Ensuring Spring Boot Startup Code Execution with Automated Tests

Running specific code upon application startup is a common requirement, often used for tasks like database migrations or cache initialization. This blog post demonstrates how to implement such functionality in Spring Boot and, crucially, how to ensure its continued execution through automated testing.

Implementing Startup Code in Spring Boot

Spring Boot provides a straightforward mechanism for executing code during application initialization. By using the @EventListener annotation in conjunction with the ApplicationReadyEvent, you can designate a method within a Spring-managed bean to run after the application context has been fully initialized.

@Component
public class DataMigrationBean {

    private static boolean migrationFinished = false;

    @EventListener(ApplicationReadyEvent.class)
    public void migrateData() throws Exception {
        // Migration logic here...
        migrationFinished = true;
    }

    public static boolean isMigrationFinished() {
        return migrationFinished;
    }
}

In this example, the migrateData() method will be executed automatically when the application is ready. The migrationFinished flag serves as an indicator that the migration process has completed.

Verifying Startup Execution with Tests

While implementing the startup logic is simple, ensuring its continued execution requires a robust testing strategy. A dedicated test can verify that the designated method runs as expected during application startup. Here’s how to achieve this using a Spring Boot test:

@ExtendWith(SpringExtension.class)
@ContextConfiguration(classes = { TestConfig.class })
class DataMigrationStartupTest {

    @Test
    void verifyMigrationOnStartUp() {
        Assertions.assertThat(DataMigrationBean.isMigrationFinished()).isTrue();
    }
}

To avoid loading the entire application context, which can be resource-intensive, a dedicated test configuration class is used. This class defines the necessary beans and configurations required for the test:

@Configuration
@ComponentScan(basePackages = "your.package.containing.migrationbean") // Replace with your package
public class TestConfig {

     @Bean
     public DataMigrationBean dataMigrationBean() {
         return new DataMigrationBean(); 
     }
}

The @ComponentScan annotation ensures that the DataMigrationBean is picked up and registered in the test context. This focused approach significantly reduces test execution time.

This approach ensures that any changes or refactoring won’t inadvertently break the startup functionality, providing a safety net and ensuring application stability.