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：

public static void Register(HttpConfiguration config)
{
    // Web API configuration and services
    // Web API routes
     config.MapHttpAttributeRoutes();

     config.Routes.MapHttpRoute(name: "PhysicianApi",
                routeTemplate: "{controller}/{action}/{id}",
                defaults: new { id = RouteParameter.Optional });
}

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：

/// <summary>
/// File streaming API
/// </summary>
[RoutePrefix("filestreaming")]
[RequestModelValidator]
public class StreamFilesController : ApiController
{
    /// <summary>
    /// Get File meta data
    /// </summary>
    /// <param name="fileName">FileName value</param>
    /// <returns>FileMeta data response.</returns>
    [Route("getfilemetadata")]
    public HttpResponseMessage GetFileMetaData(string fileName)
    {
        // .........................................
        // Full code available in the source control
        // .........................................

    }

    /// <summary>
    /// Search file and return its meta data in all download directories
    /// </summary>
    /// <param name="fileName">FileName value</param>
    /// <returns>List of file meta datas response</returns>
    [HttpGet]
    [Route("searchfileindownloaddirectory")]
    public HttpResponseMessage SearchFileInDownloadDirectory(string fileName)
    {
        // .........................................
        // Full code available in the source control
        // .........................................
    }

    /// <summary>
    /// Asynchronous Download file
    /// </summary>
    /// <param name="fileName">FileName value</param>
    /// <returns>Tasked File stream response</returns>
    [Route("downloadasync")]
    [HttpGet]
    public async Task<HttpResponseMessage> DownloadFileAsync(string fileName)
    {
        // .........................................
        // Full code available in the source control
        // .........................................
    }

    /// <summary>
    /// Download file
    /// </summary>
    /// <param name="fileName">FileName value</param>
    /// <returns>File stream response</returns>
    [Route("download")]
    [HttpGet]
    public HttpResponseMessage DownloadFile(string fileName)
    {
        // .........................................
        // Full code available in the source control
        // .........................................
    }

    /// <summary>
    /// Upload file(s)
    /// </summary>
    /// <param name="overWrite">An indicator to overwrite a file if it exist in the server</param>
    /// <returns>Message response</returns>
    [Route("upload")]
    [HttpPost]
    public HttpResponseMessage UploadFile(bool overWrite)
    {
        // .........................................
        // Full code available in the source control
        // .........................................
    }

    /// <summary>
    /// Asynchronous Upload file
    /// </summary>
    /// <param name="overWrite">An indicator to overwrite a file if it exist in the server</param>
    /// <returns>Tasked Message response</returns>
    [Route("uploadasync")]
    [HttpPost]
    public async Task<HttpResponseMessage> UploadFileAsync(bool overWrite)
    {
        // .........................................
        // Full code available in the source control
        // .........................................
    }
}

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。

/// <summary>
/// Download file
/// </summary>
/// <param name="fileName">FileName value<param>
/// <returns>File stream response<returns>
[Route("download")]
[HttpGet]
public HttpResponseMessage DownloadFile(string fileName)
{
    HttpResponseMessage response = Request.CreateResponse();
    FileMetaData metaData = new FileMetaData();
    try
    {
        string filePath = Path.Combine(this.GetDownloadPath(), @"\", fileName);
        FileInfo fileInfo = new FileInfo(filePath);

        if (!fileInfo.Exists)
        {
            metaData.FileResponseMessage.IsExists = false;
            metaData.FileResponseMessage.Content = string.Format("{0} file is not found !", fileName);
            response = Request.CreateResponse(HttpStatusCode.NotFound, metaData, new MediaTypeHeaderValue("text/json"));
        }
        else
        {
            response.Headers.AcceptRanges.Add("bytes");
            response.StatusCode = HttpStatusCode.OK;
            response.Content = new StreamContent(fileInfo.ReadStream());
            response.Content.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment");
            response.Content.Headers.ContentDisposition.FileName = fileName;
            response.Content.Headers.ContentType = new MediaTypeHeaderValue("application/octet-stream");
            response.Content.Headers.ContentLength = fileInfo.Length;
        }
    }
    catch (Exception exception)
    {
        // Log exception and return gracefully
        metaData = new FileMetaData();
        metaData.FileResponseMessage.Content = ProcessException(exception);
        response = Request.CreateResponse(HttpStatusCode.InternalServerError, metaData, new MediaTypeHeaderValue("text/json"));
    }
    return response;
}

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：

/// <summary>
/// Upload file(s)
/// </summary>
/// <param name="overWrite">An indicator to overwrite a file if it exist in the server.</param>
/// <returns>Message response</returns>
[Route("upload")]
[HttpPost]
public HttpResponseMessage UploadFile(bool overWrite)
{
    HttpResponseMessage response = Request.CreateResponse();
    List<FileResponseMessage> fileResponseMessages = new List<FileResponseMessage>();
    FileResponseMessage fileResponseMessage = new FileResponseMessage { IsExists = false };

    try
    {
        if (!Request.Content.IsMimeMultipartContent())
        {
            fileResponseMessage.Content = "Upload data request is not valid !";
            fileResponseMessages.Add(fileResponseMessage);
            response = Request.CreateResponse(HttpStatusCode.UnsupportedMediaType, fileResponseMessages, new MediaTypeHeaderValue("text/json"));
        }

        else
        {
            response = ProcessUploadRequest(overWrite);
        }
    }
    catch (Exception exception)
    {
        // Log exception and return gracefully
        fileResponseMessage = new FileResponseMessage { IsExists = false };
        fileResponseMessage.Content = ProcessException(exception);
        fileResponseMessages.Add(fileResponseMessage);
        response = Request.CreateResponse(HttpStatusCode.InternalServerError, fileResponseMessages, new MediaTypeHeaderValue("text/json"));

    }
    return response;
}

/// <summary>
/// Asynchronous Upload file
/// </summary>
/// <param name="overWrite">An indicator to overwrite a file if it exist in the server.<param>
/// <returns>Tasked Message response</returns>
[Route("uploadasync")]
[HttpPost]
public async Task<HttpResponseMessage> UploadFileAsync(bool overWrite)
{
    return await new TaskFactory().StartNew(
       () =>
       {
           return UploadFile(overWrite);
       });
}

/// <summary>
/// Process upload request in the server
/// </summary>
/// <param name="overWrite">An indicator to overwrite a file if it exist in the server.</param>
/// </returns>List of message object</returns>
private HttpResponseMessage ProcessUploadRequest(bool overWrite)
{
    // .........................................
    // Full code available in the source control
    // .........................................
}

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。

/// <summary>
/// Download file
/// </summary>
/// <returns>Awaitable Task object</returns>
private static async Task DownloadFile()
{
    Console.ForegroundColor = ConsoleColor.Green;
    Console.WriteLine("Please specify file name  with extension and Press Enter :- ");
    string fileName = Console.ReadLine();
    string localDownloadPath = string.Concat(@"c:\", fileName); // the path can be configurable
    bool overWrite = true;
    string actionURL = string.Concat("downloadasync?fileName=", fileName);

    try
    {
        Console.WriteLine(string.Format("Start downloading @ {0}, {1} time ",
            DateTime.Now.ToLongDateString(),
            DateTime.Now.ToLongTimeString()));


        using (HttpClient httpClient = new HttpClient())
        {
            httpClient.BaseAddress = baseStreamingURL;
            HttpRequestMessage request = new HttpRequestMessage(HttpMethod.Get, actionURL);

            await httpClient.SendAsync(request, HttpCompletionOption.ResponseHeadersRead).
                ContinueWith((response)
                    =>
                {
                    Console.WriteLine();
                    try
                    {
                        ProcessDownloadResponse(localDownloadPath, overWrite, response);
                    }
                    catch (AggregateException aggregateException)
                    {
                        Console.ForegroundColor = ConsoleColor.Red;
                        Console.WriteLine(string.Format("Exception : ", aggregateException));
                    }
                });
        }
    }
    catch (Exception ex)
    {
        Console.ForegroundColor = ConsoleColor.Red;
        Console.WriteLine(ex.Message);
    }
}


/// <summary>
/// Process download response object
/// </summary>
/// <param name="localDownloadFilePath">Local download file path</param>
/// <param name="overWrite">An indicator to overwrite a file if it exist in the client.</param>
/// <param name="response">Awaitable HttpResponseMessage task value</param>
private static void ProcessDownloadResponse(string localDownloadFilePath, bool overWrite,
    Task<HttpResponseMessage> response)
{
    if (response.Result.IsSuccessStatusCode)
    {
        response.Result.Content.DownloadFile(localDownloadFilePath, overWrite).
            ContinueWith((downloadmessage)
                =>
            {
                Console.ForegroundColor = ConsoleColor.Green;
                Console.WriteLine(downloadmessage.TryResult());
            });
    }
    else
    {
        ProcessFailResponse(response);
    }
}

 

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。

/// <summary>
/// Upload file
/// </summary>
/// <returns>Awaitable task object</returns>
private static async Task UploadFile()
{
    try
    {
        string uploadRequestURI = "uploadasync?overWrite=true";

        MultipartFormDataContent formDataContent = new MultipartFormDataContent();

        // Validate the file and add to MultipartFormDataContent object
        formDataContent.AddUploadFile(@"c:\nophoto.png");
        formDataContent.AddUploadFile(@"c:\ReadMe.txt");

        if (!formDataContent.HasContent()) // No files found to be uploaded
        {
            Console.ForegroundColor = ConsoleColor.Red;
            Console.Write(formDataContent.GetUploadFileErrorMesage());
            return;
        }
        else
        {
            string uploadErrorMessage = formDataContent.GetUploadFileErrorMesage();
            if (!string.IsNullOrWhiteSpace(uploadErrorMessage)) // Some files couldn't be found
            {
                Console.ForegroundColor = ConsoleColor.Red;
                Console.Write(uploadErrorMessage);
            }

            HttpRequestMessage request = new HttpRequestMessage(HttpMethod.Post, uploadRequestURI);
            request.Content = formDataContent;

            using (HttpClient httpClient = new HttpClient())
            {
                Console.ForegroundColor = ConsoleColor.Green;
                Console.WriteLine(string.Format("Start uploading @ {0}, {1} time ",
                DateTime.Now.ToLongDateString(),
                DateTime.Now.ToLongTimeString()));

                httpClient.BaseAddress = baseStreamingURL;
                await httpClient.SendAsync(request).
                      ContinueWith((response)
                          =>
                          {
                              try
                              {
                                  ProcessUploadResponse(response);
                              }
                              catch (AggregateException aggregateException)
                              {
                                  Console.ForegroundColor = ConsoleColor.Red;
                                  Console.WriteLine(string.Format("Exception : ", aggregateException));
                              }
                          });
            }
        }
    }
    catch (Exception ex)
    {
        Console.ForegroundColor = ConsoleColor.Red;
        Console.WriteLine(ex.Message);
    }
}

/// <summary>
/// Process download response object
/// </summary>
/// <param name="response">Awaitable HttpResponseMessage task value</param>
private static void ProcessUploadResponse(Task<HttpResponseMessage> response)
{
    if (response.Result.IsSuccessStatusCode)
    {
        string uploadMessage = string.Format("\nUpload completed @ {0}, {1} time ",
                    DateTime.Now.ToLongDateString(),
                    DateTime.Now.ToLongTimeString());
        Console.ForegroundColor = ConsoleColor.Green;
        Console.WriteLine(string.Format("{0}\nUpload Message : \n{1}", uploadMessage,
            JsonConvert.SerializeObject(response.Result.Content.ReadAsAsync<List<FileResponseMessage>>().TryResult(), Formatting.Indented)));
    }
    else
    {
        ProcessFailResponse(response);
    }
}

 

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”

数据流是数据传输中的重要部分，学习了本节内容有助于大家更好地进行ASP.NET的开发。当然，还可以借助一些开发工具来助力开发过程。ComponentOne Studio for ASP.NET 提供了一整套完备的开发工具包，用于在各种浏览器中创建和设计具有现代风格的Web应用程序。

 

下载源代码

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

 

原文链接：http://www.cnblogs.com/powertoolsteam/p/5029475.html