.NET Core控制台应用ConsoleApp读取appsettings.json配置文件

// Program.cs
using System;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Hello World!");
        }
    }
}

{
  "ConnectionStrings": {
    "DefaultConnectionString":  "Data Source=localhost;Database=db;User ID=user;PassWord=pwd"
  }
}

PM> Install-Package Microsoft.Extensions.Configuration -Version 2.1.1 -Verbose
PM> Install-Package Microsoft.Extensions.Configuration.Json -Version 2.1.1 -Verbose

// Program.cs
using Microsoft.Extensions.Configuration;
using System;
using System.IO;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            IConfigurationRoot configuration = new ConfigurationBuilder()
                .SetBasePath(Directory.GetCurrentDirectory())
                .AddJsonFile(path: "appsettings.json", optional: true, reloadOnChange: true)
                .Build();

            string defaultConnectionString = configuration.GetConnectionString("DefaultConnectionString");

            Console.WriteLine(defaultConnectionString);
            Console.ReadKey();
        }
    }
}