How can i access connection string form appsetting.json file

Question

I have connection string in appsettings.json file. I need to access that connection string Class library Project. i done the following code to access connection stirng but still i am getting null.

 

startup.cs

public Startup(IConfiguration configuration)
{
Configuration = configuration;
}
public IConfiguration Configuration { get; }
// This method gets called by the runtime. Use this method to add services to the container.
public void ConfigureServices(IServiceCollection services)
{
services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);
services.AddSingleton<IConfiguration>(Configuration);
}

In class library project

protected string ConnectionString;
protected int CommandTimeout;
private IConfiguration _config;
#endregion
public Database(IConfiguration configuration)
{
_config = configuration;
}
#region Constructor
public Database()
{
ConnectionString = _config.GetConnectionString("DefaultConnection");
CommandTimeout = 60;
}

Please give me solution for this ASAP

 

and i gone through the below link

 

https://stackoverflow.com/questions/51304432/how-to-read-connection-string-inside-net-standard-class-library-project-from-as

 

but i could not understand to inject the connection stings