An example of how to use Mozilla Rhino to execute JavaScript within Java.

EvaluateStock.java

package com.iankwalter.rhinostockexample;

import org.mozilla.javascript.Context;
import org.mozilla.javascript.Scriptable;
import org.mozilla.javascript.ScriptableObject;

/**
 * An example of how to use Mozilla Rhino to execute JavaScript within Java
 *
 * @author Ian Kennington Walter
 */
public class EvaluateStock {

  /**
   * Evaluates whether a Stock is undervalued based on logic within a JS script
   *
   * @param args
   */
  public static void main(String[] args) {

    // Define evaluation JavaScript. Typically this would be stored in a file or a database.
    String evaluationScript =
      "var earnings = stock.getNetIncome() * 10; " +
      "earnings += (stock.getTotalCash() - stock.getTotalDebt()); " +
      "if (earnings > stock.getMarketCap()) { " +
      "    stock.setUndervalued(true); " +
      "} else { " +
      "    stock.setUndervalued(false); " +
      "} ";

    // Create a Stock object to evaluate.
    Stock stock = new Stock();
    stock.setNetIncome(10.0);
    stock.setTotalCash(100.0);
    stock.setTotalDebt(0.0);
    stock.setMarketCap(150.0);

    // Create and enter a Context. A Context stores information about the execution environment of a script.
    Context cx = Context.enter();
    try {
      // Initialize the standard objects (Object, Function, etc.). This must be done before scripts can be
      // executed. The null parameter tells initStandardObjects
      // to create and return a scope object that we use
      // in later calls.
      Scriptable scope = cx.initStandardObjects();

      // Pass the Stock Java object to the JavaScript context
      Object wrappedStock = Context.javaToJS(stock, scope);
      ScriptableObject.putProperty(scope, "stock", wrappedStock);

      // Execute the script
      cx.evaluateString(scope, evaluationScript, "EvaluationScript", 1, null);
    } catch (Exception e) {
      e.printStackTrace();
    } finally {
      // Exit the Context. This removes the association between the Context and the current thread and is an
      // essential cleanup action. There should be a call to exit for every call to enter.
      Context.exit();
    }

    // Output whether the stock was determined to be undervalued.
    System.out.println("Is stock undervalued?");
    System.out.println(stock.isUndervalued());
  }

}