Note: This article reflects my personal point of view and insights based on my development experience.
The structure, formatting, and language refinement were assisted by AI to ensure clarity and readability.

Java has been a cornerstone of backend development for decades, powering everything from enterprise systems to cloud-native microservices. Kotlin, first released in 2011 and officially supported by Spring since 2017, offers a modern JVM alternative that has steadily gained traction among developers.

In 2025, both Java and Kotlin are mature, production-ready, and well-supported in the Spring ecosystem. But when starting a new project, it’s worth asking: which language provides more advantages today?

Built-In Features vs. External Dependencies

In Java, some advanced capabilities require additional libraries, such as:

• jSpecify – for nullability annotations
• Vavr – for functional programming utilities
• Lombok – for reducing boilerplate code
• MapStruct – for object mapping

These libraries are useful, but they add extra setup, dependency management, and potential compatibility issues over time.

Kotlin includes many similar capabilities natively. The result is:

• Cleaner code with fewer dependencies
• Reduced maintenance overhead
• Consistent, “built-in” language-level support rather than relying on third-party solutions

Tooling and Developer Experience

Java has made great strides in reducing verbosity, particularly with features like records, var, and pattern matching. However, Kotlin takes this a step further with language constructs that are inherently more concise and expressive.

This difference is not just about avoiding getters and setters. Kotlin’s design encourages:

• Declarative, readable code
• Fewer repetitive patterns
• A smoother learning curve for developers coming from modern languages

Java’s Rapid Evolution — and Kotlin’s Advantage

Java now follows a twice-yearly release cycle, which has brought meaningful improvements to the language. But some of Kotlin’s core features may take years to appear in Java — if they appear at all.

Because Kotlin runs on the JVM and is fully interoperable with Java, it benefits from JVM improvements and continues to add its own language features independently.

Key Kotlin Features for Modern Spring Development

Here are some Kotlin features that many teams find hard to give up once adopted:

1. Null-Safety and Nullability – Built into the type system to prevent NullPointerException.
2. Extension Functions – Add methods to existing classes without modifying them.
3. Higher-Order Functions – Functional programming as a first-class citizen.
4. Inline Functions & Lambdas with Receivers – Enable clean DSLs and reduce overhead.
5. Data Classes – Concise, immutable by default, and with auto-generated methods.
6. Default & Named Parameters – Avoids excessive constructor overloading.
7. Smart Casts – Automatic safe casting without extra syntax.
8. Destructuring Declarations – Unpack objects into variables easily.
9. Top-Level Functions – Functions outside classes for cleaner APIs.
10. Type Inference Everywhere – Less boilerplate, more clarity.
11. Rich Standard Library for Collections – Expressive and powerful operations.
12. Immutability by Default – Encourages safer and more predictable code.

Conclusion

When starting a new Spring project in 2025, both Java and Kotlin are solid choices.

• Java offers unmatched stability, a massive ecosystem, and rapid ongoing improvements.
• Kotlin provides modern language features, reduced boilerplate, and a developer experience that’s both concise and expressive from day one.

For teams looking to balance productivity, readability, and long-term maintainability, Kotlin presents a compelling option — especially when building new services on top of the Spring framework.