Parsing deeply nested JSON properties with Jackson

Question

I am trying to find a clean way of parsing nested properties from a payload from an API.

Here is a rough generalisation of the JSON payload:

{
  "root": {
    "data": {
      "value": [
        {
          "user": {
            "id": "1",
            "name": {
              "first": "x",
              "last": "y"
            }
          }
        }
      ]
    }
  }
}

My goal is to have an array of User objects which have firstName and lastName fields.

Does anyone know a good way to parse this cleanly?

Right now I am trying to create a Wrapper class and within that have static inner classes for data, value, user etc. but this seems like a messy way of doing this just to read the array of first/last properties.

I am using restTemplate.exchange() to call the endpoint.

Answer 1

JsonPath library allows one to select only required fields and thn you can use Jackson to convert raw data to POJO class. Example solution could look as follows:

import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.type.CollectionType;
import com.jayway.jsonpath.JsonPath;

import java.io.File;
import java.util.List;
import java.util.Map;

public class JsonPathApp {

    public static void main(String[] args) throws Exception {
        File jsonFile = new File("./resource/test.json").getAbsoluteFile();

        List<Map> nodes = JsonPath.parse(jsonFile).read("$..value[*].user.name");

        ObjectMapper mapper = new ObjectMapper();
        CollectionType usersType = mapper.getTypeFactory().constructCollectionType(List.class, User.class);
        List<User> users = mapper.convertValue(nodes, usersType);
        System.out.println(users);
    }
}

class User {

    @JsonProperty("first")
    private String firstName;

    @JsonProperty("last")
    private String lastName;

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    @Override
    public String toString() {
        return "User{" +
                "firstName='" + firstName + '\'' +
                ", lastName='" + lastName + '\'' +
                '}';
    }
}

Above code prints:

[User{firstName='x', lastName='y'}]