Jackson start deserialization two levels down

Question

I have an awkwardly constructed json file like this:

{
"clientByClientId" : {
  "123" : {
    "clientId" : "123"
     "moreFields" : "moreData"
   }
  "456" : {
    "clientId" : "456"
     "moreFields" : "moreData"
   }
 }
}

As you can see, the top two levels of this json are superfluous. What is the best way to deserialize this into a collection of Client objects? I tried using online json to pojo tools, but they ended up generating classes called "123" and "456". Ideally, I'd like to use Jackson, but am open to other solutions.

Answer 1

Small note: your JSON is malformed, as it is missing a few commas. Once those are added, then this will work for you.

First off, you'll need a class to represent a Client:

public class Client {
    private final int clientId;
    private final String moreFields;

    @JsonCreator
    public Client(@JsonProperty("clientId") int clientId, 
                  @JsonProperty("moreFields") String moreFields) {
        this.clientId = clientId;
        this.moreFields = moreFields;
    }

    @Override
    public String toString() {
        return "Client[clientId=" + clientId + ", moreFields=" + moreFields + "]";
    }
}

Now, you just need to create your ObjectMapper and iterate over the elements of your clientByClientId map, which can be done with the following:

ObjectMapper objectMapper = new ObjectMapper();
JsonNode node = objectMapper.readTree(json).get("clientByClientId");
Map<Integer, Client> clientMap = objectMapper.readValue(node.traverse(),
        new TypeReference<Map<Integer, Client>>() {});
System.out.println(clientMap.values());

The output of this code is:

[Client[clientId=123, moreFields=moreData], Client[clientId=456, moreFields=moreData]]