Spring MockHttpServletResponse - handle multiple values for Content-Language header

Affects: 6.x+

It seems that if we provide multiple values for CONTENT_LANGUAGE as an array like:

ResponseEntity.ok()
      .header(HttpHeaders.CONTENT_LANGUAGE, contentLanguage.toArray(new String[0]))
      .body(body);

It won't work nicely with MockHttpServletResponse.

The logic we have there in setSpecialHeader method:

https://github.com/spring-projects/spring-framework/blob/8b14bf86efd590247b2b6fd4843023ee283768d0/spring-test/src/main/java/org/springframework/mock/web/MockHttpServletResponse.java#L756-L767

expects that all the values are sent in a value.

but from debugging, I saw that ServletServerHttpResponse will call setSpecialHeader of MockHttpServletResponse for each header's value.

https://github.com/spring-projects/spring-framework/blob/8b14bf86efd590247b2b6fd4843023ee283768d0/spring-web/src/main/java/org/springframework/http/server/ServletServerHttpResponse.java#L113-L119

Thus, only the last value will be present in the response.

Comment From: bclozel

Thanks for the report @Romster this has been fixed for the next set of maintenance releases.

Comment From: Romster

Wow! That was fast! Thank you @bclozel !