fq's are always intersections, if you want to union multiple queries you have to specify them in a single fq -- that's not a SolrJ/URL thing, that's just a low level detail of how solr caches & intersects filters.
from SolrJ you just have to do a single addFilterQuery() call containing your union query (using whatever query parser you choose) There's been an open issue for a while talking about the logistics of making unioned fq's more feasible. I recently posted some thoughts there on what i *think* would be a fairly straight forward way to do support this in a relatively non-invasive and robust way, which you may want to look at if you are comfortable working with java and would like to try your hand at implementing it in solr... https://issues.apache.org/jira/browse/SOLR-1223 https://issues.apache.org/jira/browse/SOLR-1223?focusedCommentId=13450929&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-13450929 -Hoss
