阿里巴巴数据源Druid使用时报discard connection异常，为什么

2014-11-06 22:36:28,537 ERROR [com.alibaba.druid.pool.DruidDataSource] - discard connection
com.mysql.jdbc.CommunicationsException: The last communications with the server was 28816 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.

配置了testWhileIdle=true，validationQuery=SELECT 'x'

timeBetweenEvictionRunsMillis=60000

minEvictableIdleTimeMillis=300000