public static void Main(string[] args)
  {var host = new WebHostBuilder()
      .UseKestrel()
      .UseStartup<Startup>()
      .UseContentRoot(Directory.GetCurrentDirectory())
      .UseWebRoot(Directory.GetCurrentDirectory() + @"\wwwroot\")
      .UseEnvironment(EnvironmentName.Development)
      .Build();
   host.Run();
  }

 public void Configure(IApplicationBuilder app, IHostingEnvironment env)
  {
   app.UseStaticFiles();
   app.UseMvc();
  }

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
  {
   app.UseMvc();

   app.UseStaticFiles(new StaticFileOptions()
   {
    FileProvider = new PhysicalFileProvider(@"C:\Users\Administrator\Desktop"),
    RequestPath = new PathString("/Static")
   });

   //app.UseStaticFiles("/Static");
  }

public async Task Invoke(HttpContext context)
  {
   var fileContext = new StaticFileContext(context, _options, _matchUrl, _logger, _fileProvider, _contentTypeProvider);

   if (!fileContext.ValidateMethod())//靜態(tài)文件的請(qǐng)求方式只能是Get或者Head
   {
    _logger.LogRequestMethodNotSupported(context.Request.Method);
   }　　　　　　　//判斷請(qǐng)求的路徑和配置的請(qǐng)求路徑是否匹配。如請(qǐng)求路徑為http://localhost:5000/static/1.txt 　　　　　　　//配置為RequestPath = new PathString("/Static")　　　　  //則匹配，并將文件路徑賦值給StaticFileContext中點(diǎn)的_subPath
   else if (!fileContext.ValidatePath())
   {
    _logger.LogPathMismatch(fileContext.SubPath);
   }　　　　　　　//通過獲取要訪問文件的擴(kuò)展名，獲取此文件對(duì)應(yīng)的MIME類型,　　　　　　　//如果找到文件對(duì)應(yīng)的MIME，返回True，并將MIME類型賦值給StaticFileContext中的_contextType　　　　　　　//沒有找到返回False.
   else if (!fileContext.LookupContentType())
   {
    _logger.LogFileTypeNotSupported(fileContext.SubPath);
   }　　　　　　　//判斷訪問的文件是否存在?！　　　　　?//如果存在返回True,并根據(jù)文件的最后修改時(shí)間和文件的長(zhǎng)度，生成Hash值,并將值賦值給_etag，也就是相應(yīng)頭中的Etag?！　　　　　　?/如果不存在 返回False，進(jìn)入下一個(gè)中間件中處理
   else if (!fileContext.LookupFileInfo())
   {
    _logger.LogFileNotFound(fileContext.SubPath);
   }
   else
   {
    fileContext.ComprehendRequestHeaders();　　　　　　　　　　//根據(jù)StaticFileContext中的值，加上對(duì)應(yīng)的相應(yīng)頭，并發(fā)送響應(yīng)。具體調(diào)用方法在下面
    switch (fileContext.GetPreconditionState())
    {
     case StaticFileContext.PreconditionState.Unspecified:
     case StaticFileContext.PreconditionState.ShouldProcess:
      if (fileContext.IsHeadMethod)
      {
       await fileContext.SendStatusAsync(Constants.Status200Ok);
       return;
      }
      try
      {
       if (fileContext.IsRangeRequest)
       {
        await fileContext.SendRangeAsync();
        return;
       }
       await fileContext.SendAsync();
       _logger.LogFileServed(fileContext.SubPath, fileContext.PhysicalPath);
       return;
      }
      catch (FileNotFoundException)
      {
       context.Response.Clear();
      }
      break;
     case StaticFileContext.PreconditionState.NotModified:
      _logger.LogPathNotModified(fileContext.SubPath);
      await fileContext.SendStatusAsync(Constants.Status304NotModified);
      return;
     case StaticFileContext.PreconditionState.PreconditionFailed:
      _logger.LogPreconditionFailed(fileContext.SubPath);
      await fileContext.SendStatusAsync(Constants.Status412PreconditionFailed);
      return;
     default:
      var exception = new NotImplementedException(fileContext.GetPreconditionState().ToString());
      Debug.Fail(exception.ToString());
      throw exception;
    }
   }　　　　　　 //進(jìn)入下一個(gè)中間件中處理
   await _next(context);
  }

public void ApplyResponseHeaders(int statusCode)
  {
   _response.StatusCode = statusCode;
   if (statusCode < 400)
   {
    if (!string.IsNullOrEmpty(_contentType))
    {
     _response.ContentType = _contentType;
    }　　　　　　　　　　//設(shè)置響應(yīng)頭中最后修改時(shí)間、ETag和accept-ranges
    _responseHeaders.LastModified = _lastModified;
    _responseHeaders.ETag = _etag;
    _responseHeaders.Headers[HeaderNames.AcceptRanges] = "bytes";
   }
   if (statusCode == Constants.Status200Ok)
   {
    _response.ContentLength = _length;
   }
   _options.OnPrepareResponse(new StaticFileResponseContext()
   {
    Context = _context,
    File = _fileInfo,
   });
  }

public bool LookupFileInfo()
  {
   _fileInfo = _fileProvider.GetFileInfo(_subPath.Value);
   if (_fileInfo.Exists)
   {
    _length = _fileInfo.Length;
    DateTimeOffset last = _fileInfo.LastModified;
    _lastModified = new DateTimeOffset(last.Year, last.Month, last.Day, last.Hour, last.Minute, last.Second, last.Offset).ToUniversalTime();
　　　　　　　　　　//通過修改時(shí)間和文件長(zhǎng)度，得到ETag的值
    long etagHash = _lastModified.ToFileTime() ^ _length;
    _etag = new EntityTagHeaderValue('\"' + Convert.ToString(etagHash, 16) + '\"');
   }
   return _fileInfo.Exists;
  }