Custom Auto-Configuration in SpringBoot

The blog is originally published on my blog jsblogs.github.io

• Introduction
• Technologies used
• Project Structure
• Create config classes

Introduction

The goal of this blog is to understand the autoconfiguration provided by SpringBoot. I'll be creating a logging library for demo purpose and that will include Auto-Configuration class to create all required beans for that library.

Technologies used

• Java 11
• Spring Boot 2.2.4
• Gradle 6.0.1

Project Structure

I'm using a Gradle multi-module project. The module logging-library will be a shared library that will be used in the service module.

Create config classes

Now It's time to create required config classes. I've created a config class called LoggingAutoConfiguration and marked as @Configuration and created one conditional bean.

@Configuration
public class LoggingAutoConfiguration {

    // We can define beans here

    @ConditionalOnMissingBean(Logger.class)
    @Bean
    public Logger getLogger() {
        return new ConsoleLogger();
    }
}

As of now this class is just a normal spring configuration and to make it auto-configuration class we need to follow 2 steps:

Step 1: Create spring.factories file

Create a file inlogging-library with name spring.factories under resources\META-INF\ directory.

Step 2: Register the auto-config class

Now add your configuration class into the spring.factories.

org.springframework.boot.autoconfigure.EnableAutoConfiguration=tutorials.logging.LoggingAutoConfiguration

That's it!!!

Now we can inject the module in service and we don't need to specify any package to scan from logging-library our auto-configuration class will take care of that.

You can find the running code here