javaee(cookie和session)

系统管理员 2022-06-06 11:42 156阅读 0赞

cookie记录最后浏览时间

@WebServlet(urlPatterns = "/demo1")
    public class demo1 extends HttpServlet {
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            resp.setContentType("text/css; charset=utf-8");
            PrintWriter writer = resp.getWriter();
            //获取客户端最后访问时间
            Cookie[] cookies = req.getCookies();
            for(int i=0;cookies!=null&&i<cookies.length;i++){
                if("last".equals(cookies[i].getName()))
                writer.write("你最后访问的时间是"+new Date().toLocaleString());
            }
            //创建cookie，并把信息写回客户端
           Cookie ck=new Cookie("last",System.currentTimeMillis()+"");
            //写入cookie
            resp.addCookie(ck);
        }
    }

默认情况下cookie存续浏览器内存中，用户退出浏览器就删除，若希望浏览器将cookie存储在磁盘中

则需要maxAge,以秒为单位时间，最大值设0则是命令浏览器删除该cookie。

注意！！！

上下文中的不同地址的cookie是可以访问的，但前提是访问的路径以cookie的path开始的路径，浏览器就带，否则不带。

如果想让上下文都可以访问cookie，则使用cookie.setPath（"/上下文名称"）,来设置为顶层的cookie

ck.setPath("/上下文名称");//低级
            ck.setPath(req.getContextPath());//中级   上下文名称
            ck.setPath("/");//高级    这个和上面等同，当前上下文的名称

保存用户名

js网页 在jsp获得cookie和在获取cookie后checked保持选择状态

<html>
    <head>
        <title>Title</title>
    </head>
    <body>
        <%Cookie[] c=request.getCookies();
        String name="";
        String checked="";
            for(int i=0;c!=null&&i<c.length;i++){
                if(c[i].getName().equals("user")){
                    name=c[i].getValue();
                    checked="checked='checked'";
                }
            }
        %>
        <form action="${pageContext.request.contextPath}/cookie1" method="post">
            姓名：<input name="name" type="text" value="<%=name%>">
            密码：<input name="pwd" type="password">
            记住用户名：<input id="remember" type="checkbox" name="remember" <%=checked%>>
            <input type="submit" value="登录">
        </form>
    </body>
    </html>

servlet 注意：path设置全局路径，获得表单文本控件没有输入为空字符串，而单选按钮和button则为null。

@WebServlet(urlPatterns = "/cookie1")
    public class CookieDemo1 extends HttpServlet {
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            resp.setContentType("text/html;charset=UTF-8");
            PrintWriter writer = resp.getWriter();
            String name = req.getParameter("name");
            String pwd = req.getParameter("pwd");
            String remember = req.getParameter("remember");
            Cookie ck=new Cookie("user",name);
            ck.setPath("/");
            if("tom".equals(name)&&"123".equals(pwd)){
                //表单类型不输入是空字符串，但是复选框和单选按钮不选是null
                if(remember!=null){
                    ck.setMaxAge(Integer.MAX_VALUE);
                }else{
                    ck.setMaxAge(0);
                }
                resp.addCookie(ck);
                writer.write("登录成功！");
            }else{
                writer.write("登录失败");
                //设置两秒跳到重新登录
                resp.setHeader("refresh","2;url="+req.getContextPath()+"/denglu.jsp");
            }
        }
    
        @Override
        protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            doGet(req,resp);
        }
    }

浏览器历史记录

//实体类（书）

public class Book {
        private  String id;
        private String name;
        private String price;
        private String author;
        public Book(String id, String name, String price, String author) {
            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 String getPrice() {
            return price;
        }
        public void setPrice(String price) {
            this.price = price;
        }
        public String getAuthor() {
            return author;
        }
        public void setAuthor(String author) {
            this.author = author;
        }
    }

数据源（采用map存的数据，返回单个Book和整个map）

public class DBUtil {
        private  static Map<String,Book> books=new HashMap<>();
        static {
            books.put("1",new Book("1","java编程思想","20","小明"));
            books.put("2",new Book("2","java深入虚拟机","25","小明"));
            books.put("3",new Book("3","java设计模式","10","小明"));
            books.put("4",new Book("4","java并发","10","小明"));
            books.put("5",new Book("5","python编程","10","小明"));
        }
        //获取所有的书map类型
        public static Map<String,Book> getBooks(){
            return books;
        }
        //获取指定的书 根据id
        public static Book findBook(String id){
            return books.get(id);
        }
    }

主页列出所有书籍（并且查看是否有对应的cookie）

@WebServlet(urlPatterns = "/showBook")
    public class ShowAllBookServlet extends HttpServlet {
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            doPost(req,resp);
        }
        protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            resp.setContentType("text/html;charset=UTF-8");
            Map<String, Book> books = DBUtil.getBooks();
            PrintWriter writer = resp.getWriter();
            writer.write("本网站的有以下的好书：<br/>");
            for (Map.Entry<String,Book> book:books.entrySet()) {
                writer.write("<a href='"+req.getContextPath()+"/findBook?id="+book.getValue().getId()+"' target='_blank'>"+book.getValue().getName()+"</a><br>");
            }
            writer.write("<hr/>你最近浏览过的书有：<br/>");
            Cookie[] ck = req.getCookies();
            for(int i=0;i<ck.length;i++){
                //cookie带historyBookId的是浏览记录的id序列，进行切割获取id队友的Book（队列）
                if("historyBookId".equals(ck[i].getName())){
                    String value=ck[i].getValue();
                    String[] valuess = value.split("-");
                    for (String s:valuess) {
                        Book book = DBUtil.findBook(s);
                        writer.print(""+book.getName());
                    }
                }
            }
        }
    }

点击查看单个书籍，并且添加到cookie中

@WebServlet(urlPatterns = "/findBook")
    public class findBook extends HttpServlet {
        protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            doGet(request, response);
        }
        protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            response.setContentType("text/html;charset=UTF-8");
            //获取get提交id参数
            String id = request.getParameter("id");
            Book book = DBUtil.findBook(id);
            PrintWriter writer = response.getWriter();
            writer.write("书籍名称:" + book.getName() + "<br>");
            writer.write("书籍价格:" + book.getPrice() + "<br>");
            writer.write("书籍作者:" + book.getAuthor() + "<br>");
            //把当前浏览过的书写会回到客户端
            String historyBook = organzeId(id, request);
            Cookie ck = new Cookie("historyBookId", historyBook);
            ck.setPath("/");
            ck.setMaxAge(Integer.MAX_VALUE);
            response.addCookie(ck);
        }
    
        /**
         * 没有cookie                             把当前的id给添加进去
         * 有cookie，但是没有historyBookId       把当前的id给添加进去
         * historyBookId                              2
         */
        private String organzeId(String id, HttpServletRequest request) {
            Cookie[] cookies = request.getCookies();
            if (cookies == null) {
                //如果没有cookies就直接返回当前id
                return id;
            }
            //查找cookies名字是historyBookId的
            Cookie historyBookId = null;
            for (int i = 0; i < cookies.length; i++) {
                if("historyBookId".equals(cookies[i].getName())){
                    historyBookId=cookies[i];
                }
            }
            if(historyBookId==null){
                return id;
            }
            //不管存储几个
            String value = historyBookId.getValue();
            String[] values = value.split("-");
            LinkedList<String> ls = new LinkedList<>(Arrays.asList(values));
    
            //历史记录最多保持3个(队列    先进先出)
            if(ls.size()<3){
                //如果浏览记录里面有重复的id就删除掉。
                if(ls.contains(id)){
                    ls.remove(id);
                }
            }else{
                //超过3个就浏览记录就删除最后一个或者包含的id
                if(ls.contains(id)){
                    ls.remove(id);
                }else{
                    ls.removeLast();
                }
            }
            ls.addFirst(id);//添加到最前面
            StringBuffer sb = new StringBuffer();
            for (int i=0;i<ls.size();i++){
                if(i>0){
                    sb.append("-");
                }
                sb.append(ls.get(i));
            }
            return sb.toString();
        }
    }

HttpSession对象原理

1.获取名称为JSESSIONID的cookie的值

2.没有这样的cookie,创建一个新的session对象，分配唯一的SessionId，并且向客户端写一个名字叫JSESSION=sessionID的cookie

3.有这个样的Cookie,获取cookie的值，从服务器内存中根据ID找那个session对象。

HttpSession对象状态

出生request.getSession();

活着：应用运行时

搁置：内存溢出，服务器重启，会在tomcat目录的work下持久化，等启动服务器后，session就自动的回调进内存（放心大胆的重启服务器，不用担心session的丢失）

持久化：存盘，IO实现serializable

死亡：超时，默认30分钟，setMaxInactiveInterval(int);

Session,invalidate()；强制销毁

在xml中配置<session-config>单位分钟