spring中mongdb连接池配置，最大连接数

可参考博客https://blog.youkuaiyun.com/qazwsx081/article/details/50924352，讲的不错
可参考官网：

http://docs.spring.io/spring-data/data-mongodb/docs/current/reference/html/

http://api.mongodb.org/java/current/com/mongodb/MongoOptions.html#connectionsPerHost