在ASP.Net Core Web API中使用Log4Net

1、引用Log4Net

在Nuget中引入Log4Net和Microsoft.Extensions.Logging.Log4Net.AspNetCore。

2、配置Log4Net

(1) 整理配置文件

<?xml version="1.0" encoding="utf-8" ?>
<log4net>
    <appender name="RollingLogFileAppender" type="log4net.Appender.RollingFileAppender">
      <file value="log\log.txt" />
      
      <!-- 追加日志内容 -->
      <appendToFile value="true" />

      <!-- 修小锁定模型：允许多个进程写入同一个文件 -->
      <lockingModel type="log4net.Appender.FileAppender+MinimalLock" />

      <!-- 备份文件格式 -->
      <datePattern value="yyyyMMdd.txt" />

      <!-- 仅根据文件大小滚动文件 -->
      <rollingStyle value="Size" />

      <!-- 备份文件的个数(-1不做限制) -->
      <maxSizeRollBackups value="-1" />

      <!-- 单个日志文件最大的大小 -->
      <maximumFileSize value="50MB" />
      
      <layout type="log4net.Layout.PatternLayout">
          <conversionPattern value="%date [%thread] %-5level %logger [%property{NDC}] - %message%newline" />
      </layout>
    </appender>
    <root>
        <level value="ALL" />
        <appender-ref ref="RollingLogFileAppender" />
    </root>
</log4net>

(2) 在Program类中配置Log4Net

public static IHostBuilder CreateHostBuilder(string[] args) =>
	Host.CreateDefaultBuilder(args)
		.ConfigureLogging(loggingBuilder =>
		{
			//支持IOC控制反转
			loggingBuilder.AddLog4Net("Config/log4net.config");
		})
		.ConfigureWebHostDefaults(webBuilder =>
		{
			webBuilder.UseStartup<Startup>();
		});

3、使用Log4Net

通过依赖注入使用Logger。

[ApiController]
[Route("api/[controller]")]
public class WeatherForecastController : ControllerBase
{
	private static readonly string[] Summaries = new[]
	{
		"Freezing", "Bracing", "Chilly", "Cool", "Mild", "Warm", "Balmy", "Hot", "Sweltering", "Scorching"
	};

	private readonly ILogger<WeatherForecastController> _logger;

	public WeatherForecastController(ILogger<WeatherForecastController> logger)
	{
		_logger = logger;
	}

	[HttpGet]
	public IEnumerable<WeatherForecast> Get()
	{
		_logger.LogInformation("Get WeatherForecast");

		var rng = new Random();
		return Enumerable.Range(1, 5).Select(index => new WeatherForecast
		{
			Date = DateTime.Now.AddDays(index),
			TemperatureC = rng.Next(-20, 55),
			Summary = Summaries[rng.Next(Summaries.Length)]
		})
		.ToArray();
	}
}

4、过滤系统日志

//过滤日志
loggingBuilder.AddFilter("System", LogLevel.Information);
loggingBuilder.AddFilter("System", LogLevel.Warning);
loggingBuilder.AddFilter("Microsoft", LogLevel.Information);
loggingBuilder.AddFilter("Microsoft", LogLevel.Warning);
loggingBuilder.AddFilter("Microsoft.Hosting.Lifetime", LogLevel.Information);
loggingBuilder.AddFilter("Microsoft.Hosting.Lifetime", LogLevel.Warning);