spring-postconstruct-predestroy

Posted on: 2019-10-08 2019-10-08
Tags: Spring

Spring PostConstruct and PreDestroy Annotations

Spring

1. Introduction

Spring allows us to attach custom actions to
bean
creation and destruction. We can, for example, do it by implementing
the InitializingBean and DisposableBean interfaces.

In this short tutorial, we’ll look at a second possibility:
the @PostConstruct and @PreDestroy annotations.

2. @PostConstruct

Spring calls methods annotated with @PostConstruct only once, just
after the initialization of bean properties. Keep in mind that
these methods will run even if there is nothing to initialize.

The method annotated with @PostConstruct can have any access level but
it can’t be static.

One example usage of @PostConstruct is populating a database. During
development, for instance, we might want to create some default users:

@Component
public class DbInit {

    @Autowired
    private UserRepository userRepository;

    @PostConstruct
    private void postConstruct() {
        User admin = new User("admin", "admin password");
        User normalUser = new User("user", "user password");
        userRepository.save(admin, normalUser);
    }
}

The above example will first initialize UserRepository and then run
@PostConstruct method.

3. @PreDestroy

A method annotated with @PreDestroy runs only once, just before Spring
removes our bean from the application context.

Same as with @PostConstruct, the methods annotated with @PreDestroy
can have any access level but can’t be static.

@Component
public class UserRepository {

    private DbConnection dbConnection;
    @PreDestroy
    public void preDestroy() {
        dbConnection.close();
    }
}

The purpose of this method should be to release resources or perform any
other cleanup tasks before the bean gets destroyed, for example closing
a database connection.

4. Java 9+

Note that both @PostConstruct and @PreDestroy annotations are part
of Java EE. And since
Java EE has been
deprecated in Java 9 and removed in Java 11 we have to add an
additional dependency to use these annotations:

<dependency>
    <groupId>javax.annotation</groupId>
    <artifactId>javax.annotation-api</artifactId>
    <version>1.3.2</version>
</dependency>

5. Conclusion

In this short tutorial, we’ve learned how to use @PreConstruct and
@PreDestroy annotations.

As always all source code is available on
GitHub.

getdocs

3043