Error reading Excel .XLSX with Apache POI

The method using the above code has a single parameter - FileInputStream. The first line in the code snippet is very much part of the code, but part of the invoking method. Since the method in question did not have knowledge of the Excel format or even a file extension to make an educated guess, I decided that I would first try to read the FileInputStream using HSSF API as below:

Sheet sheet = null;
try {

    POIFSFileSystem poifs = new POIFSFileSystem(inputFS);
    Workbook workbook = new HSSFWorkbook(poifs);
    sheet = workbook.getSheetAt(0);
}
catch (Exception e) {
}

if (sheet == null) {

    try {

        Workbook workbook = new XSSFWorkbook(inputFS);
        sheet = workbook.getSheetAt(0);
    }
    catch (Exception e) {
    }
}

The problem with the above code is that the state of the inputFS object during the second attempt of opening it via the XSSF API is unknown. And this yielded a read error. I replaced the above with the following code, which works fine and the issue appears to be resolved:

Sheet sheet = null;
try {

    Workbook workbook = WorkbookFactory.create(inputFS);
    sheet = workbook.getSheetAt(0);
}
catch (Exception e) {
}

I tested this with both XLS (older, binary) and XLSX (newer, XML-based) formats and it works. Thanks for everyone's help and input!

The exception indicates that there's something up with your InputStream. However, if you have a file, then pass that in to POI directly!. Using an InputStream requires buffering of everything into memory, which eats up space. Since you don't need to do that buffering, don't! Avoiding that buffering ought to fix your problem anyway

If you're running with the latest nightly builds of POI, then it's very easy. Your code becomes:

File file = new File("test.xlsx");
OPCPackage opcPackage = OPCPackage.open(file);
XSSFWorkbook workbook = new XSSFWorkbook(opcPackage);

Otherwise, it's very similar:

File file = new File("test.xlsx");
OPCPackage opcPackage = OPCPackage.open(file.getAbsolutePath());
XSSFWorkbook workbook = new XSSFWorkbook(opcPackage);

If you're not sure if your file is a HSSFWorkbook or XSSFWorkbook, then you can use the WorkbookFactory to open the appropriate one for you:

File file = new File("test.xlsx");
Workbook workbook = WorkbookFactory.create(file);