Question

I m using Jersey and want to output the following JSON with only the fields listed:

[
    {
      "name": "Holidays",
      "value": "http://www.google.com/calendar/feeds/usa__en%40holiday.calendar.google.com/public/basic"
    },
    {
      "name": "Personal",
      "value": "http://www.google.com/calendar/feeds/myprivatefeed/basic"
    }
]

If I must, I can surround that JSON with {"feeds": ... }, but having this be optional would be best. I want to pull this information from a list of CalendarFeeds that are stored in a Member POJO that is retrieved via Hibernate. Here are the simplified POJOs:

public class Member {
    private String username;
    private String password;
    private Set<CalendarFeed> calendarFeeds = new HashSet<CalendarFeed>();
}

public class CalendarFeed {
    public enum FeedType { GCAL, EVENT };
    private Member owner;
    private String name;
    private String value;
    private FeedType type;
}

Currently, I ve got a Jersey resource called CalendarResource that manually outputs JSON with the calendar feeds information:

@Path("/calendars")
public class CalendarResource {

    @Inject("memberService")
    private MemberService memberService;

    @GET
    @Produces(MediaType.APPLICATION_JSON)
    public String getCalendars() {
        // Get currently logged in member
        Member member = memberService.getCurrentMember();

        StringBuilder out = new StringBuilder("[");
        boolean first = true;
        for (CalendarFeed feed : member.getPerson().getCalendarFeeds()) {
            if (!first) {
                out.append(",");
            }
            out.append("{"");
            out.append(feed.getName());
            out.append("":"");
            out.append(feed.getValue());
            out.append(""}");
            first = false;
        }
        out.append("]");
        return out.toString();
    }
}

But I m not sure how to go about automating this. I m just starting to use Jersey and am not clear on how to use it to return JSON. It sounds like it has a way to do this built in, but it looks like I need to add annotations to my POJOs. Also, I read others saying that I need to use Jackson. I ve been googling and can t seem to locate a good and simple example of returning JSON from a Jersey resource. Anyone know of any? Or can you show me how to use Jackson or Jersey to create JSON for for the above example?

Answer 1

I figured out how to do this using Jackson 1.4. I m not using jersey-json since it is based on an older version of Jackson and I needed version 1.4 to use JsonViews.

Here is the annotated pojo:

public class CalendarFeed {
    public enum FeedType { GCAL, EVENT };
    @JsonIgnore
    private Member owner;
    private String name;
    private String value;
    @JsonIgnore
    private FeedType type;
}

Here is the jersey resource:

@Path("/calendar")
public class CalendarResource {

 @Inject("memberService")
 private MemberService memberService;

 @Inject
 private ObjectMapper mapper;

 @GET
 @Produces(MediaType.APPLICATION_JSON)
 public String getCalendars() {
  Member member = memberService.getCurrentMember();
  try {
   return mapper.writeValueAsString(member.getCalendarFeeds());
  } catch (JsonGenerationException e) {
  } catch (JsonMappingException e) {
  } catch (IOException e) {
  }
  return "{}";
 }
}

Here is my spring bean:

<!-- Jackson JSON ObjectMapper -->
<bean id="objectMapper" class="org.codehaus.jackson.map.ObjectMapper"/>

The output is exactly what I need. And using JsonViews, I can customize what fields get output for different situations.

Hopefully this will help someone else!

Answer 2

This has changed since the accepted answer was written.

If you turn on the pojoMappingFeature the objectMapper will be automatically invoked by jersey. In a servlet environment do the following inside your jersey definition:

<init-param>
    <param-name>com.sun.jersey.api.json.POJOMappingFeature</param-name>
    <param-value>true</param-value>
</init-param>

You can now simply return the feeds from the endpoint.

@GET
@Produces(MediaType.APPLICATION_JSON)
public Collection<CalendarFeeds> getCalendars() {
    Member member = memberService.getCurrentMember();
    return member.getCalendarFeeds();
}

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