DBCP错误：java.sql.SQLException: Already closed.
遇到这个错误，搜索了一下解决方法，经测试好用。
原因：You're probably running into the fact that MYSQL closes connections
which have been open "too long".
Probably if you make the request to the server again, you'll find that
it works because the connection is reopened.
解决方法： One way to deal with this is to add the following to your context.xml
Resource:
validationQuery="select 1"
代价：This causes a very cheap test query to always be run first; if the
connection has been closed, this gets the failure, and
then a new connection is opened
java.sql.SQLException: Already closed.
at org.apache.tomcat.dbcp.dbcp.PoolableConnection.close(PoolableConnection.java:84)
at org.apache.tomcat.dbcp.dbcp.PoolingDataSource$PoolGuardConnectionWrapper.close(PoolingDataSource.java:181)
at com.lwjlaser.citation2DB.Citation.controller(Citation.java:84)
at com.lwjlaser.citation2DB.DealCitation.doPost(DealCitation.java:46)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:852)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
at java.lang.Thread.run(Thread.java:619)
原因：You're probably running into the fact that MYSQL closes connections
which have been open "too long".
Probably if you make the request to the server again, you'll find that
it works because the connection is reopened.
解决方法： One way to deal with this is to add the following to your context.xml
Resource:
validationQuery="select 1"
代价：This causes a very cheap test query to always be run first; if the
connection has been closed, this gets the failure, and
then a new connection is opened