return Map from rest service in json format

Question

I have a method which is returning Map<String, ArrayList<EntityClass>>. code is as follow of Definition class:

public Map<String, ArrayList<EntityClass>> webMethod1(){
    ArrayList<EntityClass> arr = new ArrayList<>();
    for (int i=0;i<5;i++){
        arr.add(new EntityClass(i, String.valueOf(i)));
    }
    Map<String, ArrayList<EntityClass>> map = new HashMap<>();
    map.put("Entity", arr);
}

Further this is called by a web service as follow:

@GET
@Path("/m1")
@Produces(MediaType.APPLICATION_JSON)
public Map<String, ArrayList<EntityClass>> m1(){
    return new Definition().webMethod1();
}

but i am getting following on the console:

MessageBodyWriter not found for media type=application/json, type=class java.util.HashMap, genericType=class java.util.HashMap.

and HTTP 500 as error.

how to resolve this error

You need to transform you `Map` into json, with whatever wrapper/class Jersey is offering you. — Matthieu, May 23 '16 at 06:54
Have you read the documentation?https://jersey.java.net/documentation/1.19.1/json.html — Matthieu, May 23 '16 at 07:01
See also [another question](http://stackoverflow.com/q/26518996/1098603). A little search cannot be bad... — Matthieu, May 23 '16 at 07:05
This [answer](http://stackoverflow.com/a/37250802/1426227) will be useful. — cassiomolin, May 23 '16 at 07:09
@CássioMazzochiMolin first i am not using maven, second that question you told, in that, error is because of moxy jar as i faced the same error. mine in different because maps are not top level element in json, we have to implement at our own, by using MessageBodyWriter in jersey. — Stark, May 23 '16 at 08:12
Get rid of moxy and use [Jackson](http://stackoverflow.com/a/30424031/2587435). Moxy sucks with Maps — Paul Samsotha, May 23 '16 at 10:59

score 1 · Answer 1 · answered May 23 '16 at 09:36

May be you should consider using a simple marshaller library like GSON. I end up with this code :

@GET
@Path("/m1")
@Produces(MediaType.APPLICATION_JSON)
public String webMethod1(){
    ArrayList<EntityClass> arr = new ArrayList<>();
    for (int i=0;i<5;i++){
        arr.add(new EntityClass(i, "\"-'"+String.valueOf(i)));
    }
    Map<String, List<EntityClass>> map = new HashMap<>();
    map.put("Entity", arr);

    GsonBuilder builder = new GsonBuilder();
    Gson gson = builder.create();

    return gson.toJson(map);
}

This does the job pretty well to me and don't add a lot of complexity as writing a MessageBodyWriter which is pointless for simple POJO classes and structures.

return Map from rest service in json format

1 Answers1