listing dirs in current webapp...

hi, I'm trying to detect subdirectories in current webapp, not sure how 
to filter dirs from files that are not dirs..  found something here,
http://www.exampledepot.com/egs/java.io/GetFiles.html?l=rel

  File dir = new File("directoryName");

     String[] children = dir.list();
     if (children == null) {
         // Either dir does not exist or is not a directory
     } else {
         for (int i=0; i<children.length; i++) {
             // Get filename of file or directory
             String filename = children[i];
         }
     }


but it how do you tell it to filter dirs ONLY?????
   (once we do String[] children = dir.list(); we can't test for 
isDirectory() anymore, since isDirectory() method cannot be applied to 
strings..)

am simply trying to detect which files in current dir (i.e., current 
webapp) are directories..

thank you...