Why Java Server‑Side Developers Hesitate to Adopt Kotlin – Key Insights

After 15 years of using Java, the author wrote his first line of Kotlin five years ago, replacing Spring with Utterlyidle and using Totallylazy for functional programming, while remaining loyal to IntelliJ and its Java tools.

Initially the team also experimented with Scala, but its complexity and slow build times limited its appeal.

In 2017 Google announced Kotlin as an official Android language, prompting the team to evaluate Kotlin for server‑side development, and most developers tried it.

The author was impressed by Kotlin’s efficiency and safety, noting its excellent interoperability with Java that allows incremental adoption without disrupting existing work.

Motivated by this interest, they created http4k, a Kotlin HTTP application toolkit, and organized Kotlin workshops to help other teams adopt the language.

Despite growing usage, many teams still resist Kotlin for various reasons, which the author outlines below.

“We don’t have time to learn a new language”

This reflects the common “busy chopping wood, no time sharpening the axe” scenario, often tied to deeper technical debt and productivity issues. A capable Java developer can grasp Kotlin basics in hours and improve efficiency within days.

“Every Java version gets better”

While Java evolves rapidly, it still lags behind Kotlin for simple tasks like handling nulls, and Kotlin offers many features that can be adopted incrementally.

“As Java developers we’re proud of our language”

Identity tied to a language can hinder change, yet no Java developer has fallen behind by using Kotlin; instead, they seek tools that fit their needs.

“Kotlin is hype and its future is uncertain”

Since Google’s endorsement, frameworks like Spring and Micronaut have embraced Kotlin, reducing earlier resistance.

“I use Eclipse and don’t want to switch to IntelliJ”

Kotlin support in Eclipse is limited compared to JetBrains IDEs, which remain the best experience for Kotlin development.

“Kotlin developers are expensive and hard to hire”

Salary data shows Kotlin engineers earn slightly more, but senior Java developers often adopt Kotlin first, creating the perception of higher cost; however, hiring is not unusually difficult.

“Kotlin is too complex”

Kotlin balances ease of use with advanced features and good Java interop, but teams should start with basic features and gradually adopt more sophisticated ones to keep code understandable.

“Using two languages in one codebase is confusing”

When Kotlin and Java coexist, converting old Java code to Kotlin first can avoid massive rewrites and enable incremental migration.

“We prefer Java”

Some projects work fine with Java, but resistance usually stems from lack of time or interest rather than technical limitations.

“I don’t see any benefit from Kotlin”

Java developers may overlook Kotlin’s conciseness and safety, but once they try it, many realize the advantages.

Some Thoughts

Adopting a new language in an ongoing project is challenging; resistance is influenced by project needs, personal reasons, and language characteristics. The author encourages Java server‑side developers to give Kotlin a try when the opportunity arises.