现在有一个appsetting.json配置文件，里面有个setting下的url地址，需要读取，如下：

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft": "Warning",
      "Microsoft.Hosting.Lifetime": "Information"
    }
  },
  "Setting": {
    "Url": "127.0.0.1:8080"
  }
}

不添加任何类，直接读取appsetting.json的两种方法：

1.利用ConfigurationBuilder

var builder = new ConfigurationBuilder()
            .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true);
        IConfigurationRoot configuration = builder.Build();
        var value = configuration["Setting:Url"];
        Console.log($"Url地址是: {value}");

2.利用IConfiguration，注入IConfiguration

[ApiController]
[Route("[controller]/[action]")]
public class TestController: ControllerBase
{
    public IConfiguration _configuration { get; set; }
    public TestController(IConfiguration configuration)
    {
        _configuration = configuration;
    }
    /// <summary>
    /// 利用IConfiguration直接读取单个值的3个方法
    /// </summary>
    [HttpGet, HttpPost]
    public void GetConfiguration()
    {
        var url = _configuration["Setting:Url"]; // http://127.0.0.1:8080/
        var url2 = _configuration.GetValue<string>("Setting:Url"); // http://127.0.0.1:8080/
        var url3 = _configuration.GetSection("Setting").GetSection("Url").Value; // http://127.0.0.1:8080/
    }
}