On Wed, Jan 11, 2017 at 3:45 AM, <victor.n...@gmail.com> wrote:
> Hi,
>
> I am familiar with the issues
> https://github.com/FasterXML/jackson-databind/issues/265 (i.e., using
> @JsonUnwrapped within a @JsonCreator) and others, but in the end, I couldn't
> find the correct way of using @JsonUnwrapped with @JsonCreator (i.e., I want
> to avoid having mutable objects whose fields are modified by Jackson).
>
> If we take the example from the wiki:
>
> class Location {
> public final int latitude, longitude;
>
> public Location(int latitude, int longitude) { ... }
> }
>
>
> class Place {
> public final String name;
> @JsonUnwrapped public final Location location;
>
> @JsonCreator
> public Place(@JsonProperty("name") String name, ????) { ... }
> }
>
>
> What is the correct way of defining the Place constructor?
>
> If I use:
>
> @JsonCreator
> public Place(@JsonProperty("name") String name,
> @JsonProperty("latitude") int latitude,
> @JsonProperty("longitude") int longitude) {
> this.name = name;
> this.location = new Location(latitude, longitude);
> }
>
>
> Then I get an error from Jackson because it tries, after SUCCESSFULLY
> creating the Place object including its location, to then set the
> @JsonUnwrapped annotated fields and fails because it can't create Location,
> and even if it could, it has already consumed the stream so it can't read
> the proper values for location.
Consumption is not a problem (or, at least, shouldn't), since
buffering will be used automatically for all @JsonUnwrapped fields.
> If I use (expecting Jackson to set the location field using the rest of the
> information from the stream):
>
> @JsonCreator
> public Place(@JsonProperty("name") String name) {
> this.name = name;
> this.location = null;
> }
>
>
> Then it also fails because I'm not sure why it can't read the rest of the
> stream (I didn't investigate this too much because I got fed up and thought
> I would come asking here :).
>
> So is there a way to make that work and how?
>
> I am using Jackson 2.7.8 for now because of dropwizard integration, but I
> should be able to use a newer version maybe…
My preferred course would be to just not trying to handle `latitude`
and `longitude`, and instead have a setter for location.
That should work fine; that is, constructor only taking `name`.
Otherwise removing of `@JsonUnwrapped` annotation should work, and you
could instead define something like:
@JsonAnyGetter
public Map<String> stuff() {
// construct Map with `latitude` and `longitude`
return mapWithLatLong;
}
I am not sure if it'd be possible to make your attempt work: challenge
is that deserializer for Place really does not have much information
on what is contained within @JsonUnwrapped pojo; handling is too
indirect.
So there is nothing linking properties lat/long passed to creator, and
contents of `Location`, from deserializer perspective.
Still... if you could file an issue, perhaps something could be done
for special case where all properties are handled, so there is nothing
to hand to @JsonUnwrapped handlers, call would be avoided and everyone
would be happy.
This is not fool-proof, even if so, since current handling of
unwrapped values combines ALL potential properties (as they can not be
separated); but could be an improvement.
-+ Tatu +-
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