一个项目使用了druid作为数据源，每过几十分钟刷新页面就会出现 java.net.SocketException: 断开的管道 (Write failed) 错误。
后来给连接池配置部分加上了
问题得到了解决，应该是长时间没有刷新页面导致数据库连接断开了，再次访问的时候使用了断开的数据库连接，所以出现报错，加入了
testOnBorrow 属性对数据库连接的有效性进行了验证，集群某实例宕掉时，如果连接刚好不处于通信阶段，tcp连接正处于CLOSE_WAIT状态或已关闭，当应用通过连接池getConnection时，
在borrow时会检测连接，由于连接已关闭，于是报了如下报错，并重新建立新连接，此时的新连接到集群的其他实例上了。后面能正常通信。
com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
Caused by: java.io.EOFException: Can not read response from server. Expected to read 4 bytes, read 0 bytes before connection was unexpectedly lost.
at com.mysql.jdbc.MysqlIO.readFully(MysqlIO.java:3143)
at com.mysql.jdbc.MysqlIO.readPacket(MysqlIO.java:597)
... 21 more
