> 装free 版本的onlinejudge的时候出现下面的问题:::
> 该怎么解决呢??? 谢谢
> 
> Exception Occurred
> 
>   
> Exception stack 
> java.lang.NullPointerException
> 	at com.pku.judgeonline.common.FormattedOut.printHead(Unknown Source)
> 	at com.pku.judgeonline.servlet.Index.doGet(Unknown Source)
> 	at javax.servlet.http.HttpServlet.service(HttpServlet.java:690)
> 	at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
> 	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:269)
> 	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
> 	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:210)
> 	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:174)
> 	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
> 	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:117)
> 	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:108)
> 	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:151)
> 	at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:870)
> 	at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:665)
> 	at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:528)
> 	at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:81)
> 	at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:685)
> 	at java.lang.Thread.run(Unknown Source)
> 
>  Go Back  Contact Administrator
> 
> Welcome to JudgeOnline
>   Problem Set is the place where you can find large amount of problems from different programming contests. Online Judge System allows you to test your solution for every problem.
> 
>   First of all, read carefully Frequently Asked Questions.
>   Then, choose problem, solve it and submit it.
> 
>   If you want to publish your problems or setup your own online contest, just write us
> 
> 
>   Designer: Ying Fuchen
>   Developer:Xu Pengcheng   Ying Fuchen
>  
> 
> Home Page   Go Back  To top
> 
> 是数据库版本不对，要安装mysql4，我安装mysql5出现这个问题.