这将是一个冗长的问题，但请耐心等待。我正在尝试为我们的应用程序创建一个日志组件，它可以扩展到插件新的日志框架（NLog、Log4Net ec）。现在我知道我们已经有了 Ben Foster 编写的 Common.Logging 外观，但我想尝试一些更定制的东西。在我们的案例中，主要要求之一是我们需要一种使用日志框架（在本例中为 NLog）将单个参数/值记录到数据库的自定义机制。所以我有一个简单的日志接口：
/// <summary>
/// Interface for implementing a Logger Provider.
/// </summary>
public interface ILogger
{
/// <summary>
/// Logs an Info level diagnostics message.
/// </summary>
/// <param name="logInfo">The Log Info object.</param>
void Info(LogInfo logInfo);
/// <summary>
/// Logs a Warn level diagnostics message.
/// </summary>
/// <param name="logInfo">The Log Info object.</param>
void Warn(LogInfo logInfo);
/// <summary>
/// Logs a Debug level diagnostics message.
/// </summary>
/// <param name="logInfo">The Log Info object.</param>
void Debug(LogInfo logInfo);
/// <summary>
/// Logs an Error level diagnostics message.
/// </summary>
/// <param name="logInfo">The Log Info object.</param>
void Error(LogInfo logInfo);
/// <summary>
/// Logs an Fatal level diagnostics message.
/// </summary>
/// <param name="logInfo">The Log Info object.</param>
void Fatal(LogInfo logInfo);
}
LogInfo 对象包含所有必要的日志记录信息。我有一个实现接口的抽象类：
public abstract class NLogLoggerBase : ILogger
{
....
}
它被细分为：
public class NLogDatabaseLogger : NLogLoggerBase
{
public NLogDatabaseLogger(ILogUtility logUtility)
: base(logUtility)
{
//Make sure the custom target is registered for use BEFORE using it.
ConfigurationItemFactory.Default.Targets.RegisterDefinition("DatabaseLog", typeof(DatabaseLogTarget));
//initialize the _logger
_logger = LogManager.GetLogger("DatabaseLogger");
}
}
和
public class NLogFileLogger : NLogLoggerBase
{
....
}
数据库记录器使用自定义的 DatabaseTarget（继承自 NLog 中的 TargetWithLayout）来登录数据库，文件记录器也是如此。NLog 的基本设置连接在 App.Config 中：
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<configSections>
<section name="nlog" type="NLog.Config.ConfigSectionHandler, NLog" />
</configSections>
<nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
autoReload="true" throwExceptions="false" internalLogFile="C:\Temp\nlog.txt" internalLogLevel="Info"
internalLogToConsole="false">
<targets async="true">
<target name="CustomDatabaseLog" xsi:type="DatabaseLog" />
<target name="CustomFileLog" xsi:type="File" />
</targets>
<rules>
<logger name="DatabaseLogger" minlevel="Info" writeTo="CustomDatabaseLog" />
<logger name="FileLogger" minlevel="Info" writeTo="CustomFileLog" />
</rules>
</nlog>
</configuration>
到目前为止，一切都很好。我对每个记录器进行了几次测试，它们可以很好地记录到各自的目标。
然后我写了一个 Logger 工厂，它将根据记录器类型返回 ILogger 接口的正确实现：
/// <summary>
/// Provides an interface for a factory which returns a logger component.
/// </summary>
public interface ILoggerFactory
{
/// <summary>
/// Creates an instance of logger component based on dependency registration key.
/// </summary>
/// <param name="loggerName">The dependency registration key.</param>
/// <returns>An Instance of logger component.</returns>
ILogger CreateLogger(string loggerName);
}
和实施：
/// <summary>
/// Implementation of ILoggerFactory interface.
/// </summary>
public class NLogLoggerFactory : ILoggerFactory
{
private readonly ILogger _nlogDatabaseLogger;
private readonly ILogger _nlogFileLogger;
public NLogLoggerFactory(ILogger nlogDatabaseLogger, ILogger nlogFileLogger)
{
if (nlogDatabaseLogger == null)
throw new ArgumentNullException("nlogDatabaseLogger");
if (nlogFileLogger == null)
throw new ArgumentNullException("nlogFileLogger");
_nlogDatabaseLogger = nlogDatabaseLogger;
_nlogFileLogger = nlogFileLogger;
}
/// <summary>
/// Creates an instance of logger component based on dependency registration key.
/// </summary>
/// <param name="loggerKey">The dependency registration key.</param>
/// <returns>An Instance of logger component.</returns>
public ILogger CreateLogger(string loggerKey)
{
if (loggerKey.Equals(DependencyRegistrationKeys.NLogDatabaseLoggerKey))
return _nlogDatabaseLogger;
if (loggerKey.Equals(DependencyRegistrationKeys.NLogFileLoggerKey))
return _nlogFileLogger;
throw new ArgumentException("Invalid loggerKey");
}
所以我去用 Unity 把它连接起来。这是我敲出的快速测试用例（我知道它需要重构，但仅用于说明目的）：
[Test]
public void Test_if_logger_factory_returns_correct_implementation()
{
var container = new UnityContainer();
container.RegisterType<ILogUtility, NLogUtility>();
container.RegisterType<ILogger, NLogDatabaseLogger>(DependencyRegistrationKeys.NLogDatabaseLoggerKey);
container.RegisterType<ILogger, NLogFileLogger>(DependencyRegistrationKeys.NLogFileLoggerKey);
container.RegisterType<ILoggerFactory, NLogLoggerFactory>(
new InjectionConstructor(
new ResolvedParameter<ILogger>(DependencyRegistrationKeys.NLogDatabaseLoggerKey),
new ResolvedParameter<ILogger>(DependencyRegistrationKeys.NLogFileLoggerKey)));
var loggerFactory = container.Resolve<ILoggerFactory>();
Assert.IsAssignableFrom<NLogLoggerFactory>(loggerFactory);
var logger = loggerFactory.CreateLogger(DependencyRegistrationKeys.NLogDatabaseLoggerKey);
Assert.IsNotNull(logger);
Assert.IsAssignableFrom<NLogDatabaseLogger>(logger);
}
一切都很好，直到我上线：
var loggerFactory = container.Resolve<ILoggerFactory>();
这似乎按预期击中了 NLogDatabaseLogger 的构造函数，并在这条线上爆炸，但有一个例外：
//initialize the _logger
_logger = LogManager.GetLogger("DatabaseLogger");
例外：
Required parameter 'FileName' on 'File Target[CustomFileLog_wrapped]' was not specified.
我的猜测是 Unity 正在努力获取 NLog，以获取命名记录器实例。有没有人遇到过这个？有没有办法解决？我整个早上都在为此头疼，但没有骰子。任何帮助将非常感激！