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[ASP.net教程]WebAPI接收JSON参数注意事项


运行环境:ASP.NET 4.5.2。

当我们向GlobalConfiguration.Configuration.MessageHandlers添加一个DelegatingHandler派生类后,很容易发生即使命中了Action,但方法参数值为null的问题。

在大多数情况下,我们会在DelegatingHandler派生类里,重写async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)方法。

在方法内,做一些事情,比如说访问日志记录,任意校验,添加Header,修改URL(重写)等工作。

其中最重要需要注意的一点在于request.Content,当我们在方法内访问了request.Content (get)之后,而不对request.Content进行赋值(set)的话,会发生什么呢?

这会导致我们的方法(action)无法获取到客户端Post上来的数据,导致方法参数值为null。

这是为什么呢,这个中原因,我没去深究。

现在附上解决代码:

 1 public class DefaultHandler : DelegatingHandler 2 { 3   protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) 4   { 5     request.RequestUri = new Uri(request.RequestUri.ToString()); 6  7     MediaTypeHeaderValue contentType = request.Content.Headers.ContentType; 8  9     if (contentType != null)10     {11       switch (contentType.MediaType)12       {13         case "application/x-www-form-urlencoded":14           {15             NameValueCollection formData = await request.Content.ReadAsFormDataAsync(cancellationToken);16             request.Content = new FormUrlEncodedContent(Correct(formData));17             //TODO:在这里对formData进行业务处理18           }19           break;20         case "multipart/form-data":21           {22             NameValueCollection formData = await request.Content.ReadAsFormDataAsync(cancellationToken);23             request.Content = new FormUrlEncodedContent(Correct(formData));24             //TODO:在这里对formData进行业务处理25           }26           break;27         case "application/json":28           {29             HttpContentHeaders oldHeaders = request.Content.Headers;30             string formData = await request.Content.ReadAsStringAsync();31             request.Content = new StringContent(formData);32             ReplaceHeaders(request.Content.Headers, oldHeaders);33             //TODO:在这里对formData进行业务处理34           }35           break;36         default:37           throw new Exception("Implement It!");38       }39     }40 41     return await base.SendAsync(request, cancellationToken);42   }43 44   private static IEnumerable<KeyValuePair<string, string>> Correct(NameValueCollection formData)45   {46     return formData.Keys.Cast<string>().Select(key => new KeyValuePair<string, string>(key, formData[key])).ToList();47   }48 49   private static void ReplaceHeaders(HttpHeaders currentHeaders, HttpHeaders oldHeaders)50   {51     currentHeaders.Clear();52     foreach (var item in oldHeaders)53       currentHeaders.Add(item.Key, item.Value);54   }55 }

 

在Global.asax添加代码:

1 protected void Application_Start()2 {3   GlobalConfiguration.Configure(WebApiConfig.Register);4   GlobalConfiguration.Configuration.MessageHandlers.Add(new DefaultHandler());5 }

模型类:

 1 public class TestModel 2 { 3   [JsonProperty(PropertyName ="I")] 4   public long Id { get; set; } 5  6   [JsonProperty(PropertyName = "N")] 7   public string Name { get; set; } 8  9   [JsonProperty(PropertyName = "M")]10   public decimal Money { get; set; }11 12   [JsonProperty(PropertyName = "IE")]13   public bool IsEnable { get; set; }14 15   [JsonProperty(PropertyName = "CD")]16   public DateTime CreateDate { get; set; }17 18   [JsonProperty(PropertyName = "UD")]19   public DateTime? UpdateDate { get; set; }20 }

ApiController:

1 public class DefaultController : ApiController2 {3   [HttpPost]4   public TestModel Find(TestModel model)5   {6     return model;7   }8 }

Request Body:

{"I":10000,"N":"TestModel","M":21547855.0001,"IE":true,"CD":"2015-12-10 12:12:12","UD":"2016-01-01 01:01:01"}

Fiddler4测试:

测试结果:

解决办法来自:http://stackoverflow.com/questions/27333419/modify-request-content-in-webapi-delegatinghandler