session和cookie的区别

new Cookie(String key,String value);
String getName();//获取cookie的key(名称)
String getValue();//获取cookie的值
void setMaxAge(int);//设置cookie在浏览器存活时间，单位：秒
//如果设置成0：表示删除高cookie(前提：路径必须一致)
void setPath(String path);//设置cookie的路径
//当我们访问的路径中包含次cookie的path,才会携带cookie
//默认访问路径：访问Servlet的路径，从"/项目名称"开始，到最后一个"/"结束。比如：/demo/a/b，默认路径为/demo/a
//手动设置路径：以"/项目名称"开始，以"/"结尾

response.addCookie(Cookie);

Cookie[] request.getCookies();

/**
 * 根据 cookie名称获取Cookie 的工具类
 */
public class CookieUtils {
    public static Cookie getCookieByName(String name,Cookie[] cookies){
        if(cookies != null){
            for(Cookie cookie : cookies){
                if(name.equals(cookie.getName())){
                    return cookie;
                }
            }
        }
        return null;
    }
}
public class RecordServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1.设置编码
        response.setContentType("text/html;charset=utf-8");
        PrintWriter w = response.getWriter();

        //2.获取指定名称的Cookie
        Cookie cookie = CookieUtils.getCookieByName("record",request.getCookies());

        //3.判断cookie是否为空；
        // 若为null,则说明是第一次访问；
        // 若不为 null,则根据cookie显示上一次的访问时间
        if(cookie == null){
            w.write("这是您第一次访问");
        }else{
            long lastTime= Long.parseLong(cookie.getValue());
            w.write("您上次访问的时间："+ new Date(lastTime).toLocaleString());
        }

        //4.记录当前访问时间，并且该信息存入cookie中
        Cookie c = new Cookie("record",System.currentTimeMillis()+"");
        //设置cookie的有效期是 1 小时
        c.setMaxAge(60*60);
        response.addCookie(c);
    }

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

/**
 * 记录商品浏览记录，只展示3个商品
 */
public class CategoryServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //获取当前访问商品的id
        String id = request.getParameter("id");

        Cookie c = CookieUtils.getCookieByName("ids",request.getCookies());

        //判断该 cookie 是否为空
        String ids="";
        if(c == null){
            //若为空,说明之前没有访问记录
            //将当前商品的id放入ids中
            ids = id;
        }else{
            //若不为空,获取值。也就是之前浏览的商品编号，使用 "-"进行连接
            ids = c.getValue();

            //将 ids 通过"-"进行分割，然后存入list中，方便后续的操作
            String[] categoryIds = ids.split("-");
            LinkedList<String> categories = new LinkedList<>();
            if(categories != null){
                for(String categoryId : categoryIds){
                    categories.add(categoryId);
                }
            }
            //判断之前记录中有无该商品
            if(categories.contains(id)){
                //若有，删除原来的id,将当前的id放入前面
                categories.remove(id);
            }else{
                // 若没有
                // 继续判断长度是否>=3
                // 若>=3,移除最后一个,将当前的id放入最前面
                // 若<3,直接将当前的id放入最前面.
                if(categories.size() >= 3){
                    categories.removeLast();
                }
            }
            //不管如何，id都是最新浏览的，直接加入到前面
            categories.addFirst(id);

            ids="";
            for(String categoryId : categories){
                ids += (categoryId + "-");
            }
            ids = ids.substring(0,ids.length()-1);
        }

        //创建cookie
        c=new  Cookie("ids",ids);
        //设置访问路径
        c.setPath(request.getContextPath()+"/");
        //设置存活时间
        c.setMaxAge(60);

        //写回浏览器
        response.addCookie(c);

        //跳转到指定的商品页面上
        response.sendRedirect(request.getContextPath()+"/category_info"+id+".htm");
    }

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

<ul style="list-style: none;">
    <%
        //获取指定名称的cookie ids
        Cookie c= CookieUtils.getCookieByName("ids", request.getCookies());

        //判断ids是否为空
        if(c==null){
    %>
    <h2>暂无浏览记录</h2>
    <%
    }else{//ids=3-2-1
        String[] arr=c.getValue().split("-");
        for(String id:arr){
    %>
    <li style="width: 150px;height: 216;float: left;margin: 0 8px 0 0;padding: 0 18px 15px;text-align: center;"><img src="category/0<%=(Integer.parseInt(id)-1) %>.jpg" width="130px" height="130px" /></li>
    <%
            }
        }
    %>
</ul>

/**
 * 清空浏览记录
 */
public class ClearServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        Cookie c = new Cookie("ids","");

        //cookie的路径与 CategoryServlet中的cookie中的路径要相同
        c.setPath(request.getContextPath()+"/");
        //直接将cookie设置成无效
        c.setMaxAge(0);
        response.addCookie(c);

        //重定向
        response.sendRedirect(request.getContextPath()+"/category_list.jsp");
    }

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

HttpSession getSession(); //request.getSession()

xxxAttribute  //存放私有数据

public void invalidate()

public class CartServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html;charset=utf-8");
        PrintWriter out=response.getWriter();

        //1.获取商品名称
        String name = request.getParameter("name");

        //2.获取购物车，实际上就是存入session的map
        HashMap<String,Integer> map = (HashMap<String, Integer>) request.getSession().getAttribute("cart");

        Integer num = null;

        //3.判断购物车是否为空
        if(map==null){
            //3.1 购物车为空，说明是第一次将商品放入购物车
            //先创建购物车,
            map = new HashMap<>();
            request.getSession().setAttribute("cart",map);
            num = 1;
        }else{
            //3.2 购物车不为空，判断该商品之前是否已经加入购物车
            num = map.get(name);
            if(num == null){
                //num==null,说明该商品之前未加入购物车
                num = 1;
            }else{
                num ++ ;
            }
        }
        map.put(name,num);

        //4.提示信息
        out.print("<center>已经将<b>"+name+"</b>添加到购物车中<hr></center>");
        out.print("<center><a href=‘"+request.getContextPath()+"/category_list.jsp‘>继续购物</a></center><br/>");
        out.print("<center><a href=‘"+request.getContextPath()+"/cart.jsp‘>查看购物车</a><center>");
    }

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

<body>
    <div class="container">
        <a href="${pageContext.request.contextPath}/category_list.jsp">继续购物</a>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
        <a href="${pageContext.request.contextPath}/clearCart">清空购物车</a>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
        <div class="row">
            <div style="margin:0 auto; margin-top:10px;width:950px;">
                <strong style="font-size:16px;margin:5px 0;">订单详情</strong>
                <table class="table table-bordered">
                    <tbody>
                    <tr class="warning" align="center">
                        <th>商品</th>
                        <th>数量</th>
                    </tr>
                    <%
                        HashMap<String,Integer> map = (HashMap<String,Integer>)request.getSession().getAttribute("cart");
                        if(map==null){
                            out.print("<tr><th colspan=‘2‘>亲,购物车空空,先去逛逛~~</th></tr>");
                        }else{
                            for(String name : map.keySet()){
                                out.print("<tr class=‘active‘>");

                                out.print("<td width=‘30%‘>");
                                out.print(name);
                                out.print("</td>");
                                out.print("<td width=‘20%‘>");
                                out.print(map.get(name));
                                out.print("</td>");

                                out.print("</tr>");
                            }
                        }
                    %>
                    </tbody>
                </table>
            </div>
        </div>
    </div>
</body>

public class ClearCartServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.getSession().invalidate();

        response.sendRedirect(request.getContextPath()+"/cart.jsp");
    }

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

Cookie c =new Cookie("name","value"); //创建Cookie 
c.setMaxAge(60*60*24); //设置最大时效，此处设置的最大时效为一天
response.addCookie(c); //把Cookie放入到HTTP响应中

String name ="name"; 
Cookie[]cookies =request.getCookies(); 
if(cookies !=null){ 
   for(int i= 0;i<cookies.length;i++){ 
        Cookie cookie =cookies[i]; 
        if(name.equals(cookis.getName())) 
        //something is here. 
        //you can get the value 
        cookie.getValue(); 
   }
}

<input type="hidden" name ="session" value="..."/>