On 28/06/2010 13:48, Ockleford Paul (NHS Connecting for Health) wrote: > Hi, > > Thanks very much for confirming that and for providing me with more > information. One thing I still find strange though is how SupplementaryEdit > (in the webapp) is able to call a class loaded by the "common" classloader? > Does it not work the other way round as well?
So, to clarify something, there is a symlink in common/lib which points to a jar which is actually inside your application WEB-INF/lib? p > Thanks, > > Paul > > -----Original Message----- > From: Shay Rojansky [mailto:r...@roji.org] > Sent: 28 June 2010 13:35 > To: Tomcat Users List > Subject: Re: Classloading > > Hi Paul. > > Yes, this is the normal behavior. As you found out, Tomcat uses a different > classloader for the "common" classes than that used for for loading your > webapp classes. > > Basically, when your application loads PracCalc, Tomcat looks first in the > "common" directory and loads it from there. Then, since the reference to > SupplementaryEdit is from PracCalc, PracCalc's classloader (the "common" > one) is used to search for the dependency, SupplementaryEdit. Since the > "common" classloader knows nothing about your webapp's classes, a > ClassNotFoundException is thrown. > > You have to plan well how to manage your JARs and classes. One solution is > to put all dependencies in your webapp, another is to make sure that if you > put a dependency in Tomcat's common directory, all of the dependency's > dependencies must also be there. > > Shay > > On Mon, Jun 28, 2010 at 8:22 AM, Ockleford Paul (NHS Connecting for Health) > <paul.ocklef...@nhs.net> wrote: > >> Hi, >> >> I had a problem this morning that took me a while to sort out, and now I >> know what the issue is I was hoping somebody could explain why the problem >> was happening. I assume it is because one class had been loaded by a >> different classloader, and so wasn't available to the second class. >> >> I have 2 classes in different packages but within the same web application: >> >> SupplementaryEdit - webapps/WEB-INF/classes >> PracCalc - webapps/WEB-INF/classes >> >> I added a method to SupplementaryEdit and then called it within this class >> and it worked ok. Next I created an object of SupplementaryEdit in PracCalc >> and tried to call this new method. I got a classnotfoundexception for >> SupplementaryEdit at the point of instantiation and I was struggling to find >> out why. >> >> After spending ages trying different things I started looking through the >> common classes in tomcat and found that someone had previously created a >> symlink to the package PracCalc is in there. I read a little on tomcat >> classloading and came to the conclusion that this was causing PracCalc to be >> loaded by a different loader to SupplementaryEdit. >> >> If someone could confirm this that would be good, and also could someone >> explain why the class in the web app isn't available to the class referenced >> in common/lib? >> >> I don't understand because I get a runtime exception in the block where the >> object is created, and not on initial class use (as I used the class without >> triggering the code block fine), and I also don't understand why at runtime >> the common classloader is not able to resolve the class, as I have tested by >> calling a class that creates a SupplementaryEdit object before trying from >> PracCalc and it still didn't work. >> >> To resolve the issue I moved the method into PracCalc as this still made >> sense logically and the code now works, just looking for some general >> help\guidance. >> >> Thanks, >> >> Paul >> >> >> ******************************************************************************************************************** >> >> This message may contain confidential information. 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