ASP.NET CORE MVC 2.0 如何在Filter中使用依赖注入来读取AppSettings，及.NET Core控制台项目中读取AppSettings

问：

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ASP.NET CORE MVC 如何在Filter中使用依赖注入来读取AppSettings

答:

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Dependency injection is possible in filters as well.

Here is a simple way to get connection string

public class EBisUserAuthResourceFilter : Attribute, IResourceFilter
{
    private readonly string connectionString;

    public EBisUserAuthResourceFilter(IConfiguration configuration)
    {
        this.connectionString = configuration
                   .GetSection("ConnectionStrings:DefaultConnection").Value;
    }
    public void OnResourceExecuted(ResourceExecutedContext context)
    {
        // use this.connectionString
    }

    public void OnResourceExecuting(ResourceExecutingContext context)
    {
        // use this.connectionString
    }
}

Now you can use this filter

[ServiceFilter(typeof(EBisUserAuthResourceFilter))]
public class HomeController : Controller
{  }

You also need to add this Filter to the service collection

public void ConfigureServices(IServiceCollection services)
{
   services.AddScoped<EBisUserAuthResourceFilter>();

   // your existing code to add other services
}

Another solution is to have a class representing the structure of the content of AppSettings.json file or a sub section and load that in your Startup classes' ConfigureServices method

services.Configure<SiteSettings>(Configuration);

and now you can inject IOptions<SiteSettings> in the constructor of your filter and use the needed property values. I prefer this as it is less magic strings in my code.

public class EBisUserAuthResourceFilter : Attribute, IResourceFilter
{
    private readonly string connectionString;

    public EBisUserAuthResourceFilter(IOptions<SiteSettings> settings)
    {
        this.connectionString = settings.Value.connectionString ;
    }
    public void OnResourceExecuted(ResourceExecutedContext context)
    {
        // use this.connectionString
    }

    public void OnResourceExecuting(ResourceExecutingContext context)
    {
        // use this.connectionString
    }
}

原文链接

补充：

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当然还有个更简单的办法，就是在Filter里面直接通过.Net Core App的方式来读取AppSettings的值，这个方法是最灵活的:

appsettings.json

{
  "Logging": {
    "IncludeScopes": false,
    "LogLevel": {
      "Default": "Warning"
    }
  },
  "AppSettings": {
    "CacheTimeSpan": 1200,
    "MD5PrivateKey": "KOPX&VDtt!890912hjk",
    "Auth_UserName": "Username",
    "Auth_Token": "Token"
  }
}

构造一个AppSettings类来反序列化appsettings.json文件中AppSettings节点下的内容：

public class AppSettings
{
    public int CacheTimeSpan { get; set; }
    public string MD5PrivateKey { get; set; }
    public string Auth_UserName { get; set; }
    public string Auth_Token { get; set; }
}

在Filter的构造函数中，构造AppSettings并读取其值：

public class AuthenticationFilterAttribute : Attribute, IAuthorizationFilter
{
    public AuthenticationFilterAttribute()
    {
        var builder = new ConfigurationBuilder()
                            .SetBasePath(Directory.GetCurrentDirectory())
                            .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true);

        IConfigurationRoot configuration = builder.Build();

        var appSettings=configuration.GetSection("AppSettings").Get<AppSettings>();
        int cacheTimeSpanValue = appSettings.CacheTimeSpan;
    }

    public void OnAuthorization(AuthorizationFilterContext context)
    {

    }
}

.NET Core控制台项目读取AppSettings

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其实在.NET Core控制台项目中也可以创建和读取AppSettings

首先你需要在.NET Core控制台项目中确保引用了下面四个Nuget包：

• Microsoft.Extensions.Configuration
• Microsoft.Extensions.Configuration.Binder
• Microsoft.Extensions.Configuration.FileExtensions
• Microsoft.Extensions.Configuration.Json

接下来，我们就可以在.NET Core控制台项目中创建一个appsettings.json文件如下：

{
  "AppSettings": {
    "CacheTimeSpan": 1200,
    "MD5PrivateKey": "YUIOOASSA!@!##",
    "Auth_UserName": "Username",
    "Auth_Token": "Token"
  }
}

注意要将appsettings.json文件的属性做修改，将"Copy to Output Directory"选项设置为"Copy if newer"，如下：

然后同样定义一个AppSettings类来反序列化appsettings.json文件中AppSettings节点下的内容：

public class AppSettings
{
    public int CacheTimeSpan { get; set; }
    public string MD5PrivateKey { get; set; }
    public string Auth_UserName { get; set; }
    public string Auth_Token { get; set; }
}

然后在.NET Core控制台项目的Main方法中，按照如下代码读取AppSettings的值即可：

using Microsoft.Extensions.Configuration;
using System;
using System.IO;

namespace NetCoreEnvironmentVariable
{
    class Program
    {
        static void Main(string[] args)
        {
            var builder = new ConfigurationBuilder()
                            .SetBasePath(Directory.GetCurrentDirectory())
                            .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true);

            IConfigurationRoot configuration = builder.Build();

            var appSettings = configuration.GetSection("AppSettings").Get<AppSettings>();
            int cacheTimeSpanValue = appSettings.CacheTimeSpan;
            string authUserName = appSettings.Auth_UserName;

            Console.WriteLine($"CacheTimeSpan={cacheTimeSpanValue}");
            Console.WriteLine($"Auth_UserName={authUserName}");

            Console.WriteLine("Press any key to end...");
            Console.ReadKey();
        }
    }
}

执行结果如下：

使用AddEnvironmentVariables方法配置读取操作系统的环境变量

我们还可以配置IConfigurationBuilder去加载操作系统环境变量的值，为此我们需要在.NET Core控制台项目中再引用一个Nuget包：

• Microsoft.Extensions.Configuration.EnvironmentVariables

接下来我们在Windows操作系统中，添加两个环境变量：

AppSettings:CacheTimeSpan为5000

AppSettings:Password为abc123456

如下图所示：

之后，最好重启一下计算机，因为AddEnvironmentVariables方法使用类似于EnvironmentVariableTarget.Process参数的机制，来加载操作系统环境变量，所以需要重启计算机后才能够读取到操作系统环境变量的值。

然后我们将.NET Core控制台项目的Main方法改为如下：

using Microsoft.Extensions.Configuration;
using System;
using System.IO;

namespace NetCoreEnvironmentVariable
{
    class Program
    {
        static void Main(string[] args)
        {
            var builder = new ConfigurationBuilder()
                            .SetBasePath(Directory.GetCurrentDirectory())
                            .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
                            .AddEnvironmentVariables();//使用AddEnvironmentVariables方法，配置让IConfigurationBuilder加载操作系统中的环境变量，由于这里AddEnvironmentVariables方法在上面的AddJsonFile方法的后面，所以在"appsettings.json"文件中与操作系统环境变量同名的键值，会被操作系统环境变量的值所覆盖

            IConfigurationRoot configuration = builder.Build();

            var appSettings = configuration.GetSection("AppSettings").Get<AppSettings>();
            int cacheTimeSpanValue = appSettings.CacheTimeSpan;//由于在操作系统环境变量中，我们定义了AppSettings:CacheTimeSpan为5000，所以"appsettings.json"文件中CacheTimeSpan为1200的值会被覆盖，所以这里实际上得到的是操作系统环境变量AppSettings:CacheTimeSpan的值5000
            string authUserName = appSettings.Auth_UserName;//由于在操作系统环境变量中，没有定义AppSettings:Auth_UserName，所以这里得到的还是"appsettings.json"文件中Auth_UserName的值Username
            string password = configuration["AppSettings:Password"];//获取操作系统环境变量AppSettings:Password的值abc123456

            Console.WriteLine($"CacheTimeSpan={cacheTimeSpanValue}");
            Console.WriteLine($"Auth_UserName={authUserName}");
            Console.WriteLine($"Password={password}");

            Console.WriteLine("Press any key to end...");
            Console.ReadKey();
        }
    }
}

注意"appsettings.json"文件中的json类型层次结构，可以用冒号":"来进行表达，所以我们可以看到，上面代码中操作系统环境变量AppSettings:CacheTimeSpan，等同于"appsettings.json"文件中AppSettings属性下的CacheTimeSpan属性。

运行上面代码，执行结果如下：

可以看到，我们成功地读出了操作系统环境变量AppSettings:CacheTimeSpan和AppSettings:Password的值。