用户密码md5加密，md5加密的密码怎么解密

? ? 之前一直搞不清楚md5加密，从网上查了好多资料、看了几个视频都没实现成功。这一次参加学校的集中实习，培训老师带我们简单实现了一下。

? ? 要简单实现并不难，先从网上down一个简单的md5算法：

package com.train.util;import java.math.BigInteger;import java.security.MessageDigest;import java.security.NoSuchAlgorithmException;public class MD5Utils {/** * 使用md5的算法进行加密 */public static String md5(String plainText) {byte[] secretBytes = null;try {secretBytes = MessageDigest.getInstance("md5").digest(plainText.getBytes());} catch (NoSuchAlgorithmException e) {throw new 美国高防vps RuntimeException("没有md5这个算法！");}String md5code = new BigInteger(1, secretBytes).toString(16);// // 16进制数字// 如果生成数字未满32位，需要前面补0for (int i = 0; i < 32 - md5code.length(); i++) {md5code = "0" + md5code;}return md5code;}｝

然后在?Servlet或者控制器里直接调用MD5的这个静态方法就可以了：

protected void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {request.setCharacterEncoding("utf-8");String userName = request.getParameter("userName");String passWord = MD5Utils.md5(request.getParameter("passWord"));userModel model = new userModel();model.setUserName(userName);model.setPassWord(passWord);userService service = new userService();try {userModel m = service.selectByName(model.getUserName());if (m == null) { // 如果找不到同名的记录，则可以注册int i = service.save(model);if (i > 0) {request.setAttribute("msg", "注册成功！请登录！");request.getRequestDispatcher("login.jsp").forward(request, response);} else {request.setAttribute("msg", "注册失败！请重新注册！");request.getRequestDispatcher("index.jsp").forward(request, response);}} else {request.setAttribute("msg", "用户名重复！请重新注册！");request.getRequestDispatcher("index.jsp").forward(request, response);}} catch (Exception e) {e.printStackTrace();}}

这样注册进去的就是经过md5加密后的密文了。

然后登录功能要比对密码的时候，从数据库中取出的是密文，需要将用户输入的密码再进行md5加密以后再比对，否则就会失败：

protected void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {request.setCharacterEncoding("utf-8");String userName = request.getParameter("userName");String passWord = MD5Utils.md5(request.getParameter("passWord"));userModel model = new userModel();model.setUserName(userName);model.setPassWord(passWord);userService service = new userService();if (request.getSession().getAttribute("checkcode_session").equals(request.getParameter("checkCode"))) {try {userModel md = service.selectByNameAndPass(model);if (md != null) {// 找到记录，登录成功request.getSession().setAttribute("userName", md.getUserName());request.getRequestDispatcher("welcome.jsp").forward(request, response);} else {request.setAttribute("msg", "登录失败！请重试！");request.getRequestDispatcher("login.jsp").forward(request, response);}} catch (Exception e) {e.printStackTrace();}} else {request.setAttribute("msg", "验证码输入有误！请重试！");request.getRequestDispatcher("login.jsp").forward(request, response);}}

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