使用Apache POI库从Excel(xlsx)文件读取会引发NullPointerException [英] Reading from an Excel (xlsx) file using Apache POI library throws NullPointerException
问题描述
我正在使用Eclipse IDE构建JSP Web应用程序.Web应用程序在Tomcat服务器版本7上加载没有问题.我们有一个新的要求，可以读取xls和xlsx文件.因此，我们已使用Apache POI库(4.1.2)来实现此目的，如下所示:我已经删除了其他代码，因为它们与本文无关.
I 'm building a JSP web application using Eclipse IDE. The web application loads without issue on tomcat server ver 7. We got a new requirement to read from xls and xlsx file. So we have used Apache POI library (4.1.2) to implement this as follows: I have taken out other codes as they are not relevant for this post
FileInputStream file = new FileInputStream(new File(args[0]));
//Create Workbook instance holding reference to .xlsx file
XSSFWorkbook workbook = new XSSFWorkbook(file); //<- This is where the exception occurs
//Get first/desired sheet from the workbook
XSSFSheet sheet = workbook.getSheetAt(0);
//Iterate through each rows one by one
Iterator<Row> rowIterator = sheet.iterator();
但是在执行时，我们得到以下异常.我曾尝试使用Google谷歌搜索，但未找到相关帮助.你能帮忙吗?
But when executing we are getting the below exception. I have tried googling but didn't find relevant help. Can you please assist?
SEVERE: Servlet.service() for servlet [UploadEstimates] in context with path [/AD] threw exception [Servlet execution threw an exception] with root cause
java.lang.NullPointerException
at org.apache.xmlbeans.impl.schema.ClassLoaderResourceLoader.getResourceAsStream(ClassLoaderResourceLoader.java:33)
at org.apache.xmlbeans.impl.schema.SchemaTypeSystemImpl$XsbReader.getLoaderStream(SchemaTypeSystemImpl.java:2249)
at org.apache.xmlbeans.impl.schema.SchemaTypeSystemImpl$XsbReader.<init>(SchemaTypeSystemImpl.java:1522)
at org.apache.xmlbeans.impl.schema.SchemaTypeSystemImpl.initFromHeader(SchemaTypeSystemImpl.java:273)
at org.apache.xmlbeans.impl.schema.SchemaTypeSystemImpl.<init>(SchemaTypeSystemImpl.java:185)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at schemaorg_apache_xmlbeans.system.sD023D6490046BA0250A839A9AD24C443.TypeSystemHolder.loadTypeSystem(Unknown Source)
at schemaorg_apache_xmlbeans.system.sD023D6490046BA0250A839A9AD24C443.TypeSystemHolder.<clinit>(Unknown Source)
at sun.misc.Unsafe.ensureClassInitialized(Native Method)
at sun.reflect.UnsafeFieldAccessorFactory.newFieldAccessor(Unknown Source)
at sun.reflect.ReflectionFactory.newFieldAccessor(Unknown Source)
at java.lang.reflect.Field.acquireFieldAccessor(Unknown Source)
at java.lang.reflect.Field.getFieldAccessor(Unknown Source)
at java.lang.reflect.Field.get(Unknown Source)
at org.apache.xmlbeans.XmlBeans.typeSystemForClassLoader(XmlBeans.java:775)
at org.openxmlformats.schemas.drawingml.x2006.main.ThemeDocument.<clinit>(Unknown Source)
at org.openxmlformats.schemas.drawingml.x2006.main.ThemeDocument$Factory.parse(Unknown Source)
at org.apache.poi.xssf.model.ThemesTable.<init>(ThemesTable.java:86)
at org.apache.poi.ooxml.POIXMLFactory.createDocumentPart(POIXMLFactory.java:61)
at org.apache.poi.ooxml.POIXMLDocumentPart.read(POIXMLDocumentPart.java:684)
at org.apache.poi.ooxml.POIXMLDocument.load(POIXMLDocument.java:180)
at org.apache.poi.xssf.usermodel.XSSFWorkbook.<init>(XSSFWorkbook.java:288)
at org.apache.poi.xssf.usermodel.XSSFWorkbook.<init>(XSSFWorkbook.java:342)
at com.MyClient.AD.util.UploadEstimateUT.start(UploadEstimateUT.java:85)
at com.MyClient.AD.util.UploadEstimates.doPost(UploadEstimates.java:107)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:754)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:847)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:110)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:492)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:165)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:104)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:1025)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:452)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1195)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:654)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:319)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Unknown Source)这是我引用POI文件的方式:MyProject->右键单击->构建路径->配置构建路径->库选项卡，并添加以下jars
This is how I referenced the POI files: MyProject -> Right Click -> Build Path -> Configure Built Path -> Libraries tab and added the following jars
这就是我执行应用程序的方式运行->运行配置...->类路径选项卡->确保此处引用了所有jar文件，包括Apache POI->应用和/或运行.
And this is how I execute the application Run -> Run Configuration... -> Classpath tab -> Making sure all jar files are referenced here including Apache POI's -> Apply and/or Run.
更新1(2020年2月28日)
我尝试了与Java应用程序相同的代码(使用POI库从excel读取)，并且按预期方式工作.
I tried the same code (that reads from excel using POI library) as java application and it worked as expected.
我在调试JSP Web应用程序时注意到的另一件事是，控件直接转移到了finally块，而不是常规的Exception块.不知道为什么.
Another thing I noted when debugging the JSP web application is that the control is transferred directly to the finally block instead of the general Exception block. Not sure why.
更新2(2020年3月3日)
我在同事系统中配置了该项目，该系统也具有Eclipse IDE，但其Tomcat服务器版本为9.0.31，并且可以在他的计算机中使用.
I configured the project in my colleagues system who also has Eclipse IDE but with Tomcat server version 9.0.31 and it worked in his machine.
然后，我安装了9.0.31版的Tomcat服务器，并从单独的工作区配置了该项目，但是在执行时，我遇到了相同的异常.我不明白有什么区别.
Then I installed Tomcat server version 9.0.31 and configured the project from a separate workspace but when executing I face the same exception. I'm not able to understand what could the difference.
我们俩都将Eclipse IDE用于企业Java开发人员.版本:2019-09 R(4.13.0)内部版本:20190917-1200
We both are using Eclipse IDE for Enterprise Java Developers. Version: 2019-09 R (4.13.0) Build id: 20190917-1200
更新3(2020年3月6日)
魔术师，我将其更新为出厂方法后得到了以下异常
magicmn, I get the below exception after updating to factory method
SEVERE: Servlet.service() for servlet [UploadEstimates] in context with path [/AD] threw exception [Servlet execution threw an exception] with root cause
java.lang.NullPointerException
at org.apache.xmlbeans.impl.schema.ClassLoaderResourceLoader.getResourceAsStream(ClassLoaderResourceLoader.java:33)
at org.apache.xmlbeans.impl.schema.SchemaTypeSystemImpl$XsbReader.getLoaderStream(SchemaTypeSystemImpl.java:2249)
at org.apache.xmlbeans.impl.schema.SchemaTypeSystemImpl$XsbReader.<init>(SchemaTypeSystemImpl.java:1522)
at org.apache.xmlbeans.impl.schema.SchemaTypeSystemImpl.initFromHeader(SchemaTypeSystemImpl.java:273)
at org.apache.xmlbeans.impl.schema.SchemaTypeSystemImpl.<init>(SchemaTypeSystemImpl.java:185)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at schemaorg_apache_xmlbeans.system.sD023D6490046BA0250A839A9AD24C443.TypeSystemHolder.loadTypeSystem(Unknown Source)
at schemaorg_apache_xmlbeans.system.sD023D6490046BA0250A839A9AD24C443.TypeSystemHolder.<clinit>(Unknown Source)
at sun.misc.Unsafe.ensureClassInitialized(Native Method)
at sun.reflect.UnsafeFieldAccessorFactory.newFieldAccessor(Unknown Source)
at sun.reflect.ReflectionFactory.newFieldAccessor(Unknown Source)
at java.lang.reflect.Field.acquireFieldAccessor(Unknown Source)
at java.lang.reflect.Field.getFieldAccessor(Unknown Source)
at java.lang.reflect.Field.get(Unknown Source)
at org.apache.xmlbeans.XmlBeans.typeSystemForClassLoader(XmlBeans.java:775)
at org.openxmlformats.schemas.drawingml.x2006.main.ThemeDocument.<clinit>(Unknown Source)
at org.openxmlformats.schemas.drawingml.x2006.main.ThemeDocument$Factory.parse(Unknown Source)
at org.apache.poi.xssf.model.ThemesTable.<init>(ThemesTable.java:86)
at org.apache.poi.ooxml.POIXMLFactory.createDocumentPart(POIXMLFactory.java:61)
at org.apache.poi.ooxml.POIXMLDocumentPart.read(POIXMLDocumentPart.java:684)
at org.apache.poi.ooxml.POIXMLDocument.load(POIXMLDocument.java:180)
at org.apache.poi.xssf.usermodel.XSSFWorkbook.<init>(XSSFWorkbook.java:288)
at org.apache.poi.xssf.usermodel.XSSFWorkbookFactory.createWorkbook(XSSFWorkbookFactory.java:97)
at org.apache.poi.xssf.usermodel.XSSFWorkbookFactory.createWorkbook(XSSFWorkbookFactory.java:125)
at org.apache.poi.ss.usermodel.WorkbookFactory.create(WorkbookFactory.java:327)
at org.apache.poi.ss.usermodel.WorkbookFactory.create(WorkbookFactory.java:295)
at org.apache.poi.ss.usermodel.WorkbookFactory.create(WorkbookFactory.java:276)
at com.MyClient.AD.util.UploadEstimateUT.start(UploadEstimateUT.java:90)
at com.MyClient.AD.util.UploadEstimates.doPost(UploadEstimates.java:108)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:660)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:688)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:367)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1639)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Unknown Source)
推荐答案
在这意味着_classLoader为空._classLoader传递给构造函数.
Which means that _classLoader is null. _classLoader is passed to the constructor.
The ClassLoaderResourceLoader object is created at line 182 of SchemaTypeSystemImpl:
_classloader = indexclass.getClassLoader();
...
_resourceLoader = new ClassLoaderResourceLoader(_classloader);
这意味着_classloader为null，这意味着indexclass.getClassLoader()为null.
Which means that _classloader is null, which means that indexclass.getClassLoader() is null.
getClassLoader()何时可以返回null?文档说:
When can getClassLoader() return null? The documentation says:
某些实现可能使用null来表示引导类装载机.在这种实现中，此方法将返回null该类由引导类加载器加载.
Some implementations may use null to represent the bootstrap class loader. This method will return null in such implementations if this class was loaded by the bootstrap class loader.
引导程序?它会响吗?是的，您将所有的jar放在Bootstrap条目中，这意味着它们是由bootstrap类加载器加载的.正如我在评论中说的那样(您似乎已经忽略了)，罐子的正确位置是应用程序的WEB-INF \ lib目录.因此，只需将它们放在其中即可使用.
Bootstrap? Does it ring a bell? Yes, you put all your jars in the Bootstrap Entries, which means that they are loaded by the bootstrap class loader. As I said in a comment (which you seem to have ignored), the correct location for jars is the WEB-INF\lib directory of the application. So just put them in there and it will work.
这篇关于使用Apache POI库从Excel(xlsx)文件读取会引发NullPointerException的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
