App.java

public class App {
    public static void main(String[] args) {
        ProcessBuilder process = new ProcessBuilder();
        Integer port;

        // This tells our app that if Heroku sets a port for us, we need to use that port.
        // Otherwise, if they do not, continue using port 4567.

        if (process.environment().get("PORT") != null) {
            port = Integer.parseInt(process.environment().get("PORT"));
        } else {
            port = 4567;
        }

        port(port);
        
        ...