Devops Monk

Every year, someone asks: “Should we use Spring Boot or Quarkus?” In 2026, both frameworks are mature, both run natively, and both work well on Kubernetes. The differences come down to developer experience, ecosystem size, and specific performance characteristics.

This is an honest comparison with real numbers, not marketing claims.

The Frameworks at a Glance

Spring Boot 4 (November 2025): Built on Spring Framework 7. The de-facto standard for enterprise Java. Powers 55–65% of enterprise Java applications (JetBrains 2025 survey). Strong ecosystem from years of investment.

Quarkus 3.x (ongoing): Red Hat’s Kubernetes-native Java framework. Designed from the ground up for containers and serverless. Compile-time dependency injection (no reflection), developer services, live coding.

Micronaut is included where relevant — it occupies similar ground to Quarkus and is worth knowing.

Benchmark Numbers

Numbers from a standardised benchmark: REST API with one PostgreSQL query, running on 4 vCPU / 8 GB host.

Startup Time

Spring Boot JVM startup is slower because of classpath scanning, bean post-processing, and JIT compilation warm-up. Quarkus does much of this at build time.

In native mode, all three are fast (under 150ms). For most production services that run 24/7, startup time difference is irrelevant. For AWS Lambda cold starts, 49ms vs 104ms matters.

Memory Usage (idle)

Spring Boot uses more memory at idle because of its larger runtime footprint. Spring Boot 4’s modularisation reduces this compared to Boot 3.

Throughput (req/s under load, 200 concurrent)

Under sustained I/O-bound load, throughput differences are small (10–15%). Both frameworks handle modern production workloads easily. The throughput gap narrows further with PGO (Profile-Guided Optimization) on GraalVM.

Build Time

Quarkus’s live reload for JVM mode is faster than Spring DevTools because Quarkus does less work at runtime (more processed at build time). Spring Boot 4’s native builds are slightly slower than Quarkus native.

Developer Experience

Spring Boot Strengths

Ecosystem depth: Spring Security, Spring Data, Spring Batch, Spring Integration, Spring AI, Spring Modulith — all mature, extensively documented, with years of Stack Overflow answers.

Flexibility: Spring Boot supports JPA, JDBC, reactive, WebFlux, MVC, and virtually any library. If a library exists in Java, there’s probably a Spring Boot starter for it.

Familiarity: 65% of Java developers know Spring. Hiring is easier. Onboarding is faster.

Spring AI: The most complete AI integration layer for Java, with support for Claude, OpenAI, Gemini, Ollama, vector stores, RAG, and MCP. Quarkus has LangChain4j integration but it’s less mature.

Spring Boot DevTools: Live reload for development, though slower than Quarkus.

Quarkus Strengths

Dev Services: Start your app in dev mode and Quarkus automatically spins up Docker containers for PostgreSQL, Redis, Kafka — no configuration needed:

quarkus dev
# Quarkus automatically starts: postgres:15, redis:7, kafka:3.5
# No docker-compose.yaml needed

This is genuinely impressive for developer experience. Spring Boot’s equivalent requires manual TestApplication setup.

Live coding: Quarkus’s live reload is nearly instant — it hot-deploys Java class changes without a restart.

Unified native build UX: Quarkus’s native image support has fewer issues than Spring Boot’s in practice. The @RegisterForReflection annotation and automatic hint discovery work more reliably for third-party libraries.

Dev UI: Built-in web UI at http://localhost:8080/q/dev showing beans, configuration, extensions, OpenAPI, Swagger UI — useful during development.

Spring Boot Feature: Condition Evaluation Report

# Spring Boot shows exactly why each auto-configuration fired or was skipped
java -jar app.jar --debug 2>&1 | grep -A3 "CONDITIONS EVALUATION REPORT"

Quarkus Feature: Arc Container Diagnostics

# Quarkus shows the CDI bean graph at startup
quarkus dev -Dquarkus.arc.dump-build-time-output=true

Code Comparison

A simple REST endpoint looks nearly identical:

Spring Boot:

@RestController
@RequestMapping("/orders")
public class OrderController {

    private final OrderService orderService;

    public OrderController(OrderService orderService) {
        this.orderService = orderService;
    }

    @GetMapping("/{id}")
    public ResponseEntity<Order> getOrder(@PathVariable Long id) {
        return orderService.findById(id)
            .map(ResponseEntity::ok)
            .orElse(ResponseEntity.notFound().build());
    }
}

Quarkus:

@Path("/orders")
@Produces(MediaType.APPLICATION_JSON)
public class OrderResource {

    @Inject
    OrderService orderService;

    @GET
    @Path("/{id}")
    public Response getOrder(@PathParam("id") Long id) {
        return orderService.findById(id)
            .map(order -> Response.ok(order).build())
            .orElse(Response.status(Response.Status.NOT_FOUND).build());
    }
}

Spring Boot uses Spring MVC annotations; Quarkus uses JAX-RS. Both are readable. The choice doesn’t significantly affect productivity.

Database access comparison:

Spring Boot with Spring Data JPA:

public interface OrderRepository extends JpaRepository<Order, Long> {
    List<Order> findByCustomerIdAndStatusOrderByCreatedAtDesc(Long customerId, OrderStatus status);
}

Quarkus with Panache:

@ApplicationScoped
public class OrderRepository implements PanacheRepository<Order> {
    public List<Order> findByCustomerAndStatus(Long customerId, OrderStatus status) {
        return find("customerId = ?1 and status = ?2 order by createdAt desc", customerId, status).list();
    }
}

Both are concise. Spring Data’s method name convention works for simple queries; Quarkus Panache’s query strings are more flexible for complex cases.

Ecosystem and Library Support

Spring Boot wins on ecosystem breadth

Where Quarkus is competitive or better

• Reactive: Quarkus Mutiny (reactive library) is more idiomatic than Spring WebFlux
• gRPC: Both have solid support; Quarkus’s is slightly simpler to configure
• Serverless (AWS Lambda): Quarkus’s native startup advantage matters here
• Kubernetes-native: Quarkus generates K8s YAML, Helm charts, and Knative configuration automatically

Migration Complexity

Spring Boot → Quarkus

Significant rewrite required:

• @Autowired → @Inject
• Spring MVC annotations → JAX-RS
• Spring Data JPA → Panache or standard JPA
• Spring Security → Quarkus OIDC/Security
• application.properties → application.properties (similar format, different keys)

Estimate: 2–4 weeks for a mid-sized service, plus ramp-up time for the team.

Spring Boot 2.x → 4.x (same framework)

Covered in the Spring Boot Migration Guide. Automated tooling (OpenRewrite) handles most of the mechanical changes.

Decision Framework

Choose Spring Boot when:

• Your team knows Spring — retraining costs are real
• You need Spring Batch, Spring Integration, or Spring AI
• You have a large existing codebase in Spring
• You need maximum library compatibility
• You’re hiring — Spring skills are more available in the market
• Your service is long-running (startup time irrelevance)

Choose Quarkus when:

• You’re building serverless functions (Lambda, Knative) where cold start is critical
• Your team is starting fresh and open to learning
• Memory per pod cost is a significant operational concern (autoscaling at scale)
• You want the best Kubernetes-native development experience
• You’re building a reactive, event-driven system

The honest answer for most teams

If you’re already on Spring Boot, upgrading to Spring Boot 4 is the right move. The performance improvements (Boot 4 modularisation + Virtual Threads + GraalVM native) close most of the startup and memory gap with Quarkus.

If you’re starting a brand new greenfield project and your team has no Spring background, Quarkus is a legitimate choice — especially for serverless workloads.

Summary

Spring Boot and Quarkus are both production-ready in 2026. Quarkus has better startup time and memory usage in JVM mode; the gap narrows significantly in native mode. Spring Boot wins on ecosystem breadth, team familiarity, and library compatibility. For existing Spring Boot teams, upgrading to Boot 4 is a better investment than migrating to Quarkus. For new greenfield projects (especially serverless), Quarkus is worth serious consideration.