Additional Request Completion Methods that support Futures

Describe the feature Adding more request completion methods (eg: Context#result(...) that support futures as you don’t always need to specify a response body for a request, sometimes a Status Code of 401 Unauthorized is fine.

Additional context

Some of the methods that I am thinking of are as follows but please note that all the methods outlined assume that the generic type variable from the CompletableFuture is Nullable.

Context#status(int)
Context#status(CompletableFuture<Integer>)

Context#json(Any)
Context#json(CompletableFuture<Any>) 

Context#result(String)
Context#result(CompleteableFuture<String>)
Context#result(byte[])
Context#result(CompleteableFuture<Byte[]>)
Context#(InputStream)
Context#result(CompleteableFuture<InputStream>)

One useful usecase would be if you are querying for a document from a database and then going to return that response (if any) as json as it makes for neater code:

Context#json(CompletableFuture.supplyAsync(() -> {
  final Document document = this.mongo.find(Filters.eq("_id", ctx.pathParam("id", ObjectId.class).get())).first();

  if (document == null) {
    ctx.status(HttpStatus.NO_CONTENT_204);
    return null; // Hello Javalin I don't have any Object for you to convert to Json using JavalinJson do not set the ContentType.JSON do not add a Response Body please.
  }

  Context#status(HttpStatus.OK_200);
  return document; // Hello Javalin please convert this Object to Json using JavalinJson
}));

One thing to note about this example is serializing a Bson Document to json isn’t going to give your returned response as a valid response you would want. You actually have to tell Bson to write as a json string first, for example:

ctx -> {
    ctx.status(HttpStatus.OK);
    ctx.contentType(ContentType.JSON);
    ctx.result(Document#toJson(JsonWriterSettings, Encoder));
}

This leads me onto the next thing; having a Context#json(String jsonString) method that sets the Content Type to JSON and then sets the body to the jsonString value would also be useful. Sometimes I already have the jsonString due to Bson so I can’t use Context#json(String) because that then serializes my jsonString AGAIN, causing issues. Also in case I haven’t mentioned this, Context#json(String) does not support a null argument so I have to hack around all of this with:

Context.result(CompleteableFuture.supplyAsync(() -> {
  final Document document = this.mongo.find(Filters.eq("_id", ctx.pathParam("id", ObjectId.class).get())).first();

  if (document == null) {
    ctx.status(HttpStatus.NO_CONTENT_204);
    return null;
  }
  
  ctx.statusCode(HttpStatus.OK_200);
  ctx.contentType(ContentType.JSON); // Notice how we specify this all of the time?
  
  return this.gson.toJson(document); // Again, for Mongo you'd do Document#toJson(JsonWriterSettings, Encoder) instead of gson.
}));

[tipsy]

Merged a change here: https://github.com/tipsy/javalin/commit/b0a2e1abda4cd10a22960f2e5a1f0b31309851d4

[tipsy]

It’s now:

fun json(future: CompletableFuture<*>) = result(future.thenApply {
    if (it != null) JavalinJson.toJson(it).also { contentType("application/json") } else ""
})

And these assertions pass:

assertThat(contentResponse.status).isEqualTo(200)
assertThat(contentResponse.body).isEqualTo("""{"value1":"FirstValue","value2":"SecondValue"}""")
assertThat(contentResponse.headers.getFirst(Header.CONTENT_TYPE)).isEqualTo("application/json")

assertThat(noContentResponse.status).isEqualTo(204)
assertThat(noContentResponse.body).isEqualTo(null)
assertThat(noContentResponse.headers.getFirst(Header.CONTENT_TYPE)).isEqualTo("text/plain")