Session and Cookies 2
编程技术 / houtizong 发布于 3年前 83
- The J2EE blueprints say not to bother
- There are no race conditions when multiple different users access the page simultaneously
- On the face of it, it seems practically impossible for the same user to access the session concurrently
- The rise of Ajax makes synchronization mportant
- With Ajax calls, it is actually quite likely that two requests from the same user could arrive concurrently
- Performance tip
- Don’t do “synchronized(this)”!
- Use the session or perhaps the value from the session as the label of the synchronized block
- getAttribute
Extracts a previously stored value from a session object. Returns null if no value is associated with given name.
- setAttribute
Associates a value with a name. Monitor changes: valuesimplement HttpSessionBindingListener.
- removeAttribute
Removes values associated with name. - getAttributeNames
Returns names of all attributes in the session. -
getId
Returns the unique identifier. -
isNew
Determines if session is new to client (not to page) - getCreationTime
Returns time at which session was first created - getLastAccessedTime
Returns time at which session was last sent from client - getMaxInactiveInterval, setMaxInactiveInterval
Gets or sets the amount of time session should go without access before being invalidated
- invalidate
Invalidates current session
转载自：http://www.java-programming.info/tutorial/pdf/csajsp2/08-Session-Tracking.pdf
http://www.java2s.com/Code/Java/Servlets/Usecookietosavesessiondata.htm
Session Tracking
HttpSession session = request.getSession();synchronized(session) {SomeClass value =(SomeClass)session.getAttribute("someID");if (value == null) { value = new SomeClass(...);}doSomethingWith(value);session.setAttribute("someID", value);}
HttpSession Methods:
Use cookie to save session data:
import java.io.IOException;import java.io.PrintWriter;import java.io.UnsupportedEncodingException;import java.net.URLEncoder;import javax.servlet.ServletException;import javax.servlet.http.Cookie;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class ShoppingCartViewerCookie extends HttpServlet { public void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException { res.setContentType("text/html"); PrintWriter out = res.getWriter(); String sessionid = null; Cookie[] cookies = req.getCookies(); if (cookies != null) { for (int i = 0; i < cookies.length; i++) { if (cookies[i].getName().equals("sessionid")) { sessionid = cookies[i].getValue(); break; } } } // If the session ID wasn't sent, generate one. // Then be sure to send it to the client with the response. if (sessionid == null) { sessionid = generateSessionId(); Cookie c = new Cookie("sessionid", sessionid); res.addCookie(c); } out.println("<HEAD><TITLE>Current Shopping Cart Items</TITLE></HEAD>"); out.println("<BODY>"); // Cart items are associated with the session ID String[] items = getItemsFromCart(sessionid); // Print the current cart items. out.println("You currently have the following items in your cart:<BR>"); if (items == null) { out.println("<B>None</B>"); } else { out.println("<UL>"); for (int i = 0; i < items.length; i++) { out.println("<LI>" + items[i]); } out.println("</UL>"); } // Ask if they want to add more items or check out. out.println("<FORM ACTION=\"/servlet/ShoppingCart\" METHOD=POST>"); out.println("Would you like to<BR>"); out.println("<INPUT TYPE=SUBMIT VALUE=\" Add More Items \">"); out.println("<INPUT TYPE=SUBMIT VALUE=\" Check Out \">"); out.println("</FORM>"); // Offer a help page. out.println("For help, click <A HREF=\"/servlet/Help" + "?topic=ShoppingCartViewerCookie\">here</A>"); out.println("</BODY></HTML>"); } private static String generateSessionId() throws UnsupportedEncodingException { String uid = new java.rmi.server.UID().toString(); // guaranteed unique return URLEncoder.encode(uid,"UTF-8"); // encode any special chars } private static String[] getItemsFromCart(String sessionid) { return new String[]{"a","b"}; }}
请勿发布不友善或者负能量的内容。与人为善，比聪明更重要！
技术博客集 - 网站简介：
前后端技术：
后端基于Hyperf2.1框架开发,前端使用Bootstrap可视化布局系统生成
网站主要作用：
1.编程技术分享及讨论交流，内置聊天系统;
2.测试交流框架问题，比如：Hyperf、Laravel、TP、beego;
3.本站数据是基于大数据采集等爬虫技术为基础助力分享知识，如有侵权请发邮件到站长邮箱，站长会尽快处理;
4.站长邮箱：[email protected];
文章归档
文章标签
友情链接
