.NET Core中的泛型主机实现

主机 Host

一、泛型主机

泛型主机主要基于 HostBuilder 类

1. 对于普通的泛型主机，它的实现方式是：

class Program
{
    static async Task Main(string[] args)
    {
        await CreateHostBuilder(args).Build().RunAsync();
    }
    public static IHostBuilder CreateHostBuilder(string[] args) =>
        Host.CreateDefaultBuilder(args)
        // .ConfigureHostConfiguration(configHost =>
        // {
        //     configHost.SetBasePath(Directory.GetCurrentDirectory());
        //     configHost.AddJsonFile("hostsettings.json", optional: true);
        //     configHost.AddEnvironmentVariables(prefix: "DOTNET_");
        //     configHost.AddCommandLine(args);
        // })
        // 配置各种配置
        .ConfigureAppConfiguration((hostingContext, config) =>
        {
            var env = hostingContext.HostingEnvironment;
            config.AddEnvironmentVariables(prefix: "DOTNET_");
            config.AddJsonFile("hostsettings.json", optional: true, reloadOnChange: true)
                 .AddJsonFile($"hostsettings.{env.EnvironmentName}.json", optional: true, reloadOnChange: true);
            config.AddCommandLine(args);
        })
        // 直接配置环境变量
        //.UseEnvironment("Development")
        // 配置注册服务
        .ConfigureServices((hostContext, services) =>
        {
            services.AddHostedService<LifetimeEventsHostedService>();
        })
        .ConfigureLogging(logging =>
        {
            logging.ClearProviders();
            logging.AddConsole();
        });
}

2. 对于LifetimeEventsHostedService类：

    internal class LifetimeEventsHostedService : IHostedService
    {
        private readonly ILogger _logger;
        private readonly IHostApplicationLifetime _appLifetime;
        private readonly IConfiguration _config;

        public LifetimeEventsHostedService(
            ILogger<LifetimeEventsHostedService> logger,
            IHostApplicationLifetime appLifetime, IConfiguration config)
        {
            _logger = logger;
            _appLifetime = appLifetime;
            _config = config;
        }
        public Task StartAsync(CancellationToken cancellationToken)
        {
            _appLifetime.ApplicationStarted.Register(OnStarted);
            _appLifetime.ApplicationStopping.Register(OnStopping);
            _appLifetime.ApplicationStopped.Register(OnStopped);

            return Task.CompletedTask;
        }

        public Task StopAsync(CancellationToken cancellationToken)
        {
            return Task.CompletedTask;
        }

        private void OnStarted()
        {
            _logger.LogInformation("OnStarted has been called.");
            var appName = _config.GetValue<string>("AppName");
            _logger.LogInformation($"Current AppName Environment:{appName}");
            // Perform post-startup activities here
            
        }

        private void OnStopping()
        {
            _logger.LogInformation("OnStopping has been called.");

            // Perform on-stopping activities here
        }

        private void OnStopped()
        {
            _logger.LogInformation("OnStopped has been called.");

            // Perform post-stopped activities here
        }
    }

3. 应用不同的配置：我们一般使用环境变量来区分

hostsettings.json
hostsettings.{Environment}.json