首先给出正确和错误做法，然后对比这两种做法。

1正确的做法

public class AvaterController : BaseApiController
{
	[HttpPost]
 public async Task<IHttpActionResult> UploadAvater(int userId)
 {
 AvatarBLL pictureBLL = new AvatarBLL(this.Request);
 await pictureBLL.UploadAvatar(userId);
 return Ok();
	 }
	 
	//其他Action
}
 
public class AvatarBLL
{
	private HttpRequestMessage HttpRequestMessage;
	public AvatarBLL(HttpRequestMessage httpRequestMessage)
	{
	 this.HttpRequestMessage = httpRequestMessage;
	}
	public async Task UploadAvatar(int userId)
 {
 if (!HttpRequestMessage.Content.IsMimeMultipartContent("form-data"))
 {
 //抛异常
 }
	//获得客户端传递到服务器的数据
 List<byte> list = new List<byte>();
 await HttpRequestMessage.Content.ReadAsMultipartAsync().ContinueWith(multipartContent => 
 {
 if (multipartContent.IsFaulted || multipartContent.IsCanceled)
 {
 //抛异常
 }
 
 foreach (var content in multipartContent.Result.Contents)
 {
 var b = content.ReadAsByteArrayAsync().Result;
 list.AddRange(b);
 }
	 });
	 
	//其他部分（将数据存入Mongodb以及其他的业务逻辑）
	}
}

2错误的做法

public class AvaterController : BaseApiController
{
	[HttpPost]
 public IHttpActionResult UploadAvater(int userId)
 {
 AvatarBLL pictureBLL = new AvatarBLL(this.Request);
 pictureBLL.UploadAvatar(userId);
 return Ok();
	 }
	 
	//其他Action
}
public class AvatarBLL
{
	private HttpRequestMessage HttpRequestMessage;
	public AvatarBLL(HttpRequestMessage httpRequestMessage)
	{
	 this.HttpRequestMessage = httpRequestMessage;
	}
	public void UploadAvatar(int userId)
 {
 if (!HttpRequestMessage.Content.IsMimeMultipartContent("form-data"))
 {
 //抛异常
 }
	//获得客户端传递到服务器的数据
 List<byte> list = new List<byte>();
 MemoryStream ms = new MemoryStream();
 try
 {
 MultipartMemoryStreamProvider mmsp = new MultipartMemoryStreamProvider();
 var task = 						 HttpRequestMessage.Content.ReadAsMultipartAsync<MultipartMemoryStreamProvider>(mmsp, 100000);
 task.Wait();
 var contents = task.Result.Contents;
 
 foreach (var c in contents)
 {
 var b = c.ReadAsByteArrayAsync();
 b.Wait();
 list.AddRange(b.Result);
 }
 }
 catch (AggregateException ex)
 	 { }
 
	//其他部分（将数据存入Mongodb以及其他的业务逻辑）
	}
}

3 错误现象：

采用第二种方式，如果客户端上传到服务的数据量（调用UploadAvater上传的数据）小于服务端设置的缓冲区的大小，那么可正常上传文件，如果大于服务端设置的缓冲区的大小，则无法正常上传，调试服务端代码，当执行到task.Wait();这行语句时，客户端一直等待，直到客户端调用超时，永远也无法返回调用结果，发生了死锁！！！使用HttpRequestMessage.Content.ReadAsMultipartAsync<MultipartMemoryStreamProvider>(mmsp, 1000);设置缓冲区大小为1000bit。这个方法有几个重载的方法，其中一个是不显示设置缓冲区大小，那么缓冲区大小为默认的。