Simplify Spring Event Listeners with @EventListener and Async Configuration

Explanation

This article uses Spring 4.2+ as an example (earlier versions differ slightly). The author has been using Spring events since 2014 and created JFinal-event, which mirrors Spring's usage to simplify listener implementation.

Usage

Creating Event Listener

In Spring 4.2+ you no longer need separate listener classes; simply annotate a Spring bean method with @EventListener.

/**
 * Account listener, handles post‑creation logic
 */
@Component
public class AccountListener {

    /**
     * 1. Send email, SMS
     */
    @EventListener
    public void processAccountCreatedEvent1(AccountCreatedEvent event) {
        // TODO
    }

    /**
     * 2. Add points, etc. Use @Order(100) to set execution order
     */
    @EventListener
    @Order(100)
    public void processAccountCreatedEvent2(AccountCreatedEvent event) {
        // TODO
    }

    /**
     * 3. Create Lucene index, etc. Use @Async for asynchronous execution
     */
    @EventListener
    @Async
    public void processAccountCreatedEvent3(AccountCreatedEvent event) {
        // TODO
    }
}

Sending Event

Example of publishing an account‑creation event in MyBatis. Note: JPA provides its own event mechanism, so manual publishing is unnecessary when using JPA.

@Autowired
private ApplicationEventPublisher publisher;

@Override
public boolean save(Account account) {
    // pseudo‑code, assume DB save succeeds
    if (true) {
        publisher.publishEvent(new AccountCreatedEvent(account));
    }
    return false;
}

@EventListener Annotation Attributes

The value (or classes) attribute specifies one or more event types to listen for, allowing a single method to handle a hierarchy of events. The condition attribute accepts a Spring EL expression for additional filtering, e.g., #event.account.age > 10.

Listener Execution Order

Use @Order(100) to define the order in which listeners are invoked. In asynchronous scenarios, ordering only guarantees the order of task submission to the thread pool; actual execution depends on thread scheduling.

Async Execution

Mark a listener method with @Async to run it asynchronously. Ensure that @EnableAsync is present in the configuration to activate Spring’s async support.

Spring Boot Async Configuration

This section is based on the async configuration from the mica project.

Enable asynchronous processing with @EnableAsync and scheduled tasks with @EnableScheduling. The MicaAsyncProperties class configures the thread pool.

mica.async.core-pool-size: default 2 (core thread count)

mica.async.keep-alive-seconds: default 300 (thread keep‑alive time)

mica.async.max-pool-size: default 50 (maximum thread count)

mica.async.queue-capacity: default 10000 (task queue capacity)

References

[1] https://gitee.com/596392912/JFinal-event [2] mica: https://gitee.com/596392912/mica