JavaWeb基础——Cookie和Session

1、什么是Cookie和Session

什么是会话？





2、Cookie技术



创建Cookie

package cn.itcast.cookie;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Date;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
* Servlet implementation class CookieDemo1
*/
@WebServlet("/CookieDemo1")
public class CookieDemo1 extends HttpServlet {
private static final long serialVersionUID = 1L;

/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
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();

out.print("您上次访问的时间是：");

//获得用户的时间cookie
Cookie cookies[]=request.getCookies();//创建Cookie，返回一个数组，Cookie最多保存300个
for(int i=0;cookies!=null && i<cookies.length;i++) {
if(cookies[i].getName().equals("lastAccessTime")) {
long cookieValue=Long.parseLong(cookies[i].getValue());//cookies[i].getValue()返回的是字符串
Date date=new Date(cookieValue);
out.print(date.toLocaleString());
}
}
//给用户回送最新的访问时间
Cookie cookie=new Cookie("lastAccessTime",System.currentTimeMillis()+"");
cookie.setMaxAge(1*30*24*3600);//设置最大的cookie保存时间

/*cookie.setPath()此处的参数，是相对于应用服务器存放应用的文件夹的根目录而言的(比如tomcat下面的webapp)，
* 因此cookie.setPath("/");之后，可以在webapp文件夹下的所有应用共享cookie，
* 而cookie.setPath("/webapp_b/");是指cas应用设置的cookie只能在webapp_b应用下的获得，
* 即便是产生这个cookie的cas应用也不可以。
*
*
* */
cookie.setPath("/day2");//获取cookie的访问地
response.addCookie(cookie);
}

/**
* @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);
}

}

删除Cookie

CookieDemo2.java

package cn.itcast.cookie;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Date;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
* 点击超链接删除该Cookie记录
*/
@WebServlet("/CookieDemo2")
public class CookieDemo2 extends HttpServlet {
private static final long serialVersionUID = 1L;

/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
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();

out.print("<a href='/day2/CookieDemo2_1'>清除上次访问时间</a><br/>");
out.print("您上次访问的时间是：");

//获得用户的时间cookie
Cookie cookies[]=request.getCookies();
for(int i=0;cookies!=null && i<cookies.length;i++) {
if(cookies[i].getName().equals("lastAccessTime")) {
long cookieValue=Long.parseLong(cookies[i].getValue());
Date date=new Date(cookieValue);
out.print(date.toLocaleString());
}
}
//给用户会送最新的访问时间
Cookie cookie=new Cookie("lastAccessTime",System.currentTimeMillis()+"");
cookie.setMaxAge(1*30*24*3600);//设置最大的cookie保存时间
cookie.setPath("/day2");
response.addCookie(cookie);
}

/**
* @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);
}

}

CookieDemo2_1.java

package cn.itcast.cookie;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
* Servlet implementation class CookieDemo2_1
*/
@WebServlet("/CookieDemo2_1")
public class CookieDemo2_1 extends HttpServlet {
private static final long serialVersionUID = 1L;

/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
Cookie cookie=new Cookie("lastAccessTime",System.currentTimeMillis()+"");//相当于覆盖，但设置Cookie存储期限为0由此达到删除目的
cookie.setMaxAge(0);
cookie.setPath("/day2");
response.addCookie(cookie);

}

/**
* @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);
}

}

Cookie案例——显示历史清单

Demo1.java

package cn.itcast.cookieAplication;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.LinkedHashMap;
import java.util.Map;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
* Servlet implementation class Demo1
*/
@WebServlet("/Demo1")
public class Demo1 extends HttpServlet {
private static final long serialVersionUID = 1L;

/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
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();

//1、输出网站所有商品
out.write("本网站有如下商品:<br/>");
Map<String,Book>map=Db.getAll();
for(Map.Entry<String, Book>entry:map.entrySet()) {
Book book=entry.getValue();
out.print("<a href='Demo2?id="+book.getId()+"' target='_blank'>"+book.getName()+"</a><br/>");
}//每一个都是超链接

//2、显示用户曾经看过的商品
out.print("<br/>您曾经看过的商品:<br/>");
Cookie cookies[]=request.getCookies();
for(int i=0;cookies!=null && i<cookies.length;i++) {
if(cookies[i].getName().equals("bookHistory")) {
String ids[]=cookies[i].getValue().split("\\,");
for(String id:ids) {
Book book=(Book)Db.getAll().get(id);
out.print(book.getName()+"<br/>");
}
}
}

}

/**
* @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 Db{
private static Map<String,Book> map=new LinkedHashMap();
static {
map.put("1", new Book("1","javaweb开发","老张","一本好书"));
map.put("2", new Book("2","jdbc开发","老张","一本好书"));
map.put("3", new Book("3","spring开发","老黎","一本好书"));
map.put("4", new Book("4","struts开发","老毕","一本好书"));
map.put("5", new Book("5","android开发","老黎","一本好书"));
}
public static Map getAll() {
return map;
}
}

class Book{
public Book() {
super();
// TODO Auto-generated constructor stub
}
public Book(String id, String name, String author, String description) {
super();
this.id = id;
this.name = name;
this.author = author;
this.description = description;
}
private String id;
private String name;
private String author;
private String description;

public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getAuthor() {
return author;
}
public void setAuthor(String author) {
this.author = author;
}
public String getDescription() {
return description;
}
public void setDescription(String description) {
this.description = description;
}

}

Demo2.java

package cn.itcast.cookieAplication;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.LinkedList;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
* 显示商品详细信息的Servlet
*/
@WebServlet("/Demo2")
public class Demo2 extends HttpServlet {
private static final long serialVersionUID = 1L;

/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
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();
//1、根据用户带过来的id，显示相应商品的详细信息
String id=request.getParameter("id");
Book book=(Book)Db.getAll().get(id);
out.write(book.getId()+"<br/>");
out.write(book.getName()+"<br/>");
out.write(book.getDescription()+"<br/>");
out.write(book.getAuthor()+"<br/>");

//2、构建cookie，回写给浏览器
String cookieValue=buildCookie(id,request);
Cookie cookie=new Cookie("bookHistory",cookieValue);
cookie.setMaxAge(1*30*24*3600);
cookie.setPath("/day2");
response.addCookie(cookie);
}

private String buildCookie(String id, HttpServletRequest request) {
// TODO Auto-generated method stub

//bookHistory=null      1   1
//bookHistory=2,5,1     1   1,2,5
//bookHistory=2,5,4     1   1,2,5
//bookHistory=2,5       1   1,2,5
String bookHistory=null;
Cookie cookies[]=request.getCookies();
for(int i=0;cookies!=null && i<cookies.length;i++) {
if(cookies[i].getName().equals("bookHistory")) {
bookHistory=cookies[i].getValue();
}
}
if(bookHistory==null) {
return id;
}
LinkedList<String> list=new LinkedList(Arrays.asList(bookHistory.split("\\,")));
/*
if(list.contains(id)) {
//bookHistory=2,5,1     1   1,2,5
list.remove(id);
list.addFirst(id);
}else {
//bookHistory=2,5,4     1   1,2,5

if(list.size()>=3) {
list.removeLast();
list.addFirst(id);
}else {
//bookHistory=2,5       1   1,2,5
list.addFirst(id);
}
}
*/
if(list.contains(id)) {
list.remove(id);
}else {
if(list.size()>=3) {
list.removeLast();
}
}
list.addFirst(id);

StringBuffer sb=new StringBuffer();
for(String bid:list) {
sb.append(bid+",");
}

return sb.deleteCharAt(sb.length()-1).toString();
}

/**
* @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);
}

}

3、Session

<%@ 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=ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
<a href="SessionDemo1">购买</a>
<a href="SessionDemo1_1">结账</a>
</body>
</html>

example1

解决禁用Cookie的解决方案

package cn.itcast.session;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
* 禁用Cookie的解决方案
*/
@WebServlet("/WelcomeServlet")
public class WelcomeServlet extends HttpServlet {
private static final long serialVersionUID = 1L;

/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
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();

String url1=response.encodeURL("SessionDemo1");//URL重写，在后面自动跟上session的id号
String url2=response.encodeURL("SessionDemo1_1");//若没有禁用cookie则不会重写URL，没有就会自动重写URL

out.print("<a href='"+url1+"'>购买</a>");
out.print("<a href='"+url2+"'>结账</a>");

}

/**
* @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);
}

}

购买servlet

package cn.itcast.session;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
* 购买的Servlet
*
* Session的生命周期：
* 当访问程序时，程序里面调用了getSession时Session生
* 当会话关闭（不关，但当30分钟后也会死，这个时间可以在web.xml中通过session-config设置）后30分钟，Session才结束，它是由服务器管的
*
*
*/
@WebServlet("/SessionDemo1")
public class SessionDemo1 extends HttpServlet {
private static final long serialVersionUID = 1L;

/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
HttpSession session=request.getSession();//有session就不创建，没session就创建
//下面的代码依据Session原理，回写sessionid到cookie中，并保持与session同样的有效期
//能解决关闭浏览器后，仍可获取到sessionid
String sessionid=session.getId();//获取session的id
//将sessionid以cookie的方式存在磁盘中，有效期为30min
Cookie cookie=new Cookie("JSESSIONID",sessionid);
cookie.setPath("/day2");
cookie.setMaxAge(30*60);

session.setAttribute("name", "洗衣机");

//  request.getSession(false);//不创建session，只获取session

//  session.invalidate();//这句话也能摧毁session
}

/**
* @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);
}

}

结账servlet

package cn.itcast.session;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
* 结账的Servlet，如果另外再开一个浏览器访问结账是拿不到的，它只为一个会话服务。
*/
@WebServlet("/SessionDemo1_1")
public class SessionDemo1_1 extends HttpServlet {
private static final long serialVersionUID = 1L;

/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
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();

HttpSession session=request.getSession();
String product=(String)session.getAttribute("name");
out.write("您购买的商品是："+product);
}

/**
* @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);
}

}

example2

login.html

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
<form action="LoginServlet" method=post>
用户名:<input type="text" name="username"><br/>
密码:<input type="password" name="password"><br/>
<input type="submit" value="登陆">

</form>
</body>
</html>

User.java

package cn.itcast.session;

public class User {
private String username;
private String password;

public User(String username, String password) {
super();
this.username = username;
this.password = password;
}

public User() {
super();
// TODO Auto-generated constructor stub
}

public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}

}

LoginServlet.java

package cn.itcast.session;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
* Servlet implementation class LoginServlet
*/
@WebServlet("/LoginServlet")
public class LoginServlet extends HttpServlet {
private static final long serialVersionUID = 1L;

/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
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();

String username=request.getParameter("username");
String password=request.getParameter("password");

List<User>list=DB.getAll();
for(User user:list) {
if(user.getUsername().equals(username) && user.getPassword().equals(password)) {
request.getSession().setAttribute("user",user);//登陆成功，向session中存入一个登陆标识
response.sendRedirect("LoginIndex.jsp");
return;
}
}
out.write("用户名或密码不对！！");
}

/**
* @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 DB{

public static List list=new ArrayList();
static {
list.add(new User("aaa","123"));
list.add(new User("bbb","123"));
list.add(new User("ccc","123"));
}
public static List getAll() {
return list;
}
}

LoginIndex.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=ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
欢迎您：$(User.username) <a href="">登陆</a><br/><!--取出session中的user对象  -->
<a href="LogoutServlet">退出登录</a>
<br/><br/><br/>
</body>
</html>

LogoutServlet.java

package cn.itcast.session;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
* 完成用户注销
*/
@WebServlet("/LogoutServlet")
public class LogoutServlet extends HttpServlet {
private static final long serialVersionUID = 1L;

/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
HttpSession session=request.getSession(false);
if(session==null) {
response.sendRedirect("login.html");
return;
}
session.removeAttribute("user");
response.sendRedirect("login.html");
}

/**
* @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);
}

}

example3（购买书籍、禁用cookie、关闭浏览器的应用）

Session1

package cn.itcast.sessionAplication;

import java.io.IOException;
import java.io.PrintWriter;
import java.io.Serializable;
import java.util.LinkedHashMap;
import java.util.Map;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
* 代表网站首页，列出所有书
*/
@WebServlet("/Session1")
public class Session1 extends HttpServlet {
private static final long serialVersionUID = 1L;

/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
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();
out.print("本网站有如下商品:<br/>");

request.getSession();//只有在此处得到了session,才能在response.encodeURL()中得到session的Id号

Map<String,Book>map=Db.getAll();
for(Map.Entry<String, Book>entry:map.entrySet()) {
Book book=entry.getValue();

//out.print(book.getName()+"<a href='BuyServlet?id="+book.getId()+"'target='_blank'>购买</a><br/>");
//用于解决禁用Cookie的写法
String url=response.encodeURL("BuyServlet?id="+book.getId());
out.print(book.getName()+"<a href='"+url+"' target='_blank'>购买</a><br/>");
}
}
/**
* @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 Db{
private static Map<String,Book> map=new LinkedHashMap();
static {
map.put("1", new Book("1","javaweb开发","老张","一本好书"));
map.put("2", new Book("2","jdbc开发","老张","一本好书"));
map.put("3", new Book("3","spring开发","老黎","一本好书"));
map.put("4", new Book("4","struts开发","老毕","一本好书"));
map.put("5", new Book("5","android开发","老黎","一本好书"));
}
public static Map getAll() {
return map;
}
}

class Book implements Serializable{
public Book() {
super();
// TODO Auto-generated constructor stub
}
public Book(String id, String name, String author, String description) {
super();
this.id = id;
this.name = name;
this.author = author;
this.description = description;
}
private String id;
private String name;
private String author;
private String description;

public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getAuthor() {
return author;
}
public void setAuthor(String author) {
this.author = author;
}
public String getDescription() {
return description;
}
public void setDescription(String description) {
this.description = description;
}

}

BuyServlet.java

package cn.itcast.sessionAplication;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
* 完成购买
*/
@WebServlet("/BuyServlet")
public class BuyServlet extends HttpServlet {
private static final long serialVersionUID = 1L;

/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String id=request.getParameter("id");
Book book=(Book)Db.getAll().get(id);

//HttpSession session=request.getSession();
HttpSession session=request.getSession(false);//配合禁用cookie的写法
//手工以cookie形式发sessionid，以解决关闭浏览器后，上次买的东西还在

//从session得到用户用于保存所有书的集合（购物车）
List list=(List)session.getAttribute("list");
if(list==null) {
list=new ArrayList();
session.setAttribute("list", list);

}
list.add(book);
//配合禁用cookie的写法
String url=response.encodeRedirectURL("ListCartServlet");
response.sendRedirect(url);

//response.sendRedirect(request.getContextPath()+"ListCartServlet");

}

/**
* @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);
}

}

ListCartServlet.java

package cn.itcast.sessionAplication;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
* 显示用户购买的商品
*/
@WebServlet("/ListCartServlet")
public class ListCartServlet extends HttpServlet {
private static final long serialVersionUID = 1L;

/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
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();

HttpSession session=request.getSession(false);
if(session==null) {
out.write("您没有购买任何商品！！");
return;
}
out.write("您购买了如下商品：<br/>");
List<Book>list=(List)session.getAttribute("list");
for(Book book:list) {
out.write(book.getName());
}
}

/**
* @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);
}

}

example4 (防止表单重复提交)

javascript防表单重复提交（不能完全解决）

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
<script type="text/javascript">
<!-- javascript防表单重复提交方式一
var iscommitted=false;
function dosubmit(){
if(!iscommited){
iscommited=true;
return true;
}else{
return false;
}
}
-->
<!-- javascript防表单重复提交方式二-->
function dosubmit(){
var input=document.getElementById("submit");
input.disabled='disabled';
return true;
}
</script>
</head>
<body>
<form action="DoFormServlet" method="post" onsubmit="return dosubmit()">
用户名:<input type="text" name="username">
<input type="submit" value="提交">

</form>
</body>
</html>

base64编码



服务器端和前端同时防止表单重复提交

FormServlet.java

package cn.itcast.sessionAplication1;

import java.io.IOException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Random;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import sun.misc.BASE64Encoder;

/**
* 产生表单
*/
@WebServlet("/FormServlet")
public class FormServlet extends HttpServlet {
private static final long serialVersionUID = 1L;

/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//产生随机数（表单）
TokenProcessor tp=TokenProcessor.getInstance();
String token=tp.generateToken();

request.getSession().setAttribute("token", token);

request.getRequestDispatcher("formServletJS.jsp").forward(request, response);

}

/**
* @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{   //创建一个令牌
/*
* 1、把构建方法私有
* 2、自己创建一个
* 3、对外暴露一个方法，允许获取上面创建的对象
*
* */

private TokenProcessor() {};
private static final TokenProcessor instance=new TokenProcessor();
public static TokenProcessor getInstance(){
return instance;
}
//随机数发生器
public String generateToken() {
//获取随机数，但由此获取到的随机数长度可能不一样，但它们的摘要一样，所以为了保证它们的长度一致选用它们的数据摘要
String token=System.currentTimeMillis()+new Random().nextInt()+"";//获取随机数
try {
//通过md5算法得到数据摘要，无论数据有多大，它的数据摘要始终是128位
MessageDigest md=MessageDigest.getInstance("md5");//
byte[]md5=md.digest(token.getBytes());//返回的是任意二进制字节数组

//return new String(md5);//这样行不通，因为没有没有指定码表，它会默认查GB2312码表，然而它与二进制字节数组不一定有对应的码值，所以必定是个乱码
//为了让它不是乱码，所以采用base64编码
BASE64Encoder encoder=new BASE64Encoder();
return encoder.encode(md5);
}catch(NoSuchAlgorithmException e){
throw new RuntimeException(e);
}
}
}

formServletJS.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=ISO-8859-1">
<title>Insert title here</title>
<script type="text/javascript">
function dosubmit(){
var input=document.getElementById("submit");
input.disabled='disabled';
return true;
}

</script>
</head>
<body>
<form action="DoFormServlet" onsubmit="return dosubmit()" method="post">
<input type="hidden" name="token" value="$(token)">
用户名:<input type="text" name="username"><br/>
<input type="submit" value="提交">
</form>
</body>
</html>

DoFormServlet.java

package cn.itcast.sessionAplication1;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
* 处理表单提交请求
*/
@WebServlet("/DoFormServlet")
public class DoFormServlet extends HttpServlet {
private static final long serialVersionUID = 1L;

/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
boolean b=isTokenValid(request);
if(!b) {
System.out.println("请不要重复提交");
return;
}
request.getSession().removeAttribute("token");
System.out.println("向数据库注册用户----");
}
//判断表单号是否有效
private boolean isTokenValid(HttpServletRequest request) {
// TODO Auto-generated method stub
String client_token=request.getParameter("token");//客户端的token表单
if(client_token==null) {
return false;
}
String server_token=(String)request.getSession().getAttribute("token");//获取服务器中的token表单
if(server_token==null) {
return false;
}
if(!client_token.equals(server_token)) {
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);
}

}

example5 验证码校验

Checkcode1.java

package cn.itcast.sessionCheckcode;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
* Servlet implementation class Checkcode1
*/
@WebServlet("/Checkcode1")
public class Checkcode1 extends HttpServlet {
private static final long serialVersionUID = 1L;

public static final int WIDTH=120;
public static final int HEIGHT=25;
/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
BufferedImage image=new BufferedImage(WIDTH,HEIGHT,BufferedImage.TYPE_INT_RGB);//构建出一张图片
Graphics g=image.getGraphics();//使得能在图片上进行设置

//1、设置背景色
setBackGround(g);
//2、设置边框
setBorder(g);
//3、画干扰线
drawRandomLine(g);
//4、写随机数
String random=drawRandomNum((Graphics2D) g);
request.getSession().setAttribute("imagecheckcode",random);

//5、图形写给浏览器
//发头控制浏览器不要缓存,如果没有这步的话当我们访问Register网页时不点刷新，直接按回车，图片还是保持不变
//点击刷新的时候会产生两个动作：一是重新清空缓存；二是重新运行程序
response.setDateHeader("expire", -1);//控制所有浏览器都不要缓存
response.setHeader("Cache-Control", "no-cache");
response.setHeader("Pragma", "no-cache");

response.setContentType("image/jpeg");
ImageIO.write(image, "jpg", response.getOutputStream());

}

private String drawRandomNum(Graphics2D g) {
// TODO Auto-generated method stub
g.setColor(Color.RED);
g.setFont(new Font("宋体",Font.BOLD,20));

String base="\u6d4e\u8499\u68cb\u7aef\u817f\u62db\u91ca\u4ecb\u70e7\u8bef";

StringBuffer sb=new StringBuffer();
//[\u4e00-\u9fa5]
int x=5;
for(int i=0;i<4;i++) {

int degree=new Random().nextInt()%30;//从-30-30之间产生一个随机数

//Graphics2D类才有旋转功能
//new Random().nextInt(base.length())：在base的长度以内产生一个随机数
String ch=base.charAt(new Random().nextInt(base.length()))+"";
sb.append(ch);
g.rotate(degree*Math.PI/180,x,20);//设置旋转角度
g.drawString(ch, x, 20);
g.rotate(-degree*Math.PI/180,x,20);//转回去
x+=30;
}
return sb.toString();
}

private void drawRandomLine(Graphics g) {
// TODO Auto-generated method stub
g.setColor(Color.GREEN);
for(int i=0;i<5;i++) {
int x1=new Random().nextInt(WIDTH);
int y1=new Random().nextInt(HEIGHT);

int x2=new Random().nextInt(WIDTH);
int y2=new Random().nextInt(HEIGHT);
g.drawLine(x1, y1, x2, y2);
}
}

private void setBorder(Graphics g) {
// TODO Auto-generated method stub
g.setColor(Color.BLUE);
g.drawRect(1, 1,WIDTH-2, HEIGHT-2);
}

private void setBackGround(Graphics g) {
// TODO Auto-generated method stub
g.setColor(Color.WHITE);
g.fillRect(0, 0, WIDTH, HEIGHT);
}

/**
* @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);
}

}

Checkcode.html

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>

<script type="text/javascript">
function changeImage(img){
//如果只写img.src=img.src则点击不会变，它会调用缓存中的图片（我们没刷新，也没访问之前的地址），当我们给它加上"？"后则每次请求的都是新地址
//缓存中自然没有之前的图片，所以会调用新的图片（没有后面的new Date().getTime()也能运行）
img.src=img.src+"?"+new Date().getTime();
}
</script>

</head>
<body>
<!-- 点击图片时验证码更换 -->
<form action="RegisterServlet" method="post">
用户名：<input type="text" name="username"><br/>
密码：<input type="password" name="password"><br/>
认证码：<input type="text" name="checkcode">
<img src="Checkcode1" onclick="changeImage(this)" alt="换一张" style="cursor:pointer "><br/>
<input type="submit" value="注册">
</form>
</body>
</html>

RegisterServlet.java

package cn.itcast.sessionCheckcode;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
* Servlet中的context域用的地方：产生的数据，页面不仅显示，等会儿用完了，还要给其他的servlet用
* request域的用处：产生的数据，显示完了，就不用了
* session：产生的数据，显示完了，还要用
*/
@WebServlet("/RegisterServlet")
public class RegisterServlet extends HttpServlet {
private static final long serialVersionUID = 1L;

/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

request.setCharacterEncoding("utf-8");//没有这句，则我们输入的中文，c_checkcode收到的将是乱码

//处理注册请求之前，校验认证码是否有效
String c_checkcode=request.getParameter("checkcode");
String s_checkcode=(String) request.getSession().getAttribute("imagecheckcode");
if(c_checkcode!=null && s_checkcode!=null && c_checkcode.equals(s_checkcode)) {
System.out.println("处理注册请求！");
}else {
System.out.println("认证码错误！");
}
}

/**
* @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);
}

}