使用Spring+SpringMVC+myBatis+Mysql开发一个应用服务端，由于在测试阶段没有上线，所以没有人会链接服务器。
放假回来才发现数据库被关闭了，而且要重启tomcat才有效，都不知道myBatis为什么会没有自动重连数据库的功能。
异常信息：
23-Sep-2017 09:43:39.880 SEVERE [http-nio-8081-exec-93] org.apache.catalina.core.StandardWrapperValve.invoke Servlet.service() for servlet [dispatcher] in context with path [/project] threw exception [Request processing failed; nested exception is org.springframework.dao.DataAccessResourceFailureException:
### Error querying database. Cause: com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: No operations allowed after connection closed.
### The error may exist in file [/www/apache-tomcat-8081/webapps/project/WEB-INF/classes/com/test/system/mapper/xml/cateMapper.xml]
### The error may involve com.test.system.mapper.SdGoodsCateMapper.getCateByGroup
### The error occurred while executing a query
### SQL: SELECT b.* FROM …..;
### Cause: com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: No operations allowed after connection closed.
; SQL []; No operations allowed after connection closed.; nested exception is com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: No operations allowed after connection closed.] with root cause
java.net.SocketException: Broken pipe (Write failed)
at java.net.SocketOutputStream.socketWrite0(Native Method)
at java.net.SocketOutputStream.socketWrite(SocketOutputStream.java:111)
at java.net.SocketOutputStream.write(SocketOutputStream.java:155)
at java.io.BufferedOutputStream.flushBuffer(BufferedOutputStream.java:82)
at java.io.BufferedOutputStream.flush(BufferedOutputStream.java:140)
at com.mysql.jdbc.MysqlIO.send(MysqlIO.java:3728)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2509)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2680)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2490)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2448)
at com.mysql.jdbc.StatementImpl.executeQuery(StatementImpl.java:1381)
at com.mysql.jdbc.DatabaseMetaData.getUserName(DatabaseMetaData.java:6274)
at org.apache.commons.dbcp.DelegatingConnection.toString(DelegatingConnection.java:123)
at org.apache.commons.dbcp.PoolingDataSource$PoolGuardConnectionWrapper.toString(PoolingDataSource.java:355)
at java.lang.String.valueOf(String.java:2994)
at java.lang.StringBuilder.append(StringBuilder.java:131)
at org.mybatis.spring.transaction.SpringManagedTransaction.openConnection(SpringManagedTransaction.java:87)
at org.mybatis.spring.transaction.SpringManagedTransaction.getConnection(SpringManagedTransaction.java:68)
at org.apache.ibatis.executor.BaseExecutor.getConnection(BaseExecutor.java:315)
at org.apache.ibatis.executor.SimpleExecutor.prepareStatement(SimpleExecutor.java:75)
at org.apache.ibatis.executor.SimpleExecutor.doQuery(SimpleExecutor.java:61)
at org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:303)
at org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:154)
at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:102)
at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:82)
at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:120)
at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:113)
at sun.reflect.GeneratedMethodAccessor2495.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:408)
at com.sun.proxy.$Proxy408.selectList(Unknown Source)
at org.mybatis.spring.SqlSessionTemplate.selectList(SqlSessionTemplate.java:206)
at org.apache.ibatis.binding.MapperMethod.executeForMany(MapperMethod.java:122)
at org.apache.ibatis.binding.MapperMethod.execute(MapperMethod.java:64)
at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:53)
at com.sun.proxy.$Proxy434.getCateByGroup(Unknown Source)
at com.test.system.service.HomeServiceImpl.getHomeAlbumByHot(HomeServiceImpl.java:95)
at com.test.app.controller.HomeController.getAlbumByHot(HomeController.java:60)
at sun.reflect.GeneratedMethodAccessor2778.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:222)
at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:137)
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:110)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:814)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:737)
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:959)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893)
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:969)
at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:860)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:845)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:292)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:121)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:212)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:94)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:504)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:141)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:620)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:502)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1132)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:684)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1533)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1489)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:748)
原因分析：
查看了Mysql的文档，以及Connector/J的文档以及在线说明发现，出现这种异常的原因是：
Mysql服务器默认的“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。这就是问题的所在，在C3P0 pools中的connections如果空闲超过8小时，Mysql将其断开，而C3P0并不知道该connection已经失效，如果这时有Client请求connection，C3P0将该失效的Connection提供给Client，将会造成上面的异常。
解决方案：
加上如下配置：
//SQL查询,用来验证从连接池取出的连接,在将连接返回给调用者之前.如果指定,则查询必须是一个SQL SELECT并且必须返回至少一行记录
validationQuery = select 1
//指明连接是否被空闲连接回收器(如果有)进行检验.如果检测失败,则连接将被从池中去除.
testWhileIdle = true
//在空闲连接回收器线程运行期间休眠的时间值,以毫秒为单位.如果设置为非正数,则不运行空闲连接回收器线程
timeBetweenEvictionRunsMillis = 3600000
//1000 * 60 * 30 连接在池中保持空闲而不被空闲连接回收器线程,(如果有)回收的最小时间值，单位毫秒
minEvictableIdleTimeMillis = 18000000
//指明是否在从池中取出连接前进行检验,如果检验失败,则从池中去除连接并尝试取出另一个.
testOnBorrow = true
validationQuery参考：
validationQuery是用来验证数据库连接的查询语句，这个查询语句必须是至少返回一条数据的SELECT语句。每种数据库都有各自的验证语句，下表中收集了几种常见数据库的validationQuery。
DataBase validationQuery hsqldb select 1 from INFORMATION_SCHEMA.SYSTEM_USERS Oracle select 1 from dual DB2 select 1 from sysibm.sysdummy1 MySql select 1 Microsoft SqlServer select1 postgresql select version() ingres select 1 derby values 1 H2 select 1
BasicDataSource Configuration Parameters：
http://commons.apache.org/proper/commons-dbcp/configuration.html
