Using EJBs in thread spawned from Servlet - bad practice? - servlets

Question

We have a servlet as follows:
public class CacheRefresher extends HttpServlet {
private static final long START_TIMEOUT = 120*1000;
public void init(ServletConfig servletConfig) throws ServletException {
super.init(servletConfig);
new Thread(new Worker()).start();
}
private class Worker implements Runnable {
public Worker() { }
public void run() {
try {
Thread.sleep(START_TIMEOUT);
} catch (InterruptedException e) {
}
while(true) {
MyService myService = null;
try {
myService = ServiceFactory.getInstance().getMyService();
myService.doSomething();
} catch (Exception ex){
ex.printStackTrace();
}finally {
ServiceFactory.getInstance().releaseMyService(myService);
}
try {
Thread.sleep(timeout);
} catch (InterruptedException e) {
}
}
}
}
}
Its purpose is to periodically call a service. There will only be a single instance of this Servlet, which will be created on server startup. MyService is an EJB.
How bad is this? I know spawning threads from EJBs is not allowed, but what about the other way around? What will happen on server shutdown?

Answer 1

Conceptualy i dont see a problem with invoking ejb methods from multiple threads (even if you created the threads yourself). For the ejb-container that will be just another client among others.
From your example it looks like the soul purpose of you servlet is to start a bunch of timers. If you can use ejb 3.1, there is java ee standard way to do that.
First a Singleton ejb that launches the timers on startup
import javax.annotation.PostConstruct;
import javax.ejb.EJB;
import javax.ejb.Singleton;
import javax.ejb.Startup;
#Singleton
#Startup
public class SingletonBean {
#EJB
LabBean labBean;
#PostConstruct
public void init() {
long interval = 4000;
long initialExpiration = 2000;
labBean.startTimer(initialExpiration, interval, "MyTimer");
}
}
Then a SLSB that handles the timeout:
import javax.annotation.Resource;
import javax.ejb.Stateless;
import javax.ejb.Timeout;
import javax.ejb.Timer;
import javax.ejb.TimerConfig;
import javax.ejb.TimerService;
#Stateless
public class LabBean {
#Resource
protected TimerService timerService;
#Timeout
public void timeoutHandler(Timer timer) {
String name = timer.getInfo().toString();
System.out.println("Timer name=" + name);
}
public void stopTimer(String name) {
for (Object o : this.timerService.getTimers())
if (((Timer) o).getInfo().toString().startsWith(name)){
((Timer)o).cancel();
}
}
public void startTimer(long initialExpiration, long interval, String name){
stopTimer(name);
TimerConfig config = new TimerConfig();
config.setInfo(name);
config.setPersistent(false);
timerService.createIntervalTimer(initialExpiration, interval, config);
}
}