Helidon
By Oracle
Helidon is a set of Java libraries from Oracle for building microservices, available in two programming models: Helidon SE, a small, dependency-light framework built directly on Java's reactive and virtual-thread capabilities, and Helidon…
Definition
Helidon is a set of Java libraries from Oracle for building microservices, available in two programming models: Helidon SE, a small, dependency-light framework built directly on Java's reactive and virtual-thread capabilities, and Helidon MP, which implements the MicroProfile specification for teams wanting a more familiar Jakarta EE-style programming model. It is designed for cloud-native deployment, with fast startup and low memory footprint that make it well suited to containerized and serverless environments.
Overview
Helidon was created by Oracle to give Java developers a modern option for building microservices that could compete with the fast startup times and resource efficiency increasingly demanded by containerized and Kubernetes-based deployments, an area where traditional Java application servers historically struggled. Rather than offering a single opinionated model, Oracle split Helidon into two distinct flavors so it could serve both developers who want minimal abstraction over the JVM and developers who prefer the standardized, annotation-driven MicroProfile programming model already familiar from the broader Jakarta EE ecosystem. Mechanically, Helidon SE exposes a functional, builder-style API for defining routes, handlers, and configuration directly in Java code, historically built around a reactive programming model and more recently updated to take advantage of Java's virtual threads for simpler concurrent code without sacrificing throughput. Helidon MP, by contrast, implements the Eclipse MicroProfile specification, letting developers use familiar annotations like `@Path` and `@Inject` from JAX-RS and CDI, so teams already comfortable with Jakarta EE conventions can adopt Helidon with less relearning. Both flavors compile to fast-starting, low-memory-footprint applications and support GraalVM native-image compilation for further startup and footprint reduction. Helidon's closest competitors are Quarkus and Micronaut, both of which target the same cloud-native, fast-startup niche with native-image support; the distinguishing factor is largely ecosystem and vendor: Helidon comes from Oracle and leans on MicroProfile standardization for its MP flavor, while Quarkus is Red Hat-backed with a larger extension ecosystem, and Micronaut emphasizes compile-time dependency injection to avoid reflection overhead. Compared to Spring Boot, all three newer frameworks generally offer faster startup and lower memory usage, at the cost of Spring's much larger and more mature ecosystem of integrations. In practice, Helidon is used by teams building microservices for Kubernetes or serverless platforms who want low resource consumption per instance, particularly those already invested in Oracle's cloud or database ecosystem, or teams wanting the option to choose between a minimal functional API (SE) and a standards-based annotation model (MP) within the same overall project family. Oracle also uses Helidon internally for some of its own cloud services, providing a degree of production validation. Helidon's main limitation relative to Quarkus and Micronaut is a smaller third-party extension ecosystem and community size, meaning fewer pre-built integrations for niche libraries or cloud services exist without custom work. Teams also need to choose between SE and MP early, since the two have different programming models and are not simply interchangeable, and switching between them later requires meaningful rework rather than a configuration change.
Key Features
- Offers two programming models: functional Helidon SE and MicroProfile-based Helidon MP
- Targets fast startup times and low memory footprint for cloud deployment
- Supports GraalVM native-image compilation in both programming models
- Helidon SE leverages Java virtual threads for simplified concurrency
- Helidon MP implements standard JAX-RS and CDI annotations from MicroProfile
- Built and maintained by Oracle with production use in its own cloud services
- Provides built-in health check and metrics support via MicroProfile specs
- Designed specifically for containerized and Kubernetes-native microservices