Kotlin originated at JetBrains, the company behind IntelliJ IDEA, in 2010, and has been open source since 2012. The Kotlin team currently has more than 90 full-time members from JetBrains, and the Kotlin project on GitHub has more than 300 contributors. JetBrains uses Kotlin in many of its products including its flagship IntelliJ IDEA.
Kotlin is a great fit for developing server-side applications, allowing to write concise and expressive code while maintaining full compatibility with existing Java-based technology stacks and a smooth learning curve:
- — Expressiveness: Kotlin’s innovative language features, such as its support for type-safe builders and delegated properties, help build powerful and easy-to-use abstractions.
- — Scalability: Kotlin’s support for coroutines helps build server-side applications that scale to massive numbers of clients with modest hardware requirements.
- — Interoperability: Kotlin is fully compatible with all Java-based frameworks, which lets you stay on your familiar technology stack while reaping the benefits of a more modern language.
- — Migration: Kotlin supports gradual, step by step migration of large codebases from Java to Kotlin. You can start writing new code in Kotlin while keeping older parts of your system in Java.
- — Tooling: In addition to great IDE support in general, Kotlin offers framework-specific tooling (for example, for Spring) in the plugin for IntelliJ IDEA Ultimate.
- — Learning Curve: For a Java developer, getting started with Kotlin is very easy. The automated Java to Kotlin converter
included in the Kotlin plugin helps with the first steps. Kotlin Koans offer a guide through the key features of the language
with a series of interactive exercises.
Frameworks for Server-side Development with Kotlin
- — Spring makes use of Kotlin’s language features to offer more concise APIs, starting with version 5.0. The online project
generator allows to quickly generate a new project in Kotlin.
- — Vert.x, a framework for building reactive Web applications on the JVM, offers dedicated support for Kotlin, including full documentation.
- — Ktor is a Kotlin-native Web framework built by JetBrains, making use of coroutines for high scalability and offering an easy to use and idiomatic API.
- — kotlinx.html is a DSL that can be used to build HTML in a Web application. It serves as an alternative to traditional templating systems such as JSP and FreeMarker.
- — The available options for persistence include direct JDBC access, JPA, as well as using NoSQL databases through their Java drivers. For JPA, the kotlin-jpa compiler plugin adapts Kotlin-compiled classes to the requirements of the framework.
Deploying Kotlin Server-side Applications
Kotlin applications can be deployed into any host that supports Java Web applications, including Amazon Web Services, Google
Cloud Platform and more.
To deploy Kotlin applications on Heroku, you can follow the official Heroku tutorial.
AWS Labs provides a sample project showing the use of Kotlin for writing AWS Lambda functions.
Users of Kotlin on the Server Side
Corda is an open-source distributed ledger platform, supported by major banks, and built entirely in Kotlin.
JetBrains Account, the system responsible for the entire license sales and validation process at JetBrains, is written in 100% Kotlin and has been running in production since 2015 with no major issues.
The Creating Web Applications with Http Servlets and Creating a RESTful Web Service with Spring Boot tutorials show you how you can build and run very small Web applications in Kotlin.
For a more in-depth introduction to the language, check out the reference documentation on this site and Kotlin Koans.
Using Kotlin for Android Development
Kotlin is a great fit for developing Android applications, bringing all of the advantages of a modern language to the Android
platform without introducing any new restrictions:
- — Compatibility: Kotlin is fully compatible with JDK 6, ensuring that Kotlin applications can run on older Android devices with no issues. The Kotlin tooling is fully supported in Android Studio and compatible with the Android build system.
- — Performance: A Kotlin application runs as fast as an equivalent Java one, thanks to very similar bytecode structure. With Kotlin’s support for inline functions, code using lambdas often runs even faster than the same code written in Java.
- — Interoperability: Kotlin is 100% interoperable with Java, allowing to use all existing Android libraries in a Kotlin application. This includes annotation processing, so databinding and Dagger work too.
- — Footprint: Kotlin has a very compact runtime library, which can be further reduced through the use of ProGuard. In a real application, the Kotlin runtime adds only a few hundred methods and less than 100K to the size of the .apk file.
- — Compilation Time: Kotlin supports efficient incremental compilation, so while there’s some additional overhead for clean builds, incremental builds are usually as fast or faster than with Java.
- — Learning Curve: For a Java developer, getting started with Kotlin is very easy. The automated Java to Kotlin converter included in the Kotlin plugin helps with the first steps. Kotlin Koans offer a guide through the key features of the language with a series of interactive exercises.
Kotlin for Android Case Studies
Kotlin has been successfully adopted by major companies, and a few of them have shared their experiences:
- — Pinterest has successfully introduced Kotlin into their application, used by 150M people every month.
- — Basecamp’s Android app is 100% Kotlin code, and they report a huge difference in programmer happiness and great improvements in work quality and speed.
- — Keepsafe’s App Lock app has also been converted to 100% Kotlin, leading to a 30% decrease in source line count and 10% decrease in method count.
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