How to create a Spring Library and consumers can import all the beans automatically?

Do you want your custom Spring Boot library to seamlessly integrate into consumer applications, automatically registering necessary beans without manual configuration? This approach, similar to official Spring Boot starters, can be achieved through custom auto-configuration.

Here’s a comprehensive guide to creating a Spring Boot library that integrates smoothly, providing necessary beans automatically:

1. Design Your Auto-Configuration Class

Create a configuration class within your library to declare the beans. Annotate it with @Configuration and use conditional annotations to manage bean creation [3, 4].

package com.example.customautoconfig.config;

import com.example.customautoconfig.service.CustomService;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;

@Configuration
public class CustomAutoConfiguration {

    @Bean
    @ConditionalOnMissingBean
    public CustomService customService() {
        return new CustomService();
    }
}

• @Configuration: Indicates that the class can be used by the Spring IoC container as a source of bean definitions.
• @Bean: Marks a method as a bean producer for the application context.
• @ConditionalOnMissingBean: Ensures that a bean is created only if the application context does not already contain a bean of the same type[1].

2. Register Your Auto-Configuration

Register the auto-configuration class in the META-INF/spring.factories file [1, 2, 6]. Create this file in the src/main/resources/META-INF directory of your library.

# META-INF/spring.factories
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
com.example.customautoconfig.config.CustomAutoConfiguration

This entry tells Spring Boot to apply your auto-configuration when the library is a dependency.

3. Package and Distribute

Package your library as a JAR file for distribution.

4. Integrate into Consumer Applications

When a Spring Boot application includes your library as a dependency, the auto-configuration is applied automatically. Developers don’t need to manually import configuration classes; beans defined in your auto-configuration become available for injection[3].

Best Practices for Spring Boot Library Design

• Conditional Annotations: Use annotations like @ConditionalOnClass and @ConditionalOnProperty to control when auto-configuration is applied [4, 5].
• Prevent Bean Overriding: Use @ConditionalOnMissingBean to avoid conflicts[1].
• Testing: Thoroughly test your auto-configuration[4].
• Starter Module: Create a starter module that provides a dependency to the autoconfigure module as well as the library and any additional dependencies that are typically useful [1, 2].

By following these steps and best practices, you can create a Spring Boot library that provides a smooth integration experience for developers, automatically providing the necessary beans without extra configuration.

Citations:
[1] https://docs.spring.io/spring-boot/reference/features/developing-auto-configuration.html
[2] https://docs.spring.io/spring-boot/docs/2.1.7.RELEASE/reference/html/boot-features-developing-auto-configuration.html
[3] https://www.codingshuttle.com/spring-boot-hand-book/spring-boot-auto-configuration/
[4] https://docs.spring.io/spring-boot/docs/2.0.3.RELEASE/reference/html/boot-features-developing-auto-configuration.html
[5] https://docs.spring.io/spring-boot/docs/1.5.11.RELEASE/reference/html/boot-features-developing-auto-configuration.html
[6] https://stackoverflow.com/questions/41815871/spring-boot-autowire-beans-from-library-project
[7] https://piotrminkowski.wordpress.com/2020/08/04/guide-to-building-spring-boot-library/
[8] https://dzone.com/articles/spring-beans-with-auto-generated-implementations-how-to
[9] https://onthecode.co.uk/blog/how-to-create-a-bean-of-class-from-a-java-library-in-spring-boot
[10] https://stackoverflow.com/questions/42248718/create-auto-configure-spring-library-to-spring-boot-application
[11] https://www.baeldung.com/spring-boot-custom-auto-configuration
[12] https://www.marcobehler.com/guides/spring-boot-autoconfiguration
[13] https://www.codingshuttle.com/spring-boot-hand-book/spring-boot-auto-configuration/
[14] https://spring.io/blog/2020/04/23/spring-tips-configuration/
[15] https://github.com/spring-projects/spring-boot/issues/12941
[16] https://digma.ai/10-spring-boot-performance-best-practices/
[17] https://spring.io/blog/2019/01/21/manual-bean-definitions-in-spring-boot/
[18] https://docs.spring.io/spring-boot/reference/features/developing-auto-configuration.html
[19] https://docs.spring.io/spring-boot/docs/2.1.7.RELEASE/reference/html/boot-features-developing-auto-configuration.html
[20] https://piotrminkowski.wordpress.com/2020/08/04/guide-to-building-spring-boot-library/
[21] https://www.sivalabs.in/spring-boot-best-practices/
[22] https://stackoverflow.com/questions/38047799/spring-boot-implicitly-auto-register-a-3rd-party-bean/38048241
[23] https://docs.spring.io/spring-boot/docs/2.0.3.RELEASE/reference/html/boot-features-developing-auto-configuration.html
[24] https://docs.spring.io/spring-boot/reference/using/auto-configuration.html
[25] https://docs.spring.io/spring-boot/docs/1.5.11.RELEASE/reference/html/boot-features-developing-auto-configuration.html
[26] https://github.com/spring-projects/spring-framework/issues/18353