Do I really need to start from a main to run a Schedule in java?

Question

I am developing a web application, and now I have reached a point where I will have a process running in parallel in my application(in background) every day at a time x. To test the process, I made a class within the project with a main, and I ran it separately, Everything worked out as I expected.

But when I went to try to keep the code running normally, deleting the main and leaving only one class, I had the following error "Syntax Error, Constructorheadername Expected Instead."

Schedula the process.

package backgroundProcesses;

import java.sql.*;
import java.util.Calendar;
import java.util.Timer;
import java.util.TimerTask;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

import com.microsoft.sqlserver.jdbc.*;

public class ScheduleBases {

    public static void main(String[] args) {

        Calendar today = Calendar.getInstance();
        today.set(Calendar.HOUR_OF_DAY, 17);
        today.set(Calendar.MINUTE, 24);
        today.set(Calendar.SECOND, 0);


          // creating timer task, timer
        Timer timer = new Timer();
        tarefaDiaria td = new tarefaDiaria();

          // scheduling the task at fixed rate delay
          timer.scheduleAtFixedRate(td,today.getTime(), TimeUnit.MILLISECONDS.convert(1, TimeUnit.DAYS));      
       }
}

Action that will run at the specified time

package backgroundProcesses;

import java.util.TimerTask;

public class tarefaDiaria extends TimerTask  {

    @Override
    public void run() {
        System.out.println("OPA FUNCINOU!");

    }

}

Moral of the story, I need that when I "turn on" my server and run my web application, this process is activated, and run at the time I specified... I tried to rotate leaving the main, but it does not rotate on time, and when taking the main got the error.

---

(Edit: I’m running on a common Tomcat)

Answer 1

The most standard way to do this is to use timers of Javaee.

In your example, you could do so:

@Singleton
public class ScheduleBases {

@Schedule(hour="02/24", minute="30")
public void scheduledTask() {

    System.out.println("OPA FUNCINOU!");
}

Thus the "scheduledTask" method would run at 02:30 am, and after that, every 24 hours again.

Answer 2

I arrived at the solution using a webListener:

@WebListener
public class ScheduleBases implements ServletContextListener {


    @Override
    public void contextInitialized(ServletContextEvent arg0) {
        System.out.println("entrei no schedule valendo!");
        Calendar today = Calendar.getInstance();
        today.set(Calendar.HOUR_OF_DAY, 14);
        today.set(Calendar.MINUTE, 31);
        today.set(Calendar.SECOND, 0);

        // creating timer task, timer
        Timer timer = new Timer();
        tarefaDiaria td = new tarefaDiaria();

        // scheduling the task at fixed rate delay
        timer.scheduleAtFixedRate(td,today.getTime(), TimeUnit.MILLISECONDS.convert(1, TimeUnit.DAYS));
    }



    @Override
    public void contextDestroyed(ServletContextEvent arg0) {




    }        

}

my thread started at 14:31 exactly.