webapi读取配置文件内容

1.读取默认的配置文件appsettings.json

appsettings.json内容
{
  "Logging": {"Default": "Information",
      "Microsoft": "Warning",
  },
  "AllowedHosts": "*",
  "ConnectionString": "Server=.;Database=Carina;User ID=sa;Password=pass****;"
}

public class WeatherForecastController : ControllerBase
  {
    private IConfiguration _configuration;

    private readonly ILogger<WeatherForecastController> _logger;
　　//依赖注入configuration，就可以在controller中使用configuration了
    public WeatherForecastController(ILogger<WeatherForecastController> logger, IConfiguration configuration)
    {
      _logger = logger;
      _configuration = configuration;  //
    }
　　//读取单个值
　　var connectionStr =_configuration["ConnectionString"] ； 

　　//var connectionStr =_configuration.GetValue<string>("ConnectionString")
　　//获取对象中的值
　　var connectionStr =_configuration["Logging:Default"]  //返回”Information“

}

若要读出一个对象，需要先声明一个类，然后读取出来。若要依赖注入该配置文件对象，需要再startup类中声明

public class Logging{
      public string Default{get;set;},
      public string Microsoft{get;set}
}

//controller类中
var config = _configuration.GetSection("logging1").Get<Logging>();


//若要依赖注入配置文件的对象。
//startup类
public void ConfigureServices(IServiceCollection services)
        {
            services.AddControllers();
            services.Configure<Logging>(Configuration.GetSection("Logging"));
        }

//controller类中
   private IConfiguration _configuration;
    private Logging logging;

    private readonly ILogger<WeatherForecastController> _logger;

    public WeatherForecastController(ILogger<WeatherForecastController> logger, IConfiguration configuration, IOptions<Logging> options)
    {
      _logger = logger;
      _configuration = configuration;
      logging = options.Value; //logging对象即包含配置文件的信息
    }

　　单独类读取配置文件信息

  public static class ConfigurationManager
    {
        public readonly static IConfiguration Configuration;

        static ConfigurationManager()
        {
            Configuration = new ConfigurationBuilder()
               .SetBasePath(Directory.GetCurrentDirectory())
               .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
               .Build();
        }

        public static T GetSection<T>(string key) where T : class, new()
        {
            return new ServiceCollection()
                .AddOptions()
                .Configure<T>(Configuration.GetSection(key))
                .BuildServiceProvider()
                .GetService<IOptions<T>>()
                .Value;
        }

        public static string GetSection(string key)
        {
            return Configuration.GetValue<string>(key);
        }
    }