For very large expressions (e.g. with a complex search string) we'll hit the max HTTP GET limit since SolrJ does not enforce POST for all expressions. This goes at least for FacetStream, StatsStream and TimeSeriesStream, and I'll link a Pull Request fixing these three.
Here is an example of a stack trace when using TimeSeriesStream with a very large expression: https://gist.github.com/ea626cf1ec579daaf253aeb805d1532c
The fix is simply to use new QueryRequest(parameters, SolrRequest.METHOD.POST); to explicitly force POST.
See also solr-user thread http://lucene.472066.n3.nabble.com/Streaming-Expressions-GET-vs-POST-td4415044.html