Apache Solr facet 分组查询

介绍一下Solr的分组查询方式：

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() 方法就是返回一个CommonsHttpSolrServer
   SolrQuery query = new SolrQuery();
   if(qStr!=null&&qStr.length()>0)
    query.setQuery(qStr);
   else
    query.setQuery("*:*");//如果没有查询语句，必须这么写，否则会报异常
   query.setIncludeScore(false);//是否按每组数量高低排序
   query.setFacet(true);//是否分组查询
   query.setRows(0);//设置返回结果条数，如果你时分组查询，你就设置为0
   query.addFacetField(groupField);//增加分组字段
   query.setFacetSort(true);//分组是否排序
   query.setFacetLimit(pageSize);//限制每次返回结果数
   query.setSortField(sortField,asc ? SolrQuery.ORDER.asc :SolrQuery.ORDER.desc );//分组排序字段
   query.set(FacetParams.FACET_OFFSET,(pageNum-1)*pageSize);//当前结果起始位置
   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;
 }