如何在log4net日志中添加堆栈跟踪、类及方法名？

问题根源 #

你的封装Logger类直接调用log4net的ILog方法时，log4net默认捕获的是Logger类内部的方法（如Debug/Info），而非业务代码中实际调用日志的位置。同时默认的%M（方法名）、%C（类名）转换符只能识别直接调用log4net API的层级，导致日志显示的是封装类的信息，而非业务代码的调用位置。

解决方案 #

方案1：修改Logger类，传递真实调用者信息 #

利用C#的CallerMemberName特性或StackFrame获取业务代码的调用位置，手动注入到log4net的LoggingEvent中：

using System;
using System.IO;
using System.Reflection;
using log4net;
using log4net.Core;
using System.Runtime.CompilerServices;

public class Logger : ILogger
{
    private readonly ILog _logger;
    private readonly Type _declaringType;

    public Logger()
    {
        _declaringType = MethodBase.GetCurrentMethod()?.DeclaringType ?? typeof(Logger);
        _logger = LogManager.GetLogger(_declaringType);
    }

    public void Debug(string message, 
        [CallerMemberName] string memberName = "", 
        [CallerFilePath] string filePath = "", 
        [CallerLineNumber] int lineNumber = 0)
    {
        Log(Level.Debug, message, null, memberName, filePath, lineNumber);
    }

    public void Info(string message, 
        [CallerMemberName] string memberName = "", 
        [CallerFilePath] string filePath = "", 
        [CallerLineNumber] int lineNumber = 0)
    {
        Log(Level.Info, message, null, memberName, filePath, lineNumber);
    }

    public void Error(string message, Exception? ex = null, 
        [CallerMemberName] string memberName = "", 
        [CallerFilePath] string filePath = "", 
        [CallerLineNumber] int lineNumber = 0)
    {
        Log(Level.Error, message, ex, memberName, filePath, lineNumber);
    }

    public void Warning(string message, 
        [CallerMemberName] string memberName = "", 
        [CallerFilePath] string filePath = "", 
        [CallerLineNumber] int lineNumber = 0)
    {
        Log(Level.Warn, message, null, memberName, filePath, lineNumber);
    }

    private void Log(Level level, string message, Exception? ex, string memberName, string filePath, int lineNumber)
    {
        if (!_logger.IsEnabledFor(level))
            return;

        var log4netLogger = _logger.Logger;
        var loggingEvent = new LoggingEvent(_declaringType, log4netLogger.Repository, log4netLogger.Name, level, message, ex);

        // 通过StackFrame获取真实的业务类名和方法名（偏移2：跳过Log和Debug/Info等封装方法）
        var stackFrame = new StackFrame(2, false);
        var method = stackFrame.GetMethod();
        if (method != null)
        {
            loggingEvent.Properties["CallerClass"] = method.DeclaringType?.Name;
            loggingEvent.Properties["CallerMethod"] = method.Name;
        }

        // 注入调用文件和行号
        loggingEvent.Properties["CallerFile"] = Path.GetFileName(filePath);
        loggingEvent.Properties["CallerLine"] = lineNumber;

        log4netLogger.Log(loggingEvent);
    }
}

方案2：调整log4net配置，输出自定义信息 #

修改log4net.config中的conversionPattern，使用自定义属性输出真实调用位置，同时添加%exception显示异常堆栈：

<configuration>
<log4net>
    <appender name="Console" type="log4net.Appender.ConsoleAppender">
        <layout type="log4net.Layout.PatternLayout">
            <conversionPattern value="%date [%-4thread] %-5level %logger [%property{CallerClass}.%property{CallerMethod} (%property{CallerFile}:%property{CallerLine})] - %message%newline%exception" />
        </layout>
    </appender>

    <appender name="RollingFileAppender" type="log4net.Appender.RollingFileAppender">
        <file value="Log.txt" />
        <appendToFile value="false" />
        <rollingStyle value="Size" />
        <maxSizeRollBackups value="10" />
        <maximumFileSize value="50MB" />
        <staticLogFileName value="true" />
        <layout type="log4net.Layout.PatternLayout">
            <conversionPattern value="%date [%-4thread] %-5level %logger [%property{CallerClass}.%property{CallerMethod} (%property{CallerFile}:%property{CallerLine})] - %message%newline%exception" />
        </layout>
    </appender>

    <root>
        <level value="INFO" />
        <appender-ref ref="Console" />
        <appender-ref ref="RollingFileAppender" />
    </root>
</log4net>
</configuration>

简化方案（无需修改代码） #

如果不想改动Logger类，可以直接使用%stacktrace转换符并指定偏移量，跳过封装层：

<conversionPattern value="%date [%-4thread] %-5level %logger %stacktrace{2} - %message%newline%exception" />

%stacktrace{2}表示跳过堆栈中的前2层（即Logger类的封装方法），直接显示业务代码的调用位置，输出格式类似：at MyApp.MqttService.Connect() in D:\Projects\MyApp\Services\MqttService.cs:line 45

效果验证 #

修改后日志输出会显示类似内容：

2022-11-08 10:02:41,161 [1234] WARN  Logger [MqttService.Disconnect (MqttService.cs:67)] - Disconnected from the MQTT broker
2022-11-08 10:02:41,161 [1234] ERROR Logger [MqttService.Connect (MqttService.cs:45)] - Failed to connect to the MQTT broker
System.Net.Sockets.SocketException: 连接失败
   at System.Net.Sockets.TcpClient.Connect(String hostname, Int32 port)
   at MyApp.MqttService.Connect() in D:\Projects\MyApp\Services\MqttService.cs:line 42

内容的提问来源于stack exchange，提问作者fuba