c#異常的處理

public static void DownIMG(String uri, String path)        {            WebResponse response = null;            Stream reader = null;            FileStream writer = null;            try            {                WebRequest request = WebRequest.Create(uri);                request.Timeout = Timeout.Infinite;                response = request.GetResponse();                String type = response.ContentType;                if (type.StartsWith("image/png"))                {                    path += ".png";                }                else                {                    path += ".jpg";                }                reader = response.GetResponseStream();                writer = new FileStream(path, FileMode.OpenOrCreate, FileAccess.Write);                byte[] buff = new byte[512];                int c = 0; //實際讀取的位元組數                while ((c = reader.Read(buff, 0, buff.Length)) > 0)                {                    writer.Write(buff, 0, c);                }            }            catch (Exception e)            {                throw e;//在這裡拋出異常是可以的，finally裡面的代碼依然會執行，會先運行到這裡，再運行finally，再運行調用該方法的try            }            finally            {                if (writer != null)                {                    writer.Close();                    writer.Dispose();                }                if (reader != null)                {                    reader.Close();                    reader.Dispose();                }                if (response != null)                {                    response.Close();                }            }        }