Question

I have an application which throws this error (happens only with xlsx-files):

java.lang.NullPointerException
at java.io.File.<init>(File.java:222)
at de.mpicbg.tds.core.ExcelLayout.openWorkbook(ExcelLayout.java:75)

The method ‘openWorkbook’ looks like this:

    private void openWorkbook() throws IOException {
    File excelFile = new File(fileName);

    timestamp = excelFile.lastModified();

    // open excel file
    if (fileName.endsWith(".xlsx")) {
        InputStream excelStream = new BufferedInputStream(new FileInputStream(excelFile));
        this.workbook = new XSSFWorkbook((excelStream));

    } else {
        this.workbook = new HSSFWorkbook(new POIFSFileSystem(new FileInputStream(excelFile)));
    }
}

If I execute everything in debug mode, everything goes smoothly and the error message does not appear. I don’t have any explanation for this behaviour nor any idea how to fix it.
Can anybody help?

Answer 1

The error message says your fileName is null

If you cannot reproduce this when debugging you can add a log message at the start of you method.

System.out.println("The fileName is `" + fileName+"`");

Instead of using a field which may or may not be set, I suggest you use a parameter.

private void openWorkbook(String fileName) throws IOException {
    assert fileName != null;