Content Negotiation

// Client sends: Accept: application/xml
// Spring finds Jaxb2 converter → returns XML

@RestController
@RequestMapping("/orders")
public class OrderController {

    // Endpoint produces both JSON and XML — client chooses via Accept header
    @GetMapping(value = "/{id}",
                produces = {MediaType.APPLICATION_JSON_VALUE,
                            MediaType.APPLICATION_XML_VALUE})
    public Order getOrder(@PathVariable Long id) {
        return orderService.findById(id).orElseThrow();
        // GET /orders/1  Accept: application/json  → {"id":1,...}
        // GET /orders/1  Accept: application/xml   → <Order><id>1</id>...</Order>
    }

    // Restrict endpoint to only accept JSON request body
    @PostMapping(value = "/",
                 consumes = MediaType.APPLICATION_JSON_VALUE,
                 produces = MediaType.APPLICATION_JSON_VALUE)
    public ResponseEntity<Order> createOrder(@RequestBody OrderRequest req) {
        // Will return 415 Unsupported Media Type if client sends XML
        return ResponseEntity.ok(orderService.create(req));
    }
}

// XML support requires JAXB annotations on the entity
@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public class Order { ... }

// Custom CSV converter for list endpoints
@Component
public class CsvHttpMessageConverter extends AbstractHttpMessageConverter<List<?>> {

    public CsvHttpMessageConverter() {
        super(new MediaType("text", "csv"));
    }

    @Override
    protected boolean supports(Class<?> clazz) {
        return List.class.isAssignableFrom(clazz);
    }

    @Override
    protected List<?> readInternal(Class<? extends List<?>> clazz,
                                   HttpInputMessage inputMessage) {
        throw new UnsupportedOperationException("Read not supported");
    }

    @Override
    protected void writeInternal(List<?> list,
                                  HttpOutputMessage outputMessage) throws IOException {
        PrintWriter writer = new PrintWriter(outputMessage.getBody());
        // Write CSV header + rows using reflection or explicit mapping
        list.forEach(item -> writer.println(toCsvLine(item)));
        writer.flush();
    }
}

// Register if not auto-detected via @Component
@Configuration
public class WebConfig implements WebMvcConfigurer {
    @Override
    public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
        converters.add(0, new CsvHttpMessageConverter());  // prepend
    }
}

// Now: GET /orders  Accept: text/csv  → returns CSV
// Now: GET /orders  Accept: application/json  → returns JSON

// Jackson global customisation (Spring Boot 3)
@Bean
public Jackson2ObjectMapperBuilderCustomizer jsonCustomizer() {
    return builder -> builder
        .featuresToDisable(
            SerializationFeature.WRITE_DATES_AS_TIMESTAMPS,  // ISO-8601 dates
            DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES)
        .featuresToEnable(MapperFeature.DEFAULT_VIEW_INCLUSION)
        .simpleDateFormat("yyyy-MM-dd'T'HH:mm:ssZ");
}

// @JsonView — field visibility per view
public class Views {
    public interface Summary {}
    public interface Detail extends Summary {}   // Detail includes Summary fields
}

public class Order {
    @JsonView(Views.Summary.class)
    private Long id;
    @JsonView(Views.Summary.class)
    private String status;
    @JsonView(Views.Detail.class)
    private List<OrderItem> items;    // only in Detail view
    @JsonView(Views.Detail.class)
    private String shippingAddress;   // only in Detail view
}

// Controller selects view
@GetMapping
@JsonView(Views.Summary.class)         // list endpoint: id + status only
public List<Order> listOrders() { ... }

@GetMapping("/{id}")
@JsonView(Views.Detail.class)          // detail endpoint: all fields
public Order getOrder(@PathVariable Long id) { ... }