getting "Null Pointer Exception" while export excel file with xlsx extension in displaytag
我想在我的项目中打开带有 xlsx 扩展名的 Excel 文件(项目已经存在一个用于导出 xls 的显示标签)。我也想使用相同的显示标签 jar 来导出 xlsx。我只是按照" stackoverflow"用于在 displaytag 中导出带有 xlsx 扩展名的 excel 文件，在按照上述步骤运行项目时低于"空指针异常"。
注意：我在我的 jsp 文件中使用 eclipse IDE、Tomcat 7.0 和装饰器类，使用已用于导出 xls 的显示标签 -1.2 jar。
错误如下，
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 | root cause java.lang.Class.forName0(Native Method) java.lang.Class.forName(Unknown Source) org.displaytag.util.ReflectHelper.classForName(ReflectHelper.java:43) org.displaytag.export.ExportViewFactory.registerExportView(ExportViewFactory.java:95) org.displaytag.export.ExportViewFactory.<init>(ExportViewFactory.java:67) org.displaytag.export.ExportViewFactory.getInstance(ExportViewFactory.java:79) org.displaytag.tags.TableTag.doStartTag(TableTag.java:753) org.apache.jsp.jsp.commonmodule.ISpaceScreen52_jsp._jspx_meth_display_005ftable_005f0(ISpaceScreen52_jsp.java:548) org.apache.jsp.jsp.commonmodule.ISpaceScreen52_jsp._jspService(ISpaceScreen52_jsp.java:291) org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70) javax.servlet.http.HttpServlet.service(HttpServlet.java:728) org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432) org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390) org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334) javax.servlet.http.HttpServlet.service(HttpServlet.java:728) org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:88) org.apache.jasper.runtime.JspRuntimeLibrary.include(JspRuntimeLibrary.java:954) org.apache.jasper.runtime.PageContextImpl.doInclude(PageContextImpl.java:684) org.apache.jasper.runtime.PageContextImpl.include(PageContextImpl.java:678) org.apache.tiles.jsp.context.JspTilesRequestContext.include(JspTilesRequestContext.java:103) org.apache.tiles.jsp.context.JspTilesRequestContext.dispatch(JspTilesRequestContext.java:96) org.apache.tiles.renderer.impl.UntypedAttributeRenderer.write(UntypedAttributeRenderer.java:61) org.apache.tiles.renderer.impl.AbstractBaseAttributeRenderer.render(AbstractBaseAttributeRenderer.java:103) org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:659) org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:337) org.apache.tiles.jsp.taglib.InsertAttributeTag.render(InsertAttributeTag.java:234) org.apache.tiles.jsp.taglib.InsertAttributeTag.render(InsertAttributeTag.java:211) org.apache.tiles.jsp.taglib.RenderTag.doEndTag(RenderTag.java:220) org.apache.jsp.jsp.layout.DefaultLayout_jsp._jspx_meth_tiles_005finsertAttribute_005f3(DefaultLayout_jsp.java:362) org.apache.jsp.jsp.layout.DefaultLayout_jsp._jspService(DefaultLayout_jsp.java:210) org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70) javax.servlet.http.HttpServlet.service(HttpServlet.java:728) org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432) org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390) org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334) javax.servlet.http.HttpServlet.service(HttpServlet.java:728) org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:88) org.apache.tiles.servlet.context.ServletTilesRequestContext.forward(ServletTilesRequestContext.java:241) org.apache.tiles.servlet.context.ServletTilesRequestContext.dispatch(ServletTilesRequestContext.java:222) org.apache.tiles.renderer.impl.TemplateAttributeRenderer.write(TemplateAttributeRenderer.java:44) org.apache.tiles.renderer.impl.AbstractBaseAttributeRenderer.render(AbstractBaseAttributeRenderer.java:103) org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:659) org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:678) org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:633) org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:322) org.apache.struts2.views.tiles.TilesResult.doExecute(TilesResult.java:105) org.apache.struts2.dispatcher.StrutsResultSupport.execute(StrutsResultSupport.java:186) com.opensymphony.xwork2.DefaultActionInvocation.executeResult(DefaultActionInvocation.java:362) com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:266) 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:243) 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:485) org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:77) org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:91) org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:368) org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:109) org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:83) org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380) org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:97) org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380) org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:100) org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380) org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:78) org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380) org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:54) org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380) org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:35) org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380) org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:187) org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380) org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:105) org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380) org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:79) org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380) org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:169) org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:237) org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:167) org.displaytag.filter.ResponseOverrideFilter.doFilter(ResponseOverrideFilter.java:125) enter code here |
此处提供示例代码
ExportViewFactory.java 的代码
在 ExportViewFactory.java 的代码中，它从
如果你已经指定并且你已经编辑了
除非你设置
，否则它不会被使用
1 | export.[mymedia]=true |
如果您已经指定了类的名称，并且如果它没有适当的构造函数，则错误可能出现在 ExportViewFactory.java at
1 2 3 4 | try { exportClass.newInstance(); } |
但是您在 ExportViewFactory.java 中的
中得到
1 2 3 4 | try { exportClass = ReflectHelper.classForName(viewClassName); } |
这只是意味着
请检查您的
1 | export.[mymedia].class=com.displaytag.export.views.myExcel2007ExportView |
确保你的包名和类名正确且存在。