ASP.NET Core | Startup class

Startup class is responsible for configuration related things as below.

• It configures the services which are required by the app.
• It defines the app's request handling pipeline as a series of middleware components.
• But You can emit this class and Program.cs file contains all startup code.

// Startup class example
public class Startup 
{
    public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }

    public IConfiguration Configuration { get; }

    public void ConfigureServices(IServiceCollection services)
    {
        services.AddRazorPages();
    }

    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }
        else
        {
            app.UseExceptionHandler("/Error");
            app.UseHsts();
        }

        app.UseHttpsRedirection();
        // other middleware components
    }
}

Startup class is specified inside the 'CreateHostBuilder' method when the host is created.
Multiple Startup classes can also be defined for different environments, At run time appropriate startup classes are used.