How would you ensure that your custom starter doesn’t interfere with Spring Boot's own auto-configuration?

Question

Accepted Answer

A custom Spring Boot starter avoids interfering with the framework's own auto-configuration by using conditional annotations that back off whenever the user or another starter has already provided an equivalent bean, class, or property.

Key Points:
• @ConditionalOnMissingBean skips a bean definition if one already exists in the context, letting user configuration take precedence.
• @ConditionalOnClass only activates configuration when a required library is actually on the classpath.
• @ConditionalOnProperty gates configuration behind an explicit property, so behavior can be toggled or opted out of entirely.
• Placing these conditions on every auto-configuration class keeps the starter additive rather than overriding, which is the convention Spring Boot itself follows internally.
• Ordering auto-configuration classes with @AutoConfigureAfter or @AutoConfigureBefore avoids conflicts when a starter depends on beans from another auto-configuration.

Example:
A custom caching starter defines a default CacheManager bean guarded by @ConditionalOnMissingBean(CacheManager.class), so if the consuming application defines its own CacheManager, the starter's default quietly steps aside instead of causing a conflict.

Code Example:
```
@Configuration
@ConditionalOnClass(CacheManager.class)
public class AcmeCacheAutoConfiguration {

@Bean
    @ConditionalOnMissingBean
    public CacheManager cacheManager() {
        return new ConcurrentMapCacheManager();
    }
}
```

Interview Tip:
A concise interview answer is:

"I guard every bean in the starter's auto-configuration with @ConditionalOnMissingBean, @ConditionalOnClass, or @ConditionalOnProperty, so it only supplies a default when nothing else has already defined it. That mirrors how Spring Boot's own starters behave, and it means my starter adds functionality without ever fighting the application's own configuration."