@Override public void setDateTimePattern(String dateTimePattern) { this.dateTimePattern = dateTimePattern; DateTimeConverter dtConverter = (DateTimeConverter) converters.lookup(Date.class); dtConverter.setDateTimePattern(dateTimePattern); dateCellStyle = workbook.createCellStyle(); CreationHelper helper = workbook.getCreationHelper(); dateCellStyle.setDataFormat(helper.createDataFormat().getFormat(dateTimePattern)); }