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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE document PUBLIC "-//APACHE//DTD Documentation V1.1//EN" "../dtd/document-v11.dtd">
<document>
<header>
<title>Formula Evaluation</title>
<authors>
<person email="amoweb@yahoo.com" name="Amol Deshmukh" id="AD"/>
</authors>
</header>
<body>
<section><title>Introduction</title>
<p>The POI formula evaluation code enables you to calculate the result of
formulas in Excels sheets read-in, or created in POI. This document explains
how to use the API to evaluate your formulas.
</p>
<note> This code currently lives the scratchpad area of the POI SVN repository.
Ensure that you have the scratchpad jar or the scratchpad build area in your
classpath before experimenting with this code. You are advised
to make use of a recent SVN checkout, as new functions are
being supported fairly frequently.
</note>
</section>
<anchor id="Status"/>
<section><title>Status</title>
<p> The code currently provides implementations for all the arithmatic operators.
It also provides implementations for approx. 100 built in
functions in Excel. The framework however makes is easy to add
implementation of new functions. See the <link href="eval-devguide.html"> Formula
evaluation development guide</link> for details. </p>
<p> Note that user-defined functions are not supported, and is not likely to done
any time soon... at least, not till there is a VB implementation in Java!
</p>
</section>
<section><title>User API How-TO</title>
<p>The following code demonstrates how to use the HSSFFormulaEvaluator
in the context of other POI excel reading code.
</p>
<p>There are several ways in which you can use the HSSFFormulaEvalutator API.</p>
<anchor id="Evaluate"/>
<section><title>Using HSSFFormulaEvaluator.<strong>evaluate</strong>(HSSFCell cell)</title>
<p>This evaluates a given cell, and returns the new value,
without affecting the cell</p>
<source>
FileInputStream fis = new FileInputStream("c:/temp/test.xls");
HSSFWorkbook wb = new HSSFWorkbook(fis);
HSSFSheet sheet = wb.getSheetAt(0);
HSSFFormulaEvaluator evaluator = new HSSFFormulaEvaluator(sheet, wb);
// suppose your formula is in B3
CellReference cellReference = new CellReference("B3");
HSSFRow row = sheet.getRow(cellReference.getRow());
HSSFCell cell = row.getCell(cellReference.getCol());
evaluator.setCurrentRow(row);
HSSFFormulaEvaluator.CellValue cellValue = evaluator.evaluate(cell);
switch (cellValue.getCellType()) {
case HSSFCell.CELL_TYPE_BOOLEAN:
System.out.println(cellValue.getBooleanValue());
break;
case HSSFCell.CELL_TYPE_NUMERIC:
System.out.println(cellValue.getNumberValue());
break;
case HSSFCell.CELL_TYPE_STRING:
System.out.println(cellValue.getStringValue());
break;
case HSSFCell.CELL_TYPE_BLANK:
break;
case HSSFCell.CELL_TYPE_ERROR:
break;
// CELL_TYPE_FORMULA will never happen
case HSSFCell.CELL_TYPE_FORMULA:
break;
}
</source>
<p>Thus using the retrieved value (of type
HSSFFormulaEvaluator.CellValue - a nested class) returned
by HSSFFormulaEvaluator is similar to using a HSSFCell object
containing the value of the formula evaluation. CellValue is
a simple value object and does not maintain reference
to the original cell.
</p>
</section>
<anchor id="EvaluateFormulaCell"/>
<section><title>Using HSSFFormulaEvaluator.<strong>evaluateFormulaCell</strong>(HSSFCell cell)</title>
<p><strong>evaluateFormulaCell</strong>(HSSFCell 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</p>
<p>The return of the function is the type of the
formula result, such as HSSFCell.CELL_TYPE_BOOLEAN</p>
<source>
FileInputStream fis = new FileInputStream("/somepath/test.xls");
HSSFWorkbook wb = new HSSFWorkbook(fis);
HSSFSheet sheet = wb.getSheetAt(0);
HSSFFormulaEvaluator evaluator = new HSSFFormulaEvaluator(sheet, wb);
// suppose your formula is in B3
CellReference cellReference = new CellReference("B3");
HSSFRow row = sheet.getRow(cellReference.getRow());
HSSFCell cell = row.getCell(cellReference.getCol());
evaluator.setCurrentRow(row);
if (cell!=null) {
switch (<strong>evaluator.evaluateFormulaCell</strong>(cell)) {
case HSSFCell.CELL_TYPE_BOOLEAN:
System.out.println(cell.getBooleanCellValue());
break;
case HSSFCell.CELL_TYPE_NUMERIC:
System.out.println(cell.getNumberCellValue());
break;
case HSSFCell.CELL_TYPE_STRING:
System.out.println(cell.getStringCellValue());
break;
case HSSFCell.CELL_TYPE_BLANK:
break;
case HSSFCell.CELL_TYPE_ERROR:
System.out.println(cell.getErrorCellValue());
break;
// CELL_TYPE_FORMULA will never occur
case HSSFCell.CELL_TYPE_FORMULA:
break;
}
}
</source>
</section>
<anchor id="EvaluateInCell"/>
<section><title>Using HSSFFormulaEvaluator.<strong>evaluateInCell</strong>(HSSFCell cell)</title>
<p><strong>evaluateInCell</strong>(HSSFCell 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.</p>
<source>
FileInputStream fis = new FileInputStream("/somepath/test.xls");
HSSFWorkbook wb = new HSSFWorkbook(fis);
HSSFSheet sheet = wb.getSheetAt(0);
HSSFFormulaEvaluator evaluator = new HSSFFormulaEvaluator(sheet, wb);
// suppose your formula is in B3
CellReference cellReference = new CellReference("B3");
HSSFRow row = sheet.getRow(cellReference.getRow());
HSSFCell cell = row.getCell(cellReference.getCol());
evaluator.setCurrentRow(row);
if (cell!=null) {
switch (<strong>evaluator.evaluateInCell</strong>(cell).getCellType()) {
case HSSFCell.CELL_TYPE_BOOLEAN:
System.out.println(cell.getBooleanCellValue());
break;
case HSSFCell.CELL_TYPE_NUMERIC:
System.out.println(cell.getNumberCellValue());
break;
case HSSFCell.CELL_TYPE_STRING:
System.out.println(cell.getStringCellValue());
break;
case HSSFCell.CELL_TYPE_BLANK:
break;
case HSSFCell.CELL_TYPE_ERROR:
System.out.println(cell.getErrorCellValue());
break;
// CELL_TYPE_FORMULA will never occur
case HSSFCell.CELL_TYPE_FORMULA:
break;
}
}
</source>
</section>
<anchor id="EvaluateAll"/>
<section><title>Re-calculating all formulas in a Workbook</title>
<source>
FileInputStream fis = new FileInputStream("/somepath/test.xls");
HSSFWorkbook wb = new HSSFWorkbook(fis);
for(int sheetNum = 0; sheetNum < wb.getNumberOfSheets(); sheetNum++) {
HSSFSheet sheet = wb.getSheetAt(sheetNum);
HSSFFormulaEvaluator evaluator = new HSSFFormulaEvaluator(sheet, wb);
for(Iterator rit = sheet.rowIterator(); rit.hasNext();) {
HSSFRow r = (HSSFRow)rit.next();
evaluator.setCurrentRow(r);
for(Iterator cit = r.cellIterator(); cit.hasNext();) {
HSSFCell c = (HSSFCell)cit.next();
if(c.getCellType() == HSSFCell.CELL_TYPE_FORMULA) {
evaluator.evaluateFormulaCell(c);
}
}
}
}
wb.write(new FileOutputStream("/somepath/changed.xls"));
</source>
</section>
</section>
<anchor id="Performance"/>
<section><title>Performance Notes</title>
<ul>
<li>Generally you should have to create only one HSSFFormulaEvaluator
instance per sheet, but there really is no overhead in creating
multiple HSSFFormulaEvaluators per sheet other than that of the
HSSFFormulaEvaluator object creation.
</li>
<li>Also note that HSSFFormulaEvaluator maintains a reference to
the sheet and workbook, so ensure that the evaluator instance
is available for garbage collection when you are done with it
(in other words don't maintain long lived reference to
HSSFFormulaEvaluator if you don't really need to - unless
all references to the sheet and workbook are removed, these
don't get garbage collected and continue to occupy potentially
large amounts of memory).
</li>
<li>CellValue instances however do not maintain reference to the
HSSFCell or the sheet or workbook, so these can be long-lived
objects without any adverse effect on performance.
</li>
</ul>
</section>
</body>
</document>
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