Parsing nested JSON data using GSON

Question

I'm trying to parse some JSON data using gson in Java that has the following structure but by looking at examples online, I cannot find anything that does the job.

Would anyone be able to assist?

{
    "data":{
        "id":[
            {
                "stuff":{

                },
                "values":[
                    [
                        123,
                        456
                    ],
                    [
                        123,
                        456
                    ],
                    [
                        123,
                        456
                    ],

                ],
                "otherStuff":"blah"
            }
        ]
    }
}

Answer 1

You just need to create a Java class structure that represents the data in your JSON. In order to do that, I suggest you to copy your JSON into this online JSON Viewer and you'll see the structure of your JSON much clearer...

Basically you need these classes (pseudo-code):

class Response
  Data data

class Data
  List<ID> id

class ID
  Stuff stuff
  List<List<Integer>> values
  String otherStuff

Note that attribute names in your classes must match the names of your JSON fields! You may add more attributes and classes according to your actual JSON structure... Also note that you need getters and setters for all your attributes!

Finally, you just need to parse the JSON into your Java class structure with:

Gson gson = new Gson();
Response response = gson.fromJson(yourJsonString, Response.class);

And that's it! Now you can access all your data within the response object using the getters and setters...

For example, in order to access the first value 456, you'll need to do:

int value = response.getData().getId().get(0).getValues().get(0).get(1);

Answer 2

Depending on what you are trying to do. You could just setup a POJO heirarchy that matches your json as seen here (Preferred method). Or, you could provide a custom deserializer. I only dealt with the id data as I assumed it was the tricky implementation in question. Just step through the json using the gson types, and build up the data you are trying to represent. The Data and Id classes are just pojos composed of and reflecting the properties in the original json string.

public class MyDeserializer implements JsonDeserializer<Data>
{

  @Override
  public Data deserialize(JsonElement je, Type type, JsonDeserializationContext jdc) throws JsonParseException
  {
    final Gson gson = new Gson();
    final JsonObject obj = je.getAsJsonObject(); //our original full json string
    final JsonElement dataElement = obj.get("data");
    final JsonElement idElement = dataElement.getAsJsonObject().get("id");
    final JsonArray idArray = idElement.getAsJsonArray();

    final List<Id> parsedData = new ArrayList<>();
    for (Object object : idArray)
    {
      final JsonObject jsonObject = (JsonObject) object;
      //can pass this into constructor of Id or through a setter
      final JsonObject stuff = jsonObject.get("stuff").getAsJsonObject();
      final JsonArray valuesArray = jsonObject.getAsJsonArray("values");
      final Id id = new Id();
      for (Object value : valuesArray)
      {
        final JsonArray nestedArray = (JsonArray)value;
        final Integer[] nest =  gson.fromJson(nestedArray, Integer[].class);
        id.addNestedValues(nest);
      }
      parsedData.add(id);
   }
   return new Data(parsedData);
  }

}

Test:

  @Test
  public void testMethod1()
  {
    final String values = "[[123, 456], [987, 654]]";
    final String id = "[ {stuff: { }, values: " + values + ", otherstuff: 'stuff2' }]";
    final String jsonString = "{data: {id:" + id + "}}";
    System.out.println(jsonString);
    final Gson gson = new GsonBuilder().registerTypeAdapter(Data.class, new MyDeserializer()).create();
    System.out.println(gson.fromJson(jsonString, Data.class));
  }

Result:

Data{ids=[Id {nestedList=[[123, 456], [987, 654]]}]}

POJO:

public class Data
{

  private List<Id> ids;

  public Data(List<Id> ids)
  {
   this.ids = ids;
  }

  @Override
  public String toString()
  {
    return "Data{" + "ids=" + ids + '}';
  }
 }


 public class Id
 {

   private List<Integer[]> nestedList;

   public Id()
   {
    nestedList = new ArrayList<>();
   }

   public void addNestedValues(final Integer[] values)
   {
    nestedList.add(values);
   }

   @Override
   public String toString()
   {
    final List<String> formattedOutput = new ArrayList();
    for (Integer[] integers : nestedList)
    {
     formattedOutput.add(Arrays.asList(integers).toString());
    }
    return "Id {" + "nestedList=" + formattedOutput + '}';
  }
}