Spring Boot auto-configuration is a powerful feature that can drastically simplify application configuration. In this post, we'll take a deep dive into how auto-configuration works and how it can be used to simplify your application development.
Spring Boot auto-configuration is triggered by the presence of certain classes on the classpath. When Spring Boot detects one of these classes, it will automatically configure a beans of that type. For example, if Spring Boot detects Hibernate on the classpath, it will automatically configure a Hibernate SessionFactory.
There are a few different ways to customize the auto-configuration process. One is to use the @Conditional annotation to specify conditions under which a particular configuration should be applied. Another is to use the @ConfigurationProperties annotation to map property values to bean properties.
As an example, let's configure a Spring Data JPA repository using auto-configuration. First, we'll add the following dependencies to our build: spring-boot-starter-data-jpa, h2, and mysql.
Next, we'll create a JpaRepository class:
@Repository
public interface MyRepository extends JpaRepository<User, Long> {
}
We can then enable auto-configuration by adding the @EnableAutoConfiguration annotation to our Application class:
@SpringBootApplication
@EnableAutoConfiguration
public class Application {
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
}
Finally, we can configure our application properties:
spring.datasource.url=jdbc:mysql://localhost:3306/test
spring.datasource.username=root
spring.datasource.password=password
spring.jpa.database=MYSQL
spring.jpa.show-sql=true
Spring Boot will automatically configure a DataSource and JpaRepository based on the properties we've configured. We can inject our repository into a service class and use it to save and retrieve data:
@Service
public class MyService {
@Autowired
private MyRepository repository;
public void save(User user) {
repository.save(user);
}
public List<User> findAll() {
return repository.findAll();
}
}
Auto-configuration can be a huge time-saver when developing Spring Boot applications. In most cases, it will Just Work(tm) without any configuration required. When it doesn't, the configuration is usually straightforward.