Add the ability to specify the charset UTF-8 in AdviceTrait

Not sure I got the issue title right! Feel free to change it!

My problem was that my french error messages assertions were failing because the UTF-8 encoding was not specified in the response content type. Here’s a piece of my unit test:

...
final FooDto dto = new FooDto();
dto.setCode(ALPHANUMERIC_GENERATOR.generate(11));
mockMvc
    .perform(
        put("/api/foo/{id}", 1)
            .header("accept-language", "fr")
            .contentType(MediaType.APPLICATION_JSON)
            .content(toJsonBytes(dto)))
    // Verify that the response status is BAD_REQUEST (400).
    .andExpect(status().isBadRequest())
    // Verify that the response content type is compatible with application/problem+json
    .andExpect(content().contentTypeCompatibleWith(MediaType.APPLICATION_PROBLEM_JSON))
    // Verify the content, which is supposed to be the validation errors.
    .andExpect(jsonPath("$.status").value(HttpStatus.BAD_REQUEST.value()))
    .andExpect(jsonPath("$.title").value("Constraint Violation"))
    .andExpect(jsonPath("$.violations", hasSize(1)))
    .andExpect(jsonPath("$.violations[0].field", equalTo("code")))
    .andExpect(jsonPath("$.violations[0].message", equalTo("La longueur maximal du code est de 10 caractères")));
...

This test was failing with the following error message:

Expected: “La longueur maximal du code est de 30 caractères” but: was “La longueur maximal du code est de 30 caractères”

In order to get this to work, I had to override AdviceTrait#negociate in my ControllerAdvice annotated class (witch implements ProblemHandling) as followed:

@Override
public Optional<MediaType> negotiate(final NativeWebRequest request) {

  final Optional<MediaType> mediaType = ProblemHandling.super.negotiate(request);
  return mediaType
      .filter(PROBLEM::equals)
      .map(type -> Optional.of(MediaType.APPLICATION_PROBLEM_JSON_UTF8))
      .orElse(mediaType);
}

By the way, I use Spring Boot 2.0.0.M7 and so far this is the only issue I got. So I think that #121 won’t be a hard one.

[whiskeysierra]

I think spring.http.encoding.force=true is a good enough workaround for tests. As far as I can tell, it works in production, and that’s my main priority. I’m closing this for now. Feel free to challenge and re-open.

[sbraconnier]

If it can help, I did some digging into this problem and found the source of it.

When we perform a request using MockMvc, a MockHttpServletResponse is created, with a charsetEncoding initialized to: private String characterEncoding = WebUtils.DEFAULT_CHARACTER_ENCODING; which is public static final String DEFAULT_CHARACTER_ENCODING = "ISO-8859-1";

Then, when the content of the request is get, this default encoding is used, causing the assertion failure:

public String getContentAsString() throws UnsupportedEncodingException {
	flushBuffer();
	return (this.characterEncoding != null ?
			this.content.toString(this.characterEncoding) : this.content.toString());
}

Now, here is the setContentType implementation of MockHttpServletResponse:

@Override
public void setContentType(String contentType) {
	this.contentType = contentType;
	if (contentType != null) {
		try {
			MediaType mediaType = MediaType.parseMediaType(contentType);
			if (mediaType.getCharset() != null) {
				this.characterEncoding = mediaType.getCharset().name();
				this.charset = true;
			}
		}
		catch (Exception ex) {
			// Try to get charset value anyway
			int charsetIndex = contentType.toLowerCase().indexOf(CHARSET_PREFIX);
			if (charsetIndex != -1) {
				this.characterEncoding = contentType.substring(charsetIndex + CHARSET_PREFIX.length());
				this.charset = true;
			}
		}
		updateContentTypeHeader();
	}
}

Since the charset is not provided in the content type when using application/problem+json only, ISO-8859-1 is always used. This is why the failure goes away once we use application/problem+json;charset=UTF-8 instead.

That being said, I’m not sure what would be the best way to fix this…