Calling functions using reflection from Lambdaj

I wanna call functions using reflection from on() made object used in Lambdaj. for example this is the normal use for on() function in LambdaJ:

Map<Long, Tbl> _Map = index(_list, on(Tbl.class).getId());  

but in my case the call of the function getId() through reflection. because i need to access functions dynamically with the use of Lambdaj.