How to Create and Download File with Ajax in ASP.NET MVC

Introduction

When you use the Ajax call in ASP.NET MVC, you can just return a JSON object but not a file. If you want to do that, you need to create and save the file in server and return its path to Ajax.

After that, you can call a redirect link for downloading the file, because this is a temp file, so you should need to delete it after download.

Using the Code

The below demo code is just for creating and downloading an Excel file:

1. Create an Action for generating the Excel:
   C#

   [HttpPost]
   public JsonResult ExportExcel()
   {
       DataTable dt = DataService.GetData();
       var fileName = "Excel_" + DateTime.Now.ToString("yyyyMMddHHmm") + ".xls";
       
       //save the file to server temp folder
       string fullPath = Path.Combine(Server.MapPath("~/temp"), fileName);
   
       using (var exportData = new MemoryStream())
       {
           //I don't show the detail how to create the Excel, this is not the point of this article,
           //I just use the NPOI for Excel handler
           Utility.WriteDataTableToExcel(dt, ".xls", exportData);
   
           FileStream file = new FileStream(fullPath, FileMode.Create, FileAccess.Write);
           exportData.WriteTo(file);
           file.Close();
       }
   
       var errorMessage = "you can return the errors in here!";
   
       //return the Excel file name
       return Json(new { fileName = fileName, errorMessage = "" });
   }

2. Create the download Action:
   C#

   [HttpGet]
   [DeleteFileAttribute] //Action Filter, it will auto delete the file after download, 
                         //I will explain it later
   public ActionResult Download(string file)
   {
       //get the temp folder and file path in server
       string fullPath = Path.Combine(Server.MapPath("~/temp"), file);
   
       //return the file for download, this is an Excel 
       //so I set the file content type to "application/vnd.ms-excel"
       return File(fullPath, "application/vnd.ms-excel", file);
   }

3. We need to auto delete the file after download, so we need to create an Action Filter:
   C#

   public class DeleteFileAttribute : ActionFilterAttribute
   {
       public override void OnResultExecuted(ResultExecutedContext filterContext)
       {
           filterContext.HttpContext.Response.Flush();
   
           //convert the current filter context to file and get the file path
           string filePath = (filterContext.Result as FilePathResult).FileName;
           
           //delete the file after download
           System.IO.File.Delete(filePath);
       }
   }

4. Use the Ajax call in frontend:
   JavaScript

   //I use blockUI for loading...
   $.blockUI({ message: '<h3>Please wait a moment...</h3>' });    
   $.ajax({
       type: "POST",
       url: '@Url.Action("ExportExcel","YourController")', //call your controller and action
       contentType: "application/json; charset=utf-8",
       dataType: "json",
   }).done(function (data) {
       //console.log(data.result);
       $.unblockUI();
   
       //get the file name for download
       if (data.fileName != "") {
           //use window.location.href for redirect to download action for download the file
           window.location.href = "@Url.RouteUrl(new 
               { Controller = "YourController", Action = "Download"})/?file=" + data.fileName;
       }
   });