Deserialize JSON Array with different POJOs in java with Jackson

Question

How can I deserialize this JSON structure ?

[
  {
    "page": 1,
    "per_page": "50"
  },
  [
    {
      "id": "IC.BUS.EASE.XQ",
      "name": "ion"
    },
    {
      "id": "OIUPOIUPOIU",
      "name": "lal alalalal"
    }
  ]
]

( I get this back from the WorldBank Api, it is a bit simplified, the exact response you find here ).

The problem is, that i get an array of objects, where the first element is a POJO and the second element is an array of POJOs of a specific type.

The only way that I found out to deserialize this is to be very generic which results in Lists and Maps.

List<Object> indicators = mapper.readValue(jsonString, new TypeReference<List<Object>>() {});

Is there a better way to deserialize this JSON to get an Array or a List, where the first element is of the Object "A" and the second a List of Objects "B" ?

Answer 1

If I were you, I would do something like this. It's not possible to represent your data in a good way in one list on java without using a common base class. In your case this unfortunately is Object . You can help a bit by manipulating the response list though.

    ArrayNode arrayNode = (ArrayNode) mapper.readTree(this.getScrape().getScrapetext());

    A a = mapper.readValue(arrayNode.get(0), A.class);

    arrayNode.remove(0);

    List<B> b = mapper.readValue(arrayNode.toString(), new TypeReference<List<B>>()
    {
    });

Answer 2

Given that the structure is rather irregular, in that there is no Java class definition that structurally matches a JSON Array with magic type definitions for elements by index, you probably need to do 2-pass binding.

First, you bind JSON into either List (or just Object ) or JsonNode . And from that, you can use ObjectMapper.convertValue() to extract and convert elements into actual types you want. Something like:

JsonNode root = mapper.readTree(jsonSource);
HeaderInfo header = mapper.convertValue(jsonSource.get(0), 
   HeaderInfo.class);
IdNamePair[] stuff = mapper.convertValue(jsonSource.get(1),
   IdNamePair[].class);

would let you get typed values from original JSON Array.