java程序常用的工具类。检查对象是否为空，是否数字，是否小数，是否邮箱，自动补零，获取当前时间，获取随机数，字符加密等(Commonly used tool classes for Java programs. Check whether the object is empty, whether the number, whether the decimal, whether the mailbox, automatic zero compensation, access to the current time, access to random numbers, character encryption, etc.)