OpenFeature Java SDK

OpenFeature is an open specification that provides a vendor-agnostic, community-driven API for feature flagging that works with your favorite feature flag management tool.

🚀 Quick start

Requirements

• Java 8+ (compiler target is 1.8)

Note that this library is intended to be used in server-side contexts and has not been evaluated for use on mobile devices.

Install

Maven

<dependency>
    <groupId>dev.openfeature</groupId>
    <artifactId>sdk</artifactId>
    <version>1.10.0</version>
</dependency>

If you would like snapshot builds, this is the relevant repository information:

<repositories>
    <repository>
        <snapshots>
            <enabled>true</enabled>
        </snapshots>
        <id>sonatype</id>
        <name>Sonatype Repository</name>
        <url>https://s01.oss.sonatype.org/content/repositories/snapshots/</url>
    </repository>
</repositories>

Gradle

dependencies {
    implementation 'dev.openfeature:sdk:1.10.0'
}

Usage

public void example(){

    // flags defined in memory
    Map<String, Flag<?>> myFlags = new HashMap<>();
    myFlags.put("v2_enabled", Flag.builder()
        .variant("on", true)
        .variant("off", false)
        .defaultVariant("on")
        .build());

    // configure a provider
    OpenFeatureAPI api = OpenFeatureAPI.getInstance();
    api.setProviderAndWait(new InMemoryProvider(myFlags));

    // create a client
    Client client = api.getClient();

    // get a bool flag value
    boolean flagValue = client.getBooleanValue("v2_enabled", false);
}

API Reference

See here for the Javadocs.

🌟 Features

Status	Features	Description
✅	Providers	Integrate with a commercial, open source, or in-house feature management tool.
✅	Targeting	Contextually-aware flag evaluation using evaluation context.
✅	Hooks	Add functionality to various stages of the flag evaluation life-cycle.
✅	Logging	Integrate with popular logging packages.
✅	Domains	Logically bind clients with providers.
✅	Eventing	React to state changes in the provider or flag management system.
✅	Shutdown	Gracefully clean up a provider during application shutdown.
✅	Transaction Context Propagation	Set a specific evaluation context for a transaction (e.g. an HTTP request or a thread).
✅	Extending	Extend OpenFeature with custom providers and hooks.

_{Implemented: ✅ | In-progress: ⚠️ | Not implemented yet: ❌}

Providers

Providers are an abstraction between a flag management system and the OpenFeature SDK. Look here for a complete list of available providers. If the provider you're looking for hasn't been created yet, see the develop a provider section to learn how to build it yourself.

Once you've added a provider as a dependency, it can be registered with OpenFeature like this:

Synchronous

To register a provider in a blocking manner to ensure it is ready before further actions are taken, you can use the setProviderAndWait method as shown below:

    OpenFeatureAPI api = OpenFeatureAPI.getInstance();
    api.setProviderAndWait(new MyProvider());

Asynchronous

To register a provider in a non-blocking manner, you can use the setProvider method as shown below:

    OpenFeatureAPI.getInstance().setProvider(new MyProvider());

In some situations, it may be beneficial to register multiple providers in the same application. This is possible using domains, which is covered in more detail below.

Targeting

Sometimes, the value of a flag must consider some dynamic criteria about the application or user, such as the user's location, IP, email address, or the server's location. In OpenFeature, we refer to this as targeting. If the flag management system you're using supports targeting, you can provide the input data using the evaluation context.

// set a value to the global context
OpenFeatureAPI api = OpenFeatureAPI.getInstance();
Map<String, Value> apiAttrs = new HashMap<>();
apiAttrs.put("region", new Value(System.getEnv("us-east-1")));
EvaluationContext apiCtx = new ImmutableContext(apiAttrs);
api.setEvaluationContext(apiCtx);

// set a value to the client context
Map<String, Value> clientAttrs = new HashMap<>();
clientAttrs.put("region", new Value(System.getEnv("us-east-1")));
EvaluationContext clientCtx = new ImmutableContext(clientAttrs);
Client client = api.getInstance().getClient();
client.setEvaluationContext(clientCtx);

// set a value to the invocation context
Map<String, Value> requestAttrs = new HashMap<>();
requestAttrs.put("email", new Value(session.getAttribute("email")));
requestAttrs.put("product", new Value("productId"));
String targetingKey = session.getId();
EvaluationContext reqCtx = new ImmutableContext(targetingKey, requestAttrs);

boolean flagValue = client.getBooleanValue("some-flag", false, reqCtx);

Hooks

Hooks allow for custom logic to be added at well-defined points of the flag evaluation life-cycle Look here for a complete list of available hooks. If the hook you're looking for hasn't been created yet, see the develop a hook section to learn how to build it yourself.

Once you've added a hook as a dependency, it can be registered at the global, client, or flag invocation level.

  // add a hook globally, to run on all evaluations
  OpenFeatureAPI api = OpenFeatureAPI.getInstance();
  api.addHooks(new ExampleHook());
  
  // add a hook on this client, to run on all evaluations made by this client
  Client client = api.getClient();        
  client.addHooks(new ExampleHook());
  
  // add a hook for this evaluation only
  Boolean retval = client.getBooleanValue(flagKey, false, null,
          FlagEvaluationOptions.builder().hook(new ExampleHook()).build());

Logging

The Java SDK uses SLF4J. See the SLF4J manual for complete documentation. Note that in accordance with the OpenFeature specification, the SDK doesn't generally log messages during flag evaluation.

Logging Hook

The Java SDK includes a LoggingHook, which logs detailed information at key points during flag evaluation, using SLF4J's structured logging API. This hook can be particularly helpful for troubleshooting and debugging; simply attach it at the global, client or invocation level and ensure your log level is set to "debug".

See hooks for more information on configuring hooks.

Domains

Clients can be assigned to a domain. A domain is a logical identifier which can be used to associate clients with a particular provider. If a domain has no associated provider, the global provider is used.

FeatureProvider scopedProvider = new MyProvider();

// registering the default provider
OpenFeatureAPI.getInstance().setProvider(LocalProvider());
// registering a provider to a domain
OpenFeatureAPI.getInstance().setProvider("my-domain", new CachedProvider());

// A client bound to the default provider
Client clientDefault = OpenFeatureAPI.getInstance().getClient();
// A client bound to the CachedProvider provider
Client domainScopedClient = OpenFeatureAPI.getInstance().getClient("my-domain");

Providers for domains can be set in a blocking or non-blocking way. For more details, please refer to the providers section.

Eventing

Events allow you to react to state changes in the provider or underlying flag management system, such as flag definition changes, provider readiness, or error conditions. Initialization events (PROVIDER_READY on success, PROVIDER_ERROR on failure) are dispatched for every provider. Some providers support additional events, such as PROVIDER_CONFIGURATION_CHANGED.

Please refer to the documentation of the provider you're using to see what events are supported.

// add an event handler to a client
Client client = OpenFeatureAPI.getInstance().getClient();
client.onProviderConfigurationChanged((EventDetails eventDetails) -> {
    // do something when the provider's flag settings change
});

// add an event handler to the global API
OpenFeatureAPI.getInstance().onProviderStale((EventDetails eventDetails) -> {
    // do something when the provider's cache goes stale
});

Shutdown

The OpenFeature API provides a close function to perform a cleanup of all registered providers. This should only be called when your application is in the process of shutting down.

// shut down all providers
OpenFeatureAPI.getInstance().shutdown();

Transaction Context Propagation

Transaction context is a container for transaction-specific evaluation context (e.g. user id, user agent, IP). Transaction context can be set where specific data is available (e.g. an auth service or request handler) and by using the transaction context propagator it will automatically be applied to all flag evaluations within a transaction (e.g. a request or thread). By default, the NoOpTransactionContextPropagator is used, which doesn't store anything. To register a ThreadLocal context propagator, you can use the setTransactionContextPropagator method as shown below.

// registering the ThreadLocalTransactionContextPropagator
OpenFeatureAPI.getInstance().setTransactionContextPropagator(new ThreadLocalTransactionContextPropagator());

Once you've registered a transaction context propagator, you can propagate the data into request-scoped transaction context.

// adding userId to transaction context
OpenFeatureAPI api = OpenFeatureAPI.getInstance();
Map<String, Value> transactionAttrs = new HashMap<>();
transactionAttrs.put("userId", new Value("userId"));
EvaluationContext transactionCtx = new ImmutableContext(transactionAttrs);
api.setTransactionContext(transactionCtx);

Additionally, you can develop a custom transaction context propagator by implementing the TransactionContextPropagator interface and registering it as shown above.

Extending

Develop a provider

To develop a provider, you need to create a new project and include the OpenFeature SDK as a dependency. This can be a new repository or included in the existing contrib repository available under the OpenFeature organization. You’ll then need to write the provider by implementing the FeatureProvider interface exported by the OpenFeature SDK.

public class MyProvider implements FeatureProvider {
    @Override
    public Metadata getMetadata() {
        return () -> "My Provider";
    }

    @Override
    public ProviderState getState() {
        // optionally indicate your provider's state (assumed to be READY if not implemented)
    }

    @Override
    public void initialize(EvaluationContext evaluationContext) throws Exception {
        // start up your provider
    }

    @Override
    public void shutdown() {
        // shut down your provider
    }

    @Override
    public ProviderEvaluation<Boolean> getBooleanEvaluation(String key, Boolean defaultValue, EvaluationContext ctx) {
        // resolve a boolean flag value
    }

    @Override
    public ProviderEvaluation<String> getStringEvaluation(String key, String defaultValue, EvaluationContext ctx) {
        // resolve a string flag value
    }

    @Override
    public ProviderEvaluation<Integer> getIntegerEvaluation(String key, Integer defaultValue, EvaluationContext ctx) {
        // resolve an int flag value
    }

    @Override
    public ProviderEvaluation<Double> getDoubleEvaluation(String key, Double defaultValue, EvaluationContext ctx) {
        // resolve a double flag value
    }

    @Override
    public ProviderEvaluation<Value> getObjectEvaluation(String key, Value defaultValue, EvaluationContext ctx) {
        // resolve an object flag value
    }
}

If you'd like your provider to support firing events, such as events for when flags are changed in the flag management system, extend EventProvider.

class MyEventProvider extends EventProvider {
    @Override
    public Metadata getMetadata() {
        return () -> "My Event Provider";
    }

    @Override
    public ProviderState getState() {
        // indicate your provider's state (required for EventProviders)
    }

    @Override
    public void initialize(EvaluationContext evaluationContext) throws Exception {
        // emit events when flags are changed in a hypothetical REST API
        this.restApiClient.onFlagsChanged(() -> {
            ProviderEventDetails details = ProviderEventDetails.builder().message("flags changed in API!").build();
            this.emitProviderConfigurationChanged(details);
        });
    }

    @Override
    public void shutdown() {
        // shut down your provider
    }

    // remaining provider methods...
}

Built a new provider? Let us know so we can add it to the docs!

Develop a hook

To develop a hook, you need to create a new project and include the OpenFeature SDK as a dependency. This can be a new repository or included in the existing contrib repository available under the OpenFeature organization. Implement your own hook by conforming to the Hook interface.

class MyHook implements Hook {

    @Override
    public Optional before(HookContext ctx, Map hints) {
        // code that runs before the flag evaluation
    }

    @Override
    public void after(HookContext ctx, FlagEvaluationDetails details, Map hints) {
        // code that runs after the flag evaluation succeeds
    }

    @Override
    public void error(HookContext ctx, Exception error, Map hints) {
        // code that runs when there's an error during a flag evaluation
    }

    @Override
    public void finallyAfter(HookContext ctx, Map hints) {
        // code that runs regardless of success or error
    }
};

Built a new hook? Let us know so we can add it to the docs!

⭐️ Support the project

• Give this repo a ⭐️!
• Follow us on social media:
  • Twitter: @openfeature
  • LinkedIn: OpenFeature
• Join us on Slack
• For more, check out our community page

🤝 Contributing

Interested in contributing? Great, we'd love your help! To get started, take a look at the CONTRIBUTING guide.

Thanks to everyone who has already contributed

Made with contrib.rocks.