Re: Questions regarding the Context interface

[Stephen McConnell]

[EMAIL PROTECTED] wrote:

Thanks very much - you were extremely thorough.  I'll process your comments 
now. 

Actually I neglected to mention one of Merlin's more eosteric context 
management features.  If you want to change the contextualization 
interface that is applied to a component - well - you can.  For example, 
lets imagine you want to do something like:

 public void contextualize( MyContext context )
 {
     File dir = context.getDirectory(); // look dad - no casting
 }
All you need to do is to write the interface, declare the context 
strategy dependency, provide a context handler extension, and your 
done.  There is a tutorial on this subject in CVS under 
merlin/merlin-platform/tutorials/contextualization.  Assuming you have 
built both avalon-sandbox/meta and avalon-sandbox/merlin, all you need 
to do to run the demo is:

 $ cd merlin/merlin-platform/tutorials/contextualization
 $ maven validate
Stephen.

Thanks, 
Alex 

 

From: Stephen McConnell <[EMAIL PROTECTED]> 
Date: 2003/08/18 Mon PM 01:02:29 EDT 
To: Avalon framework users <[EMAIL PROTECTED]> 
Subject: Re: Questions regarding the Context interface 



[EMAIL PROTECTED] wrote: 

   

Hello,  

My questions regard the use of the Context interface.  I have used the less  
portable means for getting a context object from the contextualize method 
     

in  
 

the past when using phoenix for my components - namely the following form:  

public void contextualize( Context context )  
       throws ContextException  
   {  
       BlockContext tContext = ( BlockContext ) context;  
   }  

As you can see the BlockContext is from phoenix.  I found myself doing this  
because I could get a path to the base phoenix directory via the  
getBaseDirectory() method.  I would like to use the recommended portable  
mechanism now that LDAPd is going to use more than one container.  The  
question is how do I make the container add the appropriate Context entry.  
     

I  
 

would image that would be container implementation specific.  So how would 
     

I  
 

add this entry using say Merlin and Fortress:  

 <entry key="avalon:work" type="java.io.File"/>  
 

     

If you declare the following <entry/> declaration in a type descriptor  
(manually or via an @avalon.entry) then Merlin will take care of this  
for you.  This declaration is based on the meta-info model declarations  
which means its as close as you can get to an Avalon standard. 

 <context> 
   <entry key="urn:avalon:home" type="java.io.File"/> 
 </context> 

Please note that the following two file related keys are available  
(which is slighlty different to what you described above): 

 "urn:avalon:work" - a transient directory that will be desoyed 
                     following decommissioning of the component 
 "urn:avalon:home" - persistent directory for the component 

   

to be able to get  

 File workDirectory = ( File ) context.get( "avalon:work" ) ;  

as is the recommended way in the javadocs page for the Context interface 
     

here:  
 

     

http://avalon.apache.org/framework/api/org/apache/avalon/framework/context/Context.html  
   

If you want to use a friendly castable context interface then you need  
to declare this under the @avalon.context type="MyContextInterface" tag  
which generates the following: 

 <context type="MyContextInterface"> 
   <!-- plus any entries --> 
 </context> 

In your code you can safely case the supplied context to the declared  
interface just like you do in Phoenix. This is also covered by the  
meta-info model but Merlin is probably the only container to provide  
support for this capability at this time. 

  public void contextualize( Context context ) 
  { 
      MyContextInterface myContext = (MyContextInterface) context; 
      File file = myContext.getMyFile(); 
  } 

There is also a working demonstration of this in the merlin tutorial  
content. 

$ cd merlin-platform\tutorials\context_casting 
$ maven 
$ merlin -execute target\classes 

[INFO   ] (tutorial.hello): listing values resolved from domain specific  
context 
[INFO   ] (tutorial.hello): supplied context class:  
tutorial.DemoContextProvider 
[INFO   ] (tutorial.hello): name: hello 
[INFO   ] (tutorial.hello): partition: /tutorial/ 
[INFO   ] (tutorial.hello): home: [you-directory]\home\tutorial\hello 
[INFO   ] (tutorial.hello): temp: C:\TEMP\tutorial\hello 

Stephen. 

   

Thanks much,  
Alex  



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--  

Stephen J. McConnell 
mailto:[EMAIL PROTECTED] 
http://www.osm.net 

Sent via James running under Merlin as an NT service. 
http://avalon.apache.org/sandbox/merlin 



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--

Stephen J. McConnell
mailto:[EMAIL PROTECTED]
http://www.osm.net
Sent via James running under Merlin as an NT service.
http://avalon.apache.org/sandbox/merlin


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