首先配置web.config文件
1.添加如下节点
<!--log4net配置 BEGIN-->
<configSections>
    <section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler, log4net"/>
</configSections>

<log4net debug="true">
    <appender name="LogFileAppender" type="log4net.Appender.FileAppender">
      <param name="File" value="SysLog/ErrorLog.txt"/>
      <layout type="log4net.Layout.PatternLayout">
        <param name="ConversionPattern" value="%d [%t] %-5p %c %m%n"/>
      </layout>
    </appender>

<logger name="File">
      <level value="All" />
      <appender-ref ref="LogFileAppender" />
    </logger>
</log4net>
<!--log4net配置 END-->

2.然后配置global.asax

void Application_Start(object sender, EventArgs e)
{
//注册日志配置
log4net.Config.XmlConfigurator.Configure();

}
void Application_Error(object sender, EventArgs e)
{
//在出现未处理的错误时运行的代码
NetFan.Core.Logger.Log.Error(e.ToString());
}

3.新建一个全局使用的类Logger

/// <summary>
/// 类，事件日志类。
/// 单态封装log4net
/// </summary>
public class Logger
{
private static log4net.ILog log = null;
private static object lockHelper = new object();

public static log4net.ILog Log
{
get
{
if (log == null)
lock (lockHelper)
if (log == null)
log = log4net.LogManager.GetLogger("File");
return log;
}
}
}

4.上面ok后, 就可以使用了.
方法是:

Try
{
//处理信息
}

catch(Exception ex)
{
//出错后执行日志.IP如果是127.0.0.1可以不用写入日志.
Logger.Log.Error("错误来自:"+Request.UserHostAddress,ex);

}
公司项目的配置:

<configuration>
  <configSections>
    <section name="SSO" type="SXT.SSO.Client.SSOEntry,SXT.SSO.Client"/>
    <section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler, log4net"/>

......

<!--log4net配置 BEGIN-->
    <log4net debug="true">
        <appender name="LogFileAppender" type="log4net.Appender.RollingFileAppender">
            <file value="../Log/RES"/>
            <AppendToFile value="true"/>
            <rollingstyle value="date"/>
            <datePattern value="yyyy-MM-dd'.log'"/>
            <StaticLogFileName value="false"/>
            <maxSizeRollBackups value="100"/>
            <layout type="log4net.Layout.PatternLayout">
                <param name="ConversionPattern" value="记录时间：%date 线程ID:[%thread] 日志级别：%-5level 错误描述：%message%newline"/>
            </layout>
        </appender>
        <appender name="ConsoleAppender" type="log4net.Appender.ConsoleAppender">
            <layout type="log4net.Layout.PatternLayout">
                <conversionPattern value="%date [%thread] %-5level %logger [%property{NDC}] - %message%newline" />
            </layout>
        </appender>
        <root>
            <level value="debug"/>
            <appender-ref ref="LogFileAppender"/>
            <!--<appender-ref ref="ConsoleAppender"/>-->
        </root>
    </log4net>
  <!--log4net配置 END-->