using System.Collections.Generic;


namespace WebApiDownload.Models
{
 public class DemoData
 {
  public static readonly List<List<string Contacts = new List<List<string();
  public static readonly List<string> File1 = new List<string>
  {
   "f_1_test_1@example.com",
   "f_1_test_2@example.com",
   "f_1_test_3@example.com",
   "f_1_test_4@example.com",
   "f_1_test_5@example.com"
  };
  public static readonly List<string> File2 = new List<string>
  {
   "f_2_test_1@example.com",
   "f_2_test_2@example.com",
   "f_2_test_3@example.com",
   "f_2_test_4@example.com",
   "f_2_test_5@example.com"
  };
  public static readonly List<string> File3 = new List<string>
  {
   "f_3_test_1@example.com",
   "f_3_test_2@example.com",
   "f_3_test_3@example.com",
   "f_3_test_4@example.com",
   "f_3_test_5@example.com"
  };

  public static List<List<string GetMultiple
  {
   get
   {
    if (Contacts.Count <= 0)
    {
     Contacts.Add(File1);
     Contacts.Add(File2);
     Contacts.Add(File3);
    }
    return Contacts;
   }
  }
 }
}

using System.Linq;
using System.Net.Http;
using System.Text;
using System.Web.Http;
using Ionic.Zip;
using WebApiDownload.Models;
using System;
using System.IO;
using System.Net;
using System.Net.Http.Headers;
using System.Threading;
using System.Web;


namespace WebApiDownload.Controllers
{
 [RoutePrefix("download")]
 public class DownloadController : ApiController
 {
  [HttpGet, Route("single")]
  public HttpResponseMessage DownloadSingle()
  {
   var response = new HttpResponseMessage();
   //从List集合中获取byte[]
   var bytes = DemoData.File1.Select(x => x + "\n").SelectMany(x => Encoding.UTF8.GetBytes(x)).ToArray();
   try
   {
    var fileName = string.Format("download_single_{0}.txt", DateTime.Now.ToString("yyyyMMddHHmmss"));
    var content = new ByteArrayContent(bytes);
    response.Content = content;
    response.Content.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment")
    {
     FileName = fileName
    };
    response.Content.Headers.ContentType = new MediaTypeHeaderValue("application/octet-stream");
   }
   catch (Exception ex)
   {
    response.StatusCode = HttpStatusCode.InternalServerError;
    response.Content = new StringContent(ex.ToString());
   }
   return response;
  }
  [HttpGet, Route("zip")]
  public HttpResponseMessage DownloadZip()
  {
   var response = new HttpResponseMessage();
   try
   {
    var zipFileName = string.Format("download_compressed_{0}.zip", DateTime.Now.ToString("yyyyMMddHHmmss"));
    var downloadDir = HttpContext.Current.Server.MapPath($"~/downloads/download");
    var archive = $"{downloadDir}/{zipFileName}";
    var temp = HttpContext.Current.Server.MapPath("~/downloads/temp");

    // 清空临时文件夹中的所有临时文件
    Directory.EnumerateFiles(temp).ToList().ForEach(File.Delete);
    ClearDownloadDirectory(downloadDir);
    // 生成新的临时文件
    var counter = 1;
    foreach (var c in DemoData.GetMultiple)
    {
     var fileName = string.Format("each_file_{0}_{1}.txt", counter, DateTime.Now.ToString("yyyyMMddHHmmss"));
     if (c.Count <= 0)
     {
      continue;
     }
     var docPath = string.Format("{0}/{1}", temp, fileName);
     File.WriteAllLines(docPath, c, Encoding.UTF8);
     counter++;
    }
    Thread.Sleep(500);
    using (var zip = new ZipFile())
    {
     // Make zip file
     zip.AddDirectory(temp);
     zip.Save(archive);
    }
    response.Content = new StreamContent(new FileStream(archive, FileMode.Open, FileAccess.Read));
    response.Content.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment") { FileName = zipFileName };
    response.Content.Headers.ContentType = new MediaTypeHeaderValue("application/octet-stream");
   }
   catch (Exception ex)
   {
    response.StatusCode = HttpStatusCode.InternalServerError;
    response.Content = new StringContent(ex.ToString());
   }
   return response;
  }

  private void ClearDownloadDirectory(string directory)
  {
   var files = Directory.GetFiles(directory);
   foreach (var file in files)
   {
    try
    {
     File.Delete(file);
    }
    catch
    {
    }
   }
  }
 }
}