.NET-Core中 HttpContext.Response.Write() 中文输出乱码

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app.Use((context, next) =>

{

    var res = next(context);

    if (context.Response.StatusCode == 404)

    {

        context.Response.StatusCode = 200;

        context.Response.ContentType = "text/plain; charset=utf-8";

        context.Response.Body.WriteAsync(Encoding.UTF8.GetBytes("访问页面不存在，若要继续访问，请返回主页，谢谢！！"));

    }

    return res;

});