Deconstructing the Pluggable Styling

In the previous section we have seen two references to style resources but have only been told that they 'come from the pluggable style module'. Let's look at how the forum-web module obtains it's style.

In both of the cases above, the style links.xml and the XSLT transform, the style resource was located in the path ffcpl:/style/.... If we examine the forum-web module.xml we see the following entry in the mapping section...

This mapping shows that any resource in the ffcpl:/style/ path is actually dynamically sourced by executing the script source-style.bsh with the required uri appended as the 'uri' argument. The script is shown below...

import com.ten60.netkernel.urii.aspect.*;

main()
{   uri = context.getThisRequest().getArgument("uri");
    styleModule = context.sourceAspect("ffcpl:/forum-system-stylemodule",
        IAspectString.class).getString();
    req = context.createSubRequest();
    req.setURI("active:wormhole");
    req.addArgument("module",styleModule);
    req.addArgument("resource",uri);
    result = context.issueSubRequest(req);
    response = context.createResponseFrom(result);
    response.setCacheable();
    response.setExpiryPeriod(24*60*60*1000);
    context.setResponse(response);
}

                    

The script acts as a bridge to the style module. First it obtains the URI of the style module by issuing a sourceAspect request for ffcpl:/forum-system-stylemodule - which is a service provided by the data services module. Next it sources the uri by using the wormhole accessor. The wormhole accessor acts like a hyperspace wormhole through NetKernel's URI address spaces - it allows requests on the specified module's public interface to be made even when that module is not imported into the calling module's address space. If you look at the forum-style module you'll see that it contains just static XSL transforms, images and templates - these are effectively dynamically mapped into the forum-web module via this wormhole bridge.

This wormhole pattern means that the application's styling resources can be located in an arbitrary module without modifying the forum-web module's imports - the net effect is that the whole application is dynamically skinnable.