JAVAEE HttpSession

HttpSession

昨天博客已经提到了会话有两个技术 第一种是已经解释的cookie 第二种就是今天要谈论的session

session

是一个服务端技术

服务器会为每一个用户创建一个独立的

HttpSession

HttpSession 原理:

1. 当用户第一次访问servlet 服务器端会给该用户创建一个独立的session

2. 并且生成一个sessionID

3. 这个SessID 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

4. 当用户再一次访问servlet的时候 请求中会携带着 cookie中的sessionID 来访问

5. 服务器会根据这个sessionID 来查看是否有对应的sessionID 对象 有就取出使用 否则就创建新的session(相当于用户第一次访问)

因此session 和 之前的 request 和 context 很像 是一个 域对象 他们的范围大小是 Context 域 > Session 域 > request 域

session域特点是 session域 只要会话不结束 就会存在 但是 Session有默认的存活时间 30分钟

创建第一个session

// Demo01.java
public class Demo01 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);
System.out.println(session.getId());

}

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

}
// Demo02.java
public class Demo02 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中的数据
HttpSession session = request.getSession();
String username = (String) session.getAttribute("username");
// 响应到网页
response.getWriter().write(username +" "+ session.getId());
}
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
}

简单购物车问题

ShowAllBooks.java
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");
PrintWriter out = response.getWriter();
HashMap<String,Book> books = Bookutil.getBooks();

Set<String> keySet = books.keySet();
for (String string : keySet) {
Book book = books.get(string);
out.write("<div><a href='"+request.getContextPath()+"/addbook?id="+book.getId()+"'>"+book.getName()+"</a></div>");

}
// 添加查看购物车连接
out.write("<div><a href='" + request.getContextPath() + "/showbook'>查看购物车</a></div>");
// 设置session的有效时间
HttpSession session = request.getSession();
session.setMaxInactiveInterval(10);
}

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

Book.java
public class Book implements Serializable{

/**
* Session
* 钝化 服务器停止 如果你在session中保存了对象 并且该对象实现了序列化接口Serializable
*      系统会把你保存的session 序列化到 服务器的work文件夹 work文件夹下
*
* 活化
*  当你重新启动服务器 系统会重新把钝化下的文件加载回session中
*/
private static final long serialVersionUID = 1L;
private String id;
private String name;

public Book() {
// TODO Auto-generated constructor stub
}

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 "Book [id=" + id + ", name=" + name + "]";
}
}

Bookutil.java
public class Bookutil {
// 声明一个保存书的容器
private static HashMap<String, Book> books = new HashMap<>();
// 添加数据
static {
books.put("1", new Book("1", "葵花宝典"));
books.put("2", new Book("2", "辟邪剑谱"));
books.put("3", new Book("3", "九阴真经"));
books.put("4", new Book("4", "JAVA编程思想"));
}

// 获取集合的方法
public static HashMap<String, Book> getBooks() {

return books;
}
// 按id 查找对应书的方法
public static Book findBookById(String id) {
return books.get(id);
}
}

AddBook.java
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");

String id = request.getParameter("id");
HttpSession session = request.getSession();
// 获取点击的是哪本书
Book books = Bookutil.findBookById(id);
// 创建一个容器
// 把这个容器添加到session中
// 两种情况 1. 书已经添加 2. 书没有添加
ArrayList<Book> book = (ArrayList<Book>) session.getAttribute("id");
if (book == null) {
// 相当于 第一次访问 创建容器
book = new ArrayList<>();
}
// 把书添加到容器中
book.add(books);
// 把容器添加到session中
session.setAttribute("id", book);
// 显示添加成功 1秒后返回商品列表
response.getWriter().write("添加成功 1秒钟后跳转");
response.setHeader("refresh", "1;url=/sh-web-servlet04/showallbooks");
}

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

}

ShowBook.java

public class ShowBook extends HttpServlet {

public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
request.setCharacterEncoding("UTF-8");

HttpSession session = request.getSession();
ArrayList<Book> list = (ArrayList<Book>) session.getAttribute("id");
if (list != null) {
for (Book book : list) {
response.getWriter().write(book.getName() + "<br/>");
}
} else {
response.getWriter().write("暂无商品" + "<br/>");
response.setHeader("refresh", "1;url=/sh-web-servlet04/showallbooks");
}
}

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

}