Communications link failure due to underlying exception异常处理（转）

最近的一个项目在Hibernate使用C3P0的连接池，数据库为Mysql。开发测试没有问题，在运行中每个一段长的空闲时间就出现异常:

java 代码

org.hibernate.exception.JDBCConnectionException: could not execute query

at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:74)

at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:43)

.......

Caused by: com.mysql.jdbc.exceptions.MySQLNonTransientConnectionException: No operations allowed after connection closed.Connection was implicitly closed due to underlying exception/error:

** BEGIN NESTED EXCEPTION **

com.mysql.jdbc.CommunicationsException

MESSAGE: Communications link failure due to underlying exception:

** BEGIN NESTED EXCEPTION **

java.net.SocketException

MESSAGE: Broken pipe

STACKTRACE:

java.net.SocketException: Broken pipe

at java.net.SocketOutputStream.socketWrite0(Native Method)

......

** END NESTED EXCEPTION **

查看了Mysql的文档，以及Connector/J的文档以及在线说明发现，出现这种异常的原因是：

Mysql服务器默认的“wait_timeout”是8小时，也就是说一个connection空闲超过8个小时，Mysql将自动断开该connection。这就是问题的所在，在C3P0 pools中的connections如果空闲超过8小时，Mysql将其断开，而C3P0并不知道该connection已经失效，如果这时有Client请求connection，C3P0将该失效的Connection提供给Client，将会造成上面的异常。

解决的方法有3种：

增加wait_timeout的时间。
减少Connection pools中connection的lifetime。
测试Connection pools中connection的有效性。

当然最好的办法是同时综合使用上述3种方法，下面就DBCP和C3P0分别做一说明，假设wait_timeout为默认的8小时

DBCP增加以下配置信息:

//set to 'SELECT 1'

validationQuery = "SELECT 1"

//set to 'true'

testWhileIdle = "true"

//some positive integer

timeBetweenEvictionRunsMillis = 3600000

//set to something smaller than 'wait_timeout'

minEvictableIdleTimeMillis = 18000000

//if you don't mind a hit for every getConnection(), set to "true"

testOnBorrow = "true"

C3P0增加以下配置信息:

//获取connnection时测试是否有效

testConnectionOnCheckin = true

//自动测试的table名称

automaticTestTable=C3P0TestTable

//set to something much less than wait_timeout, prevents connections from going stale

idleConnectionTestPeriod = 18000

//set to something slightly less than wait_timeout, preventing 'stale' connections from being handed out

maxIdleTime = 25000

//if you can take the performance 'hit', set to "true"

testConnectionOnCheckout = true

更多的配置信息大家可以查看C3P0文档，Connector/J文档，以及DBCP的文档。