For quite a long time, running a Java server application
required an actual application server.
For example,
Tomcat was and still is one of the more popular server containers to
run Java applications. That generally involved packaging your Java
application as a WAR zip file and then dropping that file into the
Tomcat deployment directory.
The app server would then extract the app,
deploy it, and make it available for use. Spring Boot changes paradigm
for Java Spring apps. No more WAR files are needed.
Instead, Spring Boot embedded the application container inside of itself and
deployed the Java app to the container under the covers.
What this ultimately means as a developer is that you create a basic Java
application using the public static void main method as seen here and Spring
Boot will then Bootstrap your Spring application,
prepare it, and get it deployed.
If you're using Spring Web or Spring MVC with your application,
that would mean that Spring Boot would actually take your code,
deploy it to the embedded Tomcat servlet container, and then
fire up the server and make it available for use. This simple
change to running just as a Java application makes deploying
your app much easier, as now,
wherever you plan to run the application, that place just simply needs to be
able to run Java. That makes working with Spring Boot easy,
whether it's in development or on a cloud platform.