javaweb-day07-1&2(Servlet - Cookie)
2015-02-13 22:25
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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Cookie Cookie[] 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Cookie Cookie 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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