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)
- 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.
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.