code: public static String keepSeqUnique(final String keys) {
      String[] keysArray = split(keys, ",");
      List<String> keyList = CollectUtils.newArrayList();
      for (int i = 0; i < keysArray.length; i++) {
        if (!keyList.contains(keysArray[i])) {
          keyList.add(keysArray[i]);
        }
      }
      StringBuilder keyBuf = new StringBuilder();
      for (Iterator<String> iter = keyList.iterator(); iter.hasNext();) {
        keyBuf.append(iter.next());
        if (iter.hasNext()) {
          keyBuf.append(",");
        }
      }
      return keyBuf.toString();
    }
docs: 保持逗号分隔的各个单词都是唯一的。并且按照原来的顺序存放。
  
  @param keys
  a {@link java.lang.String} object.
  @return a {@link java.lang.String} object.