Java中怎么实现一个Group功能

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 : 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"}}]

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