Whenever you are creating a Java application, deployment can be done via two methods:
Using an application container that is external.
Embedding the container inside your jar file.
Spring Boot contains Jetty, Tomcat, and Undertow servers, all of which are embedded.
Jetty – Used in a wide number of projects, Eclipse Jetty can be embedded in framework, application servers, tools, and clusters.
Tomcat – Apache Tomcat is an open source JavaServer Pages implementation which works well with embedded systems.
Undertow – A flexible and prominent web server that uses small single handlers to develop a web server.