Session学习:防止用户重复提交表单(单态设计模式-原子设计模式+MD5技术&Base64算法)

1,FormServlet.java 设计一个表单提交数据,防止用户重复提交数据到服务器,实现阻止代码如下:

import java.io.IOException;  
import java.io.PrintWriter;  
import java.security.MessageDigest;  
import java.security.NoSuchAlgorithmException;  
import java.util.Random;  
import javax.servlet.ServletException;  
import javax.servlet.http.HttpServlet;  
import javax.servlet.http.HttpServletRequest;  
import javax.servlet.http.HttpServletResponse;  
import sun.misc.BASE64Encoder;  
  
//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{//使用令牌生成随机数 使用到MD5技术 和 BASE 64技术   
      
    /* 
     *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  43434384   
        String token = (System.currentTimeMillis() + new Random().nextInt(999999999)) + "";   
        //数据指纹   128位长   16个字节  md5   
        try {  
            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   adfsdfsdfsf   
            BASE64Encoder encoder = new BASE64Encoder();  
            return encoder.encode(md5);  
              
        } catch (NoSuchAlgorithmException e) {  
            throw new RuntimeException(e);  
        }  
          
    }  
      
}  

2,DoFormServlet.java 分别在客户端和服务器端阻止重复提交数据功能实现,代码如下:

import java.io.IOException;  
  
import javax.servlet.ServletException;  
import javax.servlet.http.HttpServlet;  
import javax.servlet.http.HttpServletRequest;  
import javax.servlet.http.HttpServletResponse;  
  
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){//判断客户端令牌是否为空   
            return true;  
        }  
          
        String server_token = (String) request.getSession().getAttribute("token");  
        if(server_token==null){//判断服务器端令牌是否为空   
            return true;  
        }  
          
        if(!client_token.equals(server_token)){//判断客服端令牌与服务器端令牌是否一致   
            return true;  
        }  
          
        return false;  
    }  
  
    public void doPost(HttpServletRequest request, HttpServletResponse response)  
            throws ServletException, IOException {  
  
        doGet(request, response);  
    }  
  
}