JavaWeb详细讲述Cookie和Session的概念

Cookie[] cookies = req.getCookies(); //获得cookie
cookie.getName() //获得cookie中的键
cookie.getValue() //获得cookie中的值	
new Cookie("LastLoginTime",System.currentTimeMillis()+"") //新建一个cookie
cookie.setMaxAge(24*60*60); //设置cookie有效期
resp.addCookie(cookie); //响应给客户端一个cookie

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    //解决中文乱码
    req.setCharacterEncoding("utf-8");
    resp.setCharacterEncoding("utf-8");
    resp.setContentType("text/html; charset=utf-8");
    PrintWriter out = resp.getWriter();
    Cookie[] cookies = req.getCookies();
    //判断cookie是否存在
    if(cookies == null){
        out.println("第一次访问网站");
    }else{
        out.write("您上一次访问的时间是：");
        for (Cookie cookie : cookies) {
            if("LastLoginTime".equals(cookie.getName())){
                //获取cookie中的值
                long time = Long.parseLong(cookie.getValue());
                Date date = new Date(time);
                DateFormat dfd = DateFormat.getDateInstance(DateFormat.MEDIUM,Locale.CHINA);
                DateFormat dft = DateFormat.getTimeInstance(DateFormat.MEDIUM, Locale.CHINA);
                out.write(dfd.format(date)+dft.format(date));
            }
        }
    }
    Cookie cookie = new Cookie("LastLoginTime",System.currentTimeMillis()+"");
    //设置cookie有效期为一天
    cookie.setMaxAge(24*60*60);
    resp.addCookie(cookie);
}

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    //解决乱码
    req.setCharacterEncoding("utf-8");
    resp.setCharacterEncoding("utf-8");
    resp.setContentType("text/html; charset=utf-8");
    PrintWriter out = resp.getWriter();
    //得到Session
    HttpSession session = req.getSession();
    //给session中存东西
    session.setAttribute("name",new Person("张三",18));
    //获取session的id
    String id = session.getId();
    //判断session是不是新创建的
    if(session.isNew()){
        out.write("session创建成功，ID:"+id);
    }else{
        out.write("session已经存在，id："+id);
    }
    //Session创建的时候做了什么事
    //        Cookie jsessionid = new Cookie("JSESSIONID", id);
    //        resp.addCookie(jsessionid);
}
//Person类
public class Person {
    private String name;
    private int age;
    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
    public Person() {
    }
    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
}

//得到Session
HttpSession session = req.getSession();
Person name = (Person) session.getAttribute("name");
System.out.println(name);

//得到Session
HttpSession session = req.getSession();
session.removeAttribute("name");
//注销session
session.invalidate();

<!--    设置Session的默认失效时间-->
    <session-config>
<!--        15分钟后session自动失效，以分钟为单位-->
        <session-timeout>15</session-timeout>
    </session-config>