ASP.NET CORE读取json格式配置文件

ASP.NET Core 读取 JSON 格式配置文件的流程：

1. 在 appsettings.json 文件中定义所需的配置项。

2. 在 Program.cs 文件中使用 CreateDefaultBuilder(args) 方法创建 IHostBuilder 对象，并在 ConfigureAppConfiguration(...) 方法中添加读取配置文件的功能。

3. 在需要使用配置项的组件中注入 IConfiguration 对象，并使用 GetSection(...) 方法获取对应节点下的配置项。

下面是一个完整的示例：

Step 1：定义配置项和设置文件路径

在 appsettings.json 文件中定义需要的配置项，如下所示：

{
  "AppSettings": {
    "Title": "My Website",
    "Version": "1.0.0",
    "Database": {
      "Type": "SqlServer",
      "ConnectionString": "Server=(local);Database=mydb;Trusted_Connection=True;"
    }
  }
}

在 Program.cs 文件中设置配置文件路径，如下所示：

public static IHostBuilder CreateHostBuilder(string[] args) =>
    Host.CreateDefaultBuilder(args)
        .ConfigureAppConfiguration((hostingContext, config) =>
        {
            config.SetBasePath(Directory.GetCurrentDirectory()); // 设置配置文件路径
            config.AddJsonFile("appsettings.json", optional: false, reloadOnChange: true); // 添加配置文件
        })
        .ConfigureWebHostDefaults(webBuilder =>
        {
            webBuilder.UseStartup<Startup>();
        });

Step 2：在Startup.cs中获取配置项

在 Startup.cs 文件中通过构造函数注入 IConfiguration 对象，并使用 GetSection(...) 方法来获取指定配置项。

public class Startup
{
    private readonly IConfiguration _configuration;

    public Startup(IConfiguration configuration)
    {
        _configuration = configuration;
    }

    public void ConfigureServices(IServiceCollection services)
    {
        // 获取配置项
        string title = _configuration.GetSection("AppSettings:Title").Value;
        string version = _configuration.GetSection("AppSettings:Version").Value;
        string dbType = _configuration.GetSection("AppSettings:Database:Type").Value;
        string connectionString = _configuration.GetSection("AppSettings:Database:ConnectionString").Value;

        // 将配置项注册到依赖注入容器中
        services.AddSingleton(new AppSettings(title, version, new DatabaseSettings(dbType, connectionString)));

        services.AddControllers();
    }

    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
        ...
    }
}

示例一：在控制器中获取配置项

[Route("api/[controller]")]
[ApiController]
public class ConfigController : ControllerBase
{
    private readonly AppSettings _appSettings;

    public ConfigController(AppSettings appSettings)
    {
        _appSettings = appSettings;
    }

    [HttpGet]
    public IActionResult GetConfig()
    {
        return Ok(new
        {
            Title = _appSettings.Title,
            Version = _appSettings.Version,
            Database = _appSettings.Database
        });
    }
}

示例二：在中间件中获取配置项

public class CustomMiddleware
{
    private readonly RequestDelegate _next;
    private readonly AppSettings _appSettings;

    public CustomMiddleware(RequestDelegate next, AppSettings appSettings)
    {
        _next = next;
        _appSettings = appSettings;
    }

    public async Task Invoke(HttpContext httpContext)
    {
        // 使用配置项
        string title = _appSettings.Title;
        string version = _appSettings.Version;
        string dbType = _appSettings.Database.Type;
        string connectionString = _appSettings.Database.ConnectionString;

        await _next(httpContext);
    }
}