JsonFacetingResponse and its series of dependent classes hold a variety of count fields for bucket counts and various optional properties (allBuckets, numBuckets, etc.). Currently, some of the code that parses these values out of the originating NamedList either stores or casts the values as ints. When doc counts are low this works fine. But when the doc counts become larger and stray into "long" territory, SolrJ is liable to blow up with ClassCastExceptions.
A user on the list reported on of these with the partial stack trace:
We should fix this so that these classes can be used without incident for any doc counts.