Java——Web開發之Session的使用
阿新 • • 發佈：2018-11-27
Session會話：是基於Cookie的一種會話機制，資料存放在伺服器端。
- Session建立：如果有在Servlet裡面呼叫了request.getSession()。
- Session銷燬：session會話時間過期或者關閉伺服器就會被銷燬。設定會話時間過期時間到伺服器的web.xml裡設定，比如說tomcat的設定。
設定會話時間過期時間，這裡用tomcat為例子：在tomcat中，預設為30分鐘
Java裡使用Session時使用到的方法：
- HttpSession session= request.getSession();
- 得到會話ID：String id=session.getId();
- 存資料：session.setAttribute(arg0, arg1);
- 取資料：session.getAttribute(arg0);
- 移除資料：session.removeAttribute(arg0);
- 強制讓會話無效：session.invalidate();
方法使用案例：這個案例是模擬任務個數的開啟，清除所有任務。當點選超連結時，通過使用session的方式將資料臨時儲存到伺服器上，並進行下一次操作。
product_list.jsp
<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%> <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <title>Insert title here</title> </head> <body> <a href="shopServlet?id=0"><h2>aa</h2></a><br> <a href="shopServlet?id=1"><h2>bb</h2></a><br> <a href="shopServlet?id=2"><h2>cc</h2></a><br> <a href="shopServlet?id=3"><h2>dd</h2></a><br> <a href="shopServlet?id=4"><h2>ee</h2></a><br> <a href="shopServlet?id=5"><h2>ff</h2></a><br> </body> </html>
shopServlet.java
package c.session; import java.io.IOException; import java.util.LinkedHashMap; import java.util.Map; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; /** * Servlet implementation class shopServlet */ public class shopServlet extends HttpServlet { protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // TODO Auto-generated method stub response.setContentType("text/html;charset=utf-8"); //1.獲取要新增工作列的id int id=Integer.parseInt(request.getParameter("id")); String[] names={"aa","bb","cc","dd","ee","ff"}; String name=names[id]; //2.獲取工作列存放任務的session Map<String,Integer> aa 3 //把一個map物件存放到session裡面去，並且保證只儲存一次 Map<String, Integer> map=(Map<String, Integer>)request.getSession().getAttribute("shop"); //session裡面沒有存放過任何東西 if(map==null){ map=new LinkedHashMap<String, Integer>(); request.getSession().setAttribute("shop", map); } //3.判斷工作列有沒有該任務 if(map.containsKey(name)){ map.put(name, map.get(name)+1); //在原來的基礎上+1 }else{ map.put(name, 1); //沒有該任務，置為1 } //4.輸出介面(跳轉) response.getWriter().write("<a href='product_list.jsp'><h2>繼續執行</h2></a><br>"); response.getWriter().write("<a href='shop.jsp'><h2>所有任務</h2></a>"); } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // TODO Auto-generated method stub } }
shop.jsp
<%@page import="java.util.Map"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
<h2>您的工作列如下：</h2>
<%
//1.先獲取到map
Map<String,Integer> map=(Map<String,Integer>)session.getAttribute("shop");
//2.遍歷map
if(map!=null){
for(String key: map.keySet()){
int value=map.get(key);
%>
<h3>名稱：<%=key %> 數量：<%=value %></h3><br>
<%
}
}
%>
<a href="clearshopServlet"><h4>清空工作列</h4></a>
</body>
</html>clearshopServlet.java
package c.session;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
/**
* Servlet implementation class clearshopServlet
*/
public class clearshopServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// TODO Auto-generated method stub
HttpSession session=request.getSession();
//強制幹掉會話，裡面存放的任何資料都沒有了 session.invalidate();
//從session中移除某一個數據
session.removeAttribute("shop");
response.sendRedirect("shop.jsp");
}
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// TODO Auto-generated method stub
}
}