the lifetime of this webapp.

So he would like to do this once (per hostname), and then be able at 
each request, to efficiently retrieve pointers to the appropriate 
"thing" that has been initialised once, from whichever servlet belongs 
to the webapp and is invoked in the context of this Host.

What is also not clear yet, is if this initialisation could be done 
once, at Tomcat start, or would have to be redone if for instance the 
webapp is stopped and restarted, or unloaded and reloaded.
Or, if these are individual webapps per Host, if one of these 
Host-specific webapps must be able to be stopped/started independently 
of the other Host-specific webapps.
Or, to which extent this overlaps the idea of a "session" (as I 
understand it however, it does not, and the initialisation is to be 
valid for all subsequent requests to the same hostname, whether they 
belong to the same client session or not).

To the above general requirement, for which possibly there would be 
several possible solutions, there is then an additional requirement 
added about there being "a single webapp, or context, or whatever" which 
I do not fully understand, but which may be valid and restrict the 
choices available.

That's how I see it anyway.


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