I've never played with tomcats class loaders but I was wondering why you
want to place a "distinct" class so high in the Tomcat classloader tree.
See the http://tomcat.apache.org/tomcat-4.1-doc/class-loader-howto.html
I think the only reason it could have behaved at all as distinct classes in
the first place is because of Tomcats unusual class loading behavior...
In "normal class loading" theres a "ask your mama" principle at work... so
this is the wrong impression.....
All the advice I've found through searching the web suggests this cannot
happen because the two apps use different class loaders. But it definitely
is happening.
A class loader will normally "ask its mama" before it tries to load a
class.... so one would expect it to move up the tree. If 2 children share
the same "mama" and mama can see the class, mama will load it.... normally.
Webapps break this rule.... if they can see the class, then they ignore
mama.... but if they cant see the class, then they will ask mama.... this is
unusual in terms of class loading, but its there for our sanity, because as
users, the classes we stick in the web app, we expect to come first because
we thinking in the box.... however for normal applications if the class has
been loaded by mama already, we dont care where it comes from.
I would expect in a normal application, for the class to be shared... and
this goes for tomcat as well, EXCEPT if the classes were ALSO in the web-app
lib.
So.... and I'm guessing.... I think all thats happened is those classes have
been taken out of the Web-App/lib and if you stick them back in there, they
will behave distinctly again. They have no choice now but to ask mama....
and if mama has already loaded the class... she wont do it again, she'll
share it.
Remember that this may happen indirectly.... and this is wot I'm not sure
of... if an lib under web-app/lib referred to the common class, then I'm not
sure wot the class loader would do... ie the web-app class loader will pull
the class in from web-app/libs and when it finds the dependency.... will it
get it from mama and treat it as a web-app class... or as a common one???
Thing about class loaders is they are left very much up to the discretion of
the programmer... can make them do anything, so the only thing that matters
is how the tomcat developers want you to use them...
Anyway... I think you playing with fire... I mean if you stuck a singleton
in a common classloader... you would expect it to be shared.... so why dont
you just move them down the tree.... take them out of common and give each
web-app its own copy.... unless you want it to behave as a shared static
class.
I think the way its structured now, static fields sharing makes sense...
that they behaved distinctly at all... is weird.
----- Original Message -----
From: "Roger Parkinson" <[EMAIL PROTECTED]>
To: <users@tomcat.apache.org>
Sent: Monday, May 07, 2007 5:02 PM
Subject: [Fwd: static fields suddenly started sharing]
I have two different applications and they both make use of a common jar
library. The common library has several static fields.
Up until last week the static fields in one application never saw the
static fields in the other but I changed something and suddenly they do.
All the advice I've found through searching the web suggests this cannot
happen because the two apps use different class loaders. But it definitely
is happening.
I'm getting it on Tomcat 4.1 and 5.5 (my two live platforms).
I am trying to figure out what I changed to make this happen because it is
causing me problems. The changes I made were a restructure, shifting
things around into different folders in my eclipse project, but the same
jar files are in WEB-INF/lib as there always were.
Can anyone suggest where I should be looking? I'm wondering if I am
managing to call something I shouldn't too early in the application
initialisation. Each of the apps has a context listener that does some
stuff on startup of the app (including initialising some statics), but
they haven't changed since it was working. I still have the older
structure and it still works, and I can't see any relevant changes,
Thanks for any help
Roger
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