ASP.NET Core 下载文件

本文使用 ASP .NET Core，适用于 .NET Core 3.1、.NET 5、.NET 6和.NET 8。

另请参阅：
如何在将文件发送到浏览器后自动删除该文件。
如何将文件从浏览器上传到服务器。
如何在 ASP.NET Core 应用程序中从 URL/URI 下载文件。
如果使用.NET Framework，请参阅如何使用 .NET Framework 下载文件。

当返回文件时，FileResult方法返回类型可以像一样使用IActionResult。

下载文件最快捷、最简单的方法是使用虚拟路径指定文件名。MIME-Type/Content-Type 也是必需的。有效值不限于“image/jpeg”、“image/gif”、“image/png”、“text/plain”、“application/x-zip-compressed”和“application/json”。

System.Net.Mime.MediaTypeNames.Application.Json

using Microsoft.AspNetCore.Mvc;

下载的另一种方法是附加内容处置标头。别担心，ASP.NET Core 使用 MVC 5 使它比过去更简单。

using Microsoft.AspNetCore.Mvc;

namespace Website.Controllers
{
   public class HomeController : Controller
   {
       public IActionResult Index()
       {
           return View();
       }
       public FileResult DownloadFile() // can also be IActionResult
       {
           // this will append the content-disposition header and download the file to the computer as "downloaded_file.txt"
           return File("/test.txt", "text/plain", "downloaded_file.txt");
       }
   }
}

另一种方法是使用Stream。此示例中的代码量大大增加，但其功能与示例 1 相同。

using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Mvc;
using System.IO;

namespace Website.Controllers
{
   public class HomeController : Controller
   {
       private IWebHostEnvironment env { get; }

public HomeController(IWebHostEnvironment env) => this.env = env;

       public IActionResult Index()
       {
           return View();
       }
       public FileResult DownloadFile() // can also be IActionResult
       {
           string file = System.IO.Path.Combine(env.WebRootPath, "test.txt");
           return File(new FileStream(file, FileMode.Open), "text/plain"); // could have specified the downloaded file name again here
       }
   }
}

另一种方法是从文件中读取字节，但这需要更多的内存并且在处理文件时效率不高。

using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Mvc;

namespace Website.Controllers
{
   public class HomeController : Controller
   {
       private IWebHostEnvironment env { get; }

public HomeController(IWebHostEnvironment env) => this.env = env;

       public IActionResult Index()
       {
           return View();
       }
       public FileResult DownloadFile() // can also be IActionResult
       {
           string file = System.IO.Path.Combine(env.WebRootPath, "test.txt");
           byte[] data = System.IO.File.ReadAllBytes(file);
           return File(data, "text/plain"); // could have specified the downloaded file name again here
       }
   }
}

以下是下载 zip 文件的示例。请注意，FileStream fs已关闭，zip.Close();因此必须重新打开。

using ICSharpCode.SharpZipLib.Zip;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Mvc;

namespace Website.Controllers
{
   public class HomeController : Controller
   {
       private IWebHostEnvironment env { get; }

public HomeController(IWebHostEnvironment env) => this.env = env;

       public IActionResult Index()
       {
           return View();
       }
       public FileResult DownloadFile() // can also be IActionResult
       {
           string file = System.IO.Path.Combine(env.WebRootPath, "temp.zip"); // in production, would probably want to use a GUID as the file name so that it is unique
           System.IO.FileStream fs = System.IO.File.Create(file);
           using (ZipOutputStream zip = new ZipOutputStream(fs))
           {
               byte[] data;
               ZipEntry entry;
               entry = new ZipEntry("downloaded_file.txt");
               entry.DateTime = System.DateTime.Now;
               zip.PutNextEntry(entry);
               data = System.IO.File.ReadAllBytes(System.IO.Path.Combine(env.WebRootPath, "test.txt"));
               zip.Write(data, 0, data.Length);
               zip.Finish();
               zip.Close();
               fs.Dispose(); // must dispose of it
               fs = System.IO.File.OpenRead(file); // must re-open the zip file
               data = new byte[fs.Length];
               fs.Read(data, 0, data.Length);
               fs.Close();
               System.IO.File.Delete(file);
               return File(data, "application/x-zip-compressed", "downloaded_file.zip"); // recommend specifying the download file name for zips
           }
       }
   }
}

这也同样有效（用于System.Net.Mime.MediaTypeNamesContent-Type）：

using ICSharpCode.SharpZipLib.Zip;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Mvc;

namespace Website.Controllers
{
   public class HomeController : Controller
   {
       private IWebHostEnvironment env { get; }

public HomeController(IWebHostEnvironment env) => this.env = env;

       public IActionResult Index()
       {
           return View();
       }
       public FileResult DownloadFile() // can also be IActionResult
       {
           string file = System.IO.Path.Combine(env.WebRootPath, "temp.zip"); // in production, would probably want to use a GUID as the file name so that it is unique
           System.IO.FileStream fs = System.IO.File.Create(file);
           using (ZipOutputStream zip = new ZipOutputStream(fs))
           {
               byte[] data;
               ZipEntry entry;
               entry = new ZipEntry("downloaded_file.txt");
               entry.DateTime = System.DateTime.Now;
               zip.PutNextEntry(entry);
               data = System.IO.File.ReadAllBytes(System.IO.Path.Combine(env.WebRootPath, "test.txt"));
               zip.Write(data, 0, data.Length);
               zip.Finish();
               zip.Close();
               fs.Dispose(); // must dispose of it
               fs = System.IO.File.OpenRead(file); // must re-open the zip file
               data = new byte[fs.Length];
               fs.Read(data, 0, data.Length);
               fs.Close();
               System.IO.File.Delete(file);
               return File(data, System.Net.Mime.MediaTypeNames.Application.Zip, "downloaded_file.zip"); // ZIP
           }
       }
   }
}

就像这样：

using ICSharpCode.SharpZipLib.Zip;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Mvc;

namespace Website.Controllers
{
   public class HomeController : Controller
   {
       private IWebHostEnvironment env { get; }

public HomeController(IWebHostEnvironment env) => this.env = env;

       public IActionResult Index()
       {
           return View();
       }
       public FileResult DownloadFile() // can also be IActionResult
       {
           string file = System.IO.Path.Combine(env.WebRootPath, "temp.zip"); // in production, would probably want to use a GUID as the file name so that it is unique
           System.IO.FileStream fs = System.IO.File.Create(file);
           using (ZipOutputStream zip = new ZipOutputStream(fs))
           {
               byte[] data;
               ZipEntry entry;
               entry = new ZipEntry("downloaded_file.txt");
               entry.DateTime = System.DateTime.Now;
               zip.PutNextEntry(entry);
               data = System.IO.File.ReadAllBytes(System.IO.Path.Combine(env.WebRootPath, "test.txt"));
               zip.Write(data, 0, data.Length);
               zip.Finish();
               zip.Close();
               fs.Dispose(); // must dispose of it
               fs = System.IO.File.OpenRead(file); // must re-open the zip file
               data = new byte[fs.Length];
               fs.Read(data, 0, data.Length);
               fs.Close();
               System.IO.File.Delete(file);
               return File(data, System.Net.Mime.MediaTypeNames.Application.Octet, "downloaded_file.zip"); // OCTET
           }
       }
   }
}

或者使用System.IO.Compression创建zip 档案：

using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Mvc;
using System.IO.Compression;
using System.Text;

namespace Website.Controllers
{
   public class ZipController : Controller
   {
       public ZipController() {}

       public IActionResult Index()
       {
           return View();
       }
       public async Task<FileResult> DownloadFile() // can also be IActionResult
       {
           using (MemoryStream zipoutput = new MemoryStream())
           {
               using (ZipArchive archive = new ZipArchive(zipoutput, ZipArchiveMode.Create, false))
               {
                   ZipArchiveEntry entry = archive.CreateEntry("test.txt", CompressionLevel.Optimal);
                   using (var entryStream = entry.Open())
                   {
                       byte[] buffer = Encoding.UTF8.GetBytes("This is a test!!!");
                       using (var ms = new MemoryStream(buffer))
                       {
                           await ms.CopyToAsync(entryStream);
                       }
                   }
                   entry = archive.CreateEntry("test2.txt", CompressionLevel.Optimal);
                   using (var entryStream = entry.Open())
                   {
                       byte[] buffer = Encoding.UTF8.GetBytes("This is another test!!!");
                       using (var ms = new MemoryStream(buffer))
                       {
                           await ms.CopyToAsync(entryStream);
                       }
                   }
               }
               return File(zipoutput.ToArray(), "application/x-zip-compressed", "test-txt-files.zip");
           }
       }
   }
}

或者从中读取简单字节MemoryStream：

using Microsoft.AspNetCore.Mvc;

namespace Website.Controllers
{
   public class HomeController : Controller
   {
       public IActionResult Index()
       {
           return View();
       }
       public FileResult DownloadFile() // can also be IActionResult
       {
           using (var ms = new System.IO.MemoryStream())
           {
               ms.WriteByte((byte)'a');
               ms.WriteByte((byte)'b');
               ms.WriteByte((byte)'c');
               byte[] data = ms.ToArray();
               return File(data, "text/plain", "downloaded_file.txt");
           }
       }
   }
}