Apache Solr facet 分組查詢

介紹一下Solr的分組查詢方式：

public static Map<String, Integer> queryByGroup(String qStr,String groupField,String sortField,boolean asc,Integer pageSize,Integer pageNum){
  Map<String, Integer> rmap = new LinkedHashMap<String, Integer>();
try {
   SolrServer server = getSolrServer();//getSolrServer() 方法就是返回一個CommonsHttpSolrServer
   SolrQuery query = new SolrQuery();
if(qStr!=null&&qStr.length()>0)
    query.setQuery(qStr);
else
    query.setQuery("*:*");//如果沒有查詢語句，必須這麼寫，否則會報異常
   query.setIncludeScore(false);//是否按每組數量高低排序
   query.setFacet(true);//是否分組查詢
   query.setRows(0);//設定返回結果條數，如果你時分組查詢，你就設定為0
   query.addFacetField(groupField);//增加分組欄位
   query.setFacetSort(true);//分組是否排序
   query.setFacetLimit(pageSize);//限制每次返回結果數
   query.setSortField(sortField,asc ? SolrQuery.ORDER.asc :SolrQuery.ORDER.desc );//分組排序欄位
   query.set(FacetParams.FACET_OFFSET,(pageNum-1)*pageSize);//當前結果起始位置
   QueryResponse rsp = server.query( query );   

   List<Count> countList = rsp.getFacetField(groupField).getValues();
   List<Count> returnList = new ArrayList<Count>();
if(pageNum*pageSize<countList.size())
    returnList = countList.subList((pageNum-1)*pageSize,pageNum*pageSize);
else
    returnList = countList.subList((pageNum-1)*pageSize,countList.size()-1);

for (Count count : returnList) {
if(count.getCount()>0)
     rmap.put(count.getName(), (int) count.getCount());
   }
  } catch (Exception e) {
   e.printStackTrace();
  }
return rmap;
 }