The ASF is made up of more than 150 top level projects which cover a wide range of technologies. Chances are if you are looking for a rewarding experience in Open Source, you are going to find it here.
Scalable machine learning library
Rule based XML->Java object mapping module
The Digester package lets you configure an XML->Java object mapping module which triggers certain actions called rules whenever a particular pattern of nested XML elements is recognized.
Apache Axis2 is a service hosting and consumption framework that makes it easy to use SOAP and Web Services
Apache Axis2 is a toolkit for creating and using Web Services, including SOAP, MTOM, XML/HTTP and advanced WS-* standards such as WSRM and WSSecurity. Axis2 includes a very fast runtime engine, together with tooling support for WSDL and WS-Policy, and plugin support for WS-Addressing, WS-ReliableMessaging, WS-Security, WS-Eventing, WS-Transactions, WS-Trust and WS-SecureConversation. Axis2 runs either standalone or hosted in Tomcat or other servlet containers.