com.mysql.jdbc.exceptions.jdbc4.CommunicationsException/com.atomikos.datasource.ResourceException异常解决
tomcat+mysql部署，每天早晨第一次访问web项目，出现mysql的连接timeout异常：com.mysql.jdbc.exceptions.jdbc4.CommunicationsException或com.atomikos.datasource.ResourceException。
############################################################################ com.atomikos.datasource.ResourceException: XA resource ‘center‘: resume for XID ‘3139322E3136382E312E35332E746D30303030363030303530:3139322E3136382E312E35332E746D37‘ raised 0: unknown com.mysql.jdbc.jdbc2.optional.MysqlXAException: The last packet successfully received from the server was 50,024,067 milliseconds ago. The last packet sent successfully to the server was 50,024,068 milliseconds ago. 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. ############################################################################ The error occurred while applying a parameter map. --- Check the ts_user.ibatorgenerated_selectByExample-InlineParameterMap. --- Check the statement (query failed). --- Cause: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: The last packet successfully received from the server was 232,007,469 milliseconds ago. The last packet sent successfully to the server was 232,007,485 milliseconds ago. 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.ibatis.common.jdbc.exception.NestedSQLException: --- The error occurred while applying a parameter map. --- Check the ts_user.ibatorgenerated_selectByExample-InlineParameterMap. --- Check the statement (query failed). --- Cause: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: The last packet successfully received from the server was 232,007,469 milliseconds ago. The last packet sent successfully to the server was 232,007,485 milliseconds ago. 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.
原因
mysql5连接的等待时间（wait_timeout）默认是8小时。
查看方法
show global variables like ‘wait_timeout‘;
查看结果：
+---------------+-------+
| Variable_name | Value
|
+---------------+-------+
| wait_timeout | 28800
|
+---------------+-------+
1 row in set (0.00
sec)
在wait_timeout时间里，mysql的connection处于等待状态，过了这时间mysql5就关闭了，但是java
application的连接池仍然有合法的connection，当你再操作数据库时，就会出现这样的问题。
解决方法
mysql5之前的版本，可以在jdbc连接的url中加入：autoReconnect = true
mysql5中wait_timeout在window中最大为24天，在linux中最大为365天。
a、修改配置
如果在window中设置为21天，改mysql5的安装文件夹中的my.ini
如果在linux中/etc/my.cnf，添加一行：wait_timeout = 1814400，重启mysql，添加效果如下：
b、直接用sql命令行修改(重启有还原为28800，不推荐)
mysql> set global wait_timeout=1814400; mysql> show global variables like ‘wait_timeout‘;
查看mysql版本
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