Plug-in Manager for Logging - Configure MSEL2 On the fly

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Introduction 

This is a simple plugin for logging actions and exception may happened in your application.
Also we will take a look how to configure MS Enterprise Library for .NET Framework 2.0 programatically.

Using the code

In this Article we have these technical points:

1-    What is a plug-in? and how to be implemented in out case (Logging Plugin Manager)?<o:p __designer:dtid="1407374883553308">

2-    What will be the benefits of implementing singleton pattern in our case?<o:p __designer:dtid="1407374883553315">

3-    How to load assemlies dynamically in a configurable way?<o:p __designer:dtid="1407374883553322">

4-    How to configure MSEL 2 Logging block on the fly without need for the pre-setting with MS configuraiton tool?<o:p __designer:dtid="1407374883553329">

<o:p __designer:dtid="1407374883553332">     

What is a plug-in? and how to be implemented in out case (Logging Plugin Manager)?<o:p __designer:dtid="1407374883553337">

.NET allows the dynamic loading of assemblies that is necessary for a good plug-in implementation.

Plug-in systems provide extensibility and flexibility. By using our Plug-in we will be able to attach more than implementation for many logging 3rd parties. And use the selector to select or activate one of them. <o:p __designer:dtid="1407374883553342">

<o:p __designer:dtid="1407374883553345">     

How to build a plug-in?<o:p __designer:dtid="1407374883553349">

This part contains a lot of old and well known information; but it is nice chance to refresh our knowledge. <o:p __designer:dtid="1407374883553352">

The first step in making the logging plug-in, after creating a solution workspace, is to create a common project LoggingManager.ExceptionsHandlerInterface. You'll use it to hold classes that will be accessed by both the plug-ins and the application that calls them. The object of doing this is to keep the dependencies down; there is little advantage in creating plug-ins if the application has to refer to the plug-in project to compile or run.<o:p __designer:dtid="1407374883553355">

<o:p __designer:dtid="1407374883553358">     

The interface used here is IExceptionsHandler. interface has a main method: Log() with 4 overloads:<o:p __designer:dtid="1407374883553361">

1- Simple logging with only choosing the target. <o:p __designer:dtid="1407374883553364">

bool Log(LogTarget oLogTarget, string LoggedString);<o:p __designer:dtid="1407374883553370">

<o:p __designer:dtid="1407374883553373">     

2- Logging with choosing the target and the severity level. <o:p __designer:dtid="1407374883553376">

bool Log(LogTarget oLogTarget, string LoggedString, LoggedDataLevel oLoggedDataLevel);<o:p __designer:dtid="1407374883553383">

<o:p __designer:dtid="1407374883553386">     

3- Logging with choosing the target and type for the logged info.<o:p __designer:dtid="1407374883553389">

bool Log(LogTarget oLogTarget, string LoggedString, LoggedDataType oLoggedDataType);<o:p __designer:dtid="1407374883553396">

<o:p __designer:dtid="1407374883553399">     

4- Logging with choosing the target and type for the logged info and everity.<o:p __designer:dtid="1407374883553402">

bool Log(LogTarget oLogTarget, string LoggedString, LoggedDataType oLoggedDataType, LoggedDataLevel oLoggedDataLevel);        <o:p __designer:dtid="1407374883553411">

<o:p __designer:dtid="1407374883553414">     

<o:p __designer:dtid="1407374883553417">     

Now I would like to attach some of 3rd parties logging tools and dlls to my project . <o:p __designer:dtid="1407374883553421">

For each tool (log4net and MSEL for example): I will create its own plug-in (interface  implementation).<o:p __designer:dtid="1407374883553426">

Each plug-in is in its own separate project, as it will be in its own assembly that is loaded by the application. The project for each plug-in uses a project reference to refer to the main interface.<o:p __designer:dtid="1407374883553431">

So we will create a project LoggingManager.MSELexpceptionsHandling and implement our logging interface in the class MSELExceptionsHandler.cs<o:p __designer:dtid="1407374883553435">

<o:p __designer:dtid="1407374883553438">     

What will be the benefits of implementing singleton pattern in our case?<o:p __designer:dtid="1407374883553443">

Why to use Singleton pattern or model ?<o:p __designer:dtid="1407374883553447">

To ensure that  a class has only one instance and provide a global point of access to it.<o:p __designer:dtid="1407374883553450">

<o:p __designer:dtid="1407374883553453">     

How to Implement Singleton ? <o:p __designer:dtid="1407374883553459">

1-      Simply by making a static global instance of the class and check is it found or not? For example the next code:<o:p __designer:dtid="1407374883553466">

class Singleton
 {
   private static Singleton instance;\\private variable declared

   // Note: Constructor is 'protected'
   protected Singleton()
   {
   }

   public static Singleton Instance()\\property declared which is used to access the privateVariable
   {
     // Use 'Lazy initialization'
     if (instance == null)
     {
       instance = new Singleton();
     }

     return instance;
   }
 }<o:p __designer:dtid="1407374883553489">

2-      Or by making a static constructor or Static ctor <o:p __designer:dtid="1407374883553496">

<o:p __designer:dtid="1407374883553499">     

And in our application we used Static ctor because it is thread safe according to ECMA standard section 9.5.3 For More information take a look at this page. <o:p __designer:dtid="1407374883553502">

http://jilc.sourceforge.net/ecma_p2_cil.shtml#_Toc524940486 <o:p __designer:dtid="1407374883553507">

 

How to load assemlies dynamically in a configurable way?<o:p __designer:dtid="1407374883553514">

In the configuration file (for example web.config or app.config) we define the assembly name for each of our plugins:<o:p __designer:dtid="1407374883553517">

<add key="MSELPlugin" value="MSELexpceptionsHandling.dll"/><!--    MSLE Plugin    --><o:p __designer:dtid="1407374883553534">

<add key="Net4LogPlugin" value="N4LexpceptionsHandling.dll"/><!--    N4L Plugin    --><o:p __designer:dtid="1407374883553551">

<o:p __designer:dtid="1407374883553554">     

Then we have a selector Key (this key will be the key which is called from our code) <o:p __designer:dtid="1407374883553557">

And set its value with the desired plug-in name. <o:p __designer:dtid="1407374883553560">

<add key="SelectedExHPlugin" value="MSELPlugin"/><!--MSLE Plugin--><o:p __designer:dtid="1407374883553575">

<o:p __designer:dtid="1407374883553578">     

Then our call in the code will be simply finding the value of this key:<o:p __designer:dtid="1407374883553581">

// Read the selected plugin (web config key) from the web config <o:p __designer:dtid="1407374883553584">

string strSelectedExHPlugin = ConfigurationManager.AppSettings["SelectedExHPlugin"];<o:p __designer:dtid="1407374883553590">

<o:p __designer:dtid="1407374883553593">     

Finally we build our configurable solution <o:p __designer:dtid="1407374883553596">

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<o:p __designer:dtid="1407374883553601">

<o:p __designer:dtid="1407374883553604">     

How to configure MSEL 2 Logging block on the fly without need for the pre-setting with MS configuraiton tool?<o:p __designer:dtid="1407374883553607">

<o:p __designer:dtid="1407374883553610">     

What will the benefits which we will gain from using this methodology ?<o:p __designer:dtid="1407374883553614">

1- Simply we will put our known readable keys in our web/app.config file for example:<o:p __designer:dtid="1407374883553617">

<o:p __designer:dtid="1407374883553620">     

<add key="LoggingFile" value="c:\Logging.txt"/><o:p __designer:dtid="1407374883553633">

<add key="LoggingFileSeperator" value="--------------------"/><o:p __designer:dtid="1407374883553647">

<o:p __designer:dtid="1407374883553650">     

Wihtout need to use the external tool or know external XML scehams and node will be added in external config file or evern our web/app.config file. <o:p __designer:dtid="1407374883553653">

<o:p __designer:dtid="1407374883553656">     

2- We will use more Sink (event logging method : event viewer ; file ; mail etc) in a more simple parameterized way without setting up policies and choose policies from the code. <o:p __designer:dtid="1407374883553659">

We will simply build our LoggingType enum and choose the suitable value to log from its values. <o:p __designer:dtid="1407374883553662">

<o:p __designer:dtid="1407374883553665">     

Then how to configure the MSEL on the fly?<o:p __designer:dtid="1407374883553668">

Special thanks for Alois Kraus for his most valuable article on his blog:

http://geekswithblogs.net/akraus1/archive/2006/02/16/69784.aspx

<o:p __designer:dtid="1407374883553676">

We built our ConfigLessLogger to configure the MSEL programatically (Add/Remove/Choose sinks)

Then we built an overlay class which is the implementer of our main logging interface. MSELExceptionsHandler.cs which will be used to build our MSEL assembly plugin; then we programmatically load this assembly from our code:

<o:p __designer:dtid="1407374883553684">

// use the returned web-config key name from the above step in getting the assembly name of <o:p __designer:dtid="1407374883553687">

// the selected implementation for the base ExH interface from the web config.<o:p __designer:dtid="1407374883553690">

            System.Reflection.Assembly asmSelectedPlugin = System.Reflection.Assembly.LoadFrom(ConfigurationManager.AppSettings[strSelectedExHPlugin]);<o:p __designer:dtid="1407374883553697">

<o:p __designer:dtid="1407374883553700">     

I hope that you Enjoy the code J