我们知道log4net的日志功能非常强大,而使用方法也比较复杂;在ASP.NET Core 2.0下,可以通过一个第三方的扩展方法来降低我们的使用难度,具体使用方法如下:
我们先新建一个自己的静态类Log4Net,用于之后调用记录日志:

    public static class Log4Net
{
    private static readonly log4net.ILog log =
    log4net.LogManager.GetLogger(typeof(Log4Net));

    static void SetConfig()
    {
        XmlDocument log4netConfig = new XmlDocument();
        log4netConfig.Load(File.OpenRead("log4net.config"));

        var repo = log4net.LogManager.CreateRepository(
            Assembly.GetEntryAssembly(), typeof(log4net.Repository.Hierarchy.Hierarchy));

        log4net.Config.XmlConfigurator.Configure(repo, log4netConfig["log4net"]);
    }

    /// <summary>
    /// 信息
    /// </summary>
    /// <param name="Message"></param>
    public static void LogInfo(string Message)
    {
        if (!log.IsInfoEnabled)
            SetConfig();
        log.Info(Message);
    }

    /// <summary>
    /// 信息
    /// </summary>
    /// <param name="Message"></param>
    /// <param name="ex"></param>
    public static void LogInfo(string Message, Exception ex)
    {
        if (!log.IsInfoEnabled)
            SetConfig();
        log.Info(Message, ex);
    }

    /// <summary>
    /// 错误日志
    /// </summary>
    /// <param name="Message"></param>
    public static void ErrorInfo(string Message)
    {
        if (!log.IsErrorEnabled)
            SetConfig();
        log.Error(Message);
    }

    /// <summary>
    /// 错误日志
    /// </summary>
    /// <param name="Message"></param>
    /// <param name="ex"></param>
    public static void Error(Exception ex)
    {
        if (!log.IsInfoEnabled)
            SetConfig();
        log.Error("异常", ex);
    }

    /// <summary>
    /// 错误日志
    /// </summary>
    /// <param name="Message"></param>
    /// <param name="ex"></param>
    public static void ErrorInfo(string Message, Exception ex)
    {
        if (!log.IsErrorEnabled)
            SetConfig();
        log.Error(Message, ex);
    }

    /// <summary>
    /// Debug日志
    /// </summary>
    /// <param name="Message"></param>
    public static void DebugInfo(string Message)
    {
        if (!log.IsDebugEnabled)
            SetConfig();
        log.Debug(Message);
    }

    /// <summary>
    /// Debug日志
    /// </summary>
    /// <param name="Message"></param>
    /// <param name="ex"></param>
    public static void DebugInfo(string Message, Exception ex)
    {
        if (!log.IsDebugEnabled)
            SetConfig();
        log.Debug(Message, ex);
    }

    /// <summary>
    /// 警告
    /// </summary>
    /// <param name="Message"></param>
    public static void WarnInfo(string Message)
    {
        if (!log.IsWarnEnabled)
            SetConfig();
        log.Warn(Message);
    }

    /// <summary>
    /// 警告
    /// </summary>
    /// <param name="Message"></param>
    /// <param name="ex"></param>
    public static void WarnInfo(string Message,Exception ex)
    {
        if (!log.IsWarnEnabled)
            SetConfig();
        log.Warn(Message,ex);
        
    }

    /// <summary>
    /// 致命错误
    /// </summary>
    /// <param name="Message"></param>
    public static void FataInfo(string Message)
    {
        if (!log.IsFatalEnabled)
            SetConfig();
        log.Fatal(Message);
    }

    /// <summary>
    /// 致命错误
    /// </summary>
    /// <param name="Message"></param>
    /// <param name="ex"></param>
    public static void FataInfo(string Message,Exception ex)
    {
        if (!log.IsFatalEnabled)
            SetConfig();
        log.Fatal(Message, ex);
    }

该类下需要通过NuGet安装下面几个扩展:

  1. Microsoft.Extensions.Logging

  2. Microsoft.Extensions.Logging.Log4Net.AspNetCore

  3. log4net

之后log4net.config配置文件内容:

<log4net>
    <appender name="Console" type="log4net.Appender.ConsoleAppender">
        <layout type="log4net.Layout.PatternLayout">
            <!-- Pattern to output the caller's file name and line number -->
            <conversionPattern value="%5level [%thread] - STACK: %exception{stacktrace} - MESSAGE: %message%newline" />
        </layout>
    </appender>

    <appender name="RollingFile" type="log4net.Appender.RollingFileAppender">
        <!--<file value="Log4Net" />
        <appendToFile value="true" />
    <rollingStyle value="Date" />
    <datePattern value="yyyyMMdd&quot;.log&quot;" />
        <maximumFileSize value="100KB" />
        <maxSizeRollBackups value="2" />-->
    <param name="File" value="logfile/" />
    <param name="AppendToFile" value="true" />
    <param name="RollingStyle" value="Date" />
    <param name="DatePattern" value="yyyyMMdd&quot;.log&quot;" />
    <param name="StaticLogFileName" value="false" />

        <layout type="log4net.Layout.PatternLayout">
            <!--<conversionPattern value="%level %thread - STACK: %exception{stacktrace} - MESSAGE: %message%newline" />-->
      <param name="ConversionPattern" value="%d [%t] %-5p %c - %m%n" />
        </layout>
    </appender>

    <root>
        <level value="ALL" />
        <appender-ref ref="Console" />
        <appender-ref ref="RollingFile" />
    </root>
</log4net>

最后,修改Startup.cs文件的Configure方法,增加新参数如下:

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)

在Configure方法中,添加:

loggerFactory.AddLog4Net();

完整如下:

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            loggerFactory.AddLog4Net();

            app.UseStaticFiles();

            app.UseMvc();
        }

测试:
我们写个测试的来看看,在Program类的静态方法中,添加段代码测试一下:

        public static void Main(string[] args)
        {
            Logger.Log4Net.LogInfo("test测试");

            try
            {
                int a = 5;
                int b = 1 / (a - 5);
            }
            catch (Exception e)
            {
                Logger.Log4Net.ErrorInfo("异常信息", e);
            }
            BuildWebHost(args).Run();
        }

运行之后,我们会在根目录下的logfile文件夹中,看到出现了一个日志文件:20180513.log
打开,内容如下:

2018-05-13 22:43:12,039 [1] INFO  Biz126.Logger.Log4Net - test测试
2018-05-13 22:43:12,930 [1] ERROR Biz126.Logger.Log4Net - 异常信息
System.DivideByZeroException: Attempted to divide by zero.
   at Biz126.WebAPI.Program.Main(String[] args) in D:\Items\Log测试\Biz126.WebAPI\Program.cs:line 23
2018-05-13 22:43:18,274 [5] INFO  Microsoft.AspNetCore.Hosting.Internal.WebHost - Request starting HTTP/1.1 GET http://localhost:65176/api/values  
2018-05-13 22:43:18,753 [5] INFO  Microsoft.AspNetCore.Hosting.Internal.WebHost - Request finished in 479.9045ms 404 

符合预期,以上。