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：
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"}}]上述内容就是Java中怎么实现一个Group功能，你们学到知识或技能了吗？如果还想学到更多技能或者丰富自己的知识储备，欢迎关注亿速云行业资讯频道。
