JAVA消息摘要算法. 包含MD2,MD5,SHA1,SHA256,SHA384,SHA512-MessageDigest Util. contains MD2,MD5,SHA1,SHA256,SHA384,SHA512.

MD5 签名算法在 jdk 中早已实现（如 MessageDigest 类）， 出于稳定性考虑，此处直接展示如何用这个类将密码进行MD5加密。-MD5 signature algorithm has already achieved in the jdk (if MessageDigest class), for stability considerations, here directly show how this class will be MD5 encrypted password