Does every spring boot application create a tomcat container to be able to run?

Question

For example, I understand adding specific dependencies like spring-boot-starter-web that contains tomcat as transitive dependency triggers the spring framework to initialize tomcat container but I want to know if we say a spring-boot application is running, does it imply always that tomcat is also running?

Answer 1

I want to know if we say a spring-boot application is running, does it imply always that tomcat is also running?

No, it doesn't.

Spring boot can be used for both web applications and non-web applications. For web applications you can use tomcat/jetty/undertow/netty for example, its up to you to chose what works for you the best.

If you don't want to run an embedded version of the web server you can opt for creating a WAR file and place it into the web server prepared in-advance.

If you don't want to run web application at all (something that is built around "Request - Response" way of work in the most broad sense) - you can create a "CommandLineRunner" - in this case you don't need to depend on neither web-mvc nor webflux. For more information about Command Line Runners read here for example

Answer 2

You can have an embedded server in your JAR that is able to be run on its own. By default it is Tomcat but you can change this to others, like Jetty. Additional details:

• https://docs.spring.io/spring-boot/docs/2.0.6.RELEASE/reference/html/howto-embedded-web-servers.html

If you don't want to have an embedded server and you want to deploy your application you can also create WAR files instead of JAR files. Additional details:

• https://www.baeldung.com/spring-boot-no-web-server
• https://spring.io/guides/gs/convert-jar-to-war/