最后，我是将json字符串，利用jackson转换成map，然后利用map一层一层扒的，最后返回的才是一个数值

db.xxx.findOne({"_id":"37389873"}, {"Date.name.count": 1}).Date.name.count

运行效果

~/tmp
▶ cat mmm.js
#!/usr/bin/env mongo

var db = connect('test');
db.xxx.drop();
db.xxx.insert({
  "_id": "37389873",
  "Date":{
         "name":{"count":"7",
                 "user": "liyang",
                 }

         }

 });

print( db.xxx.findOne({"_id":"37389873"}, {"Date.name.count": 1}).Date.name.count );


~/tmp
▶ ./mmm.js
MongoDB shell version: 2.6.3
connecting to: test
connecting to: test
7

http://jongo.org/
也许这个是你想找的

spring 的 mongodb 插件就可以满足

BasicQuery query = new BasicQuery(query,fields);

query 是查询条件
fields是要查询的字段

collections.find(docQuery).projection(keys)