session应用及问题

session和cookie的区别

• cookie是把用户的数据写给浏览器，浏览器保存（可以保存多个）；
• session是把用户的数据写到用户独占的session中，服务器端保存（保存重要的信息，避免服务器的资源浪费）；
• session由服务器创建

简单例子

public class SessionDemo01 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        //解决乱码问题
        req.setCharacterEncoding("UTF-8");
        resp.setCharacterEncoding("UTF-8");
        resp.setContentType("text/html;charset=utf-8");
        //获取session
        HttpSession session = req.getSession();
        //给session存值
        session.setAttribute("name", "狂神");
        //获取session的id
        String id = session.getId();
        if (session.isNew()) {
            resp.getWriter().write("session创建成功，id:" + id);
        } else {
            resp.getWriter().write("session已经在服务器中存在了，id:" + id);
        }
        resp.getWriter().flush();
        //session创建的时候做了什么
//        Cookie cookie = new Cookie("JSESSIONID", id);
//        resp.addCookie(cookie);

    }

session存储对象

//创建实体类
public class Person {
    private String name;
    private int age;

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

//向session中存取对象
public class SessionDemo01 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        //解决乱码问题
        req.setCharacterEncoding("UTF-8");
        resp.setCharacterEncoding("UTF-8");
        resp.setContentType("text/html;charset=utf-8");
        //获取session
        HttpSession session = req.getSession();
        //给session存值
        session.setAttribute("person", new Person("zyy", 18));
        //获取session的id
        String id = session.getId();
        if (session.isNew()) {
            resp.getWriter().write("session创建成功，id:" + id);
        } else {
            resp.getWriter().write("session已经在服务器中存在了，id:" + id);
        }
        resp.getWriter().flush();
        //session创建的时候做了什么
//        Cookie cookie = new Cookie("JSESSIONID", id);
//        resp.addCookie(cookie);

    }

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

//跨页面调用session
public class SessionDemo02 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        //解决乱码问题
        req.setCharacterEncoding("UTF-8");
        resp.setCharacterEncoding("UTF-8");
        resp.setContentType("text/html;charset=utf-8");
        //获取session
        HttpSession session = req.getSession();
        //给session存值
        Person person = (Person) session.getAttribute("person");
        System.out.println(person.getName());

    }

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

//销毁session
public class SessionDemo03 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        //解决乱码问题
        req.setCharacterEncoding("UTF-8");
        resp.setCharacterEncoding("UTF-8");
        resp.setContentType("text/html;charset=utf-8");
        //获取session
        HttpSession session = req.getSession();
        //手动注销session
        session.invalidate();
    }

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