Spring MVC - Setting Default Content Type with ContentNegotiationConfigurer

In Spring MVC, if none of the enabled ContentNegotiationStrategies can determine the requested content type then 406 code (Not Acceptable) is returned. One way to avoid that; we can set a default content type to be used. In the following example, we are going to set json as default media type by using ContentNegotiationConfigurer#defaultContentType() method.

Example

Setting default content type

@EnableWebMvc
@Configuration
@ComponentScan
public class MyWebConfig extends WebMvcConfigurerAdapter {
  
  @Override
  public void configureContentNegotiation (ContentNegotiationConfigurer configurer) {
      configurer.defaultContentType(MediaType.APPLICATION_JSON);
  }
}

Writing Controller

@Controller
@RequestMapping("user")
public class UserController {
  
  @RequestMapping
  @ResponseBody
  public User getUserById (@RequestParam("id") long userId) {
      //creating dummy user
      User user = new User();
      user.setId(userId);
      user.setName("joe");
      user.setEmailAddress("joe@example.com");
      return user;
  }
}

@XmlRootElement
public class User implements Serializable {
  private Long id;
  private String name;
  private String password;
  private String emailAddress;
    .............
}

Adding Jackson dependency

We also need to include Jackson dependency so that MappingJackson2HttpMessageConverter can be used to produce JSON response.

pom.xml

<dependency>
   <groupId>com.fasterxml.jackson.core</groupId>
   <artifactId>jackson-databind</artifactId>
   <version>2.8.9</version>
</dependency>

Writing JUnit tests

In this test, we are not going to use 'Accept' header, or path extension or request parameter ('format') so that our default JSON media type can be used to returned the response:

@RunWith(SpringJUnit4ClassRunner.class)
@WebAppConfiguration
@ContextConfiguration(classes = MyWebConfig.class)
public class UserTests {
  
  @Autowired
  private WebApplicationContext wac;
  private MockMvc mockMvc;
  
  @Before
  public void setup () {
      DefaultMockMvcBuilder builder = MockMvcBuilders.webAppContextSetup(this.wac);
      this.mockMvc = builder.build();
  }
  
  @Test
  public void testUserRequest () throws Exception {
      
      MockHttpServletRequestBuilder builder =
                MockMvcRequestBuilders.get("/user")
                                      .param("id", "100");
      
      this.mockMvc.perform(builder)
                  .andExpect(MockMvcResultMatchers.status()
                                                  .isOk())
                  .andDo(MockMvcResultHandlers.print());
  }
}

Output

mvn -q test -Dtest=UserTests#testUserRequest

MockHttpServletRequest:
      HTTP Method = GET
      Request URI = /user
       Parameters = {id=[100]}
          Headers = {}

Handler:
             Type = com.logicbig.example.UserController
           Method = public com.logicbig.example.User com.logicbig.example.UserController.getUserById(long)

Async:
    Async started = false
     Async result = null

Resolved Exception:
             Type = null

ModelAndView:
        View name = null
             View = null
            Model = null

FlashMap:
       Attributes = null

MockHttpServletResponse:
           Status = 200
    Error message = null
          Headers = {Content-Type=[application/json;charset=UTF-8]}
     Content type = application/json;charset=UTF-8
             Body = {"id":100,"name":"joe","password":null,"emailAddress":"joe@example.com"}
    Forwarded URL = null
   Redirected URL = null
          Cookies = []

As seen in the output, we got JSON output in the body.

Note that, the browser (like Chrome) will always have XML response, that's because the browser implicitly sends multiple 'Accept' headers in the request which includes XML media type as well. That means HeaderContentNegotiationStrategy will be utilized before our default content types will be used.

Example Project

Dependencies and Technologies Used:

• spring-webmvc 4.3.10.RELEASE: Spring Web MVC.
• spring-test 4.3.10.RELEASE: Spring TestContext Framework.
• javax.servlet-api 3.1.0 Java Servlet API
• jackson-databind 2.8.9: General data-binding functionality for Jackson: works on core streaming API.
• junit 4.12: JUnit is a unit testing framework for Java, created by Erich Gamma and Kent Beck.
• JDK 1.8
• Maven 3.3.9