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Is it possible to implement a background process in a servlet!?
Let me explain.
I have a servlet that shows some data and generate some reports.
The generation of the report implies that the data is already present, and it is this: someone else upload these data.
In addition to report generation, I should implement a way to send an email on arrival of new data (uploaded).
The functional requirement is unclear, but to answer the actual question: yes, it's possible to run a background process in servletcontainer.
If you want an applicationwide background thread, use ServletContextListener to hook on webapp's startup and shutdown and use ExecutorService to run it.
@WebListener
public class Config implements ServletContextListener {
private ExecutorService executor;
public void contextInitialized(ServletContextEvent event) {
executor = Executors.newSingleThreadExecutor();
executor.submit(new Task()); // Task should implement Runnable.
}
public void contextDestroyed(ServletContextEvent event) {
executor.shutdown();
}
}
If you're not on Servlet 3.0 yet and thus can't use @WebListener, register it as follows in web.xml instead:
<listener>
<listener-class>com.example.Config</listener-class>
</listener>
If you want a sessionwide background thread, use HttpSessionBindingListener to start and stop it.
public class Task extends Thread implements HttpSessionBindingListener {
public void run() {
while (true) {
someHeavyStuff();
if (isInterrupted()) return;
}
}
public void valueBound(HttpSessionBindingEvent event) {
start(); // Will instantly be started when doing session.setAttribute("task", new Task());
}
public void valueUnbound(HttpSessionBindingEvent event) {
interrupt(); // Will signal interrupt when session expires.
}
}
On first creation and start, just do
request.getSession().setAttribute("task", new Task());
Thank you! I was wondering whether this should be better done inside of an request scope like:
public class StartServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
request.getSession().setAttribute("task", new Task());
}
}
This way, the process is stopped when the user leaves the page.
