求助。网页报空指针异常

Question

用struts2和mysql写的网站，大致就是从数据库读取信息列表，再刚启动tomcat的时候都没有问题，可是时间一长（可能么大概要好几个小时，没法准确定位时间），就出现空指针异常的错误，刷新一下又能正常显示（多次刷新还是会出现报错），重启tomcat之后在一段时间内不会出现这种情况，贴下部分报错信息Stacktracesjava.lang.NullPointerException    com.kongtrolink.service.impl.NewsDaoImpl.queryAllNews(NewsDaoImpl.java:36)     com.kongtrolink.action.NewsAction.query(NewsAction.java:28)     sun.reflect.GeneratedMethodAccessor122.invoke(Unknown Source)     sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)     java.lang.reflect.Method.invoke(Method.java:497)     com.opensymphony.xwork2.DefaultActionInvocation.invokeAction(DefaultActionInvocation.java:441)     com.opensymphony.xwork2.DefaultActionInvocation.invokeActionOnly(DefaultActionInvocation.java:280)     com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:243)     com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:165)     com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)     com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)     com.opensymphony.xwork2.validator.ValidationInterceptor.doIntercept(ValidationInterceptor.java:252)     org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor.doIntercept(AnnotationValidationInterceptor.java:68)     com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)     com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)     com.opensymphony.xwork2.interceptor.ConversionErrorInterceptor.intercept(ConversionErrorInterceptor.java:122)     com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)     com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:195)     com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)     com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)     com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:195)     com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)     com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)     com.opensymphony.xwork2.interceptor.StaticParametersInterceptor.intercept(StaticParametersInterceptor.java:179)     com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)     org.apache.struts2.interceptor.MultiselectInterceptor.intercept(MultiselectInterceptor.java:75)     com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)     org.apache.struts2.interceptor.CheckboxInterceptor.intercept(CheckboxInterceptor.java:94)     com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)     org.apache.struts2.interceptor.FileUploadInterceptor.intercept(FileUploadInterceptor.java:235)     com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)     com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor.intercept(ModelDrivenInterceptor.java:89)     com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)     com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor.intercept(ScopedModelDrivenInterceptor.java:130)     com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)     org.apache.struts2.interceptor.debugging.DebuggingInterceptor.intercept(DebuggingInterceptor.java:267)     com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)     com.opensymphony.xwork2.interceptor.ChainingInterceptor.intercept(ChainingInterceptor.java:126)     com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)     com.opensymphony.xwork2.interceptor.PrepareInterceptor.doIntercept(PrepareInterceptor.java:138)     com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)     com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)     com.opensymphony.xwork2.interceptor.I18nInterceptor.intercept(I18nInterceptor.java:165)     com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)     org.apache.struts2.interceptor.ServletConfigInterceptor.intercept(ServletConfigInterceptor.java:164)     com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)     com.opensymphony.xwork2.interceptor.AliasInterceptor.intercept(AliasInterceptor.java:179)     com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)     com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept(ExceptionMappingInterceptor.java:176)     com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)     org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:52)     org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:488)     org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:77)     org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:91)     com.kongtrolink.filter.UeditorFilter.doFilter(UeditorFilter.java:23)     org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)     org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)     org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:217)     org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)     org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)     org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142)     org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)     org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)     org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:518)     org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091)     org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:673)     org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1500)     org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1456)     java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)     java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)     org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)     java.lang.Thread.run(Thread.java:745)