Differences between jar and war in Spring Boot?

Spring Boot can be told to produce a 'fat JAR' which includes all of your module/service's dependencies and can be run with java -jar <your jar>. See "Create an executable JAR with Maven" here.

Spring Boot can also be told to produce a WAR file, in which case you'll likely choose to deploy it to a web container such as Tomcat or Jetty.

Plenty more details on Spring Boot deployment here.

Depends on your deployment. If you are planning to deploy your application to an existing Java EE Application Server (e.g. Tomcat), then standard approach is to perform a war build.

When you use fat jar approach, your application will be deployed on embedded application container provided by spring boot. Conduct Deploying Spring Boot Applications for more information.

Running spring-boot application as fat *.jar

It is possible to build so called fat JAR that is executable *.jar file with embedded application container (Tomcat as default option).There are spring-boot plugins for various build systems. Here is the one for maven: spring-boot-maven-plugin

To execute the kind of fat *.jar you could simple run command:

java -jar *.jar

Or using spring-boot-maven goal:

mvn spring-boot:run

Building spring-boot application as *.war archive

The other option is to ship your application as old-fashioned war file. It could be deployed to any servlet container out there. Here is step by step how-to list:

1. Change packaging to war (talking about maven's pom.xml)
2. Inherit main spring-boot application class from SpringBootServletInitializer and override SpringApplicationBuilder configure(SpringApplicationBuilder) method (see javadoc)
3. Make sure to set the scope of spring-boot-starter-tomcat as provided

More info in spring-boot documentation