code: public int getSourceTree(
            String base, String urlString, SourceLocator locator, XPathContext xctxt)
              throws TransformerException
    {
  
      // System.out.println("getSourceTree");
      try
      {
        Source source = this.resolveURI(base, urlString, locator);
  
        // System.out.println("getSourceTree - base: "+base+", urlString: "+urlString+", source: "+source.getSystemId());
        return getSourceTree(source, locator, xctxt);
      }
      catch (IOException ioe)
      {
        throw new TransformerException(ioe.getMessage(), locator, ioe);
      }
  
      /* catch (TransformerException te)
       {
         throw new TransformerException(te.getMessage(), locator, te);
       }*/
    }
docs: Get the source tree from the a base URL and a URL string.
  
  @param base The base URI to use if the urlString is relative.
  @param urlString An absolute or relative URL string.
  @param locator The location of the caller, for diagnostic purposes.
  
  @return should be a non-null reference to the node identified by the
  base and urlString.
  
  @throws TransformerException If the URL can not resolve to a node.