Formula Evaluation

Using FormulaEvaluator.evaluate(Cell cell)

This evaluates a given cell, and returns the new value, without affecting the cell

FileInputStream fis = new FileInputStream("c:/temp/test.xls");
Workbook wb = new HSSFWorkbook(fis); //or new XSSFWorkbook("c:/temp/test.xls")
Sheet sheet = wb.getSheetAt(0);
FormulaEvaluator evaluator = wb.getCreationHelper().createFormulaEvaluator();

// suppose your formula is in B3
CellReference cellReference = new CellReference("B3"); 
Row row = sheet.getRow(cellReference.getRow());
Cell cell = row.getCell(cellReference.getCol()); 

CellValue cellValue = evaluator.evaluate(cell);

switch (cellValue.getCellType()) {
    case Cell.CELL_TYPE_BOOLEAN:
        System.out.println(cellValue.getBooleanValue());
        break;
    case Cell.CELL_TYPE_NUMERIC:
        System.out.println(cellValue.getNumberValue());
        break;
    case Cell.CELL_TYPE_STRING:
        System.out.println(cellValue.getStringValue());
        break;
    case Cell.CELL_TYPE_BLANK:
        break;
    case Cell.CELL_TYPE_ERROR:
        break;

    // CELL_TYPE_FORMULA will never happen
    case Cell.CELL_TYPE_FORMULA: 
        break;
}				
        

Thus using the retrieved value (of type FormulaEvaluator.CellValue - a nested class) returned by FormulaEvaluator is similar to using a Cell object containing the value of the formula evaluation. CellValue is a simple value object and does not maintain reference to the original cell.

Using FormulaEvaluator.evaluateFormulaCell(Cell cell)

evaluateFormulaCell (Cell cell) will check to see if the supplied cell is a formula cell. If it isn't, then no changes will be made to it. If it is, then the formula is evaluated. The value for the formula is saved alongside it, to be displayed in excel. The formula remains in the cell, just with a new value

The return of the function is the type of the formula result, such as Cell.CELL_TYPE_BOOLEAN

FileInputStream fis = new FileInputStream("/somepath/test.xls");
Workbook wb = new HSSFWorkbook(fis); //or new XSSFWorkbook("/somepath/test.xls")
Sheet sheet = wb.getSheetAt(0);
FormulaEvaluator evaluator = wb.getCreationHelper().createFormulaEvaluator();

// suppose your formula is in B3
CellReference cellReference = new CellReference("B3"); 
Row row = sheet.getRow(cellReference.getRow());
Cell cell = row.getCell(cellReference.getCol()); 

if (cell!=null) {
    switch (evaluator.evaluateFormulaCell(cell)) {
        case Cell.CELL_TYPE_BOOLEAN:
            System.out.println(cell.getBooleanCellValue());
            break;
        case Cell.CELL_TYPE_NUMERIC:
            System.out.println(cell.getNumericCellValue());
            break;
        case Cell.CELL_TYPE_STRING:
            System.out.println(cell.getStringCellValue());
            break;
        case Cell.CELL_TYPE_BLANK:
            break;
        case Cell.CELL_TYPE_ERROR:
            System.out.println(cell.getErrorCellValue());
            break;

        // CELL_TYPE_FORMULA will never occur
        case Cell.CELL_TYPE_FORMULA: 
            break;
    }
}
				

Using FormulaEvaluator.evaluateInCell(Cell cell)

evaluateInCell (Cell cell) will check to see if the supplied cell is a formula cell. If it isn't, then no changes will be made to it. If it is, then the formula is evaluated, and the new value saved into the cell, in place of the old formula.

FileInputStream fis = new FileInputStream("/somepath/test.xls");
Workbook wb = new HSSFWorkbook(fis); //or new XSSFWorkbook("/somepath/test.xls")
Sheet sheet = wb.getSheetAt(0);
FormulaEvaluator evaluator = wb.getCreationHelper().createFormulaEvaluator();

// suppose your formula is in B3
CellReference cellReference = new CellReference("B3");
Row row = sheet.getRow(cellReference.getRow());
Cell cell = row.getCell(cellReference.getCol()); 

if (cell!=null) {
    switch (evaluator.evaluateInCell
(cell).getCellType()) {
        case Cell.CELL_TYPE_BOOLEAN:
            System.out.println(cell.getBooleanCellValue());
            break;
        case Cell.CELL_TYPE_NUMERIC:
            System.out.println(cell.getNumericCellValue());
            break;
        case Cell.CELL_TYPE_STRING:
            System.out.println(cell.getStringCellValue());
            break;
        case Cell.CELL_TYPE_BLANK:
            break;
        case Cell.CELL_TYPE_ERROR:
            System.out.println(cell.getErrorCellValue());
            break;

        // CELL_TYPE_FORMULA will never occur
        case Cell.CELL_TYPE_FORMULA:
            break;
    }
}

        

Re-calculating all formulas in a Workbook

FileInputStream fis = new FileInputStream("/somepath/test.xls");
Workbook wb = new HSSFWorkbook(fis); //or new XSSFWorkbook("/somepath/test.xls")
FormulaEvaluator evaluator = wb.getCreationHelper().createFormulaEvaluator();
for(int sheetNum = 0; sheetNum < wb.getNumberOfSheets(); sheetNum++) {
    Sheet sheet = wb.getSheetAt(sheetNum);
    for(Row r : sheet) {
        for(Cell c : r) {
            if(c.getCellType() == Cell.CELL_TYPE_FORMULA) {
                evaluator.evaluateFormulaCell(c);
            }
        }
    }
}
        

Alternately, if you know which of HSSF or XSSF you're working with, then you can call the static evaluateAllFormulaCells method on the appropriate HSSFFormulaEvaluator or XSSFFormulaEvaluator class.

Recalculation of Formulas

In certain cases you may want to force Excel to re-calculate formulas when the workbook is opened. Consider the following example:

Open Excel and create a new workbook. On the first sheet set A1=1, B1=1, C1=A1+B1. Excel automatically calculates formulas and the value in C1 is 2. So far so good.

Now modify the workbook with POI:

  Workbook wb = WorkbookFactory.create(new FileInputStream("workbook.xls"));

  Sheet sh = wb.getSheetAt(0);
  sh.getRow(0).getCell(0).setCellValue(2);  // set A1=2

  FileOutputStream out = new FileOutputStream("workbook2.xls");
  wb.write(out);
  out.close();
      

Now open workbook2.xls in Excel and the value in C1 is still 2 while you expected 3. Wrong? No! The point is that Excel caches previously calculated results and you need to trigger recalculation to updated them. It is not an issue when you are creating new workbooks from scratch, but important to remember when you are modifing existing workbooks with formulas. This can be done in two ways:

1. Re-evaluate formuals with POI's FormulaEvaluator:

  Workbook wb = WorkbookFactory.create(new FileInputStream("workbook.xls"));

  Sheet sh = wb.getSheetAt(0);
  sh.getRow(0).getCell(0).setCellValue(2);  // set A1=2

  wb.getCreationHelper().createFormulaEvaluator().evaluateAll();
        

2. Delegate re-calculation to Excel. The application will perform a full recalculation when the workbook is opened:

  Workbook wb = WorkbookFactory.create(new FileInputStream("workbook.xls"));

  Sheet sh = wb.getSheetAt(0);
  sh.getRow(0).getCell(0).setCellValue(2);  // set A1=2

  wb.setForceFormulaRecalculation(true);