My ABC class is extending the gxt api class (com.extjs.gxt.ui.client.data.BaseModel) and also other API classes, now how can marshall this class to transfer the object from client to errai service and vice versa.
You can map third-party classes via the ErraiApp.properties file. Please refer to the documentation here for how to do that: http://docs.jboss.org/errai/2.0.CR1/errai/reference/html_single/#sid-5931328