Question

I was looking for some solution around here and I didnt find any correct answer to my question so I would like to ask you.

I have POJO with some simple attribs. and one List of another POJOs.

public class Standard implements Serializable {
    private String id;
    private String title;
    private String description;
    private Set<Interpretation> interpretations = new LinkedHashSet<Interpretation>();
}

public class Interpretation implements Serializable {
    private String id;
    private String title;
    private String description;
}

In my controller class, I am returning Standard POJO with GSON.

@RequestMapping(value="/fillStandard", method= RequestMethod.GET)
public @ResponseBody String getStandard(@RequestParam String id) {
    Standard s = DAOFactory.getInstance().getStandardDAO().findById(id);
    return new Gson().toJson(s);
}

The question is, am I able to get the list of interpretations in my Standard POJO using jQuery ? Something like :

function newStandard() {
$.get("standard/fillStandard.htm", {id:"fe86742b2024"}, function(data) {
    alert(data.interpretations[0].title);
});

}

Thanks a lot !

EDIT:
Well, thanks to @Atticus, there is solution of my problem. Hope that it will help somebody.

@RequestMapping(value="/fillStandard", method= RequestMethod.GET, produces="application/json")
    public @ResponseBody Standard getStandard(@RequestParam String id) {
        Standard s = DAOFactory.getInstance().getStandardDAO().findById(id);
        return s;
    }

Using @ResponseBody allows you to return the whole POJO, but you need to add produces="application/json" to your @RequestMapping annotation. Then you will be able to catch a returning object as JSON in jQuery like as I supposed.

function newStandard() {
$.get("standard/fillStandard.htm", {id:"idOfStandard"}, function(data) {
    alert(data.id);    //Standard id
    alert(data.interpretations[0].title);   //id of Interpretation on first place in array
});

Answer 1

Well you have to create and register your custom serializer.

It goes like this:

//You create your builder that registers your custom serializer with the class you want to serialize
GsonBuilder builder = new GsonBuilder();
builder.registerTypeAdapter(Standard.class, new StandardSerializer());

//Then you create your Gson object
Gson gson = builder.create();
//Then you pass your object to the gson like
Standard s = DAOFactory.getInstance().getStandardDAO().findById(id);
gson.toJson(s);

Your serializer looks like this:

public class StandardSerializer implements JsonSerializer<Standard>{

    @Override
    public JsonElement serialize(Standard src, Type typeOfSrc,
            JsonSerializationContext context) {

            JsonObject obj = new JsonObject();
            //You put your simple objects in like this
            obj.add("id",new JsonPrimitive(src.getId()));
            //You put your complex objects in like this
            JsonObject interpretations = new JsonObject();
            //Here you need to parse your LinkedHashSet object and set up the values. 
            //For the sake of simplicity I just access the properties (even though I know this would not compile)
            interpretations.add("title", src.getInterpretation().getTitle());
            obj.add("interpretations", interpretations);
            return obj;
        }

}

In this case your Json would look something like:

{"id":"idValue", "title":"titleValue", "description":"descriptionValue", "interpretations":["id":"interpretationIdValue"]}

Now, you can access your data with jQuery like this:

function newStandard() {
$.get("standard/fillStandard.htm", {id:"fe86742b2024"}, function(data) {
    alert(data.interpretations.title);
});
}

I hope this helps.

EDIT:
I see that your response gets converted to the declared method argument type which is String (as stated here: 16.3.3.2 Supported method return types). But what you really want is your Standrad POJO converted to JSON. I am not very familiar with Spring but as I have read here (16.3.2.6 Producible Media Types) there is another, maybe easier solution. If you want to return a JSON object, then change the return type of the
getStandard method to Standard instead of String and add produces="application/json" to your @RequestMapping annotation. As far as I have read this should tell Spring that the return type should be converted to JSON. In this case you do not need to use Gson.