用來對使用者的密碼進行加密，增加安全性

import java.security.MessageDigest;

/**
 *
 * @author changxuan
 */
public class MD5password {
     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();
            MessageDigest mdInst = MessageDigest.getInstance("MD5");
            mdInst.update(btInput);
            byte[] md=mdInst.digest();
            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;
        }
        
    }
 

}