Взаимодействие с java приложением

Вы можете воспользоваться движком Nashorn

Example.java

public class Example {
    public static void main(String[] args) {
        ScriptEngineManager factory = new ScriptEngineManager();
        ScriptEngine engine = factory.getEngineByName("nashorn");
        File script = new File("script.js");
        try (BufferedReader reader = new BufferedReader(
          new InputStreamReader(
            new FileInputStream(script), "UTF8"))) {
            engine.eval(reader);
        }
        catch (ScriptException exc) {
            exc.printStackTrace();
        }
        catch (IOException exc) {
            exc.printStackTrace();
        }
    }
    public static class EMail {
        private String addr;
        private String subject;
        private String text;
        public EMail() {}
        public EMail(String addr, String subject, String text) {
            this.addr = addr;
            this.subject = subject;
            this.text = text;
        }
        // Аксессоры
        public void send() {
            System.out.format("Отправка письма с темой '%s' на адрес %s\n", subject, addr);
        }
    }
}

scripts.js

var EMail = Java.type("Example.EMail");
var email = new EMail("test@mail.ru", "Тест", "Проверка");
email.send();