Web API 2：Action的返回类型

Web API 2：Action的返回类型

Web API控制器中的Action方法有如下几种返回类型：

  1. void
  2. HttpResponseMessage
  3. IHttpActionResult
  4. 其它类型
基于上面几种不同的返回类型，Web API创建HTTP响应消息的机制也不同。
返回类型Web API创建HTTP响应消息的机制
void 返回HTTP状态码204(无内容)
HttpResponseMessage 直接转换成HTTP响应消息
IHttpActionResult 调用接口的ExecuteAsync方法创建一个HttpResponseMessage对象，然后转换成HTTP响应消息
其它类型 把序列化后的返回值写入响应正文，并且返回HTTP状态码200(OK)
下面详细介绍几种返回类型

void

如果返回类型是void， Web API 会返回一个HTTP状态码204(无内容)的空HTTP响应消息
示例代码：
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    public class ReturnValueDemoController : ApiController
    {
          //返回类型为void        
          public void Get()
        {           
        }
    }
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HTTP响应消息：
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HTTP/1.1 204 No Content
Cache-Control: no-cache
Pragma: no-cache
Expires: -1
Server: Microsoft-IIS/8.0
X-AspNet-Version: 4.0.30319
X-SourceFiles: =?UTF-8?B?RTpcV29ya1NwYWNlXERvdE5ldFxNdmNEZW1vXE12Y0RlbW8uV2ViVUlcYXBpXFJldHVyblZhbHVlRGVtbw==?=
X-Powered-By: ASP.NET
Date: Wed, 04 Mar 2015 14:34:09 GMT
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HttpResponseMessage

如果返回类型是HttpResponseMessage ，Web API直接把返回值转换成HTTP响应消息，HttpResponseMessage对象的属性对应响应消息的属性。你可以灵活的设置响应标头和响应正文，这就给了你对响应消息的更大的控制权。如下例：
    
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 public class ReturnValueDemoController : ApiController
    {
        //返回类型为HttpResponseMessage
        public HttpResponseMessage Get()
        {
            HttpResponseMessage response = Request.CreateResponse(HttpStatusCode .OK, "hello");
            response.Content = new StringContent ( "hello wep api", Encoding .Unicode);
            response.Headers.CacheControl = new CacheControlHeaderValue
            {
                MaxAge = TimeSpan .FromSeconds(600)
            };
            return response;
        }
    } 
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响应：
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HTTP/1.1 200 OK
Cache-Control: max-age=600
Content-Type: text/plain; charset=utf-16
Vary: Accept-Encoding
Server: Microsoft-IIS/8.0
X-AspNet-Version: 4.0.30319
X-SourceFiles: =?UTF-8?B?RTpcV29ya1NwYWNlXERvdE5ldFxNdmNEZW1vXE12Y0RlbW8uV2ViVUlcYXBpXFJldHVyblZhbHVlRGVtbw==?=
X-Powered-By: ASP.NET
Date: Wed, 04 Mar 2015 15:14:05 GMT
Content-Length: 26
 
hello wep api
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如果你给CreateResponse方法传入了一个领域模型， Web API就会把序列化后的领域模型写入响应正文。
示例：
    public HttpResponseMessage Get()
        {
            IQueryable <Product > products = repository.GetProducts();
            HttpResponseMessage response = Request.CreateResponse(HttpStatusCode .OK, products);
            return response;
        }
响应：
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HTTP/1.1 200 OK
Cache-Control: no-cache
Pragma: no-cache
Content-Type: application/json; charset=utf-8
Expires: -1
Server: Microsoft-IIS/8.0
X-AspNet-Version: 4.0.30319
X-SourceFiles: =?UTF-8?B?RTpcV29ya1NwYWNlXERvdE5ldFxNdmNEZW1vXE12Y0RlbW8uV2ViVUlcYXBpXFJldHVyblZhbHVlRGVtbw==?=
X-Powered-By: ASP.NET
Date: Wed, 04 Mar 2015 15:37:51 GMT
Content-Length: 264
 
[{"ProductId":1,"Name":" 苹果","Description":null,"Price":1.0,"Category":"水果"},{"ProductId":2,"Name":"鼠标","Description":null,"Price":50.0,"Category":"电脑配件"},{"ProductId":3,"Name":"洗发水","Description":null,"Price":20.0,"Category":"日用品"}]
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IHttpActionResult

IHttpActionResult接口是在Web API 2才引入进来的，本质上，它定义了一个HttpResponseMessage工厂类。IHttpActionResult接口只定义了一个ExecuteAsync方法，该方法异步方式创建一个HttpResponseMessage实例。
public interface IHttpActionResult
{
    Task<HttpResponseMessage> ExecuteAsync(CancellationToken cancellationToken);
}
如果控制器的Action返回类型是IHttpActionResult，Web API就会调用接口的ExecuteAsync方法创建一个HttpResponseMessage对象，然后转换成HTTP响应消息。以下是一个IHttpActionResult接口的实现，它创建了一个普通文本响应消息。
  
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public class PlainTextResult : IHttpActionResult
    {
        private string text;
        private HttpRequestMessage request;
 
        public PlainTextResult(string text, HttpRequestMessage request)
        {
            this .text = text;
            this .request = request;
        }
        public Task < HttpResponseMessage> ExecuteAsync(CancellationToken cancellationToken)
        {
            HttpResponseMessage response=new HttpResponseMessage
            {
                Content = new StringContent (text, Encoding.Unicode),
                RequestMessage = request
            };
            return Task .FromResult(response);
        }
    }
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控制器Action代码：
//返回类型是IHttpActionResult
        public IHttpActionResult Get()
        {
            return new PlainTextResult( "plain text result" ,Request);
        }
响应：
复制代码
HTTP/1.1 200 OK
Cache-Control: no-cache
Pragma: no-cache
Content-Type: text/plain; charset=utf-16
Expires: -1
Vary: Accept-Encoding
Server: Microsoft-IIS/8.0
X-AspNet-Version: 4.0.30319
X-SourceFiles: =?UTF-8?B?RTpcV29ya1NwYWNlXERvdE5ldFxNdmNEZW1vXE12Y0RlbW8uV2ViVUlcYXBpXFJldHVyblZhbHVlRGVtbw==?=
X-Powered-By: ASP.NET
Date: Wed, 04 Mar 2015 16:17:30 GMT
Content-Length: 34
 
plain text result
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通常情况下，你无须自己去实现IHttpActionResult接口， 在System.Web.Http.Results命名空间下已经包含了很多实现该接口的Action返回类型。ApiContoller类也定义了很多方法获取这些内置的Action返回类型。
在下面的例子里，如果没有找到某个产品，控制器调用ApiController.NotFound方法创建一个404 (Not Found)的响应消息。
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HTTP/1.1 404 Not Found
Cache-Control: no-cache
Pragma: no-cache
Expires: -1
Server: Microsoft-IIS/8.0
X-AspNet-Version: 4.0.30319
X-SourceFiles: =?UTF-8?B?RTpcV29ya1NwYWNlXERvdE5ldFxNdmNEZW1vXE12Y0RlbW8uV2ViVUlcYXBpXFJldHVyblZhbHVlRGVtb1w1?=
X-Powered-By: ASP.NET
Date: Wed, 04 Mar 2015 16:54:21 GMT
Content-Length: 0
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如果找到了，控制器调用ApiController.OK方法创建一个HTTP状态码200(OK)响应正文是产品信息的响应消息。
复制代码
HTTP/1.1 200 OK
Cache-Control: no-cache
Pragma: no-cache
Content-Type: application/json; charset=utf-8
Expires: -1
Server: Microsoft-IIS/8.0
X-AspNet-Version: 4.0.30319
X-SourceFiles: =?UTF-8?B?RTpcV29ya1NwYWNlXERvdE5ldFxNdmNEZW1vXE12Y0RlbW8uV2ViVUlcYXBpXFJldHVyblZhbHVlRGVtb1wx?=
X-Powered-By: ASP.NET
Date: Wed, 04 Mar 2015 16:53:16 GMT
Content-Length: 82
 
{"ProductId":1,"Name":" 苹果","Description":null,"Price":1.0,"Category":"水果"}
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其它返回类型

对于其它的返回类型，Web API会对返回值序列化，然后把序列化后的返回值写入到响应正文里，并且响应状态码是200(OK)。   
public IQueryable < Product> GetpProducts()
        {
            return repository.GetProducts();
        }
响应：
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HTTP/1.1 200 OK
Cache-Control: no-cache
Pragma: no-cache
Content-Type: application/json; charset=utf-8
Expires: -1
Server: Microsoft-IIS/8.0
X-AspNet-Version: 4.0.30319
X-SourceFiles: =?UTF-8?B?RTpcV29ya1NwYWNlXERvdE5ldFxNdmNEZW1vXE12Y0RlbW8uV2ViVUlcYXBpXFJldHVyblZhbHVlRGVtb1w=?=
X-Powered-By: ASP.NET
Date: Wed, 04 Mar 2015 17:03:13 GMT
Content-Length: 264
 
[{"ProductId":1,"Name":" 苹果","Description":null,"Price":1.0,"Category":"水果"},{"ProductId":2,"Name":"鼠标","Description":null,"Price":50.0,"Category":"电脑配件"},{"ProductId":3,"Name":"洗发水","Description":null,"Price":20.0,"Category":"日用品"}]
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使用这种返回类型的一个缺点就是你不能直接返回一个错误代码，例如404。不过，你可以通过抛出HttpResponseException异常来解决这个问题。
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public Product GetProductById( int id)
        {
            Product product = repository.GetProductById(id);
            if (product==null )
                throw new HttpResponseException ( HttpStatusCode.NotFound);
 
            return product;
        }
复制代码
 
分类: WebAPI
标签: WebAPI
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原文地址：https://www.cnblogs.com/Leo_wl/p/4314799.html