欢迎您访问程序员文章站本站旨在为大家提供分享程序员计算机编程知识！
您现在的位置是： 首页

Session and Cookies 2

程序员文章站 2022-05-11 22:59:16
...

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);
}

 

  •  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

 

      HttpSession Methods:

  • 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: values 

    implement 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

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"};  
  }
}

 

相关标签： Session Cookies

上一篇： 跨域获取cookie的办法

下一篇： cookies提取

推荐阅读