Servlet container - duplicate class definition

[Tomasz Szymanski]

Hi there,
do you know if I can count on any predictible behaviour of a servlet container if I have a duplicate class definition in the classpath (for example the same class packaged in two different JARs in /WEB-INF/lib)?
Is that kind of situation addressed anywhere in the servlet specification? Or perhaps in the general JVM (classloader) specification?

[Bear Bibeault]

There is nothing the Servlet Spec regarding this. Don't do it.

[Jeanne Boyarsky]

No. And I've seen unpredictable behavior. Well, it is predictable in that "it depends on which code is loaded first." But that's not something one can rely on.

[Tomasz Szymanski]

That's what I meant, Jeanne - I was wondering whether you can rely on any particular class loading order. And thus - if it's theoretically possible to "patch" a web application without replacing an old JAR, but by adding a new one, which would kind of override the old one. But from what you both said - it isn't. Thanks, both of you.

[Bear Bibeault]

Correct. it isn't.

You like Russian Roulette?

[amit punekar]

Hi,
Would loading the Class in Parent class loader help in such cases?
Based on the principle - "If webapp class loader needs some class it would check if Parent has one and if it is not there then it will try to load it from WEB-INF\lib or WEB-INF\classes".

[Bear Bibeault]

I repeat, you like Russian Roulette?

[Jeanne Boyarsky]

And once the class is loaded, it is even worse. You have some classes referring to one version and others pointing to another. Bear is correct. Abandon this idea!