封装一个基于NLog+NLog.Mongo的日志记录工具类LogUtil，nloglogutil

封装一个基于NLog+NLog.Mongo的日志记录工具类LogUtil，代码比较简单，主要是把MongoTarget的配置、FileTarget的配置集成到类中，同时利用缓存依赖来判断是否需要重新创建Logger类，完整代码如下：

using NLog;
using NLog.Config;
using NLog.Mongo;
using NLog.Targets;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Reflection;
using System.Web;
using System.Collections.Concurrent;
using NLog.Targets.Wrappers;

/// <summary>
/// 日志工具类(基于NLog.Mongo组件)
/// Author：左文俊
/// Date：2017/12/11
/// </summary>
public class LogUtil
{
    private NLog.Logger _Logger = null;
    private const string cacheKey_NLogConfigFlag = "NLogConfigFlag";
    private const string defaultMongoDbName = "SysLog";
    private static readonly object syncLocker = new object();
    private static readonly ConcurrentDictionary<string, LogUtil> cacheLogUitls = new ConcurrentDictionary<string, LogUtil>();
    private string loggerCacheDependencyFilePath = "";
    private bool needWriteLogToFile = true;
    private string mongoDbName = defaultMongoDbName;
    private string mongoDbCollectionName = "";
    private bool asyncWriteLog = true;

    public static LogUtil GetInstance(string mongoDbCollName, string loggerCacheDependencyFilePath = null, bool needWriteLogToFile = true)
    {
        string key = string.Format("{0}_{1}", defaultMongoDbName, mongoDbCollName);
        return cacheLogUitls.GetOrAdd(key, new LogUtil()
        {
            LoggerCacheDependencyFilePath = string.IsNullOrEmpty(loggerCacheDependencyFilePath) ? HttpContext.Current.Server.MapPath("~/Web.config") : loggerCacheDependencyFilePath,
            NeedWriteLogToFile = needWriteLogToFile,
            MongoDbName = defaultMongoDbName,
            MongoDbCollectionName = mongoDbCollName
        });
    }
    public string LoggerCacheDependencyFilePath
    {
        get
        {
            return loggerCacheDependencyFilePath;
        }
        set
        {
            if (!File.Exists(value))
            {
                throw new FileNotFoundException("日志配置缓存依赖文件不存在：" + value);
            }
            string oldValue = loggerCacheDependencyFilePath;
            loggerCacheDependencyFilePath = value;
            PropertyChanged(oldValue, loggerCacheDependencyFilePath);
        }
    }

    public bool NeedWriteLogToFile
    {
        get
        {
            return needWriteLogToFile;
        }
        set
        {
            bool oldValue = needWriteLogToFile;
            needWriteLogToFile = value;
            PropertyChanged(oldValue, needWriteLogToFile);
        }
    }

    public string MongoDbCollectionName
    {
        get
        {
            return mongoDbCollectionName;
        }
        set
        {
            string oldValue = mongoDbCollectionName;
            mongoDbCollectionName = value;
            PropertyChanged(oldValue, mongoDbCollectionName);
        }
    }

    /// <summary>
    /// 同一个项目只会用一个DB，故不对外公开，取默认DB
    /// </summary>
    private string MongoDbName
    {
        get
        {
            return mongoDbName;
        }
        set
        {
            string oldValue = mongoDbName;
            mongoDbName = value;
            PropertyChanged(oldValue, mongoDbName);
        }
    }

    public bool AsyncWriteLog
    {
        get
        {
            return asyncWriteLog;
        }
        set
        {
            bool oldValue = asyncWriteLog;
            asyncWriteLog = value;
            PropertyChanged(oldValue, asyncWriteLog);
        }
    }

    private void PropertyChanged<T>(T oldValue, T newValue) where T : IEquatable<T>
    {
        if (!oldValue.Equals(newValue) && _Logger != null)
        {
            lock (syncLocker)
            {
                _Logger = null;
            }
        }
    }

    private Logger GetLogger()
    {

        if (_Logger == null || HttpRuntime.Cache[cacheKey_NLogConfigFlag] == null)
        {
            lock (syncLocker)
            {
                if (_Logger == null || HttpRuntime.Cache[cacheKey_NLogConfigFlag] == null)
                {
                    string mongoDbConnectionSet = ConfigUtil.GetAppSettingValue("MongoDbConnectionSet");
                    if (!string.IsNullOrEmpty(mongoDbConnectionSet))
                    {
                        mongoDbConnectionSet = AESDecrypt(mongoDbConnectionSet);//解密字符串,若未加密则无需解密
                    }

                    LoggingConfiguration config = new LoggingConfiguration();

                    #region 配置MONGODB的日志输出对象

                    try
                    {
                        MongoTarget mongoTarget = new MongoTarget();
                        mongoTarget.ConnectionString = mongoDbConnectionSet;
                        mongoTarget.DatabaseName = mongoDbName;
                        mongoTarget.CollectionName = mongoDbCollectionName;
                        mongoTarget.IncludeDefaults = false;
                        AppendLogMongoFields(mongoTarget.Fields);

                        Target mongoTargetNew = mongoTarget;
                        if (AsyncWriteLog)
                        {
                            mongoTargetNew = WrapWithAsyncTargetWrapper(mongoTarget);//包装为异步输出对象，以便实现异步写日志
                        }

                        LoggingRule rule1 = new LoggingRule("*", LogLevel.Debug, mongoTargetNew);
                        config.LoggingRules.Add(rule1);
                    }
                    catch
                    { }

                    #endregion

                    #region 配置File的日志输出对象

                    if (NeedWriteLogToFile)
                    {
                        try
                        {
                            FileTarget fileTarget = new FileTarget();
                            fileTarget.Layout = @"[${date}] <${threadid}> - ${level} - ${event-context:item=Source} - ${event-context:item=UserID}: ${message};
                                                  StackTrace:${stacktrace};Other1:${event-context:item=Other1};Other2:${event-context:item=Other2};Other3:${event-context:item=Other3}";

                            string procName = System.Diagnostics.Process.GetCurrentProcess().ProcessName;
                            fileTarget.FileName = "${basedir}/Logs/" + procName + ".log";
                            fileTarget.ArchiveFileName = "${basedir}/archives/" + procName + ".{#}.log";
                            fileTarget.ArchiveNumbering = ArchiveNumberingMode.DateAndSequence;
                            fileTarget.ArchiveAboveSize =  *  * ;
                            fileTarget.ArchiveDateFormat = "yyyyMMdd";
                            fileTarget.ArchiveEvery = FileArchivePeriod.Day;
                            fileTarget.MaxArchiveFiles = ;
                            fileTarget.ConcurrentWrites = true;
                            fileTarget.KeepFileOpen = false;
                            fileTarget.Encoding = System.Text.Encoding.UTF8;

                            Target fileTargetNew = fileTarget;
                            if (AsyncWriteLog)
                            {
                                fileTargetNew = WrapWithAsyncTargetWrapper(fileTarget);//包装为异步输出对象，以便实现异步写日志
                            }

                            LoggingRule rule2 = new LoggingRule("*", LogLevel.Debug, fileTargetNew);
                            config.LoggingRules.Add(rule2);
                        }
                        catch
                        { }
                    }

                    #endregion

                    LogManager.Configuration = config;

                    _Logger = LogManager.GetCurrentClassLogger();

                    HttpRuntime.Cache.Insert(cacheKey_NLogConfigFlag, "Nlog", new System.Web.Caching.CacheDependency(loggerCacheDependencyFilePath));
                }
            }
        }

        return _Logger;

    }

    private void AppendLogMongoFields(IList<MongoField> mongoFields)
    {
        mongoFields.Clear();
        Type logPropertiesType = typeof(SysLogInfo.LogProperties);
        foreach (var pro in typeof(SysLogInfo).GetProperties(BindingFlags.Public | BindingFlags.Instance))
        {
            if (pro.PropertyType == logPropertiesType) continue;

            string layoutStr = string.Empty; //"${event-context:item=" + pro.Name + "}";
            if (pro.Name.Equals("ThreadID") || pro.Name.Equals("Level") || pro.Name.Equals("MachineName"))
            {
                layoutStr = "${" + pro.Name.ToLower() + "}";
            }
            else if (pro.Name.Equals("LogDT"))
            {
                layoutStr = "${date:format=yyyy-MM-dd HH\\:mm\\:ss}";
            }
            else if (pro.Name.Equals("Msg"))
            {
                layoutStr = "${message}";
            }

            if (!string.IsNullOrEmpty(layoutStr))
            {
                mongoFields.Add(new MongoField(pro.Name, layoutStr, pro.PropertyType.Name));
            }
        }
    }

    private Target WrapWithAsyncTargetWrapper(Target target)
    {
        var asyncTargetWrapper = new AsyncTargetWrapper();
        asyncTargetWrapper.WrappedTarget = target;
        asyncTargetWrapper.Name = target.Name;
        target.Name = target.Name + "_wrapped";
        target = asyncTargetWrapper;
        return target;
    }

    private LogEventInfo BuildLogEventInfo(LogLevel level, string msg, string source, string uid, string detailTrace = null, string other1 = null, string other2 = null, string other3 = null)
    {
        var eventInfo = new LogEventInfo();
        eventInfo.Level = level;
        eventInfo.Message = msg;
        eventInfo.Properties["DetailTrace"] = detailTrace;
        eventInfo.Properties["Source"] = source;
        eventInfo.Properties["Other1"] = other1;
        eventInfo.Properties["Other2"] = other2;
        eventInfo.Properties["Other3"] = other3;

        eventInfo.Properties["UserID"] = uid;

        return eventInfo;
    }

    public void Info(string msg, string source, string uid, string detailTrace = null, string other1 = null, string other2 = null, string other3 = null)
    {
        try
        {
            var eventInfo = BuildLogEventInfo(LogLevel.Info, msg, source, uid, detailTrace, other1, other2, other3);
            var logger = GetLogger();
            logger.Log(eventInfo);
        }
        catch
        { }
    }

    public void Warn(string msg, string source, string uid, string detailTrace = null, string other1 = null, string other2 = null, string other3 = null)
    {
        try
        {
            var eventInfo = BuildLogEventInfo(LogLevel.Warn, msg, source, uid, detailTrace, other1, other2, other3);

            var logger = GetLogger();
            logger.Log(eventInfo);
        }
        catch
        { }
    }

    public void Error(string msg, string source, string uid, string detailTrace = null, string other1 = null, string other2 = null, string other3 = null)
    {
        try
        {
            var eventInfo = BuildLogEventInfo(LogLevel.Error, msg, source, uid, detailTrace, other1, other2, other3);

            var logger = GetLogger();
            logger.Log(eventInfo);
        }
        catch
        { }
    }

    public void Error(Exception ex, string source, string uid, string other1 = null, string other2 = null, string other3 = null)
    {
        try
        {
            var eventInfo = BuildLogEventInfo(LogLevel.Error, ex.Message, source, uid, ex.StackTrace, other1, other2, other3);

            var logger = GetLogger();
            logger.Log(eventInfo);
        }
        catch
        { }
    }

    public void Log(LogLevel level, string msg, string source, string uid, string detailTrace = null, string other1 = null, string other2 = null, string other3 = null)
    {
        try
        {
            var eventInfo = BuildLogEventInfo(level, msg, source, uid, detailTrace, other1, other2, other3);
            var logger = GetLogger();
            logger.Log(eventInfo);
        }
        catch
        { }
    }

    public class SysLogInfo
    {
        public DateTime LogDT { get; set; }

        public int ThreadID { get; set; }

        public string Level { get; set; }

        public string Msg { get; set; }

        public string MachineName { get; set; }

        public LogProperties Properties { get; set; }

        public class LogProperties
        {
            public string Source { get; set; }

            public string DetailTrace { get; set; }

            public string UserID { get; set; }

            public string Other1 { get; set; }

            public string Other2 { get; set; }

            public string Other3 { get; set; }
        }
    }

}

封装这个日志工具类的目的就是为了保证日志格式的统一，同时可以快速的复制到各个项目中使用，而省去需要配置文件或因配置文件修改导致日志记录信息不一致的情况。

从代码中可以看出，若一旦属性发生改变，则缓存标识会失效，意味着会重新生成Logger对象，这样保证了Logger时刻与设置的规则相同。

另一点就是异步日志记录功能AsyncWriteLog，如果是基于配置文件，则只需要更改配置文件targets中配置async="true"即为异步。默认或写false都为同步，而代码上如何实现异步网上并没有介绍，我通过分析NLOG源代码找到关键点，即通过AsyncTargetWrapper异步目标包裹器来包装一次即可。