1. The specific error is as follows:
2014-5-2 21:38:29 com. opensymphony. xwork2.util. logging. jdk. jdkLogger error severe: Exception occurred during processing request: nulljava. lang. nullPointerExceptionat com.you.file.upload.action.FileUploadAction.exe cute (FileUploadAction. java: 56) at sun. reflect. nativeMethodAccessorImpl. invoke0 (Native Method) at sun. reflect. nativeMethodAccessorImpl. invoke (NativeMethodAccessorImpl. java: 39) at sun. reflect. delegatingMethodAccessorImpl. invoke (DelegatingMethodAccessorImpl. java: 25) at java. lang. reflect. method. invoke (Method. java: 597) at com. opensymphony. xwork2.defaactionactioninvocation. invokeAction (defaactionactioninvocation. java: 450) at com. opensymphony. xwork2.defaactionactioninvocation. invokeActionOnly (defaactionactioninvocation. java: 289) at com. opensymphony. xwork2.defaactionactioninvocation. invoke (defaactionactioninvocation. java: 252) at org. apache. struts2.interceptor. deprecationInterceptor. intercept (DeprecationInterceptor. java: 41) at com. opensymphony. xwork2.defaactionactioninvocation. invoke (defaactionactioninvocation. java: 246) at org. apache. struts2.interceptor. debugging. debuggingInterceptor. intercept (DebuggingInterceptor. java: 256) at com. opensymphony. xwork2.defaactionactioninvocation. invoke (defaactionactioninvocation. java: 246) at com. opensymphony. xwork2.interceptor. defaultWorkflowInterceptor. doIntercept (DefaultWorkflowInterceptor. java: 167) at com. opensymphony. xwork2.interceptor. methodFilterInterceptor. intercept (MethodFilterInterceptor. java: 98) at com. opensymphony. xwork2.defaactionactioninvocation. invoke (defaactionactioninvocation. java: 246) at com. opensymphony. xwork2.validator. validationInterceptor. doIntercept (ValidationInterceptor. java: 265) at org. apache. struts2.interceptor. validation. annotationValidationInterceptor. doIntercept (AnnotationValidationInterceptor. java: 68) at com. opensymphony. xwork2.interceptor. methodFilterInterceptor. intercept (MethodFilterInterceptor. java: 98) at com. opensymphony. xwork2.defaactionactioninvocation. invoke (defaactionactioninvocation. java: 246) at com. opensymphony. xwork2.interceptor. conversionErrorInterceptor. intercept (ConversionErrorInterceptor. java: 138) at com. opensymphony. xwork2.defaactionactioninvocation. invoke (defaactionactioninvocation. java: 246) at com. opensymphony. xwork2.interceptor. parametersInterceptor. doIntercept (ParametersInterceptor. java: 249) at com. opensymphony. xwork2.interceptor. methodFilterInterceptor. intercept (MethodFilterInterceptor. java: 98) at com. opensymphony. xwork2.defaactionactioninvocation. invoke (defaactionactioninvocation. java: 246) at com. opensymphony. xwork2.interceptor. parametersInterceptor. doIntercept (ParametersInterceptor. java: 249) at com. opensymphony. xwork2.interceptor. methodFilterInterceptor. intercept (MethodFilterInterceptor. java: 98) at com. opensymphony. xwork2.defaactionactioninvocation. invoke (defaactionactioninvocation. java: 246) at com. opensymphony. xwork2.interceptor. staticParametersInterceptor. intercept (StaticParametersInterceptor. java: 191) at com. opensymphony. xwork2.defaactionactioninvocation. invoke (defaactionactioninvocation. java: 246) at org. apache. struts2.interceptor. multiselectInterceptor. intercept (MultiselectInterceptor. java: 73) at com. opensymphony. xwork2.defaactionactioninvocation. invoke (defaactionactioninvocation. java: 246) at org. apache. struts2.interceptor. checkboxInterceptor. intercept (CheckboxInterceptor. java: 91) at com. opensymphony. xwork2.defaactionactioninvocation. invoke (defaactionactioninvocation. java: 246) at org. apache. struts2.interceptor. fileUploadInterceptor. intercept (FileUploadInterceptor. java: 252) at com. opensymphony. xwork2.defaactionactioninvocation. invoke (defaactionactioninvocation. java: 246) at com. opensymphony. xwork2.interceptor. modelDrivenInterceptor. intercept (ModelDrivenInterceptor. java: 100) at com. opensymphony. xwork2.defaactionactioninvocation. invoke (defaactionactioninvocation. java: 246) at com. opensymphony. xwork2.interceptor. scopedModelDrivenInterceptor. intercept (ScopedModelDrivenInterceptor. java: 141) at com. opensymphony. xwork2.defaactionactioninvocation. invoke (defaactionactioninvocation. java: 246) at com. opensymphony. xwork2.interceptor. chainingInterceptor. intercept (ChainingInterceptor. java: 145) at com. opensymphony. xwork2.defaactionactioninvocation. invoke (defaactionactioninvocation. java: 246) at com. opensymphony. xwork2.interceptor. prepareInterceptor. doIntercept (PrepareInterceptor. java: 171) at com. opensymphony. xwork2.interceptor. methodFilterInterceptor. intercept (MethodFilterInterceptor. java: 98) at com. opensymphony. xwork2.defaactionactioninvocation. invoke (defaactionactioninvocation. java: 246) at com. opensymphony. xwork2.interceptor. i18nInterceptor. intercept (I18nInterceptor. java: 139) at com. opensymphony. xwork2.defaactionactioninvocation. invoke (defaactionactioninvocation. java: 246) at org. apache. struts2.interceptor. servletConfigInterceptor. intercept (ServletConfigInterceptor. java: 164) at com. opensymphony. xwork2.defaactionactioninvocation. invoke (defaactionactioninvocation. java: 246) at com. opensymphony. xwork2.interceptor. aliasInterceptor. intercept (AliasInterceptor. java: 193) at com. opensymphony. xwork2.defaactionactioninvocation. invoke (defaactionactioninvocation. java: 246) at com. opensymphony. xwork2.interceptor. predictionmappinginterceptor. intercept (ExceptionMappingInterceptor. java: 189) at com. opensymphony. xwork2.defaactionactioninvocation. invoke (defaactionactioninvocation. java: 246) at org. apache. struts2.interceptor. fileUploadInterceptor. intercept (FileUploadInterceptor. java: 252) at com. opensymphony. xwork2.defaactionactioninvocation. invoke (defaactionactioninvocation. java: 246) at org.apache.struts2.impl.StrutsActionProxy.exe cute (StrutsActionProxy. java: 54) at org. apache. struts2.dispatcher. dispatcher. serviceAction (Dispatcher. java: 562) at org.apache.struts2.dispatcher.ng.ExecuteOperations.exe cuteAction (ExecuteOperations. java: 77) at org. apache. struts2.dispatcher. ng. filter. strutsPrepareAndExecuteFilter. doFilter (StrutsPrepareAndExecuteFilter. java: 99) at org. apache. catalina. core. applicationFilterChain. internalDoFilter (ApplicationFilterChain. java: 243) at org. apache. catalina. core. applicationFilterChain. doFilter (ApplicationFilterChain. java: 210) at org. apache. catalina. core. standardWrapperValve. invoke (StandardWrapperValve. java: 222) at org. apache. catalina. core. standardContextValve. invoke (StandardContextValve. java: 123) at org. apache. catalina. authenticator. authenticatorBase. invoke (AuthenticatorBase. java: 472) at org. apache. catalina. core. standardHostValve. invoke (StandardHostValve. java: 171) at org. apache. catalina. valves. errorReportValve. invoke (ErrorReportValve. java: 99) at org. apache. catalina. valves. accessLogValve. invoke (AccessLogValve. java: 953) at org. apache. catalina. core. standardEngineValve. invoke (StandardEngineValve. java: 118) at org. apache. catalina. connector. coyoteAdapter. service (CoyoteAdapter. java: 408) at org. apache. coyote. http11.20.acthttp11processor. process (AbstractHttp11Processor. java: 1023) at org. apache. coyote. abstractProtocol $ AbstractConnectionHandler. process (AbstractProtocol. java: 589) at org.apache.tomcat.util.net. aprEndpoint $ SocketProcessor. run (AprEndpoint. java: 1852) at java. util. concurrent. threadPoolExecutor $ Worker. runTask (ThreadPoolExecutor. java: 886) at java. util. concurrent. threadPoolExecutor $ Worker. run (ThreadPoolExecutor. java: 908) at java. lang. thread. run (Thread. java: 619)
2. Error cause
No file is uploaded, so a null pointer is reported.
3. Solution
Select an appropriate file type