How to serialize declarative links (jersey) with jackson

Question

I am using declarative linking in my project. My jackson mapper configuration is

final ObjectMapper mapper = new ObjectMapper();
    mapper.configure(MapperFeature.DEFAULT_VIEW_INCLUSION, false);
    mapper.configure(MapperFeature.AUTO_DETECT_FIELDS, false);
    mapper.configure(MapperFeature.AUTO_DETECT_IS_GETTERS, false);
    mapper.configure(MapperFeature.AUTO_DETECT_GETTERS, false);
    mapper.configure(MapperFeature.AUTO_DETECT_SETTERS, false);
    mapper.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);
    mapper.configure(SerializationFeature.INDENT_OUTPUT, true);

As I have disabled any kind of auto detection, injected links like

    @InjectLinks({

@InjectLink(rel = "bookmark", resource = ConnectionsResource.class, style = Style.ABSOLUTE_PATH) })
@JsonProperty("links")
Link[] links;

are serialized to an empty JSON object (because none of the fields in "Link" is annotated with @JsonProperty).

How to enable serialization for Links only for the fields rel and href without changing my global mapper configuration?

Answer 1

So one way to make this work is to use a customer serializer. You would have to add a new module for this serializer to the ObjectMapper, but this should not effect the rest of the configurations.

Here's the serializer

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.SerializerProvider;
import java.io.IOException;
import javax.ws.rs.core.Link;

public class LinkSerializer extends JsonSerializer<Link>{

    @Override
    public void serialize(Link link, JsonGenerator jg, SerializerProvider sp) 
            throws IOException, JsonProcessingException {
        jg.writeStartObject();
        jg.writeStringField("rel", link.getRel());
        jg.writeStringField("href", link.getUri().toString());
        jg.writeEndObject();
    }
}

Here a test class

public class TestClass {

    @JsonProperty("links")
    protected List<Link> links;
    protected String name;
    protected String id;
    // getter and setters
}

And the test run

public static void main(String[] args) throws Exception{

    ObjectMapper mapper = new ObjectMapper();
    mapper.configure(MapperFeature.DEFAULT_VIEW_INCLUSION, false);
    mapper.configure(MapperFeature.AUTO_DETECT_FIELDS, false);
    mapper.configure(MapperFeature.AUTO_DETECT_IS_GETTERS, false);
    mapper.configure(MapperFeature.AUTO_DETECT_GETTERS, false);
    mapper.configure(MapperFeature.AUTO_DETECT_SETTERS, false);
    mapper.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);
    mapper.configure(SerializationFeature.INDENT_OUTPUT, true);

    SimpleModule simpleModule = new SimpleModule();
    simpleModule.addSerializer(Link.class, new LinkSerializer());
    mapper.registerModule(simpleModule);

    Link link1 = Link.fromUri(URI.create("http://localhost:8080/")).rel("one").build();
    Link link2 = Link.fromUri(URI.create("http://localhost:8080/")).rel("two").build();
    TestClass test = new TestClass();
    test.getLinks().add(link1);
    test.getLinks().add(link2);
    String json = mapper.writeValueAsString(test);
    System.out.println(json);
}

produces this result

{
  "links" : [ {
    "rel" : "one",
    "href" : "http://localhost:8080/"
  }, {
    "rel" : "two",
    "href" : "http://localhost:8080/"
  } ]
}

Hope this helps.

Answer 2

Here is an example of using the Jackson mixin annotation for serializing and deserializing the Link object including all the properties:

@JsonAutoDetect(
        fieldVisibility = JsonAutoDetect.Visibility.NONE,
        getterVisibility = JsonAutoDetect.Visibility.NONE,
        isGetterVisibility = JsonAutoDetect.Visibility.NONE)
@JsonDeserialize(using = LinkMixin.LinkDeserializer.class)
public abstract class LinkMixin extends Link {

    private static final String HREF = "href";

    @JsonProperty(HREF)
    @Override
    public abstract URI getUri();

    @JsonAnyGetter
    public abstract Map<String, String> getParams();

    public static class LinkDeserializer extends JsonDeserializer<Link> {

        @Override
        public Link deserialize(
                final JsonParser p,
                final DeserializationContext ctxt) throws IOException {
            final Map<String, String> params = p.readValueAs(
                    new TypeReference<Map<String, String>>() {});
            if (params == null) {
                return null;
            }
            final String uri = params.remove(HREF);
            if (uri == null) {
                return null;
            }
            final Builder builder = Link.fromUri(uri);
            params.forEach(builder::param);
            return builder.build();
        }
    }
}