如何在ASP.NET Web API 2中实现JSON垂直格式化输出

我搭建了一个ASP.NET Web API 2项目，尝试以JSON格式返回数据，但在Google Chrome中显示为无缩进的单行结构，同时出现「此XML文件似乎没有关联的样式信息」提示。我期望得到带缩进的垂直结构化JSON格式。

当前Chrome显示效果 #

This XML file does not appear to have any style information associated with it. The document tree is shown below. [{"UserId":23,"Name":"Emily","Access":3,"Mobile":"07419231"},{"UserId":31,"Name":"Lydia","Access":5,"Mobile":"67567587"},{"UserId":45,"Name":"Peter","Access":1,"Mobile":"90345853"},{"UserId":56,"Name":"Lebron","Access":4,"Mobile":"43895449"},{"UserId":73,"Name":"Amber","Access":0,"Mobile":"45788477"}]

期望的JSON格式 #

[
    {
        "UserId":23,
        "Name":"Emily",
        "Access":3,
        "Mobile":"07419231"
    },
    {
        "UserId":31,
        "Name":"Lydia",
        "Access":5,
        "Mobile":"67567587"
    },
    {
        "UserId":45,
        "Name":"Peter",
        "Access":1,
        "Mobile":"90345853"
    },
    {
        "UserId":56,
        "Name":"Lebron",
        "Access":4,
        "Mobile":"43895449"
    },
    {
        "UserId":73,
        "Name":"Amber",
        "Access":0,
        "Mobile":"45788477"
    }
]

我的实现代码 #

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Web.Http;
using System.Data;
using System.Data.SqlClient;
using Newtonsoft.Json;

namespace ApiTesting.Controllers
{
    public class TestController : ApiController
    {
        SqlConnection con = new SqlConnection(@"server=DESKTOP-US2AF5N; database=Test; integrated security=true;");

        public string Get()
        {
            SqlDataAdapter da = new SqlDataAdapter("Select * From TblDraft", con);
            DataTable dt = new DataTable();
            da.Fill(dt);

            if (dt.Rows.Count > 0)
            {
                return JsonConvert.SerializeObject(dt);
            }
            else
            {
                return "No Data Found";
            }
        }
    }
}

问题根源有两点：一是方法返回string类型时，Web API默认会将内容包装为XML返回，导致Chrome识别为XML文件；二是直接序列化的JSON字符串未开启缩进格式。以下是几种解决方式：

方法一：直接返回格式化JSON对象 #

修改控制器方法返回类型为IHttpActionResult，使用Json()方法返回数据，该方法会自动输出格式化JSON并正确设置Content-Type为application/json：

public IHttpActionResult Get()
{
    SqlDataAdapter da = new SqlDataAdapter("Select * From TblDraft", con);
    DataTable dt = new DataTable();
    da.Fill(dt);

    if (dt.Rows.Count > 0)
    {
        return Json(dt);
    }
    else
    {
        return Ok("No Data Found");
    }
}

方法二：全局配置默认返回格式化JSON #

如果希望所有接口都返回格式化JSON，可在WebApiConfig.cs中添加全局配置：

using System.Web.Http;
using Newtonsoft.Json;

namespace ApiTesting
{
    public static class WebApiConfig
    {
        public static void Register(HttpConfiguration config)
        {
            // Web API路由配置
            config.MapHttpAttributeRoutes();
            config.Routes.MapHttpRoute(
                name: "DefaultApi",
                routeTemplate: "api/{controller}/{id}",
                defaults: new { id = RouteParameter.Optional }
            );

            // 开启JSON缩进格式化
            config.Formatters.JsonFormatter.SerializerSettings.Formatting = Formatting.Indented;
            // 移除XML格式化器，默认返回JSON
            config.Formatters.Remove(config.Formatters.XmlFormatter);
        }
    }
}

方法三：手动序列化并指定响应类型 #

若坚持使用JsonConvert.SerializeObject，可指定格式化参数并手动设置响应的Content-Type：

public HttpResponseMessage Get()
{
    SqlDataAdapter da = new SqlDataAdapter("Select * From TblDraft", con);
    DataTable dt = new DataTable();
    da.Fill(dt);

    string json;
    if (dt.Rows.Count > 0)
    {
        json = JsonConvert.SerializeObject(dt, Formatting.Indented);
    }
    else
    {
        json = "\"No Data Found\"";
    }

    var response = new HttpResponseMessage(HttpStatusCode.OK);
    response.Content = new StringContent(json, System.Text.Encoding.UTF8, "application/json");
    return response;
}

内容的提问来源于stack exchange，提问作者user19613128