使用 Apache POI 库从 Excel (xlsx) 文件中读取会引发 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 构建一个 JSP Web 应用程序.web 应用程序在 tomcat 服务器 ver 7 上加载没有问题.我们有一个新的要求从 xls 和 xlsx 文件中读取.所以我们使用了 Apache POI 库(4.1.2)来实现如下:我删除了其他代码，因为它们与这篇文章无关

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.我试过谷歌搜索，但没有找到相关的帮助.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 -> 确保在此处引用所有 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)，并且它按预期工作.

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将控制直接转移到 finally 块而不是一般的 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)

我在我的同事系统中配置了该项目，他们也有 Eclipse IDE，但使用 Tomcat 服务器版本 9.0.31，并且在他的机器上运行.

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 Tomcat 服务器版本 9.0.31 并从单独的工作区配置了项目，但是在执行时我遇到了同样的异常.我不明白这有什么区别.

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.

我们都使用面向企业 Java 开发人员的 Eclipse IDE.版本:2019-09 R (4.13.0) 版本号: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)

magicmn，更新到工厂方法后出现以下异常

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 ClassLoaderResourceLoader.该行是:

return _classLoader.getResourceAsStream(resourceName);

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.

ClassLoaderResourceLoader 对象是在 SchemaTypeSystemImpl:

The ClassLoaderResourceLoader object is created at line 182 of SchemaTypeSystemImpl:

_classloader = indexclass.getClassLoader();
...
_resourceLoader = new ClassLoaderResourceLoader(_classloader);

即_classloader为null，即indexclass.getClassLoader()为null.

Which means that _classloader is null, which means that indexclass.getClassLoader() is null.

getClassLoader() 什么时候可以返回 null?文档 说:

When can getClassLoader() return null? The documentation says:

某些实现可能使用 null 来表示 bootstrap 类装载机.如果这样，则此方法将在此类实现中返回 null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?它敲响了警钟吗?是的，您将所有 jar 放在 Bootstrap Entries 中，这意味着它们由引导类加载器加载.正如我在评论中所说(您似乎忽略了)，jar 的正确位置是应用程序的 WEB-INF\lib 目录.所以只要把它们放在那里，它就会起作用.

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) 文件中读取会引发 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！