How to get absolute path in ASP.Net Core alternative way for Server.MapPath

.NET Core 3.0

Var 1:

string path = System.IO.Directory.GetCurrentDirectory();

Var 2:

string path = AppDomain.CurrentDomain.BaseDirectory.Substring(0, AppDomain.CurrentDomain.BaseDirectory.IndexOf("\\bin"));

* Hack * Not recommended, but FYI you can get an absolute path from a relative path with var abs = Path.GetFullPath("~/Content/Images/Sample.PNG").Replace("~\\","");

Prefer the DI/Service approaches above, but if you are in a non-DI situation (e.g., a class instantiated with Activator) this will work.

.Net Core 3

For example I want to locate ~/wwwroot/CSS

public class YourController : Controller 
{
    private readonly IWebHostEnvironment _webHostEnvironment;

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

    public IActionResult Index()
    {
        string webRootPath = _webHostEnvironment.WebRootPath;
        string contentRootPath = _webHostEnvironment.ContentRootPath;

        string path ="";
        path = Path.Combine(webRootPath , "CSS");
        //or path = Path.Combine(contentRootPath , "wwwroot" ,"CSS" );
        return View();
    }
}

Some Tricks

Also if you don't have a controller or service,follow last Part and register it's class as a singleton. Then, in Startup.ConfigureServices:

services.AddSingleton<your_class_Name>();

Finally, inject your_class_Name where you need it.

.Net Core 2

For example I want to locate ~/wwwroot/CSS

public class YourController : Controller
{
    private readonly IHostingEnvironment _HostEnvironment;

    public YourController (IHostingEnvironment HostEnvironment)
    {
        _HostEnvironment= HostEnvironment;
    }

    public ActionResult Index()
    {
        string webRootPath = _HostEnvironment.WebRootPath;
        string contentRootPath = _HostEnvironment.ContentRootPath;

        string path ="";
        path = Path.Combine(webRootPath , "CSS");
        //or path = Path.Combine(contentRootPath , "wwwroot" ,"CSS" );
        return View();
    }
}

MoreDetails

Thanks to @NKosi but IHostingEnvironment is obsoleted in MVC core 3!!

according to this :

Obsolete types (warning):

Microsoft.Extensions.Hosting.IHostingEnvironment
Microsoft.AspNetCore.Hosting.IHostingEnvironment
Microsoft.Extensions.Hosting.IApplicationLifetime
Microsoft.AspNetCore.Hosting.IApplicationLifetime
Microsoft.Extensions.Hosting.EnvironmentName
Microsoft.AspNetCore.Hosting.EnvironmentName

New types:

Microsoft.Extensions.Hosting.IHostEnvironment
Microsoft.AspNetCore.Hosting.IWebHostEnvironment : IHostEnvironment
Microsoft.Extensions.Hosting.IHostApplicationLifetime
Microsoft.Extensions.Hosting.Environments 

So you must use IWebHostEnvironment instead of IHostingEnvironment.

A better solution is to use the IFileProvider.GetFileInfo() method.

    public IActionResult ResizeCat([FromServices] IFileProvider fileProvider)
    {
        // get absolute path (equivalent to MapPath)
        string absolutePath = fileProvider.GetFileInfo("/assets/images/cat.jpg").PhysicalPath;  
        ... 
    }

You must register IFileProvider like this to be able to access it through DI:

    // This method gets called by the runtime. Use this method to add services to the container.
    public void ConfigureServices(IServiceCollection services)
    {
        // Add framework services.
        services.AddMvc();

        var physicalProvider = _hostingEnvironment.ContentRootFileProvider;
        var embeddedProvider = new EmbeddedFileProvider(Assembly.GetEntryAssembly());
        var compositeProvider = new CompositeFileProvider(physicalProvider, embeddedProvider);

        // choose one provider to use for the app and register it
        //services.AddSingleton<IFileProvider>(physicalProvider);
        //services.AddSingleton<IFileProvider>(embeddedProvider);
        services.AddSingleton<IFileProvider>(compositeProvider);
    }

As you can see this logic (for where a file comes from) can get quite complex, but your code won't break if it changes.

You can create a custom IFileProvider with new PhysicalFileProvider(root) if you have some special logic. I had a situation where I want to load an image in middleware, and resize or crop it. But it's an Angular project so the path is different for a deployed app. The middleware I wrote takes IFileProvider from startup.cs and then I could just use GetFileInfo() like I would have used MapPath in the past.

If you are accessing it from Startup/Program routines, it is available under WebApplicationBuilder.Environment e.g.

 public static void Main(string[] args)
 {
        var builder = WebApplication.CreateBuilder(args);

        var webRootPath = builder.Environment.WebRootPath;

        ConfigureServices(builder);

        ...
 }