In recent years, Kotlin has received tremendous popularity as a programming language among developers, reasons for this popularity are its conciseness, expressiveness, and its interoperability with Java language. Adopting Kotlin for server-side development can offer a number of advantages such as increasing productivity, safer code, and robustness.

To leverage these benefits of Kotlin language developers rely on Framework that supports Kotlin for server-side programming. Today in this article we will look into to top seven server-side Kotlin frameworks that are widely adopted by developers and businesses.

What is Kotlin?

Kotlin is a modern programming language that was introduced in 2011 as an alternative to Java, targeting the Java Virtual Machine (JVM). Kotlin was initially launched to be used as a plugin in Android Studio. Later in May 2017, it was declared the official Android development language by Google. Kotlin is not limited to Android development but is also used in various software development domains, which include backend development, desktop application development, and data science and analytics.

The reason for introducing Kotlin language was to address various lacking features in existing programming languages, mainly Java while maintaining seamless interoperability with Java. Nowadays, Kotlin has become the most popular among developers, and its community has increased on a large scale. The reasons behind Kotlin’s increasing adoption in server-side development are its elegant features such as null safety, coroutine, scope functions, concise syntax, and more. It presents a more modern, effective as well as fun development experience by fixing many issues in Java without breaking compatibility with current Java codebases.

Why Kotlin for Server-Side Development?

Several factors influence Kotlin’s server-side development adoption, including:

• Conciseness and Readability: Kotlin eliminates the need for writing repetitive code, allowing developers to concentrate on crafting succinct and legible codes. This ensures a faster time to market and less complicated maintenance processes.

• Null Safety: The most common cause of Java runtime errors is null pointer exceptions. This potentiality is reduced in Kotlin which has the feature of built-in null safety thereby enhancing code reliability.

• Coroutines for Asynchronous Programming: With coroutines, Kotlin eases asynchronous programming thus making it easier to write non-blocking code. In a server-side application where concurrent requests have to be handled effectively, this is particularly useful.

• Interoperability with Java: Due to its compatibility with Java, developers using Kotlin can take advantage of already made Java frameworks and libraries. Consequently, enterprises migrating from Java to Kotlin are able to progressively adapt without changing their entire source code.

• Expressive Syntax: The modern syntax style utilized in Kotlin like extension functions, smart casts, or data classes helps improve the quality of code produced by developers as well as their productivity levels.

Top 7 Server-Side Kotlin Framework

Here are the 7 best Kotlin frameworks that are widely adopted by developers and businesses to build high-performing and scalable server-side applications:

1. Ktor

Ktor is a lightweight asynchronous framework that is developed by JetBrains(Creator of Kotln) and written with Kotlin language, mainly used to build asynchronous servers and clients easily. Ktor offers simple and intuitive Domain Specific Language(DSL) that enables developers to define routes, manage requests, and configure server requirements. Ktor supports built-in Websockets, HTTP/2, and coroutine that enable developers to develop high-performance and more scalable server applications easily.

Key Features

• A lightweight and flexible framework that helps in building asynchronous server and client applications.
• Initiative DSL support for route defining, managing requests, and configuring servers.
• Leverages built-in support for WebSockets, HTTP/2, and coroutine.
• Supports seamless integration of Kotlin features that enable developers to enhance productivity.

Limitations of Ktor

• Third-party libraries are very limited compared to other well-established frameworks such as Spring Boot.
• Smaller community support compared to other frameworks.

2. Sprint Boot

Sprint Boot is a popular and widely used Java framework that can be easily integrated with Kotlin and offers a rich ecosystem for building enterprise applications. Using Kotlin’s powerful features such as concise syntax, null safety, and coroutine developers can leverage the power of Spring Boot for creating RESTful APIs, Web applications, and microservices. Spring Boot provides support for Dependency Injections, data access, and security, making it an ideal choice for creating scalable and maintainable server-side applications.

Key Features

• A rich ecosystem and large community benefit developers to build efficient enterprise applications.
• An ideal choice for building RESTful APIs, microservices, and Web apps.
• Allows seamless Integration with Kotlin and leverages its features such as null safety, and code conciseness.
• Excellent choice for businesses for production-ready applications.

Limitations of Spring boot

• It has a Steeper learning curve mainly for beginners with a Spring Boot environment.
• Consumes higher memory than other lightweight frameworks such as Ktor.

3. Vert.X

Vert.X is a reactive toolkit that is used to build event-driven and high-performance applications on JVM. Vert.X provides a complete environment that allows developers to use multiple programming languages such as Java, Kotlin, and JavaScript. Developers can leverage its reactive programming principles which enable developers to implement I/O operations which makes it the perfect option to choose for responsive server-side applications. Vert.X supports modular architecture and a rich ecosystem that allows developers to build reusable high-performance server-side applications.

Key Features

• Offers reactive toolkit that enables developers to build event-driven, high-performance applications.
• For responsive and resilient applications Vert.X supports Non-blocking I/O operations solutions.
• Modular architecture helps in writing easy maintainable and scalable code.
• Ideal choice for creating scalable and manageable systems.

Limitations of Vert.X

• Developers who are new to reactive programming may find difficulties in understanding complex structures.
• Limited community support compared to other frameworks.

4. Ktor-GraphQL

Creating GraphQL APIs using Kotlin becomes easier and more fun with Ktor-GraphQL, as its tool is specifically designed for Kotlin and GraphQL. It works seamlessly with Ktor and allows developers an easy way to configure GraphQL easily. This configuration includes steps such as structuring data and how to manage them. Developers can leverage Kotlin’s features such as null safety, and concise syntax to develop efficient GraphQL APIs, which means it allows developers to build APIs that can work well with modern apps and can changed when needed.

Key Features

• Leverages Kotlin’s type safety and concise syntax for building high-performance GraphQL APIs.
• Offers rapid prototyping and deploying GraphQL APIs seamlessly.
• Allows developers to write flexible and efficient APIs with the use of GraphQL’s query-based approach.
• Promotes Kotlin-specific implementation of GraphQL specification.

Limitations of Ktor-GraphQL

• Limited resources and documentation make it difficult for beginners.
• Limited community support compared.

5. Jooby

On number 5th in our list is Jooby which is a lightweight and modular framework used for building web applications using Kotlin and Java. By using Jooby’s design and expressive DSL, it became easier to develop RESTful APIs, Web services, and microservices. The modular architecture of Jooby allows developers to use various components such as Dependency Injections, routing, and templating as per business requirements. Jooby promotes convention over configuration which adds consistency in code mainly when multiple developers are working on the same project.

Key Feature

• The lightweight and modular Kotlin framework allows developers to build modern web applications.
• Simplifies the RestfulAPI development with the use of expressive DSL.
• An ideal choice for building scalable and maintainable server-side applications.
• Promoting conventions over configuration helps developers maintain the codebase easily.

Limitations of Jooby

• Limited adoption among developers and businesses.
• Limited community support compared to Ktor and Spring Boot.

6. KGraphQL

KGraphQL is also called the Kotlin-first library and is used for building type-safe GraphQL servers with a minimal boilerplate codebase. By leveraging powerful features of Kotlin such as DSLs and type interfaces it offers intuitive APIs for defining schemas. It supports static typing which identifies errors at compile time and helps in eliminating run-time errors. Its lightweight and extensible design nature encourages developers to rapidly prototype applications.

Key Features

• Kotlin-first library for building type-safe(null safety) GraphQL servers.
• Support of statically typed checks helps in eliminating errors that can occur at run time.
• Offers a lightweight and extensible design that makes it an excellent choice for rapid prototyping.
• Supportive API for defining GraphQL schemas and resolvers.

Limitations of KGraphQL

• Fewer features are available compared to mature frameworks such as Ktor and Spring Boot.
• KGraphQL is less favorable for large-scale industry projects.

7. Http4k

Another lightweight toolkit in our list is Http4k which allows developers to build cloud-native applications using Kotlin. Http4k follows functional programming principles that enforce immutability and compositions to create HTTP servers and client applications with concise code. It focuses mainly on simplicity that enables developers to build scalable and testable HTTP endpoints by eliminating complex code structures. Http4k provides a complete server-side Kotlin development solution for developing microservices and serverless functions.

Key Features

• Functional programming principles support and promote concise and expressive code.
• Http4k is an ideal Kotlin framework for developing serverless functions and microservices.
• Allows developers to create scalable and easily testable HTTP endpoints with composition and immutability.
• Its focus on simplicity and minimalism makes it a perfect choice for server-side Kotlin development.

Limitations of Http4k

• Compared to a mature and rich framework Http4k has limited advanced features.
• Http4k has a smaller community and less mature ecosystem compared to other frameworks.

Top 7 Server Side Kotlin Framework: Comparison Table