Adding scripting to java applications

Many of our applications require scripting support (allowing users to create scripts to customize workflow within the application). Java provides very straightforward scripting via the javax.script script-engine library. A simple integration is shown below where a Javascript onSave method provided by the user is called, if available, passing a business-logic object “item”:

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

public class Scripting extends Base {
 private ScriptEngineManager mgr;
 private ScriptEngine engine;
 private Invocable invocable;

 private boolean initialize (String script) {
  mgr = new ScriptEngineManager();
  engine = mgr.getEngineByName("js");
  try {
   engine.eval(script);
  } catch (ScriptException e) {
   warn("The script could not be loaded: " + e.getMessage());
   return false;
  }
  invocable = (Invocable)engine;
  return true;
 }

 public void onSave(Item item) {
  try {
   invocable.invokeFunction("onSave", item);
  } catch (ScriptException e) {
   warn("The onSave method of the script caused an error: " + e.getMessage());
  } catch (NoSuchMethodException e) {
   // no onSave method provided by the user - that's OK, just ignore it
  }
 }
}

Note: the javax.script library supports multiple scripting engines including javascript, python, groovy and java. Javascript was the easiest to get working because the Rhino Javascript engine is included in JDK 6.