Your main problem is the lanuage incomaptabilities
As far as i understand there is no direct way that Java (jar) and .net (DDL) assembles can talk to each other.
Question is what does the jar file do ? and can the same be done using .NET
If not then you are going to have to create a java application using somethign like Netbeans to act as a kind of middle man
Then when the asp.net application does a function call the call gets serialised into a file
The java app should then look for the file (in a thread or something) pulling the data and writing the response data to the file
While asp.net looks for changes in the file and pulls the data back from the file once java has written
There are other options such as web service and TCP IP socket server to communicate
But Long story short there is no clear cut way as far as i am aware of that there is not clear cut way of making java and .net talk to each other .
A quick google search did bring up http://www.ikvm.net/userguide/tutorial.html
] which seems to be promising.
Hope this helps
Oh and i found this
Using Java Classes in your .NET Application