Support Javalin async request handling [Context#future(...)]

[LoonyRules]

This PR adds support for async request handling for Javalin users, using the Context#future(...) method as per the discussion in #154

[SentryMan]

Can you also put an async path on the javalin-jsonb test controller?

[LoonyRules]

Can you also put an async path on the javalin-jsonb test controller?

@SentryMan I actually cannot do that as the generator creates 2 global variable fields with the same signature instead of just knowing what fields have been created, and use it, if it detects a same signature would've been created. This is something I mentioned to you on discord a couple of weeks ago but looks like we forgot to make a ticket.

Here's the code change:

  @Hidden
  @Get
  List<HelloDto> getAll() {
    return myService.findAll();
  }

  // Added this method
  @Get("/async")
  CompletableFuture<List<HelloDto>> getAllAsync() {
    return CompletableFuture.supplyAsync(() -> {
      // Simulate a delay as if an actual IO operation is being executed.
      // This also helps ensure that we aren't just getting lucky with timings.
      try {
        Thread.sleep(10L);
      } catch (InterruptedException e) {
        throw new RuntimeException(e);
      }

      return myService.findAll();
    }, Executors.newSingleThreadExecutor()); // Example of how to use a custom executor.
  }

both of these methods would have the same JsonType signature and variable names so that's what causes the error:

  private final JsonType<List<HelloDto>> listHelloDtoJsonType;
  private final JsonType<List<HelloDto>> listHelloDtoJsonType;
  private final JsonType<HelloDto> helloDtoJsonType;

  public HelloController$Route(HelloController controller, Validator validator, Jsonb jsonB) {
    this.controller = controller;
    this.validator = validator;
    this.listHelloDtoJsonType = jsonB.type(HelloDto.class).list(); // GET /hello (getAll)
    this.listHelloDtoJsonType = jsonB.type(HelloDto.class).list(); // GET /hello (getAllAsync)
    this.helloDtoJsonType = jsonB.type(HelloDto.class);
  }

variable listHelloDtoJsonType is already defined in class org.example.myapp.web.HelloController$Route

[SentryMan]

you need to add a check here so that the raw type of the future doesn't get written twice.

[SentryMan]

I guess either modify the jsontypes map, or create a set that tracks what future types have been written. Other non- types do not get duplicates.

[SentryMan]

I'm thinking of doing something like this. Add futureSet as a Set field then modify your for loops like so.

      for (UType type : jsonTypes.values()) {
        // Support for CompletableFuture's.
        if ("java.util.concurrent.CompletableFuture".equals(type.mainType())) {
          type = type.paramRaw();
          if (jsonTypes.containsKey(type.full()) || !futureSet.add(type.full())) {
            continue;
          }
        }
// the rest is fine

[SentryMan]

You'll probably need to take out the throw IllegalStateException from the JsonbUtil and put it into the first for loop in the ControllerWriter.

[LoonyRules]

Now sure how I didn't notice the jsonTypes map and that it could be used to fix the issue I came across.

I've moved the CompletableFuture generic validation over to the ControllerMethodWriter for Javalin as it should then provide better context (controller + method) in regards to what is wrongly defined. This is just an assumption though, not sure how Avaje handles exceptions when writing sources.

Async tests in test-javalin-json have also been added.

[SentryMan]

LGTM