.NET Core日志配置的方法

熟悉ASP.NET的开发者一定对web.config文件不陌生。在ASP.NET环境中，要想添加配置参数，一般也都会在此文件中操作。其中最常用的莫过于AppSettings与ConnectionStrings两项。而要在代码中获得文件中的配置信息，ConfigurationManager则是必不可少需要引入的程序集。

然而到了ASP.NET Core时代，存储与读取配置的方式都发生了改变。

如果对ASP.NET Core项目有所了解的话，应该会看到过appsettings.json这个文件。这里就从JSON文件配置方式开始解释ASP.NET Core中是如何读取配置信息的。

假设有预先设置的appsettings.json文件：

{
 "option1": "value1_from_json",
 "option2": 2,

 "subsection": {
  "suboption1": "subvalue1_from_json"
 },
 "wizards": [
  {
   "Name": "Gandalf",
   "Age": "1000"
  },
  {
   "Name": "Harry",
   "Age": "17"
  }
 ]
}

在代码中读取可以按下面的方式操作：

public class Program
{
  public static IConfiguration Configuration { get; set; }

  public static void Main(string[] args = null)
  {
    var builder = new ConfigurationBuilder()
      .SetBasePath(Directory.GetCurrentDirectory())
      .AddJsonFile("appsettings.json");

    Configuration = builder.Build();

    Console.WriteLine($"option1 = {Configuration["Option1"]}");
    Console.WriteLine($"option2 = {Configuration["option2"]}");
    Console.WriteLine(
      $"suboption1 = {Configuration["subsection:suboption1"]}");
    Console.WriteLine();

    Console.WriteLine("Wizards:");
    Console.Write($"{Configuration["wizards:0:Name"]}, ");
    Console.WriteLine($"age {Configuration["wizards:0:Age"]}");
    Console.Write($"{Configuration["wizards:1:Name"]}, ");
    Console.WriteLine($"age {Configuration["wizards:1:Age"]}");
    Console.WriteLine();

    Console.WriteLine("Press a key...");
    Console.ReadKey();
  }
}

首先，实例化一个ConfigurationBuilder对象，接着设置基础路径。

SetBasePath的操作其实是在ConfigurationBuilder的属性字典里设置FileProvider的值。
public static IConfigurationBuilder SetBasePath(this IConfigurationBuilder builder, string basePath)
{
  ...
  
  return builder.SetFileProvider(new PhysicalFileProvider(basePath));
}

public static IConfigurationBuilder SetFileProvider(this IConfigurationBuilder builder, IFileProvider fileProvider)
{
  ...

  builder.Properties[FileProviderKey] = fileProvider ?? throw new ArgumentNullException(nameof(fileProvider));
  return builder;
}

然后是添加JSON文件。

public static IConfigurationBuilder AddJsonFile(this IConfigurationBuilder builder, IFileProvider provider, string path, bool optional, bool reloadOnChange)
{
  ...

  return builder.AddJsonFile(s =>
  {
    s.FileProvider = provider;
    s.Path = path;
    s.Optional = optional;
    s.ReloadOnChange = reloadOnChange;
    s.ResolveFileProvider();
  });
}

public static IConfigurationBuilder AddJsonFile(this IConfigurationBuilder builder, Action<JsonConfigurationSource> configureSource)
  => builder.Add(configureSource);								 
 1/3    1 2 3 下一页 尾页