看到一段代码:
public long getNextKeyFromMaxId(String columnName) throws SysException, AppException { String sql1 = "UPDATE MAX_IDS SET MAX_ID = MAX_ID + 1 where COLUMN_NAME = ?"; String sql2 = "SELECT MAX_ID FROM MAX_IDS where COLUMN_NAME = ?"; List params = new ArrayList(); params.add(columnName); JdbcServiceUtil.update(sql1, params); List list = JdbcServiceUtil.select(sql2, params); if ((list != null) && (list.size() > 0)) { return (Long.valueOf(((HashMap) list.get(0)).get("MAX_ID") .toString())).longValue(); } else { throw new AppException("", "MAX_ID 表中没有关于" + columnName + " 的记录!"); } }
意思就是制造一个最大值作为ID编码,以免重复。既然是从数据库中MAX_IDS表中取一个最大值,该表作为一个共享资源,在多线程环境中取ID会不会出问题呢?