Spring scheduled tasks: from XML to annotation

Question

In our Spring web-application, we are moving from XML based configuration to Annotation based configuration.

I'm stuck with a scheduled task defined with this XML

<task:scheduled-tasks scheduler="cacheScheduler">
    <task:scheduled ref="currencyExchangeRateTask" method="cacheCurrencyExchangeRates" cron="0 0 8,20 * * *" />
</task:scheduled-tasks>

There are multiple schedulers in our web-application. And this task needs to be executed on the scheduler with id cacheScheduler.

I have now the following annotation in place

@Scheduled(cron = "0 0 8,20 * * *")
public void cacheCurrencyExchangeRates() {
    ...
}

This is executing on the default scheduler.

How can this be fixed without XML configuration?

Answer 1

You can't do it through @Scheduled directly. It doesn't provide any annotation members to specify a bean reference name.

Instead, you have to use SchedulingConfigurer. Define a @Configuration class. Annotate it with @EnableScheduling and @ComponentScan for the packages with component types that have @Scheduled annotated methods. Then have the class implement SchedulingConfigurer.

The ScheduledTaskRegistrar provided through its configureTasks method lets you set a task scheduler.

For example:

@Configuration
@ComponentScan("com.example.tasks")
@EnableScheduling
class Tasks implements SchedulingConfigurer {
    @Bean
    public TaskScheduler cacheScheduler() {
        return new ThreadPoolTaskScheduler();
    }

    @Override
    public void configureTasks(ScheduledTaskRegistrar taskRegistrar) {
        taskRegistrar.setTaskScheduler(cacheScheduler());
    }
}

All the @Scheduled methods discovered through this @Configuration class will now be using the TaskScheduler defined within.

If you need different @Scheduled methods to use different TaskScheduler instances, you'll need different @Configuration classes, similarly to needing different <task:scheduled-tasks .../> elements.