.Netcore 2.2 和3.1 的模板

WebHost.CreateDefaultBuilder(args)
.UseStartup<Startup>();

  public static IWebHostBuilder CreateDefaultBuilder(string[] args)
  {

　　var builder = new WebHostBuilder();
　　　　....
　　return builder;
}

Host.CreateDefaultBuilder(args)
.ConfigureWebHostDefaults(webBuilder =>
{
webBuilder.UseStartup<Startup>();
});

public static IHostBuilder ConfigureWebHost(this IHostBuilder builder, Action<IWebHostBuilder> configure)
{
var webhostBuilder = new GenericWebHostBuilder(builder);
configure(webhostBuilder);
builder.ConfigureServices((context, services) => services.AddHostedService<GenericWebHostService>());
return builder;
}