using jni and jnative to access unknow dlls.

I am having some dlls to be accessed from java.I have the code for it but i do not know what code structure jnative or jni responds to.To be more precise - i know that jnative's constructor accespts dll name and function name as parameters - i do not know where the function name should be put in -what class it should be put in.if i blindly create a new project with a projectname/dllname and any class with a function.....the dll is loaded but the function name is not found - which is a bit obvious since there is no way to know where the function comes from.I tried more variations like Classname.functionname....but still the function is not found.Can some one tell me what the structure of the dll should be and how it should be called from jnative.
The jnative gives example use of user32.dll but i do not have the decompiled code of user32.dll.
Can anyone tell me how i can decompile user32.dll