Re: [struts-chain] Writing a command to process a Tiles Definition

[Craig R. McClanahan]

Jing Zhou wrote:

----- Original Message ----- 
From: "Craig R. McClanahan" <[EMAIL PROTECTED]>
To: "Struts Developers List" <[EMAIL PROTECTED]>
Sent: Wednesday, October 01, 2003 11:24 AM
Subject: Re: [struts-chain] Writing a command to process a Tiles Definition

 

There's a "conditional behavior" use case in the existing code as well;
when validation fails, we want to redisplay the input form.  Originally,
I modelled this command as a Chain that conditionally executed its child
commands, but that seemed a little hokey.  Now, this command definition
says:
   <command
   

className="org.apache.struts.chain.servlet.ValidateActionForm"
 

     failureCommand="servlet-validation-failure"/>

so I'm declaring the name of another chain to go execute if validation
fails.  The actual code that does the conditional execution looks like
this (in the abstract base class):
   // Call the environment-specific protected validate() method in our
implementation class
   ActionErrors errors = validate(context, actionConfig, actionForm);
   // If there were no errors, proceed normally
   if ((errors == null) || (errors.isEmpty()) {
       return (false); // Proceed with the main chain
   }
   // Execute the specified validation failure command
   try {
       Catalog catalog = (Catalog)
         context.get(getCatalogKey());
       Command command = catalog.getCommand(getFailureCommand());
       command.execute(context);
   } catch (Exception e) {
       ... deal with exception ...
   }
   return (true); // Terminate the main chain
This approach seems more scalable -- for example, you can have several
different conditional options, you aren't binding all the behavior
definitions into a single chain definition, and you can decide based on
your needs whether to return false or true from the main command (which
dictates whether the owning chain thinks processing is complete or not).
Craig

   

I am wondering how I could implement a "jump behavior" in the main
chain. The use case for a "jump behavior" is that the main chain should
continue with several commands skipped over. For example, I would like
to jump to the last command in the main chain after the current command.
Any ideas?
Jing
 

Didn't your O-O programming classes explain to you the evils of the 
"goto" statement? :-)

More seriously, if I was faced with that choice, I would refactor it 
into an "if" decision rather than a "skip" decision, just like I would 
refactor any code where a "goto" seemed like the right answer to use an 
"if" instead.  Just because we're talking about scripting languages 
(which is what we're doing when we talk about using chain definitions as 
the definition of control flows) does not change the use of correct 
design principles.

Craig



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