C# Ftp方式下载文件（无用户认证方式,支持断点续传）-优快云博客

本文介绍了一种基于C#的FTP断点续传下载功能的实现方法。通过获取远程文件大小并比较本地文件大小来判断是否需要进行续传操作。代码详细展示了如何设置FTP请求参数、读取远程文件内容及更新本地文件。

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类代码：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Net;
using System.IO; 

namespace ConsoleTest
{
    class FtpDlder
    {
        public void download(String url, String localFile)
        {
            FtpWebRequest remoteFileLenReq; // 此请求是为了获取远程文件长度
            FtpWebRequest remoteFileReadReq;// 此请求是为了读取文件
            Stream readStream = null;       // 读取流
            FileStream writeStream = null;  // 写本地文件流

            try
            {
                writeStream = new FileStream(localFile, FileMode.Append);
                long startPosition=writeStream.Length;// 读出本地文件已有长度

                // 下面代码目的是取远程文件长度
                remoteFileLenReq = (FtpWebRequest)FtpWebRequest.Create(url);
                remoteFileLenReq.UseBinary = true;
                remoteFileLenReq.ContentOffset = 0;
                remoteFileLenReq.Method = WebRequestMethods.Ftp.GetFileSize;
                FtpWebResponse rsp = (FtpWebResponse)remoteFileLenReq.GetResponse();
                long totalByte = rsp.ContentLength;
                rsp.Close();

                if (startPosition >= totalByte)
                {
                    System.Console.WriteLine("本地文件长度" + startPosition + "已经大于等于远程文件长度" + totalByte);
                    writeStream.Close();

                    return;
                }

                // 初始化读取远程文件请求
                remoteFileReadReq = (FtpWebRequest)FtpWebRequest.Create(url);
                remoteFileReadReq.UseBinary = true;
                remoteFileReadReq.KeepAlive = false;
                remoteFileReadReq.ContentOffset = startPosition;
                remoteFileReadReq.Method = WebRequestMethods.Ftp.DownloadFile;
                FtpWebResponse response = (FtpWebResponse)remoteFileReadReq.GetResponse();
                readStream = response.GetResponseStream();

                long downloadedByte = startPosition;
                int bufferSize = 512;
                byte[] btArray = new byte[bufferSize];
                int contentSize = readStream.Read(btArray, 0, btArray.Length);

                while (contentSize > 0)
                {
                    downloadedByte += contentSize;
                    int percent = (int)(downloadedByte * 100 / totalByte);
                    System.Console.WriteLine("percent=" + percent + "%");

                    writeStream.Write(btArray, 0, contentSize);
                    contentSize = readStream.Read(btArray, 0, btArray.Length);
                }
                readStream.Close();
                writeStream.Close();
                response.Close();
                return;
            }
            catch (Exception)
            {
                return;

            }
            finally
            {
                if (readStream != null)
                {
                    readStream.Close();
                }
                if (writeStream != null)
                {
                    writeStream.Close();
                }
            }  
        }
    }
}

使用示例：

        static void Main(string[] args)
        {
            // Ftp下载测试，无用户身份测试
            FtpDlder fd = new FtpDlder();
            fd.download("ftp://192.168.0.109/jump.jpg", "c:\\asd\\jump.jpg");
        }