在非关系型数据库MongoDB中，并没有任何现成的框架可以像SQL那样通过GroupBy就轻松实现数据库的分组功能。如果我们想要实现MongoDB的Group功能，就必须写原生态
接口方法如下：
/*** keyColumn : new String[]{"xxxName","xxxType"}* condition : 查询条件 ，，可为空
* initial : 分组统计初始变量，为空时自动为每列提供初始变量
* reduce ： 记录处理function
* finalize : finalize函数，可为空
*/public BasicDBList group(String[] keyColumn, DBObject condition,DBObject initial, String reduce, String finalize) {DBCollection coll = getCollection();DBObject key = new BasicDBObject();for (int i = 0; i < keyColumn.length; i++) {key.put(keyColumn[i], true);}condition = (condition == null) ? new BasicDBObject() : condition;if (StringUtils.isEmpty(finalize)) {finalize = null;}if (initial == null) {//定义一些初始变量initial = new BasicDBObject();for (int i = 0; i < keyColumn.length; i++) {DBObject index = new BasicDBObject();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);}}BasicDBList resultList = (BasicDBList) coll.group(key, condition,initial, reduce, finalize);return resultList;}
实现案例：
//任务统计@Action(value = "getTaskStatistic", results = { @Result(name = "success", type = "json", params = {"includeProperties", "jsonResult" }) })public String getTaskStatistic() {DBObject initial = new BasicDBObject();DBObject index = new BasicDBObject();index.put("count", 0);index.put("taskStatus", "");initial.put("taskStatus", index);String reduce = "function (doc, out) { "+ " out.taskStatus.count = out.taskStatus.count+=1; "+ " out.taskStatus.inspectStatus = doc.taskStatus;"+ "}";BasicDBList group = (BasicDBList) taskStatusService.group(new String[] { "taskStatus"}, null, initial, reduce, null);this.jsonResult = group.toString();return SUCCESS;}返回数据：
[ { "taskStatus" : { "count" : 4.0 , "taskStatus" : "Finished"}} , { "taskStatus" : { "count" : 3.0 , "taskStatus" : "Received"}} , { "taskStatus" : { "count" : 2.0 , "taskStatus" : "UnReceive"}}]本文出自 “尘风随影的天空” 博客，请务必保留此出处