业务场景：

业务需求要求，需要对 WebApi 接口服务统一返回参数，也就是把实际的结果用一定的格式包裹起来，比如下面格式：

{
    "response":{
        "code":200,
        "msg":"Remote service error",
        "result":""
    }
}

具体实现：

using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Filters;

public class WebApiResultMiddleware : ActionFilterAttribute
{
    public override void OnResultExecuting(ResultExecutingContext context)
    {
        //根据实际需求进行具体实现
        if (context.Result is ObjectResult)
        {
            var objectResult = context.Result as ObjectResult;
            if (objectResult.Value == null)
            {
                context.Result = new ObjectResult(new { code = 404, sub_msg = "未找到资源", msg = "" });
            }
            else
            {
                context.Result = new ObjectResult(new { code = 200, msg = "", result = objectResult.Value });
            }
        }
        else if (context.Result is EmptyResult)
        {
            context.Result = new ObjectResult(new { code = 404, sub_msg = "未找到资源", msg = "" });
        }
        else if (context.Result is ContentResult)
        {
            context.Result = new ObjectResult(new { code = 200, msg = "", result= (context.Result as ContentResult).Content });
        }
        else if (context.Result is StatusCodeResult)
        {
            context.Result = new ObjectResult(new { code = (context.Result as StatusCodeResult).StatusCode, sub_msg = "", msg = "" });
        }
    }
}

Startup添加对应配置：

public void ConfigureServices(IServiceCollection services)
{
    services.AddMvc(options =>
    {
        options.Filters.Add(typeof(WebApiResultMiddleware));
        options.RespectBrowserAcceptHeader = true;
    });
}