LocalDateTime Formmatter.java

@Configuration
@EnableWebMvc
public class MvcConfig implements WebMvcConfigurer {

  ...

  @Override
  public void extendMessageConverters(final List<HttpMessageConverter<?>> converters) {
    DateTimeFormatter formatter = DataTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");

    ObjectMapper objectMapper = Jackson2ObjectMapperBuilder
        .json()
        .serializerByType(LocalDateTime.class, new LocalDateTimeSerializer(formatter)) // LocalDateTime 타입 객체를 위한 변환 패턴
        .build();
    converters.add(0, new MappingJackson2HttpMessageConverter(objectMapper));
  }

}