How to change App.config to json config file in .Net Core

Question

my project uses App.config to read config property. Example: ConfigurationManager.AppSettings["MaxThreads"] Do you know of a library which I can use to read config from json. Thanks.

Solution

The ConfigurationManager static class is not generally available in ASP.NET Core. Instead you should use the new ConfigurationBuilder system and strongly typed configuration.

For example, by default, a configuration is built up in your Startup class using something similar to the following:

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

This will load configuration from the appsettings.json file and append the keys the configuration root. If you have an appsettings file like the following:

{
  "Logging": {
    "IncludeScopes": false,
    "LogLevel": {
    "Default": "Debug",
    "System": "Information",
    "Microsoft": "Information"
    }
  },
  "ThreadSettings" : {
     "MaxThreads" : 4
  }
}

Then you can then create a strongly typed ThreadSettings class similar to the following:

public class ThreadSettings
{
    public int MaxThreads {get; set;}
}

Finally, you can bind this strongly typed settings class to your configuration by adding a Configure method to your ConfigureServices method.

using Microsoft.Extensions.Configuration;
public void ConfigureServices(IServiceCollection services)
{
    services.Configure<ThreadSettings>(Configuration.GetSection("ThreadSettings"));
}

You can then inject and access your settings class from anyother place by injecting it into the constructor. For example:

public class MyFatController
{
    private readonly int _maxThreads;
    public MyFatController(ThreadSettings settings)
    {
        maxThreads = settings.MaxThreads;
    }
}

Finally, if you really need access to the underlying configuration you can also inject that in ConfigureServices to make it available in your classes.

public void ConfigureServices(IServiceCollection services)
{
    services.AddSingleton(Configuration);
}

You can read more about configuration on the docs or on various blogs