Spring-Data-REST: Custom serialization of @Embeddable in HAL

Question

I have an entity which looks like this (I'll omit getters, setters and constuctors for the sake of brevity):

@Entity
public class System {
    @NotNull
    @Column(name = "SYSTEMID", nullable = false)
    @Embedded
    private SystemId systemId;
}

with SystemId looking like this:

@Embeddable
@JsonSerialize(using = SystemIdSerializer.class)
@JsonDeserialize(using = SystemIdDeserializer.class)
public class SystemId {
    @Column(name = "SYSTEMID", nullable = false)
    private String value;
}

My custom serializer does nothing but write out value, which works for 'normal' JSON, just not the HAL representation which looks like this:

{
    "systemId": {
        "content": "1"
    }
}

I would like to have it like this

{
    "systemId": "1"
}

as well. Is there any way to do it? I've spent some time googling but wasn't successful. Thanks.

Answer 1

Perhaps the projection can help you...

@Projection(name="withSystemId", types = System.class)
public interface WithSystemId {

    @JsonProperty("systemId")
    @Value("#{target.systemId.value}")
    String getSysId();

    // Other getters of System properties...
}

Then try GET your System:

http://localhost:8080/api/systems?projection=withSystemId

UPDATED

Concerning the custom serializer - just add @JsonUnwrapped annotation to systemId:

@Entity
public class System {

    @Embedded
    @JsonUnwrapped
    private SystemId systemId;
} 

Then you must get what you expect

{
    "systemId": "1"
} 

And I assume that your serializer looks like this:

public class SystemIdSerializer extends StdSerializer<SystemId> {

    public SystemIdSerializer() {
        this(null);
    }

    protected SystemIdSerializer(Class<SystemId> t) {
        super(t);
    }

    @Override
    public void serialize(SystemId id, JsonGenerator gen, SerializerProvider provider) throws IOException {
        gen.writeStartObject();
        gen.writeNumberField("systemId", id.value());
        gen.writeEndObject();
    }
}

---

Working example is here. See Member and nested MemberSkill classes. Then try to launch the app and GET http://localhost:8080/api/members