1.什么是重复提交及重复提高带来的什么问题？：很严重
2.解决方案：
方案一.利用javaScript
方案二.请求重定向到另一个界面：Redirect After （Google）：
方案三：利用HTTPSession防止表单的重复提交（推荐使用）：
1 import java.io.IOException; 2 3 import javax.servlet.ServletException; 4 import javax.servlet.http.HttpServlet; 5 import javax.servlet.http.HttpServletRequest; 6 import javax.servlet.http.HttpServletResponse; 7 import javax.servlet.http.HttpSession; 8 9 public class RegistServlet extends HttpServlet { 10 11 public void doGet(HttpServletRequest request, HttpServletResponse response) 12 throws ServletException, IOException { 13 14 String iToken = request.getParameter("token"); 15 HttpSession session = request.getSession(); 16 String sToken = (String) session.getAttribute("token"); 17 if(iToken.equals(sToken)){ 18 String name = request.getParameter("name"); 19 System.out.println(name); 20 response.getWriter().write("sucess"); 21 session.removeAttribute("token"); 22 }else{ 23 response.getWriter().write("resubmit occured"); 24 } 25 } 26 27 public void doPost(HttpServletRequest request, HttpServletResponse response) 28 throws ServletException, IOException { 29 doGet(request, response); 30 } 31 32 }
1 <%@ page import="java.util.*" pageEncoding="UTF-8"%> 2 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 3 <html> 4 <head> 5 <title>title</title> 6 <meta http-equiv="pragma" content="no-cache"> 7 <meta http-equiv="cache-control" content="no-cache"> 8 <meta http-equiv="expires" content="0"> 9 <!-- 10 <link rel="stylesheet" type="text/css" href="styles.css"> 11 --> 12 13 </head> 14 15 <body> 16 保存成功 17 </body> 18 </html>
1 <%@ page import="java.util.*" pageEncoding="UTF-8"%> 2 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 3 <html> 4 <head> 5 <title>新用户注册</title> 6 <meta http-equiv="pragma" content="no-cache"> 7 <meta http-equiv="cache-control" content="no-cache"> 8 <meta http-equiv="expires" content="0"> 9 <!-- 10 <link rel="stylesheet" type="text/css" href="styles.css"> 11 --> 12 13 </head> 14 15 <body> 16 <% 17 String token = UUID.randomUUID().toString(); 18 pageContext.setAttribute("token", token); 19 session.setAttribute("token", token); 20 %> 21 <form action="${pageContext.request.contextPath}/servlet/RegistServlet" method="post"> 22 <input type="hidden" name="token" value="${token}"/> 23 姓名：<input type="text" name="name"/><br/> 24 <input type="submit" value="注册"/> 25 </form> 26 <script type="text/javascript"> 27 window.onload=function(){ 28 document.getElementById("btn1").onclick=function(){ 29 document.forms[0].submit(); 30 document.getElementById("btn1").disabled=true; 31 } 32 } 33 </script> 34 </body> 35 </html>
自定义标签防止重复提交表单：
标签：
1 import java.io.IOException; 2 import java.util.UUID; 3 4 import javax.servlet.jsp.JspException; 5 import javax.servlet.jsp.JspWriter; 6 import javax.servlet.jsp.PageContext; 7 import javax.servlet.jsp.tagext.SimpleTagSupport; 8 9 public class TokenSimpleTag extends SimpleTagSupport { 10 //向HttpSession中放一个令牌；输出input hidden的表单域 11 public void doTag() throws JspException, IOException { 12 try { 13 String token = UUID.randomUUID().toString(); 14 PageContext pc = (PageContext)getJspContext(); 15 pc.getSession().setAttribute("token", token); 16 JspWriter out = pc.getOut(); 17 out.write("<input type=\"hidden\" name=\"token\" value=\""+token+"\"/>"); 18 } catch (Exception e) { 19 throw new RuntimeException(e); 20 } 21 } 22 23 }
tld文件：
1 <?xml version="1.0" encoding="UTF-8"?> 2 <taglib xmlns="http://java.sun.com/xml/ns/javaee" 3 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 4 xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-jsptaglibrary_2_1.xsd" 5 version="2.1"> 6 7 <tlib-version>1.0</tlib-version> 8 <short-name>itheima</short-name> 9 <uri>http://www.itheima.com/framework/core</uri> 10 <tag> 11 <name>token</name> 12 <tag-class>com.itheima.tag.TokenSimpleTag</tag-class> 13 <body-content>empty</body-content> 14 </tag> 15 </taglib>
xml文件：
1 <?xml version="1.0" encoding="UTF-8"?> 2 <web-app version="2.5" 3 xmlns="http://java.sun.com/xml/ns/javaee" 4 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 5 xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 6 http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"> 7 <display-name></display-name> 8 <filter> 9 <filter-name>TokenFilter</filter-name> 10 <filter-class>com.itheima.filter.TokenFilter</filter-class> 11 </filter> 12 <filter-mapping> 13 <filter-name>TokenFilter</filter-name> 14 <url-pattern>/servlet/*</url-pattern> 15 </filter-mapping> 16 <servlet> 17 <servlet-name>RegistServlet</servlet-name> 18 <servlet-class>com.itheima.servlet.RegistServlet</servlet-class> 19 </servlet> 20 <servlet-mapping> 21 <servlet-name>RegistServlet</servlet-name> 22 <url-pattern>/servlet/RegistServlet</url-pattern> 23 </servlet-mapping> 24 <welcome-file-list> 25 <welcome-file>index.jsp</welcome-file> 26 </welcome-file-list> 27 </web-app>
过滤器：
1 import java.io.IOException; 2 3 import javax.servlet.Filter; 4 import javax.servlet.FilterChain; 5 import javax.servlet.FilterConfig; 6 import javax.servlet.ServletException; 7 import javax.servlet.ServletRequest; 8 import javax.servlet.ServletResponse; 9 import javax.servlet.http.HttpServletRequest; 10 import javax.servlet.http.HttpServletResponse; 11 import javax.servlet.http.HttpSession; 12 13 public class TokenFilter implements Filter { 14 15 public void init(FilterConfig filterConfig) throws ServletException { 16 17 } 18 19 public void doFilter(ServletRequest req, ServletResponse resp, 20 FilterChain chain) throws IOException, ServletException { 21 HttpServletRequest request; 22 HttpServletResponse response; 23 try{ 24 request = (HttpServletRequest)req; 25 response = (HttpServletResponse)resp; 26 }catch(Exception e){ 27 throw new RuntimeException(e); 28 } 29 30 String iToken = request.getParameter("token"); 31 HttpSession session = request.getSession(); 32 String sToken = (String) session.getAttribute("token"); 33 if(iToken==null){ 34 throw new RuntimeException("form must use itheima:token"); 35 } 36 if(iToken.equals(sToken)){ 37 session.removeAttribute("token"); 38 chain.doFilter(request, response); 39 }else{ 40 response.getWriter().write("resubmit occured"); 41 } 42 } 43 44 public void destroy() { 45 46 } 47 48 }
Servlet文件：
1 import java.io.IOException; 2 3 import javax.servlet.ServletException; 4 import javax.servlet.http.HttpServlet; 5 import javax.servlet.http.HttpServletRequest; 6 import javax.servlet.http.HttpServletResponse; 7 import javax.servlet.http.HttpSession; 8 9 public class RegistServlet extends HttpServlet { 10 11 public void doGet(HttpServletRequest request, HttpServletResponse response) 12 throws ServletException, IOException { 13 System.out.println(request.getParameter("name")); 14 15 } 16 17 public void doPost(HttpServletRequest request, HttpServletResponse response) 18 throws ServletException, IOException { 19 doGet(request, response); 20 } 21 22 }
jsp文件：
1 <%@ page import="java.util.*" pageEncoding="UTF-8"%> 2 <%@ taglib uri="http://www.itheima.com/framework/core" prefix="itheima"%> 3 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 4 <html> 5 <head> 6 <title>新用户注册</title> 7 <meta http-equiv="pragma" content="no-cache"> 8 <meta http-equiv="cache-control" content="no-cache"> 9 <meta http-equiv="expires" content="0"> 10 <!-- 11 <link rel="stylesheet" type="text/css" href="styles.css"> 12 --> 13 14 </head> 15 16 <body> 17 <form action="${pageContext.request.contextPath}/servlet/RegistServlet" method="post"> 18 姓名：<input type="text" name="name"/><br/> 19 <input type="submit" value="注册"/> 20 <itheima:token/> 21 </form> 22 </body> 23 </html>
1 <%@ page import="java.util.*" pageEncoding="UTF-8"%> 2 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 3 <html> 4 <head> 5 <title>title</title> 6 <meta http-equiv="pragma" content="no-cache"> 7 <meta http-equiv="cache-control" content="no-cache"> 8 <meta http-equiv="expires" content="0"> 9 <!-- 10 <link rel="stylesheet" type="text/css" href="styles.css"> 11 --> 12 13 </head> 14 15 <body> 16 保存成功 17 </body> 18 </html>