Question

I am storing data in application scope. I want to clear this data after every hour. Infact using it as cache for one hour. What is the best way to implement this? Earlier we used session scope to store this data and it used to get expired after session gets expired. As this data is unique across the application we want to store it in application scope.

Answer 1

We found a way to clear application scope variables using ServletContextListener and Timer.

public class SampleListener implements ServletContextListener {

public static final long _startTimerDelayMin = 10; // In minutes
public static final long _startTimerPeriodMin = 60; // In minutes

Timer timer;
ServletContext context =null;       

public void contextInitialized(ServletContextEvent contextEvent) {      
    context = contextEvent.getServletContext();     
    scheduleTimer();        
}   

public void scheduleTimer() {
    long delay = _startTimerDelayMin * 60000;   //initial delay set to _startTimerDelayMin minutes as per msecs
    long period = _startTimerPeriodMin * 60000;   //subsequent rate set to _startTimerPeriodMin minutes as per msecs
    timer = new Timer();
    timer.scheduleAtFixedRate(new RemindTask(), delay, period); 
}

public void contextDestroyed(ServletContextEvent arg0) {
    //Stopping Timer Thread once context destroyed
    timer.cancel();
}

private static String getPropertyValue(String key){
    String value = "";
    try{
        value = Util.getPropertyValueOfKey(key).trim();
    }catch(IOException e){

    }
    return value;
}

/**
 * This class is invoked at given interval to clear the application scope variable for browse call which have not been used for given time
 *
 */
class RemindTask extends TimerTask {

    public void run() {
        clearScopeVariables();
    } 

    /**
     * This function has logic to clear the application scope variable for browse call which have not been used for given time
     */
    public void clearScopeVariables() {
        Date dt = new Date();
        Enumeration<String> applicationScopeVarNames = (Enumeration<String>)context.getAttributeNames();
                    // TODO: clear the scope variables
    }       
}   

Add Listener in web.xml