Enterprise Library2.0（2）：Logging Application Block学习-阿里云开发者社区

摘要：Logging Application Block可以使开发人员在其应用程序中集成日志监测功能，看看随着2.0的推出给我们带来了哪些改变。

一．改进的地方

1 ．Logging Application Block首先带来的是名称上的改变，在1.1下它的全称应该是Logging and Instrumentation Application Block，一般把它翻译为日志和检测应用程序块，而2.0下却完全变成了日志应用程序块。

2 ．在1.1下，每个LogEntry只能被记录到一个Sink，而这种情况在2.0下已经不复存在，对于每个LogEntry对象，我们都可以通过Category指定很多的Sink。回忆一下在1.1时记录一个日志项：

LogEntry logEntry = new LogEntry();

logEntry.EventId = 100 ;

logEntry.Priority = 2 ;

logEntry.Message = " Informational message " ;

// 只能设置一个

logEntry.Categorys = " UI Events " ;

Logger.Write(logEntry);

2.0 下可以添加多次：

LogEntry logEntry = new LogEntry();

logEntry.EventId = 100 ;

logEntry.Priority = 2 ;

logEntry.Message = " Informational message " ;

// 设置多个Category

logEntry.Categories.Add( " Trace " );

logEntry.Categories.Add( " UI Events " );

Logger.Write(logEntry);

3 ．可以在代码中查询哪些日志项将被过滤，例如：

LogEntry logEntry = new LogEntry();

logEntry.Priority = 2 ;

logEntry.Categories.Add( " Trace " );

logEntry.Categories.Add( " UI Events " );

if (Logger.ShouldLog(logEntry))

{

// Event will be logged according to currently configured filters.

}

else

{

// Event will not be logged.

}

4 ．配置文件的改变。在1.1下关于Logging & Instrumentation Application Block的信息记录在loggingconfiguration.config文件中，2.0下所有的信息都放在了Web.config或App.config中，如：

< configuration >

< configSections >

< section name ="loggingConfiguration" type ="Microsoft.Practices.EnterpriseLibrary.Logging.Configuration.LoggingSettings, Microsoft.Practices.EnterpriseLibrary.Logging" />

</ configSections >

< loggingConfiguration tracingEnabled ="true" defaultCategory ="General" >

< logFilters >

< add

name ="Category"

type ="Microsoft.Practices.EnterpriseLibrary.Logging.Filters.CategoryFilter, Microsoft.Practices.EnterpriseLibrary.Logging"

categoryFilterMode ="AllowAllExceptDenied" >

< categoryFilters >

< add name ="UI Events" />

</ categoryFilters >

</ add >

< add

name ="Priority"

type ="Microsoft.Practices.EnterpriseLibrary.Logging.Filters.PriorityFilter, Microsoft.Practices.EnterpriseLibrary.Logging"

minimumPriority ="2"

< add name ="LogEnabled Filter"

type ="Microsoft.Practices.EnterpriseLibrary.Logging.Filters.LogEnabledFilter, Microsoft.Practices.EnterpriseLibrary.Logging, Version=2.0.0.0, Culture=neutral, PublicKeyToken=null"

enabled ="true"

</ logFilters >

</ loggingConfiguration >

</ configuration >

二．记录日志信息

1 ．添加相关的引用

using Microsoft.Practices.EnterpriseLibrary.Common.Configuration;

using Microsoft.Practices.EnterpriseLibrary.Logging;

using Microsoft.Practices.EnterpriseLibrary.Logging.Configuration;

using Microsoft.Practices.EnterpriseLibrary.Logging.ExtraInformation;

using Microsoft.Practices.EnterpriseLibrary.Logging.Filters;

2 ．创建一个日志项

LogEntry log = new LogEntry();

log.EventId = 300 ;

log.Message = " Sample message " ;

log.Categories.Add( " UI Events " );

log.Severity = TraceEventType.Information;

log.Priority = 5 ;

3 ．调用Logger.Write()方法

Logger.Write(log);

三．记录日志项的扩展属性

使用基于泛型的Dictionary来记录，如下

// Create the dictionary to hold the extra information, and populate it

// with managed security information.

Dictionary < string , object > dictionary = new Dictionary < string , object > ();

ManagedSecurityContextInformationProvider informationHelper = new ManagedSecurityContextInformationProvider();

informationHelper.PopulateDictionary(dictionary);

// Add a custom property for screen resolution

int width = Screen.PrimaryScreen.Bounds.Width;

int height = Screen.PrimaryScreen.Bounds.Height;

string resolution = String.Format( " {0}x{1} " , width, height);

dictionary.Add( " Screen resolution " , resolution);

// Write the log entry that contains the extra information

Logger.Write( " Log entry with extra information " , dictionary);

四．跟踪活动并记录上下文信息

1 ．调用DoDataAccess方法，完成后释放Trace对象

using ( new Tracer( " Trace " ))

{

DoDataAccess();

}

2 ．创建DoDataAccess方法

private void DoDataAccess()

{

using (new Tracer("Data Access Events"))

{

// Peform work here

// Assume an error condition was detected - perform some troubleshooting.

DoTroubleShooting();

}

3 ．创建另一个方法DoTroubleShooting，并在其中创建LogEntry。

private void DoTroubleShooting()

{

string logMessage = "Simulated troubleshooting message for Logging QuickStart. " +

"Current activity=\"" + Trace.CorrelationManager.ActivityId + "\"";

LogEntry logEntry = new LogEntry();

logEntry.Categories.Clear();

logEntry.Categories.Add("Troubleshooting");

logEntry.Priority = 5;

logEntry.Severity = TraceEventType.Error;

logEntry.Message = logMessage;

Logger.Write(logEntry);

}

五．检测日志项是否被记录

创建一个日志项并设置它的信息，调用Logger.ShouldLog()方法

LogEntry logEntry = new LogEntry();

logEntry.Priority = 2 ;

logEntry.Categories.Add( " Trace " );

logEntry.Categories.Add( " UI Events " );

if (Logger.GetFilter < CategoryFilter > ().ShouldLog(logEntry))

{

// Event will be logged according to currently configured filters.

// Perform operations (possibly expensive) to gather additional information

// for the event to be logged.

}

else

{

// Event will not be logged. Your application can avoid the performance

// penalty of collecting information for an event that will not be

// logged.

}

LogEntry logEntry = new LogEntry();

logEntry.Priority = 2 ;

logEntry.Categories.Add( " Trace " );

logEntry.Categories.Add( " UI Events " );

if (Logger.ShouldLog(logEntry))

{

// Event will be logged according to currently configured filters.

}

else

{

// Event will not be logged.

}

六．创建自定义的Trace Listener

1 ．添加特性ConfigurationElementType，需要继承自CustomTraceListener

[ConfigurationElementType( typeof (CustomTraceListenerData))]

public class DebugTraceListener : CustomTraceListener

{

}

2 ．覆写TraceData方法

public override void TraceData(TraceEventCache eventCache, string source, TraceEventType eventType, int id, object data)

{

if (data is LogEntry && this.Formatter != null)

{

this.WriteLine(this.Formatter.Format(data as LogEntry));

}

else

{

this.WriteLine(data.ToString());

}

3 ．覆写Write()和WriteLine()方法

/// <summary>

/// Writes a message to the debug window

/// </summary>

/// <param name="message">The string to write to the debug window</param>

public override void Write( string message)

{

Debug.Write(message);

}

/// <summary>

/// Writes a message to the debug window

/// </summary>

/// <param name="message">The string to write to the debug window</param>

public override void WriteLine( string message)

{

Debug.WriteLine(message);

}

七．创建自定义的Formatter

1 ．在自定义的类上添加特性ConfigurationElementType，并实现接口ILogFormatter

[ConfigurationElementType( typeof (CustomFormatterData))]

public class MyFormatter : ILogFormatter

{

}

2 ．构造函数接受一个类型为NameValueCollection的参数

public MyFormatter (NameValueCollection attributes)

{

}

3 ．添加Format方法，它接受一个LogEntry的参数

public string Format(LogEntry log)

{

}

八．使用场景

如果你的应用程序需要挟日志到Event Log, E-mail, Database, Message Queue, Windows Management Instrumentation (WMI), TextFile,你就应该考虑使用日志组件来提供这些功能，特别如果你需要基于分类和优先级来过滤日志消息，需要格式化消息，或者需要不改动代码的情况下改变消息的目的地。日志组件同时被设计成可扩展的，包括方便的创建客户订制的Formatter和TraceListener。

参考资料：Enterprise Libaray –January 2006帮助文档

本文转自lihuijun51CTO博客，原文链接： http://blog.51cto.com/terrylee/67620 ，如需转载请自行联系原作者

Enterprise Library2.0（2）：Logging Application Block学习

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