如何理解solr的core和collection

/****多核查询测试*@throwsException*/publicstaticvoidqueryMultiCore()throwsException{//查询a和b下面的数据，HttpSolrClientsc=newHttpSolrClient("a");Stringshards="192.168.1.215:8983/solr/a,192.168.1.214:8983/solr/b";ModifiableSolrParamssolrParams=newModifiableSolrParams();solrParams.set("q","sname:北京奇虎科技有限公司");//solrParams.set("q.op","AND");//设置查询关系solrParams.set("fl","*,score");//设置过滤solrParams.set("shards",shards);//设置shardQueryResponsersp=sc.query(solrParams);system.out.println("命中数量："+rsp.getResults().getNumFound());for(SolrDocumentsd:rsp.getResults()){System.out.println(sd);}sc.close();}