Find list of Classes used by a Class in java

Question

I am using an xStream whitelist to restrict the packages that can be de-serialized by my application. To keep this whitelist restrictive enough in this huge project,

I need to find all the classes used by specific classes that are to be de-serialized.

I have tried using the org.reflections, but the scanners don't return all the used classes.

Any help would be appreciated, Thanks!