Java SDK

The Java SDK provides a thread-safe client for evaluating feature flags in Java applications.

Installation

Maven

<dependency>
  <groupId>com.featuresignals</groupId>
  <artifactId>sdk-java</artifactId>
  <version>0.1.0</version>
</dependency>

Gradle

implementation 'com.featuresignals:sdk-java:0.1.0'

Requirements: Java 17+

Quick Start

import com.featuresignals.sdk.*;

public class Main {
    public static void main(String[] args) throws Exception {
        var options = new ClientOptions("production")
            .baseURL("http://localhost:8080");

        var client = new FeatureSignalsClient("fs_srv_your_api_key", options);
        client.waitForReady(5000);

        var ctx = new EvalContext("user-123")
            .withAttribute("country", "US")
            .withAttribute("plan", "enterprise");

        boolean enabled = client.boolVariation("new-feature", ctx, false);
        System.out.println("Feature enabled: " + enabled);

        client.close();
    }
}

Configuration

var options = new ClientOptions("production")
    .baseURL("http://localhost:8080")          // API server URL
    .pollingInterval(Duration.ofSeconds(30))   // Polling interval
    .streaming(true)                           // Enable SSE
    .sseRetry(Duration.ofSeconds(5))          // SSE reconnect delay
    .timeout(Duration.ofSeconds(10))          // HTTP timeout
    .context(new EvalContext("server"));       // Default context

Options Reference

Method	Default	Description
baseURL(String)	https://api.featuresignals.com	API server URL
pollingInterval(Duration)	30s	Refresh interval
streaming(boolean)	false	Enable SSE streaming
sseRetry(Duration)	5s	SSE reconnect delay
timeout(Duration)	10s	HTTP timeout
context(EvalContext)	new EvalContext("server")	Default context

Evaluation Context

// Simple context
var ctx = new EvalContext("user-123");

// With attributes
var attrs = Map.of("country", "US", "plan", "enterprise");
var ctx = new EvalContext("user-123", attrs);

// Builder style
var ctx = new EvalContext("user-123")
    .withAttribute("country", "US")
    .withAttribute("plan", "enterprise");

Variation Methods

// Boolean
boolean enabled = client.boolVariation("flag-key", ctx, false);

// String
String theme = client.stringVariation("theme", ctx, "light");

// Number (returns double)
double limit = client.numberVariation("rate-limit", ctx, 100.0);

// JSON (generic, uses Gson internally)
MyConfig config = client.jsonVariation("feature-config", ctx, defaultConfig);

Callbacks

client.setOnReady(v -> System.out.println("Ready!"));
client.setOnError(err -> System.err.println("Error: " + err));
client.setOnUpdate(flags -> System.out.println("Updated: " + flags.size() + " flags"));

Readiness

// Blocking wait
client.waitForReady(5000); // throws InterruptedException

// Non-blocking
if (client.isReady()) {
    // flags are loaded
}

Getting All Flags

Map<String, Object> allFlags = client.allFlags();

Shutdown

client.close();

// Or with try-with-resources
try (var client = new FeatureSignalsClient(key, options)) {
    // use client
}

The client implements AutoCloseable for use with try-with-resources.

OpenFeature Integration

See OpenFeature for using the Java SDK with OpenFeature.