net core获取appsetting.json的另外一种思路（全局，实时变化无需重启项目）

最近在写net core的项目，在非controller和service里面需要用到appsetting.json文件里面的一些配置，查资料大概有几种思路：

• 注入，然后config.GetSection("xxx")
• 写一个监听，filewatch，去监听appsetting.json的变化，读取key-value。
• 工具类里面传入再走一遍 new ConfigurationBuilder() .SetBasePath(Directory.GetCurrentDirectory()).AddJsonFile($"appsettings.json", optional: true, reloadOnChange: true)

• 使用IOptions<TOptions>，创建对应的实体类

我在查资料的时候发现了一个IOptionsMonitor<T>，这个可以监听到文件的变化，结合IOptionsMonitor<T>，我写了一个工具类，具体使用办法如下：

（1）创建appsetting.json对应的实体类文件，属性的名字要与配置文件里面的一一对应。

 public class AllSetting
 {
         ///// <summary>
         ///// 数据库配置
         ///// </summary>
         public ConnectionSetting ConnectionStrings { get; set; }

         ///// <summary>
         ///// 日志模块
         ///// </summary>
         public LoggingSetting Logging { get; set; }

         ///// <summary>
         ///// AllowedHosts
         ///// </summary>
         public string AllowedHosts { get; set; }
 }

 {
     "ConnectionStrings": {
         "DefaultConnection": "xxxx"
         //"PgSqlConnection": "xxxx",
         //"MySqlConnection": "xxxx",
         //"OracleConnection": "xxxx"
     },
     "Logging": {
         "LogLevel": {
             "Default": "Warning"
         }
     },
     "AllowedHosts": "*",
     "Gateway": {
         "Uri": "xxxx"
     }
 }

(2) 编写工具类AppsettingsUtility

  /// <summary>
     /// 全局获取app的设置工具类
     /// </summary>
     public class AppsettingsUtility
     {
         /// <summary>
         /// log4net
         /// </summary>
         private readonly ILog log;

         /// <summary>
         /// serviceProvider
         /// </summary>
         private static ServiceProvider serviceProvider;

         /// <summary>
         /// _services
         /// </summary>
         private static IServiceCollection _services;

         /// <summary>
         /// _configuration
         /// </summary>
         private static IConfiguration _configuration;

         /// <summary>
         /// 初始化工具类
         /// </summary>
         /// <param name="provider"></param>
         public AppsettingsUtility(IServiceCollection services, IConfiguration configuration)
         {
             _services = services;
             _configuration = configuration;
             // 仓库名 统一的
             log = LogManager.GetLogger("仓库名", typeof(AppsettingsUtility));
             if (_services == null || _configuration == null)
             {
                 log.Error("初始化配置工具类发生异常:_services或_configuration为空");
                 throw new NullReferenceException("初始化配置工具类发生异常");
             }
             try
             {
                 serviceProvider = _services.BuildServiceProvider();
             }
             catch (Exception ex)
             {
                 log.Error("_services.BuildServiceProvider()失败:" + ex.ToString());
             }
         }

         /// <summary>
         /// 获取IOptionsMonitor<T>
         /// </summary>
         /// <typeparam name="T">泛型</typeparam>
         /// <returns>IOptionsMonitor<T></returns>
         public static IOptionsMonitor<T> GetMonitor<T>()
         {
             if (serviceProvider == null)
             {
                 throw new NullReferenceException("获取失败,ServiceProvider为空");
             }
             if (typeof(T) != typeof(AllSetting))
             {
                 // TODO: 要限定传递的参数值或者每个setting都注册一遍
             }
             return serviceProvider.GetRequiredService<IOptionsMonitor<T>>();
         }

         /// <summary>
         /// 获取单个的设置实体
         /// </summary>
         /// <typeparam name="T">泛型</typeparam>
         /// <returns>T</returns>
         public static T GetSettingsModel<T>()
         {
             if (serviceProvider == null)
             {
                 throw new NullReferenceException("获取失败,ServiceProvider为空");
             }
             if (typeof(T) != typeof(AllSetting))
             {
                 // TODO: 要限定传递的参数值或者每个setting都注册一遍
             }
             return serviceProvider.GetRequiredService<IOptionsMonitor<T>>().CurrentValue;
         }

         /// <summary>
         /// 通过key获取设置
         /// </summary>
         /// <param name="key">key</param>
         /// <returns>设置内容</returns>
         public static string GetSetting(string key)
         {
             if (_configuration == null)
             {
                 throw new NullReferenceException("获取失败,IConfiguration为空");
             }
             if (string.IsNullOrEmpty(key))
             {
                 throw new NullReferenceException("获取失败,key不能为空");
             }
             return _configuration.GetSection(key).Value;
         }
     }

（3）在Startup中注册

  // 注入设置类到管道中
 services.AddOptions();
 services.Configure<AllSetting>(Configuration);
 // 初始化工具类
 new AppsettingsUtility(services,Configuration);

（4）使用

 var aa = AppsettingsUtility.GetMonitor<AllSetting>().CurrentValue;
 var bb = AppsettingsUtility.GetSettingsModel<JwtSetting>();
 var bb = AppsettingsUtility.GetSetting("Appsetting:xxx");

如果把配置文件改变了，再调用获取设置的时候，设置的值会更新，项目不用重启。这样做对性能的影响没有测试。

如果我这边的思路有什么错误的话，还望批评指出。