Use Application objects.
Simply described as follows:
Maintain a session object when the user logs in: UserInfo class instance, and the UserInfo class implements the javax.servlet.http.httpsessionBindingListener interface:
Import java.util.map;
Import java.util.hashmap;
Import javax.servlet.http. *;
Import javax.servlet.servletContext;
Public Class UserInfo Implements httpsessionBindingListener {
// User Info
INT userid;
String username;
......
/ **
* Trigger this event when the UserInfo class is bound to session
* For specific information, see Servlet / JSPS specification
* /
Public void valuebound (httpsessionBindingEvent evenet) {
HttpSession session = event.getations ();
ServletContext CTX = session.getServletContext ();
Map Map = (MAP) CTX.getaTribute ("Users");
if (Map == NULL) {// If the first login user after the server is started, create a new container
Map = new hashmap ();
CTX.SetAttribute ("Users", Map);
}
Map.put (username, this); // Add yourself to the container
}
/ **
* Toned this event when the UserInfo class is deleted from the session
* For specific information, see Servlet / JSPS specification
* /
Public void valueunbound (httpsessionBindingEvent evenet) {
HttpSession session = event.getations ();
ServletContext CTX = session.getServletContext ();
Map Map = (MAP) CTX.getaTribute ("Users");
Map.remove (this); // Remove yourself from your container
}
......
}
In the future, you can display the number of online users in JSP:
<%
INT usercount = 0;
Java.util.map Map = (java.util.map) Application.GetaTribute ("Users");
IF (MAP == 0) usercount = 0;
Else Usercount = map.size ();
%>
Of course, you can also do this in the Javax.Servlet.http.httpsessoinbindlisenter interface, and use your own program to implement this feature, but this method is the most insurance, the simplest
