ASP.NET Web API 应用教程（一） ——数据流使用

 

相信已经有很多文章来介绍ASP.Net Web API 技术，本系列文章主要介绍如何使用数据流，HTTPS，以及可扩展的Web API 方面的技术，系列文章主要有三篇内容。

主要内容如下：

I  数据流

II 使用HTTPS

III 可扩展的Web API 文档

项目环境要求

  • VS 2012（SP4）及以上，
  • .Net 框架4.5.1
  • Nuget包,可在packages.config 文件中查寻

本文涉及的知识点

  1. ActionFilter
  2. AuthorizationFilter
  3. DelegateHandler
  4. Different Web API routing 属性
  5. MediaTypeFormatter
  6. OWIN
  7. Self Hosting
  8. Web API 文档及可扩展功能

.Net 框架

  1. Async/Await
  2. .NET reflection
  3. Serialization
  4. ASP.NET Web API/MVC Error handling
  5. IIS ,HTTPS 及Certificate
  6. 设计准则及技术

前言

自从ASP.NET MVC 4之后.Net 框架开始支持ASP.NET Web API ，ASP.NET Web API 基于HTTP 协议建立的，是构建 RESTful 服务和处理数据的理想平台，旨在使用HTTP 技术实现对多平台的支持。

ASP.NET Web API 以request-response 的消息转换模式为主，客户端向服务器发送请求，服务器端响应客户端请求。响应可同步或异步。

个人认为使用Web API创建应用需要注意的三个关键点：

  • 采用服务及方法满足的目标
  • 每个方法的输入，如请求
  • 每个方法的输出，如响应

通常情况下，Asp.Net Web API 定义method语法与HTTP方法一一对应的，如自定义方法名 GetPysicians()，则与HTTP中Get 方法匹配。下图是常用匹配表。

但是此方法在很多情况下，并不实用，假如你想在单个API controller 类中定义多个Get 或Post 方法，在这种情况下，需要定义包含action 的路径，将Action 作为URI 的一部分。以下是配置代码：

  1.    1:  public static void Register(HttpConfiguration config)
  1.    2:  {
  1.    3:      // Web API configuration and services
  1.    4:      // Web API routes
  1.    5:       config.MapHttpAttributeRoutes();
  1.    6:      
  1.    7:       config.Routes.MapHttpRoute(name: "PhysicianApi",
  1.    8:                  routeTemplate: "{controller}/{action}/{id}",
  1.    9:                  defaults: new { id = RouteParameter.Optional });
  1.   10:  }

但是此方法不足以应对所有情况，如果想实现从中央仓库删除文件，并且想调用同一个方法来获取文件，这种情况下，Web API 框架需要伪装Get 及Delete对应的HTTP 方法属性。如图所示：

RemoveFile 方法可被Delete(HttpDelete) 或 Get(HttpGet)方法同时调用，从某种程度来说，HTTP 方法使开发人员命名 API“方法”变得简单而标准。

Web API框架也提供了一些其他功能来处理路径方面的问题，与MVC 的路径处理方法相似。因此可定义不同类型的Action方法。

数据流

网络App 最常见的执行操作就是获取数据流。ASP.NET Web API 能够处理客户端与服务器端传输的重量级的数据流，数据流可来源于目录文件，也可是数据库中的二进制文件。本文主要介绍两种方法“Download”和“Upload”实现数据流相关的功能，Download是从服务器下载数据操作，而Upload则是上传数据到服务器。

相关项目

  • WebAPIDataStreaming
  • WebAPIClient
  • POCOLibrary

在对代码解释之前，首先来了解如何配置IIS（7.5）和Web API 服务Web.Config 文件。

1. 保证Downloads/Uploads 涉及的文件具有读写权限。

2. 保证有足够容量的内容或因公安空间处理大文件。

3. 如果文件较大

a. 配置Web.Config 文件时，保证 maxRequestLength 时响应时间 executionTimeout 合理。具体的值主要依赖于数据大小，允许一次性上传的最大数据为2 GB

b. 保证 maxAllowedContentLength 在requestFiltering部分配置下正确设置，默认值为30MB，最大值4GB

一旦完成预先配置，那么创建数据流服务就非常简单了，首先 需要定义文件流“ApiController”，如下：

  1.    1:  /// <summary>
  1.    2:  /// File streaming API
  1.    3:  /// </summary>
  1.    4:  [RoutePrefix("filestreaming")]
  1.    5:  [RequestModelValidator]
  1.    6:  public class StreamFilesController : ApiController
  1.    7:  {
  1.    8:      /// <summary>
  1.    9:      /// Get File meta data
  1.   10:      /// </summary>
  1.   11:      /// <param name="fileName">FileName value</param>
  1.   12:      /// <returns>FileMeta data response.</returns>
  1.   13:      [Route("getfilemetadata")]
  1.   14:      public HttpResponseMessage GetFileMetaData(string fileName)
  1.   15:      {
  1.   16:          // .........................................
  1.   17:          // Full code available in the source control
  1.   18:          // .........................................
  1.   19:   
  1.   20:      }
  1.   21:   
  1.   22:      /// <summary>
  1.   23:      /// Search file and return its meta data in all download directories
  1.   24:      /// </summary>
  1.   25:      /// <param name="fileName">FileName value</param>
  1.   26:      /// <returns>List of file meta datas response</returns>
  1.   27:      [HttpGet]
  1.   28:      [Route("searchfileindownloaddirectory")]
  1.   29:      public HttpResponseMessage SearchFileInDownloadDirectory(string fileName)
  1.   30:      {
  1.   31:          // .........................................
  1.   32:          // Full code available in the source control
  1.   33:          // .........................................
  1.   34:      }
  1.   35:   
  1.   36:      /// <summary>
  1.   37:      /// Asynchronous Download file
  1.   38:      /// </summary>
  1.   39:      /// <param name="fileName">FileName value</param>
  1.   40:      /// <returns>Tasked File stream response</returns>
  1.   41:      [Route("downloadasync")]
  1.   42:      [HttpGet]
  1.   43:      public async Task<HttpResponseMessage> DownloadFileAsync(string fileName)
  1.   44:      {
  1.   45:          // .........................................
  1.   46:          // Full code available in the source control
  1.   47:          // .........................................
  1.   48:      }
  1.   49:   
  1.   50:      /// <summary>
  1.   51:      /// Download file
  1.   52:      /// </summary>
  1.   53:      /// <param name="fileName">FileName value</param>
  1.   54:      /// <returns>File stream response</returns>
  1.   55:      [Route("download")]
  1.   56:      [HttpGet]
  1.   57:      public HttpResponseMessage DownloadFile(string fileName)
  1.   58:      {
  1.   59:          // .........................................
  1.   60:          // Full code available in the source control
  1.   61:          // .........................................
  1.   62:      }
  1.   63:   
  1.   64:      /// <summary>
  1.   65:      /// Upload file(s)
  1.   66:      /// </summary>
  1.   67:      /// <param name="overWrite">An indicator to overwrite a file if it exist in the server</param>
  1.   68:      /// <returns>Message response</returns>
  1.   69:      [Route("upload")]
  1.   70:      [HttpPost]
  1.   71:      public HttpResponseMessage UploadFile(bool overWrite)
  1.   72:      {
  1.   73:          // .........................................
  1.   74:          // Full code available in the source control
  1.   75:          // .........................................
  1.   76:      }
  1.   77:   
  1.   78:      /// <summary>
  1.   79:      /// Asynchronous Upload file
  1.   80:      /// </summary>
  1.   81:      /// <param name="overWrite">An indicator to overwrite a file if it exist in the server</param>
  1.   82:      /// <returns>Tasked Message response</returns>
  1.   83:      [Route("uploadasync")]
  1.   84:      [HttpPost]
  1.   85:      public async Task<HttpResponseMessage> UploadFileAsync(bool overWrite)
  1.   86:      {
  1.   87:          // .........................................
  1.   88:          // Full code available in the source control
  1.   89:          // .........................................
  1.   90:      }
  1.   91:  }

Download 服务方法首先需要确认请求的文件是否存在，如果未找到，则返回错误提示“file is not found”,如果找到此文件，内容则转换为字节附加到响应对象，为“application/octet-stream” MIMI 内容类型。

  1.    1:  /// <summary>
  1.    2:  /// Download file
  1.    3:  /// </summary>
  1.    4:  /// <param name="fileName">FileName value<param>
  1.    5:  /// <returns>File stream response<returns>
  1.    6:  [Route("download")]
  1.    7:  [HttpGet]
  1.    8:  public HttpResponseMessage DownloadFile(string fileName)
  1.    9:  {
  1.   10:      HttpResponseMessage response = Request.CreateResponse();
  1.   11:      FileMetaData metaData = new FileMetaData();
  1.   12:      try
  1.   13:      {
  1.   14:          string filePath = Path.Combine(this.GetDownloadPath(), @"\", fileName);
  1.   15:          FileInfo fileInfo = new FileInfo(filePath);
  1.   16:   
  1.   17:          if (!fileInfo.Exists)
  1.   18:          {
  1.   19:              metaData.FileResponseMessage.IsExists = false;
  1.   20:              metaData.FileResponseMessage.Content = string.Format("{0} file is not found !", fileName);
  1.   21:              response = Request.CreateResponse(HttpStatusCode.NotFound, metaData, new MediaTypeHeaderValue("text/json"));
  1.   22:          }
  1.   23:          else
  1.   24:          {
  1.   25:              response.Headers.AcceptRanges.Add("bytes");
  1.   26:              response.StatusCode = HttpStatusCode.OK;
  1.   27:              response.Content = new StreamContent(fileInfo.ReadStream());
  1.   28:              response.Content.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment");
  1.   29:              response.Content.Headers.ContentDisposition.FileName = fileName;
  1.   30:              response.Content.Headers.ContentType = new MediaTypeHeaderValue("application/octet-stream");
  1.   31:              response.Content.Headers.ContentLength = fileInfo.Length;
  1.   32:          }
  1.   33:      }
  1.   34:      catch (Exception exception)
  1.   35:      {
  1.   36:          // Log exception and return gracefully
  1.   37:          metaData = new FileMetaData();
  1.   38:          metaData.FileResponseMessage.Content = ProcessException(exception);
  1.   39:          response = Request.CreateResponse(HttpStatusCode.InternalServerError, metaData, new MediaTypeHeaderValue("text/json"));
  1.   40:      }
  1.   41:      return response;
  1.   42:  }

Upload服务方法则会在multipart/form-data MIMI 内容类型执行，首先会检测HTTP 请求的内容类型是否是多主体，如果是，则对比内容长度是否超过最大尺寸，如果没有超过，则开始上传内容，当操作完成之后，则提示相应的信息。

代码片段如下：

  1.    1:  /// <summary>
  1.    2:  /// Upload file(s)
  1.    3:  /// </summary>
  1.    4:  /// <param name="overWrite">An indicator to overwrite a file if it exist in the server.</param>
  1.    5:  /// <returns>Message response</returns>
  1.    6:  [Route("upload")]
  1.    7:  [HttpPost]
  1.    8:  public HttpResponseMessage UploadFile(bool overWrite)
  1.    9:  {
  1.   10:      HttpResponseMessage response = Request.CreateResponse();
  1.   11:      List<FileResponseMessage> fileResponseMessages = new List<FileResponseMessage>();
  1.   12:      FileResponseMessage fileResponseMessage = new FileResponseMessage { IsExists = false };
  1.   13:   
  1.   14:      try
  1.   15:      {
  1.   16:          if (!Request.Content.IsMimeMultipartContent())
  1.   17:          {
  1.   18:              fileResponseMessage.Content = "Upload data request is not valid !";
  1.   19:              fileResponseMessages.Add(fileResponseMessage);
  1.   20:              response = Request.CreateResponse(HttpStatusCode.UnsupportedMediaType, fileResponseMessages, new MediaTypeHeaderValue("text/json"));
  1.   21:          }
  1.   22:   
  1.   23:          else
  1.   24:          {
  1.   25:              response = ProcessUploadRequest(overWrite);
  1.   26:          }
  1.   27:      }
  1.   28:      catch (Exception exception)
  1.   29:      {
  1.   30:          // Log exception and return gracefully
  1.   31:          fileResponseMessage = new FileResponseMessage { IsExists = false };
  1.   32:          fileResponseMessage.Content = ProcessException(exception);
  1.   33:          fileResponseMessages.Add(fileResponseMessage);
  1.   34:          response = Request.CreateResponse(HttpStatusCode.InternalServerError, fileResponseMessages, new MediaTypeHeaderValue("text/json"));
  1.   35:   
  1.   36:      }
  1.   37:      return response;
  1.   38:  }
  1.   39:   
  1.   40:  /// <summary>
  1.   41:  /// Asynchronous Upload file
  1.   42:  /// </summary>
  1.   43:  /// <param name="overWrite">An indicator to overwrite a file if it exist in the server.<param>
  1.   44:  /// <returns>Tasked Message response</returns>
  1.   45:  [Route("uploadasync")]
  1.   46:  [HttpPost]
  1.   47:  public async Task<HttpResponseMessage> UploadFileAsync(bool overWrite)
  1.   48:  {
  1.   49:      return await new TaskFactory().StartNew(
  1.   50:         () =>
  1.   51:         {
  1.   52:             return UploadFile(overWrite);
  1.   53:         });
  1.   54:  }
  1.   55:   
  1.   56:  /// <summary>
  1.   57:  /// Process upload request in the server
  1.   58:  /// </summary> 
  1.   59:  /// <param name="overWrite">An indicator to overwrite a file if it exist in the server.</param>
  1.   60:  /// </returns>List of message object</returns>
  1.   61:  private HttpResponseMessage ProcessUploadRequest(bool overWrite)
  1.   62:  {
  1.   63:      // .........................................
  1.   64:      // Full code available in the source control
  1.   65:      // .........................................
  1.   66:  }

调用download 及 upload 文件方法是控制台应用，App 假定文件流服务通过HttpClient和相关类。基本下载文件代码，创建下载HTTP 请求对象。

  1.    1:  /// <summary>
  1.    2:  /// Download file
  1.    3:  /// </summary>
  1.    4:  /// <returns>Awaitable Task object</returns>
  1.    5:  private static async Task DownloadFile()
  1.    6:  {
  1.    7:      Console.ForegroundColor = ConsoleColor.Green;
  1.    8:      Console.WriteLine("Please specify file name  with extension and Press Enter :- ");
  1.    9:      string fileName = Console.ReadLine();
  1.   10:      string localDownloadPath = string.Concat(@"c:\", fileName); // the path can be configurable
  1.   11:      bool overWrite = true;
  1.   12:      string actionURL = string.Concat("downloadasync?fileName=", fileName);
  1.   13:   
  1.   14:      try
  1.   15:      {
  1.   16:          Console.WriteLine(string.Format("Start downloading @ {0}, {1} time ",
  1.   17:              DateTime.Now.ToLongDateString(),
  1.   18:              DateTime.Now.ToLongTimeString()));
  1.   19:   
  1.   20:   
  1.   21:          using (HttpClient httpClient = new HttpClient())
  1.   22:          {
  1.   23:              httpClient.BaseAddress = baseStreamingURL;
  1.   24:              HttpRequestMessage request = new HttpRequestMessage(HttpMethod.Get, actionURL);
  1.   25:   
  1.   26:              await httpClient.SendAsync(request, HttpCompletionOption.ResponseHeadersRead).
  1.   27:                  ContinueWith((response)
  1.   28:                      =>
  1.   29:                  {
  1.   30:                      Console.WriteLine();
  1.   31:                      try
  1.   32:                      {
  1.   33:                          ProcessDownloadResponse(localDownloadPath, overWrite, response);
  1.   34:                      }
  1.   35:                      catch (AggregateException aggregateException)
  1.   36:                      {
  1.   37:                          Console.ForegroundColor = ConsoleColor.Red;
  1.   38:                          Console.WriteLine(string.Format("Exception : ", aggregateException));
  1.   39:                      }
  1.   40:                  });
  1.   41:          }
  1.   42:      }
  1.   43:      catch (Exception ex)
  1.   44:      {
  1.   45:          Console.ForegroundColor = ConsoleColor.Red;
  1.   46:          Console.WriteLine(ex.Message);
  1.   47:      }
  1.   48:  }
  1.   49:   
  1.   50:   
  1.   51:  /// <summary>
  1.   52:  /// Process download response object
  1.   53:  /// </summary>
  1.   54:  /// <param name="localDownloadFilePath">Local download file path</param>
  1.   55:  /// <param name="overWrite">An indicator to overwrite a file if it exist in the client.</param>
  1.   56:  /// <param name="response">Awaitable HttpResponseMessage task value</param>
  1.   57:  private static void ProcessDownloadResponse(string localDownloadFilePath, bool overWrite,
  1.   58:      Task<HttpResponseMessage> response)
  1.   59:  {
  1.   60:      if (response.Result.IsSuccessStatusCode)
  1.   61:      {
  1.   62:          response.Result.Content.DownloadFile(localDownloadFilePath, overWrite).
  1.   63:              ContinueWith((downloadmessage)
  1.   64:                  =>
  1.   65:              {
  1.   66:                  Console.ForegroundColor = ConsoleColor.Green;
  1.   67:                  Console.WriteLine(downloadmessage.TryResult());
  1.   68:              });
  1.   69:      }
  1.   70:      else
  1.   71:      {
  1.   72:          ProcessFailResponse(response);
  1.   73:      }
  1.   74:  }

注意上述代码中HttpClient 对象发送请求，并等待响应发送Header内容（HttpCompletionOption.ResponseHeadersRead ）。而不是发送全部的响应内容文件。一旦Response header 被读，则执行验证，一旦验证成功，则执行下载方法。

以下代码调用upload 文件流，与下载方法类似，创建多主体表单数据，并发送给服务器端。

  1.    1:  /// <summary>
  1.    2:  /// Upload file
  1.    3:  /// </summary>
  1.    4:  /// <returns>Awaitable task object</returns>
  1.    5:  private static async Task UploadFile()
  1.    6:  {
  1.    7:      try
  1.    8:      {
  1.    9:          string uploadRequestURI = "uploadasync?overWrite=true";
  1.   10:   
  1.   11:          MultipartFormDataContent formDataContent = new MultipartFormDataContent();
  1.   12:   
  1.   13:          // Validate the file and add to MultipartFormDataContent object
  1.   14:          formDataContent.AddUploadFile(@"c:\nophoto.png");
  1.   15:          formDataContent.AddUploadFile(@"c:\ReadMe.txt");
  1.   16:   
  1.   17:          if (!formDataContent.HasContent()) // No files found to be uploaded
  1.   18:          {
  1.   19:              Console.ForegroundColor = ConsoleColor.Red;
  1.   20:              Console.Write(formDataContent.GetUploadFileErrorMesage());
  1.   21:              return;
  1.   22:          }
  1.   23:          else
  1.   24:          {
  1.   25:              string uploadErrorMessage = formDataContent.GetUploadFileErrorMesage();
  1.   26:              if (!string.IsNullOrWhiteSpace(uploadErrorMessage)) // Some files couldn't be found
  1.   27:              {
  1.   28:                  Console.ForegroundColor = ConsoleColor.Red;
  1.   29:                  Console.Write(uploadErrorMessage);
  1.   30:              }
  1.   31:   
  1.   32:              HttpRequestMessage request = new HttpRequestMessage(HttpMethod.Post, uploadRequestURI);
  1.   33:              request.Content = formDataContent;
  1.   34:   
  1.   35:              using (HttpClient httpClient = new HttpClient())
  1.   36:              {
  1.   37:                  Console.ForegroundColor = ConsoleColor.Green;
  1.   38:                  Console.WriteLine(string.Format("Start uploading @ {0}, {1} time ",
  1.   39:                  DateTime.Now.ToLongDateString(),
  1.   40:                  DateTime.Now.ToLongTimeString()));
  1.   41:   
  1.   42:                  httpClient.BaseAddress = baseStreamingURL;
  1.   43:                  await httpClient.SendAsync(request).
  1.   44:                        ContinueWith((response)
  1.   45:                            =>
  1.   46:                            {
  1.   47:                                try
  1.   48:                                {
  1.   49:                                    ProcessUploadResponse(response);
  1.   50:                                }
  1.   51:                                catch (AggregateException aggregateException)
  1.   52:                                {
  1.   53:                                    Console.ForegroundColor = ConsoleColor.Red;
  1.   54:                                    Console.WriteLine(string.Format("Exception : ", aggregateException));
  1.   55:                                }
  1.   56:                            });
  1.   57:              }
  1.   58:          }
  1.   59:      }
  1.   60:      catch (Exception ex)
  1.   61:      {
  1.   62:          Console.ForegroundColor = ConsoleColor.Red;
  1.   63:          Console.WriteLine(ex.Message);
  1.   64:      }
  1.   65:  } 
  1.   66:   
  1.   67:  /// <summary>
  1.   68:  /// Process download response object
  1.   69:  /// </summary>
  1.   70:  /// <param name="response">Awaitable HttpResponseMessage task value</param>
  1.   71:  private static void ProcessUploadResponse(Task<HttpResponseMessage> response)
  1.   72:  {
  1.   73:      if (response.Result.IsSuccessStatusCode)
  1.   74:      {
  1.   75:          string uploadMessage = string.Format("\nUpload completed @ {0}, {1} time ",
  1.   76:                      DateTime.Now.ToLongDateString(),
  1.   77:                      DateTime.Now.ToLongTimeString());
  1.   78:          Console.ForegroundColor = ConsoleColor.Green;
  1.   79:          Console.WriteLine(string.Format("{0}\nUpload Message : \n{1}", uploadMessage,
  1.   80:              JsonConvert.SerializeObject(response.Result.Content.ReadAsAsync<List<FileResponseMessage>>().TryResult(), Formatting.Indented)));
  1.   81:      }
  1.   82:      else
  1.   83:      {
  1.   84:          ProcessFailResponse(response);
  1.   85:      }
  1.   86:  }

数据流项目由可扩展类和方法组成，本文就不再详述。下篇文章中将介绍“使用HTTPS 开发项目”

下载源代码

原文链接：http://www.codeproject.com/Articles/838274/Web-API-Thoughts-of-Data-Streaming#Hist

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