How to send a Map in JSON

1. Key always should be string.
2. Why it still doesn't work? Because the error is caused by the redundant brace inside of "elementsToUpdate". Below is an example:

"elementsToUpdate": {
  {  // redundant
    "1": {
      "country": "USA",
      "title": "string"
    }
  }  // redundant
}

correct one : 
"elementsToUpdate": {
    "1": {
      "country": "USA",
      "title": "string"
    }
}

Below is the complete example where I have converted a class to JSON string and back. You can use the same as reference. The point here is I have used TypeReference class to tell JSON that I have a class Contribution of type MovieRequest. Your code inside the project which reads the JSON has to be like this.

The Main Test Class

public class Test1
{
    public static void main(String[] args) throws IOException{
        //Creating object of the contribution class.
       Contribution<MovieRequest> c = new Contribution<>();

        Set<MovieRequest> set = new HashSet<>();
        set.add(getMovieObject());
        set.add(getMovieObject());
        set.add(getMovieObject());

        Map<Long, MovieRequest> map = new HashMap<>();
        map.put(1L, getMovieObject());
        map.put(2L, getMovieObject());
        map.put(3L, getMovieObject());

        Set<Long> set2 = new HashSet<>();
        set2.add(1L);
        set2.add(2L);
        set2.add(3L);

        c.setElementsToAdd(set);
        c.setElementsToUpdate(map);
        c.setIdsToDelete(set2);

        //Using Jackson for Conversion.
        ObjectMapper mapper = new ObjectMapper();
        String value = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(c);
        //JSON String
        System.out.println(value);

        //Converting JSON string back to Object
        //here I am using TyperReference to tell JSON that this is the type of the class
        Contribution<MovieRequest> c1 =  mapper.readValue(value,  new TypeReference<Contribution<MovieRequest>>() { });
        System.out.println(c1);
    }

    //Just some class to spit out random strings. You can ignore it in ur example. Just add some random strings and return objects.
    private static MovieRequest getMovieObject()
    {
        MovieRequest m1 = new MovieRequest();
        m1.setCountry(randomString());
        m1.setTitle(randomString());
        return m1;
    }


    //This is a random string generator. Ignore this.
    public static String randomString()
    {
        return RandomStringUtils.randomAlphanumeric(17);
    }
}

The Bean classes

class Contribution<T extends MovieRequest>
{
    private Set<T> elementsToAdd;

    private Map<Long, T> elementsToUpdate;

    private Set<Long> idsToDelete;

    /**
     * @return the elementsToAdd
     */
    public Set<T> getElementsToAdd()
    {
        return elementsToAdd;
    }

    /**
     * @param elementsToAdd
     *            the elementsToAdd to set
     */
    public void setElementsToAdd(Set<T> elementsToAdd)
    {
        this.elementsToAdd = elementsToAdd;
    }

    /**
     * @return the elementsToUpdate
     */
    public Map<Long, T> getElementsToUpdate()
    {
        return elementsToUpdate;
    }

    /**
     * @param elementsToUpdate
     *            the elementsToUpdate to set
     */
    public void setElementsToUpdate(Map<Long, T> elementsToUpdate)
    {
        this.elementsToUpdate = elementsToUpdate;
    }

    /**
     * @return the idsToDelete
     */
    public Set<Long> getIdsToDelete()
    {
        return idsToDelete;
    }

    /**
     * @param idsToDelete
     *            the idsToDelete to set
     */
    public void setIdsToDelete(Set<Long> idsToDelete)
    {
        this.idsToDelete = idsToDelete;
    }

    /**
     * @inheritDoc
     */
    @JsonIgnore
    @Override
    public String toString()
    {
        return "Contribution [elementsToAdd=" + elementsToAdd + ", elementsToUpdate="
                + elementsToUpdate + ", idsToDelete=" + idsToDelete + "]";
    }

}

class MovieRequest
{
    private String country;

    private String title;

    /**
     * @return the country
     */
    public String getCountry()
    {
        return country;
    }

    /**
     * @param country
     *            the country to set
     */
    public void setCountry(String country)
    {
        this.country = country;
    }

    /**
     * @return the title
     */
    public String getTitle()
    {
        return title;
    }

    /**
     * @param title
     *            the title to set
     */
    public void setTitle(String title)
    {
        this.title = title;
    }

    /**
     * @inheritDoc
     */
    @JsonIgnore
    @Override
    public String toString()
    {
        return "MovieRequest [country=" + country + ", title=" + title + "]";
    }

}

Output

{
  "elementsToAdd" : [ {
    "country" : "08Pv3v048kXbz9gRg",
    "title" : "ljuih0hctsTRC2FfY"
  }, {
    "country" : "847JRWP65Fum3Ttm5",
    "title" : "Z7kS3YGbyjKOVTX6p"
  }, {
    "country" : "JmkjGDW81BMDyyPgj",
    "title" : "X3c5J0xurKsbXNgCY"
  } ],
  "elementsToUpdate" : {
    "1" : {
      "country" : "ItZF8GgzFMAs8WRk5",
      "title" : "tMnb1z1ooSUOuqEMS"
    },
    "2" : {
      "country" : "HOhk142Q6brYmOMWC",
      "title" : "7FQv9TVj6nOjxU2Ri"
    },
    "3" : {
      "country" : "hJYbY33KOsMbJN2o6",
      "title" : "uW5zEkoosux9QsC44"
    }
  },
  "idsToDelete" : [ 1, 2, 3 ]
}
Contribution [elementsToAdd=[MovieRequest [country=08Pv3v048kXbz9gRg, title=ljuih0hctsTRC2FfY], MovieRequest [country=847JRWP65Fum3Ttm5, title=Z7kS3YGbyjKOVTX6p], MovieRequest [country=JmkjGDW81BMDyyPgj, title=X3c5J0xurKsbXNgCY]], elementsToUpdate={1=MovieRequest [country=ItZF8GgzFMAs8WRk5, title=tMnb1z1ooSUOuqEMS], 2=MovieRequest [country=HOhk142Q6brYmOMWC, title=7FQv9TVj6nOjxU2Ri], 3=MovieRequest [country=hJYbY33KOsMbJN2o6, title=uW5zEkoosux9QsC44]}, idsToDelete=[1, 2, 3]]