准备

.NET core和.NET项目配置上有了很大的改变，支持的也更加丰富了比如命令行，环境变量，内存中.NET对象，设置文件等等。.NET项目我们常常把配置信息放到webConfig 或者appConfig中。配置相关的源码https://github.com/aspnet/Extensions；如果打开源码项目 如果遇到以下错误，未遇到直接跳过。

错误提示： error : The project file cannot be opened by the project system, because it is missing some critical imports or the referenced SDK cannot be found. Detailed Information:

解决办法：查看本地安装的sdk 与 global.json中制定的版本是否一致：然后修改即可

开始

新建个Asp.net Core web应用程序系统默认创建了appsettings.json ；在应用启动生成主机时调用CreateDefaultBuilder方法，默认会加载appsettings.json。代码如下：

public static IHostBuilder CreateDefaultBuilder(string[] args)
        {
            var builder = new HostBuilder();
​
            builder.UseContentRoot(Directory.GetCurrentDirectory());
            builder.ConfigureHostConfiguration(config =>
            {
                config.AddEnvironmentVariables(prefix: "DOTNET_");
                if (args != null)
                {
                    config.AddCommandLine(args);
                }
            });
​
            builder.ConfigureAppConfiguration((hostingContext, config) =>
            {
                var env = hostingContext.HostingEnvironment;
​
                config.AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
                      .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true, reloadOnChange: true);
​
                if (env.IsDevelopment() && !string.IsNullOrEmpty(env.ApplicationName))
                {
                    var appAssembly = Assembly.Load(new AssemblyName(env.ApplicationName));
                    if (appAssembly != null)
                    {
                        config.AddUserSecrets(appAssembly, optional: true);
                    }
                }

利用 GetValue，GetSection，GetChildren读取appsettings.json 键值对 。我们打开appsettings.json文件：

将文件读入配置时，会创建一下唯一的分层健来保存配置值：

• Logging:LogLevel:Default

• Logging:LogLevel:System

• Logging:LogLevel:Microsoft

• Logging:LogLevel:Microsoft.Hosting.Lifetime

• AllowedHosts

 var jsonValue = $"AllowedHosts:{_config["AllowedHosts"]}"+ "\r\n";
            jsonValue += "Logging:LogLevel:Default：" + _config.GetValue<string>("Logging:LogLevel:Default")+ "\r\n";
​
            //GetSection 返回IConfigurationSection；如果未匹配到 返回null
            //jsonValue += "---" + _config.GetSection("Logging:LogLevel:System");
            jsonValue += "Logging:LogLevel:System：" + _config.GetSection("Logging:LogLevel:System").Value+ "\r\n\n";
          
            var logSection = _config.GetSection("Logging:LogLevel");
            var configurationSections = logSection.GetChildren();
            foreach (var sections in configurationSections) 
            {
                jsonValue += $"{sections.Path}:{sections.Value}";
                jsonValue += "\r\n";
            }
            jsonValue += "\r\n";

配置指定json文件绑定至类

新建一个json文件-AAAppSettings.json

{
  "AA": {
    "RabbitMqHostUrl": "rabbitmq://localhost:5672",
    "RabbitMqHostName": "localhost",
    "RabbitMqUserName": "admin",
    "RabbitMqPassword": "123"
  }
}

使用ConfigureAppConfiguration方法配置指定的json文件

public static IHostBuilder CreateHostBuilder(string[] args) =>
            Host.CreateDefaultBuilder(args)
            .ConfigureAppConfiguration((hostingContext, config) =>
            {
                config.SetBasePath(Directory.GetCurrentDirectory());
                config.AddJsonFile("AAAppSettings.json", optional: true, reloadOnChange: true);
            })

使用bind方法绑定到新建的类上如：   

 public partial class AAConfig
    {
        public string RabbitMqHostUrl { get; set; }
        public string RabbitMqHostName { get; set; }
        public string RabbitMqUserName { get; set; }
        public string RabbitMqPassword { get; set; }
    }

var aaConfig = new AAConfig();
_config.GetSection("AA").Bind(aaConfig);
jsonValue += aaConfig.RabbitMqHostUrl + "\r\n";
jsonValue += aaConfig.RabbitMqHostName + "\r\n";
jsonValue += aaConfig.RabbitMqUserName + "\r\n";
jsonValue += aaConfig.RabbitMqPassword + "\r\n";
return jsonValue;

运行输出：