code: private void appendRows(WritableSheet sheet, FileColumn[] columns, 
          List<String[]> lines, String sheetName)
          throws WriteException
      {
          WritableFont headerFont = new WritableFont(WritableFont.ARIAL, 10, WritableFont.BOLD); 
          WritableCellFormat headerFormat = new WritableCellFormat(headerFont);
          WritableCellFeatures features = new WritableCellFeatures();
          features.removeDataValidation();
  
          int size = sheet.getRows();
          for(int i = 0; i < lines.size(); i++)
          {
              String[] line = lines.get(i);
  
              if((i+size) > MAX_ROWS)
              {
                  logger.severe("the worksheet '"+sheetName
                      +"' has exceeded the maximum rows and will be truncated");
                  break;
              }
  
              for(int j = 0; j < line.length; j++)
              {
                  WritableCell cell = null;
                  String data = line[j];
                  if(data == null)
                      data = "";
  
                  // Get a cell with the correct formatting
                  if(columns != null && j < columns.length)
                  {
                      cell = getCell(columns[j], j, i+size, data);
                  }
                  else // Try to figure out the type of the column
                  { 
                      try
                      {
                          double num = Double.parseDouble(data);
                          cell = new Number(j, i+size, num);
                      }
                      catch(NumberFormatException e)
                      {
                          cell = new Label(j, i+size, data);
                      }
                  }
  
                  if(cell != null)
                  {
                      if((i+size) == 0 && hasHeaders())
                          cell.setCellFormat(headerFormat);
                      else
                          cell.setCellFeatures(features);
                      sheet.addCell(cell);
                  }
              }
          }
      }
docs: Appends the given lines to the bottom of the given sheet.
  @param sheet The sheet to add the lines to
  @param columns The column definitions for the worksheet
  @param lines The list of lines to be added to the worksheet
  @param sheetName The name of the worksheet to be added
  @return The array of column widths following the addition