Make column read-only using apache poi

I am using apache-poi for generating the excel file. I need to make the 4th column read-only and the remaining 2 columns will be editable by the user.

I am using XSSFCellStyle to achieve this but it's not working for me.

The entire code is:

Map<String, XSSFCellStyle> styles = new HashMap<String, XSSFCellStyle>();

XSSFCellStyle style5 = wb.createCellStyle();
XSSFFont headerFont = wb.createFont();
headerFont.setBold(true);
style5.setFillForegroundColor(IndexedColors.GREY_25_PERCENT.getIndex());
style5.setFillPattern(XSSFCellStyle.SOLID_FOREGROUND);
style5.setFont(headerFont);
style5.setLocked(true); // this line does not get executed.
styles.put("header", style5);