javaweb-day07-1&2(Servlet - Cookie)
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会话
- 什么是会话?
- 会话可简单理解为:用户开一个浏览器,点击多个超链接,访问服务器多个web资源,然后关闭浏览器,整个过程称之为一个会话。
- 会话过程中要解决的一些问题?
- 每个用户在使用浏览器与服务器进行会话的过程中,不可避免各自会产生一些数据,程序要想办法为每个用户保存这些数据。
- 例如:用户点击超链接通过一个servlet购买了一个商品,程序应该想办法保存用户购买的商品,以便于用户点结帐servlet时,结帐servlet可以得到用户购买的商品为用户结帐。
- 思考:用户购买的商品保存在request或servletContext中行不行?
保存会话数据的两种技术
在多个会话过程中多个web资源之间实现数据共享:
- 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资源处理的就是用户各自的数据了。
- 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一个用户的浏览器创建一个其独享的session对象,由于session为用户浏览器独享,所以用户在访问服务器的web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它web资源时,其它web资源再从用户各自的session中取出数据为用户服务。
Cookie技术
Session技术
Cookie API
- javax.servlet.http.Cookie类用于创建一个Cookie,response接口中也定义了一个addCookie方法,它用于在其响应头中增加一个相应的Set-Cookie头字段。同样,request接口中也定义了一个getCookies方法,它用于获取客户端提交的Cookie。
- Cookie类的方法:
- public Cookie(String name,String value)
- setValue与getValue方法,设置和获取Cookie的值
- setMaxAge与getMaxAge方法,设置Cookie的有效期,默认为整个会话过程,关掉浏览器就销毁。
- setPath与getPath方法 ,设置和获取访问服务器的有效路径,例如:/day06,只会在访问服务器的day06下面的web资源的时候才会带Cookie来。
- setDomain与getDomain方法,设置和获取服务器的有效域名,例如:.sina.com
- getName方法
- 要明白三点:怎么把数据用Cookie进行封装、怎么把Cookie打给浏览器、怎么获取浏览器带过来的Cookie?
- 用Cookie的构造方法进行封装数据到Cookie
- 用Response的addCookie()方法,将Cookie打给浏览器。
- 用Request的getCookies()方法,获取浏览器带过来的所有Cookie。
Cookie应用:显示用户上次访问时间
package cn.mengmei.cookie;import java.io.IOException;import java.util.Date;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 CookieDemo1 extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {//获取浏览器带过来的名为lastDate的CookieCookie[] cookies = request.getCookies();String lastDate = "";if(cookies != null){for(Cookie cook : cookies){if(cook.getName().equals("lastDate")){lastDate = cook.getValue();}}}//将时间打印到浏览器显示response.setContentType("text/html;charset=UTF-8");response.getWriter().write("上次访问时间:"+lastDate);//最新时间值String newTime = new Date(System.currentTimeMillis()).toLocaleString();//将当前时间封装到Cookie,设置有效期为30天。Cookie cookie = new Cookie("lastDate", newTime);cookie.setMaxAge(30*24*3600); //设置为0,可以将该Cookie从硬盘删掉。//没有设置有效path,默认是本Servlet所在目录: /myday07/servlet//必须在本Servlet所在目录 /myday07/servlet 下的Servlet才能够将此Cookie删除。//假如你在这里设置了有效目录,那么在你删的时候也必须设置相同的有效目录才能够删除。//将Cookie打给浏览器response.addCookie(cookie);}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}
浏览器地址栏输入:http://localhost:8080/myday07/servlet/CookieDemo1
第一次访问没有时间值,第二次访问显示第一次访问的时间,浏览器关掉再打开还能显示:
上次访问时间:2015-2-12 23:05:23
Cookie的细节
- 一个Cookie只能标识一种信息,它至少含有一个标识该信息的名称(NAME)和设置值(VALUE)。
- 一个WEB站点可以给一个WEB浏览器发送多个Cookie,一个WEB浏览器也可以存储多个WEB站点提供的Cookie。
- 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。
- 如果创建了一个cookie,并将他发送到浏览器,默认情况下它是一个会话级别的cookie(即存储在浏览器的内存中),用户退出浏览器之后即被删除。若希望浏览器将该cookie存储在磁盘上,则需要使用maxAge,并给出一个以秒为单位的时间。将最大时效设为0则是命令浏览器删除该cookie。
- 注意,删除cookie时,path必须一致,否则不会删除
Cookie应用:显示用户上次浏览过的商品
实现过程:
显示商品列表的首页Servlet:
package cn.mengmei.cookie;import java.io.IOException;import java.io.PrintWriter;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 MainServlet extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.setContentType("text/html;charset=UTF-8");//联合使用以下三个响应消息头,控制浏览器不要缓存。response.setHeader("Expires", "-1"); response.setHeader("Cache-Control", "no-cache"); response.setHeader("Pragma", "no-cache"); PrintWriter out = response.getWriter();out.write("<a href='/myday07/servlet/DetailServlet?id=1'>JSP教程 张孝祥</a><br/>");out.write("<a href='/myday07/servlet/DetailServlet?id=2'>HTML+CSS+JS 雷拓</a><br/>");out.write("<a href='/myday07/servlet/DetailServlet?id=3'>JAVA就业教程 王山海</a><br/>");out.write("<a href='/myday07/servlet/DetailServlet?id=4'>structs框架从入门到精通</a><br/>");out.write("<a href='/myday07/servlet/DetailServlet?id=5'>Windows编程 MFC</a><br/><br/><br/>");out.write("您最近浏览过的历史记录:<br/>");Cookie[] cookies = request.getCookies();if(cookies!=null){for(Cookie cook : cookies){if(cook.getName().equals("bookHistory")){String history = cook.getValue();String[] ids = history.split(","); for (String id : ids) { switch (id) { case "1": out.write("JSP教程 张孝祥<br/>"); break; case "2": out.write("HTML+CSS+JS 雷拓<br/>"); break; case "3": out.write("JAVA就业教程 王山海<br/>"); break; case "4": out.write("structs框架从入门到精通<br/>"); break; case "5": out.write("Windows编程 MFC<br/>"); break; default: break; } }}}}}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}
详细页面:
package cn.mengmei.cookie;import java.io.IOException;import java.io.PrintWriter;import java.util.Arrays;import java.util.LinkedList;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.setContentType("text/html;charset=UTF-8");String id = request.getParameter("id");boolean flag = true;Cookie[] cookies = request.getCookies();if(cookies!=null){for(Cookie cook : cookies){if(cook.getName().equals("bookHistory")){flag = false;String history = cook.getValue();if(!history.contains(id)){StringBuilder sb = new StringBuilder(history);sb.insert(0, id+",");history = sb.toString();System.out.println(history);cook.setValue(history);cook.setMaxAge(30*24*3600);response.addCookie(cook);}else{history = history.replaceAll("["+id+"]", "");StringBuilder sb = new StringBuilder(history);sb.insert(0, id+",");history = sb.toString();history = history.replaceAll("\\W*(\\W{1})", "$1");while(history.startsWith(",")){history = history.substring(1);}while(history.endsWith(",")){history = history.substring(0, history.length()-1);}System.out.println(history);cook.setValue(history);cook.setMaxAge(30*24*3600);response.addCookie(cook);}}}if(flag){Cookie cookie = new Cookie("bookHistory", id);cookie.setMaxAge(30*24*3600);response.addCookie(cookie);}}else{Cookie cookie = new Cookie("bookHistory", id);cookie.setMaxAge(30*24*3600);response.addCookie(cookie);}PrintWriter out = response.getWriter();switch (id) {case "1":out.write("JSP教程 张孝祥---详细信息页面。。。。。。。。。。。");break;case "2":out.write("HTML+CSS+JS 雷拓---详细信息页面。。。。。。。。。。。");break;case "3":out.write("JAVA就业教程 王山海---详细信息页面。。。。。。。。。。。");break;case "4":out.write("structs框架从入门到精通---详细信息页面。。。。。。。。。。。");break;case "5":out.write("Windows编程 MFC---详细信息页面。。。。。。。。。。。");break;default:break;}}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}
浏览器地址栏输入:http://localhost:8080/myday07/servlet/MainServlet
效果:
老师讲的标准代码:
package cn.mengmei.cookie;import java.io.IOException;import java.io.PrintWriter;import java.util.LinkedHashMap;import java.util.Map;import java.util.Set;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 MainServlet extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {//显示商品列表response.setContentType("text/html;charset=UTF-8");response.setHeader("Expires", "-1"); response.setHeader("Cache-Control", "no-cache"); response.setHeader("Pragma", "no-cache"); PrintWriter out = response.getWriter();out.write("首页图书展示:<br/>");Map<String,Book> map = DB.getAll();Set<Map.Entry<String, Book>> set = map.entrySet();for(Map.Entry<String, Book> me : set){Book book = me.getValue();String name = book.getName();String id = book.getId();out.write("<a href='/myday07/servlet/DetailServlet?id="+id+"' target='_black'>"+name+"</a><br/>");}out.write("<br/>");//最近浏览out.write("最近浏览:<br/>");Cookie[] cookies = request.getCookies();String bookHistory = null;for(int i=0; cookies!=null && i<cookies.length; i++){if(cookies[i].getName().equals("bookHistory")){bookHistory = cookies[i].getValue();}}if(bookHistory != null){String[] ids = bookHistory.split("\\_");for(String id :ids){Book book = map.get(id);if(book != null){out.write(book.getName()+"<br/>");}}}}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}class DB{private static Map<String,Book> map = new LinkedHashMap<String,Book>();static{map.put("1", new Book("1","javaweb教程","张孝祥","一本好书!"));map.put("2", new Book("2","structs精通","黎活明","很棒!"));map.put("3", new Book("3","Hibernate教程","方立勋","哈哈好书!"));map.put("4", new Book("4","Spring讲解","刘云山","好书书书!"));}public static Map getAll(){return DB.map;}}class Book{private String id;private String name;private String author;private String descrip;public Book() {super();}public Book(String id, String name, String author, String descrip) {super();this.id = id;this.name = name;this.author = author;this.descrip = descrip;}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 getDescrip() {return descrip;}public void setDescrip(String descrip) {this.descrip = descrip;}}
package cn.mengmei.cookie;import java.io.IOException;import java.io.PrintWriter;import java.util.Arrays;import java.util.LinkedList;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 {//根据id显示商品详细信息response.setContentType("text/html;charset=UTF-8");PrintWriter out = response.getWriter();out.write("商品详细:<br/>");String id = request.getParameter("id");Book book = (Book) DB.getAll().get(id);out.write("id:"+book.getId()+"<br/>");out.write("书名:"+book.getName()+"<br/>");out.write("作者:"+book.getAuthor()+"<br/>");out.write("描述:"+book.getDescrip()+"<br/>");//给浏览器端发送CookieCookie cookie = new Cookie("bookHistory", makeHistory(request,id));cookie.setMaxAge(30*24*3600);response.addCookie(cookie);}private String makeHistory(HttpServletRequest request, String id) {Cookie[] cookies = request.getCookies();String bookHistory = null;for(int i=0; cookies!=null && i<cookies.length; i++){if(cookies[i].getName().equals("bookHistory")){bookHistory = cookies[i].getValue();}}LinkedList<String> link = new LinkedList();if(bookHistory != null){String[] ids = bookHistory.split("\\_");link.addAll(Arrays.asList(ids));if(link.contains(id)){link.remove(id);}link.addFirst(id);while(link.size() > 3){link.removeLast();}}else{link.add(id);}StringBuilder sb = new StringBuilder();for(String i : link){sb.append(i+"_");}sb.deleteCharAt(sb.length()-1);return sb.toString();}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}
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