code: public void setAttachment(String type, String url, Boolean is_reusable)
      {
          this.message_attachment.put("type", type);
          this.message_attachment.put("url", url);
          this.message_attachment.put("is_reusable", String.valueOf(is_reusable));
      }
docs: Set Attachment
  
  @param type the attachment type
  @param url the attachment url
  @param is_reusable whether to be reusable or not