用dotnet的类库FtpWebRequest 开发应用已经不是什么新鲜话题。
在这里说的是一个怪问题，小组总共四人，两人下载文件正常，两人总是从缓存中下载文件（即便文件已经更新）。显然这是本地计算机的缓存策略在作怪，可是大家的开发环境基本一致为什么会出现不同的结果呢？
查阅了一下msdn：
Only content received using the DownloadFile command is cached.
The following table describes the effects of FTP caching policies on FtpWebRequest.
| Policy | Effect |
|---|---|
| Returns the cached resource if the resource is fresh, the content length is accurate, and the expiration, modification, and content length attributes are present. | |
| Returns the resource from the server. | |
| Returns the cached resource if the content length is present and matches the entry size; otherwise, throws a WebException. | |
| Returns the cached resource if the content length is provided and matches the entry size; otherwise, the resource is downloaded from the server and is returned to the caller. | |
| Returns the cached resource if the timestamp of the cached resource is the same as the time stamp of the resource on the server; otherwise, the resource is downloaded from the server, stored in the cache, and returned to the caller. | |
| Downloads the resource from the server, stores it in the cache, and returns the resource to the caller. | |
| If a cached resource exists, it is deleted. The resource is downloaded from the server and is returned to the caller. |
在ftp操作之前强制设置了一下：
FtpWebRequest.DefaultCachePolicy = new System.Net.Cache.RequestCachePolicy(System.Net.Cache.RequestCacheLevel.Reload);
一切OK了。估计是dotnet framework配置文件不一样导致了这个问题，配置文件是什么样的，还得继续研究....