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Java Session 会话技术

article 2025/8/25 21:07:09

一、Session简介

Session技术是将数据存储在服务器端的技术，会每个客户端都创建一块内存空间存储客户的数据，但客户端需要都携带一个标识ID去服务器中寻找属于自己的内存空间。所以说Session的实现是基于Cookie，Session需要借助于Cookie存储客户的唯一性标识JSESSIONID

二、Session获取

1、获得Session对象

HttpSession session = request.getSession();

此方法会获得专属于当前会话的Session对象，如果服务器端没有该会话的Session对象会创建一个新的Session返回，如果已经有了属于该会话的Session直接将已有的Session返回（实质就是根据JSESSIONID 判断该客户端是否在服务器上已经存在 Session）

三、Session存取数据&生命周期

1、怎样向session中存取数据（session也是一个域对象），有如下三个方法

session.setAttrbute(String name, Object obj);

session.getAttrbute(String name);

session.removeAttrbute(String name);

2、Session对象的生命周期

创建：第一次执行 request.getSession()时创建
销毁：
服务器（非正常）关闭时
session过期/失效（默认30分钟）

可以在工程的web.xml中进行配置

<session-config>
<session-timeout>30</session-timeout>
</session-config>

四、Session的持久化

由于Session的创建和获取是取决于Cookie中的JSESSIONID决定的，所以如果Cookie被清除了，服务器就无法找到对应的Session了，因此如果想要持久化Session就必须对Cookie中的JSESSIONID进行持久化

五、Java Servlet Session 实例

1、创建Session

@WebServlet(name = "SessionServlet",urlPatterns = "/session")
public class SessionServlet extends HttpServlet {protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {}protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {//第一次访问时没有session，服务器会自动创建一个session对象//之后再次访问的时候已经存在了session对象，这个直接获取这个对象HttpSession session = request.getSession();String sessionId = session.getId();response.getWriter().write("JESSIONID="+sessionId);}
}

2、保存Session

@WebServlet(name = "SaveSessionServlet",urlPatterns = "/saveSession")
public class SaveSessionServlet extends HttpServlet {protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {}protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {HttpSession session = request.getSession();//创建一个cookie覆盖之前服务器自动生成的JSESSIONIDCookie cookie = new Cookie("JSESSIONID", session.getId());//设置持久化时间cookie.setMaxAge(60*60);response.addCookie(cookie);session.setAttribute("goods","cup");}
}

3、获取Session

@WebServlet(name = "GetSessionServlet",urlPatterns = "/getSession")
public class GetSessionServlet extends HttpServlet {protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {}protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {//获取sessionHttpSession session = request.getSession();String goods = (String) session.getAttribute("goods");response.getWriter().write(goods+"");}
}

六、购物车的简单应用

1、添加购物车

@WebServlet(name = "AddCartServlet",urlPatterns = "/addCart")
public class AddCartServlet extends HttpServlet {protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {}protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {//1 获取到商品的信息String name = request.getParameter("name");// 2 需要保存商品信息到sessionHttpSession session = request.getSession();List list = (List) session.getAttribute("list");//第一次访问的时候list不存在，需要创建一个listif (list==null){list=new ArrayList();}list.add(name);session.setAttribute("list",list);// session的持久化操作，也就是持久化JSESSIONIDCookie cookie = new Cookie("JSESSIONID", session.getId());cookie.setMaxAge(60*60*24);cookie.setPath("/hello");response.addCookie(cookie);}
}

2、前端简单展示

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
<center><h1>商品列表</h1><a href="/hello/addCart?name=杯子">杯子</a><br><a href="/hello/addCart?name=书包">书包</a><br><a href="/hello/addCart?name=笔记本">笔记本</a><br></center>
</body>
</html>

3、获取购物车数据

@WebServlet(name = "GetCartServlet",urlPatterns = "/getCart")
public class GetCartServlet extends HttpServlet {protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {}protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {HttpSession session = request.getSession();List<String> list= (List<String>) session.getAttribute("list");response.setContentType("text/html;charset=utf-8");for (String s : list) {response.getWriter().write(s+"<br/>");}}
}

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