protected MediaType getContentType(MediaType contentType, ServerHttpRequest request, ServerHttpResponse response) {
        return FastJsonHttpMessageConverter.APPLICATION_JAVASCRIPT;
    }
Return the content type to set the response to.
This implementation always returns "application/javascript".

@param contentType the content type selected through content negotiation
@param request the current request
@param response the current response
@return the content type to set the response to
fastjson1-compatible/src/main/java/com/alibaba/fastjson/support/spring/JSONPResponseBodyAdvice.java