Scheduling: execute tasks only one time in spring boot

Question

Im trying to manage scheduled tasks using spring boot. I want to execute my job only one time at a particular date ( specified by the user ). User can add dates for execution as much as he wants.Here is my Job :

@Component
public class JobScheduler{

    @Autowired
    ServiceLayer service;

    @PostConstruct
    public void executeJob(){
        try {
            service.execute();
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }
}

And here is the execute method :

private TaskScheduler scheduler;

Runnable exampleRunnable = new Runnable(){
    @Override
    public void run() {
        System.out.println("do something ...");
    }
};

@Override
    @Async
    public void execute() throws Exception {
        try {

            List<Date> myListOfDates = getExecutionTime();  // call dao to get dates insered by the user

            ScheduledExecutorService localExecutor = Executors.newSingleThreadScheduledExecutor();
            scheduler = new ConcurrentTaskScheduler(localExecutor);
            for(Date d : myListOfDates ){
            scheduler.schedule(exampleRunnable, d);
            }

        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }

Issue 1 : Im using PostConstruct annotation. Thus, when executeJob method is called, there is no dates in the List 'myListOfDates'.

Issue 2 : Supposing that myListOfDates contains dates, how can i get the latest dates in case user entered another one?

Issue 3 : If i use @Scheduled(initailDelay=10000, fixedRate=20000) instead of @PostConstruct annotation, it will resolve the first issue, but it will execute my job every 20s for instance.

Any clue ?

Answer 1

From what I can infer from your question is, you are asking how to make jobs triggered based on some list of date when spring started.

First , instead of using @PostConstruct in a bean/component, I think it's better to hook it into application level event listener instead. See http://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/context/event/ContextRefreshedEvent.html

That way,you can make sure you all beans initialized, hence you can load myListOfDates , and then start the scheduler.

Second , like what I said in my comment, I would suggest you to uses existing 3rd-party library instead. I only ever uses Quartz in java, so I will ilustrate using Quartz.

Third , I guess you are storing myListOfDates in some kind of database (not memory), hence the ability of user to modify the scheduled dates. If you follow my suggestion in using 3rd-party library, Quartz have JobStore using JDBC See http://www.quartz-scheduler.org/documentation/quartz-2.x/tutorials/tutorial-lesson-09.html#TutorialLesson9-JDBCJobStore

Honestly I never uses that one, but I believe the library have mechanism to trigger the job based on what saved in the database. This might be what you are looking for.