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

深碍√TFBOYSˉ_ 2022-10-02 03:49 127阅读 0赞

[2019独角兽企业重金招聘Python工程师标准>>> ][2019_Python_] ![hot3.png][]

**问题描述：**

程序在运行的时候，刷新页面，会出现以下错误

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：

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

**解决方法补充：**

1、上述解决方法中修改了wait\_timeout ，但是我的是Linux 中的MySql版本是5.6的，我试着修改了下mysql/my.cnf 中的max\_connetions=1814400 ，然后测试了一下也是可以的。

转载于:https://my.oschina.net/xiaominmin/blog/2999284

[2019_Python_]: https://my.oschina.net/u/2663968/blog/3061697
[hot3.png]: /images/20220113/6b66cfef5f104ee5a63202d487fede24.png

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

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