title: Limitation while generating excel drop down list with Apache POI
body: <p>I'm trying to generate an excel file with some validations, I've read the <a href="http://poi.apache.org/spreadsheet/quick-guide.html#Validation" rel="noreferrer">poi dev guides</a> for implementing it.  During implementation, I got an exception (<code>String literals in formulas can't be bigger than 255 characters ASCII</code>). POI concatenates all drop down options into '0' deliminated string and checking its length and giving me exception. :(  <br> I'm using latest version of POI 3.8 beta 5.
  <br>And my code is:</p>
  
  <pre><code>try {
      HSSFWorkbook wb = new HSSFWorkbook();
      HSSFSheet sheet = wb.createSheet("new sheet");
      HSSFRow row = sheet.createRow((short) 0);
      //CellRangeAddressList from org.apache.poi.ss.util package
      CellRangeAddressList addressList = new CellRangeAddressList(0, 0, 0, 0);
      DVConstraint dvConstraint = DVConstraint.createExplicitListConstraint(getCountries());
      DataValidation dataValidation = new HSSFDataValidation(addressList, dvConstraint);
      dataValidation.setSuppressDropDownArrow(false);
      sheet.addValidationData(dataValidation);
      FileOutputStream fileOut = new FileOutputStream("c:\\test.xls");
      wb.write(fileOut);
      fileOut.close();
      } catch (IOException e) {
         e.printStackTrace();
    }
  </code></pre>
  
  <p>After that I have tried with XSSFWorkBook with this code:</p>
  
  <pre><code>XSSFWorkbook wb = new XSSFWorkbook();
  XSSFSheet sheet = wb.createSheet("new sheet");
  DataValidationHelper validationHelper = new XSSFDataValidationHelper(sheet);
  DataValidationConstraint constraint = validationHelper.createExplicitListConstraint(getCountries());
  CellRangeAddressList addressList = new CellRangeAddressList(0, 0, 0, 0);
  DataValidation dataValidation = validationHelper.createValidation(constraint, addressList);
  dataValidation.setErrorStyle(DataValidation.ErrorStyle.STOP);
  dataValidation.setSuppressDropDownArrow(true);
  sheet.addValidationData(dataValidation);
  FileOutputStream fileOut = new FileOutputStream("c:\\test.xlsx");
  </code></pre>
  
  <p>Unfortunately, no success with such result which is comma delimenated long string in one cell:</p>
  
  <p><img src="https://i.stack.imgur.com/0D7Ul.png" alt="enter image description here"><br></p>
  
  <p>But manually in excel, I can create dropdown cells with this long country list.<br>Is there any way generate dropdown with long strings, or API does not support? </p>