cookie&session
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1. 什么是会话
是指浏览器和服务端之间的数据传输（用户登录，购物车等）
会话管理就是管理浏览器和服务端会话过程产生的会话数据
常用的会话技术：
数据保存在浏览器的Cookie技术
数据保存在服务端的Session技术
2. Cookie技术
1. 什么是Cookie
Cookie是客户端技术，程序把每个用户的数据以cookie的形式写给用户各自的浏览器，当用户使用浏览器再去访问服务器中的web资源时，就会带着各自的数据去。这样，web资源处理的就是各自用户自己的数据了
2. Cookie技术核心API
Cookie类：用于存储会话数据，常用方法如下：
- 构造Cookie对象
Cookie(String name,String value)- 设置cookie
void setPath(String uri)：设置cookie的有效访问路径void setMaxAge(int expiry)：设置cookie的有效时间void setValue(String newValue)：设置cookie的值- 发送cookie到浏览器保存
void response.addCookie(Cookie cookie)：发送cookie- 服务器端接收cookie
Cookie[] request.getCookies()：接收cookieDemo:
public class CookieDemo extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // 1.创建Cookie对象 Cookie cookie = new Cookie("name", "value"); // 2.设置Cookie参数 // 2.1设置Cookie的有效路径 cookie.setPath("/hello");// 默认就是web项目的地址 // 2.2设置Cookie的有效时间 cookie.setMaxAge(20);// 此cookie只存活20秒，从最后不调此cookie开始计算 cookie.setMaxAge(-1);// 此cookie保存在浏览器内存中，关闭浏览器则销毁此cookie cookie.setMaxAge(0);// 删除与此cookie同名的cookie // 3.把数据发送到浏览器 response.addCookie(cookie); // 4.服务端接收来自浏览器的cookie // 方法一: // String name=request.getHeader("cookie"); // System.out.println(name); // 方法二: Cookie[] cookies = request.getCookies(); for (Cookie c : cookies) { String name = c.getName(); String value = c.getValue(); System.out.println(name + "=" + value); } } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); }}3. Cookie原理
- 服务器创建Cookie对象，把会话数据存储到Cookie对象中
new Cookie("name","value");- 服务器发送cookie信息到浏览器
response.addCookie(cookie);//其实是隐藏发送了一个set-cookie名称的响应头- 浏览器得到服务器发送的cookie，然后保存在浏览器端
- 浏览器下次访问服务器时，会带着cookie信息
包含在http的请求头里- 服务器接收到浏览器带来的cookie信息
request.getCookies();4.Cookie的细节
- void setPath(String uri)：设置cookie的有效访问路径，有效访问路径指的是Cookie的有效路径保存在哪里，那么浏览器在有效路径下访问服务器时就会带着Cookie信息，否则不带Cookie信息，默认是在当前web项目的路径下
void setMaxAge(int expiry)：设置cookie的有效时间
expiry可以是正整数，负整数和零
正整数：表示Cookie数据保存浏览器的缓存到硬盘中，数值表示保存的时间
负整数：表示Cookie数据保存到浏览器的内存中，浏览器关闭Cookie就丢失了
零：表示删除同名的Cookie数据
- Cookie数据类型只能保存非中文字符串类型的。可以保存多个Cookie，但是浏览器一般只允许存放300个Cookie，每个站点最多存放20个Cookie，每个Cookie的大小限制为4kb
5. Cookie应用：显示用户上次访问的时间
功能实现逻辑：
把时间保存在Cookie中，每次访问从Cookie里面调用
第一次访问：
1. 获取当前时间，显示到浏览器上
2. 创建Cookie对象，时间作为cookie值，名为：lastTime
3. 把cookie发送到浏览器保存
第n次访问：
1. 获取cookie的数据，取出名为lastTime的cookie
2. 得到cookie的值(上次访问时间)
3. 显示上次访问时间到浏览器上
4. 更新名为lastTime的cookie，值设置为当前时间
5. 把更新后的cookie发送给浏览器保存
代码实现：
public class CookieDemo2 extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html;charset=UTF-8"); // 获取当前时间 SimpleDateFormat t = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss"); String curTime = t.format(new Date()); // 取得cookie Cookie[] cookies = request.getCookies(); String lastTime = null; // 第n次访问 if (cookies != null) { for (Cookie cookie : cookies) { if (cookie.getName().equals("lastTime")) { // 有lastTime的cookie,已经是第n次访问 lastTime = cookie.getValue();//上次访问的时间 // 第n次访问 // 1.把上次访问时间显示到浏览器上 response.getWriter().write( "欢迎回来,你上次访问的时间是: " + lastTime + ",当前时间为: "+ curTime); // 2.更新cookie cookie.setValue(curTime); cookie.setMaxAge(1 * 30 * 24 * 60 * 60); // 3.把更新后的cookie发送到浏览器 response.addCookie(cookie); break; } } } // 第一次访问 没有cookie 或有cookie但没有名为lastTime的cookie if (cookies == null || lastTime == null) { // 1.显示当前时间到浏览器上 response.getWriter().write("你是首次访问本网站,当前时间是: " + curTime); // 2.创建Cookie对象 Cookie cookie = new Cookie("lastTime", curTime); cookie.setMaxAge(1 * 30 * 24 * 60 * 60); // 3.把cookie发送到浏览器保存 response.addCookie(cookie); } } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); }}6. Cookie应用：查看用户浏览过的商品
功能实现逻辑：
代码实现：
import java.io.IOException;import java.io.PrintWriter;import java.util.Map.Entry;import javax.servlet.ServletException;import javax.servlet.http.Cookie;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class ListServlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setCharacterEncoding("UTF-8"); response.setContentType("text/html; charset=UTF-8"); PrintWriter out = response.getWriter(); // 显示商品列表 out.write("书籍列表: <br/>"); for (Entry<String, Book> b : Db.getBooks().entrySet()) { out.write("<a href='" + request.getContextPath() + "/servlet/detailServlet?id=" + b.getKey() + "' target='_blank'>" + b.getValue().getName() + "</a><br/>"); } // 显示浏览过的商品 out.write("<br/>浏览过的 : <br/>"); Cookie[] cookies = request.getCookies(); for (int i = 0; cookies != null && i < cookies.length; i++) { if (cookies[i].getName().equals("history")) { String[] ids = cookies[i].getValue().split("\\-"); for (String s : ids) { out.write(Db.getBooks().get(s).getName() + "<br/>"); } } } } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); }}import java.io.IOException;import java.io.PrintWriter;import java.util.Arrays;import java.util.LinkedList;import java.util.Map.Entry;import javax.servlet.ServletException;import javax.servlet.http.Cookie;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class DetailServlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setCharacterEncoding("UTF-8"); response.setContentType("text/html; charset=UTF-8"); PrintWriter out = response.getWriter(); // 显示商品详情 out.write("书籍详情: <br/>"); String id = request.getParameter("id"); for (Entry<String, Book> b : Db.getBooks().entrySet()) { if (id.equals(b.getKey())) { out.write(b.getValue().getId() + "<br/>"); out.write(b.getValue().getName() + "<br/>"); out.write(b.getValue().getPrice() + "<br/>"); out.write(b.getValue().getAuthor() + "<br/>"); } } // 回写cookie，保存最后浏览的商品id String history = buildIds(id, request); Cookie cookie = new Cookie("history", history); cookie.setMaxAge(1 * 30 * 24 * 60 * 60); cookie.setPath("/cookieTest"); response.addCookie(cookie); } private String buildIds(String id, HttpServletRequest request) { String history = null; Cookie[] cookies = request.getCookies(); for (int i = 0; cookies != null && i < cookies.length; i++) { if (cookies[i].getName().equals("history")) { history = cookies[i].getValue(); } } if (history == null) { System.out.println(id); return id; } LinkedList<String> ids = new LinkedList<String>(Arrays.asList(history .split("\\-"))); if (ids.contains(id)) { ids.remove(id); } else { if (ids.size() >= 3) { // 最多显示3条浏览历史 ids.removeLast(); } } ids.addFirst(id); StringBuffer sb = new StringBuffer(); for (int j = 0; j < ids.size(); j++) { if (j != ids.size() - 1) { sb.append(ids.get(j)).append("-"); } else { sb.append(ids.get(j)); } } System.out.println(sb); return sb.toString(); } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); }}public class Book { private String id; private String name; private double price; private String author; public Book(String id, String name, double price, String author) { super(); this.id = id; this.name = name; this.price = price; this.author = author; } 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 double getPrice() { return price; } public void setPrice(double price) { this.price = price; } public String getAuthor() { return author; } public void setAuthor(String author) { this.author = author; }}import java.util.LinkedHashMap;import java.util.Map;class Db { private static Map<String, Book> books = new LinkedHashMap<String, Book>(); static { books.put("1", new Book("1", "红楼梦", 15, "曹雪芹")); books.put("2", new Book("2", "大漠谣", 20, "桐华")); books.put("3", new Book("3", "诛仙", 15, "萧鼎")); books.put("4", new Book("4", "朝花夕拾", 25, "鲁迅")); } public static Map<String, Book> getBooks() { return books; }}3. Session技术
1. 什么是Session
Session是服务器端技术，利用这个技术，服务器在运行时可以为每个用户的浏览器创建一个其独享的HttpSession对象，由于session为用户浏览器独享，所以用户在访问服务器的资源时，可以把各自的数据放在各自的session中，当用户再去访问服务器中的其他web资源时，其他的web资源再从用户的各自session中取出数据为用户服务
2. Session的核心技术
HttpSession类：用于保存会话数据，常用方法如下：
- 创建或得到session对象
HttpSession getSession():直接创建一个Session对象HttpSession getSession():接收布尔值，设置为true时，在没有找到匹配Session编号的对象时新建一个Session对象如果设置为false，则当找不到匹配的Session时，返回null- 设置session对象
void setMaxInactiveInterval(int interval):设置session的有效时间默认30分钟自动回收session对象String getId():得到session编号void invalidate():销毁session对象- 保存会话数据到session对象
void setAttribute(String name,object value):保存数据Object getAttribute(String name):获取数据void removeAttribute(String name):清除数据- 如何避免浏览器的JSESSIONID的cookie随着浏览器关闭而丢失的问题
解决方法是手动发送一个硬盘保护的cookie给浏览器Demo:
public class SessionServletDemo extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // 1.创建Session对象 HttpSession session = request.getSession(); // 2.保存会话数据 session.setAttribute("name", "eric"); // 3.取出会话数据 String name = (String) session.getAttribute("name"); System.out.println(name); // 4.1拿到session的id System.out.println(session.getId()); // 4.2修改session的有效时间 session.setMaxInactiveInterval(20); // 4.3销毁session if (session != null) { session.invalidate(); } // 5.手动发送一个硬盘保存的cookie给浏览器 Cookie c = new Cookie("JSESSION", session.getId()); c.setMaxAge(60 * 60); response.addCookie(c); } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); }}3. Session原理
代码解读：HttpSession session=request.getSession();
伪码分析执行过程
1. 第一次访问创建Session对象，给Session对象分配一个唯一的ID，叫JSESSIONID
new HttpSession();- 把JSESSIONID作为Cookie的值发送给浏览器保存
Cookie cookie = new Cookie("JSESSIONID",sessionID);response.addCookie(cookie);- 第二次访问时，浏览器带着JSESSIONID的cookie访问服务器
- 服务器得到JSESSIONID，在服务器的内存中搜索是否存放对应编号的session对象
- 如果找到对应编号的session对象，直接返回此对象
- 如果找不到对应编号的session对象，创建新的session对象，继续走1的流程
结论：通过JSESSION的cookie值在服务器中找session对象
4. Session应用：用户登录效果
需求：实现用户登录效果，如果登录成功，显示欢迎回来，xxx。如果失败显示登录失败
默认登录页面：
<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>登录页面</title></head><body> <form action="/cookieTest/servlet/loginServlet" method="post"> 用户名:<input type="text" name="userName" /> <br /> 密码:<input type="text" name="userPwd" /> <br /> <input type="submit" value="登录" /> </form></body></html>登录失败页面：
<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>信息提示页面</title></head><body> <font color='red' size='3'>亲，你的用户名或密码输入有误！请重新输入！</font> <br /> <a href="/cookieTest/index.html">返回登录界面</a></body></html>表单提交后的主处理逻辑：
import java.io.IOException;import java.io.PrintWriter;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;public class IndexServlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html;charset=UTF-8"); PrintWriter out = response.getWriter(); String html = ""; HttpSession session = request.getSession(false); if (session == null) { response.sendRedirect(request.getContextPath() + "/index.html"); return; } String userName = (String) session.getAttribute("userName"); if (userName == null) { response.sendRedirect(request.getContextPath() + "/index.html"); return; } html = "<html><body>欢迎回来，" + userName + "，<a href='" + request.getContextPath() + "/servlet/logoutServlet'>安全退出</a></body></html>"; out.write(html); } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); }}登录处理逻辑：
import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;public class LoginServlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { request.setCharacterEncoding("UTF-8"); String userName = request.getParameter("userName"); String userPwd = request.getParameter("userPwd"); if ("eric".equals(userName) && "123456".equals(userPwd)) { HttpSession session = request.getSession(); session.setAttribute("userName", userName); response.sendRedirect(request.getContextPath() + "/servlet/indexServlet"); } else { response.sendRedirect(request.getContextPath() + "/fail.html"); } } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); }}退出处理逻辑：
import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;public class LogoutServlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { HttpSession session = request.getSession(false); if (session != null) { session.removeAttribute("userName"); } response.sendRedirect(request.getContextPath() + "/index.html"); } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); }}5. Session应用：购物车
public class Book { private String id; private String name; private double price; private String author; public Book(String id, String name, double price, String author) { super(); this.id = id; this.name = name; this.price = price; this.author = author; } 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 double getPrice() { return price; } public void setPrice(double price) { this.price = price; } public String getAuthor() { return author; } public void setAuthor(String author) { this.author = author; }}import java.util.LinkedHashMap;import java.util.Map;class Db { private static Map<String, Book> books = new LinkedHashMap<String, Book>(); static { books.put("1", new Book("1", "红楼梦", 15, "曹雪芹")); books.put("2", new Book("2", "大漠谣", 20, "桐华")); books.put("3", new Book("3", "诛仙", 15, "萧鼎")); books.put("4", new Book("4", "朝花夕拾", 25, "鲁迅")); } public static Map<String, Book> getBooks() { return books; } public static Book findBookById(String id){ return books.get(id); }}import java.io.IOException;import java.io.PrintWriter;import java.util.Map;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class ListServlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html;charset=UTF-8"); PrintWriter out = response.getWriter(); out.print("本网站有以下书籍：<br/>"); Map<String, Book> books = Db.getBooks(); for (Map.Entry<String, Book> book : books.entrySet()) { String url = request.getContextPath() + "/servlet/addCart?id=" + book.getKey(); out.print("<a href='" + response.encodeURL(url) + "'>" + book.getValue().getName() + "</a><br/>"); } String url2 = request.getContextPath() + "/servlet/showCart"; out.print("<a href='" + response.encodeURL(url2) + "'>查看购物车</a>"); } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); }}import java.io.IOException;import java.io.PrintWriter;import java.util.ArrayList;import java.util.List;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;public class AddCart extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html;charset=UTF-8"); PrintWriter out = response.getWriter(); String id = request.getParameter("id"); Book book = Db.findBookById(id); HttpSession session = request.getSession(); List<Book> list = (List<Book>) session.getAttribute("cart"); if (list == null) { list = new ArrayList<Book>(); } list.add(book); session.setAttribute("cart", list); out.print("购买成功！"); } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); }}import java.io.IOException;import java.io.PrintWriter;import java.util.List;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;public class ShowCart extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html;charset=UTF-8"); PrintWriter out = response.getWriter(); out.print("购物车有以下书籍：<br/>"); HttpSession session = request.getSession(); List<Book> books = (List<Book>) session.getAttribute("cart"); if (books == null) { out.print("你还什么都没买呢"); response.setHeader("refresh", "2;url=" + request.getContextPath() + "/servlet/listServlet"); return; } for (Book book : books) { out.write(book.getName() + "<br/>"); } } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); }}阅读全文
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