How auto-configuration works in Spring Boot - Try It Yourself

How auto-configuration works

📖 Scenario: You are building a simple Spring Boot application that automatically configures a greeting service based on the presence of a property.

🎯 Goal: Learn how Spring Boot auto-configuration works by creating a configuration class that sets up a greeting service bean automatically when a property is set.

📋 What You'll Learn

Create a Spring Boot application class

Create a configuration class with @Configuration and @ConditionalOnProperty

Define a bean method that returns a greeting message

Use the auto-configured bean in the main application

💡 Why This Matters

🌍 Real World

Auto-configuration helps developers avoid writing boilerplate setup code by letting Spring Boot create beans automatically based on conditions like properties or classpath.

💼 Career

Understanding auto-configuration is essential for Spring Boot developers to customize and extend applications efficiently without manual wiring.

1

Create the Spring Boot application class

Create a class called AutoConfigApplication annotated with @SpringBootApplication and add a main method that runs SpringApplication.run(AutoConfigApplication.class, args).

Spring Boot

// Your code here

Need a hint?

This is the standard way to start a Spring Boot app. Use @SpringBootApplication on the class and a main method to launch.

2

Create a configuration class with conditional property

Create a class called GreetingAutoConfiguration annotated with @Configuration and @ConditionalOnProperty(name = "greeting.enabled", havingValue = "true").

Spring Boot

import org.springframework.context.annotation.Configuration;
import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;

// Your code here

Need a hint?

Use @Configuration to mark the class as config. Use @ConditionalOnProperty to activate only when greeting.enabled=true.

3

Define a greeting bean method

Inside GreetingAutoConfiguration, add a method called greetingMessage annotated with @Bean that returns the string "Hello from auto-configured bean!".

Spring Boot

import org.springframework.context.annotation.Bean;

// Your code here

Need a hint?

Use @Bean on a method that returns the greeting string. This creates a bean in the app context.

4

Use the auto-configured greeting bean

In AutoConfigApplication, add a @Bean method called runner that takes a String greetingMessage parameter and returns a CommandLineRunner which prints the greeting message.

Spring Boot

import org.springframework.boot.CommandLineRunner;

// Your code here

Need a hint?

Use a CommandLineRunner bean to run code at startup. Inject the greetingMessage bean and print it.