C# 下载PDF文件（http与ftp）

1.下载http模式的pdf文件（以ASP.NET为例，将PDF存在项目的目录下，可以通过http直接打开项目下的pdf文件）

 #region 调用本地文件使用返回pdfbyte数组

        /// <summary>
        /// 调用本地文件使用返回pdfbyte数组
        /// </summary>
        /// <param name="srcPdfFile">‘D:in2434341555551.pdf’</param>
        /// <returns></returns>

        public static byte[] GetSignaturePDFByte(string srcPdfFile)
        {
            using (FileStream fsRead = new FileStream(srcPdfFile, FileMode.Open, FileAccess.Read, FileShare.Read))
            {
                int fsLen = (int)fsRead.Length;
                byte[] hebyte = new byte[fsLen];
                fsRead.Read(hebyte, 0, hebyte.Length);
                return hebyte;
            }
        }

        #endregion 调用本地文件使用返回pdfbyte数组

        #region 从网站上下载pdf，转化为字节流


        /// <summary>
        /// 从网站上下载pdf，转化为字节流
        /// </summary>
        /// <param name="srcPdfFile">文件地址：'https://******/group2/M00/00/04/wKj-mlpcoZ2IUbK5AACrpaV6k98AAAB6gAAAAAAAKu9562.pdf'</param>

        /// <returns></returns>
        public static Byte[] GetByteByRemoteURL(string srcPdfFile)
        {
            byte[] arraryByte;
            HttpWebRequest req = (HttpWebRequest)HttpWebRequest.Create(srcPdfFile);
            req.Method = "GET";
            using (WebResponse wr = req.GetResponse())
            {
                StreamReader responseStream = new StreamReader(wr.GetResponseStream(), Encoding.UTF8);
                int length = (int)wr.ContentLength;
                byte[] bs = new byte[length];

                HttpWebResponse response = wr as HttpWebResponse;
                Stream stream = response.GetResponseStream();

                //读取到内存
                MemoryStream stmMemory = new MemoryStream();
                byte[] buffer1 = new byte[length];
                int i;
                //将字节逐个放入到Byte 中
                while ((i = stream.Read(buffer1, 0, buffer1.Length)) > 0)
                {
                    stmMemory.Write(buffer1, 0, i);
                }
                arraryByte = stmMemory.ToArray();
                stmMemory.Close();
            }
            return arraryByte;
        }

        #endregion 从网站上下载pdf，转化为字节流

        #region 从网站上下载文件，保存到其他路径

        /// <summary>
        /// 从网站上下载文件，保存到其他路径
        /// </summary>
        /// <param name="pdfFile">文件地址</param>
        /// <param name="saveLoadFile">保存文件路径：D:12221.pdf</param>
        /// <returns></returns>
        public string SaveRemoteFile( string saveLoadFile , string pdfFile)
        {
            //bool flag = false;
            var f = saveLoadFile + Guid.NewGuid().ToString("D") + ".pdf";
            Uri downUri = new Uri(pdfFile);
            //建立一个ＷＥＢ请求，返回HttpWebRequest对象
            HttpWebRequest hwr = (HttpWebRequest)WebRequest.Create(downUri);
            //流对象使用完后自动关闭
            using (Stream stream = hwr.GetResponse().GetResponseStream())
            {
                //文件流，流信息读到文件流中，读完关闭
                using (FileStream fs = File.Create(f))
                {
                    //建立字节组，并设置它的大小是多少字节
                    byte[] bytes = new byte[102400];
                    int n = 1;
                    while (n > 0)
                    {
                        //一次从流中读多少字节，并把值赋给Ｎ，当读完后，Ｎ为０,并退出循环
                        n = stream.Read(bytes, 0, 10240);
                        fs.Write(bytes, 0, n);　//将指定字节的流信息写入文件流中
                    }
                }
            }

            //return flag;
            //return _outPath + saveLoadFile;
            return f;
        }

        #endregion 从网站上下载文件，保存到其他路径

2.ftp模式的pdf文件

  /// <summary>
        /// 下载FTP文件。
        /// </summary>
        /// <param name="offsetPath">相对路径</param>
        /// <param name="fileName">文件名称</param>
        /// <returns>下载结果，本地文件路径</returns>
        public string DownLoad(string offsetPath,string fileName)
        {
            try
            {
                FtpWebRequest ftpWeb = (FtpWebRequest)WebRequest.Create(_ftpRootPath + offsetPath + fileName);
                ftpWeb.Method = WebRequestMethods.Ftp.DownloadFile;
                ftpWeb.UseBinary = true;
                var resp = ftpWeb.GetResponse();
                using (FileStream fs = new FileStream(_outPath + fileName, FileMode.Create))
                {
                    using (var s = resp.GetResponseStream())
                    {
                        if (s == null) { return "文件不存在!"; }

                        int readCout = 0;
                        byte[] bytes = new byte[1024];
                        readCout = s.Read(bytes, 0, 1024);
                        while (readCout > 0)
                        {
                            fs.Write(bytes, 0, readCout);
                            readCout = s.Read(bytes, 0, 1024);
                        }
                    }
                }
                resp.Close();
                return _outPath + fileName;
            }
            catch (Exception e)
            {
                return e.Message;
            }
            
        }

        /// <summary>
        /// 判断文件是否存在
        /// </summary>
        /// <param name="offsetPath"></param>
        /// <param name="fileName"></param>
        /// <returns></returns>
        public bool FileExists(string offsetPath, string fileName)
        {
            try
            {
                FtpWebRequest ftpWeb = (FtpWebRequest)WebRequest.Create(_ftpRootPath + offsetPath + fileName);
                ftpWeb.Method = WebRequestMethods.Ftp.DownloadFile;
                ftpWeb.UseBinary = true;
                var resp = (FtpWebResponse)ftpWeb.GetResponse();
                resp.Close();
                return true;
            }
            catch (Exception)
            {
                return false;
            }
        }

        /// <summary>
        /// 获取目录下所有文件
        /// </summary>
        /// <returns></returns>
        public string[] Files(string offsetPath)
        {
            try
            {
                FtpWebRequest ftpWeb = (FtpWebRequest)WebRequest.Create(_ftpRootPath + offsetPath);
                ftpWeb.Method = WebRequestMethods.Ftp.ListDirectory;
                Stream stream = ftpWeb.GetResponse().GetResponseStream();
                if (stream == null)
                {
                    return null;
                }
                List<string> fileList = new List<string>();
                using (StreamReader sr = new StreamReader(stream))
                {
                    StringBuilder sb = new StringBuilder();
                    do
                    {
                        sb.Append(sr.ReadLine());
                        if (sb.Length > 0)
                        {
                            fileList.Add(sb.ToString());
                            sb.Clear();
                        }
                        else
                        {
                            break;
                        }
                    } while (true);
                }
                return fileList.ToArray();
            }
            catch (Exception)
            {
                 return null;
            }
        }