ASP.NET WebApi文件下载

[RoutePrefix("api")]
public class DownloadController : ApiController
{

    [HttpGet]
    [Route("~/download")]
    public HttpResponseMessage Get()
    {
        var FilePath = HttpContext.Current.Server.MapPath("~/upload_files/1/1000/201804/7adc1e7a-b34c-46bf-8023-0aca56f95e38.jpg");
        FileStream stream = File.OpenRead(FilePath);
        HttpResponseMessage httpResponseMessage = new HttpResponseMessage(HttpStatusCode.OK);
        httpResponseMessage.Content = new StreamContent(stream);
        httpResponseMessage.Content.Headers.ContentType = new MediaTypeHeaderValue("image/jpg");
        httpResponseMessage.Content.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment")
        {
            FileName = HttpUtility.UrlEncode(Path.GetFileName(FilePath))
        };
        return httpResponseMessage;
    }
}