How to Use Spring MVC Content Negotiation to Serve JSON and XML Dynamically

Our service originally returned JSON to downstream systems, but a new requirement demanded XML for an older system. Instead of duplicating the interface, we can leverage Spring MVC's content negotiation mechanism.

Principle

When a client sends an HTTP request, it can include an Accept header indicating the MIME types it can handle, such as application/json. Spring MVC examines this header and selects an appropriate HttpMessageConverter to produce the response. Accept:application/json By configuring Spring MVC to recognize the Accept header, we can dynamically choose the response format.

Content Negotiation

Spring MVC provides a content negotiation mechanism where the client declares the desired MIME type, and the server returns data in that format (JSON or XML) based on configuration.

Spring MVC version based on Spring MVC 5.3.9 .

Server‑side Configuration

The negotiation is managed by ContentNegotiationManager and can be configured via ContentNegotiationConfigurer.

First, add Jackson's XML module to the project:

<dependency>
  <groupId>com.fasterxml.jackson.dataformat</groupId>
  <artifactId>jackson-dataformat-xml</artifactId>
</dependency>

Then implement the configuration in a class that implements WebMvcConfigurer:

@Configuration
public class WebConfig implements WebMvcConfigurer {
    @Override
    public void configureContentNegotiation(ContentNegotiationConfigurer configurer) {
        configurer.favorParameter(true)
                .parameterName("format")
                .mediaType("xml", MediaType.APPLICATION_XML)
                .mediaType("json", MediaType.APPLICATION_JSON);
    }
}

After this, the client can specify the desired format with a query parameter (default name format).

Request JSON:

https://yourapi?format=json

You can omit the format parameter because JSON is the default; to change the default MIME type, call defaultContentType .

Request XML: https://yourapi?format=xml The controller method only needs to declare the supported media types:

@GetMapping(value = "/get", produces = {"application/json", "application/xml"})
public Map<String, String> doGet(@RequestParam String foo, String bar) {
    Map<String, String> map = new HashMap<>();
    map.put("foo", foo);
    map.put("bar", bar);
    return map;
}

It is crucial to specify the produces attribute in @RequestMapping (or its shortcut annotations) so that Spring can select the appropriate converter.

Other Strategies

Spring MVC also supports suffix‑based negotiation (e.g., /yourapi.json or /yourapi.xml) and direct Accept header declarations, but using a query parameter is often simpler.