本文实例讲述了Java实现MD5加密的方法。分享给大家供大家参考。具体实现方法如下：
import java.security.MessageDigest; import java.security.NoSuchAlgorithmException; public class MD5HashUtil { private MessageDigest md = null; private static MD5HashUtil md5 = null; private static final char[] hexChars ={'0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F'}; /** * Constructor is private so you must use the getInstance method */ private MD5HashUtil() throws NoSuchAlgorithmException { md = MessageDigest.getInstance("MD5"); } /** * This returns the singleton instance */ public static MD5HashUtil getInstance()throws NoSuchAlgorithmException { if (md5 == null) { md5 = new MD5HashUtil(); } return (md5); } public static String hashCode(String dataToHash) throws NoSuchAlgorithmException{ return getInstance().hashData(dataToHash.getBytes()); } public static String hashCode(byte[] dataToHash) throws NoSuchAlgorithmException{ return getInstance().hashData(dataToHash); } public String hashData(byte[] dataToHash) { return hexStringFromBytes((calculateHash(dataToHash))).toLowerCase(); } private byte[] calculateHash(byte[] dataToHash) { md.update(dataToHash, 0, dataToHash.length); return (md.digest()); } public String hexStringFromBytes(byte[] b) { String hex = ""; int msb; int lsb = 0; int i; // MSB maps to idx 0 for (i = 0; i < b.length; i++) { msb = ((int)b[i] & 0x000000FF) / 16; lsb = ((int)b[i] & 0x000000FF) % 16; hex = hex + hexChars[msb] + hexChars[lsb]; } return(hex); } public static void main(String args[]) throws NoSuchAlgorithmException { String string = "my name is zhangli"; System.out.println(string); System.out.println(hashCode(string)); } } 如上代码为java语言实现md5加密算法，输出为加密后的密文！
通常将加密后的密文保存在数据库中，如果需要比较只比较他们的用md5加密过后的密文。
同时，md5加密算法是不可逆的，破解的难度很高，虽然有人破解了md5,但是他们所用的硬件环境不是我们普通的计算机所比拟的，山大的一位很牛的女教授也破解了md5,不过不怎么了解
希望本文所述对大家的java程序设计有所帮助。