最近发现了一个现象，观察到的生产环境，不要有一段时间操作，然后另一个操作，首先将有一个数据库连接：java.sql.SQLException: Already closed.，例如下列：

error log:  ( org.springframework.dao.RecoverableDataAccessException: PreparedStatementCallback; SQL [select user_id,login_name from t_sys_user where login_name=?

and password=?]; The last packet successfully received from the server was1290665 seconds ago.The
last packet sent successfully to the server was 1290665 seconds ago, which is longer than the server configured value of 'wait_timeout'. You should consider either expiring and/or testing connection validity before use in your application, increasing the server
configured values for client timeouts, or using the Connector/J connection property 'autoReconnect=true' to avoid this problem.; nested exception is com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: The last packet successfully received from the server
was1290665 seconds ago.The last packet sent successfully to the server was 1290665 seconds ago, which is longer than the server configured value of 'wait_timeout'. You should consider either expiring and/or testing connection validity before use in your application,
increasing the server configured values for client timeouts, or using the Connector/J connection property 'autoReconnect=true' to avoid this problem. )

数据源是用tomcat dbcp 基于jndi配置管理的。查了下。例如以下：

原因：

You're probably running into the fact that MYSQL closes connections  which have been open "too long". 

Probably if you make the request to the server again, you'll find that  it works because the connection is reopened.

解决方法：

One way to deal with this is to add the following to your context.xml  Resource:

validationQuery="select 1" 
(基于mysql)

validationQuery="select
1 from dual"  (基于oracle)

代价：

This causes a very cheap test query to always be run first; if the  connection has been closed, this gets the failure,
and 

then a new connection is opened.

细想下原来用weblogic jdbc jndi的配置有一个专门的配置项来配置这个test query，配置tomcat时粗心大意了 ：(

[2015-04-30 11:15:46,939 ERROR [com.tencent.vsuning.aop.LogAdvice] - org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException:
Data source rejected establishment of connection,  message from server: "Too many connections"]  数据库连接池耗尽异常...