Find number of active sessions created from a given client IP

Question

Is there a way to determine the number of active sessions created from a given client IP address?

Answer 1

The standard Servlet API doesn't offer facilities for that. Best what you can do is to maintain a Map<HttpSession, String> yourself (where the String is the IP address) with and check on every ServletRequest if the HttpSession#isNew() and add it to the Map along with ServletRequest#getRemoteAddr(). Then you can get the amount of IP addresses with an active session using Collections#frequency() on Map#values(). You only need to ensure that you remove the HttpSession from the Map during HttpSessionListener#sessionDestroyed().

This all can be done in a single Listener implementing the ServletContextListener, HttpSessionListener and ServletRequestListener.

Here's a kickoff example:

public class SessionCounter implements ServletContextListener, HttpSessionListener, ServletRequestListener {

    private static final String ATTRIBUTE_NAME = "com.example.SessionCounter";
    private Map<HttpSession, String> sessions = new ConcurrentHashMap<HttpSession, String>();

    @Override
    public void contextInitialized(ServletContextEvent event) {
        event.getServletContext().setAttribute(ATTRIBUTE_NAME, this);
    }

    @Override
    public void requestInitialized(ServletRequestEvent event) {
        HttpServletRequest request = (HttpServletRequest) event.getServletRequest();
        HttpSession session = request.getSession();
        if (session.isNew()) {
            sessions.put(session, request.getRemoteAddr());
        }
    }

    @Override
    public void sessionDestroyed(HttpSessionEvent event) {
        sessions.remove(event.getSession());
    }

    @Override
    public void sessionCreated(HttpSessionEvent event) {
        // NOOP. Useless since we can't obtain IP here.
    }

    @Override
    public void requestDestroyed(ServletRequestEvent event) {
        // NOOP. No logic needed.
    }

    @Override
    public void contextDestroyed(ServletContextEvent event) {
        // NOOP. No logic needed. Maybe some future cleanup?
    }

    public static SessionCounter getInstance(ServletContext context) {
        return (SessionCounter) context.getAttribute(ATTRIBUTE_NAME);
    }

    public int getCount(String remoteAddr) {
        return Collections.frequency(sessions.values(), remoteAddr);
    }

}

Define it in web.xml like follows:

<listener>
    <listener-class>com.example.SessionCounter</listener-class>
</listener>

You can use it in any servlet like follows:

SessionCounter counter = SessionCounter.getInstance(getServletContext());
int count = counter.getCount("127.0.0.1");

Answer 2

Very nice example Balus C. We solved this problem by using an Observer Listener. Here is nice example/tutorial for the same.

http://www.big-oh.net/BigOhSoftwareWeb/content/tutorials/requestObserverListener.jsp

Just thought it will be helpful to other visitors. :)

Edit : *** April 2017 **

Looks like the http://www.big-oh.net/ site that contains the source above is dead. Here is the source from web.archive.org. Also the added the file referred webpage in github gist. Gist source and its html preview

Answer 3

I needed to get this information quickly without new deploys. It can be done by altering JSP and add the following snippet. (Only sessions with activity will get the value set):

<%
 // Set user agent and ip in session
 session.setAttribute("agent", request.getHeader("user-agent") + "@" + request.getRemoteAddr());
%>

Then create a groovy script to query jmx:

import javax.management.remote.*
import javax.management.*
import groovy.jmx.builder.*

// Setup JMX connection.
def connection = new JmxBuilder().client(port: 4934, host: '192.168.10.6')
connection.connect()

// Get the MBeanServer.
def mbeans = connection.MBeanServerConnection

def mbean = new GroovyMBean(mbeans, 'Catalina:type=Manager,host=localhost,context=/')
println "Active sessions: " + mbean['activeSessions']

def sessions = mbean.listSessionIds().tokenize(' ');

def ips = [:];
def agents = [:];

sessions.each
{
    def agentString = mbean.getSessionAttribute(it, "agent");
    if(agentString != null)
    {
        agent = agentString.tokenize('@');
    }
    else
    {   
        agent = ['unknown', 'unknown'];
    }

    if(agents[agent[0]] == null)
    {
        agents[agent[0]] = [];
    }
    agents[agent[0]] += [it];

    if(ips[agent[1]] == null)
    {
        ips[agent[1]] = [];
    }
    ips[agent[1]] += it;


};

println "Ips"
ips = ips.sort { -it.value.size }
ips.each
{
    ip, list ->
    println "${ip}\t${list.value.size}";
    //println list;
    //println "";
}

println ""
println "Agents"
agents = agents.sort { -it.value.size }
agents.each
{
    agent, list ->
    println "${agent}\t${agents[agent].size}";
    //println list;
    //println "";
}

Result

Active sessions: 729
Ips
unknown 102
68.180.230.118  11
80.213.88.107   11
157.55.39.127   9
81.191.247.166  2
...

Agents
Mozilla/5.0 (compatible; MJ12bot/v1.4.5; http://www.majestic12.co.uk/bot.php?+) 117
unknown 102
Mozilla/5.0 (compatible; bingbot/2.0; +http://www.bing.com/bingbot.htm) 55
Mozilla/5.0 (compatible; Yahoo! Slurp; http://help.yahoo.com/help/us/ysearch/slurp) 29
...