Legend has it that this is the proper way of performing validation on a RestEasy/JAX-RS endpoint when there is no nested object:

@Value
public class PayloadWithNotNull {
    @NotNull Long mSomeLong; // Long is an object, but it's still "Just a long"
}

...

@POST
@Path("test1")
@Produces(MediaType.APPLICATION_JSON)
public Response test1(
    final @Valid @NotNull PayloadWithNotNull payload
) {
    return ok();
}

Notice how parameter payload has both @Valid and @NotNull, but mSomeLong only has @NotNull.

Here is what I observe depending on the request’s json body :

• Sending null -> 400 with explicit message “test1.payload must not be null”
• Sending {} -> 400 without an explicit message!
• Sending { "someLong": null } -> 400 without an explicit message!
• Sending { "someLong": "not a long" } -> 400 without an explicit message!

However, if I add @Valid on the class field:

@Value
public class PayloadWithValidNotNull {
    @Valid @NotNull Long mSomeLong;
}

• Sending null -> 400 with explicit message “test1.payload must not be null”
• Sending {} -> 400 with explicit message “test1.payload.someLong must not be null”
• Sending { "someLong": null } -> 400 with explicit message “test1.payload.someLong must not be null”
• Sending { "someLong": "not a long" } -> 400 without an explicit message! (that’s lame but at least the behaviour is consistent)

I was under the impression that @Valid is only required for nested objects. I seem to read that everywhere. And yet, it seems absolutely required for this Long field, which despite being itself an object does not have nested objects.

Am I missing something?

Bonus question : is there a simple way to get an explicit error message for “not a long” ?