如何为 log4net 中的多行日志条目添加缩进？

Question

我知道this question 并且我同意这个答案，但是我可以使用 log4net 执行以下操作吗？

而不是：

2013-04-09 12:54:47.093 INFO Main: Line 1 Line 1 Line 1
Line 2 Line 2 Line 2 
Line 3 Line 3 Line 3
2013-04-09 12:54:47.093 INFO Main: Line 1 Line 1 Line 1
Line 2 Line 2 Line 2 
Line 3 Line 3 Line 3

我可以有吗：

2013-04-09 12:54:47.093 INFO Main: Line 1 Line 1 Line 1
                                   Line 2 Line 2 Line 2 
                                   Line 3 Line 3 Line 3
2013-04-09 12:54:47.093 INFO Main: Line 1 Line 1 Line 1
                                   Line 2 Line 2 Line 2 
                                   Line 3 Line 3 Line 3

是否已经支持或者我需要编写自定义附加程序或自定义布局？

Answer 1

我讨厌回答自己的问题，但由于我自己开发了答案，所以我想与你分享。

我扩展了 log4net。该解决方案继承自 PatternLayout，因此所有 PatternLayout 功能都可用。此外，还提供了一种新模式 %indentation。要获得上例中的日志记录，只需使用：

<conversionPattern value="%date - %indentation%message%newline%exception"/>

当格​​式化异常时，log4net 代码很古怪（或者我不明白）。因此，在这种情况下，您应该始终将 %exception 放入模式中，因为我硬编码了“IgnoresException = false”。使用 IgnoresException = true，log4net 完全忽略任何格式，并且您会松动缩进。

使用下面的代码来扩展 log4net：

/// <summary>
/// Converts %indentation to string
/// </summary>
public class IndentationPatternConverter : PatternConverter
{
    protected override void Convert(TextWriter writer, object state)
    {
        // do nothing - %indentation is used for indentation, so nothing should be written
    }
}

public class IndentationPatternLayout : PatternLayout
{
    private PatternConverter m_head;

    public override void Format(TextWriter writer, LoggingEvent loggingEvent)
    {
        if (writer == null)
        {
            throw new ArgumentNullException("writer");
        }
        if (loggingEvent == null)
        {
            throw new ArgumentNullException("loggingEvent");
        }

        PatternConverter c = m_head;

        IndentationWriter indentationWriter = new IndentationWriter(writer);
        // loop through the chain of pattern converters
        while (c != null)
        {
            if (c is IndentationPatternConverter)
            {
                indentationWriter.SetIndentation();
            }
            c.Format(indentationWriter, loggingEvent);
            c = c.Next;
        }
        indentationWriter.Finish();
    }

    override public void ActivateOptions()
    {
        PatternParser patternParser = CreatePatternParser(ConversionPattern);

        ConverterInfo converterInfo = new ConverterInfo()
        {
            Name = "indentation",
            Type = typeof(IndentationPatternConverter)
        };

        patternParser.PatternConverters.Add("indentation", converterInfo);
        m_head = patternParser.Parse();

        PatternConverter curConverter = m_head;
        this.IgnoresException = false;
    }
}

public class IndentationWriter : TextWriter
{
    TextWriter writer;
    int indentation = 0;
    List<string> lines = new List<string>();

    public IndentationWriter(TextWriter writer)
    {
        this.writer = writer;
    }
    public override Encoding Encoding
    {
        get { return writer.Encoding; }
    }

    public override void Write(string value)
    {
        string[] values = value.Split(new string[] { Environment.NewLine }, StringSplitOptions.None);
        for (int i = 0; i < values.Length; i++)
        {
            if (i > 0) values[i] = Environment.NewLine + values[i];
        }
        lines.AddRange(values);
    }

    public void Finish()
    {
        for (int i = 0; i < lines.Count; i++)
        {
            string line = lines[i];
            if (i < lines.Count - 1) line = lines[i].Replace(Environment.NewLine, Environment.NewLine + new string(' ', indentation));
            writer.Write(line);
        }
        lines.Clear();
    }
    public override void WriteLine(string value)
    {
        this.Write(value + Environment.NewLine);
    }

    public void SetIndentation()
    {
        foreach (string line in lines)
        {
            indentation += line.Length;
        }
    }
}