WebApi返回类型设置为json的三种方法

方法一：(改配置法) 

找到Global.asax文件，在Application_Start()方法中添加一句：

GlobalConfiguration.Configuration.Formatters.XmlFormatter.SupportedMediaTypes.Clear();

修改后：

protected void Application_Start() 
{ 
    AreaRegistration.RegisterAllAreas(); 
    WebApiConfig.Register(GlobalConfiguration.Configuration); 
    FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters); 
    RouteConfig.RegisterRoutes(RouteTable.Routes); 
    // 使api返回为json 
    GlobalConfiguration.Configuration.Formatters.XmlFormatter.SupportedMediaTypes.Clear(); 
}

这样返回的结果就都是json类型了，但有个不好的地方，如果返回的结果是String类型，如123，返回的json就会变成"123";

解决的方法是自定义返回类型(返回类型为HttpResponseMessage)

public HttpResponseMessage PostUserName(User user) 
{ 
    String userName = user.userName; 
    HttpResponseMessage result = new HttpResponseMessage { Content = new     StringContent(userName,Encoding.GetEncoding("UTF-8"), "application/json") }; 
    return result; 
}

方法二：(万金油法) 

方法一中又要改配置，又要处理返回值为String类型的json，甚是麻烦，不如就不用web 
api中的的自动序列化对象，自己序列化后再返回

public HttpResponseMessage PostUser(User user) 
{ 
    JavaScriptSerializer serializer = new JavaScriptSerializer(); 
    string str = serializer.Serialize(user); 
    HttpResponseMessage result = new HttpResponseMessage { Content = new StringContent(str, Encoding.GetEncoding("UTF-8"), "application/json") }; 
    return result; 
}

方法二是我比较推荐的方法，为了不在每个接口中都反复写那几句代码，所以就封装为一个方法这样使用就方便多了。

public static HttpResponseMessage toJson(Object obj) 
{ 
    String str; 
    if (obj is String ||obj is Char) 
    { 
        str = obj.ToString(); 
    } 
    else 
    { 
        JavaScriptSerializer serializer = new JavaScriptSerializer(); 
        str = serializer.Serialize(obj); 
    } 
    HttpResponseMessage result = new HttpResponseMessage { Content = new StringContent(str, Encoding.GetEncoding("UTF-8"), "application/json") }; 
    return result; 
}  

方法三：(最麻烦的方法) 

方法一最简单，但杀伤力太大，所有的返回的xml格式都会被毙掉，那么方法三就可以只让api接口中毙掉xml，返回json 

先写一个处理返回的类：

public class JsonContentNegotiator : IContentNegotiator 
{ 
    private readonly JsonMediaTypeFormatter _jsonFormatter; 
 
    public JsonContentNegotiator(JsonMediaTypeFormatter formatter) 
    { 
        _jsonFormatter = formatter; 
    } 
 
    public ContentNegotiationResult Negotiate(Type type, HttpRequestMessage request, IEnumerable<MediaTypeFormatter> formatters) 
    { 
        var result = new ContentNegotiationResult(_jsonFormatter, new  MediaTypeHeaderValue("application/json")); 
        return result; 
    } 
}

找到App_Start中的WebApiConfig.cs文件，打开找到Register(HttpConfiguration config)方法 

添加以下代码：

var jsonFormatter = new JsonMediaTypeFormatter(); 
config.Services.Replace(typeof(IContentNegotiator), new JsonContentNegotiator(jsonFormatter));

添加后代码如下：

public static void Register(HttpConfiguration config) 
{ 
    config.Routes.MapHttpRoute( 
        name: "DefaultApi", 
        routeTemplate: "api/{controller}/{action}/{id}", 
        defaults: new { id = RouteParameter.Optional } 
    ); 
    var jsonFormatter = new JsonMediaTypeFormatter(); 
    config.Services.Replace(typeof(IContentNegotiator), new  JsonContentNegotiator(jsonFormatter)); 
}