.NET 5 修改配置不重启自动生效

• .NET Core，.NET 5 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

设置配置文件实时生效

1.配置

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

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();
    }
}

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。

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();
    }
}