.Net Core3.0 配置Configuration

准备

.NET core和.NET项目配置上有了很大的改变，支持的也更加丰富了比如命令行，环境变量，内存中.NET对象，设置文件等等。.NET项目我们常常把配置信息放到webConfig 或者appConfig中。配置相关的源码https://github.com/aspnet/Extensions；如果打开源码项目 如果遇到以下错误，未遇到直接跳过。

错误提示： error : The project file cannot be opened by the project system, because it is missing some critical imports or the referenced SDK cannot be found. Detailed Information:

解决办法：查看本地安装的sdk 与 global.json中制定的版本是否一致：然后修改即可

开始

新建个Asp.net Core web应用程序系统默认创建了appsettings.json ；在应用启动生成主机时调用CreateDefaultBuilder方法，默认会加载appsettings.json。代码如下：

public static IHostBuilder CreateDefaultBuilder(string[] args)
{
var builder = new HostBuilder();
​
builder.UseContentRoot(Directory.GetCurrentDirectory());
builder.ConfigureHostConfiguration(config =>
{
config.AddEnvironmentVariables(prefix: "DOTNET_");
if (args != null)
{
config.AddCommandLine(args);
}
});
​
builder.ConfigureAppConfiguration((hostingContext, config) =>
{
var env = hostingContext.HostingEnvironment;
​
config.AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
.AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true, reloadOnChange: true);
​
if (env.IsDevelopment() && !string.IsNullOrEmpty(env.ApplicationName))
{
var appAssembly = Assembly.Load(new AssemblyName(env.ApplicationName));
if (appAssembly != null)
{
config.AddUserSecrets(appAssembly, optional: true);
}
}

利用 GetValue，GetSection，GetChildren读取appsettings.json 键值对 。我们打开appsettings.json文件：

将文件读入配置时，会创建一下唯一的分层健来保存配置值：

• Logging:LogLevel:Default

• Logging:LogLevel:System

• Logging:LogLevel:Microsoft

• Logging:LogLevel:Microsoft.Hosting.Lifetime

• AllowedHosts

var jsonValue = $"AllowedHosts:{_config["AllowedHosts"]}"+ "\r\n";
jsonValue += "Logging:LogLevel:Default：" + _config.GetValue<string>("Logging:LogLevel:Default")+ "\r\n";
​
//GetSection 返回IConfigurationSection；如果未匹配到 返回null
//jsonValue += "---" + _config.GetSection("Logging:LogLevel:System");
jsonValue += "Logging:LogLevel:System：" + _config.GetSection("Logging:LogLevel:System").Value+ "\r\n\n";

var logSection = _config.GetSection("Logging:LogLevel");
var configurationSections = logSection.GetChildren();
foreach (var sections in configurationSections)
{
jsonValue += $"{sections.Path}:{sections.Value}";
jsonValue += "\r\n";
}
jsonValue += "\r\n";

配置指定json文件绑定至类

新建一个json文件-AAAppSettings.json

{
"AA": {
"RabbitMqHostUrl": "rabbitmq://localhost:5672",
"RabbitMqHostName": "localhost",
"RabbitMqUserName": "admin",
"RabbitMqPassword": "123"
}
}

使用ConfigureAppConfiguration方法配置指定的json文件

public static IHostBuilder CreateHostBuilder(string[] args) =>
Host.CreateDefaultBuilder(args)
.ConfigureAppConfiguration((hostingContext, config) =>
{
config.SetBasePath(Directory.GetCurrentDirectory());
config.AddJsonFile("AAAppSettings.json", optional: true, reloadOnChange: true);
})

使用bind方法绑定到新建的类上如：   

public partial class AAConfig
{
public string RabbitMqHostUrl { get; set; }
public string RabbitMqHostName { get; set; }
public string RabbitMqUserName { get; set; }
public string RabbitMqPassword { get; set; }
}

var aaConfig = new AAConfig();
_config.GetSection("AA").Bind(aaConfig);
jsonValue += aaConfig.RabbitMqHostUrl + "\r\n";
jsonValue += aaConfig.RabbitMqHostName + "\r\n";
jsonValue += aaConfig.RabbitMqUserName + "\r\n";
jsonValue += aaConfig.RabbitMqPassword + "\r\n";
return jsonValue;

运行输出：