OpenFeature Java SDK

> 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](https://javadoc.io/doc/dev.openfeature/sdk/latest/) for the Javadocs. ## 🌟 Features | Status | Features | Description | | ------ |---------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------| | ✅ | [Providers](#providers) | Integrate with a commercial, open source, or in-house feature management tool. | | ✅ | [Targeting](#targeting) | Contextually-aware flag evaluation using [evaluation context](https://openfeature.dev/docs/reference/concepts/evaluation-context). | | ✅ | [Hooks](#hooks) | Add functionality to various stages of the flag evaluation life-cycle. | | ✅ | [Tracking](#tracking) | Associate user actions with feature flag evaluations. | | ✅ | [Logging](#logging) | Integrate with popular logging packages. | | ✅ | [Domains](#domains) | Logically bind clients with providers. | | ✅ | [Eventing](#eventing) | React to state changes in the provider or flag management system. | | ✅ | [Shutdown](#shutdown) | Gracefully clean up a provider during application shutdown. | | ✅ | [Transaction Context Propagation](#transaction-context-propagation) | Set a specific [evaluation context](https://openfeature.dev/docs/reference/concepts/evaluation-context) for a transaction (e.g. an HTTP request or a thread). | | ✅ | [Extending](#extending) | Extend OpenFeature with custom providers and hooks. | <sub>Implemented: ✅ | In-progress: ⚠️ | Not implemented yet: ❌</sub> ### Providers [Providers](https://openfeature.dev/docs/reference/concepts/provider) are an abstraction between a flag management system and the OpenFeature SDK. Look [here](https://openfeature.dev/ecosystem?instant_search%5BrefinementList%5D%5Btype%5D%5B0%5D=Provider&instant_search%5BrefinementList%5D%5Btechnology%5D%5B0%5D=Java) for a complete list of available providers. If the provider you're looking for hasn't been created yet, see the [develop a provider](#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: ```java 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: ```java 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](#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](https://openfeature.dev/specification/glossary#targeting). If the flag management system you're using supports targeting, you can provide the input data using the [evaluation context](https://openfeature.dev/docs/reference/concepts/evaluation-context). ```java // set a value to the global context OpenFeatureAPI api = OpenFeatureAPI.getInstance(); Map 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 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 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](https://openfeature.dev/docs/reference/concepts/hooks) allow for custom logic to be added at well-defined points of the flag evaluation life-cycle Look [here](https://openfeature.dev/ecosystem?instant_search%5BrefinementList%5D%5Btype%5D%5B0%5D=Hook&instant_search%5BrefinementList%5D%5Btechnology%5D%5B0%5D=Java) for a complete list of available hooks. If the hook you're looking for hasn't been created yet, see the [develop a hook](#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. ```java // 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()); ``` ### Tracking The [tracking API](https://openfeature.dev/specification/sections/tracking/) allows you to use OpenFeature abstractions to associate user actions with feature flag evaluations. This is essential for robust experimentation powered by feature flags. Note that, unlike methods that handle feature flag evaluations, calling `track(...)` may throw an `IllegalArgumentException` if an empty string is passed as the `trackingEventName`. ```java OpenFeatureAPI api = OpenFeatureAPI.getInstance(); api.getClient().track("visited-promo-page", new MutableTrackingEventDetails(99.77).add("currency", "USD")); ``` ### Logging The Java SDK uses SLF4J. See the [SLF4J manual](https://slf4j.org/manual.html) 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](#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. ```java 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](#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. ```java // 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. ```java // 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. ```java // 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. ```java // adding userId to transaction context OpenFeatureAPI api = OpenFeatureAPI.getInstance(); Map 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](https://github.com/open-feature/java-sdk-contrib) available under the OpenFeature organization. You’ll then need to write the provider by implementing the `FeatureProvider` interface exported by the OpenFeature SDK. ```java public class MyProvider implements FeatureProvider { @Override public Metadata getMetadata() { return () -> "My Provider"; } @Override public void initialize(EvaluationContext evaluationContext) throws Exception { // start up your provider } @Override public void shutdown() { // shut down your provider } @Override public ProviderEvaluation getBooleanEvaluation(String key, Boolean defaultValue, EvaluationContext ctx) { // resolve a boolean flag value } @Override public ProviderEvaluation getStringEvaluation(String key, String defaultValue, EvaluationContext ctx) { // resolve a string flag value } @Override public ProviderEvaluation getIntegerEvaluation(String key, Integer defaultValue, EvaluationContext ctx) { // resolve an int flag value } @Override public ProviderEvaluation getDoubleEvaluation(String key, Double defaultValue, EvaluationContext ctx) { // resolve a double flag value } @Override public ProviderEvaluation 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`. ```java class MyEventProvider extends EventProvider { @Override public Metadata getMetadata() { return () -> "My Event Provider"; } @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... } ``` Providers no longer need to manage their own state, this is done by the SDK itself. If desired, the state of a provider can be queried through the client that uses the provider. ```java OpenFeatureAPI.getInstance().getClient().getProviderState(); ``` > Built a new provider? [Let us know](https://github.com/open-feature/openfeature.dev/issues/new?assignees=&labels=provider&projects=&template=document-provider.yaml&title=%5BProvider%5D%3A+) 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](https://github.com/open-feature/java-sdk-contrib) available under the OpenFeature organization. Implement your own hook by conforming to the `Hook interface`. ```java 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, FlagEvaluationDetails details, Map hints) { // code that runs regardless of success or error } }; ``` > Built a new hook? [Let us know](https://github.com/open-feature/openfeature.dev/issues/new?assignees=&labels=hook&projects=&template=document-hook.yaml&title=%5BHook%5D%3A+) so we can add it to the docs! ## ⭐️ Support the project - Give this repo a ⭐️! - Follow us on social media: - Twitter: [@openfeature](https://twitter.com/openfeature) - LinkedIn: [OpenFeature](https://www.linkedin.com/company/openfeature/) - Join us on [Slack](https://cloud-native.slack.com/archives/C0344AANLA1) - For more, check out our [community page](https://openfeature.dev/community/) ## 🤝 Contributing Interested in contributing? Great, we'd love your help! To get started, take a look at the [CONTRIBUTING](CONTRIBUTING.md) guide. ### Thanks to everyone who has already contributed Made with [contrib.rocks](https://contrib.rocks).