?? sessioncounterlistener.java
字號:
package com.ora.jsp.servlets;
import javax.servlet.*;
import javax.servlet.http.*;
/**
* This class manages a counter for the number of active sessions in
* an application. The counter is made available to the rest of the
* application as a servlet context attribute of type <code>int[]</code>
* with one element.
*
* @author Hans Bergsten, Gefion software <hans@gefionsoftware.com>
* @version 1.0
*/
public class SessionCounterListener implements HttpSessionListener {
private static final String COUNTER_ATTR = "session_counter";
/**
* Increments the counter held in the session scope.
*/
public void sessionCreated(HttpSessionEvent hse) {
int[] counter = getCounter(hse);
counter[0]++;
}
/**
* Decrements the counter held in the session scope.
*/
public void sessionDestroyed(HttpSessionEvent hse) {
int[] counter = getCounter(hse);
counter[0]--;
}
/**
* Returns the counter held in the session scope, or a new
* counter if it doesn't exist.
*/
private int[] getCounter(HttpSessionEvent hse) {
HttpSession session = hse.getSession();
ServletContext context = session.getServletContext();
int[] counter = (int[]) context.getAttribute(COUNTER_ATTR);
if (counter == null) {
counter = new int[1];
context.setAttribute(COUNTER_ATTR, counter);
}
return counter;
}
}
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