Why do I need to specify @Produces/@Consumes for REST?

[t1]

I understand that the widely spread muscle memory is that you annotate everything with @Produces, but the http content negotiation should actually just involve the client (specifying the Accept hearder... or not) and the container (Quarkus with the available MessageBodyWriters), but not my application. The @Produces and @Consumes annotations are intended only for rare cases, where the application wants to have different methods invoked, depending on what the client wants.

So I'd assume that I can simply add a MessageBodyWriter (e.g. the one contained in quarkus-rest[easy]-jaxb), and my application would be ready to produce that. But instead, Quarkus only recognizes that it can produce application/json, everything else seems to be ignored until I explicitly add that other content types are available.

I've seen the limitation that JAXB doesn't currently allow to serialize lists or arrays out of the box. So I even can't simply annotate all my resource classes, I'll have to exclude those methods... but that's another issue.

I have a reproducer here for everybody to play around with.

What do you think?

[cescoffier]

\CC @geoand

[geoand]

I understand that the widely spread muscle memory is that you annotate everything with @produces, but the http content negotiation should actually just involve the client (specifying the Accept hearder... or not) and the container (Quarkus with the available MessageBodyWriters), but not my application.

This is not true. MessageBodyWriter is meant to do the actual serialization (using the negotiated type) of whatever the JAX-RS / Jakarta REST method returned. It's a different concern than what the application returns has to do - which is supply the actual object to be serialized

[t1]

I think you are repeating what I wanted to say: the application code returns an POJO entity, e.g. a Product, and it's the concern of the container, e.g. Quarkus, to serialize that in a way that the client accepts. But you write "This is not true", so I assume we misunderstand each other.

[t1]

To cite the spec: "Application classes can declare the supported request and response media types using the @Consumes and @Produces annotations respectively.... In the absence of either of these annotations, support for any media type (*/*) is assumed."

So these annotations are purely optional. And without them, all content types the container can produce, should work.

[t1]

Is this not an important topic to discuss? Although I suppose it's not trivial to implement, as it seems to be a design shortcut.