JavaWeb -- Session实例 -- 自动登录 和 防止表单重复提交(令牌产生器) MD5码

1、 自动登录

http://blog.csdn.net/xj626852095/article/details/16825659

2. 防止表单重复提交

表单Servlet 

//负责产生表单
public class FormServlet extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.setContentType("text/html;charset=UTF-8");PrintWriter out = response.getWriter();String token = TokenProccessor.getInstance().makeToken();request.getSession().setAttribute("token", token);  //在服务器端保存随机数out.println("<form action='/day07/servlet/DoFormServlet' method='post'>");out.write("<input type='hidden' name='token' value='"+token+"'>");out.println("用户名:<input type='text' name='username'>");out.println("<input type='submit' value='提交'>");out.println("</form>");}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}
}class TokenProccessor{/**单态设计模式（保证类的对象在内存中只有一个）*1、把类的构造函数私有*2、自己创建一个类的对象*3、对外提供一个公共的方法，返回类的对象* */private TokenProccessor(){}private static final TokenProccessor instance = new TokenProccessor();public static TokenProccessor getInstance(){return instance;}public String makeToken(){  //checkException//  7346734837483  834u938493493849384  43434384String token = (System.currentTimeMillis() + new Random().nextInt(999999999)) + "";//数据指纹   128位长   16个字节  md5try {MessageDigest md = MessageDigest.getInstance("md5");byte md5[] =  md.digest(token.getBytes());//base64编码--任意二进制编码明文字符   adfsdfsdfsfBASE64Encoder encoder = new BASE64Encoder();return encoder.encode(md5);} catch (NoSuchAlgorithmException e) {throw new RuntimeException(e);}}}

表单处理Servlet

public class DoFormServlet extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {boolean b = isToken(request);  //判断用户是否是重复提交if(b==true){System.out.println("请不要重复提交");return;}request.getSession().removeAttribute("token");System.out.println("处理用户提交请求！！");}private boolean isToken(HttpServletRequest request) {String client_token = request.getParameter("token");if(client_token==null){return true;}String server_token = (String) request.getSession().getAttribute("token");if(server_token==null){return true;}if(!client_token.equals(server_token)){return true;}return false;}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}