As Artem Bilan said, this problem occures because MappingJackson2HttpMessageConverter
supports response with application/json content-type only. If you can't change server code, but can change client code(I had such case), you can change content-type header with interceptor:
restTemplate.getInterceptors().add((request, body, execution) -> {
ClientHttpResponse response = execution.execute(request,body);
response.getHeaders().setContentType(MediaType.APPLICATION_JSON);
return response;
});