C# .NET 5.0 上传、下载文件

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using Microsoft.AspNetCore.Http; using System; using System.Collections.Generic; using System.IO; using System.Linq; using System.Net;   namespace MEAS.Common {     public class FileHelper     {         //定义一个用于保存静态变量的实例         private static FileHelper instance = null;         //定义一个保证线程同步的标识         private static readonly object locker = new object();         //构造函数为私有，使外界不能创建该类的实例         public static FileHelper Instance         {             get             {                 if (instance == null)                 {                     lock (locker)                     {                         if (instance == null) instance = new FileHelper();                     }                 }                 return instance;             }         }           /// 服务器文件下载         /// </summary>         /// <param name="url">服务器下载文件地址</param>         /// <param name="filepath">文件存放地址，包含文件名</param>         /// <returns></returns>         public string DownLoadFile(string fileUrl, string filepath)         {             try             {                 using (WebClient client = new WebClient())                 {                     client.DownloadFile(fileUrl, filepath);                 }             }             catch (Exception) { throw; }               return filepath;         }           /// <summary>         /// 文件上传         /// </summary>         /// <param name="files">文件集合</param>         /// <returns></returns>         public string UploadFile(List<IFormFile> files)         {             string dir = string.Empty;             string fileName = string.Empty;             string targetPath = string.Empty;               long size = files.Sum(f => f.Length);             foreach (IFormFile formFile in files)             {                 if (formFile.Length > 0)                 {                     var filePath = Path.GetTempFileName();                     dir = AppDomain.CurrentDomain.BaseDirectory + "\\ExcelTemplate\\FileUpload\\";                     fileName = DateTime.Now.ToString("yyyy-MM-dd HH.mm.ss") +" "+ formFile.FileName;                     targetPath = dir + "\\" + fileName; //文件全路径(e:\abc.txt)                     using (var stream = System.IO.File.Create(targetPath))                     {                         formFile.CopyToAsync(stream);                     }                 }             }             return targetPath;         }           /// http下载文件         /// </summary>         /// <param name="url">服务器下载文件地址</param>         /// <param name="path">文件存放地址，包含文件名</param>         /// <returns></returns>         private string HttpDownloadFile(string url, string path)         {             try             {                 // 设置参数                 HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest;                 //发送请求并获取相应回应数据                 HttpWebResponse response = request.GetResponse() as HttpWebResponse;                 //直到request.GetResponse()程序才开始向目标网页发送Post请求                 Stream responseStream = response.GetResponseStream();                 //创建本地文件写入流                 Stream stream = new FileStream(path, FileMode.Create);                 byte[] bArr = new byte[1024];                 int size = responseStream.Read(bArr, 0, (int)bArr.Length);                   while (size > 0)                 {                     stream.Write(bArr, 0, size);                     size = responseStream.Read(bArr, 0, (int)bArr.Length);                 }                   stream.Close();                 responseStream.Close();                 return path;             }             catch (Exception) { throw; }         }         } }

参考：https://docs.microsoft.com/zh-cn/aspnet/core/mvc/models/file-uploads?view=aspnetcore-6.0