Read the pom.xml

A pom.xml declares spring-boot-starter-web, spring-boot-starter-data-jpa, and nothing else related to a server. Will java -jar on the built artifact start something listening on a port? What is doing the listening?

See the answer

Yes. spring-boot-starter-web alone brings in spring-boot-starter-tomcat, so an embedded Tomcat is on the classpath and gets auto-configured regardless of what else is declared — spring-boot-starter-data-jpa adds data access, not a server, and doesn't change this.

Spring Boot