How to stop Servlet when reloading Application

[John Norris]

I have a servlet will not stop/start when the application is reloaded. The only way to currently get rid of it is to cycle the JVM. Currently each time I attempt to reload the application, I get an additional servlet running. The premise of this servlet is to process a resend queue every 5 minutes. The servlet starts onload, creates a thread that sleeps for 5 minutes then runs the resend logic.
This is old code that I'm maintaining and if there is a better way to activate the resend logic, I'm all ears. Here's the current code:

public class MgBridgeResendHelper extends HttpServlet {
private static final long serialVersionUID = 6047999961405830191L;

private static String MG_BRIDGE_MESSAGE_HANDLER_HOME = "MG_BRIDGE_MESSAGE_HANDLER_HOME";

private static long RESEND_INTERVAL;

private ResendThread thread;

MgBridgeMessageHandlerHome aiMsgHome = null;

public void init() throws ServletException {
super.init();
ResourceBundle resourceBundle = PropertyResourceBundle
.getBundle("MgBridge");
MG_BRIDGE_MESSAGE_HANDLER_HOME = resourceBundle
.getString("MG_BRIDGE_MESSAGE_HANDLER_HOME");
logger = Logger.getLogger(MgBridgeResendHelper.class);
logger
.info("Got the JNDI name MG_BRIDGE_MESSAGE_HANDLER_HOME from Resoucebundle");
String resendInterval = resourceBundle
.getString("MgBridge.cacsSend.resendInterval");
if (resendInterval == null) {
RESEND_INTERVAL = 3000 * 60;
} else {
RESEND_INTERVAL = Long.valueOf(resendInterval).longValue();
}
try {
Context ctx = new InitialContext();
aiMsgHome = (MgBridgeMessageHandlerHome) ctx
.lookup(MG_BRIDGE_MESSAGE_HANDLER_HOME);
thread = new ResendThread();
thread.setDaemon(true);
thread.start();
} catch (NamingException e) {
e.printStackTrace();
}
}

public void destroy() {
thread.interrupt();
super.destroy();
}

private class ResendThread extends Thread {
public void run() {
while (true) {
try {
Thread.sleep(RESEND_INTERVAL);
serviceResends();
} catch (Exception e) {
e.printStackTrace();
}
}
}
}

public void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
doPost(req, resp);
}

public void doPost(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
}

private void serviceResends() {
}
}

[David O'Meara]

The 'resend thread' is not a good idea in the servlet.

Firstly it should be moved into a separate processing class, but it should also have a shutdown hook to stop the thread gracefully but you will also need to have a ContextListener that stops the thread when the context gets reloaded, as this will not cause the shutdown hook to fire.

/Dave

[David O'Meara]

Oh, now i see it isn't even a real servlet, just a class that initialises when the servlet starts up.

Therefore you should stop it being a srevlet, and start and stop it from a ContextListener instead.

[Steve Luke]

Originally posted by David O'Meara:
Oh, now i see it isn't even a real servlet, just a class that initialises when the servlet starts up.

Therefore you should stop it being a srevlet, and start and stop it from a ContextListener instead.

Here is an example:

public class ResendController implements ServletContextListener, Runnable {
 
private String MG_BRIDGE_MESSAGE_HANDLER_HOME;
 
@Override
public void contextDestroyed(ServletContextEvent contextEvent) {
System.out.println("Closing Resender");
ScheduledFuture resendMonitor = (ScheduledFuture)contextEvent.getServletContext().getAttribute("luke.steven.examples.ResendMonitor");
resendMonitor.cancel(true);
}
 
@Override
public void contextInitialized(ServletContextEvent contextEvent) {
ScheduledExecutorService service = Executors.newSingleThreadScheduledExecutor();
ScheduledFuture resendMonitor = service.scheduleAtFixedRate(this, 0, 5, TimeUnit.MINUTES);
contextEvent.getServletContext().setAttribute("luke.steven.examples.ResendMonitor", resendMonitor);
}
 
@Override
public void run() {
//Do the Logic Here
//Don't include the sleep for 5 minutes, the service will handle that
System.out.println("Resending");
}
}

And it is mapped in the web.xml like this:

<listener>
<listener-class>luke.steven.examples.ResendController</listener-class>
</listener>

[John Norris]

Thanks, That's exactly what I was looking for.