[jboss-dev-forums] [Design of EJB 3.0] - VirtualFile abstraction

[thomas.diesler@jboss.com]

Carlo,

I notice with the latest EJB3 backport to jboss42 there are a lot referrences to VirtualFile commented out. This is of course correct because jboss-vfs.jar cannot be used in jboss42.

In jbossws we have a simmilar problem in our integration layers for the varios containers, wich we solved by introducing an UnifiedVirtualFile


  | /**
  |  * An adaptor to a VirtualFile from jboss-vfs.jar
  |  * jboss-vfs cannot be used in jboss-4.x because of its dependeny on jboss-common-core.jar
  |  *  
  |  * @author Thomas.Diesler at jboss.org
  |  * @since 05-May-2006
  |  */
  | public interface UnifiedVirtualFile extends Serializable
  | {
  |    UnifiedVirtualFile findChild(String child) throws IOException;
  | 
  |    URL toURL();
  | }
  | 

It turns out that we only need these two methods to find and read resources. There is a trivial implementation for jboss50 that delegates to a VirtualFile


  | /**
  |  * A JBoss50 VirtualFile adaptor
  |  *
  |  * @author Thomas.Diesler at jboss.org
  |  * @since 05-May-2006
  |  */
  | public class VirtualFileAdaptor implements UnifiedVirtualFile
  | {
  |    private static final long serialVersionUID = 6547394037548338042L;
  |    
  |    private VirtualFile root;
  | 
  |    public VirtualFileAdaptor(VirtualFile root)
  |    {
  |       this.root = root;
  |    }
  | 
  |    public UnifiedVirtualFile findChild(String child) throws IOException
  |    {
  |       VirtualFile vf = root.findChild(child);
  |       return new VirtualFileAdaptor(vf);
  |    }
  | 
  |    public URL toURL()
  |    {
  |       try
  |       {
  |          return root.toURL();
  |       }
  |       catch (Exception e)
  |       {
  |          return null;
  |       }
  |    }
  | }
  | 

and one for jboss42 that uses a resource class loader


  | /**
  |  * The default file adapter loads resources through an associated classloader.
  |  * If no classload is set, the the thread context classloader will be used.
  |  *
  |  * @author Heiko.Braun at jboss.org
  |  * @since 25.01.2007
  |  */
  | public class ResourceLoaderAdapter implements UnifiedVirtualFile
  | {
  |    private URL resourceURL;
  |    private ClassLoader loader;
  | 
  |    public ResourceLoaderAdapter()
  |    {
  |       this(Thread.currentThread().getContextClassLoader());
  |    }
  |    
  |    public ResourceLoaderAdapter(ClassLoader loader)
  |    {
  |       this.loader = loader;
  |    }
  |    
  |    private ResourceLoaderAdapter(ClassLoader loader, URL resourceURL)
  |    {
  |       this.resourceURL = resourceURL;
  |       this.loader = loader;
  |    }
  | 
  |    public UnifiedVirtualFile findChild(String resourcePath) throws IOException
  |    {
  |       URL resourceURL = null;
  |       if (resourcePath != null)
  |       {
  |          // Try the child as URL
  |          try
  |          {
  |             resourceURL = new URL(resourcePath);
  |          }
  |          catch (MalformedURLException ex)
  |          {
  |             // ignore
  |          }
  | 
  |          // Try the filename as File
  |          if (resourceURL == null)
  |          {
  |             try
  |             {
  |                File file = new File(resourcePath);
  |                if (file.exists())
  |                   resourceURL = file.toURL();
  |             }
  |             catch (MalformedURLException e)
  |             {
  |                // ignore
  |             }
  |          }
  | 
  |          // Try the filename as Resource
  |          if (resourceURL == null)
  |          {
  |             try
  |             {
  |                resourceURL = loader.getResource(resourcePath);
  |             }
  |             catch (Exception ex)
  |             {
  |                // ignore
  |             }
  |          }
  |       }
  | 
  |       if (resourceURL == null)
  |          throw new IOException("Cannot get URL for: " + resourcePath);
  | 
  |       return new ResourceLoaderAdapter(loader, resourceURL);
  |    }
  | 
  |    public URL toURL()
  |    {
  |       if (null == this.resourceURL)
  |          throw new IllegalStateException("UnifiedVirtualFile not initialized");
  |       return resourceURL;
  |    }
  | }
  | 

Maybe this would solve your abstraction problem as well.

cheers



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