UserCounterListener.java

package com.opentravelsoft.webapp.listener;

import java.util.Set;
import java.util.LinkedHashSet;

import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;

import org.springframework.security.authentication.AuthenticationTrustResolver;
import org.springframework.security.authentication.AuthenticationTrustResolverImpl;
import org.springframework.security.core.Authentication;
import org.springframework.security.core.context.SecurityContext;
import org.springframework.security.core.context.SecurityContextHolder;
import org.springframework.security.web.context.HttpSessionContextIntegrationFilter;

import com.opentravelsoft.entity.Member;

/**
 * UserCounterListener class used to count the current number of active users
 * for the applications. Does this by counting how many user objects are stuffed
 * into the session. It also grabs these users and exposes them in the servlet
 * context.
 * 
 */
public class UserCounterListener implements ServletContextListener,
    HttpSessionAttributeListener {
  /**
   * Name of user counter variable
   */
  public static final String COUNT_KEY = "userCounter";
  /**
   * Name of users Set in the ServletContext
   */
  public static final String USERS_KEY = "userNames";
  /**
   * The default event we're looking to trap.
   */
  public static final String EVENT_KEY = HttpSessionContextIntegrationFilter.SPRING_SECURITY_CONTEXT_KEY;
  private transient ServletContext servletContext;
  private int counter;
  private Set<Member> users;

  /**
   * Initialize the context
   * 
   * @param sce the event
   */
  public synchronized void contextInitialized(ServletContextEvent sce) {
    servletContext = sce.getServletContext();
    servletContext.setAttribute((COUNT_KEY), Integer.toString(counter));
  }

  /**
   * Set the servletContext, users and counter to null
   * 
   * @param event The servletContextEvent
   */
  public synchronized void contextDestroyed(ServletContextEvent event) {
    servletContext = null;
    users = null;
    counter = 0;
  }

  synchronized void incrementUserCounter() {
    counter = Integer.parseInt((String) servletContext.getAttribute(COUNT_KEY));
    counter++;
    servletContext.setAttribute(COUNT_KEY, Integer.toString(counter));
  }

  synchronized void decrementUserCounter() {
    int counter = Integer.parseInt((String) servletContext
        .getAttribute(COUNT_KEY));
    counter--;

    if (counter < 0) {
      counter = 0;
    }

    servletContext.setAttribute(COUNT_KEY, Integer.toString(counter));
  }

  @SuppressWarnings("unchecked")
  synchronized void addUsername(Member user) {
    users = (Set<Member>) servletContext.getAttribute(USERS_KEY);

    if (users == null) {
      users = new LinkedHashSet<Member>();
    }

    if (!users.contains(user)) {
      users.add(user);
      servletContext.setAttribute(USERS_KEY, users);
      incrementUserCounter();
    }
  }

  @SuppressWarnings("unchecked")
  synchronized void removeUsername(Member user) {
    users = (Set<Member>) servletContext.getAttribute(USERS_KEY);

    if (users != null) {
      users.remove(user);
    }

    servletContext.setAttribute(USERS_KEY, users);
    decrementUserCounter();
  }

  /**
   * This method is designed to catch when user's login and record their name
   * 
   * @param event the event to process
   * @see javax.servlet.http.HttpSessionAttributeListener#attributeAdded(javax.servlet.http.HttpSessionBindingEvent)
   */
  public void attributeAdded(HttpSessionBindingEvent event) {
    if (event.getName().equals(EVENT_KEY) && !isAnonymous()) {
      SecurityContext securityContext = (SecurityContext) event.getValue();
      if (securityContext.getAuthentication().getPrincipal() instanceof Member) {
        Member user = (Member) securityContext.getAuthentication()
            .getPrincipal();
        addUsername(user);
      }
    }
  }

  private boolean isAnonymous() {
    AuthenticationTrustResolver resolver = new AuthenticationTrustResolverImpl();
    SecurityContext ctx = SecurityContextHolder.getContext();
    if (ctx != null) {
      Authentication auth = ctx.getAuthentication();
      return resolver.isAnonymous(auth);
    }
    return true;
  }

  /**
   * When user's logout, remove their name from the hashMap
   * 
   * @param event the session binding event
   * @see javax.servlet.http.HttpSessionAttributeListener#attributeRemoved(javax.servlet.http.HttpSessionBindingEvent)
   */
  public void attributeRemoved(HttpSessionBindingEvent event) {
    if (event.getName().equals(EVENT_KEY) && !isAnonymous()) {
      SecurityContext securityContext = (SecurityContext) event.getValue();
      Authentication auth = securityContext.getAuthentication();
      if (auth != null && (auth.getPrincipal() instanceof Member)) {
        Member user = (Member) auth.getPrincipal();
        removeUsername(user);
      }
    }
  }

  /**
   * Needed for Acegi Security 1.0, as it adds an anonymous user to the session
   * and then replaces it after authentication.
   * http://forum.springframework.org/showthread.php?p=63593
   * 
   * @param event the session binding event
   * @see javax.servlet.http.HttpSessionAttributeListener#attributeReplaced(javax.servlet.http.HttpSessionBindingEvent)
   */
  public void attributeReplaced(HttpSessionBindingEvent event) {
    if (event.getName().equals(EVENT_KEY) && !isAnonymous()) {
      final SecurityContext securityContext = (SecurityContext) event
          .getValue();
      if (securityContext.getAuthentication() != null
          && securityContext.getAuthentication().getPrincipal() instanceof Member) {
        final Member user = (Member) securityContext.getAuthentication()
            .getPrincipal();
        addUsername(user);
      }
    }
  }
}