Auto-Configuration — Spring Technical Interview Questions & Answers

How Boot configures beans based on the classpath.

Auto-Configuration

  • Auto-configuration means Boot sets up beans for you when conditions match.
  • Trigger: @EnableAutoConfiguration (inside @SpringBootApplication).
  • Classpath check: If a JDBC driver exists, Boot may create a DataSource.
  • Conditions: Annotations like @ConditionalOnClass and @ConditionalOnMissingBean decide yes/no.
  • Your beans win: If you define your own @Bean, it can replace the default (@ConditionalOnMissingBean).
  • Where listed: Auto-config classes are registered via AutoConfiguration.imports (modern Boot) / older spring.factories.
  • Fighting auto-config without checking why a bean was created.
  • Mention @ConditionalOnMissingBean — your custom bean overrides defaults.

Technical Interview Tip: Auto-config + conditions + override with your own bean.

Code Examples for Auto-Configuration

Auto-Configuration — working example

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication // @Configuration + @EnableAutoConfiguration + @ComponentScan
public class DemoApplication {
  public static void main(String[] args) {
    SpringApplication.run(DemoApplication.class, args);
  }
}

// pom.xml / build idea:
// spring-boot-starter-web pulls Tomcat + Spring MVC

Auto-Configuration — @SpringBootApplication boots auto-config, component scan, and the app context; starters are curated dependency bundles.

How to Explain Auto-Configuration to an Interviewer

What is Auto-Configuration (sb)?

Used for a short Auto-Configuration sb example a small REST app Not just the heading

Give one small example of Auto-Configuration (sb).

the smallest Auto-Configuration sb example you can type How Boot configures beans based on the classpath

What mistake do beginners make with Auto-Configuration (sb)?

only saying “Auto-Configuration sb” with no example Show the fix

Where do you use Auto-Configuration (sb)?

a small REST app a short Auto-Configuration sb example