Re: [Simpleweb-Support] ClassLoader and prepare() problems

[Niall G. <gal...@ya...>]

Hi, 

Seems to me that you must be giving either the MapperEngine or LoaderEngine a class path entry outside the class path of the object you are trying to cast. The registry delegates to a parent class loader, like so:

ClassLoader parent = Registry.class.getClassLoader();

Thus if this parent delegates to the system classloader and the class you are using is in the classpath then you will not have the class cast exception. One thing to note is that if you dont provide a file or URL to the loader engine constructor it will use the Context.getBasePath(), perhaps this is where your issue is?

Download the demo package, it should contain working code of the situation you describe.

Niall



----- Original Message ----
From: Will Benton <wi...@cs...>
To: sim...@li...
Sent: Thursday, April 26, 2007 8:24:04 PM
Subject: [Simpleweb-Support] ClassLoader and prepare() problems

Hi all,

I'm having some trouble with prepare() methods and ClassLoaders in an  
extremely minimal application.  This application is a basic MVC  
database frontend with no static content.  I'm using Simple 3.1.3  
under Java 5 (with the Apple/Sun VM for now).

I want to be able to store a reference to a controller object in each  
of my Service classes.  If I declare the prepare() method to take the  
class of the controller object as a parameter, it will never be  
invoked.  If, on the other hand, I declare the prepare method to take  
an Object and then cast, I'll get a ClassCastException.  As far as I  
can tell, both of these happen because the Service is using a  
URLClassLoader that never delegates to the System class loader -- so  
the Class object for my controller class in the URLClassLoader is not  
equal to the one in the System class loader (which was in effect when  
I created the object that I passed to the prepare() method).

I've scanned the source, but can't figure out how to get the behavior  
I want without changing simple.http.load.Registry, which seems like a  
bad plan.  As a result, it seems to me that I must be going about  
this whole enterprise improperly.  I'd greatly appreciate it if  
someone could either

   1.  provide some example code that passes objects created in a  
context using the system classloader to a Simple service, or
   2.  explain how to set up a LoaderEngine so that the Services it  
creates will have classloaders that will delegate to the system  
classloader.

If I'm missing something even more fundamental, I'd be glad to hear  
that as well, of course.

Thanks for reading this!


best,
wb


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