解决 与MySQL 连接失败 Communications link failure Connection timed out

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

Last packet sent to the server was 26477679 ms ago.
	at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
	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.send(MysqlIO.java:3270)
	at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1932)
	at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2101)
	at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2548)
	at com.mysql.jdbc.ConnectionImpl.setAutoCommit(ConnectionImpl.java:4916)
	at org.apache.commons.dbcp.DelegatingConnection.setAutoCommit(DelegatingConnection.java:331)
	at org.apache.commons.dbcp.PoolingDataSource$PoolGuardConnectionWrapper.setAutoCommit(PoolingDataSource.java:317)
	at org.springframework.jdbc.datasource.DataSourceTransactionManager.doBegin(DataSourceTransactionManager.java:223)
	... 46 more
Caused by: java.net.SocketException: Connection timed out
	at java.net.SocketOutputStream.socketWrite0(Native Method)
	at java.net.SocketOutputStream.socketWrite(SocketOutputStream.java:113)
	at java.net.SocketOutputStream.write(SocketOutputStream.java:159)
	at java.io.BufferedOutputStream.flushBuffer(BufferedOutputStream.java:82)
	at java.io.BufferedOutputStream.flush(BufferedOutputStream.java:140)
	at com.mysql.jdbc.MysqlIO.send(MysqlIO.java:3251)
	... 53 more

这是项目部署到服务器，大半夜跑定时任务时出现的错误。我用的是dbcp 连接池，之所以出现这中情况，是MySQL 默认的“wait_timeout”是8小时，也就是说一个connection空闲超过8个小时，MySQL 将自动断开该connection。

解决办法： 

1. 增加MySQL wait_timeout 时间配置。
2. 在dbcp 配置中加入下面的配置

		  
		  
		  
		  
		  
		  
		  
			SELECT 1  
		  
		  
			true