Spring Boot vs Micronaut

Spring Boot and Micronaut are both JVM frameworks for building microservices, but they differ in architecture. Spring Boot uses runtime reflection for dependency injection and configuration. Micronaut uses compile-time annotation processing, eliminating reflection overhead entirely.

Compile-Time vs Runtime

Spring Boot scans the classpath at startup, discovers beans via reflection, and wires dependencies at runtime. This flexibility comes at a cost: slower startup and higher memory usage.

Micronaut processes annotations at compile time using Java annotation processors. By the time the application starts, all dependency injection, AOP proxies, and configuration are pre-computed. The result is near-instant startup and drastically lower memory consumption.

GraalVM Native Images

Micronaut was designed with GraalVM native compilation in mind. Since there is no runtime reflection, native images compile cleanly without extensive configuration. Spring Boot's reflection-heavy architecture requires declaring reflection classes in configuration files, making native compilation more complex.

The Ecosystem Trade-off

Spring Boot's ecosystem is the JVM world's largest: Spring Data (database access), Spring Security (authentication/authorization), Spring Cloud (distributed systems), Spring Batch (batch processing), and thousands of community libraries. Migrating from Spring Boot means giving up this ecosystem.

Micronaut covers common microservice needs (HTTP clients, service discovery, distributed tracing, configuration management) but cannot match Spring's breadth for specialized enterprise features.

System Design Perspective

For system design interviews, Micronaut signals cloud-native optimization awareness. Spring Boot signals enterprise pragmatism. Both produce solid microservice architectures. Choose based on operational priorities: startup speed (Micronaut) or ecosystem breadth (Spring Boot).

See our comparison guides and interview questions.