Generate Json from java Map

Question

I would like to generate a json formatted response from a Map.

I have tried the following for Map having String as the key and it works fine.

    private JsonNode build(Map<String, List<PlaylistUrl>> entitiesPlaylist) {

        JsonNode root = objectMapper.createObjectNode();
        JsonNode data = objectMapper.createObjectNode();

            ((ObjectNode) data).set(ENTITIES, objectMapper.valueToTree(entitiesPlaylist));

         ((ObjectNode) root).set(DATA, data);

        return root;
    }

However I now have an object as a key instead of a String and would like to have all the values of the object printed as part of the response. I am not sure what logic to use here.

private JsonNode build(Map<Entity, List<PlaylistUrl>> entitiesPlaylist) {

        JsonNode root = objectMapper.createObjectNode();
        JsonNode data = objectMapper.createObjectNode();

        for (Map.Entry<Entity, List<PlaylistUrl>> entry: entitiesPlaylist.entrySet()) {
            // what logic ?
        }
         ((ObjectNode) root).set(DATA, data);

        return root;
    }

I need the response to contain the Entity in the response as well as for each Entity the array list of Playlists.

Answer 1

Your build method could technically look something like this:

private JsonNode build(Map<Entity, List<PlayListUrl>> entitiesPlaylist) {
        ArrayNode root = objectMapper.createArrayNode();

        for (Map.Entry<Entity, List<PlayListUrl>> entry: entitiesPlaylist.entrySet()) {
            JsonNode entityPlayListUrlsJsonObject = objectMapper.valueToTree(entry);
            root.add(objectMapper.valueToTree(entityPlayListUrlsJsonObject));
        }

        return root;
    }

In this case, each JsonNode added to the root ArrayNode will have the Entity#toString as the key. So overriding and customizing toString method of your Entity (sub)class(es) is a good idea, as else you will get the <package.to.TheClass@ObjectHexedHashCode> as key for each JSON object.

So, with an uncustomized toString method of the Entity, your JSON response will look something like:

[
    {
        "com.package.to.Entity@51931956": [
            {
                // First PlayListUrl object properties of this Entity
            },
            {
                // Second PlayListUrl object properties of this Entity
            },
            ...
        ]
    },
    {
         "com.package.to.Entity@84569301": [
             {
                // First PlayListUrl object properties of this Entity
             },
             {
                // Second PlayListUrl object properties of this Entity
             }
             ...
        ]
    },
    ...
]

I hope this helps you, or others if I'm late.