打开 excel ooxml 2007 xlsx 文档返回 nullPointer 异常

如何使用 Apache POI 打开 2007 xlsx ooxml 文件？我已经将所有内容添加到我的课程路径中，但仍然得到这个java.lang.NullPointerException error:

"C:\Program Files\Java\jdk1.7.0_13\bin\java" -agentlib:jdwp=transport=dt_socket,address=127.0.0.1:1804,suspend=y,server=n -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.7.0_13\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.7.0_13\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.7.0_13\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.7.0_13\jre\lib\jce.jar;C:\Program Files\Java\jdk1.7.0_13\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.7.0_13\jre\lib\jfxrt.jar;C:\Program Files\Java\jdk1.7.0_13\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.7.0_13\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.7.0_13\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.7.0_13\jre\lib\resources.jar;C:\Program Files\Java\jdk1.7.0_13\jre\lib\rt.jar;C:\Program Files\Java\jdk1.7.0_13\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.7.0_13\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.7.0_13\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.7.0_13\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.7.0_13\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.7.0_13\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.7.0_13\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.7.0_13\jre\lib\ext\zipfs.jar;C:\Users\Patrick\Desktop\xmlChanger\out\production\xmlChanger;C:\poi-3.9\poi-3.9-20121203.jar;C:\poi-3.9\poi-examples-3.9-20121203.jar;C:\poi-3.9\poi-excelant-3.9-20121203.jar;C:\poi-3.9\poi-ooxml-3.9-20121203.jar;C:\poi-3.9\poi-ooxml-schemas-3.9-20121203.jar;C:\poi-3.9\poi-scratchpad-3.9-20121203.jar;C:\poi-3.9\lib\commons-codec-1.5.jar;C:\poi-3.9\lib\commons-logging-1.1.jar;C:\poi-3.9\lib\junit-3.8.1.jar;C:\poi-3.9\lib\log4j-1.2.13.jar;C:\poi-3.9\ooxml-lib\dom4j-1.6.1.jar;C:\poi-3.9\ooxml-lib\stax-api-1.0.1.jar;C:\poi-3.9\ooxml-lib\xmlbeans-2.3.0.jar;C:\Program Files (x86)\JetBrains\IntelliJ IDEA 12.0.1\lib\idea_rt.jar" Main
Connected to the target VM, address: '127.0.0.1:1804', transport: 'socket'
java.lang.NullPointerException
    at org.apache.poi.openxml4j.opc.OPCPackage.getPart(OPCPackage.java:625)
    at org.apache.poi.POIXMLDocumentPart.<init>(POIXMLDocumentPart.java:91)
    at org.apache.poi.POIXMLDocument.<init>(POIXMLDocument.java:56)
    at org.apache.poi.xssf.usermodel.XSSFWorkbook.<init>(XSSFWorkbook.java:183)
    at org.apache.poi.ss.usermodel.WorkbookFactory.create(WorkbookFactory.java:73)
    at Main.main(Main.java:178)
Disconnected from the target VM, address: '127.0.0.1:1804', transport: 'socket'

Process finished with exit code 0

我的代码如下：

import org.apache.poi.ss.usermodel.Row;
import org.apache.poi.ss.usermodel.Sheet;
import org.apache.poi.ss.usermodel.Workbook;
import org.apache.poi.ss.usermodel.WorkbookFactory;
import org.w3c.dom.Document;
import org.w3c.dom.NodeList;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import java.io.File;
import java.util.Iterator;

public class Main {
    public static void main(String[] args) {
        try {

            File file = new File(root_dir + "2013-03-13 iom diff.xlsx");
            Workbook workbook = WorkbookFactory.create(file); //fails here

            //...

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

我已经再次搜索过这个问题，但没有找到任何有效的答案（例如，确保目录路径正确、超出范围等）

我之前问过类似的问题，但错误不同，因为我相信在 Microsoft Excel 中保存时我仅使用正常的 xlsx 格式，而不是 OOXML xlsx 格式。

有什么想法可以让这个空指针异常来自哪里或者使抛出的异常更有意义吗？

EDIT

当我使用以下代码创建工作簿时，它将使用上面发布的代码打开：

        Workbook wb = new XSSFWorkbook();
        CreationHelper createHelper = wb.getCreationHelper();
        Sheet sheet = wb.createSheet("new sheet");


        Row r = sheet.createRow((short) 0);

        Cell cell = r.createCell(0);
        cell.setCellValue(1);


        r.createCell(1).setCellValue(1.2);
        r.createCell(2).setCellValue(createHelper.createRichTextString("This is a string"));
        r.createCell(3).setCellValue(true);

        // Write the output to a file
        FileOutputStream fileOut = new FileOutputStream("workbook.xlsx");
        wb.write(fileOut);
        fileOut.close();

这意味着格式无效，但我不确定具体是什么，因为我在 Excel 中另存为 OOXML