Today, when using POI to do an Excel export, a null pointer error is always reported. Later, after I carefully searched through the log, I found the real problem;

The error is as follows:

HTTP Status 500 – Request processing failed; nested exception is java.lang.NullPointerException

---

type Exception report

message Request processing failed; nested exception is java.lang.NullPointerException

description The server encountered an internal error that prevented it from fulfilling this request.

exception

org.springframework.web.util.NestedServletException: Request processing failed; nested exception is java.lang.NullPointerException
	org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:973)
	org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:852)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:624)
	org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
	org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	com.bool.filter.RequestFilter.doFilterInternal(RequestFilter.java:37)
	org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:108)
	org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
	org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:108)
	com.bool.filter.CorsFilter.doFilter(CorsFilter.java:31)

 

root cause

java.lang.NullPointerException
	java.io.ByteArrayInputStream.<init>(ByteArrayInputStream.java:106)
	com.bool.controller.DetectionController.historyRecordDownkoad(DetectionController.java:264)
	sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
	sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	java.lang.reflect.Method.invoke(Method.java:606)
	org.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:215)
	org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:132)
	org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:104)
	org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:749)
	org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:690)
	org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:83)
	org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:945)
	org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:876)
	org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:961)
	org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:852)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:624)
	org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
	org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	com.bool.filter.RequestFilter.doFilterInternal(RequestFilter.java:37)
	org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:108)
	org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
	org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:108)
	com.bool.filter.CorsFilter.doFilter(CorsFilter.java:31)

 

note The full stack trace of the root cause is available in the Apache Tomcat/7.0.77 logs.

However, this is not the problem; when I debugged, I found another cause of the error;

java.lang.IllegalArgumentException: The workbook already contains a sheet with this name

The workbook already contains a piece of this name;

Okay, I found the problem.

solution:

Just modify the sheet page name in the export template;

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