Introduction to the @DependsOn
Annotation
This annotation tells Spring that the bean marked with this annotation should be created after the beans that it depends on are initialized.
You can specify the beans you need to be created first in the @DependsOn
annotation parameters.
This annotation is used when a bean does not explicitly depend on the other bean (as a configuration or argument). But it can rely on the other bean's behavior or actions.
It can be used on the stereotype annotations (like @Component
, @Service
, etc.) or in methods annotated with @Bean
.
Example Scenario Using @DependsOn
Suppose your application has a set of parameters in the database, that is cached by a CacheManager
bean. This bean fetches all the parameter data and puts it into a cache.
But to fetch this parameter, CacheManager
needs the ParameterInitializer
to fill the data into the database first so CacheManager
can read it.
So the CacheManager
depends on the ParameterInitializer
execution to cache the parameter data properly.
Code Example of @DependsOn
Let’s take a look at the code:
@Component
@DependsOn("parameterInitializer")
public class CacheManager {
private static final Logger log = LoggerFactory.getLogger(CacheManager.class);
public CacheManager() {
log.info("CacheManager initialized.");
}
}
@Component("parameterInitializer")
public class ParameterInitializer {
private static final Logger log = LoggerFactory.getLogger(ParameterInitializer.class);
public ParameterInitializer() {
log.info("ParameterInitializer initialized.");
}
}
Expected Output
If you run the code, in the initialization logs you should see something like this:
2024-06-24T22:19:33.450-03:00 INFO 21436 --- [ main] c.s.m.dependson.ParameterInitializer : ParameterInitializer initialized.
2024-06-24T22:19:33.451-03:00 INFO 21436 --- [ main] c.spring.mastery.dependson.CacheManager : CacheManager initialized.
Conclusion
In this blog post, you learned about the @DependsOn
annotation and how you can use it to set dependencies between beans that aren’t directly connected.
If you like this topic, make sure to follow me. In the following days, I’ll be explaining more about Spring annotations! Stay tuned!
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