详解.Net Core中的日志组件(Logging)

  [Route("api/[controller]")]
  public class ValuesController : Controller
  {
    ILogger logger;
     //构造函数注入Logger
    public ValuesController(ILogger logger)
    {
      this.logger = logger;
    }
    [HttpGet]
    public IEnumerable Get()
    {
      logger.LogWarning("Warning");
      return new string[] { "value1", "value2" };
    }
  }

public class Program
  {
    public static void Main(string[] args)
    {
      BuildWebHost(args).Run();
    }
    public static IWebHost BuildWebHost(string[] args) =>
      WebHost.CreateDefaultBuilder(args)//在这里使用了默认配置
        .UseStartup()
        .Build();
  }

        builder.UseKestrel((builderContext, options) =>
        {
          options.Configure(builderContext.Configuration.GetSection("Kestrel"));
        })
        .ConfigureAppConfiguration((hostingContext, config) =>
        {
          var env = hostingContext.HostingEnvironment;
            //加载appsettings.json文件 使用模板创建的项目，会生成一个配置文件，配置文件中包含Logging的配置项
          config.AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
             .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true, reloadOnChange: true);
            .......
        })
        .ConfigureLogging((hostingContext, logging) =>
        { 
            //从appsettings.json中获取Logging的配置
          logging.AddConfiguration(hostingContext.Configuration.GetSection("Logging"));
            //添加控制台输出
          logging.AddConsole();
            //添加调试输出
          logging.AddDebug();
        })

public class Program
  {
    public static void Main(string[] args)
    {
      //指定配置文件路径
      var config = new ConfigurationBuilder()
                .SetBasePath(Directory.GetCurrentDirectory())//设置基础路径
                .AddJsonFile($"appsettings.json", true, true)//加载配置文件
                .AddJsonFile($"appsettings.{EnvironmentName.Development}.json", true, true)
                .Build();

      var host = new WebHostBuilder()
            .UseKestrel()
            .UseStartup()
            .UseContentRoot(Directory.GetCurrentDirectory())
            .UseConfiguration(config)//使用配置
            .UseUrls(config["AppSettings:Url"])//从配置中读取 程序监听的端口号
            .UseEnvironment(EnvironmentName.Development)//如果加载了多个环境配置，可以设置使用哪个配置 一般有测试环境、正式环境

              //.ConfigureLogging((hostingCotext, logging) => //第一种配置方法 直接在webHostBuilder建立时配置 不需要修改下面的Startup代码
                          //{
                          //     logging.AddConfiguration(hostingCotext.Configuration.GetSection("Logging"));
                          //     logging.AddConsole();
                          //})
            .Build();
      host.Run();
    }
  }

public class Startup
  {
    public IConfiguration Configuration { get; private set; }
    public IHostingEnvironment HostingEnvironment { get; private set; }
    //在构造函数中注入 IHostingEnvironment和IConfiguration，配置已经在Program中设置了，注入后就可以获取配置文件的数据
    public Startup(IHostingEnvironment env, IConfiguration config)
    {
      HostingEnvironment = env;
      Configuration = config;
    }
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddMvc();
        //第二种配置 也可以这样加上日志功能，不用下面的注入
              //services.AddLogging(builder => 
              //{
                //  builder.AddConfiguration(Configuration.GetSection("Logging"))
                //    .AddConsole();
              //});
    }
     //注入ILoggerFactory 
    public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
    {
      if (env.IsDevelopment())
      {
        app.UseDeveloperExceptionPage();
      }
       //第三种配置 注入ILogggerFactory,然后配置参数
      //添加控制台输出
      loggerFactory.AddConsole(Configuration.GetSection("Logging"));
       //添加调试输出
      loggerFactory.AddDebug();
      app.UseMvc();
    }
  }

public static IServiceCollection AddLogging(this IServiceCollection services, Action configure)
    {
      services.AddOptions();//这里会注入最基础的5个服务 option相关服务只要是跟配置文件相关，通过Option服务获取相关配置文件参数参数 

      services.TryAdd(ServiceDescriptor.Singleton());
      services.TryAdd(ServiceDescriptor.Singleton(typeof(ILogger<>), typeof(Logger<>)));
      services.TryAddEnumerable(ServiceDescriptor.Singleton>(new DefaultLoggerLevelConfigureOptions(LogLevel.Information)));

      configure(new LoggingBuilder(services));
      return services;
    }

 public static ILoggingBuilder AddConfiguration(this ILoggingBuilder builder, IConfiguration configuration)
    {
      builder.AddConfiguration();
       //下面为AddConfiguration的实现

        public static void AddConfiguration(this ILoggingBuilder builder)
            {
                builder.Services.TryAddSingleton();
                builder.Services.TryAddSingleton(typeof(ILoggerProviderConfiguration<>), typeof(LoggerProviderConfiguration<>));
            }
      builder.Services.AddSingleton>(new LoggerFilterConfigureOptions(configuration));
      builder.Services.AddSingleton>(new ConfigurationChangeTokenSource(configuration));
      builder.Services.AddSingleton(new LoggingConfiguration(configuration));

      return builder;
    }

public void Log(LogLevel logLevel, EventId eventId, TState state, Exception exception, Func formatter)    
{
       var loggers = Loggers;
      List exceptions = null;
       //loggers为LoggerInformation数组，如果你在Startup中添加了Console、Deubg日志功能了，那loggers数组值有2个，就是它俩。
      foreach (var loggerInfo in loggers)
      {  //循环遍历每一种日志打印，如果满足些日子的条件，才执行打印log方法。比如某一个日志等级为Info,
          //但是Console配置的最低打印等级为Warning，Debug配置的最低打印等级为Debug
          //则Console中不会打印，Debug中会被打印
        if (!loggerInfo.IsEnabled(logLevel))
        {
          continue;
        }
        try
        {
            //每一种类型的日志，对应的打印方法不同。执行对应的打印方法
          loggerInfo.Logger.Log(logLevel, eventId, state, exception, formatter);
        }
        catch (Exception ex)
        {
          if (exceptions == null)
          {
            exceptions = new List();
          }

          exceptions.Add(ex);
        }
      }
    }

public void Log(LogLevel logLevel, EventId eventId, TState state, Exception exception, Func formatter)
    {
       //代码太多 我就省略一些判空代码
      var message = formatter(state, exception);

      if (!string.IsNullOrEmpty(message) || exception != null)
      {
        WriteMessage(logLevel, Name, eventId.Id, message, exception);
      }
    }

    public virtual void WriteMessage(LogLevel logLevel, string logName, int eventId, string message, Exception exception)
    {
       .......
      if (logBuilder.Length > 0)
      {
        var hasLevel = !string.IsNullOrEmpty(logLevelString);
        //这里是主要的代码实现，可以看到，并没有写日志的代码，而是将日志打入到一个BlockingCollection队列中
        _queueProcessor.EnqueueMessage(new LogMessageEntry()
        {
          Message = logBuilder.ToString(),
          MessageColor = DefaultConsoleColor,
          LevelString = hasLevel ? logLevelString : null,
          LevelBackground = hasLevel ? logLevelColors.Background : null,
          LevelForeground = hasLevel ? logLevelColors.Foreground : null
        });
      }
       ......
    }

public class ConsoleLoggerProcessor : IDisposable
  {
        private const int _maxQueuedMessages = 1024;
        private readonly BlockingCollection _messageQueue = new BlockingCollection(_maxQueuedMessages);
        private readonly Thread _outputThread;
   public IConsole Console;

    public ConsoleLoggerProcessor()
    {
      //在构造函数中启动一个线程，执行ProcessLogQueue方法
       //从下面ProcessLogQueue方法可以看出，是循环遍历集合，将集合中的数据打印

      _outputThread = new Thread(ProcessLogQueue)
      {
        IsBackground = true,
        Name = "Console logger queue processing thread"public virtual void EnqueueMessage(LogMessageEntry message)
    {
      if (!_messageQueue.IsAddingCompleted)
      {
        try
        {
          _messageQueue.Add(message);
          return;
        }
        catch (InvalidOperationException) { }
      }

      WriteMessage(message);
    }

    internal virtual void WriteMessage(LogMessageEntry message)
    {
      if (message.LevelString != null)
      {
        Console.Write(message.LevelString, message.LevelBackground, message.LevelForeground);
      }

      Console.Write(message.Message, message.MessageColor, message.MessageColor);
      Console.Flush();
    }

    private void ProcessLogQueue()
    {
    
      try
        {
          //GetConsumingEnumerable()方法比较特殊，当集合中没有值时，会阻塞自己，一但有值了，知道集合中又有元素继续遍历
          foreach (var message in _messageQueue.GetConsumingEnumerable())
        {
          WriteMessage(message);
        }
      }
      catch
      {
        try
        {
          _messageQueue.CompleteAdding();
        }
        catch { }
      }
    }
  }