session防止表单重复提交
有一个生成表单号的sevlet
public class FormServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//产生随机数表单号
TokenProcessor tp = TokenProcessor.getInstance();
String token = tp.getToken();
request.getSession().setAttribute("token", token);
request.getRequestDispatcher("/form.jsp").forward(request, response);
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request,response);
}
}
class TokenProcessor{//令牌
/*1，构造方法私有
* 2。自己创建一个
* 3.对外暴露一个方法，允许获取上面对象
*/
private TokenProcessor(){};
private static final TokenProcessor instance = new TokenProcessor();
public static TokenProcessor getInstance(){
return instance;
}
public String getToken(){
//先生成随机数
String token = System.currentTimeMillis()+new Random().nextInt()+"";
//使位数固定，摘要算法
try {
MessageDigest md = MessageDigest.getInstance("md5");
byte[] md5 = md.digest(token.getBytes());
//base64编码，生成字符串
BASE64Encoder encoder = new BASE64Encoder();
return encoder.encode(md5);
} catch (NoSuchAlgorithmException e) {
throw new RuntimeException(e);
}
}
}
表单如下
<%@ page language="java" contentType="text/html; charset=utf-8"
pageEncoding="utf-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>Form</title>
</head>
<body>
<form action="/day07/DoForm" method="post">
<input type="hidden" name="token" value="${token}"><br>
用户名：<input type="text" name="username"><br>
<input type="submit" value="提交">
</form>
</body>
</html>
处理表单的sevlet
public class DoForm extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String token = request.getParameter("token");
String server_token = (String) request.getSession().getAttribute("token");
boolean b = isTokenValid(token,server_token);
if(!b){
System.out.println("Invalid token");
return;
}
request.getSession().removeAttribute("token");
System.out.println("ok");
}
//判断表单是否有效
private boolean isTokenValid(String token,String server_token) {
if(token==null){
return false;
}
if(server_token==null){
return false;
}
if(!token.equals(server_token)){
return false;
}
return true;
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request,response);
}
}