使用 Web API 上傳和下載多個檔案

原文作者：Jay Krishna Reddy

原文連結：https://www.c-sharpcorner.com/article/upload-and-download-multiple-files-using-web-api/

翻譯：沙漠盡頭的狼（Google翻譯加持，文中版本使用.NET 6 升級）

---正文開始---

今天，我們將透過一個簡單的過程介紹使用 ASP.NET Core 6.0 Web API 上傳和下載多個檔案。

步驟

首先在 Visual Studio 中建立一個空的 Web API 專案，目標框架選擇 .NET 6.0。

此專案中沒有使用外部套件。

建立一個 Services 資料夾，並在其中建立一個 FileService 類別和 IFileService 介面。

我們在這個 FileService.cs 中使用了三個方法

UploadFile
DownloadFile
SizeConverter

由於我們需要一個資料夾來儲存這些上傳檔案，因此我們在這裡新增了一個參數來將資料夾名稱作為字串傳遞，它將會儲存所有上傳的這些檔案。

FileService.cs

using System.IO.Compression;

namespace FileUploadAndDownload.Services;

public class FileService : IFileService
{
    #region Property

    private readonly IWebHostEnvironment _webHostEnvironment;

    #endregion

    #region Constructor

    public FileService(IWebHostEnvironment webHostEnvironment)
    {
        _webHostEnvironment = webHostEnvironment;
    }

    #endregion

    #region Upload File

    public void UploadFile(List<IFormFile> files, string subDirectory)
    {
        subDirectory = subDirectory ?? string.Empty;
        var target = Path.Combine(_webHostEnvironment.ContentRootPath, subDirectory);

        Directory.CreateDirectory(target);

        files.ForEach(async file =>
        {
            if (file.Length <= 0) return;
            var filePath = Path.Combine(target, file.FileName);
            await using var stream = new FileStream(filePath, FileMode.Create);
            await file.CopyToAsync(stream);
        });
    }

    #endregion

    #region Download File

    public (string fileType, byte[] archiveData, string archiveName) DownloadFiles(string subDirectory)
    {
        var zipName = $"archive-{DateTime.Now:yyyy_MM_dd-HH_mm_ss}.zip";

        var files = Directory.GetFiles(Path.Combine(_webHostEnvironment.ContentRootPath, subDirectory)).ToList();

        using var memoryStream = new MemoryStream();
        using (var archive = new ZipArchive(memoryStream, ZipArchiveMode.Create, true))
        {
            files.ForEach(file =>
            {
                var theFile = archive.CreateEntry(Path.GetFileName(file));
                using var binaryWriter = new BinaryWriter(theFile.Open());
                binaryWriter.Write(File.ReadAllBytes(file));
            });
        }

        return ("application/zip", memoryStream.ToArray(), zipName);
    }

    #endregion

    #region Size Converter

    public string SizeConverter(long bytes)
    {
        var fileSize = new decimal(bytes);
        var kilobyte = new decimal(1024);
        var megabyte = new decimal(1024 * 1024);
        var gigabyte = new decimal(1024 * 1024 * 1024);

        return fileSize switch
        {
            _ when fileSize < kilobyte => "Less then 1KB",
            _ when fileSize < megabyte =>
                $"{Math.Round(fileSize / kilobyte, 0, MidpointRounding.AwayFromZero):##,###.##}KB",
            _ when fileSize < gigabyte =>
                $"{Math.Round(fileSize / megabyte, 2, MidpointRounding.AwayFromZero):##,###.##}MB",
            _ when fileSize >= gigabyte =>
                $"{Math.Round(fileSize / gigabyte, 2, MidpointRounding.AwayFromZero):##,###.##}GB",
            _ => "n/a"
        };
    }

    #endregion
}

SizeConverter 函式用於取得我們上傳檔案到伺服器的實際大小。

IFileService.cs

namespace FileUploadAndDownload.Services;

public interface IFileService
{
    void UploadFile(List<IFormFile> files, string subDirectory);
    (string fileType, byte[] archiveData, string archiveName) DownloadFiles(string subDirectory);
    string SizeConverter(long bytes);
}

讓我們在 Program.cs 檔案中新增這個服務相依性

Program.cs

using FileUploadAndDownload.Services;

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.

builder.Services.AddControllers();
// Learn more about configuring Swagger/OpenAPI at https://aka.ms/aspnetcore/swashbuckle
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();

// 主要是新增下面這行程式碼，注入檔案服務
builder.Services.AddTransient<IFileService, FileService>();

var app = builder.Build();

// Configure the HTTP request pipeline.
if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI();
}

app.UseHttpsRedirection();

app.UseAuthorization();

app.MapControllers();

app.Run();

建立一個 FileController，並在 FileController 中的建構函式注入 IFileService。

FileController.cs

using FileUploadAndDownload.Services;
using Microsoft.AspNetCore.Mvc;
using System.ComponentModel.DataAnnotations;

namespace FileUploadAndDownload.Controllers;

[Route("api/[controller]")]
[ApiController]
public class FileController : ControllerBase
{
    private readonly IFileService _fileService;

    public FileController(IFileService fileService)
    {
        _fileService = fileService;
    }

    [HttpPost(nameof(Upload))]
    public IActionResult Upload([Required] List<IFormFile> formFiles, [Required] string subDirectory)
    {
        try
        {
            _fileService.UploadFile(formFiles, subDirectory);

            return Ok(new { formFiles.Count, Size = _fileService.SizeConverter(formFiles.Sum(f => f.Length)) });
        }
        catch (Exception ex)
        {
            return BadRequest(ex.Message);
        }
    }

    [HttpGet(nameof(Download))]
    public IActionResult Download([Required] string subDirectory)
    {
        try
        {
            var (fileType, archiveData, archiveName) = _fileService.DownloadFiles(subDirectory);

            return File(archiveData, fileType, archiveName);
        }
        catch (Exception ex)
        {
            return BadRequest(ex.Message);
        }
    }
}

我們可以在 swagger 和 postman 中測試我們的 API。