We're trying to understand the rules governing class visibility
under Tomcat. The docs say that in the hierarchy like the one
reproduced below, classloaders can access classes beneath
them, but not beside or above them. From which it follows ...
(i) webapps can't access the XML parser in crimson/xalan.jars
without 'intervention',
(ii) putting a jar containing classes that extend servlet.jar
on the CLASSPATH won't work, because servlet.jar is above
the Application Classloader, so Tomcat has to override
CLASSPATH and the class must be in lib/common or above.
We'd like to know if this is correct or not, and whether there
are rules we've missed. Thanks for your attention.
P.
The hierarchy ...
CATALINA_HOME
bin
classes
common
classes
lib
conf
lib
logs
server
classes
lib
webapps
examples
images
jsp
servlets
WEB-INF
manager
(many dirs)
ROOT
WEB-INF
classes
lib
work
TOMCAT_HOME/lib/container
(Server Classloader)
crimson.jar
facade22.jar TOMCAT_HOME/.../WEB-INF/classes
jasper.jar (Web Apps classloaders)
tomcat_modules.jar
tomcat_util.jar TOMCAT_HOME/lib/apps
xalan.jar (Apps Classloader)
commons-collections.jar
commons-dbcp.jar
commons-pool.jar
TOMCAT_HOME/lib/common
(Common Classloader)
connector_util.jar
core_util.jar
etomcat.jar
jasper-runtime.jar
servlet.jar
tomcat_core.jar
TOMCAT_HOME/lib/tomcat.jar
(Application Classloader,
CLASSPATH Classloader)
User class files
JAVA_HOME/jre/lib/ext
(JDK Extensions Classloader)
