C# .NET5.0 读取appsettings.json

基于VS2019，使用步骤：

方式一：

第一步：appsettings.json 定义配置项，可理解为定义对象属性，eg:

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft": "Warning",
      "Microsoft.Hosting.Lifetime": "Information"
    }
  },
  "MEASSettings": 
  {
    "PrintName": "wula",
    "PrintNum": 12
  },

  "AllowedHosts": "*"

}

第二步：定义实体对象，eg:

using System;

namespace Test
{
    public class MEASSettings
    {
        public string PrintName { get; set; }
        public string PrintNum { get; set; }

    }
}　

 第三步：读取配置项公共方法提取，创建DLL(基于.NET 5.0略)

注：需安装如下依赖项，略

using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Configuration.Json;
using System;

namespace MEAS.Common
{
    public class AppsettingsHelper
    {
        public IConfiguration Configuration { get; set; }

        //定义一个用于保存静态变量的实例
        private static AppsettingsHelper instance = null;
        //定义一个保证线程同步的标识
        private static readonly object locker = new object();
        //构造函数为私有，使外界不能创建该类的实例
        private AppsettingsHelper()
        {
            Configuration = new ConfigurationBuilder()
                .Add(new JsonConfigurationSource { Path = "appsettings.json", ReloadOnChange = true })
                .Build();
        }
        public static AppsettingsHelper Instance
        {
            get
            {
                if (instance == null)
                {
                    lock (locker)
                    {
                        if (instance == null) instance = new AppsettingsHelper();
                    }
                }
                return instance;
            }
        }

        /// <summary>
        /// 根据索引获取配置项value值
        /// </summary>
        /// <param name="indexPath"></param>
        /// <returns></returns>
        public string GetConfigByIndex(string indexPath)
        {
            return Configuration[indexPath].ToString();//Configuration["MEASSettings:PrintName"];
        }

        /// <summary>
        /// 根据节点获取配置文件对象实例
        /// </summary>
        /// <param name="className"></param>
        /// <returns></returns>
        public IConfiguration GetConfigObjs(string className)
        {
            //string aa = Configuration.GetSection("MEASSettings").Get<MEASSettings>().PrintName;
            return Configuration.GetSection(className);//    MEASSettings bbbb = see.Get<MEASSettings>();
        }

        /// <summary>
        /// 根据具体对象获取对象实例
        /// </summary>
        /// <typeparam name="T">对象类型</typeparam>
        /// <param name="obj">实体对象</param>
        /// <returns></returns>
        public object GetConfigObjByEntity<T>(T obj)
        {
            string className = Type.GetType(obj.ToString()).Name;
            return Configuration.GetSection(className).Get(Type.GetType(obj.ToString()));
        }

    }
}

第五步：使用方式如下所示：

            //方式一
            string aa = Configuration.GetSection("MEASSettings").Get<MEASSettings>().PrintName;
            MEASSettings aaa = Configuration.GetSection("MEASSettings").Get<MEASSettings>();
            //方式二
            string bb = ConfigHelper.Instance.GetConfigByIndex("MEASSettings:PrintName");
            //方式三
            IConfiguration cc = ConfigHelper.Instance.GetConfigObjs("MEASSettings");
            MEASSettings ccc = cc.Get<MEASSettings>();
            //方式四
            MEASSettings set = new MEASSettings();
            MEASSettings ddd = ConfigHelper.Instance.GetConfigObjByEntity<MEASSettings>(set) as MEASSettings;
            //方式五
            MEASSettings temp = ConfigHelper.Instance.GetConfigObjByEntity<MEASSettings>(new MEASSettings()) as MEASSettings;     

 方式二：

第一步，根据appsettings.json 文件创建对应的对象模型

注：选择对应的对象(选择单个对象时，只选择对应的中括号)==》下面是选择所有配置内容后自动生成对象模型

自动生成后需根据实际情况修改对应的实体类名称--修改名称略

对象如下所示：

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft": "Warning",
      "Microsoft.Hosting.Lifetime": "Information"
    }
  },
  "MEASSettings": 
  {
    "PrintName": "wula",
    "PrintNum": 12
  },

  "AllowedHosts": "*"

}

//对应实体如下所示：
using System;

namespace Test
{
    public class AppSettings
    {
        public Logging Logging { get; set; }
        public MEASSettings MEASSettings { get; set; }
        public string AllowedHosts { get; set; }
    }

    public class Logging
    {
        public Loglevel LogLevel { get; set; }
    }

    public class Loglevel
    {
        public string Default { get; set; }
        public string Microsoft { get; set; }
        public string MicrosoftHostingLifetime { get; set; }
    }

    public class MEASSettings
    {
        public string PrintName { get; set; }
        public int PrintNum { get; set; }
    }

}

第二步：根据视图对象模型，通过IConfiguration获取整个对象模型的对象

//通过对象模型获取AppSettings对象集合
var setting = new AppSettings();
Configuration.Bind(setting);
//调用使用AppSettings对象属性
string printName=setting.MEASSettings.PrintName;

 //部分绑定

var measSettings = new MEASSettings();
Configuration.GetSection("measSettings").Bind(measSettings);

方式三：注册配置选项服务

  public void ConfigureServices(IServiceCollection services)
        {
            //注册配置选项服务
            services.Configure<AppSettings>(Configuration);
            //......
       }  

 public void Configure(IApplicationBuilder app, IWebHostEnvironment env,IOptions<AppSettings> options)
        {
　　　　　　　　//使用配置选项服务
            string printName = options.Value.MEASSettings.PrintName;

            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
                app.UseSwagger();
                app.UseSwaggerUI(c => c.SwaggerEndpoint("/swagger/v1/swagger.json", "WebApplication1 v1"));
            }

            app.UseHttpsRedirection();

            app.UseRouting();

            app.UseAuthorization();

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllers();
            });
        }      

 方式四：

//自定义读取配置文件 + 注册配置选项服务
//自定义配置，注册配置选项，读取时通过options方式读取
var config = new ConfigurationBuilder().AddJsonFile("appsettings.json").Build();
string printName2=config["MEASSettings:PrintName"];
services.Configure<AppSettings>(config);