Caused by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: The last packet successfully received from the server was 2,926,157 milliseconds ago. The last packet sent successfully to the server was 2,926,158 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.
解决办法：
如果连接闲置8小时 (8小时内没有进行数据库操作), mysql就会自动断开连接, 要重启tomcat.
不用hibernate的话, connection url加参数: autoReconnect=true
用hibernate的话, 加如下属性:
<property name="hibernate.connection.provider_class">org.hibernate.connection.C3P0ConnectionProvider
</property>
<property name="hibernate.c3p0.max_size">50</property>
<property name="hibernate.c3p0.min_size">5</property>
<property name="hibernate.c3p0.timeout">10</property>
<property name="hibernate.c3p0.max_statements">50</property>
<property name="hibernate.c3p0.idle_test_period">10</property>
<property name="hibernate.c3p0.acquire_increment">2</property>