Scenario-Based Follow-Up: Your project needs to integrate a third-party library. How would you proceed to create a Starter for this library?

Creating a Spring Boot Starter for a third-party library packages auto-configuration for that library into a reusable dependency, so any project can add it and get working beans with minimal setup.

Key Points: • Set up a dedicated Maven/Gradle module and add the third-party library as a dependency. • Write @Configuration classes with @Bean methods that construct the library's client objects, guarded with @ConditionalOnClass and @ConditionalOnMissingBean. • Register the auto-configuration class in META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports (the modern replacement for spring.factories). • Expose configuration properties (via @ConfigurationProperties) so consumers can customize the library's behavior without touching code. • Publish the starter to an internal artifact repository so other teams can simply add the dependency to get plug-and-play integration.

Example: A starter wrapping a third-party geocoding library auto-configures a GeocodingClient bean from an API key property, so any service just adds the starter dependency and autowires GeocodingClient without writing any setup code.

Code Example:

@AutoConfiguration
@ConditionalOnClass(GeocodingClient.class)
public class GeocodingAutoConfiguration {

    @Bean
    @ConditionalOnMissingBean
    public GeocodingClient geocodingClient(GeocodingProperties props) {
        return new GeocodingClient(props.getApiKey());
    }
}

Interview Tip: A concise interview answer is:

"I'd wrap the library's setup in an auto-configuration class guarded by @ConditionalOnClass and @ConditionalOnMissingBean, expose its settings through @ConfigurationProperties, and register it via AutoConfiguration.imports. That turns integrating the library into just adding a dependency, instead of every team repeating the same boilerplate setup."