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

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:

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：

1. 1. 
      
2. 增加wait_timeout的时间。
3. 减少Connection pools中connection的lifetime。
4. 测试Connection pools中connection的有效性。
   1. 
      

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