考虑使用ASP.NET Web API编写的Web服务将任何数字文件作为“multipart / mixed”请求接受。辅助方法mat看起来如下（假设_client是System.Net.Http.HttpClient的实例）：
public T Post<T>(string requestUri, T value, params Stream[] streams)
{
var requestMessage = new HttpRequestMessage();
var objectContent = requestMessage.CreateContent(
value,
MediaTypeHeaderValue.Parse("application/json"),
new MediaTypeFormatter[] {new JsonMediaTypeFormatter()},
new FormatterSelector());
var content = new MultipartContent();
content.Add(objectContent);
foreach (var stream in streams)
{
var streamContent = new StreamContent(stream);
streamContent.Headers.ContentType = new MediaTypeHeaderValue("application/octet-stream");
streamContent.Headers.ContentDisposition =
new ContentDispositionHeaderValue("form-data")
{
Name = "file",
FileName = "mystream.doc"
};
content.Add(streamContent);
}
return _httpClient.PostAsync(requestUri, content)
.ContinueWith(t => t.Result.Content.ReadAsAsync<T>()).Unwrap().Result;
}
在ApiController的子类中接受请求的方法具有如下签名：
public HttpResponseMessage Post(HttpRequestMessage request)
{
/* parse request using MultipartFormDataStreamProvider */
}
理想情况下，我想像这样定义，根据“Content-Disposition”标题的“name”属性，从“multipart / mixed”内容中提取联系人，来源和目标。
public HttpResponseMessage Post(Contact contact, Stream source, Stream target)
{
// process contact, source and target
}
但是，使用我现有的签名，将数据发布到服务器会产生InvalidOperationException，并显示错误消息：
没有'MediaTypeFormatter'可用于读取类型的对象 'HttpRequestMessage'，媒体类型为'multipart / mixed'。
互联网上有很多例子说明如何使用ASP.NET Web API和HttpClient发送和接收文件。但是，我还没有找到任何显示如何处理这个问题。
我开始考虑实现自定义MediaTypeFormatter并将其注册到全局配置。然而，尽管在自定义MediaTypeFormatter中处理序列化XML和JSON很容易，但是不清楚如何处理“多部分/混合”请求，这几乎可以是任何事情。
答案 0 :(得分：13)
看一下这个论坛：http://forums.asp.net/t/1777847.aspx/1?MVC4+Beta+Web+API+and+multipart+form+data
以下是一段代码（由imran_ku07发布），可帮助您实现自定义格式化程序来处理multipart / form-data：
public class MultiFormDataMediaTypeFormatter : FormUrlEncodedMediaTypeFormatter
{
public MultiFormDataMediaTypeFormatter() : base()
{
this.SupportedMediaTypes.Add(new MediaTypeHeaderValue("multipart/form-data"));
}
protected override bool CanReadType(Type type)
{
return true;
}
protected override bool CanWriteType(Type type)
{
return false;
}
protected override Task<object> OnReadFromStreamAsync(Type type, Stream stream, HttpContentHeaders contentHeaders, FormatterContext formatterContext)
{
var contents = formatterContext.Request.Content.ReadAsMultipartAsync().Result;
return Task.Factory.StartNew<object>(() =>
{
return new MultiFormKeyValueModel(contents);
});
}
class MultiFormKeyValueModel : IKeyValueModel
{
IEnumerable<HttpContent> _contents;
public MultiFormKeyValueModel(IEnumerable<HttpContent> contents)
{
_contents = contents;
}
public IEnumerable<string> Keys
{
get
{
return _contents.Cast<string>();
}
}
public bool TryGetValue(string key, out object value)
{
value = _contents.FirstDispositionNameOrDefault(key).ReadAsStringAsync().Result;
return true;
}
}
}
然后，您需要将此格式化程序添加到您的应用程序中。如果进行自我托管，您只需添加它即可：
config.Formatters.Insert(0, new MultiFormDataMediaTypeFormatter());
在实例化HttpSelfHostServer类之前。
- 编辑 -
要解析二进制流，您需要另一个格式化程序。这是我用来解析我的一个工作项目中的图像的一个。
class JpegFormatter : MediaTypeFormatter
{
protected override bool CanReadType(Type type)
{
return (type == typeof(Binary));
}
protected override bool CanWriteType(Type type)
{
return false;
}
public JpegFormatter()
{
SupportedMediaTypes.Add(new MediaTypeHeaderValue("image/jpeg"));
SupportedMediaTypes.Add(new MediaTypeHeaderValue("image/jpg"));
SupportedMediaTypes.Add(new MediaTypeHeaderValue("image/png"));
}
protected override Task<object> OnReadFromStreamAsync(Type type, Stream stream, HttpContentHeaders contentHeaders, FormatterContext formatterContext)
{
return Task.Factory.StartNew(() =>
{
byte[] fileBytes = new byte[stream.Length];
stream.Read(fileBytes, 0, (int)fileBytes.Length);
return (object)new Binary(fileBytes);
});
}
protected override Task OnWriteToStreamAsync(Type type, object value, Stream stream, HttpContentHeaders contentHeaders, FormatterContext formatterContext, TransportContext transportContext)
{
throw new NotImplementedException();
}
}
在你的控制器/动作中你需要做的事情是：
public HttpResponseMessage UploadImage(Binary File) {
//do something with your file
}
答案 1 :(得分：2)
看一下这篇文章https://stackoverflow.com/a/17073113/1944993，Kiran Challa的答案非常好！
基本部分：
自定义内存中MultiaprtFormDataStreamProvider：
public class InMemoryMultipartFormDataStreamProvider : MultipartStreamProvider
{
private NameValueCollection _formData = new NameValueCollection();
private List<HttpContent> _fileContents = new List<HttpContent>();
// Set of indexes of which HttpContents we designate as form data
private Collection<bool> _isFormData = new Collection<bool>();
/// <summary>
/// Gets a <see cref="NameValueCollection"/> of form data passed as part of the multipart form data.
/// </summary>
public NameValueCollection FormData
{
get { return _formData; }
}
/// <summary>
/// Gets list of <see cref="HttpContent"/>s which contain uploaded files as in-memory representation.
/// </summary>
public List<HttpContent> Files
{
get { return _fileContents; }
}
public override Stream GetStream(HttpContent parent, HttpContentHeaders headers)
{
// For form data, Content-Disposition header is a requirement
ContentDispositionHeaderValue contentDisposition = headers.ContentDisposition;
if (contentDisposition != null)
{
// We will post process this as form data
_isFormData.Add(String.IsNullOrEmpty(contentDisposition.FileName));
return new MemoryStream();
}
// If no Content-Disposition header was present.
throw new InvalidOperationException(string.Format("Did not find required '{0}' header field in MIME multipart body part..", "Content-Disposition"));
}
/// <summary>
/// Read the non-file contents as form data.
/// </summary>
/// <returns></returns>
public override async Task ExecutePostProcessingAsync()
{
// Find instances of non-file HttpContents and read them asynchronously
// to get the string content and then add that as form data
for (int index = 0; index < Contents.Count; index++)
{
if (_isFormData[index])
{
HttpContent formContent = Contents[index];
// Extract name from Content-Disposition header. We know from earlier that the header is present.
ContentDispositionHeaderValue contentDisposition = formContent.Headers.ContentDisposition;
string formFieldName = UnquoteToken(contentDisposition.Name) ?? String.Empty;
// Read the contents as string data and add to form data
string formFieldValue = await formContent.ReadAsStringAsync();
FormData.Add(formFieldName, formFieldValue);
}
else
{
_fileContents.Add(Contents[index]);
}
}
}
/// <summary>
/// Remove bounding quotes on a token if present
/// </summary>
/// <param name="token">Token to unquote.</param>
/// <returns>Unquoted token.</returns>
private static string UnquoteToken(string token)
{
if (String.IsNullOrWhiteSpace(token))
{
return token;
}
if (token.StartsWith("\"", StringComparison.Ordinal) && token.EndsWith("\"", StringComparison.Ordinal) && token.Length > 1)
{
return token.Substring(1, token.Length - 2);
}
return token;
}}
然后你可以使用＆＃34; MemoryMultiPartDataStreamProvider＆＃34;在你这样的webapi：
var provider = await Request.Content.ReadAsMultipartAsync<InMemoryMultipartFormDataStreamProvider>(new InMemoryMultipartFormDataStreamProvider());
//access form data
NameValueCollection formData = provider.FormData;
//access files
IList<HttpContent> files = provider.Files;