JEXL

• learning site 

          http://commons.apache.org/jexl/

• Expression calculate

           JexlContext  defined the vars' context

           ExpressionFactory creates the Expression to use.

 

           check the following example to check how to calculate 2 expression belows

           "3+2"  and  "n1+n2+2"

 

           FormulaCalculator.java

           package JEXL;import java.util.HashMap;import java.util.Map;import org.apache.commons.jexl.Expression;import org.apache.commons.jexl.ExpressionFactory;import org.apache.commons.jexl.JexlContext;/** * * JEXL test, this Util class is used for testing the Formula Calculator * * @author shangyang * */public class FormulaCalculator {String _formula;JexlContext _jexlContext;Map _varMap;public FormulaCalculator(){_jexlContext = new JexlContext(){public Map getVars() {// TODO Auto-generated method stubreturn _varMap;}public void setVars(Map vars) {// TODO Auto-generated method stub_varMap.clear();_varMap.putAll( vars );}};}public void setFormula(String formula) throws Exception{validateFormula( formula );_formula = formula;}// set the values to the variable of the expression public void setVars(Map<String, Number> vars){_varMap = vars;}public Number calculate() throws Exception{Expression e = ExpressionFactory.createExpression( _formula );return (Number) e.evaluate( _jexlContext );}private void validateFormula( String formula ) throws Exception{// FIXME: implementation}}

           FormulaCalculatorTest.java

           package JEXL;import java.util.HashMap;import java.util.Map;import junit.framework.TestCase;import org.junit.Assert;public class FormulaCalculatorTest extends TestCase{public void testCalculate() throws Exception{String formula = "3+2";FormulaCalculator cal = new FormulaCalculator();cal.setFormula(formula);cal.setVars(null);Number n = cal.calculate();Assert.assertEquals( 5, Integer.parseInt( n.toString() ));String formula2 = "n1+n2+3";cal.setFormula(formula2);Map<String, Number> mapVars = new HashMap<String, Number>();mapVars.put( "n1", 2);mapVars.put( "n2", 3);cal.setFormula( formula2);cal.setVars( mapVars);Number n2 = cal.calculate();Assert.assertEquals(8, Integer.parseInt( n2.toString() ));}}