问题
I am following the example here http://www.tutorialspoint.com/struts_2/struts_file_uploads.htm
In this example,interceptor fileUpload and basicStack are used
<action name="upload" class="com.rwy.demo.action.UploadFile">
<interceptor-ref name="basicStack">
<interceptor-ref name="fileUpload">
<param name="allowedTypes">image/jpeg,image/gif</param>
</interceptor-ref>
<result name="success">/success.jsp</result>
<result name="error">/error.jsp</result>
</action>
After running this example,I got a NullPointerException.When I removed those interceptor( I understand that defaultStack will be used when no interceptor is specified ), it worked fine.I think the problem is that the interceptor params was not properly used/referenced
<action name="upload" class="com.rwy.demo.action.UploadFile">
<result name="success">/success.jsp</result>
<result name="error">/error.jsp</result>
</action>
However, in the basicStack, the params is included. Thus, the parameter in a form is not passed to action,causing this exception
Any response is appreciated.
The following is the full stacktrace:
java.lang.NullPointerException
java.io.File.<init>(File.java:317)
com.rwy.demo.action.UploadFile.execute(UploadFile.java:24)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
java.lang.reflect.Method.invoke(Method.java:497)
ognl.OgnlRuntime.invokeMethod(OgnlRuntime.java:891)
ognl.OgnlRuntime.callAppropriateMethod(OgnlRuntime.java:1293)
ognl.ObjectMethodAccessor.callMethod(ObjectMethodAccessor.java:68)
com.opensymphony.xwork2.ognl.accessor.XWorkMethodAccessor.callMethodWithDebugInfo(XWorkMethodAccessor.java:117)
com.opensymphony.xwork2.ognl.accessor.XWorkMethodAccessor.callMethod(XWorkMethodAccessor.java:108)
ognl.OgnlRuntime.callMethod(OgnlRuntime.java:1369)
ognl.ASTMethod.getValueBody(ASTMethod.java:90)
ognl.SimpleNode.evaluateGetValueBody(SimpleNode.java:212)
ognl.SimpleNode.getValue(SimpleNode.java:258)
ognl.Ognl.getValue(Ognl.java:494)
ognl.Ognl.getValue(Ognl.java:458)
com.opensymphony.xwork2.ognl.OgnlUtil$2.execute(OgnlUtil.java:309)
com.opensymphony.xwork2.ognl.OgnlUtil.compileAndExecute(OgnlUtil.java:340)
com.opensymphony.xwork2.ognl.OgnlUtil.getValue(OgnlUtil.java:307)
com.opensymphony.xwork2.DefaultActionInvocation.invokeAction(DefaultActionInvocation.java:423)
com.opensymphony.xwork2.DefaultActionInvocation.invokeActionOnly(DefaultActionInvocation.java:287)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:250)
org.apache.struts2.interceptor.FileUploadInterceptor.intercept(FileUploadInterceptor.java:326)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
org.apache.struts2.interceptor.DeprecationInterceptor.intercept(DeprecationInterceptor.java:41)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
com.opensymphony.xwork2.interceptor.ConversionErrorInterceptor.intercept(ConversionErrorInterceptor.java:138)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:229)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:229)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
org.apache.struts2.interceptor.MultiselectInterceptor.intercept(MultiselectInterceptor.java:73)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
org.apache.struts2.interceptor.DateTextFieldInterceptor.intercept(DateTextFieldInterceptor.java:125)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
org.apache.struts2.interceptor.CheckboxInterceptor.intercept(CheckboxInterceptor.java:91)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
com.opensymphony.xwork2.interceptor.PrepareInterceptor.doIntercept(PrepareInterceptor.java:171)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
org.apache.struts2.interceptor.ServletConfigInterceptor.intercept(ServletConfigInterceptor.java:164)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept(ExceptionMappingInterceptor.java:189)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:54)
org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:564)
org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:81)
org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:99)
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:212)
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:141)
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:616)
org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:521)
org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1096)
org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:674)
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)
回答1:
I just found what was the problem. The problem was the order of interceptor. The following code works fine:
<action name="upload" class="com.rwy.demo.action.UploadFile">
<interceptor-ref name="fileUpload">
<param name="allowedTypes">image/jpeg,image/gi,text/html</param>
</interceptor-ref>
<interceptor-ref name="basicStack"/>
<result name="success">/success.jsp</result>
<result name="error">/error.jsp</result>
</action>
来源：https://stackoverflow.com/questions/34870161/nullpointerexception-when-using-struts-fileuploading