java - HttpMediaTypeNotAcceptableException: Could not find acceptable representation in exceptionhandler

Question

I have the following image download method in my controller (Spring 4.1):

@RequestMapping(value = "/get/image/{id}/{fileName}", method=RequestMethod.GET)
public @ResponseBody byte[] showImageOnId(@PathVariable("id") String id, @PathVariable("fileName") String fileName) {
    setContentType(fileName); //sets contenttype based on extention of file
    return getImage(id, fileName);
}

The following ControllerAdvice method should handle a non-existing file and return a json error response:

@ExceptionHandler(ResourceNotFoundException.class)
@ResponseStatus(HttpStatus.NOT_FOUND)
public @ResponseBody Map<String, String> handleResourceNotFoundException(ResourceNotFoundException e) {
    Map<String, String> errorMap = new HashMap<String, String>();
    errorMap.put("error", e.getMessage());
    return errorMap;
}

My JUnit test works flawless

(EDIT this is because of extention .bla : this also works on appserver):

@Test
public void testResourceNotFound() throws Exception {
    String fileName = "bla.bla";
      mvc.perform(MockMvcRequestBuilders.get("/get/image/bla/" + fileName)
            .with(httpBasic("test", "test")))
            .andDo(print())
            .andExpect(jsonPath("$error").value(Matchers.startsWith("Resource not found")))
            .andExpect(status().is(404));
}

and gives the following output:

MockHttpServletResponse:
          Status = 404
   Error message = null
         Headers = {X-Content-Type-Options=[nosniff], X-XSS-Protection=[1; mode=block], Cache-Control=[no-cache, no-store, max-age=0, must-revalidate], Pragma=[no-cache], Expires=[0], X-Frame-Options=[DENY], Content-Type=[application/json]}
    Content type = application/json
            Body = {"error":"Resource not found: bla/bla.bla"}
   Forwarded URL = null
  Redirected URL = null
         Cookies = []

However on my appserver i get the following error message when trying to donwload non existing image:

(EDIT this is because of extention .jpg : this also fails on JUnit test with .jpg extention):

ERROR org.springframework.web.servlet.mvc.method.annotation.ExceptionHandlerExceptionResolver - Failed to invoke @ExceptionHandler method: public java.util.Map<java.lang.String, java.lang.String> nl.krocket.ocr.web.controller.ExceptionController.handleResourceNotFoundException(nl.krocket.ocr.web.backing.ResourceNotFoundException) org.springframework.web.HttpMediaTypeNotAcceptableException: Could not find acceptable representation

I have configured messageconverters in my mvc configuration as follows:

@Override
public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
    converters.add(mappingJackson2HttpMessageConverter());
    converters.add(byteArrayHttpMessageConverter());
}

@Bean
public MappingJackson2HttpMessageConverter mappingJackson2HttpMessageConverter() {
    ObjectMapper objectMapper = new ObjectMapper();
    objectMapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);
    objectMapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
    //objectMapper.registerModule(new JSR310Module());
    MappingJackson2HttpMessageConverter converter = new MappingJackson2HttpMessageConverter();
    converter.setObjectMapper(objectMapper);
    converter.setSupportedMediaTypes(getJsonMediaTypes());
    return converter;
}

@Bean
public ByteArrayHttpMessageConverter byteArrayHttpMessageConverter() {
    ByteArrayHttpMessageConverter arrayHttpMessageConverter = new ByteArrayHttpMessageConverter();
    arrayHttpMessageConverter.setSupportedMediaTypes(getImageMediaTypes());
    return arrayHttpMessageConverter;
}

What am i missing? And why is the JUnit test working?

Answer 1

You need to decide how the media type of the response should be determined by Spring. That can be done in several ways:

• path extension (eg. /image.jpg)
• URL parameter (eg. ?format=jpg)
• HTTP Accept header (eg. Accept: image/jpg)

By default, Spring looks at the extension rather than the Accept header. This behaviour can be changed if you implement a @Configuration class that extends WebMvcConfigurerAdapter (or since Spring 5.0 simply implement WebMvcConfigurer. There you can override configureContentNegotiation(ContentNegotiationConfigurer configurer) and configure the ContentNegotiationConfigurer to your needs, eg. by calling

ContentNegotiationConfigurer#favorParameter
ContentNegotiationConfigurer#favorPathExtension

If you set both to false, then Spring will look at the Accept header. Since your client can say Accept: image/*,application/json and handle both, Spring should be able to return either the image or the error JSON.

See this Spring tutorial on content negotiation for more information and examples.