java - Spring boot controller content negotiation

Question

I have a simple REST controller written in a Spring-boot application but I am not sure how to implement the content negotiation to make it return JSON or XML based on the Content-Type parameter in the request header. Could someone explain to me, what am I doing wrong?

Controller method:

@RequestMapping(value = "/message", method = RequestMethod.GET, produces = { MediaType.APPLICATION_JSON_VALUE, MediaType.APPLICATION_XML_VALUE })
  public Message getMessageXML(@RequestParam("text") String text) throws Exception {
    Message message = new Message();
    message.setDate(new Date());
    message.setName("Test");
    message.setAge(99);
    message.setMessage(text);

    return message;
  }

I always get JSON when calling this method (even if I specify the Content-Type to be application/xml or text/xml).

When I implement two methods each with different mapping and different content type, I am able to get XML from the xml one but it does not work if I specify two mediaTypes in a single method (like the provided example).

What I would like is to call the message endpoint and receive

• XML when the Content-Type of the GET request is set to application/xml
• JSON when the Content-Type is application/json

Any help is appreciated.

EDIT: I updated my controller to accept all media types

@RequestMapping(value = "/message", method = RequestMethod.GET, produces = { MediaType.APPLICATION_JSON_VALUE, MediaType.APPLICATION_XML_VALUE }, consumes = MediaType.ALL_VALUE)
  public Message getMessageXML(@RequestParam("text") String text) throws Exception {
    Message message = new Message();
    message.setDate(new Date());
    message.setName("Vladimir");
    message.setAge(35);
    message.setMessage(text);

    return message;
  }

Answer 1

You can use ContentNegotiationConfigurer

Firstly, you should override the configureContentNegotiation method in your configuration class:

@Configuration
@EnableWebMvc
public class WebConfig extends WebMvcConfigurerAdapter {

    @Override
    public void configureContentNegotiation(ContentNegotiationConfigurer configurer) {
    configurer.favorPathExtension(false).
            favorParameter(true).
            defaultContentType(MediaType.APPLICATION_JSON).
            mediaType("xml", MediaType.APPLICATION_XML);
    }
}

favorParameter(true) - enabling favoring path expressions over parameter or accept headers.

defaultContentType(MediaType.APPLICATION_JSON) - sets the default content type. this means that if you don't pass a path expression then Spring will generate JSON as response.

mediaType("xml", MediaType.APPLICATION_XML) - sets the path expression key for XML.

Now if you declare your Controller like:

@Controller
class AccountController {

    @RequestMapping(value="/accounts", method=RequestMethod.GET)
    @ResponseStatus(HttpStatus.OK)
    public @ResponseBody List<Account> list(Model model, Principal principal) {
        return accountManager.getAccounts(principal) );
    }
}

and call it something like localhost:8080/app/accounts.json, then Spring will generate JSON as response. So if you call localhost:8080/app/accounts.xml you will receive XML response

You can find more info about this here.