There is a Classloading Analysis Tool(CAT)
provided in Weblogic server(PS3) which helps you to monitor the class loading
pattern that happens with an application. It helps you in identifying any class
loading issues that can happen due to different java classes that are
duplicated with different libraries. To understand the use of CAT, you should
first know the class loading pattern in Weblogic.
Classloading in Weblogic happens in different
levels.The below image shows the hierarchy in which the class loading happens
System classloader is the
top-level classloader that loads the WebLogic implementation classes and
supporting libraries defined on the classpath (those added to setDomanEnv and
commEnv)
Domain level classloader
is a child to the SYSTEM classloader and loads libraries that are included in
the domain lib directory.
Application level classloader is the next in order.
WebLogic Server automatically creates a hierarchy of classloaders when
an application is deployed. The root classloader in this hierarchy is the
APPLICATION classloader and it loads modules defined in the application,
including EJBs, as well as java EE shared libraries and libraries included in
the configured library directories for the application.
For each web application, a child class
loader is created and it loads the shared Java
EE libraries as well as the libraries and compiled classes in the WEB-INF
folder.
What happens if the CAT find issues in the class loading
pattern of the application
WebLogic has a feature called the Filtering ClassLoader
which overrides the TOP-DOWN classloading and essentially enables child-first
classloading. When filter is enabled, priority
is given to the resources from the child of
the FilteringClassLoader (an application classloader) before the ones
from the system classloader . This will be mainly used when the version used by
systme class loader or top level class loaders are different from the one
required by the application.
Usage(in weblogic.xml)
<prefer-application-packages>
<package-name>geo.*</package-name>
</prefer-application-packages>
How to use CAT?
Login to http://host:port/wls-cat/ and enter your credentials.
Login to http://host:port/wls-cat/ and enter your credentials.
- Analyze classloading conflicts
- View the system and application classloaders
- Generate reports
CAT will suggest you solutions to overcome the conflicts which is also a good feature.
Below references give you detailed
explanation on weblogic class loading as well as fetures involved in CAT tool.
References:
