MongoDB count distinct group by JavaAPI查询

import java.net.UnknownHostException;
import com.mongodb.BasicDBList;
import com.mongodb.BasicDBObject;
import com.mongodb.DB;
import com.mongodb.DBCollection;
import com.mongodb.Mongo;
public class MongoDBTest {
private static DB db = null;

static{
Mongo mongo = null;
try {
mongo = new Mongo("localhost", 27017);
} catch (UnknownHostException e) {
e.printStackTrace();
}
db = mongo.getDB("TestDB");	//连接数据
}

/**
* select count(*) from list
*/
public Long m1() {
DBCollection collection = db.getCollection("list");
return collection.count();
}

/**
* select count(*) from list where userId = 'orange'
*/
public Long m2(){
DBCollection listCollection = db.getCollection("list");
BasicDBObject query =new BasicDBObject();
query.put("userId", "orange");
return listCollection.count(query);
}

/**
* select count(*) from list where userId = 'orange' and time >= '20101201' and time <= '20101211'
*/
public Long m3(){
DBCollection listCollection = db.getCollection("list");
BasicDBObject query =new BasicDBObject();
query.put("userId","orange");
query.put("time", new BasicDBObject("$gte", "20101201").append("$lte", "20101211"));
return listCollection.count(query);
}

/**
* select count(distinct(userId)) from detail where time >= '20101201' and time <='20101211'
*/
public int m4() {
DBCollection collection = db.getCollection("detail");
BasicDBObject query = new BasicDBObject();
query.put("time", new BasicDBObject("$gte", "20101201").append("$lte", "20101211"));
return collection.distinct("userId", query).size();
}

/**
* select date_format(time, '%Y-%m-%d %H') as sj ,count(*) from detail group by sj
*/
public void m5() {
DBCollection collection = db.getCollection("detail");
String formatDate = "function(obj,doc){"
+ "var date = new Date(doc.time);"
+ "var dateKey = date.getFullYear()+\"-\"+(date.getMonth()+1)+\"-\"+date.getDate(); "
+ "return {'time':datekey}" + "}";
BasicDBObject key = new BasicDBObject();
key.put(formatDate, true); // 要分组的列
BasicDBObject query = new BasicDBObject(); // where条件
String reduce = "function (obj, prev) {prev.count++}";
BasicDBObject initial = new BasicDBObject();
initial.append("count", 0); // 每列初始值
BasicDBList group = (BasicDBList) collection.group(key, query, initial,	reduce);
System.out.println(group);
}

}