2016-07-22 17:56:18 [ERROR]-[http-nio-8080-exec-8:1273147][DruidDataSource:com.alibaba.druid.pool.DruidDataSource.handleConnectionException(DruidDataSource.java:1241)] discard connection
com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
The last packet successfully received from the server was 295,395 milliseconds ago. The last packet sent successfully to the server was 0 milliseconds ago.
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:409)
at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1127)
at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3715)
at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3604)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4155)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2615)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2776)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2832)
at com.mysql.jdbc.ConnectionImpl.setReadOnlyInternal(ConnectionImpl.java:5508)
at com.mysql.jdbc.ConnectionImpl.setReadOnly(ConnectionImpl.java:5501)
原因：
连接池保留了连接，但是mysql数据库已经回收了连接，修改数据库配置就
my.cnf
wait_timeout
interactive_timeout