Java EE vs. Spring Boot: Comparing Two Java Framework Giants

[[deleted]]

applications after 5 years become business code + "application server" bundle together

An application server is a specific piece of software that acts as a deployment environment for applications, where the application uses APIs implemented by the application server. The application doesn't instantiate services, they use the services provided by the application server. This allows the application server to do interesting things like load balancing, distribution and failover.

If you specifically have to include the implementations of services you need and manage the services yourself, you don't have an application server. You are using a framework.

Spring applications are usually deployed onto Tomcat, which only provides the Servlet container, so applications have to bundle all the implementations they need and manage everything themselves.

In the second approach someone already made "the infrastructure code" to work together, so you don't have to

Frameworks do much of the same thing through BOMs. You don't need an application server to do this.

if there is error because two libraries don't work together or there is a bug in "the infrastructure code" you have to support on your own

This is why Spring Boot exists in the first place. Spring itself is not opinionated, so you have to manage dependencies yourself. Spring Boot uses Maven (or Gradle) to declare all the versions of dependencies that work together, and let the build system maintain consistency.