Server-Sent Events with Undertow, Spring 5, and Resteasy 4

Resteasy 3.5 introduced Server-Sent Events (SSE), and there weren’t any good resources for showing how to get it up-and-running, so I thought I’d put together a quick how-to guide.

Add your dependencies

Up your org.jboss.resteasy:resteasy-jaxrs version to 4.0.0.Beta2. This should automatically pull in a JAX-RS API version 2.1 unless you’ve specified a version of JAX-RS directly. If you have, upgrade to 2.1. This will provide access to the SSE component of JAX-RS 2.1 (SseEventSink, Sse, etc.).

Define an SSE method

@Path("test")
@Produces({MediaType.APPLICATION_JSON})
@Consumes({MediaType.APPLICATION_JSON})
public interface TestService {

  @GET
  @Path("{id}/events")
  @Produces(MediaType.SERVER_SENT_EVENTS)
  void subscribe(@PathParam("id") String id, @Context SseEventSink sink, @Context Sse sse);// It's ok to put JAX-RS annotations on the interface.  Recommended, in fact.

  @POST
  @Path("test")
  TestEntity save(TestEntity testEntity);

  @GET
  @Path("{value}")
  @Produces({MediaType.TEXT_PLAIN})
  String call(@PathParam("value") String input);
}

Implement that biz:

  public void subscribe(String id, SseEventSink sink, Sse sse) {
    service.execute(
        new Thread(
            () -> {
              try {
                sink.send(
                    sse.newEventBuilder()
                        .name("domain-progress")
                        .data(String.class, "starting domain " + id + " ...")
                        .build());
                Thread.sleep(200);
                sink.send(sse.newEvent("domain-progress", "50%"));
                Thread.sleep(200);
                sink.send(sse.newEvent("domain-progress", "60%"));
                Thread.sleep(200);
                sink.send(sse.newEvent("domain-progress", "70%"));
                Thread.sleep(200);
                sink.send(sse.newEvent("domain-progress", "99%"));
                Thread.sleep(200);
                sink.send(sse.newEvent("domain-progress", "Done."))
                    .thenAccept(
                        (Object obj) -> {
                          sink.close();
                        });
              } catch (final InterruptedException e) {
                e.printStackTrace();
              }
            }));
  }

Write a test-case:

 @Test
  void ensureSseWorks() throws InterruptedException {

    ResteasyWebTarget path =
        ((ResteasyWebTarget) webTarget).path(TestService.class).path("1/events");
    SseEventSource source =
        SseEventSource.target(path).reconnectingEvery(10, TimeUnit.SECONDS).build();
    try (SseEventSource s = source) {
      System.out.println("a");
      s.register(
          e -> {
            System.out.println("d");
            System.out.println(e.readData(String.class));
            System.out.println("e");
          },
              System.out::println);
      System.out.println("b");
      s.open();
      System.out.println("c");
      Thread.sleep(1000);
    }
  }

Experience failure

Failure 1

If you’ve done all that, it won’t work. The first error you’ll get is that your @Context SseEventSink is null. Unhork yourself by adding

  @Bean
  public SseEventSinkInterceptor sseEventSinkInterceptor() {
    return new SseEventSinkInterceptor();
  }

to your Spring configuration.

Failure 2

The second failure you’ll experience is on the client-side: No MessageBodyReader for “text/event-stream”. This is fixed by adding a

  @Bean
  public SseEventProvider sseEventOutputProvider() {
    return new SseEventProvider ();
  }

to your Spring client configuration.

Experience success

Ahh, delicious success

a
b
c
d
starting domain 1 ...
e
d
50%
e
d
60%
e
d
70%
e
d
99%
e
d
Done.
e

Sunshower-Test

Plugging Sunshower again, you can get all this goodness by annotating your test-class with @io.sunshower.test.ws.EnableJAXRS if you have io.sunshower.test:test-ws:1.0.0-SNAPSHOT as a dependency.