Customizing JSON Serialization and Deserialization in Spring Boot

In Spring Boot, customizing request and response JSON can be achieved by several approaches.

1. Use @JsonSerialize and @JsonDeserialize on fields to specify custom serializer/deserializer.

public class CustomLocalDateTimeSerializer extends JsonSerializer<LocalDateTime> {
    @Override
    public void serialize(LocalDateTime value, JsonGenerator gen, SerializerProvider serializers) throws IOException {
        gen.writeString(value.format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss")));
    }
}

public class CustomLocalDateTimeDeserializer extends JsonDeserializer<LocalDateTime> {
    @Override
    public LocalDateTime deserialize(JsonParser p, DeserializationContext ctxt) throws IOException {
        return LocalDateTime.parse(p.getValueAsString(), DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"));
    }
}

public class MyEntity {
    @JsonSerialize(using = CustomLocalDateTimeSerializer.class)
    @JsonDeserialize(using = CustomLocalDateTimeDeserializer.class)
    private LocalDateTime dateTime;
    // getters and setters
}

2. Configure a global ObjectMapper by registering a custom module.

public class CustomJacksonModule extends SimpleModule {
    public CustomJacksonModule() {
        addSerializer(LocalDateTime.class, new CustomLocalDateTimeSerializer());
        addDeserializer(LocalDateTime.class, new CustomLocalDateTimeDeserializer());
    }
}

@Bean
public Jackson2ObjectMapperBuilderCustomizer jsonCustomizer() {
    return builder -> builder.modules(new CustomJacksonModule());
}

3. Use @ControllerAdvice with @InitBinder to register a custom PropertyEditor for form data.

public class CustomLocalDateTimeEditor extends PropertyEditorSupport {
    @Override
    public void setAsText(String text) {
        setValue(LocalDateTime.parse(text, DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss")));
    }
    @Override
    public String getAsText() {
        LocalDateTime value = (LocalDateTime) getValue();
        return value.format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"));
    }
}

@ControllerAdvice
public class CustomControllerAdvice {
    @InitBinder
    public void initBinder(WebDataBinder binder) {
        binder.registerCustomEditor(LocalDateTime.class, new CustomLocalDateTimeEditor());
    }
}

4. Implement a custom HttpMessageConverter to handle specific media types.

public class CustomLocalDateTimeConverter extends MappingJackson2HttpMessageConverter {
    public CustomLocalDateTimeConverter() {
        ObjectMapper customObjectMapper = new ObjectMapper();
        customObjectMapper.registerModule(new CustomJacksonModule());
        setObjectMapper(customObjectMapper);
    }
}

@Configuration
public class WebConfig implements WebMvcConfigurer {
    @Override
    public void extendMessageConverters(List<HttpMessageConverter<?>> converters) {
        converters.add(0, new CustomLocalDateTimeConverter());
    }
}

5. Apply Spring AOP to intercept controller methods and modify input/output, though using AOP for JSON transformation is generally discouraged.

@Aspect
@Component
public class CustomSerializationAspect {
    @Before("execution(* com.example.controller..*.*(..)) && args(..,@RequestParam(..),@RequestBody(..))")
    public void beforeControllerMethod(JoinPoint joinPoint) { /* optional */ }

    @AfterReturning(pointcut = "execution(* com.example.controller..*.*(..)) && @annotation(org.springframework.web.bind.annotation.RequestMapping)", returning = "result")
    public void afterControllerMethod(JoinPoint joinPoint, Object result) { /* optional */ }
}

Choose the method that fits the project’s complexity: simple field‑level changes with annotations, global mapper configuration, or a full‑blown converter/AOP for advanced scenarios.