Setting Time in Excel using POI

I have used the following code to generate the time cell, in Excel using POI. And I am able to use the cell in

        XSSFRow row2 = sheet.createRow(25);
        XSSFCell cell1 = row2.createCell(4);
        XSSFCell cell2 = row2.createCell(5);

        CellStyle style = wb.createCellStyle();
        DataFormat df = wb.createDataFormat();
        style.setDataFormat(df.getFormat("[h]:mm:ss;@"));

        cell1.setCellFormula("TIME(0,15,00)"); // 00:15:00
        cell1.setCellType(Cell.CELL_TYPE_FORMULA);
        cell1.setCellStyle(style);
        evaluator.evaluateFormulaCell(cell1);

        cell2.setCellFormula("TIME(0,30,00)"); //00:30:00
        cell2.setCellType(Cell.CELL_TYPE_FORMULA);
        evaluator.evaluateFormulaCell(cell2);
        cell2.setCellStyle(style);

Dates and Times in Excel are normally stored as floating point numbers, as full and fractional days since 1900 or 1904. You can see this by typing 0.5 into an excel cell and formatting as a time - it'll show as 12:00:00, or set a value of 1.5 and it'll show as a date in 1900/1904 as a date, 12:00:00 as a time, or 36:00:00 if a time that allows >24 hours (it's a different format code)

What you'll want to do is fire up a copy of Excel, type in the time value you want to have displayed, and work out the format string that makes it show up as you want it to. Then, make a note of that format code, and give that to POI as the data format for the cell. Now, use something like DateUtil in POI to build up your Date object, and set that to the cell as the value. With the right format string in, Excel will show only the time part and not the date