code: protected String getETag( final StoredObject so )
      {
  
          String resourceLength = "";
          String lastModified = "";
  
          if ( so != null && so.isResource() )
          {
              resourceLength = new Long( so.getResourceLength() ).toString();
              lastModified = new Long( so.getLastModified()
                                         .getTime() ).toString();
          }
  
          return "W/\"" + resourceLength + "-" + lastModified + "\"";
  
      }
docs: Get the ETag associated with a file.
  
  @param so
  StoredObject to get resourceLength, lastModified and a hashCode of
  StoredObject
  @return the ETag