code: public final File getValidDirectory() {
  		File file = this.directory;
  		file = (file != null) ? file : getWarFileDocumentRoot();
  		file = (file != null) ? file : getExplodedWarFileDocumentRoot();
  		file = (file != null) ? file : getCommonDocumentRoot();
  		if (file == null && this.logger.isDebugEnabled()) {
  			logNoDocumentRoots();
  		}
  		else if (this.logger.isDebugEnabled()) {
  			this.logger.debug("Document root: " + file);
  		}
  		return file;
  	}
docs: Returns the absolute document root when it points to a valid directory, logging a
  warning and returning {@code null} otherwise.
  @return the valid document root