使用mongodb的java api编写程序，连接mongodb服务连不上，mongodb服务、客户端程序在不同机器上。发现有两种原因，第一：mongodb服务所在机器防火墙未关；第二：mongodb启动该时绑定ip。
以下是centos防火墙关闭、查询，及mongodb启动命令
[root@localhost Desktop]# systemctl stop firewalld.service
[root@localhost Desktop]# service firewalldstatus
[root@localhost bin]# mongod --bind_ip172.23.113.196执行上述命令后，客户端程序顺利连接上mongodb
2017-12-14 08:44:10,303 INFO cluster:76 Exception in monitor thread while connecting to server 172.23.113.196:27017
com.mongodb.MongoSocketOpenException: Exception opening socket
at com.mongodb.connection.SocketStream.open(SocketStream.java:62)
at com.mongodb.connection.InternalStreamConnection.open(InternalStreamConnection.java:126)
at com.mongodb.connection.DefaultServerMonitor$ServerMonitorRunnable.run(DefaultServerMonitor.java:114)
at java.lang.Thread.run(Thread.java:744)
Caused by: java.net.SocketTimeoutException: connect timed out
at java.net.DualStackPlainSocketImpl.waitForConnect(Native Method)
at java.net.DualStackPlainSocketImpl.socketConnect(DualStackPlainSocketImpl.java:85)
at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:339)
at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:200)
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:182)
at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:172)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
at java.net.Socket.connect(Socket.java:579)
at com.mongodb.connection.SocketStreamHelper.initialize(SocketStreamHelper.java:59)
at com.mongodb.connection.SocketStream.open(SocketStream.java:57)
... 3 more
2017-12-14 08:49:20,391 INFO connection:71 Opened connection [connectionId{localValue:12, serverValue:1}] to 172.23.113.196:27017
2017-12-14 08:49:20,403 INFO cluster:71 Monitor thread successfully connected to server with description ServerDescription{address=172.23.113.196:27017, type=STANDALONE, state=CONNECTED, ok=true, version=ServerVersion{versionList=[3, 6, 0]}, minWireVersion=0, maxWireVersion=6, maxDocumentSize=16777216, logicalSessionTimeoutMinutes=30, roundTripTimeNanos=9787930}
2017-12-14 08:49:21,921 INFO connection:71 Opened connection [connectionId{localValue:13, serverValue:2}] to 172.23.113.196:27017
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{ "_id" : { "$oid" : "5a30826af7e6ee724807d688" }, "title" : "rds learn", "description" : "rds is nosql database", "by" : "zhaogj", "url" : "http:www.rds.com", "tags" : ["rds", "database", "nosql"], "likes" : 99.0 }
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