JSON-Jackson does not handle resource returning CompletionStage<X>

[jerseyrobot]

It seems like jersey-media-json-jackson is not up to date with the latest JAX-RS 2.1 features.
I tried creating the following resource method:

@GET
@Produces({"application/json" })
@Path("async")
public CompletionStage<Hello> asyncHello(@NotNull @PathParam(value = "lang") String lang,
                                         @NotNull @Size(min = 2) @QueryParam("yo") String greet){
        return CompletableFuture.supplyAsync(() -> new Hello(lang, greet);
}

This fails with stack trace

java.lang.IllegalArgumentException: Class org.kantega.reststop.helloworld.jaxrs.Hello not subtype of [simple type, class java.util.concurrent.CompletionStage<org.kantega.reststop.helloworld.jaxrs.Hello>]
	at com.fasterxml.jackson.databind.type.TypeFactory.constructSpecializedType(TypeFactory.java:359)
	at org.glassfish.jersey.jackson.internal.jackson.jaxrs.base.ProviderBase.writeTo(ProviderBase.java:624)
	at org.glassfish.jersey.message.internal.WriterInterceptorExecutor$TerminalWriterInterceptor.invokeWriteTo(WriterInterceptorExecutor.java:266)

Returning a plain String with text/plain works as expected.

Just as a test I build my own version of Jersey with some additional code in org.glassfish.jersey.jackson.internal.jackson.jaxrs.base.ProviderBase.writeTo(...):

TypeFactory typeFactory = writer.getTypeFactory();

String typeName = genericType.getTypeName();
if(typeName.contains(CompletionStage.class.getName())) {
    Type[] actualTypeArguments = ((ParameterizedTypeImpl) genericType).getActualTypeArguments();
    genericType = actualTypeArguments[0];
}

JavaType baseType = typeFactory.constructType(genericType);

The middle part unwrapping the CompletionStage is new.
This works.

So, have I missed something, or is the CompletionStage support not complete?

[jerseyrobot]

@dandew Commented
Any traction on fixing this? It's one of the very first thing you try when switching to JAX-RS 2.1 and it's sad to see it break right away 😅

[jerseyrobot]

@computerlove Commented
As far as I see it should'nt be a big task to fix.
Not sure if the above fix/hack is the correct place to handle this.
It would be nice if someone could comment on if this is a acceptable solution, and if not point us in the general area where it should be handled.

[jerseyrobot]

• Issue Imported From: https://github.com/jersey/jersey/issues/3672
• Original Issue Raised By:@computerlove
• Original Issue Assigned To: Unassigned

[dandew]

@computerlove Maybe worth trying to send a PR with your proposed fix? This bug is turning into a showstopper.

[mageshwaranr]

Faced the exact same problem. Following lines of code helped fixed the issue.

Made a local copy of org.glassfish.jersey.jackson.internal.jackson.jaxrs.base.ProviderBase and modified writeTo method as pointed out by @jerseyrobot .

TypeFactory typeFactory = writer.getTypeFactory(); `
// Newly added statements...  after line no : 621
if (genericType instanceof ParameterizedType ) {
    Type rawType = ((ParameterizedType) genericType).getRawType();
        if (rawType instanceof Class && CompletionStage.class.isAssignableFrom((Class)rawType)) {
            // CompletionStage has only one parameterized type. So pick the first
            genericType = ((ParameterizedType) genericType).getActualTypeArguments()[0];
        }
}
JavaType baseType = typeFactory.constructType(genericType);

I modified CompletionStageTest and found it to be working.

[computerlove]

@mageshwaranr Have you created a PR? Your snippet looks like a better version of my suggestion.

[mageshwaranr]

Just now submitted a PR just now.

[edinardo]

For who is still waiting for the official fix and don't want (or can't) repack jersey-media-json-jackson with the patch for each new version, a quick simple workaround is to implement WriterInterceptor that changes the context GenericType. Both @computerlove or @mageshwaranr proposed code can be used.