利用Java自带的MD5加密

 package test.md5;

 import java.security.MessageDigest;

 public class MD5Util {
     public final static String MD5(String s) {
         char hexDigits[]={'0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F'};       

         try {
             byte[] btInput = s.getBytes();
             // 获得MD5摘要算法的 MessageDigest 对象
             MessageDigest mdInst = MessageDigest.getInstance("MD5");
             // 使用指定的字节更新摘要
             mdInst.update(btInput);
             // 获得密文
             byte[] md = mdInst.digest();
             // 把密文转换成十六进制的字符串形式
             int j = md.length;
             char str[] = new char[j * 2];
             int k = 0;
             for (int i = 0; i < j; i++) {
                 byte byte0 = md[i];
                 str[k++] = hexDigits[byte0 >>> 4 & 0xf];
                 str[k++] = hexDigits[byte0 & 0xf];
             }
             return new String(str);
         } catch (Exception e) {
             e.printStackTrace();
             return null;
         }
     }

     public static void main(String[] args) {
         System.out.println(MD5Util.MD5("20121221"));
         System.out.println(MD5Util.MD5("加密"));
     }
 }