In Spring, events let one part of your application publish something that happened, while other parts react to it without being tightly coupled.

Typical use cases:

• Send an email after user registration
• Clear a cache after data changes
• Audit an action
• Trigger async background processing
• React to transaction completion

Spring has built-in support through:

• ApplicationEventPublisher
• @EventListener
• ApplicationEvent
• @TransactionalEventListener

---

1. Define an Event

Modern Spring applications often use a plain Java object as an event. You do not have to extend ApplicationEvent.

public record UserRegisteredEvent(
        Long userId,
        String email
) {
}

You can also use a normal class:

public class UserRegisteredEvent {

    private final Long userId;
    private final String email;

    public UserRegisteredEvent(Long userId, String email) {
        this.userId = userId;
        this.email = email;
    }

    public Long getUserId() {
        return userId;
    }

    public String getEmail() {
        return email;
    }
}

---

2. Publish the Event

Inject ApplicationEventPublisher into a Spring-managed bean and call publishEvent.

import org.springframework.context.ApplicationEventPublisher;
import org.springframework.stereotype.Service;

@Service
public class UserService {

    private final ApplicationEventPublisher eventPublisher;

    public UserService(ApplicationEventPublisher eventPublisher) {
        this.eventPublisher = eventPublisher;
    }

    public void registerUser(String email) {
        // Save user, validate data, etc.
        Long userId = 42L;

        eventPublisher.publishEvent(new UserRegisteredEvent(userId, email));
    }
}

---

3. Listen for the Event

Use @EventListener on a method in a Spring bean.

import org.springframework.context.event.EventListener;
import org.springframework.stereotype.Component;

@Component
public class UserRegisteredListener {

    @EventListener
    public void handleUserRegistered(UserRegisteredEvent event) {
        System.out.println("User registered: " + event.email());

        // Send welcome email, write audit log, etc.
    }
}

Spring automatically detects listener methods and invokes them when a matching event is published.

---

4. Multiple Listeners Can React to the Same Event

You can have several independent listeners for one event.

import org.springframework.context.event.EventListener;
import org.springframework.stereotype.Component;

@Component
public class WelcomeEmailListener {

    @EventListener
    public void sendWelcomeEmail(UserRegisteredEvent event) {
        System.out.println("Sending welcome email to " + event.email());
    }
}

import org.springframework.context.event.EventListener;
import org.springframework.stereotype.Component;

@Component
public class AuditLogListener {

    @EventListener
    public void audit(UserRegisteredEvent event) {
        System.out.println("Audit log for user " + event.userId());
    }
}

This keeps the registration logic separate from email, auditing, and other side effects.

---

5. Listen Only When a Condition Matches

You can add a condition using Spring Expression Language.

import org.springframework.context.event.EventListener;
import org.springframework.stereotype.Component;

@Component
public class CorporateUserListener {

    @EventListener(condition = "#event.email().endsWith('@company.com')")
    public void handleCorporateUser(UserRegisteredEvent event) {
        System.out.println("Corporate user registered: " + event.email());
    }
}

For a JavaBean-style event class, you might use:

@EventListener(condition = "#event.email.endsWith('@company.com')")
public void handleCorporateUser(UserRegisteredEvent event) {
    // ...
}

---

6. Make Event Handling Asynchronous

By default, Spring event listeners run synchronously in the same thread as the publisher.

To run listeners asynchronously, enable async execution:

import org.springframework.context.annotation.Configuration;
import org.springframework.scheduling.annotation.EnableAsync;

@Configuration
@EnableAsync
public class AsyncConfig {
}

Then annotate the listener with @Async.

import org.springframework.context.event.EventListener;
import org.springframework.scheduling.annotation.Async;
import org.springframework.stereotype.Component;

@Component
public class AsyncWelcomeEmailListener {

    @Async
    @EventListener
    public void sendWelcomeEmail(UserRegisteredEvent event) {
        System.out.println("Sending email asynchronously to " + event.email());
    }
}

You can also configure a custom executor:

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;

import java.util.concurrent.Executor;

@Configuration
public class AsyncConfig {

    @Bean(name = "applicationEventExecutor")
    public Executor applicationEventExecutor() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setThreadNamePrefix("app-event-");
        executor.setCorePoolSize(4);
        executor.setMaxPoolSize(16);
        executor.setQueueCapacity(100);
        executor.initialize();
        return executor;
    }
}

Use it like this:

import org.springframework.context.event.EventListener;
import org.springframework.scheduling.annotation.Async;
import org.springframework.stereotype.Component;

@Component
public class AsyncAuditListener {

    @Async("applicationEventExecutor")
    @EventListener
    public void audit(UserRegisteredEvent event) {
        System.out.println("Async audit for user " + event.userId());
    }
}

---

7. Use Transaction-Aware Events

If you publish an event inside a database transaction, a normal @EventListener runs immediately, even before the transaction commits.

If you want the listener to run only after the transaction commits, use @TransactionalEventListener.

import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;
import org.springframework.context.ApplicationEventPublisher;

@Service
public class UserService {

    private final ApplicationEventPublisher eventPublisher;

    public UserService(ApplicationEventPublisher eventPublisher) {
        this.eventPublisher = eventPublisher;
    }

    @Transactional
    public void registerUser(String email) {
        Long userId = 42L;

        // Persist user here

        eventPublisher.publishEvent(new UserRegisteredEvent(userId, email));
    }
}

import org.springframework.stereotype.Component;
import org.springframework.transaction.event.TransactionalEventListener;

@Component
public class UserRegisteredTransactionalListener {

    @TransactionalEventListener
    public void afterCommit(UserRegisteredEvent event) {
        System.out.println("Transaction committed for user " + event.userId());
    }
}

By default, @TransactionalEventListener runs in the AFTER_COMMIT phase.

You can specify the phase explicitly:

import org.springframework.stereotype.Component;
import org.springframework.transaction.event.TransactionPhase;
import org.springframework.transaction.event.TransactionalEventListener;

@Component
public class UserRegisteredTransactionListener {

    @TransactionalEventListener(phase = TransactionPhase.AFTER_COMMIT)
    public void afterCommit(UserRegisteredEvent event) {
        System.out.println("After commit: " + event.email());
    }

    @TransactionalEventListener(phase = TransactionPhase.AFTER_ROLLBACK)
    public void afterRollback(UserRegisteredEvent event) {
        System.out.println("After rollback: " + event.email());
    }

    @TransactionalEventListener(phase = TransactionPhase.AFTER_COMPLETION)
    public void afterCompletion(UserRegisteredEvent event) {
        System.out.println("Transaction completed: " + event.email());
    }

    @TransactionalEventListener(phase = TransactionPhase.BEFORE_COMMIT)
    public void beforeCommit(UserRegisteredEvent event) {
        System.out.println("Before commit: " + event.email());
    }
}

---

8. Listener Ordering

If multiple listeners handle the same event, you can control their order with @Order.

import org.springframework.context.event.EventListener;
import org.springframework.core.annotation.Order;
import org.springframework.stereotype.Component;

@Component
public class OrderedListeners {

    @Order(1)
    @EventListener
    public void first(UserRegisteredEvent event) {
        System.out.println("First listener");
    }

    @Order(2)
    @EventListener
    public void second(UserRegisteredEvent event) {
        System.out.println("Second listener");
    }
}

Lower order values run first.

---

9. Returning Events from Listeners

A synchronous listener can return another event, and Spring will publish it.

import org.springframework.context.event.EventListener;
import org.springframework.stereotype.Component;

@Component
public class ChainedEventListener {

    @EventListener
    public AccountCreatedEvent handleUserRegistered(UserRegisteredEvent event) {
        return new AccountCreatedEvent(event.userId());
    }
}

Example second event:

public record AccountCreatedEvent(Long userId) {
}

Then another listener can react to it:

import org.springframework.context.event.EventListener;
import org.springframework.stereotype.Component;

@Component
public class AccountCreatedListener {

    @EventListener
    public void handleAccountCreated(AccountCreatedEvent event) {
        System.out.println("Account created for user " + event.userId());
    }
}

Avoid this pattern for complex workflows, though. It can become hard to trace.

---

10. Legacy ApplicationEvent Style

Older Spring code often defines events by extending ApplicationEvent.

import org.springframework.context.ApplicationEvent;

public class UserRegisteredApplicationEvent extends ApplicationEvent {

    private final Long userId;
    private final String email;

    public UserRegisteredApplicationEvent(Object source, Long userId, String email) {
        super(source);
        this.userId = userId;
        this.email = email;
    }

    public Long getUserId() {
        return userId;
    }

    public String getEmail() {
        return email;
    }
}

Publishing:

eventPublisher.publishEvent(
        new UserRegisteredApplicationEvent(this, userId, email)
);

Listening:

import org.springframework.context.event.EventListener;
import org.springframework.stereotype.Component;

@Component
public class LegacyUserEventListener {

    @EventListener
    public void handle(UserRegisteredApplicationEvent event) {
        System.out.println(event.getEmail());
    }
}

This still works, but plain objects or records are usually simpler.

---

Recommended Pattern

For most Spring applications:

1. Use a simple immutable event type, often a record.
2. Publish it from a service using ApplicationEventPublisher.
3. Listen with @EventListener.
4. Use @TransactionalEventListener for database-related side effects.
5. Use @Async only for work that does not need to complete before the caller continues.

Example:

public record OrderPlacedEvent(
        Long orderId,
        Long customerId
) {
}

import org.springframework.context.ApplicationEventPublisher;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

@Service
public class OrderService {

    private final ApplicationEventPublisher eventPublisher;

    public OrderService(ApplicationEventPublisher eventPublisher) {
        this.eventPublisher = eventPublisher;
    }

    @Transactional
    public void placeOrder(Long customerId) {
        Long orderId = 100L;

        // Save order

        eventPublisher.publishEvent(new OrderPlacedEvent(orderId, customerId));
    }
}

import org.springframework.stereotype.Component;
import org.springframework.transaction.event.TransactionalEventListener;

@Component
public class OrderNotificationListener {

    @TransactionalEventListener
    public void sendConfirmation(OrderPlacedEvent event) {
        System.out.println("Send confirmation for order " + event.orderId());
    }
}

This ensures the confirmation runs only after the order transaction successfully commits.