异常解决：Caused by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

问题描述：

程序在运行的时候，刷新页面，会出现以下错误

Caused by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

Last packet sent to the server was 0 ms ago.

at sun.reflect.GeneratedConstructorAccessor36.newInstance(Unknown Source)

at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)

at java.lang.reflect.Constructor.newInstance(Constructor.java:526)

at com.mysql.jdbc.Util.handleNewInstance(Util.java:406)

at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1074)

at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:2985)

at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:2871)

at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3414)

at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1936)

at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2060)

at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2536)

at com.mysql.jdbc.ConnectionImpl.setAutoCommit(ConnectionImpl.java:4874)

at com.mchange.v2.c3p0.impl.NewProxyConnection.setAutoCommit(NewProxyConnection.java:912)

at org.hibernate.connection.C3P0ConnectionProvider.getConnection(C3P0ConnectionProvider.java:83)

at org.hibernate.jdbc.ConnectionManager.openConnection(ConnectionManager.java:446)

... 78 more

Caused by: java.io.EOFException: Can not read response from server. Expected to read 4 bytes, read 0 bytes before connection was unexpectedly lost.

at com.mysql.jdbc.MysqlIO.readFully(MysqlIO.java:2431)

at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:2882)

... 87 more

上述问题是由mysql数据库的配置引起的。mysql将其连接的等待时间(wait_timeout)缺省为8小时。在其客户程序中可以这样来查看其值：

mysql> show global variables like "wait_timeout";

+---------------+---------+

| Variable_name | Value |

+---------------+---------+

| wait_timeout | 1814400 |

+---------------+---------+

1 row in set (0.00 sec)

如果在wait_timeout秒期间内，数据库连接(java.sql.Connection)一直处于等待状态，mysql就将该连接关闭。这时，你的Java应用的连接池仍然合法地持有该连接的引用。当用该连接来进行数据库操作时，就碰到上述错误。

解决办法：

1、修改MySQL数据配置文件，Windows文件名是my.ini，路径在MYSQL安装路径下；Linux中文件名是my.cnf 路径在/etc/my.cnf。修改wait_timeout = 1814400；

2、重启MySQL数据库： service mysqld restart