code: public static <T extends Entity<?>> String extractIdSeq(Collection<T> entities) {
      if (null == entities || entities.isEmpty()) { return ""; }
      StringBuilder idBuf = new StringBuilder(",");
      for (Iterator<T> iter = entities.iterator(); iter.hasNext();) {
        T element = iter.next();
        try {
          idBuf.append(String.valueOf(PropertyUtils.getProperty(element, "id")));
          idBuf.append(',');
        } catch (Exception e) {
          throw new RuntimeException(e.getMessage());
        }
      }
      return idBuf.toString();
    }
docs: <p>
  extractIdSeq.
  </p>
  
  @param entities a {@link java.util.Collection} object.
  @param <T> a T object.
  @return a {@link java.lang.String} object.