Some days ago I posted a blog entry about using Glassfish v2 EJBs with the Tomcat. At this moment I thought that I solved the problems, but last week we were setting our testing evironment on a Debian Linux box and the problems reoccured.

At this moment I thought of a glitch in the server setup but some nagging hours later I realized that my so clever solution was a dirty hack. Which works in a Microsoft Windows environment, but refuses to work on in a Linux environment.
Ok, I have to confess, that I wasn’t really happy with my first solution in the end. Renaming JARs to provide the correct order of class loading always leaves a bad taste. But at that moment I was happy, no other solution was in sight and I had absolutly no time.

Some days ago I posted a blog entry about using Glassfish v2 EJBs with the Tomcat. At this moment I thought that I solved the problems, but last week we were setting our testing evironment on a Debian Linux box and the problems reoccured.

At this moment I thought of a glitch in the server setup but some nagging hours later I realized that my so clever solution was a dirty hack. Which works in a Microsoft Windows environment, but refuses to work on in a Linux environment.
Ok, I have to confess, that I wasn’t really happy with my first solution in the end. Renaming JARs to provide the correct order of class loading always leaves a bad taste. But at that moment I was happy, no other solution was in sight and I had absolutly no time.

Enough with apologies at this moment, we were late setting up the testing environment too and there was work to do. So I decided to take a different approach and tried to find out some more about the classloading of Tomcat 6. One of my primary questions was: “Why did the Tomcat 6 developers removed the different classloading directories?”

The answer suprised me more, than I expected! After using Google for a while, trying to find out more about the differences in classloading between Tomcat 5.5 and Tomcat 6, I stumbled across a small file: The catalina.properties. This file revealed the secrets of the differnces in classloading between these two Tomcat version. The simple and quite beautyful answer is: There aren’t any real differences. The distributions have different default settings, but the classloading mechanism is quite the same. At this point I am getting some more cautious than the last time. The two mechanisms are the same, as far I can judge it from my appication developer/deployer point of view
So what is this catalina.properties all about? The catalina.properties - as I understand it - controls some major classloading and security issues while bootstrapping the Tomcat web container. It has three (for my problem) relevant entries:

common.loader=${catalina.home}/lib,${catalina.home}/lib/*.jar
[...]
server.loader=
[...]
shared.loader=

These three entries are controlling three classloader in Tomcats classloader hierachy. The server classloader, the common classloader and the shared classloader. The server classloader is resopnsible for loading the libraries of the tomcat server. It is not set in the Tomcat 6 default distribution and will default to the common classloader which will load the server related classes now. The common classloader is responsible for loading classes common to the tomcat installation. Which are in the Tomcat 6 the server classes as well as addiontional classes like the JavaMail API oder some database driver classes (if you are configuring them with JNDI i.e.). The last classloader is the shared classloader which may load classes which may be shared between different web applications. This is the place where the Amis blog entry suggests the glassfish JARs to be placed, but which I hadn’t found in the Tomcat 6 distribution.

After I discovered the secrets of the catalina.properties it took me half an hour to create a shared/lib directory in my TOMCAT_BASE and adapting the catalina.properties file. Now I had the proper place for my Glassfish files and it worked nearly instantly. Good to know that you can make the integration of Glassfish EJB and the Tomcat 6 in a proper way and also good to know about this tiny little classloading tricks of the Tomcat 6
As you say in german: “Kaum macht man es richtig, dann geht’s!” (If you starting to do it the right way it works)