MessageBodyWriter not found for media type=application/json

Question

I'm making a small RESTful service using Jetty. Using Maven as the build tool.

When I try to call a GET method that tries to access a JSON representation of an object, I get an "MessageBodyWriter" error. The method in question is as follows,

@Path("/gtfs-rt-feed")
public class GtfsRtFeed {

    @GET
    @Produces(MediaType.APPLICATION_JSON)
    public Response getGtfsRtFeed(){

        GtfsRtFeedModel feedInfo = new GtfsRtFeedModel();
        feedInfo.setStartTime(121334);
        feedInfo.setGtfsId(1);
        feedInfo.setGtfsUrl("http://www.google.com");
        Gson gson = new Gson();

        return Response.ok(feedInfo).build();
    }
    ...

The GtfsRtFeedModel for the GtfsRtFeedModel is as follows,

@XmlRootElement
public class GtfsRtFeedModel {
    private String gtfsUrl;
    private int gtfsId;
    private long startTime;

    public GtfsRtFeedModel(){}

    public String getGtfsUrl() {
        return gtfsUrl;
    }
    ...//Getters and setters for all private variables below

My Maven file includes the following along with the jetty dependencies,

    <dependency>
        <groupId>org.glassfish.jersey.core</groupId>
        <artifactId>jersey-server</artifactId>
        <version>2.19</version>
    </dependency>

    <dependency>
        <groupId>org.glassfish.jersey.containers</groupId>
        <artifactId>jersey-container-servlet-core</artifactId>
        <version>2.19</version>
    </dependency>

    <dependency>
        <groupId>org.glassfish.jersey.containers</groupId>
        <artifactId>jersey-container-jetty-http</artifactId>
        <version>2.19</version>
    </dependency>

    <dependency>
        <groupId>org.glassfish.jersey.media</groupId>
        <artifactId>jersey-media-moxy</artifactId>
        <version>2.19</version>
    </dependency>

Most of the similar questions seems to have been resolved by adding jersey-media-moxy and the required dependencies. But since I've already have them on my maven file, I can't figure out what I'm missing.

Any help would be appreciated.

EDIT: Jetty code added My Jetty code is as follows,

public static void main(String[] args) throws Exception{
    GTFSDB.InitializeDB();
    Datasource ds = Datasource.getInstance();
    ds.getConnection();

    Server server = new Server(8080);
    ServletContextHandler context = new ServletContextHandler();
    context.setContextPath("/");
    context.setResourceBase(BASE_RESOURCE);

    server.setHandler(context);

    context.addServlet(RTFeedValidatorServlet.class, "/validate");
    context.addServlet(GTFSDownloaderServlet.class, "/downloadgtfs");
    context.addServlet(FeedInfoServlet.class, "/feedInfo");
    context.addServlet(TriggerBackgroundServlet.class, "/startBackground");
    context.addServlet(GetFeedJSON.class, "/getFeed");

    context.addServlet(DefaultServlet.class, "/");

    ServletHolder jerseyServlet = context.addServlet(org.glassfish.jersey.servlet.ServletContainer.class, "/api/*");
    jerseyServlet.setInitOrder(1);
    jerseyServlet.setInitParameter("jersey.config.server.provider.packages", "edu.usf.cutr.gtfsrtvalidator.api.resource");


    server.start();
    server.join();
}

Answer 1

Normally the auto-discoverable feature registers the MoxyJsonFeature. I am not sure how it works wit the embedded Jetty. But if it is not register, we can register it ourselves. There is an <init-param> that allows us to add a arbitrary number of providers, separated by a comma. In a web.xml it would be

<init-param>
    <param-name>jersey.config.server.provider.classnames</param-name>
    <param-value>
        org.glassfish.jersey.moxy.json.MoxyJsonFeature,
        org.bar.otherresources.MyCatResource
    </param-value>
</init-param>

So in your Jetty code, you could do

jerseyServlet.setInitParameter("jersey.config.server.provider.classnames",
                               "org.glassfish.jersey.moxy.json.MoxyJsonFeature");

The MoxyJsonFeature registers the MessageBodyWriter and MessageBodyReader required to marshal and unmarshal our POJOS to and from JSON. See more at JAX-RS Entity Providers, and continued in Support for Common Media Type Representations