My code uses some new feature, compiles fine but fails when live with a "MethodNotFoundException"

You almost certainly have an older version of POI on your classpath. Quite a few runtimes and other packages will ship an older version of POI, so this is an easy problem to hit without your realising.

The best way to identify the offending earlier jar file is with a few lines of java. These will load one of the core POI classes, and report where it came from.

ClassLoader classloader = org.apache.poi.poifs.filesystem.POIFSFileSystem.class.getClassLoader(); URL res = classloader.getResource( "org/apache/poi/poifs/filesystem/POIFSFileSystem.class"); String path = res.getPath(); System.out.println("Core POI came from " + path); My code uses the scratchpad, compiles fine but fails to run with a "MethodNotFoundException"

You almost certainly have an older version earlier on your classpath. See the prior answer.

 Why is reading a simple sheet taking so long?

You've probably enabled logging. Logging is intended only for autopsy style debugging. Having it enabled will reduce performance by a factor of at least 100. Logging is helpful for understanding why POI can't read some file or developing POI itself. Important errors are thrown as exceptions, which means you probably don't need logging.

 What is the HSSF "eventmodel"?

The SS eventmodel package is an API for reading Excel files without loading the whole spreadsheet into memory. It does require more knowledge on the part of the user, but reduces memory consumption by more than tenfold. It is based on the AWT event model in combination with SAX. If you need read-only access, this is the best way to do it.

 Why can't read the document I created using Star Office 5.1?

Star Office 5.1 writes some records using the older BIFF standard. This causes some problems with POI which supports only BIFF8.

 Why am I getting an exception each time I attempt to read my spreadsheet?

It's possible your spreadsheet contains a feature that is not currently supported by POI. If you encounter this then please create the simplest file that demonstrates the trouble and submit it to Bugzilla.

 How do you tell if a spreadsheet cell contains a date?

Excel stores dates as numbers therefore the only way to determine if a cell is actually stored as a date is to look at the formatting. There is a helper method in HSSFDateUtil that checks for this. Thanks to Jason Hoffman for providing the solution.

case HSSFCell.CELL_TYPE_NUMERIC: double d = cell.getNumericCellValue(); // test if a date! if (HSSFDateUtil.isCellDateFormatted(cell)) { // format in form of M/D/YY cal.setTime(HSSFDateUtil.getJavaDate(d)); cellText = (String.valueOf(cal.get(Calendar.YEAR))).substring(2); cellText = cal.get(Calendar.MONTH)+1 + "/" + cal.get(Calendar.DAY_OF_MONTH) + "/" + cellText; } I'm trying to stream an XLS file from a servlet and I'm having some trouble. What's the problem?

The problem usually manifests itself as the junk characters being shown on screen. The problem persists even though you have set the correct mime type.

The short answer is, don't depend on IE to display a binary file type properly if you stream it via a servlet. Every minor version of IE has different bugs on this issue.

The problem in most versions of IE is that it does not use the mime type on the HTTP response to determine the file type; rather it uses the file extension on the request. Thus you might want to add a .xls to your request string. For example http://yourserver.com/myServelet.xls?param1=xx. This is easily accomplished through URL mapping in any servlet container. Sometimes a request like http://yourserver.com/myServelet?param1=xx&dummy=file.xls is also known to work.

To guarantee opening the file properly in Excel from IE, write out your file to a temporary file under your web root from your servelet. Then send an http response to the browser to do a client side redirection to your temp file. (Note that using a server side redirect using RequestDispatcher will not be effective in this case)

Note also that when you request a document that is opened with an external handler, IE sometimes makes two requests to the webserver. So if your generating process is heavy, it makes sense to write out to a temporary file, so that multiple requests happen for a static file.

None of this is particular to Excel. The same problem arises when you try to generate any binary file dynamically to an IE client. For example, if you generate pdf files using FOP, you will come across many of the same issues.

I want to set a cell format (Data format of a cell) of a excel sheet as ###,###,###.#### or ###,###,###.0000. Is it possible using POI ?

Yes. You first need to get a DataFormat object from the workbook and call getFormat with the desired format. Some examples are here.

I want to set a cell format (Data format of a cell) of a excel sheet as text. Is it possible using POI ?

Yes. This is a built-in format for excel that you can get from DataFormat object using the format string "@". Also, the string "text" will alias this format.

How do I add a border around a merged cell?

Add blank cells around where the cells normally would have been and set the borders individually for each cell. We will probably enhance HSSF in the future to make this process easier.

 I am using styles when creating a workbook in POI, but Excel refuses to open the file, complaining about "Too Many Styles".

You just create the styles OUTSIDE of the loop in which you create cells.

GOOD:

HSSFWorkbook wb = new HSSFWorkbook(); HSSFSheet sheet = wb.createSheet("new sheet"); HSSFRow row = null; // Aqua background HSSFCellStyle style = wb.createCellStyle(); style.setFillBackgroundColor(HSSFColor.AQUA.index); style.setFillPattern(HSSFCellStyle.BIG_SPOTS); HSSFCell cell = row.createCell((short) 1); cell.setCellValue("X"); cell.setCellStyle(style); // Orange "foreground", // foreground being the fill foreground not the font color. style = wb.createCellStyle(); style.setFillForegroundColor(HSSFColor.ORANGE.index); style.setFillPattern(HSSFCellStyle.SOLID_FOREGROUND); for (int x = 0; x < 1000; x++) { // Create a row and put some cells in it. Rows are 0 based. row = sheet.createRow((short) k); for (int y = 0; y < 100; y++) { cell = row.createCell((short) k); cell.setCellValue("X"); cell.setCellStyle(style); } } // Write the output to a file FileOutputStream fileOut = new FileOutputStream("workbook.xls"); wb.write(fileOut); fileOut.close();

BAD:

HSSFWorkbook wb = new HSSFWorkbook(); HSSFSheet sheet = wb.createSheet("new sheet"); HSSFRow row = null; for (int x = 0; x < 1000; x++) { // Aqua background HSSFCellStyle style = wb.createCellStyle(); style.setFillBackgroundColor(HSSFColor.AQUA.index); style.setFillPattern(HSSFCellStyle.BIG_SPOTS); HSSFCell cell = row.createCell((short) 1); cell.setCellValue("X"); cell.setCellStyle(style); // Orange "foreground", // foreground being the fill foreground not the font color. style = wb.createCellStyle(); style.setFillForegroundColor(HSSFColor.ORANGE.index); style.setFillPattern(HSSFCellStyle.SOLID_FOREGROUND); // Create a row and put some cells in it. Rows are 0 based. row = sheet.createRow((short) k); for (int y = 0; y < 100; y++) { cell = row.createCell((short) k); cell.setCellValue("X"); cell.setCellStyle(style); } } // Write the output to a file FileOutputStream fileOut = new FileOutputStream("workbook.xls"); wb.write(fileOut); fileOut.close();