Parsing a JSON file with GSON

Question

I\'m having trouble reading a JSON file into a POJO. Let me give you a snippet of what my JSON file entails:

 {
    \"Speidy\": {
        \"factionId\": \"2\",
          


        

Answer 1

If you do have control the format of the JSON, I suggest the overall list structure that jmort253 suggests in his answer, i.e. [{"name":"Speidy", ... },{"name":"ShadowSlayer272", ... }].

If you have no control over the generated JSON, here's two ways to map a JSON snippet like the one in your question {"Speidy":{ ... },"ShadowSlayer272":{ ... }} with Gson:

• Without your Container class and a little bit of TypeToken voodoo:

  // Ask Gson to deserialize the JSON snippet into a Map.
  Type type = new TypeToken>() {}.getType();
  Map nodes = gson.fromJson(json, type);
  

• With your Container class and a custom JsonDeserializer:

  class ContainerDeserializer implements JsonDeserializer {
    public Container deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context)
        throws JsonParseException {
      List nodes = new ArrayList();
      JsonObject players = json.getAsJsonObject();
      for (Entry player : players.entrySet()) {
        String playerName = player.getKey();
        JsonElement playerData = player.getValue();
        // Use Gson to deserialize all fields except
        // for the name into a Node instance ...
        Node node = context.deserialize(playerData, Node.class);
        node.name = playerName; // ... then set the name.
        nodes.add(node);
      }
      return new Container(nodes);
    }
  }
  

  This assumes a constructor like Container(List) and allows Container instances to be immutable which is usually a Good Thing.

  Register and use the custom serializer like this:

  GsonBuilder builder = new GsonBuilder();
  // Tell Gson to use the custom ContainerDeserializer whenever
  // it's asked for a Container instance.
  builder.registerTypeAdapter(Container.class, new ContainerDeserializer());
  Gson gson = builder.create();
  
  // Ask Gson to create Container instance from your JSON snippet.
  Container container = gson.fromJson(json, Container.class);