Java 之 HttpSession
HttpSession
/*
* HttpSession 服务端的技术
* 服务器会为每一个用户创建一个独立的 session
*
* HttpSession 原理
* 当用户第一次访问 Servlet 时,服务器端对给该用户创建一个独立的 Session, 并且生成一个 SessionID
* 这个 SessionID 在响应浏览器的时候,会被装进 cookie 中
* 从而被保存到浏览器中
* 当用户再一次访问 Servlet 的时候
* 请求中会携带着 cookie 中的 SessionID 去访问
* 服务器会根据这个 SessionID 去查看是否有对应的 Session 对象
* 有,则直接调用
* 无,则创建一个(相当于用户第一次访问)(看病案例)
*
* 域的范围
* Context 域 > Session 域 > Request 域
* Session 域只要会话不结束就会存在,但是Session 域有默认存活时间-30分钟
*
* 模拟购物功能
* 大概需要几个页面来完成 --- 需要几个 Servlet 类
* 需要3个 Servlet 类
* session 中保存什么数据合适,添加一个保存书的容器
* 书类:id,bookname
* 模拟假数据,逻辑和功能跑通了,再连接数据库
* 模拟假数据的类
* map 集合 HashMap
* 方法:根据 ID 获取对应的书
*/
@SuppressWarnings("serial")
public class Demo extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
request.setCharacterEncoding("UTF-8");
// 获取参数
String username = request.getParameter("username");
// 获取 session 对象
HttpSession session = request.getSession();
// 保存数据
session.setAttribute("username", username);
// 打印 SessionID
System.out.println(session.getId());
}
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
}/*
* 测试获取 session 域中的数据
*/
public class Demo extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
request.setCharacterEncoding("UTF-8");
// 获取 session 域中的数据
HttpSession session = request.getSession();
String username = (String)session.getAttribute("username");
// 响应到网页上
response.getWriter().write(username + " " + session.getId());
}
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
}public class ShowCar extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
request.setCharacterEncoding("UTF-8");
// 获取 session 对象
HttpSession session = request.getSession();
ArrayList car = (ArrayList) session.getAttribute("car");
PrintWriter out = response.getWriter();
if (car != null) {
// 遍历输出
for (Book book : car) {
out.write(book + "
");
}
out.write("会到商品页面");
} else {
out.write("当前无任何商品");
response.setHeader("refresh", "3;url=" + request.getContextPath() + "/showallbooks");
}
}
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
}
/*
* 展示商品列表
*/
public class ShowAllBooks extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
request.setCharacterEncoding("UTF-8");
/*
* 1.获取所有书 2.遍历输出到网页上 3.需要给书名添加一个连接(a 标签) 4.点击书名的时候,能知道点的是那本书
*/
PrintWriter out = response.getWriter();
HashMap books = BookUtil.getBooks();
for (String key : books.keySet()) {
Book book = books.get(key);
out.write("">" + book + "
");
}
// 添加查看购物车连接
out.write("查看购物车");
// 设置 session 有效时间
request.getSession().setMaxInactiveInterval(10);
}
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
}
/*
* 模拟假数据
*/
public class BookUtil {
// 声明一个保存书的容器
private static HashMap books = new HashMap<>();
// 添加数据
static {
books.put("1", new Book("1", "降龙十八掌"));
books.put("2", new Book("2", "打狗棒法"));
books.put("3", new Book("3", "九阴真经"));
books.put("4", new Book("4", "九阳神功"));
}
// 获取集合的方法
public static HashMap getBooks() {
return books;
}
// 按 id 查找对应书的方法
public static Book findBookById(String id) {
return books.get(id);
}
}
/*
* Session
* 钝化
* 服务器停止时
* 如果你的 session 中保存了对象
* 并且该对象实现了序列化接口 Serializable
* 系统会把你保存 session 序列化到服务器的 work 文件夹你的工程下一个文件
* 活化
* 当你重新启动了服务器,系统会重新把钝化的文件进行加载,加载回 session 中
*/
public class Book implements Serializable {
/**
* 序列化 id
*/
private static final long serialVersionUID = 1L;
private String id;
private String name;
public Book() {
super();
}
public Book(String id, String name) {
super();
this.id = id;
this.name = name;
}
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;
}
@Override
public String toString() {
return id + " " + name;
}
}
public class AddBook extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
request.setCharacterEncoding("UTF-8");
// 获取点击是哪本书(获取参数)
String id = request.getParameter("id");
Book book = BookUtil.findBookById(id);
// 创建一个容器(相当于购物车,保存买的书)
// 两种情况:1.已结存过书了;2.没存过
HttpSession session = request.getSession();
ArrayList car = (ArrayList)session.getAttribute("car");
if (car == null) {
// 相当于第一次访问,创建容器
car = new ArrayList<>();
}
// 把书添加到容器中
car.add(book);
// 把容器添加到 session 中
session.setAttribute("car", car);
// 显示添加成功
// 1秒后返回商品列表页
response.setHeader("refresh", "2;url=" + request.getContextPath() + "/showallbooks");
}
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
} http://blog.csdn.net/huzongnan/article/list