Spring boot 2 gradle plugin - Upgrade from Spring Boot 1.5

I am using Gradle 4.7 and I am trying to re-configure project build scripts for Spring boot 2. I followed the steps, but I keep getting bootJar not found exception.
‘Task ‘bootJar’ not found in project ‘:content:content-services’.’
This is a web application having dependencies of sub components structured in logical modules built on there own. Basically jar dependencies. The thing is that some of them don’t have manifest built or jar specified in gradle.buld file.
My question si what is the differenc ebetween jar and bootJar?
I tried to enable jar, because by default it is disabled,but it didn’t work. I am gettign the same error.
I could nto find in the web an example where it whos how to configure your project with bootJar built.
Do i still need jar dependencies?
I am also new to gradle so I appologize if these questions seem simplistic. i promise I thought about this and googled for some time.

bootJar would be fatpacked executable jar that spring plugin makes.

Thank you. Can you elaborate? That does not solve my problem.

sorry, unfortunately I don’t know how to help further with just this information. Can you create a demo project that replicates the error?

It would take too long. I just want to better understand why tehre is bootJar also besides jar. That understanding would lead me to solve the issue.

This sample project on spring.io has this issue.