Add JsonHelper

[DamnClin]

JsonHelper is a tool to help unit test of json serialization / deserialization

public final class JsonHelper {

  private static final ObjectMapper jsonMapper = jsonMapper();

  private JsonHelper() {}

  public static ObjectMapper jsonMapper() {
    return JsonMapper
      .builder()
      .serializationInclusion(JsonInclude.Include.NON_EMPTY)
      .addModule(new JavaTimeModule())
      .addModules(new Jdk8Module())
      .disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES)
      .disable(DeserializationFeature.FAIL_ON_MISSING_EXTERNAL_TYPE_ID_PROPERTY)
      .disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS)
      .build();
  }

  public static <T> String writeAsString(T object) {
    try {
      return jsonMapper.writeValueAsString(object);
    } catch (JsonProcessingException e) {
      throw new AssertionError("Error serializing object: " + e.getMessage(), e);
    }
  }

  public static <T> T readFromJson(String json, Class<T> clazz) {
    try {
      return jsonMapper.readValue(json, clazz);
    } catch (IOException e) {
      throw new AssertionError("Error reading value from json: " + e.getMessage(), e);
    }
  }
}

[pascalgrimaud]

When do you think we should generate this? Java base or something related to Spring Boot? I'd say the 2nd option.

[DamnClin]

I think we should add it it spring MVC.

When done we'll need to use that in code for dummy feature (#2444)