URLs: Smart resource identifiers

    "clsloader:"<resource name as for getResourceAsStream()>

public class ClassLoaderResourceHandler extends URLStreamHandler
{
    public static final String PROTOCOL = "clsloader";
    
    
    protected URLConnection openConnection (final URL url) throws IOException
    {
        return new ClassLoaderResourceURLConnection (url);
    }
    
    /**
     * This method should return a parseable string form of this URL.
     */
    protected String toExternalForm (final URL url)
    {
        return PROTOCOL.concat (":").concat (url.getFile ());
    }
    
    /**
     * Must override to prevent default parsing of our URLs as HTTP-like URLs
     * (the base class implementation eventually calls setURL(), which is tied
     * to HTTP URL syntax too much).
     */
    protected void parseURL (final URL context, final String spec,
                             final int start, final int limit)
    {
        final String resourceName =
            combineResourceNames (context.getFile (), spec.substring (start));
        
        setURL (context, context.getProtocol (), "", -1, resourceName, "");
    }
    
    /*
     * The URLConnection implementation used by this scheme. 
     */
    private static final class ClassLoaderResourceURLConnection
        extends URLConnection
    {
        public void connect ()
        {
            // Do nothing, as we will look for the resource in getInputStream().
        }
        
        public InputStream getInputStream () throws IOException
        {
            // This always uses the current thread's context loader. A better
            // strategy is to use techniques shown in
            // http://www.javaworld.com/javaworld/javaqa/2003-06/01-qa-0606-load.html.
            final ClassLoader loader = Thread.currentThread ().getContextClassLoader ();
            
            // Don't be fooled by our calling url.getFile(): it is just a string,
            // not necessarily a real filename.
            String resourceName = url.getFile ();
            if (resourceName.startsWith ("/"))
                resourceName = resourceName.substring (1);
            
            final InputStream result = loader.getResourceAsStream (resourceName);
            
            if (result == null)
                throw new IOException ("resource [" + resourceName + "] could "
                + "not be found by classloader [" + loader.getClass ().getName ()
                + "]");
            
            return result; 
        }
        protected ClassLoaderResourceURLConnection (final URL url)
        {
            super (url);
        }
    } // End of nested class.
    
    
    private static String combineResourceNames (String base, String relative)
    {
        if ((base == null) || (base.length () == 0)) return relative;
        if ((relative == null) || (relative.length () == 0)) return base;
        
        if (relative.startsWith ("/"))
            // 'relative' is actually absolute in this case.
            return relative.substring (1);
        
        if (base.endsWith ("/"))
            return base.concat (relative);
        else
        {
            // Replace the name segment after the last separator:
            final int lastBaseSlash = base.lastIndexOf ('/');
            
            if (lastBaseSlash < 0)
                return relative;
            else
                return base.substring (0, lastBaseSlash).concat ("/")
                    .concat (relative);
        }
    }
} // End of class.