Task Execution and Scheduling

The Spring Framework provides abstractions for the asynchronous execution and scheduling of tasks with the TaskExecutor and TaskScheduler interfaces, respectively. Spring also features implementations of those interfaces that support thread pools or delegation to CommonJ within an application server environment. Ultimately, the use of these implementations behind the common interfaces abstracts away the differences between Java SE and Jakarta EE environments.

Spring also features integration classes to support scheduling with the Quartz Scheduler.

The Spring `TaskExecutor` Abstraction

Executors are the JDK name for the concept of thread pools. The “executor” naming is due to the fact that there is no guarantee that the underlying implementation is actually a pool. An executor may be single-threaded or even synchronous. Spring’s abstraction hides implementation details between the Java SE and Jakarta EE environments.

Spring’s TaskExecutor interface is identical to the java.util.concurrent.Executor interface. In fact, originally, its primary reason for existence was to abstract away the need for Java 5 when using thread pools. The interface has a single method (execute(Runnable task)) that accepts a task for execution based on the semantics and configuration of the thread pool.

The TaskExecutor was originally created to give other Spring components an abstraction for thread pooling where needed. Components such as the ApplicationEventMulticaster, JMS’s AbstractMessageListenerContainer, and Quartz integration all use the TaskExecutor abstraction to pool threads. However, if your beans need thread pooling behavior, you can also use this abstraction for your own needs.

`TaskExecutor` Types

Spring includes a number of pre-built implementations of TaskExecutor. In all likelihood, you should never need to implement your own. The variants that Spring provides are as follows:

SyncTaskExecutor: This implementation does not run invocations asynchronously. Instead, each invocation takes place in the calling thread. It is primarily used in situations where multi-threading is not necessary, such as in simple test cases.
SimpleAsyncTaskExecutor: This implementation does not reuse any threads. Rather, it starts up a new thread for each invocation. However, it does support a concurrency limit that blocks any invocations that are over the limit until a slot has been freed up. If you are looking for true pooling, see ThreadPoolTaskExecutor, later in this list.
ConcurrentTaskExecutor: This implementation is an adapter for a java.util.concurrent.Executor instance. There is an alternative (ThreadPoolTaskExecutor) that exposes the Executor configuration parameters as bean properties. There is rarely a need to use ConcurrentTaskExecutor directly. However, if the ThreadPoolTaskExecutor is not flexible enough for your needs, ConcurrentTaskExecutor is an alternative.
ThreadPoolTaskExecutor: This implementation is most commonly used. It exposes bean properties for configuring a java.util.concurrent.ThreadPoolExecutor and wraps it in a TaskExecutor. If you need to adapt to a different kind of java.util.concurrent.Executor, we recommend that you use a ConcurrentTaskExecutor instead.
DefaultManagedTaskExecutor: This implementation uses a JNDI-obtained ManagedExecutorService in a JSR-236 compatible runtime environment (such as a Jakarta EE application server), replacing a CommonJ WorkManager for that purpose.

As of 6.1, ThreadPoolTaskExecutor provides a pause/resume capability and graceful shutdown through Spring’s lifecycle management. There is also a new "virtualThreads" option on SimpleAsyncTaskExecutor which is aligned with JDK 21’s Virtual Threads, as well as a graceful shutdown capability for SimpleAsyncTaskExecutor as well.

Using a `TaskExecutor`

Spring’s TaskExecutor implementations are commonly used with dependency injection. In the following example, we define a bean that uses the ThreadPoolTaskExecutor to asynchronously print out a set of messages:

import org.springframework.core.task.TaskExecutor;

public class TaskExecutorExample {

	private class MessagePrinterTask implements Runnable {

		private String message;

		public MessagePrinterTask(String message) {
			this.message = message;
		}

		public void run() {
			System.out.println(message);
		}
	}

	private TaskExecutor taskExecutor;

	public TaskExecutorExample(TaskExecutor taskExecutor) {
		this.taskExecutor = taskExecutor;
	}

	public void printMessages() {
		for(int i = 0; i < 25; i++) {
			taskExecutor.execute(new MessagePrinterTask("Message" + i));
		}
	}
}

As you can see, rather than retrieving a thread from the pool and executing it yourself, you add your Runnable to the queue. Then the TaskExecutor uses its internal rules to decide when the task gets run.

To configure the rules that the TaskExecutor uses, we expose simple bean properties:

<bean id="taskExecutor" class="org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor">
	<property name="corePoolSize" value="5"/>
	<property name="maxPoolSize" value="10"/>
	<property name="queueCapacity" value="25"/>
</bean>

<bean id="taskExecutorExample" class="TaskExecutorExample">
	<constructor-arg ref="taskExecutor"/>
</bean>

The Spring `TaskScheduler` Abstraction

In addition to the TaskExecutor abstraction, Spring has a TaskScheduler SPI with a variety of methods for scheduling tasks to run at some point in the future. The following listing shows the TaskScheduler interface definition:

public interface TaskScheduler {

	Clock getClock();

	ScheduledFuture schedule(Runnable task, Trigger trigger);

	ScheduledFuture schedule(Runnable task, Instant startTime);

	ScheduledFuture scheduleAtFixedRate(Runnable task, Instant startTime, Duration period);

	ScheduledFuture scheduleAtFixedRate(Runnable task, Duration period);

	ScheduledFuture scheduleWithFixedDelay(Runnable task, Instant startTime, Duration delay);

	ScheduledFuture scheduleWithFixedDelay(Runnable task, Duration delay);

The simplest method is the one named schedule that takes only a Runnable and an Instant. That causes the task to run once after the specified time. All of the other methods are capable of scheduling tasks to run repeatedly. The fixed-rate and fixed-delay methods are for simple, periodic execution, but the method that accepts a Trigger is much more flexible.

`Trigger` Interface

The Trigger interface is essentially inspired by JSR-236. The basic idea of the Trigger is that execution times may be determined based on past execution outcomes or even arbitrary conditions. If these determinations take into account the outcome of the preceding execution, that information is available within a TriggerContext. The Trigger interface itself is quite simple, as the following listing shows:

public interface Trigger {

	Instant nextExecution(TriggerContext triggerContext);
}

The TriggerContext is the most important part. It encapsulates all of the relevant data and is open for extension in the future, if necessary. The TriggerContext is an interface (a SimpleTriggerContext implementation is used by default). The following listing shows the available methods for Trigger implementations.

public interface TriggerContext {

	Clock getClock();

	Instant lastScheduledExecution();

	Instant lastActualExecution();

	Instant lastCompletion();
}

`Trigger` Implementations

Spring provides two implementations of the Trigger interface. The most interesting one is the CronTrigger. It enables the scheduling of tasks based on cron expressions. For example, the following task is scheduled to run 15 minutes past each hour but only during the 9-to-5 "business hours" on weekdays:

scheduler.schedule(task, new CronTrigger("0 15 9-17 * * MON-FRI"));

The other implementation is a PeriodicTrigger that accepts a fixed period, an optional initial delay value, and a boolean to indicate whether the period should be interpreted as a fixed-rate or a fixed-delay. Since the TaskScheduler interface already defines methods for scheduling tasks at a fixed rate or with a fixed delay, those methods should be used directly whenever possible. The value of the PeriodicTrigger implementation is that you can use it within components that rely on the Trigger abstraction. For example, it may be convenient to allow periodic triggers, cron-based triggers, and even custom trigger implementations to be used interchangeably. Such a component could take advantage of dependency injection so that you can configure such Triggers externally and, therefore, easily modify or extend them.

`TaskScheduler` implementations

As with Spring’s TaskExecutor abstraction, the primary benefit of the TaskScheduler arrangement is that an application’s scheduling needs are decoupled from the deployment environment. This abstraction level is particularly relevant when deploying to an application server environment where threads should not be created directly by the application itself. For such scenarios, Spring provides a DefaultManagedTaskScheduler that delegates to a JSR-236 ManagedScheduledExecutorService in a Jakarta EE environment.

Whenever external thread management is not a requirement, a simpler alternative is a local ScheduledExecutorService setup within the application, which can be adapted through Spring’s ConcurrentTaskScheduler. As a convenience, Spring also provides a ThreadPoolTaskScheduler, which internally delegates to a ScheduledExecutorService to provide common bean-style configuration along the lines of ThreadPoolTaskExecutor. These variants work perfectly fine for locally embedded thread pool setups in lenient application server environments, as well — in particular on Tomcat and Jetty.

As of 6.1, ThreadPoolTaskScheduler provides a pause/resume capability and graceful shutdown through Spring’s lifecycle management. There is also a new option called SimpleAsyncTaskScheduler which is aligned with JDK 21’s Virtual Threads, using a single scheduler thread but firing up a new thread for every scheduled task execution (except for fixed-delay tasks which all operate on a single scheduler thread, so for this virtual-thread-aligned option, fixed rates and cron triggers are recommended).

Annotation Support for Scheduling and Asynchronous Execution

Spring provides annotation support for both task scheduling and asynchronous method execution.

Enable Scheduling Annotations

To enable support for @Scheduled and @Async annotations, you can add @EnableScheduling and @EnableAsync to one of your @Configuration classes, as the following example shows:

@Configuration
@EnableAsync
@EnableScheduling
public class AppConfig {
}

You can pick and choose the relevant annotations for your application. For example, if you need only support for @Scheduled, you can omit @EnableAsync. For more fine-grained control, you can additionally implement the SchedulingConfigurer interface, the AsyncConfigurer interface, or both. See the SchedulingConfigurer and AsyncConfigurer javadoc for full details.

If you prefer XML configuration, you can use the <task:annotation-driven> element, as the following example shows:

<task:annotation-driven executor="myExecutor" scheduler="myScheduler"/>
<task:executor id="myExecutor" pool-size="5"/>
<task:scheduler id="myScheduler" pool-size="10"/>

Note that, with the preceding XML, an executor reference is provided for handling those tasks that correspond to methods with the @Async annotation, and the scheduler reference is provided for managing those methods annotated with @Scheduled.

The default advice mode for processing @Async annotations is proxy which allows for interception of calls through the proxy only. Local calls within the same class cannot get intercepted that way. For a more advanced mode of interception, consider switching to aspectj mode in combination with compile-time or load-time weaving.

The `@Scheduled` annotation

You can add the @Scheduled annotation to a method, along with trigger metadata. For example, the following method is invoked every five seconds (5000 milliseconds) with a fixed delay, meaning that the period is measured from the completion time of each preceding invocation.

@Scheduled(fixedDelay = 5000)
public void doSomething() {
	// something that should run periodically
}

By default, milliseconds will be used as the time unit for fixed delay, fixed rate, and initial delay values. If you would like to use a different time unit such as seconds or minutes, you can configure this via the timeUnit attribute in @Scheduled.

For example, the previous example can also be written as follows.

@Scheduled(fixedDelay = 5, timeUnit = TimeUnit.SECONDS)
public void doSomething() {
	// something that should run periodically
}

If you need a fixed-rate execution, you can use the fixedRate attribute within the annotation. The following method is invoked every five seconds (measured between the successive start times of each invocation):

@Scheduled(fixedRate = 5, timeUnit = TimeUnit.SECONDS)
public void doSomething() {
	// something that should run periodically
}

For fixed-delay and fixed-rate tasks, you can specify an initial delay by indicating the amount of time to wait before the first execution of the method, as the following fixedRate example shows:

@Scheduled(initialDelay = 1000, fixedRate = 5000)
public void doSomething() {
	// something that should run periodically
}

For one-time tasks, you can just specify an initial delay by indicating the amount of time to wait before the intended execution of the method:

@Scheduled(initialDelay = 1000)
public void doSomething() {
	// something that should run only once
}

If simple periodic scheduling is not expressive enough, you can provide a cron expression. The following example runs only on weekdays:

@Scheduled(cron="*/5 * * * * MON-FRI")
public void doSomething() {
	// something that should run on weekdays only
}

You can also use the zone attribute to specify the time zone in which the cron expression is resolved.

Notice that the methods to be scheduled must have void returns and must not accept any arguments. If the method needs to interact with other objects from the application context, those would typically have been provided through dependency injection.

@Scheduled can be used as a repeatable annotation. If several scheduled declarations are found on the same method, each of them will be processed independently, with a separate trigger firing for each of them. As a consequence, such co-located schedules may overlap and execute multiple times in parallel or in immediate succession. Please make sure that your specified cron expressions etc do not accidentally overlap.

As of Spring Framework 4.3, @Scheduled methods are supported on beans of any scope.

Make sure that you are not initializing multiple instances of the same @Scheduled annotation class at runtime, unless you do want to schedule callbacks to each such instance. Related to this, make sure that you do not use @Configurable on bean classes that are annotated with @Scheduled and registered as regular Spring beans with the container. Otherwise, you would get double initialization (once through the container and once through the @Configurable aspect), with the consequence of each @Scheduled method being invoked twice.

The `@Scheduled` annotation on Reactive methods or Kotlin suspending functions

As of Spring Framework 6.1, @Scheduled methods are also supported on several types of reactive methods:

methods with a Publisher return type (or any concrete implementation of Publisher) like in the following example:

@Scheduled(fixedDelay = 500)
public Publisher<Void> reactiveSomething() {
	// return an instance of Publisher
}

methods with a return type that can be adapted to Publisher via the shared instance of the ReactiveAdapterRegistry, provided the type supports deferred subscription like in the following example:

@Scheduled(fixedDelay = 500)
public Single<String> rxjavaNonPublisher() {
	return Single.just("example");
}

The CompletableFuture class is an example of a type that can typically be adapted to Publisher but doesn’t support deferred subscription. Its ReactiveAdapter in the registry denotes that by having the getDescriptor().isDeferred() method return false.

Kotlin suspending functions, like in the following example:

@Scheduled(fixedDelay = 500)
suspend fun something() {
	// do something asynchronous
}

methods that return a Kotlin Flow or Deferred instance, like in the following example:

@Scheduled(fixedDelay = 500)
fun something(): Flow<Void> {
	flow {
		// do something asynchronous
	}
}

All these types of methods must be declared without any arguments. In the case of Kotlin suspending functions, the kotlinx.coroutines.reactor bridge must also be present to allow the framework to invoke a suspending function as a Publisher.

The Spring Framework will obtain a Publisher for the annotated method once and will schedule a Runnable in which it subscribes to said Publisher. These inner regular subscriptions occur according to the corresponding cron/fixedDelay/fixedRate configuration.

If the Publisher emits onNext signal(s), these are ignored and discarded (the same way return values from synchronous @Scheduled methods are ignored).

In the following example, the Flux emits onNext("Hello"), onNext("World") every 5 seconds, but these values are unused:

@Scheduled(initialDelay = 5000, fixedRate = 5000)
public Flux<String> reactiveSomething() {
	return Flux.just("Hello", "World");
}

If the Publisher emits an onError signal, it is logged at WARN level and recovered. Because of the asynchronous and lazy nature of Publisher instances, exceptions are not thrown from the Runnable task: this means that the ErrorHandler contract is not involved for reactive methods.

As a result, further scheduled subscription occurs despite the error.

In the following example, the Mono subscription fails twice in the first five seconds. Then subscriptions start succeeding, printing a message to the standard output every five seconds:

@Scheduled(initialDelay = 0, fixedRate = 5000)
public Mono<Void> reactiveSomething() {
	AtomicInteger countdown = new AtomicInteger(2);

	return Mono.defer(() -> {
		if (countDown.get() == 0 || countDown.decrementAndGet() == 0) {
			return Mono.fromRunnable(() -> System.out.println("Message"));
		}
		return Mono.error(new IllegalStateException("Cannot deliver message"));
	})
}

When destroying the annotated bean or closing the application context, Spring Framework cancels scheduled tasks, which includes the next scheduled subscription to the Publisher as well as any past subscription that is still currently active (e.g. for long-running publishers or even infinite publishers).

The `@Async` annotation

You can provide the @Async annotation on a method so that invocation of that method occurs asynchronously. In other words, the caller returns immediately upon invocation, while the actual execution of the method occurs in a task that has been submitted to a Spring TaskExecutor. In the simplest case, you can apply the annotation to a method that returns void, as the following example shows:

@Async
void doSomething() {
	// this will be run asynchronously
}

Unlike the methods annotated with the @Scheduled annotation, these methods can expect arguments, because they are invoked in the “normal” way by callers at runtime rather than from a scheduled task being managed by the container. For example, the following code is a legitimate application of the @Async annotation:

@Async
void doSomething(String s) {
	// this will be run asynchronously
}

Even methods that return a value can be invoked asynchronously. However, such methods are required to have a Future-typed return value. This still provides the benefit of asynchronous execution so that the caller can perform other tasks prior to calling get() on that Future. The following example shows how to use @Async on a method that returns a value:

@Async
Future<String> returnSomething(int i) {
	// this will be run asynchronously
}

@Async methods may not only declare a regular java.util.concurrent.Future return type but also Spring’s org.springframework.util.concurrent.ListenableFuture or, as of Spring 4.2, JDK 8’s java.util.concurrent.CompletableFuture, for richer interaction with the asynchronous task and for immediate composition with further processing steps.

You can not use @Async in conjunction with lifecycle callbacks such as @PostConstruct. To asynchronously initialize Spring beans, you currently have to use a separate initializing Spring bean that then invokes the @Async annotated method on the target, as the following example shows:

public class SampleBeanImpl implements SampleBean {

	@Async
	void doSomething() {
		// ...
	}

}

public class SampleBeanInitializer {

	private final SampleBean bean;

	public SampleBeanInitializer(SampleBean bean) {
		this.bean = bean;
	}

	@PostConstruct
	public void initialize() {
		bean.doSomething();
	}

}

There is no direct XML equivalent for @Async, since such methods should be designed for asynchronous execution in the first place, not externally re-declared to be asynchronous. However, you can manually set up Spring’s AsyncExecutionInterceptor with Spring AOP, in combination with a custom pointcut.

Executor Qualification with `@Async`

By default, when specifying @Async on a method, the executor that is used is the one configured when enabling async support, i.e. the “annotation-driven” element if you are using XML or your AsyncConfigurer implementation, if any. However, you can use the value attribute of the @Async annotation when you need to indicate that an executor other than the default should be used when executing a given method. The following example shows how to do so:

@Async("otherExecutor")
void doSomething(String s) {
	// this will be run asynchronously by "otherExecutor"
}

In this case, "otherExecutor" can be the name of any Executor bean in the Spring container, or it may be the name of a qualifier associated with any Executor (for example, as specified with the <qualifier> element or Spring’s @Qualifier annotation).

Exception Management with `@Async`

When an @Async method has a Future-typed return value, it is easy to manage an exception that was thrown during the method execution, as this exception is thrown when calling get on the Future result. With a void return type, however, the exception is uncaught and cannot be transmitted. You can provide an AsyncUncaughtExceptionHandler to handle such exceptions. The following example shows how to do so:

public class MyAsyncUncaughtExceptionHandler implements AsyncUncaughtExceptionHandler {

	@Override
	public void handleUncaughtException(Throwable ex, Method method, Object... params) {
		// handle exception
	}
}

By default, the exception is merely logged. You can define a custom AsyncUncaughtExceptionHandler by using AsyncConfigurer or the <task:annotation-driven/> XML element.

The `task` Namespace

As of version 3.0, Spring includes an XML namespace for configuring TaskExecutor and TaskScheduler instances. It also provides a convenient way to configure tasks to be scheduled with a trigger.

The 'scheduler' Element

The following element creates a ThreadPoolTaskScheduler instance with the specified thread pool size:

<task:scheduler id="scheduler" pool-size="10"/>

The value provided for the id attribute is used as the prefix for thread names within the pool. The scheduler element is relatively straightforward. If you do not provide a pool-size attribute, the default thread pool has only a single thread. There are no other configuration options for the scheduler.

The `executor` Element

The following creates a ThreadPoolTaskExecutor instance:

<task:executor id="executor" pool-size="10"/>

As with the scheduler shown in the previous section, the value provided for the id attribute is used as the prefix for thread names within the pool. As far as the pool size is concerned, the executor element supports more configuration options than the scheduler element. For one thing, the thread pool for a ThreadPoolTaskExecutor is itself more configurable. Rather than only a single size, an executor’s thread pool can have different values for the core and the max size. If you provide a single value, the executor has a fixed-size thread pool (the core and max sizes are the same). However, the executor element’s pool-size attribute also accepts a range in the form of min-max. The following example sets a minimum value of 5 and a maximum value of 25:

<task:executor
		id="executorWithPoolSizeRange"
		pool-size="5-25"
		queue-capacity="100"/>

In the preceding configuration, a queue-capacity value has also been provided. The configuration of the thread pool should also be considered in light of the executor’s queue capacity. For the full description of the relationship between pool size and queue capacity, see the documentation for ThreadPoolExecutor. The main idea is that, when a task is submitted, the executor first tries to use a free thread if the number of active threads is currently less than the core size. If the core size has been reached, the task is added to the queue, as long as its capacity has not yet been reached. Only then, if the queue’s capacity has been reached, does the executor create a new thread beyond the core size. If the max size has also been reached, then the executor rejects the task.

By default, the queue is unbounded, but this is rarely the desired configuration, because it can lead to OutOfMemoryErrors if enough tasks are added to that queue while all pool threads are busy. Furthermore, if the queue is unbounded, the max size has no effect at all. Since the executor always tries the queue before creating a new thread beyond the core size, a queue must have a finite capacity for the thread pool to grow beyond the core size (this is why a fixed-size pool is the only sensible case when using an unbounded queue).

Consider the case, as mentioned above, when a task is rejected. By default, when a task is rejected, a thread pool executor throws a TaskRejectedException. However, the rejection policy is actually configurable. The exception is thrown when using the default rejection policy, which is the AbortPolicy implementation. For applications where some tasks can be skipped under heavy load, you can instead configure either DiscardPolicy or DiscardOldestPolicy. Another option that works well for applications that need to throttle the submitted tasks under heavy load is the CallerRunsPolicy. Instead of throwing an exception or discarding tasks, that policy forces the thread that is calling the submit method to run the task itself. The idea is that such a caller is busy while running that task and not able to submit other tasks immediately. Therefore, it provides a simple way to throttle the incoming load while maintaining the limits of the thread pool and queue. Typically, this allows the executor to “catch up” on the tasks it is handling and thereby frees up some capacity on the queue, in the pool, or both. You can choose any of these options from an enumeration of values available for the rejection-policy attribute on the executor element.

The following example shows an executor element with a number of attributes to specify various behaviors:

<task:executor
		id="executorWithCallerRunsPolicy"
		pool-size="5-25"
		queue-capacity="100"
		rejection-policy="CALLER_RUNS"/>

Finally, the keep-alive setting determines the time limit (in seconds) for which threads may remain idle before being stopped. If there are more than the core number of threads currently in the pool, after waiting this amount of time without processing a task, excess threads get stopped. A time value of zero causes excess threads to stop immediately after executing a task without remaining follow-up work in the task queue. The following example sets the keep-alive value to two minutes:

<task:executor
		id="executorWithKeepAlive"
		pool-size="5-25"
		keep-alive="120"/>

The 'scheduled-tasks' Element

The most powerful feature of Spring’s task namespace is the support for configuring tasks to be scheduled within a Spring Application Context. This follows an approach similar to other “method-invokers” in Spring, such as that provided by the JMS namespace for configuring message-driven POJOs. Basically, a ref attribute can point to any Spring-managed object, and the method attribute provides the name of a method to be invoked on that object. The following listing shows a simple example:

<task:scheduled-tasks scheduler="myScheduler">
	<task:scheduled ref="beanA" method="methodA" fixed-delay="5000"/>
</task:scheduled-tasks>

<task:scheduler id="myScheduler" pool-size="10"/>

The scheduler is referenced by the outer element, and each individual task includes the configuration of its trigger metadata. In the preceding example, that metadata defines a periodic trigger with a fixed delay indicating the number of milliseconds to wait after each task execution has completed. Another option is fixed-rate, indicating how often the method should be run regardless of how long any previous execution takes. Additionally, for both fixed-delay and fixed-rate tasks, you can specify an 'initial-delay' parameter, indicating the number of milliseconds to wait before the first execution of the method. For more control, you can instead provide a cron attribute to provide a cron expression. The following example shows these other options:

<task:scheduled-tasks scheduler="myScheduler">
	<task:scheduled ref="beanA" method="methodA" fixed-delay="5000" initial-delay="1000"/>
	<task:scheduled ref="beanB" method="methodB" fixed-rate="5000"/>
	<task:scheduled ref="beanC" method="methodC" cron="*/5 * * * * MON-FRI"/>
</task:scheduled-tasks>

<task:scheduler id="myScheduler" pool-size="10"/>

Cron Expressions

All Spring cron expressions have to conform to the same format, whether you are using them in @Scheduled annotations, task:scheduled-tasks elements, or someplace else. A well-formed cron expression, such as * * * * * *, consists of six space-separated time and date fields, each with its own range of valid values:

 ┌───────────── second (0-59)
 │ ┌───────────── minute (0 - 59)
 │ │ ┌───────────── hour (0 - 23)
 │ │ │ ┌───────────── day of the month (1 - 31)
 │ │ │ │ ┌───────────── month (1 - 12) (or JAN-DEC)
 │ │ │ │ │ ┌───────────── day of the week (0 - 7)
 │ │ │ │ │ │          (0 or 7 is Sunday, or MON-SUN)
 │ │ │ │ │ │
 * * * * * *

There are some rules that apply:

A field may be an asterisk (*), which always stands for “first-last”. For the day-of-the-month or day-of-the-week fields, a question mark (?) may be used instead of an asterisk.
Commas (,) are used to separate items of a list.
Two numbers separated with a hyphen (-) express a range of numbers. The specified range is inclusive.
Following a range (or *) with / specifies the interval of the number’s value through the range.
English names can also be used for the month and day-of-week fields. Use the first three letters of the particular day or month (case does not matter).
The day-of-month and day-of-week fields can contain an L character, which has a different meaning.
- In the day-of-month field, L stands for the last day of the month. If followed by a negative offset (that is, L-n), it means nth-to-last day of the month.
- In the day-of-week field, L stands for the last day of the week. If prefixed by a number or three-letter name (dL or DDDL), it means the last day of week (d or DDD) in the month.
The day-of-month field can be nW, which stands for the nearest weekday to day of the month n. If n falls on Saturday, this yields the Friday before it. If n falls on Sunday, this yields the Monday after, which also happens if n is 1 and falls on a Saturday (that is: 1W stands for the first weekday of the month).
If the day-of-month field is LW, it means the last weekday of the month.
The day-of-week field can be d#n (or DDD#n), which stands for the nth day of week d (or DDD) in the month.

Here are some examples:

Cron Expression Meaning

Cron Expression	Meaning
`0 0 * * * *`	top of every hour of every day
`/10 * * * *`	every ten seconds
`0 0 8-10 * * *`	8, 9 and 10 o’clock of every day
`0 0 6,19 * * *`	6:00 AM and 7:00 PM every day
`0 0/30 8-10 * * *`	8:00, 8:30, 9:00, 9:30, 10:00 and 10:30 every day
`0 0 9-17 * * MON-FRI`	on the hour nine-to-five weekdays
`0 0 0 25 DEC ?`	every Christmas Day at midnight
`0 0 0 L * *`	last day of the month at midnight
`0 0 0 L-3 * *`	third-to-last day of the month at midnight
`0 0 0 * * 5L`	last Friday of the month at midnight
`0 0 0 * * THUL`	last Thursday of the month at midnight
`0 0 0 1W * *`	first weekday of the month at midnight
`0 0 0 LW * *`	last weekday of the month at midnight
`0 0 0 ? * 5#2`	the second Friday in the month at midnight
`0 0 0 ? * MON#1`	the first Monday in the month at midnight

0 0 * * * *

top of every hour of every day

*/10 * * * * *

every ten seconds

0 0 8-10 * * *

8, 9 and 10 o’clock of every day

0 0 6,19 * * *

6:00 AM and 7:00 PM every day

0 0/30 8-10 * * *

8:00, 8:30, 9:00, 9:30, 10:00 and 10:30 every day

0 0 9-17 * * MON-FRI

on the hour nine-to-five weekdays

0 0 0 25 DEC ?

every Christmas Day at midnight

0 0 0 L * *

last day of the month at midnight

0 0 0 L-3 * *

third-to-last day of the month at midnight

0 0 0 * * 5L

last Friday of the month at midnight

0 0 0 * * THUL

last Thursday of the month at midnight

0 0 0 1W * *

first weekday of the month at midnight

0 0 0 LW * *

last weekday of the month at midnight

0 0 0 ? * 5#2

the second Friday in the month at midnight

0 0 0 ? * MON#1

the first Monday in the month at midnight

Macros

Expressions such as 0 0 * * * * are hard for humans to parse and are, therefore, hard to fix in case of bugs. To improve readability, Spring supports the following macros, which represent commonly used sequences. You can use these macros instead of the six-digit value, thus: @Scheduled(cron = "@hourly").

Macro Meaning

Macro	Meaning
`@yearly` (or `@annually`)	once a year (`0 0 0 1 1 *`)
`@monthly`	once a month (`0 0 0 1 * *`)
`@weekly`	once a week (`0 0 0 * * 0`)
`@daily` (or `@midnight`)	once a day (`0 0 0 * * *`), or
`@hourly`	once an hour, (`0 0 * * * *`)

@yearly (or @annually)

once a year (0 0 0 1 1 *)

@monthly

once a month (0 0 0 1 * *)

@weekly

once a week (0 0 0 * * 0)

@daily (or @midnight)

once a day (0 0 0 * * *), or

@hourly

once an hour, (0 0 * * * *)

Using the Quartz Scheduler

Quartz uses Trigger, Job, and JobDetail objects to realize scheduling of all kinds of jobs. For the basic concepts behind Quartz, see the Quartz Web site. For convenience purposes, Spring offers a couple of classes that simplify using Quartz within Spring-based applications.

Using the `JobDetailFactoryBean`

Quartz JobDetail objects contain all the information needed to run a job. Spring provides a JobDetailFactoryBean, which provides bean-style properties for XML configuration purposes. Consider the following example:

<bean name="exampleJob" class="org.springframework.scheduling.quartz.JobDetailFactoryBean">
	<property name="jobClass" value="example.ExampleJob"/>
	<property name="jobDataAsMap">
		<map>
			<entry key="timeout" value="5"/>
		</map>
	</property>
</bean>

The job detail configuration has all the information it needs to run the job (ExampleJob). The timeout is specified in the job data map. The job data map is available through the JobExecutionContext (passed to you at execution time), but the JobDetail also gets its properties from the job data mapped to properties of the job instance. So, in the following example, the ExampleJob contains a bean property named timeout, and the JobDetail has it applied automatically:

package example;

public class ExampleJob extends QuartzJobBean {

	private int timeout;

	/**
	 * Setter called after the ExampleJob is instantiated
	 * with the value from the JobDetailFactoryBean.
	 */
	public void setTimeout(int timeout) {
		this.timeout = timeout;
	}

	protected void executeInternal(JobExecutionContext ctx) throws JobExecutionException {
		// do the actual work
	}
}

All additional properties from the job data map are available to you as well.

By using the name and group properties, you can modify the name and the group of the job, respectively. By default, the name of the job matches the bean name of the JobDetailFactoryBean (exampleJob in the preceding example above).

Using the `MethodInvokingJobDetailFactoryBean`

Often you merely need to invoke a method on a specific object. By using the MethodInvokingJobDetailFactoryBean, you can do exactly this, as the following example shows:

<bean id="jobDetail" class="org.springframework.scheduling.quartz.MethodInvokingJobDetailFactoryBean">
	<property name="targetObject" ref="exampleBusinessObject"/>
	<property name="targetMethod" value="doIt"/>
</bean>

The preceding example results in the doIt method being called on the exampleBusinessObject method, as the following example shows:

public class ExampleBusinessObject {

	// properties and collaborators

	public void doIt() {
		// do the actual work
	}
}

<bean id="exampleBusinessObject" class="examples.ExampleBusinessObject"/>

By using the MethodInvokingJobDetailFactoryBean, you need not create one-line jobs that merely invoke a method. You need only create the actual business object and wire up the detail object.

By default, Quartz Jobs are stateless, resulting in the possibility of jobs interfering with each other. If you specify two triggers for the same JobDetail, it is possible that the second one starts before the first job has finished. If JobDetail classes implement the Stateful interface, this does not happen: the second job does not start before the first one has finished.

To make jobs resulting from the MethodInvokingJobDetailFactoryBean be non-concurrent, set the concurrent flag to false, as the following example shows:

<bean id="jobDetail" class="org.springframework.scheduling.quartz.MethodInvokingJobDetailFactoryBean">
	<property name="targetObject" ref="exampleBusinessObject"/>
	<property name="targetMethod" value="doIt"/>
	<property name="concurrent" value="false"/>
</bean>

By default, jobs will run in a concurrent fashion.

Wiring up Jobs by Using Triggers and `SchedulerFactoryBean`

We have created job details and jobs. We have also reviewed the convenience bean that lets you invoke a method on a specific object. Of course, we still need to schedule the jobs themselves. This is done by using triggers and a SchedulerFactoryBean. Several triggers are available within Quartz, and Spring offers two Quartz FactoryBean implementations with convenient defaults: CronTriggerFactoryBean and SimpleTriggerFactoryBean.

Triggers need to be scheduled. Spring offers a SchedulerFactoryBean that exposes triggers to be set as properties. SchedulerFactoryBean schedules the actual jobs with those triggers.

The following listing uses both a SimpleTriggerFactoryBean and a CronTriggerFactoryBean:

<bean id="simpleTrigger" class="org.springframework.scheduling.quartz.SimpleTriggerFactoryBean">
	<!-- see the example of method invoking job above -->
	<property name="jobDetail" ref="jobDetail"/>
	<!-- 10 seconds -->
	<property name="startDelay" value="10000"/>
	<!-- repeat every 50 seconds -->
	<property name="repeatInterval" value="50000"/>
</bean>

<bean id="cronTrigger" class="org.springframework.scheduling.quartz.CronTriggerFactoryBean">
	<property name="jobDetail" ref="exampleJob"/>
	<!-- run every morning at 6 AM -->
	<property name="cronExpression" value="0 0 6 * * ?"/>
</bean>

The preceding example sets up two triggers, one running every 50 seconds with a starting delay of 10 seconds and one running every morning at 6 AM. To finalize everything, we need to set up the SchedulerFactoryBean, as the following example shows:

<bean class="org.springframework.scheduling.quartz.SchedulerFactoryBean">
	<property name="triggers">
		<list>
			<ref bean="cronTrigger"/>
			<ref bean="simpleTrigger"/>
		</list>
	</property>
</bean>

More properties are available for the SchedulerFactoryBean, such as the calendars used by the job details, properties to customize Quartz with, and a Spring-provided JDBC DataSource. See the SchedulerFactoryBean javadoc for more information.

SchedulerFactoryBean also recognizes a quartz.properties file in the classpath, based on Quartz property keys, as with regular Quartz configuration. Please note that many SchedulerFactoryBean settings interact with common Quartz settings in the properties file; it is therefore not recommended to specify values at both levels. For example, do not set an "org.quartz.jobStore.class" property if you mean to rely on a Spring-provided DataSource, or specify an org.springframework.scheduling.quartz.LocalDataSourceJobStore variant which is a full-fledged replacement for the standard org.quartz.impl.jdbcjobstore.JobStoreTX.

Task Execution and Scheduling

The Spring TaskExecutor Abstraction

TaskExecutor Types

Using a TaskExecutor

The Spring TaskScheduler Abstraction

Trigger Interface

Trigger Implementations

TaskScheduler implementations

Annotation Support for Scheduling and Asynchronous Execution

Enable Scheduling Annotations

The @Scheduled annotation

The @Scheduled annotation on Reactive methods or Kotlin suspending functions

The @Async annotation

Executor Qualification with @Async

Exception Management with @Async

The task Namespace

The 'scheduler' Element

The executor Element

The 'scheduled-tasks' Element

Cron Expressions

Macros

Using the Quartz Scheduler

Using the JobDetailFactoryBean

Using the MethodInvokingJobDetailFactoryBean

Wiring up Jobs by Using Triggers and SchedulerFactoryBean

The Spring `TaskExecutor` Abstraction

`TaskExecutor` Types

Using a `TaskExecutor`

The Spring `TaskScheduler` Abstraction

`Trigger` Interface

`Trigger` Implementations

`TaskScheduler` implementations

The `@Scheduled` annotation

The `@Scheduled` annotation on Reactive methods or Kotlin suspending functions

The `@Async` annotation

Executor Qualification with `@Async`

Exception Management with `@Async`

The `task` Namespace

The `executor` Element

Using the `JobDetailFactoryBean`

Using the `MethodInvokingJobDetailFactoryBean`

Wiring up Jobs by Using Triggers and `SchedulerFactoryBean`