Has anyone successfully deployed a GWT app on Heroku? - gwt

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

Yes, I've got a successful deployment using the getting started with Java instructions here:
http://devcenter.heroku.com/articles/java
I use the Maven project with appassembler plugin approach but added gwt-maven-plugin to compile a GWT app during the build.
When you push to heroku you see the GWT compile process running, on one thread only so quite slow but it works fine.
The embedded Jetty instance is configured to serve up static resources at /static from src/main/resources/static and I copy the compiled GWT app to this location during the build and then reference the .nocache.js as normal.
What else do you want to know?
You've got a choice, either build the Javascript representation of your GWT app locally into your Maven project, commit it and the read it from your app, or to generate it inside Heroku via the gwt-maven-plugin as I mentioned.
The code to serve up files from a static location inside your jar via embedded Jetty is something like this inside a Guice ServletModule:
(See my other answer below for a simpler and less Guice-driven way to do this.)
protected void configureServlets() {
bind(DefaultServlet.class).in(Singleton.class);
Map<String, String> initParams = new HashMap<String, String>();
initParams.put("pathInfoOnly", "true");
initParams.put("resourceBase", staticResourceBase());
serve("/static/*").with(DefaultServlet.class, initParams);
}
private String staticResourceBase() {
try {
return WebServletModule.class.getResource("/static").toURI().toString();
}
catch (URISyntaxException e) {
e.printStackTrace();
return "couldn't resolve real path to static/";
}
}
There's a few other tricks to getting embedded Jetty working with guice-servlet, let me know if this isn't enough.

Answer 2

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/.

Answer 3

In theory, one should be able to run GWT using the embedded versions of Jetty or Tomcat, and bootstrap the server in main as described in the Heroku Java docs.