JSON Mapper - Adaptor Pattern Approach to hide Jackson API

An example to hide the dependency on Jackson directly:

public interface AbcJsonMapper<K, E> {

  E getEntity(@NotBlank String json, @NotNull Class<E> entityType);

  String getJsonString(@NotNull E entity);

  List<E> getList(@NotBlank String jsonList, @NotNull Class<E> elementClass);

  Map<K, E> getMap(

      @NotBlank String jsonMap,

      @NotNull Class<? extends Map<K, E>> mapClass,

      @NotNull Class<K> keyClass,

      @NotNull Class<E> valueClass);

}

@Value

public class Car {

  private final String color;

  private final String type;

  @JsonCreator

  public Car(@JsonProperty("color") String color, @JsonProperty("type") String type) {

    this.color = color;

    this.type = type;

  }

}

@Service

@RequiredArgsConstructor

@Slf4j

public class AbcJsonMapperImpl<K, E> implements AbcJsonMapper<K, E> {

  @SuppressWarnings("squid:S3749")

  private final ObjectMapper jacksonObjectMapper;

  @Override

  public List<E> getList(@NotBlank final String jsonList, Class<E> elementClass) {

    log.info("jsonListAsString:{}", jsonList);

    List<E> result = Collections.emptyList();

    try {

      result =

          jacksonObjectMapper.readValue(

              jsonList,

              TypeFactory.defaultInstance().constructCollectionType(List.class, elementClass));

    } catch (JsonProcessingException e) {

      throw new AbcApplicationException(

          AbcAlertMessage.ABC_APP_JSON_MSG_PARSING_EXCEPTION

              + " ### ### ### Failed to transfer to a list of"

              + elementClass

              + " from:"

              + jsonList,

          e);

    }

    log.info("result:{}", result);

    return result;

  }

  @Override

  public E getEntity(@NotBlank String json, Class<E> entityType) {

    try {

      return this.jacksonObjectMapper.readValue(json, entityType);

    } catch (JsonProcessingException e) {

      throw new AbcApplicationException(

          AbcAlertMessage.ABC_APP_JSON_MSG_PARSING_EXCEPTION

              + " ### ### ### Failed to map to "

              + entityType

              + "  from:"

              + json,

          e);

    }

  }

  @Override

  public String getJsonString(@NotNull E entity) {

    try {

      return this.jacksonObjectMapper.writeValueAsString(entity);

    } catch (JsonProcessingException e) {

      throw new AbcApplicationException(

          AbcAlertMessage.ABC_APP_JSON_MSG_PARSING_EXCEPTION

              + " ### ### ### Failed to map to Json String from entity:"

              + entity,

          e);

    }

  }

  @Override

  public Map<K, E> getMap(

      @NotBlank String jsonMap,

      @NotNull Class<? extends Map<K, E>> mapClass,

      @NotNull Class<K> keyClass,

      @NotNull Class<E> valueClass) {

    log.info("jsonMap:{}", jsonMap);

    Map<K, E> result = Collections.emptyMap();

    try {

      result =

          jacksonObjectMapper.readValue(

              jsonMap,

              TypeFactory.defaultInstance().constructMapLikeType(mapClass, keyClass, valueClass));

    } catch (JsonProcessingException e) {

      throw new AbcApplicationException(

          AbcAlertMessage.ABC_APP_JSON_MSG_PARSING_EXCEPTION

              + " ### ### ### Failed to transfer to a map of key class: "

              + keyClass

              + ", value class:"

              + valueClass

              + " from:"

              + jsonMap,

          e);

    }

    log.info("result:{}", result);

    return result;

  }

}

@Slf4j

class JsonMapperImplTest {

  private final ObjectMapper objectMapper = new ObjectMapper();

  @Test

  void testStringList() {

    AbcJson<String, String> mapper = new AbcJsonImpl<>(this.objectMapper);

    List<String> list = mapper.getList("[\"A\", \"B\"]", String.class);

    log.info("list:{}", list);

    assertEquals(2, list.size());

  }

  @Test

  void testIntegerList() {

    AbcJson<String, Integer> mapper = new AbcJsonImpl<>(this.objectMapper);

    List<Integer> list = mapper.getList("[1, 2]", Integer.class);

    log.info("list:{}", list);

    assertEquals(2, list.size());

  }

  @Test

  void testCarList() {

    AbcJson<String, Car> mapper = new AbcJsonImpl<>(this.objectMapper);

    String jsonCarListAsString =

        "[{ \"color\" : \"Black\", \"type\" : \"BMW\" }, { \"color\" : \"Red\", \"type\" : \"FIAT\" }]";

    List<Car> list = mapper.getList(jsonCarListAsString, Car.class);

    log.info("list:{}", list);

    assertEquals(2, list.size());

  }

  @Test

  void testCarMap() {

    AbcJson<String, String> mapper = new AbcJsonImpl<>(this.objectMapper);

    String jsonCarMapAsString = "{ \"color\" : \"Black\", \"type\" : \"BMW\" }";

    @SuppressWarnings("unchecked")

Map<String, String> map =

        mapper.getMap(

            jsonCarMapAsString,

            (@NotNull Class<? extends Map<String, String>>) (new HashMap<>().getClass()),

            String.class,

            String.class);

    log.info("map:{}", map);

    assertEquals(2, map.keySet().size());

  }

  @Test

  void testGetEntity() {

    AbcJson<String, Car> mapper = new AbcJsonImpl<>(this.objectMapper);

    String json = "{ \"color\" : \"Black\", \"type\" : \"BMW\" }";

    Car car = mapper.getEntity(json, Car.class);

    log.info("car:{}", car);

    assertEquals("Black", car.getColor());

    assertEquals("BMW", car.getType());

  }

  @Test

  void testgetJsonString() {

    AbcJson<String, Car> mapper = new AbcJsonImpl<>(this.objectMapper);

    Car car = new Car("Yellow", "BMW");

    String json = mapper.getJsonString(car);

    log.info("json:{}", json);

    assertEquals("{\"color\":\"Yellow\",\"type\":\"BMW\"}", json);

  }

}