session ---- 防止表单重复提交
1.
package cn.itcast.form;
import java.io.IOException;
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;
//程序导向到表单, 产生表单号
public class FormServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//产生随机数 表单号
TokenProcessor processor = TokenProcessor.getInstance();
String token = processor.generateToken();
request.getSession().setAttribute("token", token);//带给前台form并为以后校验用,所以要存session
request.getRequestDispatcher("/form.jsp").forward(request, response);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
this.doGet(req, resp);
}
}
class TokenProcessor{//令牌发生器,产生唯一表单号用,单例
private TokenProcessor(){}
private static final TokenProcessor instance = new TokenProcessor();
public static TokenProcessor getInstance(){
return instance;
}
public String generateToken(){ //指纹摘要算法
//121212 1231646466 4654646464646646 长度可能不一致,但我们需要长度一致
String token = System.currentTimeMillis() + new Random().nextInt() + "";
MessageDigest md;
try {
md = MessageDigest.getInstance("md5");
byte[] md5 = md.digest(token.getBytes()); //返回的是128位的指纹
//String pass = new String(md5); 乱码, 用base64算法返回的是明文字符串即键盘能看到的
//base64 把任意3个字节24个二进制位变成4个字节(6位/字节),但一个字节默认是8位,前面补00,
//网络上的数据传递一般都是通过base64转过去传递
BASE64Encoder encoder = new BASE64Encoder();
return encoder.encode(md5);
} catch (NoSuchAlgorithmException e) {
throw new RuntimeException(e);
}
}
}
2.
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>My JSP </title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
</head>
<body>
<form action="DoFormServlet" method="post">
<input type="hidden" name="token" value=${token} ><!-- 后台Formservlet给的表单号,等下提交到DoFormServlet去验证 -->
用户名:<input type="text" name="username">
<input type="submit" value="jsp表单提交">
</form>
</body>
</html>
3.
package cn.itcast.form;
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 {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String username = request.getParameter("username");
//模拟网络延迟
/*try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("向数据库中注册用户..." + username);*/
boolean flag = isTokenValid(request);
if(!flag){ // 令牌无效,不准进入数据库!
System.out.println("请不要重复提交");
return;
}
//todo 提交表单后的操作...
request.getSession().removeAttribute("token");
System.out.println("向数据库中注册用户..." + username);
}
//判断表单号是否有效, 闯过3关就是君子!
private boolean isTokenValid(HttpServletRequest request) {
String clientToken = request.getParameter("token");
if(clientToken == null) { //坏人自己写表单提交
return false;
}
String serveToken = (String) request.getSession().getAttribute("token");
if(serveToken == null) { //上次提交过,服务端已经清除了token
return false;
}
if(! clientToken.equals(serveToken)){
return false;
}
return true;
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
this.doGet(req, resp);
}
}
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