Spring Boot OpenFeature

This is a Spring Boot starter that integrates OpenFeature, an open standard for feature flag management. Add one starter dependency, set a few spring.openfeature.* properties, and feature flags work in your application — no manual wiring of the OpenFeature SDK.

Features

• Auto-Configuration — a ready-made dev.openfeature.sdk.Client bean, created as soon as a FeatureProvider bean is on the context.
• Declarative Flags — the @ToggleOnFlag annotation gates method execution on a flag, with SpEL evaluation context and an orElse fallback method.
• Health Indicator — a Spring Boot Actuator health check for the configured flag provider.
• Provider Starters — one starter module per feature-flag backend, each configured under its own spring.openfeature.<provider>.* prefix.
• Extension Points — ClientCustomizer, OpenFeatureAPICustomizer, and per-provider customizers let you tweak the auto-configured beans.
• Security Integration — when Spring Security is on the classpath, userId and authorities are automatically added to every flag evaluation context.

Prerequisites

• Java 17
• Maven (the repository ships the Maven wrapper ./mvnw)

Getting Started

1. Add the Dependency

Every provider has its own starter. For Unleash:

Maven

<project>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.iromu.openfeature</groupId>
            <artifactId>spring-boot-starter-openfeature-unleash</artifactId>
        </dependency>
    </dependencies>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.iromu.openfeature</groupId>
                <artifactId>spring-boot-openfeature-dependencies</artifactId>
                <version>${spring-boot-openfeature.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>
</project>

Gradle

dependencyManagement {
    imports {
        mavenBom "org.iromu.openfeature:spring-boot-openfeature-dependencies:${springBootOpenFeatureVersion}"
    }
}

dependencies {
    implementation 'org.springframework.boot:spring-boot-starter-web'
    implementation 'org.iromu.openfeature:spring-boot-starter-openfeature-unleash'
}

The BOM (spring-boot-openfeature-dependencies) pins the OpenFeature SDK and every provider library version, so you do not need to declare versions yourself.

2. Configure the Provider

Configure the provider under its spring.openfeature.<provider>.* prefix in application.yml (or application.properties). For example, Unleash:

spring:
  application:
    name: UnleashApplication
  openfeature:
    unleash:
      app-name: ${spring.application.name}
      environment: development
      unleash-api: http://unleash-instance:4242/api/
      unleash-token: 'default:development.your-api-key'

Each provider starter also accepts an enabled property (spring.openfeature.<provider>.enabled) to switch its auto-configuration on or off. Refer to the provider's own documentation for the full set of options.

3. Use the Client

Inject the auto-configured Client and evaluate flags:

import dev.openfeature.sdk.Client;
import dev.openfeature.sdk.ImmutableContext;
import dev.openfeature.sdk.Value;

@RestController
@RequestMapping("/feature")
public class FeatureController {

    private final Client client;

    public FeatureController(Client client) {
        this.client = client;
    }

    @GetMapping("{name}")
    public Boolean feature(@PathVariable("name") final String name) {
        return this.client.getBooleanValue(name, false);
    }

    @GetMapping("user/{id}")
    public Boolean featureOnUserId(@PathVariable("id") final String id) {
        return this.client.getBooleanValue("users-flag", false,
                new ImmutableContext(Map.of("userId", new Value(id))));
    }
}

4. Use @ToggleOnFlag

The @ToggleOnFlag annotation (from org.iromu.openfeature.boot.aop) conditionally executes a method based on a flag. attributes accepts a SpEL map that is evaluated into the flag evaluation context, and orElse names a fallback method invoked when the flag evaluates to false.

Given an Unleash flag defined as:

{
  "name": "users-flag",
  "enabled": true,
  "strategies": [
    {
      "name": "userWithId",
      "parameters": {
        "userIds": "111,234"
      }
    }
  ]
}

import org.iromu.openfeature.boot.aop.ToggleOnFlag;

@RestController
@RequestMapping("/feature")
public class UserController {

    @GetMapping("annotated/user/{id}")
    @ToggleOnFlag(key = "users-flag", attributes = "{'userId': #id}", orElse = "featureOnUserIdDisabled")
    public String featureOnUserIdAnnotated(@PathVariable("id") final String id) {
        return "User allowed";
    }

    public String featureOnUserIdDisabled(final String id) {
        return "User not allowed";
    }
}

OpenFeature Providers

Each backend has its own starter module under org.iromu.openfeature:

Provider	Starter artifact
ConfigCat	spring-boot-starter-openfeature-configcat
Env Var	spring-boot-starter-openfeature-envvar
flagd	spring-boot-starter-openfeature-flagd
Flagsmith	spring-boot-starter-openfeature-flagsmith
Flipt	spring-boot-starter-openfeature-flipt
GoFeatureFlag	spring-boot-starter-openfeature-gofeatureflag
GrowthBook	spring-boot-starter-openfeature-growthbook
JsonLogic	spring-boot-starter-openfeature-jsonlogic
Multi-Provider	spring-boot-starter-openfeature-multiprovider
Statsig	spring-boot-starter-openfeature-statsig
Unleash	spring-boot-starter-openfeature-unleash

To switch providers, replace the starter dependency and update the configuration as per the provider's documentation.

Example Applications

The examples/ directory contains two runnable applications (built with the examples profile or as a separate reactor; they resolve the starters from the local build or the snapshot repository):

• unleash-simple — runs on port 9998 with a bundled in-memory fake Unleash provider; no external server needed.
• unleash-advanced — runs on port 9999 against a mocked Unleash API server, using a local features.json backup file.

$ cd examples
$ mvn clean package

Then run the packaged application, for example:

$ java -jar unleash-simple/target/unleash-simple-${revision}.jar

Try the endpoints (unleash-simple):

$ curl http://localhost:9998/feature/random-boolean-flag
$ curl http://localhost:9998/feature/greet/world

And with unleash-advanced running on 9999:

$ curl http://localhost:9999/feature/annotated/user/111

Building the Project

All commands use the Maven wrapper from the repository root:

# Full build (compile, checkstyle, formatting, tests, coverage)
$ ./mvnw clean verify

# Skip tests
$ ./mvnw clean verify -DskipTests

# Build a single module and its dependencies
$ ./mvnw -pl spring-boot-starter-openfeature-unleash -am clean verify

Code style is enforced by Spring Java Format and Checkstyle, which run automatically during the validate phase.

Contributing

Contributions are welcome! See CONTRIBUTING.md for the full guide on reporting bugs, suggesting features, code style, testing, and the pull request process.

License

This project is licensed under the Apache License 2.0. See the LICENSE file for details.

Resources

• OpenFeature Documentation
• Spring Boot Documentation
• Unleash Documentation