一般的WEB应用如果是连ORACLE，要做连接池的话是在JAVA端用第三方的LIB，但对于MONGODB，官方已经有现成的实现，只需配置即可。
#控制系统在发生连接错误时是否重试 ，默认为false --boolean
mongo.options.autoConnectRetry=false
#每个主机允许的连接数（每个主机的连接池大小），当连接池被用光时，会被阻塞住 ，默认为10 --int
mongo.options.connectionsPerHost=10
#multiplier for connectionsPerHost for # of threads that can block if connectionsPerHost is 10, and threadsAllowedToBlockForConnectionMultiplier is 5, then 50 threads can block more than that and an exception will be throw --int
mongo.options.threadsAllowedToBlockForConnectionMultiplier=5
#被阻塞线程从连接池获取连接的最长等待时间（ms） --int
mongo.options.maxWaitTime
#在建立（打开）套接字连接时的超时时间（ms），默认为0（无限） --int
mongo.options.connectTimeout=0
#套接字超时时间;该值会被传递给Socket.setSoTimeout(int)。默认为0（无限） --int
mongo.options.socketTimeout=0
#This controls whether or not to have socket keep alive turned on (SO_KEEPALIVE). defaults to false --boolean
mongo.options.socketKeepAlive=false
#Override the DBCallback factory. Default is for the standard Mongo Java driver configuration --DBCallbackFactory
mongo.options.dbCallbackFactory
#//指明是否允许驱动从次要节点或者奴隶节点读取数据，默认为false --boolean
mongo.options.slaveOk=false
#如果为true，驱动每次update后会发出一个getLastError命令来保证成功，默认为false --boolean
mongo.options.safe=false
#If set, the w value of WriteConcern for the connection is set to this. Defaults to 0; implies safe = true --int
mongo.options.w=0
#If set, the wtimeout value of WriteConcern for the connection is set to this. Defaults to 0; implies safe = true --int
mongo.options.wtimeout=0
#Sets the fsync value of WriteConcern for the connection. Defaults to false; implies safe = true --boolean
mongo.options.fsync=false