Communications link failure due to underlying exception

数据库为Mysql，当登录网站操作时出现以下异常信息：

No operations allowed after connection closed.Connection was implicitly closed due to underlying exception/error: ** BEGIN NESTED EXCEPTION ** com.mysql.jdbc.CommunicationsException MESSAGE: Communications link failure due to underlying exception: ** BEGIN NESTED EXCEPTION ** java.net.SocketException MESSAGE: Software caused connection abort: socket write error STACKTRACE: java.net.SocketException: Software caused connection abort: socket write error at java.net.SocketOutputStream.socketWrite0(Native Method) at java.net.SocketOutputStream.socketWrite(Unknown Source) at java.net.SocketOutputStream.write(Unknown Source) at java.io.BufferedOutputStream.flushBuffer(Unknown Source) at java.io.BufferedOutputStream.flush(Unknown Source) at com.mysql.jdbc.MysqlIO.send(MysqlIO.java:2692) at com.mysql.jdbc.MysqlIO.send(MysqlIO.java:2621) at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1552) at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:1666) at com.mysql.jdbc.Connection.execSQL(Connection.java:2994) at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:936) at com.mysql.jdbc.PreparedStatement.executeQuery(PreparedStatement.java:1030) at org.hibernate.jdbc.AbstractBatcher.getResultSet(AbstractBatcher.java:139) at
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经查看相关资料，发现问题的原因如下：

   Mysql服务器默认的“wait_timeout”是8小时，如果connection空闲超过8个小时，Mysql将自动断开该 connection。在C3P0 pools中的connections如果空闲超过8小时，Mysql将其断开，而C3P0中的该connection仍然存在，如果这时有 Client请求connection，C3P0将该断开的Connection提供给Client，将会造成上面的异常。

可以这么解决该问题：
         使得Connection pools中connection的lifetime与Mysql的wait_timeout时间达到一致，或者测试Connection pools中connection的有效性。
在wait_timeout的时间为8小时的情况下：

C3P0增加以下配置信息:

1. //set to 'SELECT 1'      
2. preferredTestQuery = 'SELECT 1'   
3. //set to something much less than wait_timeout, prevents connections from going stale   
4. idleConnectionTestPeriod = 18000     
5. //set to something slightly less than wait_timeout, preventing 'stale' connections from being //handed out   
6. maxIdleTime = 25000   
7. //if you can take the performance 'hit', set to "true"   
8. testConnectionOnCheckout = true    

 

 

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MySQL连接如果8小时未使用，在查询使用到该连接会报：

异常名称：com.mysql.jdbc.CommunicationsException
异常信息: Communications link failure due to underlying exception

如果是MySQL5以前的版本，需要修改连接池配置中的URL，添加autoReconnect=true

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如果是MySQL5 以后的版本，需要修改my.cnf(或者my.ini)文件，在[mysqld]后面添加

wait_timeout = 172800
interactive-timeout = 172800

单位都是秒，记得必须都添加，否则不起作用，通过show variables查看wait_timeout的值。