How to use RestTemplate with application/octet-stream response type

I guess the better solution is to just add another converter, not to modify current ones:

@Bean
public RestTemplate restTemplate() {
    final RestTemplate restTemplate = new RestTemplate();
    restTemplate.getMessageConverters().add(jacksonSupportsMoreTypes());
    return restTemplate;
}


private HttpMessageConverter jacksonSupportsMoreTypes() {//eg. Gitlab returns JSON as plain text 
    MappingJackson2HttpMessageConverter converter = new MappingJackson2HttpMessageConverter();
    converter.setSupportedMediaTypes(Arrays.asList(MediaType.parseMediaType("text/plain;charset=utf-8"), MediaType.APPLICATION_OCTET_STREAM));
    return converter;
}

You need to conifigure restTemplate with message converters. In your configuration do the following:

   @Bean
    public RestOperations restTemplate() {
        RestTemplate restTemplate = new RestTemplate();
        
        MappingJackson2HttpMessageConverter converter = new MappingJackson2HttpMessageConverter();

        
        converter.setSupportedMediaTypes(
                Arrays.asList(new MediaType[]{MediaType.APPLICATION_JSON, MediaType.APPLICATION_OCTET_STREAM}));

        restTemplate.setMessageConverters(Arrays.asList(converter, new FormHttpMessageConverter()));
        return restTemplate;
    }