我們在編寫程序時，會在程序運行過程中記錄一些日志。log4net作為一款經久耐用的日志組件，值得我們信賴。在中小型公司中，往往沒有專業的日志服務器來處理應用程序產生的日志，而格式化不好的日志文件又為上線後日志的統計、分析、查找造成了困難。
Excel作為一款常用的辦公軟件，用來處理一些中小數量級的數據還是游刃有余的。如果log4net輸出的日志能夠直接導入Excel，那麼查詢和分析起來豈不是要快很多？
我們有很多方法可以實現這個功能，csv的優勢是其文件格式比較簡單，可以用任意的文本編輯器打開，而且解析起來比較方便。效果如下：
1 using System.IO;
2 using System.Text;
3
4 namespace CoderBusy.Log4Net.Layout
5 {
6 public class CsvTextWriter : TextWriter
7 {
8 private readonly TextWriter _textWriter;
9
10 public CsvTextWriter(TextWriter textWriter)
11 {
12 _textWriter = textWriter;
13 }
14
15 public override Encoding Encoding => _textWriter.Encoding;
16
17 public override void Write(char value)
18 {
19 _textWriter.Write(value);
20 if (value == '"')
21 _textWriter.Write(value);
22 }
23
24 public void WriteQuote()
25 {
26 _textWriter.Write('"');
27 }
28 }
29 }
NewFieldConverter.cs
1 using System.IO;
2 using log4net.Util;
3
4 namespace CoderBusy.Log4Net.Layout
5 {
6 public class NewFieldConverter : PatternConverter
7 {
8 protected override void Convert(TextWriter writer, object state)
9 {
10 var ctw = writer as CsvTextWriter;
11 ctw?.WriteQuote();
12
13 writer.Write(',');
14
15 ctw?.WriteQuote();
16 }
17 }
18 }
EndRowConverter.cs
1 using System.IO;
2 using log4net.Util;
3
4 namespace CoderBusy.Log4Net.Layout
5 {
6 public class EndRowConverter : PatternConverter
7 {
8 protected override void Convert(TextWriter writer, object state)
9 {
10 var ctw = writer as CsvTextWriter;
11
12 ctw?.WriteQuote();
13
14 writer.WriteLine();
15 }
16 }
17 }
CsvPatternLayout.cs
1 using System.IO;
2 using log4net.Core;
3 using log4net.Layout;
4
5 namespace CoderBusy.Log4Net.Layout
6 {
7 public class CsvPatternLayout : PatternLayout
8 {
9 public override void ActivateOptions()
10 {
11 AddConverter("newfield", typeof(NewFieldConverter));
12 AddConverter("endrow", typeof(EndRowConverter));
13 base.ActivateOptions();
14 }
15
16 public override void Format(TextWriter writer, LoggingEvent loggingEvent)
17 {
18 var ctw = new CsvTextWriter(writer);
19 ctw.WriteQuote();
20 base.Format(ctw, loggingEvent);
21 }
22 }
23 }
在書寫 log4net 的配置文件時，只要將 appender 的 layout 設置為 CoderBusy.Log4Net.Layout.CsvPatternLayout ，且設置好日志頭，日志格式即可。注意，header後需要編寫換行字符，%newfield代表字段分隔符，%endrow代表一行結束。
<layout type="CoderBusy.Log4Net.Layout.CsvPatternLayout,CoderBusy.Log4Net">
<header value="Time,Thread,Level,Logger,Message,Exception " />
<conversionPattern
value="%date{yyyy-MM-dd HH:mm:ss}%newfield%thread%newfield%level%newfield%logger%newfield%message%newfield%exception%endrow" />
</layout>
我為初學者准備了一個log4net的配置文件。這個配置文件會將日志在控制台和csv文件中同時輸出，每天一個CSV文件（本地時間），且控制台中，不同的日志級別會有不同的顏色。
1 <?xml version="1.0" encoding="utf-8"?>
2
3 <configuration>
4 <configSections>
5 <section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler, log4net" />
6 </configSections>
7 <log4net xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
8 <appender name="RollingLogFileAppender" type="log4net.Appender.RollingFileAppender">
9 <param name="File" value="Logs/" />
10 <param name="AppendToFile" value="True" />
11 <param name="MaxSizeRollBackups" value="10" />
12 <param name="StaticLogFileName" value="false" />
13 <param name="DatePattern" value="yyyy-MM-dd".csv"" />
14 <param name="RollingStyle" value="Date" />
15 <layout type="CoderBusy.Log4Net.Layout.CsvPatternLayout,CoderBusy.Log4Net">
16 <header value="Time,Thread,Level,Logger,Message,Exception " />
17 <conversionPattern
18 value="%date{yyyy-MM-dd HH:mm:ss}%newfield%thread%newfield%level%newfield%logger%newfield%message%newfield%exception%endrow" />
19 </layout>
20 </appender>
21
22 <appender name="ColoredConsoleAppender" type="log4net.Appender.ColoredConsoleAppender">
23 <mapping>
24 <level value="ERROR" />
25 <foreColor value="Red" />
26 </mapping>
27 <mapping>
28 <level value="INFO" />
29 <foreColor value="Green" />
30 </mapping>
31
32 <layout type="log4net.Layout.PatternLayout">
33 <conversionPattern value="# %date{HH:mm:ss} [%thread] %-5level %logger #%newline%message%newline" />
34 </layout>
35 <filter type="log4net.Filter.LevelRangeFilter">
36 <param name="LevelMin" value="DEBUG" />
37 <param name="LevelMax" value="FATAL" />
38 </filter>
39 </appender>
40
41 <root>
42 <!-- OFF < FATAL < ERROR < WARN < INFO < DEBUG < ALL -->
43 <level value="ALL" />
44 <appender-ref ref="RollingLogFileAppender" />
45 <appender-ref ref="ColoredConsoleAppender" />
46 </root>
47 </log4net>
48 </configuration>
配合以上配置，測試一下功能。
1 using System;
2 using log4net;
3 using log4net.Config;
4
5 [assembly: XmlConfigurator(ConfigFile = "log4net.config")]
6
7 namespace CoderBusy.Log4Net.Tests
8 {
9 internal class Program
10 {
11 public static void Main(string[] args)
12 {
13 var log = LogManager.GetLogger("Default");
14 log.Debug("Message", new Exception("Test Exception"));
15 log.Info("Hello World.");
16 log.WarnFormat("A={0} B={1}", "\"123123", Environment.NewLine);
17 Console.ReadLine();
18 }
19 }
20 }
Logs文件夾中，生成的csv文件內容如下：
Time,Thread,Level,Logger,Message,Exception
"2016-08-25 23:13:19","9","DEBUG","Default","Message","System.Exception: Test Exception
"
"2016-08-25 23:13:19","9","INFO","Default","Hello World.",""
"2016-08-25 23:13:19","9","WARN","Default","A=""123123 B=
",""
輸出字段被使用雙引號包裹，且消息體中的雙引號被重復輸出。這樣的結果表明我們的程序是正常的。本文的代碼可以在 http://pan.baidu.com/s/1hr4EOPu 下載，謝謝閱讀，並祝你成功。
