C /C++ long long to Java long

Question

I have a file on disk which I'm reading which has been written by c/c++ code. I know I have two 64-bit unsigned integers to read, but Java doesn't support unsigned integers, so the value I get when I do DataInputStream.readLong() is incorrect. (Ignore byte-order for now I'm actually using a derivative of DIS called LEDataInputStream which I downloaded from the web)

A lot of posts on here talk about using BigInteger but the javadoc for reading a bytearray only talks about loading a bytearray respresentation, and the questions seem centered on the fact that some people are going outside the positive bounds of the java long type, which I will be nowhere near with the data I'm reading.

I have a MATLab/Octave script which reads these long long values as two 32-bit integers each, then does some multiplying and adding to get the answer it wants too.

I suppose the question is - how do i read a 64-bit unsigned integer either using BigInteger, or using [LE]DataInputStream.XXX?

Thanks in advance