Introduction:

@SpringBootConfiguration annotation in Spring Boot is a class-level annotation which indicates that this class provides the application configuration.

Generally, the class with the main() method is best-suited for this annotation.

We usually use @SpringBootApplication annotation which automatically inherits the @SpringBootConfiguration annotation.

Annotation Usage:

When we mark a class with @SpringBootConfiguration, it means that the class provides @Bean definition methods. The Spring container processes the configuration class to instantiate and configure beans for our application.

Let’s see an example usage of this annotation:

@SpringBootConfiguration
public class DemoApp {

    public static void main(String[] args) {
        SpringApplication.run(DemoApp.class, args);
    }

    @Bean
    public Course course() {
        return new Course();
    }

    @Bean
    public Student student() {
        return new Student();
    }
}

@Configuration vs @SpringBootConfiguration:

As per the Spring documentation, @SpringBootConfiguration is just an alternative to the Spring standard @Configuration annotation. The only difference between the two is that the @SpringBootConfiguration allows the configuration to be found automatically.

This is specifically useful when writing tests.

@SpringBootConfiguration vs @SpringBootApplication:

As we discussed earlier, the @SpringBootApplication annotation includes @SpringBootConfiguration annotation:

@Target(value=TYPE)
@Retention(value=RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters={@ComponentScan.Filter(type
  =CUSTOM,classes=TypeExcludeFilter.class)})
public @interface SpringBootApplication

We most usually only use @SpringBootApplication which in turn includes the other one.

Please note that it is recommended to only use exactly one @SpringBootConfiguration or @SpringBootApplication annotation in our application.

IllegalStateException:: Unable to find @SpringBootConfiguration:

While writing test cases for our Spring Boot application, one of the common exceptions we encounter is:

Unable to find a @SpringBootConfiguration, 
you need to use @ContextConfiguration or @SpringBootTest(classes=...)
 with your test java.lang.IllegalStateException

The primary reason for this usually is that the test annotations like @DataJpaTest and a few others look first for the @SpringBootConfiguration annotation in the current package. In case, it’s missing in the current package, they start looking up the package hierarchy until they find this annotation.

Make sure that your test classes are either in the same package as your class marked with @SpringBootApplication or at least lower in the package hierarchy:

sample-app
  +--pom.xml
  +--src
    +--main
      +--com
        +--programmergirl
          +--Application.java
    +--test
      +--com
        +--programmergirl
          +--test
            +--SampleJpaTest.java

This should resolve this issue.

Conclusion:

In this mini-tutorial, we talked about the @SpringBootConfiguration annotation. We also saw that @SpringBootApplication includes the definition for the @SpringBootConfiguration.

And, we compared the standard Spring @Configuration with the @SpringBootConfiguration.

We have another article on Spring core Annotations that can help you learn some common annotations used in a Spring application. Please feel free to explore if you feel so.