public  void doExport(OutputStream out) throws JspException 
{
        try
        {
            HSSFWorkbook wb = new HSSFWorkbook();
            HSSFSheet sheet = wb.createSheet("-");
            int rowNum = 0;
            int colNum = 0;
            if (this.header)
            {
                // Create an header row
                HSSFRow xlsRow = sheet.createRow(rowNum++);
                HSSFCellStyle headerStyle = wb.createCellStyle();
                headerStyle.setFillPattern(HSSFCellStyle.FINE_DOTS);
                headerStyle.setFillBackgroundColor(HSSFColor.BLUE_GREY.index);
                HSSFFont bold = wb.createFont();
                bold.setBoldweight(HSSFFont.BOLDWEIGHT_BOLD);
                bold.setColor(HSSFColor.WHITE.index);
                headerStyle.setFont(bold);
                Iterator iterator = this.model.getHeaderCellList().iterator();
                while (iterator.hasNext())
                {
                    HeaderCell headerCell = (HeaderCell) iterator.next();
                    String columnHeader = headerCell.getTitle();
                    if (columnHeader == null)
                    {
                        columnHeader = StringUtils.capitalize(headerCell.getBeanPropertyName());
                    }
                    HSSFCell cell = xlsRow.createCell((short) colNum++);
                    cell.setEncoding(HSSFCell.ENCODING_UTF_16);
                    cell.setCellValue(columnHeader);
                    cell.setCellStyle(headerStyle);
                }
            }
            // get the correct iterator (full or partial list according to the exportFull field)
            RowIterator rowIterator = this.model.getRowIterator(this.exportFull);
            // iterator on rows
            while (rowIterator.hasNext())
            {
                Row row = rowIterator.next();
                HSSFRow xlsRow = sheet.createRow(rowNum++);
                colNum = 0;
                // iterator on columns
                ColumnIterator columnIterator = row.getColumnIterator(this.model.getHeaderCellList());
                while (columnIterator.hasNext())
                {
                    Column column = columnIterator.nextColumn();
                    // Get the value to be displayed for the column
                    Object value = column.getValue(this.decorated);
                    HSSFCell cell = xlsRow.createCell((short) colNum++);
                    cell.setEncoding(HSSFCell.ENCODING_UTF_16);
                    writeCell(value, cell);
                }
            }
            wb.write(out);
        }
        catch (Exception e)
        {
            throw new ExcelGenerationException(e);
        }
}

 protected String escapeColumnValue(Object rawValue) 
{
        if (rawValue == null)
        {
            return null;
        }
        String returnString = ObjectUtils.toString(rawValue);
        // escape the String to get the tabs, returns, newline explicit as \t \r \n
        returnString = StringEscapeUtils.escapeJava(StringUtils.trimToEmpty(returnString));
        // remove tabs, insert four whitespaces instead
        returnString = StringUtils.replace(StringUtils.trim(returnString), "\\t", "    ");
        // remove the return, only newline valid in excel
        returnString = StringUtils.replace(StringUtils.trim(returnString), "\\r", " ");
        // unescape so that \n gets back to newline
        returnString = StringEscapeUtils.unescapeJava(returnString);
        return returnString;
}

Escape certain values that are not permitted in excel cells.

 public String getMimeType() 
{
        return "application/vnd.ms-excel"; //$NON-NLS-1$
}

 public  void setParameters(TableModel tableModel,
    boolean exportFullList,
    boolean includeHeader,
    boolean decorateValues) 
{
        this.model = tableModel;
        this.exportFull = exportFullList;
        this.header = includeHeader;
        this.decorated = decorateValues;
}

 protected  void writeCell(Object value,
    HSSFCell cell) 
{
        if (value instanceof Number)
        {
            Number num = (Number) value;
            cell.setCellValue(num.doubleValue());
        }
        else if (value instanceof Date)
        {
            cell.setCellValue((Date) value);
        }
        else if (value instanceof Calendar)
        {
            cell.setCellValue((Calendar) value);
        }
        else
        {
            cell.setCellValue(escapeColumnValue(value));
        }
}

Write the value to the cell. Override this method if you have complex data types that may need to be exported.