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Tuesday, January 25, 2011

How to enable child-first class loading in WSO2 Application Server or Axis2

By default, WSO2 Application Server (or Axis2) uses parent-first class loading mechanism.
If you deploy an AAR service, which can load classes from the following locations.

  • CARBON_HOME/lib (CARBON_HOME is the location where you installed WSO2 Application Server)
  • CARBON_HOME/repository/deployment/server/axis2services/lib
  • AAR service/lib (lib directory under your service archive)

If your service implementation class has a package import for a class, which is available in both CARBON_HOME/repository/deployment/server/axis2services/lib and the lib directory under service archive, the class placed under CARBON_HOME/repository/deployment/server/axis2services/lib will get loaded.
Which means, the parent class always get loaded first.
The class loading sequence is CARBON_HOME/lib ---> CARBON_HOME/repository/deployment/server/axis2services/lib -----> AAR service/lib

Sometimes, we want to load the class from service archive lib first without loading the class which is available either one of above parent locations. In other words, child-first class loading will be required for some instances.
child-first class loading can be enabled simply by adding the following parameter in to services.xml in your service archive.

<parameter name="EnableChildFirstClassLoading">true</parameter>

If you set this parameter in axis2.xml of your WSO2 Application Server (or Axis2) instance, all services will use child-first class loading mechanism.

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