方法一：用js控制表单提交---》但是容易在客户端被篡改代码，还是要加的
方法二：session
先给每一个表带上唯一的标志，再把标志存入session
当session中标志和表上标志都不为空 ，且相等的情况下，提交表单成功，否则失败
下面是demo
目的：访问FormServlet----->加上标记后，转发到form.jsp----->提交的DoFormServlet.java来判断标记是否相等
FormServlet.java
/**
* 产生表单
*/
@WebServlet("/FormServlet")
public class FormServlet extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//生产随机号
TokenProcessor tp=new TokenProcessor();
String token=tp.generateToken();
//在session中存入标记
request.getSession().setAttribute("token", token);
//转发到form.jsp
request.getRequestDispatcher("/form.jsp").forward(request,response);//转发
}
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}
}
class TokenProcessor{//令牌
/**
* 1.构造方法私有
* 2.自己构造一个
* 3.对外暴露一个方法，允许获取上面创建的对象
*
*/
TokenProcessor(){};
private static final TokenProcessor instance=new TokenProcessor();
public static TokenProcessor getInstance(){
return instance;
}
public String generateToken(){
String token = System.currentTimeMillis()+new Random().nextInt()+"";//这里产生的随机数的长短不一样
try {
MessageDigest md=MessageDigest.getInstance("md5");//通过md5算法，得到数据指纹，数据指纹大小是一样的
byte[] md5=md.digest(token.getBytes());
//base64--->通过这个算法把字节转化成范围（0--63）键盘可见的字符（二进制的三个字节转化成四个字节）
BASE64Encoder encoder=new BASE64Encoder();
return encoder.encode(md5);
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
}
return null;
}
}
form.jsp
<%@ 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>Insert title here</title>
</head>
<body>
<form action="/day06/DoFormServlet" method="post ">
<input type="hidden" name="token" value="${token}">
用户名：<input type="text" name="username" />
<input type="submit" value="提交">
</body>
</html>
DoFormServlet.java
/**
* 判断标记
*/
@WebServlet("/DoFormServlet")
public class DoFormServlet extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setCharacterEncoding("UTF_8");
response.setContentType("text/html;charset=UTF-8");
PrintWriter out=response.getWriter();
boolean b=isTokenvalid(request);//判断是否重复提交
if(!b){
out.write("请不要重复提交表单");
return;
}
request.getSession(false).removeAttribute("token");//提交成功，session标记失效
out.write("处理表单");
}
/**
* @param request
* @return
*/
private boolean isTokenvalid(HttpServletRequest request) {
String client_token=request.getParameter("token");//表单上的标记不为空
if(client_token==null){
return false;
}
String token=(String) request.getSession(false).getAttribute("token");
if(token==null){//存入session中标记不为空
return false;
}
if(!token.equals(client_token)){//session中的标记和表单一致，表单未被篡改
return false;
}
return true;
}
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}
}