10 Questions About Quarkus You Were Too Shy to Ask

From performance myths to ecosystem realities – direct, no-fluff answers for Java architects evaluating Quarkus's potential and pitfalls.

Quarkus has generated significant buzz in the Java world, promising "Supersonic Subatomic Java." It boasts impressive startup times, low memory footprints, and a delightful developer experience. But beyond the headline features, maybe you've had some nagging questions – the kind you might hesitate to ask in a crowded forum or team meeting.

You're a Java developer or architect. You know your stuff. You've likely worked extensively with frameworks like Spring Boot, Jakarta EE, or others. You value productivity and solid technology. So, when a new contender like Quarkus appears, skepticism is healthy. Let's tackle some of those lingering questions directly and pragmatically.

Isn't Quarkus just another Java framework? What's really different?

It's a fair question. At first glance, it looks familiar: annotations, dependency injection, familiar APIs (JAX-RS, JPA, etc.). However, the core differentiator isn't just what it does, but when it does it.

Traditional Java frameworks (like Spring Boot in its default configuration) do a lot of work at runtime:

• Scanning the classpath for annotations.

• Building dependency injection contexts.

• Parsing configuration files.

• Setting up proxies and interceptors.

• Initializing framework components.

Quarkus fundamentally shifts this paradigm. It performs as much of this work as possible at build time. During compilation, Quarkus:

• Analyzes your code and its dependencies.

• Wires up CDI beans (using its optimized DI solution, ArC).

• Generates bytecode for proxies and framework integration.

• Records boot sequences.

• Pre-processes configuration.

The result is a lean runtime artifact (either a JAR or a native executable) that already knows how the application is structured. It doesn't need to spend precious milliseconds (or seconds) figuring things out when it starts. This build-time optimization is the secret sauce behind its speed and low resource consumption, even on the standard JVM.

Okay, but why is it so fast and memory-efficient? Is it just GraalVM?

GraalVM native compilation is a major contributor to peak performance and minimal footprint, but it's not the whole story. Quarkus is designed to be efficient even when running on a standard JVM.

• Build-Time Metadata: As mentioned above, resolving dependencies, processing annotations, and generating necessary boilerplate at build time dramatically reduces startup work.

• Optimized Extensions: Quarkus uses an extension model. Each extension (e.g., quarkus-resteasy-reactive, quarkus-hibernate-orm) is specifically designed to integrate its library efficiently, performing initialization steps at build time where possible.

• ArC (Dependency Injection): Quarkus's CDI implementation, ArC, is built with build-time processing and runtime performance in mind. It avoids runtime reflection where possible and generates optimized bean management code.

• Reactive Core: Many core components, especially networking (Vert.x underneath RESTEasy Reactive), are built on a non-blocking, reactive foundation, leading to better resource utilization under load.

GraalVM Native Image takes this further by:

• Performing aggressive static analysis.

• Eliminating dead code (classes, methods, fields not used).

• Pre-initializing parts of the application heap into the executable.

• Compiling Java bytecode directly into native machine code ahead-of-time (AOT).

This eliminates the JVM's warmup time and significantly reduces the memory overhead associated with the JVM itself and its JIT compiler. So, Quarkus is fast on the JVM; native compilation via GraalVM makes it even faster and smaller.

Do I have to use GraalVM and native compilation?

No, absolutely not. Quarkus applications run perfectly well on standard JVMs (like HotSpot or OpenJ9). Running on the JVM is often the default development and deployment target for many teams.

You get significant benefits even in JVM mode:

• Much faster startup times compared to traditional frameworks.

• Lower memory usage compared to traditional frameworks.

• Access to the full range of JVM tooling, monitoring, and debugging capabilities you're used to.

• No need to deal with potential native image limitations (see Question 8).

Native compilation is an option you choose when maximum performance, minimal footprint (e.g., for serverless functions, containers with tight resource limits), or instant startup are critical requirements. You can develop and test primarily in JVM mode and then build a native executable as part of your CI/CD pipeline if needed.

Is Quarkus only for microservices and serverless?

While Quarkus shines in resource-constrained environments like microservices and serverless functions due to its efficiency, it's not limited to them. It's a versatile framework suitable for:

• Monolithic Applications: Its efficiency benefits apply equally well to larger applications, potentially reducing hosting costs and improving performance.

• Command-Line Tools: Fast startup makes it great for CLI utilities.

• Event-Driven Applications: Excellent integration with Kafka, AMQP, and Camel makes it a strong choice for reactive systems.

• Web Applications: Both traditional MVC-style (using Qute templates or JSPs via extensions) and modern reactive front-ends are well-supported.

Think of it as a modern Java stack optimized for cloud-native environments, but flexible enough for various application types.

Can I still use my favorite Java libraries and standards (JPA, JAX-RS, Bean Validation, etc.)?

Yes, largely. Quarkus embraces established Java standards. It provides extensions for many Jakarta EE specifications and MicroProfile APIs:

• Jakarta EE: JAX-RS (RESTEasy Reactive/Classic), JPA (Hibernate ORM), CDI (ArC), Bean Validation (Hibernate Validator), JSON-B/JSON-P, JTA, and more.

• MicroProfile: Config, Health Check, Metrics, OpenAPI, Rest Client, Fault Tolerance, JWT RBAC.

Beyond standards, the Quarkus ecosystem includes extensions for popular libraries like:

• Apache Kafka Clients

• Database drivers (JDBC, Reactive SQL Clients)

• Apache Camel

• Elasticsearch clients

• Messaging (AMQP, MQTT)

• Templating engines (Qute)

• Testing frameworks (JUnit 5, REST Assured)

If a library isn't directly supported via an extension, you can often use it as a regular dependency, especially in JVM mode. For native compilation, libraries relying heavily on reflection, dynamic classloading, or JNI might require specific configuration or might not be fully compatible without a dedicated extension.

Spring Boot has a massive ecosystem. Can Quarkus compete? How do I find integrations?

Spring Boot undeniably has a vast ecosystem built over many years. Quarkus's ecosystem is younger but catching up and growing further rapidly and is arguably more curated.

• Extension Model: Quarkus focuses on high-quality, well-integrated extensions. These aren't just wrappers; they actively participate in the build-time optimization process.

• Core Use Cases: Quarkus covers the most common enterprise Java needs very well (web, data, messaging, cloud integration).

• Discoverability: You can find available extensions via:

  • The Quarkus website (quarkus.io) under "Extensions".

  • Using the Quarkus CLI: quarkus extension list.

  • The code.quarkus.io project generator.

• Community & Red Hat: Backed by Red Hat and a vibrant community, new extensions are constantly being developed.

While you might not find a Quarkus extension for every niche library that has a Spring Boot starter, the core platform is robust, and the most critical integrations are available. For libraries without extensions, JVM mode often works fine.

How does the "Developer Joy" thing actually work? Is that live reload reliable?

"Developer Joy" centers around Quarkus's Dev Mode (quarkus dev). It's more sophisticated than simple class reloading:

• Background Compilation: When you save a change (Java code, resource file, config property), Quarkus detects it and recompiles incrementally in the background.

• Request-Based Reload: The application doesn't fully restart on every change. Instead, when the next HTTP request (or other relevant event) arrives, Quarkus seamlessly serves it using the updated code.

• State Preservation (Sometimes): For simple changes, it can often preserve application state. For more significant changes (e.g., modifying bean structure), a quick restart might occur, but it's still vastly faster than traditional redeploy cycles.

• Integrated Dev UI: Provides dashboards for configuration, beans, logs, testing, etc., accessible in your browser during development.

• Continuous Testing: Run tests automatically in the background whenever code changes.

Is it reliable? Generally, yes, remarkably so. It handles changes to Java code, configuration files (application.properties), and resources smoothly. Occasionally, complex refactorings or changes to build dependencies might require a manual restart of Dev Mode, but the feedback loop is drastically shorter than traditional deploy-wait-test cycles.

What's the catch? Is it harder to debug native images? Are there limitations?

Like any technology, Quarkus involves trade-offs, particularly concerning native compilation:

• Native Build Times: Compiling a native executable takes significantly longer than building a standard JAR (minutes vs. seconds). This is typically done in CI/CD, not repeatedly during development.

• Native Debugging: Debugging a native executable is different from JVM debugging. While possible using tools like GDB and specific IDE integrations, it can be less straightforward than standard Java debugging. Often, thorough testing in JVM mode catches most issues.

• Reflection & Dynamic Features: Native compilation relies on static analysis. Code that uses reflection, dynamic classloading, JNI, or serialization heavily might require explicit configuration (using @RegisterForReflection or reflect-config.json) to tell the GraalVM native image builder which elements need to be included and accessible at runtime. Quarkus extensions handle this automatically for supported libraries, but it can be a hurdle for unsupported third-party dependencies in native mode.

• Build Environment: Building native executables requires GraalVM and potentially native build tools (like gcc, glibc-devel, zlib-devel on Linux, or Xcode Command Line Tools on macOS, or Visual Studio C++ Build Tools on Windows) to be installed. Containerized builds simplify this.

These aren't necessarily "catches" but rather known characteristics of AOT compilation. The limitations primarily affect native mode; JVM mode remains largely unaffected.

Is Quarkus mature enough for serious production use? Who's using it?

Yes. Quarkus has been production-ready for several years now.

• Backing: It's heavily backed and supported by Red Hat, which uses it in its own products and supports a downstream build called “Red Hat Build of Quarkus”.

• Adoption: It's used in production by numerous companies across various industries, from large enterprises (like Vodafone, Lufthansa Technik, Deutsche Bank - See the Quarkus website for case studies) to smaller startups.

• Release Cadence & LTS: Quarkus has a frequent release cadence for new features and regular Long-Term Support (LTS) releases for stability-focused users.

• Community & Support: There's a large, active community and commercial support available through Red Hat.

While newer than Spring Boot, it has rapidly matured and proven itself in demanding production environments.

Does Quarkus replace Spring Boot? Is it an "either/or" decision?

It's rarely a simple "either/or." They are both powerful Java stacks but have different philosophies and sweet spots.

• Quarkus Strengths: Unmatched performance/efficiency (especially native), fast dev cycle (Dev Mode), can be super optimized for containers/serverless, strong integration with Kubernetes, adherence to Jakarta EE/MicroProfile standards.

• Spring Boot Strengths: Vast community knowledge base, choice of tooling, flexible configuration options, strong track record across a huge range of application types.

Consider Quarkus when:

• You want the fastest possible developer feedback loop.

• You prefer standard Jakarta EE/MicroProfile APIs.

• Startup time and memory footprint are critical (containers, serverless, edge/embedded).

• You are building distributed cloud-native applications

Spring Boot remains a solid choice when:

• You heavily rely on specific Spring Cloud or other Spring ecosystem projects not readily available in Quarkus.

• Your team has deep existing expertise in Spring.

• The runtime performance difference isn't the primary driver for your specific application.

Many organizations use both frameworks for different projects based on specific needs. They can coexist. Quarkus offers a compelling alternative, particularly for modern, resource-sensitive applications, but it doesn't invalidate the strengths of Spring Boot.

Hopefully, this tackles some of those questions you might have been pondering. Quarkus represents a significant evolution in the Java landscape, optimizing for a cloud-native world while retaining the power and familiarity of Java. The best way to truly understand it?

Give quarkus dev a try.