poi/src/documentation/content/xdocs/faq.xml

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<!DOCTYPE faqs PUBLIC "-//APACHE//DTD FAQ V1.1//EN" "./dtd/faq-v11.dtd">

<faqs title="Frequently Asked Questions">
    <faq>
        <question>
          My code uses some new HSSF feature, compiles fine but fails when live with a "MethodNotFoundException"
        </question>
		<answer>
		 <p>You almost certainly have an older version of POI earlier 
		 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 realising.</p>
		 <p>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.</p>
		 <source>
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);
		 </source>
		</answer>
	</faq>
    <faq>
        <question>
          My code uses the scratchpad, compiles fine but fails to run with a "MethodNotFoundException"
        </question>
		<answer>
		 <p>You almost certainly have an older version earlier on your
		 classpath. See the answer to the similar question above for
		 how to track this down.</p>
		</answer>
	</faq>
    <faq>
        <question>
          Why is reading a simple sheet taking so long?
        </question>
        <answer>
          <p>You've probably enabled logging.  Logging is intended only for
          autopsie 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.</p>
        </answer>
    </faq>
    <faq>
        <question>
          What is the HSSF "eventmodel"?
        </question>
        <answer>
              <p>The HSSF eventmodel package is a new API for reading XLS files more efficiently.  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 to a given XLS file, this is the best way to do it.</p>
        </answer>

    </faq>
    <faq>
        <question>
          Why can't read the document I created using Star Office 5.1?
        </question>
        <answer>
              <p>Star Office 5.1 writes some records using the older BIFF standard.  This causes some problems
              with POI which supports only BIFF8.</p>
        </answer>
    </faq>
    <faq>
        <question>
            Why am I getting an exception each time I attempt to read my spreadsheet?
        </question>
        <answer>
            <p>It's possible your spreadsheet contains a feature that is not currently supported by HSSF.
            For example - spreadsheets containing cells with rich text are not currently supported.</p>
        </answer>
    </faq>
    <faq>
        <question>
            Does HSSF support protected spreadsheets?
        </question>
        <answer>
            <p>Protecting a spreadsheet encrypts it.  We wont touch encryption because we're not legally educated
            and don't understand the full implications of trying to implement this.  If you wish to have a go
            at this feel free to add it as a plugin module.  We wont be hosting it here however.</p>
        </answer>
    </faq>
    <faq>
        <question>
            How do you tell if a field contains a date with HSSF?
        </question>
        <answer>
            <p>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 (since the 1.7.0-dev release) that checks for this.
            Thanks to Jason Hoffman for providing the solution.</p>
            <source>
   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;
         } </source>
        </answer>
    </faq>
    <faq>
        <question>
            I'm trying to stream an XLS file from a servlet and I'm having some trouble.  What's the problem?
        </question>
        <answer>
            <p>
            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.
            </p>
            <p>
            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.
            </p>
            <p>
            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
                <strong>.xls</strong> to your request
            string. For example
                <em>http://yourserver.com/myServelet.xls?param1=xx</em>. This is
            easily accomplished through URL mapping in any servlet container. Sometimes
            a request like
                <em>http://yourserver.com/myServelet?param1=xx&amp;dummy=file.xls</em> is also
            known to work.

            </p>
            <p>
            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)
            </p>
            <p>
            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.
            </p>
            <p>
            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
                <link href="http://xml.apache.org/fop">FOP</link>, you will come across many of the same issues.

            </p>
            <!-- Thanks to Avik for the answer -->
        </answer>
    </faq>
    <faq>
        <question>
            I want to set a cell format (Data format of a cell) of a excel sheet as ###,###,###.#### or ###,###,###.0000.    Is it possible using POI ?
        </question>
        <answer>
            <p>
	   Yes.  You first need to get a HSSFDataFormat object from the workbook and call getFormat with the desired format.  Some examples are <link href="spreadsheet/quick-guide.html#DataFormats">here</link>.
            </p>
        </answer>
    </faq>
    <faq>
        <question>
            I want to set a cell format (Data format of a cell) of a excel sheet as text.    Is it possible using POI ?
        </question>
        <answer>
            <p>
	   Yes.  This is a built-in format for excel that you can get from HSSFDataFormat object using the format string "@".  Also, the string "text" will alias this format.
            </p>
        </answer>
    </faq>
    <faq>
        <question>
            How do I add a border around a merged cell?
        </question>
        <answer>
            <p>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.</p>
        </answer>
    </faq>
    <faq>
        <question>
            I tried to set cell values and Excel sheet name on my native language,
            but I failed to do it. :(
        </question>
        <answer>
            <p>By default HSSF uses cell values and sheet names as compressed unicode,
            so to support localization you should use Unicode.
            To do it you should set it manually:</p>
            <source>
                // for sheet name
                HSSFWorkbook wb = new HSSFWorkbook();
                HSSFSheet s = wb.createSheet();
                wb.setSheetName( 0, "SomeUnicodeName", HSSFWorkbook.ENCODING_UTF_16 );

                // for cell value
                HSSFRow r = s.createRow( 0 );
                HSSFCell c = r.createCell( (short)0 );
                c.setCellType( HSSFCell.CELL_TYPE_STRING );
                c.setEncoding( HSSFCell.ENCODING_UTF_16 );
                c.setCellValue( "\u0422\u0435\u0441\u0442\u043E\u0432\u0430\u044F" ); </source>
            <p>
                Make sure you make the call to setEncoding() before calling setCellValue(), otherwise what you pass in won't be interpreted properly.
            </p>
        </answer>
    </faq>
    <faq>
        <question>
            I'm having trouble creating a spreadsheet using POI using
            websphere 3.5.
        </question>
        <answer>
            <p>Make sure you have fix pack 4 installed.</p>
        </answer>
    </faq>
    <faq>
	<question>
        I am using styles when creating a workbook in POI, but Excel refuses to open the file, complaining about "Too Many Styles".
	</question>
	<answer>
	<p>You just create the styles OUTSIDE of the loop in which you create cells.</p>
	<p>GOOD:</p>
	<source>
 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 &lt; 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 &lt; 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(); </source>

	<p>BAD:</p>
	<source>
 HSSFWorkbook wb = new HSSFWorkbook();
 HSSFSheet sheet = wb.createSheet("new sheet");
 HSSFRow row = null;

 for (int x = 0; x &lt; 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 &lt; 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(); </source>
	</answer>
    </faq>
    <faq>
        <question>
            Will POI read any spreadsheet and rewrite it with modifications.
        </question>
        <answer>
            <p>POI is not guanteed to read the contents of any spreadsheet.
                Certain features may cause spreadsheets to fail to read.  More
                problematic is rewriting spreadsheets.  POI tried hard to
                preserve the records of the original spreadsheet but some
                features may cause problems.  We advise that you limit the
                formatting of spreadsheets you process so as to not be
                unpleasantly suprised at a later stage.</p>
        </answer>
    </faq>
</faqs>