Unreadable+undebuggable has been the preferred way of doing it for as long as I have seen software
Seems perfectly readable to me, and I haven't used Java professionally in over a decade. What specifically do you find problematic?
The ~12 levels of indentation and 5 layers of nesting are doing my head in personally but maybe my brainspace is too small.
I think this perspective explain the issue well: you pretty much cannot unit test this (unless you consider the whole function a unit). It becomes very unclear what each lambda expression is about, the deeper you get.