.NET5修改配置不重启自动生效

.NET Core，.NET5默认配置都是只加载一次，修改配置时都需要重启才能生效，如何能修改即时生效呢，下面来演示一遍。

一、设置配置文件实时生效

1.1配置

在Program.cs的CreateHostBuilder()处增加加载配置文件的时候，reloadOnChange:true。

这样配置文件修改的时候，程序就会监听到文件发生变化，自动重新加载了。

 public static IHostBuilder CreateHostBuilder(string[] args) =>
            Host.CreateDefaultBuilder(args)
            .ConfigureAppConfiguration((context, config) =>
            {
                config.AddJsonFile("appsettings.json", optional: true, reloadOnChange: true);
            })
                .ConfigureWebHostDefaults(webBuilder =>
                {
                    webBuilder.UseStartup<Startup>();

                });

1.2验证

appsettings.json文件内容如下

{
  "TestSetting": "123",
  "AppOptions": {
    "UserName": "zhangsan"
  }
}

代码：

 public class HomeController : Controller
    {
　　　　 private readonly ILogger<HomeController> _logger;
        private readonly IConfiguration _configuration;
        public HomeController(ILogger<HomeController> logger, IConfiguration configuration)
        {
            _logger = logger;
            _configuration = configuration;
        }

        public IActionResult Index()
        {
            string Name = _configuration["TestSetting"];
            string Name2 = _configuration["AppOptions:UserName"];
            ViewBag.Name = Name;
            ViewBag.Name2 = Name2;
            return View();
        }
}

界面显示：

 把配置文件修改为：

{
  "TestSetting": "abc",
  "AppOptions": {
    "UserName": "zhangsan123"
  }
}

刷新页面，已经发生变化：

1.3 IOptions方式实时生效

新建AppOptions.cs类

/// <summary>
    /// 配置文件
    /// </summary>
    public class AppOptions
    {
        public string UserName { get; set; }
    }

在Startup.cs处把配置加到Options

  public void ConfigureServices(IServiceCollection services)
        {
            services.AddControllersWithViews();
            services.Configure<AppOptions>(Configuration.GetSection("AppOptions"));
        }

使用：

 public class HomeController : Controller
    {
        private readonly ILogger<HomeController> _logger;
        private readonly IConfiguration _configuration;
        private IOptionsMonitor<AppOptions> _options;
        public HomeController(ILogger<HomeController> logger, IConfiguration configuration, IOptionsMonitor<AppOptions> appOptions)
        {
            _logger = logger;
            _configuration = configuration;
            _options = appOptions;
        }

        public IActionResult Index()
        {
            string Name = _configuration["TestSetting"];
            string Name2 = _options.CurrentValue.UserName;
            ViewBag.Name = Name;
            ViewBag.Name2 = Name2;
            return View();
        }
}

IOptions有三种方式

//IOptions<T> //站点启动后，获取到的值永远不变
//IOptionsMonitor<T> //站点启动后，如果配置文件有变化会发布事件 （加载配置时，reloadOnChange:true 必须为true）
//IOptionsSnapshot<T> //站点启动后，每次获取到的值都是配置文件里的最新值 （加载配置时，reloadOnChange:true 必须为true）

注意： 

IOptionsMonitor<T> 和 IOptionsSnapshot<T> 的最大区别是前者可以被其他的Singleton Services使用而后者不可以， 因为前者被注册为Singleton 而后者是被注册为Scoped，也就是说文件被修改了前者会立即Reload，而后者是在每个请求才被Reload。

例：

 public class HomeController : Controller
    {
        private readonly ILogger<HomeController> _logger;
        private UserService _userService;
        public HomeController(ILogger<HomeController> logger, UserService userService)
        {
           
            _userService = userService;
        }

        public IActionResult Index()
        {
            string Name2 = _userService.GetName();
            ViewBag.Name2 = Name2;
            return View();
        }
}

 public class UserService
    {
        private IOptionsMonitor<AppOptions> _options;
        public UserService(IOptionsMonitor<AppOptions> appOptions)
        {
            _options = appOptions;
        }
        public string GetName()
        {
            var Name = _options.CurrentValue.UserName;
            return Name;
        }
    }

 public void ConfigureServices(IServiceCollection services)
        {
            services.AddControllersWithViews();
            services.Configure<AppOptions>(Configuration.GetSection("AppOptions"));
            services.AddSingleton<UserService>();
        }

上面的UserService是单例注入的，通过IOptionsMonitor<T>的方式是可以实现配置实时刷新的，而IOptionsSnapshot<T>启动就会报错。

1.4多个配置文件加载实时生效

增加多一个db配置文件

修改Program.cs处CreateHostBuilder()，也是加载时加上reloadOnChange:true 就可以了。

  public static IHostBuilder CreateHostBuilder(string[] args) =>
            Host.CreateDefaultBuilder(args)
            .ConfigureAppConfiguration((context, config) =>
            {
                config.AddJsonFile("appsettings.json", optional: true, reloadOnChange: true);
                config.AddJsonFile("Configs/dbsetting.json", optional: true, reloadOnChange: true);
            })
                .ConfigureWebHostDefaults(webBuilder =>
                {
                    webBuilder.UseStartup<Startup>();

                });

使用也是一样的：

 public class HomeController : Controller
    {
        private readonly ILogger<HomeController> _logger;
        private readonly IConfiguration _configuration;
        private AppOptions _options;
        public HomeController(ILogger<HomeController> logger, IConfiguration configuration, IOptionsMonitor<AppOptions> appOptions)
        {
            _logger = logger;
            _configuration = configuration;
            _options = appOptions.CurrentValue;
        }

        public IActionResult Index()
        {
            string Name = _configuration["TestSetting"];
            string Name2 = _configuration["db:connection1"];
            ViewBag.Name = Name;
            ViewBag.Name2 = Name2;
            return View();
        }
}