What are the differences using spring boot with Kotlin and with Java?

Question

What are the differences using spring boot with Kotlin and with Java?

Kotlin is among the three languages you could choose to start your app with https://start.spring.io. So it's supported by the spring boot team. I used it to develop some microservices and as far as I know everything went fine at the end but I would like to have some feedback from other developers because I try to convince my new team to start our new microservices in Kotlin.

Pros:

• Null safety
• Clearer code
• Val over var

Cons:

• Mockito not Kotlin friendly (I switched to mockk)
• Code coverage was not out of the box (we had to develop our own plugin)
• Risk to have Java moving faster than Kotlin

Answer 1

Since Kotlin is simply a dependency and plugin for Maven (that's it!). It's such a nice, compact, easy-to-grok language that removes all the syntactic fat (opposed to syntactic sugar) that Java provides.

From 5.0.0 onward Kotlin has first-class support from Spring, which effectively means it has all the same guarantees as Java in terms of code working correctly.

Kotlin itself has a ton of interoperability features to smoothly integrate with any already existing Java library, which means you have the same freedom of choice.

Kotlin's Java interop is amazing, and was by no means an afterthought by Jet Brains. Thus Kotlin works nicely with Spring, which provides a lot of the boilerplate functionality for web applications, especially Spring Boot.

These are some points which You already mentioned but I will still have a say about it. Kotlin has a much more compact syntax and its type system allows for much more robust code through null-safety, sealed classes, and immutable/mutable collection distinction, which together significantly reduce development time on any project.