Microsoft.Extensions.Logging - LogError不是记录异常。

Question

我使用的是通过依赖注入获得的简单ASP.NET提供的记录器：Microsoft.Extensions.Logging.ILogger<T>。在实践中，动态类型是Microsoft.Extensions.Logging.Logger<T>。

当捕获异常时，我试图使用：_logger.LogError(exception, "message")记录它们，但是只打印消息。

namespace App
{
    public class App : IApp
    {
        private readonly ILogger<App> _logger;

        public PomParser(ILogger<App> logger)
            => _logger = logger;

        public void DoStuff()
        {
            try
            {
                DoStuffUnsafe();
            }
            catch (Exception ex)
            {
                _logger.LogError(ex,"Failed to do stuff");
            }
        }
    }
}

如何配置日志记录：

var host = new HostBuilder().ConfigureLogging(ConfigureLogging)...
...
await host.RunAsync();

        private static void ConfigureLogging(HostBuilderContext hostContext, ILoggingBuilder configLogging)
        {
            configLogging.ClearProviders();
            configLogging.AddConfiguration(hostContext.Configuration.GetSection("Logging"));
            configLogging.AddFile(
                options =>
                {
                    hostContext.Configuration.GetSection("FileLoggingOptions")
                        .Bind(options);
                }
            );
            configLogging.AddConsoleLogger();
        }

应用程序：

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "System": "Information",
      "Microsoft": "Information"
    }
  },
  "FileLoggingOptions": {
    "FileName": "app-",
    "LogDirectory": "logs",
    "FileSizeLimit": 10485760,
    "Extension": "log"
  }
}

Answer 1

请参见默认的MessageFormatter：https://github.com/aspnet/Logging/blob/master/src/Microsoft.Extensions.Logging.Abstractions/LoggerExtensions.cs

        private static string MessageFormatter(FormattedLogValues state, Exception error)
        {
            return state.ToString();
        }

它只是忽略了例外..。我实现了一个自定义控制台记录器：

public class ConsoleLoggerProvider : ILoggerProvider
{
    public void Dispose()
    {
    }

    public ILogger CreateLogger(string categoryName)
        => new ConsoleLogger(categoryName);

    private class ConsoleLogger : ILogger
    {
        private readonly string _categoryName;

        public ConsoleLogger(string categoryName)
            => _categoryName = categoryName;

        public void Log<TState>(
            LogLevel logLevel, EventId eventId, TState state, Exception exception,
            Func<TState, Exception, string> formatter
        )
        {
            if (!IsEnabled(logLevel))
            {
                return;
            }

            Console.WriteLine(
                $"{DateTime.UtcNow:yyyy-MM-dd HH:mm:ss} [{logLevel}] {_categoryName}: {state}{(exception != null ? "\n" : string.Empty)}{exception}"
            );
        }

        public bool IsEnabled(LogLevel logLevel)
            => true;

        public IDisposable BeginScope<TState>(TState state)
            => null;
    }
}

并利用它：

public static Task Main(string[] args)
    => WebHost.CreateDefaultBuilder(args)
        .ConfigureAppConfiguration(...)
        .ConfigureServices(...)
        .ConfigureLogging((hostContext, loggingBuilder) => loggingBuilder.AddProvider(new ConsoleLoggerProvider()))
        .UseStartup<Startup>()
        .Build()
        .RunAsyncSafe();

Answer 2

如果您的记录器没有记录异常，也可能是因为您意外地把传递参数的顺序弄错了：

_logger.LogError("An error occurred", e)     // WRONG: Exception will not be logged

正确的顺序是始终以第一个参数的形式提供异常对象：

_logger.LogError(e, "An error occurred")     // OK: Will log the exception

参考资料：

https://blog.rsuter.com/logging-with-ilogger-recommendations-and-best-practices/#always-pass-exception-as-first-parameter