poi/src/test/java/org/apache/poi/ss/formula/eval/TestExternalFunction.java

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   contributor license agreements.  See the NOTICE file distributed with
   this work for additional information regarding copyright ownership.
   The ASF licenses this file to You under the Apache License, Version 2.0
   (the "License"); you may not use this file except in compliance with
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       http://www.apache.org/licenses/LICENSE-2.0

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package org.apache.poi.ss.formula.eval;

import static org.junit.jupiter.api.Assertions.assertEquals;

import java.io.IOException;

import org.apache.poi.hssf.HSSFTestDataSamples;
import org.apache.poi.hssf.usermodel.HSSFCell;
import org.apache.poi.hssf.usermodel.HSSFFormulaEvaluator;
import org.apache.poi.hssf.usermodel.HSSFRow;
import org.apache.poi.hssf.usermodel.HSSFSheet;
import org.apache.poi.hssf.usermodel.HSSFWorkbook;
import org.apache.poi.ss.formula.OperationEvaluationContext;
import org.apache.poi.ss.formula.functions.FreeRefFunction;
import org.apache.poi.ss.formula.udf.AggregatingUDFFinder;
import org.apache.poi.ss.formula.udf.DefaultUDFFinder;
import org.apache.poi.ss.formula.udf.UDFFinder;
import org.junit.jupiter.api.Test;

final class TestExternalFunction {

	private static ValueEval myFunc1(ValueEval[] args, OperationEvaluationContext ec) {
		if (args.length != 1 || !(args[0] instanceof StringEval)) {
			return ErrorEval.VALUE_INVALID;
		}
		StringEval input = (StringEval) args[0];
		return new StringEval(input.getStringValue() + "abc");
	}

	private static ValueEval myFunc2(ValueEval[] args, OperationEvaluationContext ec) {
		if (args.length != 1 || !(args[0] instanceof StringEval)) {
			return ErrorEval.VALUE_INVALID;
		}
		StringEval input = (StringEval) args[0];
		return new StringEval(input.getStringValue() + "abc2");
	}

	/**
	 * Checks that an external function can get invoked from the formula evaluator.
	 */
	@Test
	void testInvoke() throws IOException {
		try (HSSFWorkbook wb = HSSFTestDataSamples.openSampleWorkbook("testNames.xls")) {
			HSSFSheet sheet = wb.getSheetAt(0);

			/*
			 * register the two test UDFs in a UDF finder, to be passed to the evaluator
			 */
			UDFFinder udff1 = new DefaultUDFFinder(new String[]{"myFunc",},
												   new FreeRefFunction[]{TestExternalFunction::myFunc1});
			UDFFinder udff2 = new DefaultUDFFinder(new String[]{"myFunc2",},
												   new FreeRefFunction[]{TestExternalFunction::myFunc2,});
			UDFFinder udff = new AggregatingUDFFinder(udff1, udff2);


			HSSFRow row = sheet.getRow(0);
			HSSFCell myFuncCell = row.getCell(1); // =myFunc("_")

			HSSFCell myFunc2Cell = row.getCell(2); // =myFunc2("_")

			HSSFFormulaEvaluator fe = HSSFFormulaEvaluator.create(wb, null, udff);
			assertEquals("_abc", fe.evaluate(myFuncCell).getStringValue());
			assertEquals("_abc2", fe.evaluate(myFunc2Cell).getStringValue());
		}
	}
}