Question

Heroku recently began supporting Java apps. Looking through the docs, it seems to resemble the Java Servlet Standard. Does anyone know of an instance where a GWT app has been successfully deployed on Heroku? If so, are there any limitations?

Answer 1

My first answer to this turned out to have problems when GWT tried to read its serialization policy. In the end I went for a simpler approach that was less Guice-based. I had to step through the Jetty code to understand why setBaseResource() was the way to go – it’s not immediately obvious from the Javadoc.

Here’s my server class – the one with the main() method that you point Heroku at via your app-assembler plugin as per the Heroku docs.

public class MyServer {

public static void main(String[] args) throws Exception {
    if (args.length > 0) {
        new MyServer().start(Integer.valueOf(args[0]));
    }
    else {
        new MyServer().start(Integer.valueOf(System.getenv("PORT")));
    }
}

public void start(int port) throws Exception {

    Server server = new Server(port);
    ServletContextHandler context = new ServletContextHandler(ServletContextHandler.SESSIONS);
    context.setBaseResource(createResourceForStatics());
    context.setContextPath("/");
    context.addEventListener(new AppConfig());
    context.addFilter(GuiceFilter.class, "/*", null);
    context.addServlet(DefaultServlet.class, "/");
    server.setHandler(context);

    server.start();
    server.join();
}

private Resource createResourceForStatics() throws MalformedURLException, IOException {
    String staticDir = getClass().getClassLoader().getResource("static/").toExternalForm();
    Resource staticResource = Resource.newResource(staticDir);
    return staticResource;
}
}

AppConfig.java is a GuiceServletContextListener.

You then put your static resources under src/main/resources/static/.