OpenFeature (Java)

PostHog provides an official OpenFeature provider for server-side JVM applications, so you can evaluate PostHog flags through the standard OpenFeature API. It is backed by the Java SDK (posthog-server) and the OpenFeature Java SDK.

• Package: com.posthog:posthog-server-openfeature
• Provider class: com.posthog.server.openfeature.PostHogProvider

The provider requires Java 11 or later, because the OpenFeature Java SDK requires it.

Installation

Look up the latest version of com.posthog.posthog-server-openfeature.

Gradle

dependencies {
  implementation 'com.posthog:posthog-server-openfeature:0.+'
}

Maven

<dependency>
  <groupId>com.posthog</groupId>
  <artifactId>posthog-server-openfeature</artifactId>
  <version>LATEST</version>
</dependency>

This adds posthog-server and dev.openfeature:sdk as dependencies.

Usage

Create and configure a PostHog client, then register the provider with the OpenFeature SDK:

import com.posthog.server.PostHog;
import com.posthog.server.PostHogConfig;
import com.posthog.server.PostHogInterface;
import com.posthog.server.openfeature.PostHogProvider;
import dev.openfeature.sdk.Client;
import dev.openfeature.sdk.EvaluationContext;
import dev.openfeature.sdk.ImmutableContext;
import dev.openfeature.sdk.OpenFeatureAPI;
import dev.openfeature.sdk.Value;
import java.util.Map;

PostHogInterface posthog = PostHog.with(
    PostHogConfig.builder("<ph_project_token>")
        .host("https://us.i.posthog.com")
        // .personalApiKey("<ph_personal_api_key>") enables local evaluation
        .build()
);

OpenFeatureAPI api = OpenFeatureAPI.getInstance();
api.setProviderAndWait(new PostHogProvider(posthog));
Client client = api.getClient();

EvaluationContext context = new ImmutableContext(
    "user_distinct_id",
    Map.of("plan", new Value("pro"))
);

boolean isEnabled = client.getBooleanValue("my-flag", false, context);

You own the PostHog client lifecycle. Call posthog.close() when your app exits. The provider's shutdown() does not close the client.

Evaluation context

The OpenFeature evaluation context maps to PostHog's flag evaluation inputs:

The PostHogProvider.GROUPS_KEY and PostHogProvider.GROUP_PROPERTIES_KEY constants hold the reserved attribute names:

import dev.openfeature.sdk.ImmutableStructure;

EvaluationContext context = new ImmutableContext("user_distinct_id", Map.of(
    PostHogProvider.GROUPS_KEY, new Value(new ImmutableStructure(Map.of("company", new Value("acme"))))
));

If the context has no targetingKey and no defaultDistinctId is set, the provider returns your default value with error_code = TARGETING_KEY_MISSING.

Supported flag types

When the flag is off, the string, number, and object methods return your default value with the DEFAULT reason. One exception: if the flag has a JSON object or array payload set for its false value, getObjectValue returns that payload with the DEFAULT reason. Check the reason, not the returned object, to tell whether the flag is enabled. A non-existent flag returns your default value with error_code = FLAG_NOT_FOUND. Calling a typed getter on an incompatible flag (for example getStringValue on a boolean flag) returns your default value with error_code = TYPE_MISMATCH, per the OpenFeature spec.

The reason is TARGETING_MATCH when the flag is enabled and DEFAULT otherwise. The Java provider does not return the DISABLED reason or the posthog_reason metadata yet.

Options

new PostHogProvider(client, options)

Pass options with PostHogProviderOptions.builder():

import com.posthog.server.openfeature.PostHogProviderOptions;

new PostHogProvider(
    posthog,
    PostHogProviderOptions.builder()
        .defaultDistinctId("anonymous")
        .build()
);

• defaultDistinctId: distinct ID used when the context has no targetingKey. Defaults to null, in which case an evaluation without a targetingKey returns your default value with error_code = TARGETING_KEY_MISSING.

Each evaluation captures a $feature_flag_called event. To turn these events off, set sendFeatureFlagEvent(false) on the PostHogConfig. This setting applies to the whole client.