I have recently started on Java EE and having a tough time understanding it. I have read some answers here on SO but I still feel like there are some gaps in my understading. Basically, Java EE is a specification and application servers like TOMCAT, Glassfish etc., have the concrete implementations. Also, anyone can provide implementation for EE.
So, I have downloaded javax.sevlet-api-4.0.1-sources.jar from Maven repo and I can see that they are just Interfaces and I assume we just use them to build the project?
In tomcat lib folder there is a servlet-api.jar. is this the tomcat implementation of Servlet? and if it is, then is it possible to replace it with another servlet version implementation?
Now, Hibernate is the implementation of Persistence API. if i want to use Hibernate with Tomcat. I just need to add the Hibernate related jars to my application and can use them for both build and run? without actually getting the contract classes.
You need the servlet-api jar file when compiling your code, because that's where e.g. HttpServletRequest is. You don't need to include that jar with your application, because it is provided already by the Servlet Container you deploy your war file to, e.g. Tomcat.
With Tomcat, the implementation of the various servlet classes are in catalina.jar, at least for Tomcat 9, e.g. ApplicationHttpRequest is the class implementing HttpServletRequest. You don't need this to compile your code.