Cookie

Cookie

利用cookie实现： 记录上次访问时间

response.setCharacterEncoding("utf-8");
        response.setContentType("text/html;charset=utf-8");

        PrintWriter out = response.getWriter();

        out.print("<a href='ServletDemo/cookieDemo2'>删除上次访问时间</a>");

        out.print("您上次的访问时间是:");

        // 获得用户的访问时间cookie
        Cookie cookies[] = request.getCookies();

        for (int i = 0; cookies != null && i < cookies.length; i++) {
            if (cookies[i].getName().equals("lastAccessTime")) {
                long value = Long.parseLong(cookies[i].getValue());
                Date date = new Date(value);
                DateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
                out.write(format.format(date));
            }
        }
        // 给用户回送最新的访问时间

        Cookie cookie = new Cookie("lastAccessTime", System.currentTimeMillis()
                + "");
        cookie.setMaxAge(3600 * 24 * 365);// 设置保存时间是以秒为单位，这里是设置保存大约1年
        cookie.setPath("ServletDemo");
        response.addCookie(cookie);

 

删除Cookie

Cookie cookie = new Cookie("lastAccessTime",System.currentTimeMillis()+"");
        cookie.setPath("ServletDemo");//原先cookie的存储路径一定要一致
        cookie.setMaxAge(0);//设置Cookie存活时间为0，关闭浏览器后，session将会被清楚

response.addCookie(cookie);
response.setCharacterEncoding("utf-8");
response.setContentType("text/html;charset=utf-8");
response.getWriter().write("删除cookie成功<br /><a href='ServletDemo/cookieDemo1'>返回</a>");

 

模拟浏览商品的Servlet

/**
 * 模拟浏览商品
 */
@WebServlet("/cookieDemo3")
public class CookieDemo3 extends HttpServlet {
    private static final long serialVersionUID = 1L;

    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.write("本店有如下商品：<br />");

        // 输出网站所有商品
        Map<String, Book> map = DB.getAll();

        for (Map.Entry<String, Book> entry : map.entrySet()) {
            Book book = entry.getValue();
            out.write("<a href='ServletDemo/cookieDemo4?id=" + book.getId() + "'>"
                    + book.getName() + "</a><br />");
        }
        // 显示用户曾经浏览过的商品
        out.write("<hr />");
        out.write("你曾经浏览过的商品：<br />");
        Cookie cookie[] = request.getCookies();
        for (int i = 0; cookie != null && i < cookie.length; i++) {
            if (cookie[i].getName().equals("bookHistory")
                    && cookie[i].getValue() != null) {
                String ids[] = cookie[i].getValue().split("\\,");
                for (String id : ids) {
                    Book book = map.get(id);
                    out.write("<a href='ServletDemo/cookieDemo4?id=" + book.getId()
                            + "' target='_blank'>" + book.getName()
                            + "</a><br />");
                }
            }
        }

    }

    protected void doPost(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }
}
//模拟数据库信息
class DB {
    private static Map<String, Book> map = new LinkedHashMap();
    static {
        map.put("1", new Book("1", "java", "1,java"));
        map.put("2", new Book("2", "html", "1,html"));
        map.put("3", new Book("3", "css", "1,css"));
        map.put("4", new Book("4", "javascript", "1,javascript"));
        map.put("5", new Book("5", "xml", "1,xml"));
        map.put("6", new Book("6", "jsp", "1,jsp"));
    }

    public static Map getAll() {
        return map;
    }

}

 class Book {
    
    public Book() {
    }

  public Book(String id, String name, String description) {
        super();
        this.id = id;
        this.name = name;
        this.description = description;
    }
　　 private String id;
    private String name;
    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 getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }

}

 

模拟展示商品详细信息的Servlet

 

/*
 * 模拟展示商品详细信息的Servlet
 * */
@WebServlet("/cookieDemo4")
public class CookieDemo4 extends HttpServlet {
    private static final long serialVersionUID = 1L;

    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 id = request.getParameter("id");

        Book book = (Book) DB.getAll().get(id);
        out.write(book.getName() + ":" + book.getDescription());

        out.write("</br><a href='ServletDemo/cookieDemo3'>返回</a>");

        // 构造Cookie 返回给浏览器
        String cookValue = buildCookieValue(id, request);
        Cookie cookie = new Cookie("bookHistory", cookValue);
        cookie.setMaxAge(3600 * 24 * 30);// 设置cookie保存时间为一个月
        cookie.setPath("ServletDemo");
        response.addCookie(cookie);
    }

    // 构造CookieValue
    private String buildCookieValue(String id, HttpServletRequest request) {
        /*
         * 分析Cookie中可能存在的bookHistory
         *          已存在值        将要插入值
　　　　　*　   bookHistory=null        1              情况1
         *    bookHistory=2,3,1       1              情况2
         *    bookHistory=2,4,5       1              情况3
         *    bookHistory=2,3         1              情况4
         */
        String bookHistory = null;
        Cookie cookie[] = request.getCookies();
        for (int i = 0; cookie != null && i < cookie.length; i++) {
            if (cookie[i].getName().equals("bookHistory")) {
                bookHistory = cookie[i].getValue();
                
                if (bookHistory == null) { //情况1
                    return id;
                }
                LinkedList list = new LinkedList(Arrays.asList(bookHistory.split("\\,")));
　　　　　　　　　//简化代码后
                if (list.contains(id)) {  //情况2
                    list.remove(id);
                } else {
                    if (list.size() >= 3) { //情况3
                        list.removeLast();
                    }
                }
　　　　　　　　　//情况4
                list.addFirst(id);
                
                StringBuffer sb = new StringBuffer();

                for (Object ids : list) {
                    sb.append(ids.toString() + ",");
                }

                return sb.deleteCharAt(sb.length() - 1).toString();
                // 简化代码前
                /*
                 *  if (list.contains(id)) { // bookHistory=2,3,1 1
                 *      list.remove(id); 
                 *      list.addFirst(id); 
                 *   } else {
                 *      if (list.size()>= 4) {// bookHistory=2,4,5 1
                 *          list.removeLast();
                 *          list.addFirst(id); 
                 *     } else { // bookHistory= 2,3 1
                 *       list.addFirst(id); 
                 *       }
　　　　　　　　　　*　　}
                 */
            }
        }
        return null;
    }

    protected void doPost(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

}