> The same class loader is used to load all classes within a particular web
> application, but there is more to the story than that. See below.
This is true for both JSP pages and for servlets, including those servlets
loaded at startup?
> There is actually a hierarchy of class loaders created when Tomcat is
> running:
> - Bootstrap class loader (Java system classes)
> - Extensions class loader (JAR files from $JAVA_HOME/jre/lib/ext)
> - System class loader (contents of CLASSPATH at startup time)
> - Webapp class loader (contents of WEB-INF/classes and WEB-INF/lib
> for your particular web application)
Sure, this is as I'd expected. And since a Tomcat can run multiple webapps,
presumably it has multiple classloaders, one for each, correct?
> * Do not rely on system extensions in $JAVA_HOME/jre/lib/ext. If you
> do, those classes are *not* allowed to reference any classes on the
> system class path, or inside your web application.
This is empty on my system.
> * Do not rely on adding classes onto your CLASSPATH (or putting them in
> $TOMCAT_HOME/lib) before starting Tomcat. Such classes will have
> problems with downward references, as described above. Also, support
> for shared library classes is ***not*** required by the servlet spec,
> so you cannot count on this facility in a portable app.
What is a "shared library class"? In my case, the problem is with classes
that are dynamically loaded, such as a JCE crypto provider or JDBC provider.
Or are you referencing JNI stuff or something else?
> * Put all classes your application needs into WEB-INF/classes, or
> in JAR files unde WEB-INF/lib. In this way, they will all be loaded
> by the same class loader and not have any referencing problems.
This is what I do, but I get the class not found exception. When I DO put
them in the CLASSPATH just before starting Tomcat, then they are found.
This is the exact opposite of what you suggest, and of course what you
suggest is what I want to happen <smile>.
Is there something I can do at the point in my code where I am trying to
load the JCE provider and I get an error to help see what's wrong? I know
the class exists in a jar file in the WEB-INF/lib...
> There are other specific issues with specific libraries, and there are
> some changes in how class loading works in Tomcat 4.0, but the above
> outline identifies what to do about the majority of class loading issues
> in servlet containers.
Do you think Tomcat 4.0 reliable enough now to use instead of 3.2.1?
David
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