парсинг json. Приложение на Spring Boot

Всем привет, пытаюсь распарсить json по ссылке. Хочу реализовать на Spring Boot, использую клиент okHttp и библиотеку гугла gson. Хочу перенести все данные в на базу данных mysql. Пока что пытаюсь просто вывести все, что распарсило на экран. В консоли выдает:

Data(id=null, dateModified=null, title=null, documentType=null, hash=null, datePublished=null, documentOf=null, format=null, url=null, jsonData=null)
JsonData(id=null, dataSet=null)

Сам аплиекйшн выглядит так

@SpringBootApplication

public class Application {
    static OkHttpClient client = new OkHttpClient();
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

    @Bean
            CommandLineRunner runner(DataService dataService, JsonDataService jsonDataService){
        return args -> {
            getData();
            getJsonData();
        };
    }
   public static String getJson (String url) throws IOException {
        Request request = new Request.Builder()
                .url(url)
                .build();
        try (Response response = client.newCall(request).execute()) {
            return Objects.requireNonNull(response.body()).string();
        }
    }
    public static void getData(){
        Set<Data> dataSet = new HashSet<>();
        String json = null;
        try {
            json = getJson(
                    "https://lb-api-sandbox.prozorro.gov.ua/api/2.4/contracts/23567e24f52746ef92c470be6059d193/documents ");
        } catch (IOException e) {
            e.printStackTrace();
        }
        Gson gson = new Gson();
        Data data = gson.fromJson(json, Data.class);

        System.out.println(data);
    }
    public static void getJsonData(){
        Set<JsonData> jsondataSet = new HashSet<>();
        String json = null;
        try {
            json = getJson(
                    "https://lb-api-sandbox.prozorro.gov.ua/api/2.4/contracts/23567e24f52746ef92c470be6059d193/documents ");
        } catch (IOException e) {
            e.printStackTrace();
        }
        Gson gson = new Gson();
        JsonData jsonData = gson.fromJson(json, JsonData.class);
        System.out.println(jsonData);
    }

Сущность data JsonData

    @lombok.Data
@NoArgsConstructor
@AllArgsConstructor
@Entity(name = "JsonData")
public class JsonData
{
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;
    @OneToMany(cascade = CascadeType.ALL, mappedBy = "jsonData")
    private Set<Data> dataSet;

Сущность Data

@NoArgsConstructor
@AllArgsConstructor
@lombok.Data
@Entity
public class Data
{
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;
    private String dateModified;
    private String title;
    private String documentType;
    private String hash;
    private String datePublished;
    private String documentOf;
    private String format;
    private String url;
    @ManyToOne
    @JoinColumn(name = "JsonDataId")
    private JsonData jsonData;
}

сам json

{"data": [{"hash": "md5:232dba893a22ac722249ad92f8bccf22", "format": "text/plain", "url": "https://public-docs-sandbox.prozorro.gov.ua/get/3500487074064bd98f1076c21fe69e9a?KeyID=1331dc52&Signature=w%252BTQLJCiU%2FDQXfp%2FxB0VfDNRzImPv7zch3e8H1jfVOZrDJZuam%2FOTVLlvpdUiz9WVLHdUzdMrQJclbl4Vs28CQ%253D%253D", "title": "11.09.2018.xlsx", "documentOf": "tender", "datePublished": "2018-09-19T13:12:21.136232+03:00", "documentType": "subContract", "dateModified": "2018-09-19T13:12:21.136263+03:00", "id": "4f6d6dc59d1844bb80143ccc2e727a2f"}, {"hash": "md5:ee80acf16c48f3b659a2132526ae9800", "format": "application/pkcs7-signature", "url": "https://public-docs-sandbox.prozorro.gov.ua/get/04a93d0ba3e44e7e93a104a1b1ec8aaf?KeyID=1331dc52&Signature=o1V0G3cmFYjuu7MqIJxTY9zhDAj7PTblieehL0PEG%2FA5uc0VZlpY%252BMhQy0ZxTPdymnkPvAVxivDEodSI4RFDCw%253D%253D", "title": "sign.p7s", "documentOf": "tender", "datePublished": "2018-09-19T13:13:07.776613+03:00", "dateModified": "2018-09-19T13:13:07.776633+03:00", "id": "a5ef4c3063d94b10a13630fa9cca90b9"}, {"hash": "md5:061044f40512fa72e03c2674d1539e0f", "format": "text/plain", "url": "https://public-docs-sandbox.prozorro.gov.ua/get/5e03ef2402bd42ddb7dc78d526c95f81?KeyID=1331dc52&Signature=VjKGxj7WlIe%252BqZpE4OJl1qtIt0VQJ%2FMff8n8KaJWVHDANkFZB%252BcZbsq%2Fr%252BzW6S81cqeSU9hYlLLnq1WGpJ%252BuCQ%253D%253D", "title": "\u0442\u0435\u0441\u0442.docx", "documentOf": "change", "datePublished": "2018-09-24T16:00:29.527286+03:00", "dateModified": "2018-09-24T16:00:29.527311+03:00", "relatedItem": "6167ab1f7a184f75881b166b9c2e9193", "id": "f58353848e744791ad72f9baf84b5734"}]}

В чем может быть проблема?