code: @Override
     public InputStream lookupFileStrict(String filename, ClassLoader cl) throws FileNotFoundException {
        InputStream is = filename == null || filename.length() == 0 ? null : getAsInputStreamFromClassLoader(filename, cl);
        if (is == null) {
           if (log.isDebugEnabled())
              log.debugf("Unable to find file %s in classpath; searching for this file on the filesystem instead.", filename);
           return new FileInputStream(filename);
        }
        return is;
     }
docs: Looks up the file, see : {@link DefaultFileLookup}.
  
  @param filename might be the name of the file (too look it up in the class path) or an url to a file.
  @return an input stream to the file or null if nothing found through all lookup steps.
  @throws FileNotFoundException if file cannot be found