Java UML and XMI

Hello All,

I'm currently working in a academic project which is related to UML Activity diagrams, use-case diagrams. mainly what i need to extract data from and imported XMI document and make java Objects. please help me to start with the work.

I need to get extract data from an XMI formatted XML file so in order to do that i need to write a xmi reader class. Please can some one tell me how to do it. and what are the opensourse libraries that has to read data from an XMI. and some source codes examples.

Please help me on this matter. Please give your ideas

Thanks
Thilini