Using Jackson to map object from specific node in JSON tree

Question

Is it possible to have Jackson\'s ObjectMapper unmarshall only from a specific node (and \'down\') in a JSON tree?

The use case is an extensible documen

Answer 1

Consider the following JSON:

{
  "firstName": "John",
  "lastName": "Doe",
  "address": {
    "street": "21 2nd Street",
    "city": "New York",
    "postalCode": "10021-3100",
    "coordinates": {
      "latitude": 40.7250387,
      "longitude": -73.9932568
    }
  }
}

And consider you want to parse the coordinates node into the following Java class:

public class Coordinates {

    private Double latitude;

    private Double longitude;

    // Default constructor, getters and setters omitted
}

To do it, parse the whole JSON into a JsonNode with ObjectMapper:

String json = "{\"firstName\":\"John\",\"lastName\":\"Doe\",\"address\":{\"street\":"
            + "\"21 2nd Street\",\"city\":\"New York\",\"postalCode\":\"10021-3100\","
            + "\"coordinates\":{\"latitude\":40.7250387,\"longitude\":-73.9932568}}}";

ObjectMapper mapper = new ObjectMapper();
JsonNode node = mapper.readTree(json);

Then use JSON Pointer to query the coordinates node and use ObjectMapper to parse it into the Coordinates class:

JsonNode coordinatesNode = node.at("/address/coordinates");
Coordinates coordinates = mapper.treeToValue(coordinatesNode, Coordinates.class);

JSON Pointer is a path language to traverse JSON. For more details, check the RFC 6901. It is available in Jackson since the version 2.3.