Set Date format using Apache POI

You can apply a CellStyle to the cell you need to fill. Here some code snippets from my past work, it's not intact but shows the basic idea:

Row row = sheet.createRow(0);
Cell cell = row.createCell((short) 0);
cell.setCellType(Cell.CELL_TYPE_NUMERIC);

SimpleDateFormat datetemp = new SimpleDateFormat("yyyy-MM-dd");
Date cellValue = datetemp.parse("1994-01-01 12:00");
cell.setCellValue(cellValue);

//binds the style you need to the cell.
CellStyle dateCellStyle = wb.createCellStyle();
short df = wb.createDataFormat().getFormat("dd-mmm");
dateCellStyle.setDataFormat(df);
cell.setCellStyle(dateCellStyle);
    

More information about date format in JDK, you should read this: http://docs.oracle.com/javase/6/docs/api/java/text/SimpleDateFormat.html