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"}}]