判断是否为有效网址

                方法1
                HttpWebRequest request = (HttpWebRequest)WebRequest.Create(RecordUrl);
                //声明一个HttpWebRequest请求
                request.Timeout = 6000;
                //设置连接超时时间
                request.Headers.Set("Pragma", "no-cache");
                HttpWebResponse response = (HttpWebResponse)request.GetResponse();
                //返回响应
                Stream streamReceive = response.GetResponseStream();
                //获取服务器的文件流
                Encoding encoding = Encoding.GetEncoding("GB2312");
                StreamReader streamReader = new StreamReader(streamReceive, encoding);
                string strResult = streamReader.ReadToEnd();

                方法2
                HttpWebRequest request = (HttpWebRequest)WebRequest.Create(RecordUrl);
                HttpWebResponse response = (HttpWebResponse)request.GetResponse();
                Stream responseStream = response.GetResponseStream();
                if (responseStream == Stream.Null)
                {
                    //得不到文件  
                    Response.Write("<script>alert('无效录音文件或无效录音文件地址!')</script>");
                }

                方法3
                if (System.IO.File.Exists(RecordUrl))
                {
                    Response.Redirect(RecordUrl);
                }
                else
                {
                    Response.Write("<script>alert('无效录音文件或无效录音文件地址!')</script>");
                }

                方法4
                WebRequest myre = WebRequest.Create(RecordUrl);  //验证是否可以连接服务器              
                myre.Timeout = 3000;//设置3秒超时                             
                myre.GetResponse();//请求响应

                Response.Redirect(RecordUrl);