本篇文章为大家展示了Java中怎么实现一个Group功能，内容简明扼要并且容易理解，绝对能使你眼前一亮，通过这篇文章的详细介绍希望你能有所收获。

接口方法如下：

/***keyColumn:newString[]{"xxxName","xxxType"}<br>*condition:查询条件，可为空<br>*initial:分组统计初始变量，为空时自动为每列提供初始变量<br>*reduce：记录处理function<br>*finalize:finalize函数，可为空<br>*/publicBasicDBListgroup(String[]keyColumn,DBObjectcondition,DBObjectinitial,Stringreduce,Stringfinalize){DBCollectioncoll=getCollection();DBObjectkey=newBasicDBObject();for(inti=0;i<keyColumn.length;i++){key.put(keyColumn[i],true);}condition=(condition==null)?newBasicDBObject():condition;if(StringUtils.isEmpty(finalize)){finalize=null;}if(initial==null){//定义一些初始变量initial=newBasicDBObject();for(inti=0;i<keyColumn.length;i++){DBObjectindex=newBasicDBObject();index.put("count",0);index.put("sum",0);index.put("max",0);index.put("min",0);index.put("avg",0);index.put("self","");initial.put(keyColumn[i],index);}}BasicDBListresultList=(BasicDBList)coll.group(key,condition,initial,reduce,finalize);returnresultList;}

实现案例：

//任务统计@Action(value="getTaskStatistic",results={@Result(name="success",type="json",params={"includeProperties","jsonResult"})})publicStringgetTaskStatistic(){DBObjectinitial=newBasicDBObject();DBObjectindex=newBasicDBObject();index.put("count",0);index.put("taskStatus","");initial.put("taskStatus",index);Stringreduce="function(doc,out){"+"out.taskStatus.count=out.taskStatus.count+=1;"+"out.taskStatus.inspectStatus=doc.taskStatus;"+"}";BasicDBListgroup=(BasicDBList)taskStatusService.group(newString[]{"taskStatus"},null,initial,reduce,null);this.jsonResult=group.toString();returnSUCCESS;}

返回数据：

[{"taskStatus":{"count":4.0,"taskStatus":"Finished"}},{"taskStatus":{"count":3.0,"taskStatus":"Received"}},{"taskStatus":{"count":2.0,"taskStatus":"UnReceive"}}]

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