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I want to create a jar file that I can add to a classpath and will basically "plug-in" to an existing spring boot application. I need it to be able to have annotations of Component, ConfigurationProperties, and all the fun things that spring boot gives you, but I want it "thin" and it will be a jar file used as part of a full spring boot web application.

I need the jar file to be externally configurable. Property files will be different for different deployments. So having a working @Configuration annotation is critical.

I look at spring-boot-starter-parent, and that has jetty, tomcat, hibernate stuff and is a huge jar file. I don't want that.

Is there a "thin" parent?

Is spring boot simply not what I want here? And I should just use a regular spring project and set my "Main" spring boot web app to do component scans to configure the jar file?

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  • Why not build your app like you normaly would do but use scope provided for every spring dependency ? This way you wont include spring code into jar. Commented Jan 2, 2018 at 22:01

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It sounds like you are trying to define your own Spring Boot Starter. That's the real power that Spring Boot gives you, the ability to include a dependency and have it auto-configure itself.

By packaging your jar the right way, Spring Boot will detect that there are configurations, components, and property files automatically. I've used this in the past for the case where I want all of my applications to log a specific way, or enforce a certain format for my REST endpoints.

The documentation gives a very thorough overview of the steps you'll need to take. But essentially, you are going to package your jar like any other (with your @Bean, @Component, @Service, and @Configuration classes in it), and provide a property file pointing to the configurations:

// Example spring.factories file org.springframework.boot.autoconfigure.EnableAutoConfiguration=\ com.mycorp.libx.autoconfigure.LibXAutoConfiguration,\ com.mycorp.libx.autoconfigure.LibXWebAutoConfiguration

Also check out the set of @ConditionalOn... annotations, they can really help with controlling what beans become active based on properties being defined, profiles being active, or dependencies being loaded.

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This is a good starting point, but to be clear, I do not want to include it as a "Dependency" in a pom file. I want to place the jar in a pre-defined external lib folder, and have spring pick it up. It would be a plug-n-play type thing, where the presence of these jars would add functionality to a base application

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