I want to create a Desktop project on Java which shows radiation dispersion. How can i Link java with QGIS?
Is there any tutorial site i can get reference from?
QGIS is written in C++ and there are Python bindings. So you can develop your own applications using those languages. You cannot use Java.
The documentation is linked very prominently on http://qgis.org.
For my opinion, it is still possible to link QGIS and Java by using C++ wrapper around your Java. Here is one link that explains how to do it: http://stackoverflow.com/questions/4536596/tool-to-generate-c-wrapper-over-java-class
However, it would be more reasonable to use PostGIS or UDig with Java.
PostGIS is similar in its functionality to ArcSever. Yet, PostGIS is open source. It comes with bundle with PostgreSQL (which is also open source). PostGreSQL is a database management system and PostGIS provides API for operation with GIS data on PostgreSQL. If you use PostGIS, you also have to connect it to some UI. PostGIS can export data in many formats. Here is the link for PostGIS: http://postgis.refractions.net/
PostGIS API can be used with many languages including Java. Here is the documentation: http://postgis.refractions.net/documentation/javadoc/overview-summary.html
For UI, you can use uDig. It is a product similar to ArcGIS and is written in Java and it is open source. Here is the link for Udig: http://udig.refractions.net/ Actually, you can use uDig for all the tasks that you need. Usage of PostGIS is an overshoot for your needs.