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

一．改進的地方

1．Logging Application Block首先帶來的是名稱上的改變，在1.1下它的全稱應該是Logging and Instrumentation Application Block，一般把它翻譯為日志和檢測應用程序塊，而2.0下卻完全變成了日志應用程序塊。

2．在1.1下，每個LogEntry只能被記錄到一個Sink，而這種情況在2.0下已經不復存在，對於每個LogEntry對象，我們都可以通過Category指定很多的Sink。回憶一下在1.1時記錄一個日志項：

LogEntry logEntry = new LogEntry();
logEntry.EventId = 100;
logEntry.Priority = 2;
logEntry.Message = "Informational message";
//只能設置一個
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";
//設置多個Category
logEntry.Categories.Add("Trace");　　　　
logEntry.Categories.Add("UI Events");

Logger.Write(logEntry);

3．可以在代碼中查詢哪些日志項將被過濾，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．配置文件的改變。在1.1下關於Logging & Instrumentation　Application Block的信息記錄在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．記錄日志信息

1．添加相關的引用

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．創建一個日志項

LogEntry log = new LogEntry();
log.EventId = 300;
log.Message = "Sample message";
log.Categories.Add("UI Events");
log.Severity = TraceEventType.Information;
log.Priority = 5;

3．調用Logger.Write()方法

Logger.Write(log);

三．記錄日志項的擴展屬性

使用基於泛型的Dictionary來記錄，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．跟蹤活動並記錄上下文信息

1．調用DoDataAccess方法，完成後釋放Trace對象

using (new Tracer("Trace"))
{
　　DoDataAccess();
}

2．創建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．創建另一個方法DoTroubleShooting，並在其中創建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．檢測日志項是否被記錄

創建一個日志項並設置它的信息，調用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．創建自定義的Trace Listener

1．添加特性ConfigurationElementType，需要繼承自CustomTraceListener

[ConfigurationElementType(typeof(CustomTraceListenerData))]
public class DebugTraceListener : CustomTraceListener
{
　　//
}

2．覆寫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．覆寫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．創建自定義的Formatter

1．在自定義的類上添加特性ConfigurationElementType，並實現接口ILogFormatter

[ConfigurationElementType(typeof(CustomFormatterData))]
public class MyFormatter : ILogFormatter
{
　　//
}

2．構造函數接受一個類型為NameValueCollection的參數

public MyFormatter (NameValueCollection attributes)
{
　　//
}

3．添加Format方法，它接受一個LogEntry的參數

public string Format(LogEntry log)
{
　　//
}

八．使用場景

如果你的應用程序需要挾日志到Event Log, E-mail, Database, Message Queue, Windows Management Instrumentation (WMI), TextFile,你就應該考慮使用日志組件來提供這些功能，特別如果你需要基於分類和優先級來過濾日志消息，需要格式化消息，或者需要不改動代碼的情況下改變消息的目的地。日志組件同時被設計成可擴展的，包括方便的創建客戶訂制的Formatter和TraceListener。