JavaEvaluatesJavascriptExample.java

package com.kiroule.ocpupgradejava8.topic9_2;

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.math.BigDecimal;
import java.time.LocalDate;

import javax.script.Invocable;
import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;

import static java.time.format.DateTimeFormatter.ISO_DATE;

/**
 * @author Igor Baiborodine
 * @see quebec-gst-tax-calculator.js
 */
public class JavaEvaluatesJavascriptExample {

  public static void main(String... args)
      throws FileNotFoundException, ScriptException, NoSuchMethodException {

    ScriptEngineManager scriptEngineManager = new ScriptEngineManager();
    ScriptEngine engine = scriptEngineManager.getEngineByName("nashorn");

    engine.eval(new FileReader("ocp-upgrade-java8/src/main/java/com/kiroule/" +
                               "ocpupgradejava8/topic9_2/quebec-gst-tax-calculator.js"));
    Invocable invocable = (Invocable) engine;

    BigDecimal purchaseAmount = new BigDecimal("100.00");
    String format = "Quebec GST tax is $%s for the amount of $%s on %s %n";

    LocalDate purchaseDate = LocalDate.of(2005, 1, 1);
    BigDecimal taxAmount = new BigDecimal((String) invocable.invokeFunction("calculateGstTax",
                                                                            purchaseDate
                                                                                .format(ISO_DATE),
                                                                            purchaseAmount));
    System.out.printf(format, taxAmount, purchaseAmount, purchaseDate);

    purchaseDate = LocalDate.now();
    taxAmount = new BigDecimal((String) invocable.invokeFunction("calculateGstTax",
                                                                 purchaseDate.format(ISO_DATE),
                                                                 purchaseAmount));
    System.out.printf(format, taxAmount, purchaseAmount, purchaseDate);
  }
}