How to read AppSettings values from a .json file in ASP.NET Core

Question

I have set up my AppSettings data in file appsettings/Config .json like this:

{   "AppSettings": {         "token": "1234"     } } 

I have searched online on how to read AppSettings values from .json file, but I could not get anything useful.

I tried:

var configuration = new Configuration(); var appSettings = configuration.Get("AppSettings"); // null var token = configuration.Get("token"); // null 

I know with ASP.NET 4.0 you can do this:

System.Configuration.ConfigurationManager.AppSettings["token"]; 

But how do I do this in ASP.NET Core?

Answer 1

This has had a few twists and turns. I've modified this answer to be up to date with ASP.NET Core 2.0 (as of 26/02/2018).

This is mostly taken from the official documentation:

To work with settings in your ASP.NET application, it is recommended that you only instantiate a Configuration in your application’s Startup class. Then, use the Options pattern to access individual settings. Let's say we have an appsettings.json file that looks like this:

{   "MyConfig": {    "ApplicationName": "MyApp",    "Version": "1.0.0"    }  } 

And we have a POCO object representing the configuration:

public class MyConfig {     public string ApplicationName { get; set; }     public int Version { get; set; } } 

Now we build the configuration in Startup.cs:

public class Startup  {     public IConfigurationRoot Configuration { get; set; }      public Startup(IHostingEnvironment env)     {         var builder = new ConfigurationBuilder()             .SetBasePath(env.ContentRootPath)             .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true);          Configuration = builder.Build();     } } 

Note that appsettings.json will be registered by default in .NET Core 2.0. We can also register an appsettings.{Environment}.json config file per environment if needed.

If we want to inject our configuration to our controllers, we'll need to register it with the runtime. We do so via Startup.ConfigureServices:

public void ConfigureServices(IServiceCollection services) {     services.AddMvc();      // Add functionality to inject IOptions<T>     services.AddOptions();      // Add our Config object so it can be injected     services.Configure<MyConfig>(Configuration.GetSection("MyConfig")); } 

And we inject it like this:

public class HomeController : Controller {     private readonly IOptions<MyConfig> config;      public HomeController(IOptions<MyConfig> config)     {         this.config = config;     }      // GET: /<controller>/     public IActionResult Index() => View(config.Value); } 

The full Startup class:

public class Startup  {     public IConfigurationRoot Configuration { get; set; }      public Startup(IHostingEnvironment env)     {         var builder = new ConfigurationBuilder()             .SetBasePath(env.ContentRootPath)             .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true);          Configuration = builder.Build();     }      public void ConfigureServices(IServiceCollection services)     {         services.AddMvc();          // Add functionality to inject IOptions<T>         services.AddOptions();          // Add our Config object so it can be injected         services.Configure<MyConfig>(Configuration.GetSection("MyConfig"));     } }