1. Introduction
Spring Boot simplifies the configuration and setup of Spring applications with various annotations that reduce boilerplate code. One such annotation is @SpringBootConfiguration, which is specialized form of @Configuration. It indicates that a class provides Spring Boot application @Configuration. In essence, it flags the annotated class as the source for bean definitions. In this blog post, we'll explore how to use the @SpringBootConfiguration annotation within a Spring Boot application.
Key Points:
1. @SpringBootConfiguration is an annotation used by Spring Boot to indicate a configuration class.
2. It is annotated with @Configuration itself, thereby inheriting all its characteristics.
3. The presence of @SpringBootConfiguration also triggers auto-configuration mechanisms in Spring Boot.
4. Typically, @SpringBootApplication includes this annotation implicitly.
5. One should not use @SpringBootConfiguration if @SpringBootApplication is already used on the application's main class.
2. Implementation Steps
1. Define a class to serve as the application's configuration source.
2. Annotate this class with @SpringBootConfiguration.
3. Add bean methods within this class if specific bean definitions are required.
4. Create the main application class to run the Spring Boot application.
5. Use the @SpringBootApplication annotation on the main class, which implicitly includes @SpringBootConfiguration.
3. Implementation Example
// Step 1: Create a class that serves as the configuration source for the application
@SpringBootConfiguration
public class AppConfig {
// Step 2: Define a bean that will be managed by the Spring container
@Bean
public MessageService messageService() {
return new MessageService("Hello, Spring Boot @SpringBootConfiguration!");
}
}
// Step 3: Create a service class that will be instantiated as a bean
class MessageService {
private final String message;
public MessageService(String message) {
this.message = message;
}
public String getMessage() {
return message;
}
}
// Step 4: Define the main application class
@SpringBootApplication // Implicitly includes @SpringBootConfiguration
public class SpringBootConfigApplication {
public static void main(String[] args) {
// Step 5: Run the Spring Boot application
ConfigurableApplicationContext context = SpringApplication.run(SpringBootConfigApplication.class, args);
// Step 6: Retrieve the message from the MessageService bean and print it
MessageService messageService = context.getBean(MessageService.class);
System.out.println(messageService.getMessage());
}
}
Output:
Hello, Spring Boot @SpringBootConfiguration!
Explanation:
1. @SpringBootConfiguration: This designates AppConfig as a configuration class for the Spring Boot application.
2. @Bean: Inside the AppConfig class, the messageService method is annotated with @Bean, signifying that it returns an object that should be registered as a bean in the Spring application context.
3. MessageService: This is a simple service class with a single method to return a message.
4. @SpringBootApplication: Used on the SpringBootConfigApplication class, it implicitly declares @SpringBootConfiguration, enabling configuration, component scanning, and auto-configuration.
5. SpringApplication.run(): This is the static method that boots the Spring Boot application.
6. getMessage(): Retrieves the message from the MessageService bean, demonstrating that the configuration has been applied.