Mastering @Order in Spring Boot 3: Real‑World Examples and Best Practices

1. Introduction

@Order is a Spring annotation that defines the priority of bean execution; it can be placed on classes, methods, or fields. It only affects the order of beans when they are injected into a collection, not the bean loading or instantiation sequence. A smaller integer value indicates a higher priority. Neither @Order nor the Ordered interface can determine the actual bean loading order, which is decided by the registration (scanning) order.

2. Practical Cases

2.1 Collection Injection

When injecting a collection of beans (e.g., multiple implementations of an interface), @Order can control their order in the collection.

<code>public interface DAO { void save(); }
@Component public class A implements DAO { public void save() { System.out.println("A..."); } }
@Component public class B implements DAO { public void save() { System.out.println("B..."); } }
@Component public class C implements DAO { public void save() { System.out.println("C..."); } }
@Resource private List<DAO> daos;
public void print() { for (DAO dao : daos) { dao.save(); } }</code>

Running the program prints A... , B... , C... . After adding @Order(2) to A , @Order(1) to B , and @Order(0) to C , the output becomes C... , B... , A... . The collection can also be an array; sorting works the same way.

2.2 ApplicationListener Event

Listeners annotated with @Order are invoked according to their order when an event is published.

<code>@Component @Order(-1) public class ListenerA implements ApplicationListener<PackEvent> { @Override public void onApplicationEvent(PackEvent event) { System.out.println("A Listener..."); } }
@Component @Order(-2) public class ListenerB implements ApplicationListener<PackEvent> { @Override public void onApplicationEvent(PackEvent event) { System.out.println("B Listener..."); } }</code>

Publishing PackEvent prints B Listener... followed by A Listener... . Implementing the Ordered interface yields the same effect.

2.3 Application/CommandLineRunner

Runner interfaces execute after the Spring Boot context is fully loaded; @Order determines their execution sequence.

<code>@Component @Order(0) public class RunnerA implements CommandLineRunner { public void run(String... args) { System.out.println("A Runner..."); } }
@Component @Order(-1) public class RunnerB implements CommandLineRunner { public void run(String... args) { System.out.println("B Runner..."); } }</code>

Output: B Runner... then A Runner... . Registration via @Bean or implementing Ordered works as well.

2.4 BeanPostProcessor

BeanPostProcessor can be ordered only by implementing Ordered (or PriorityOrdered ) and returning a custom order value.

<code>public class APostProcessor implements BeanPostProcessor, Ordered { public Object postProcessBeforeInitialization(Object bean, String beanName) { System.out.println("A BeanPostProcessor"); return bean; } public int getOrder() { return -1; } }
public class BPostProcessor implements BeanPostProcessor, Ordered { public Object postProcessBeforeInitialization(Object bean, String beanName) { System.out.println("B BeanPostProcessor"); return bean; } public int getOrder() { return -2; } }</code>

Execution result: B BeanPostProcessor then A BeanPostProcessor . The @Order annotation is not supported for BeanPostProcessor ordering.

2.5 BeanFactoryPostProcessor

Similar to BeanPostProcessor; ordering is controlled by implementing the Ordered interface.

2.6 @Aspect

Aspects can be ordered with @Order or by implementing Ordered .

<code>@Aspect @Order(-1) public static class AspectA { @Pointcut("execution(* *(..))") private void a() {} @Before("a()") public void before() { System.out.println("A before..."); } }
@Aspect @Order(-2) public static class AspectB { @Pointcut("execution(* *(..))") private void b() {} @Before("b()") public void before() { System.out.println("B before..."); } }</code>

Execution order: B before... , A before... , then the target method.

2.7 Other Sortable Components

Components such as FailureAnalyzer , ApplicationContextInitializer , ErrorPageRegistrar , ErrorViewResolver , etc., are also sortable when obtained via SpringFactoriesLoader#load(Class) .

<code>// Any object loaded through SpringFactoriesLoader.load(Class) supports ordering</code>

Images illustrating Runner ordering and aspect execution are retained below.