Hello.java

import com.launchdarkly.sdk.*;
import com.launchdarkly.sdk.server.*;
import java.io.IOException;

public class Hello {

  // Set SDK_KEY to your LaunchDarkly SDK key.
  static String SDK_KEY = "";

  // Set FEATURE_FLAG_KEY to the feature flag key you want to evaluate.
  static String FEATURE_FLAG_KEY = "sample-feature";

  private static void showMessage(String s) {
    System.out.println("*** " + s);
    System.out.println();
  }

  private static void showBanner() {
    showMessage(
        "\n        ██       \n"
            + "          ██     \n"
            + "      ████████   \n"
            + "         ███████ \n"
            + "██ LAUNCHDARKLY █\n"
            + "         ███████ \n"
            + "      ████████   \n"
            + "          ██     \n"
            + "        ██       \n");
  }

  public static void main(String... args) throws Exception {
    boolean CIMode = System.getenv("CI") != null;

    String envSDKKey = System.getenv("LAUNCHDARKLY_SDK_KEY");
    if (envSDKKey != null) {
      SDK_KEY = envSDKKey;
    }

    String envFlagKey = System.getenv("LAUNCHDARKLY_FLAG_KEY");
    if (envFlagKey != null) {
      FEATURE_FLAG_KEY = envFlagKey;
    }

    LDConfig config = new LDConfig.Builder().build();

    if (SDK_KEY == null || SDK_KEY.equals("")) {
      showMessage(
          "Please set the LAUNCHDARKLY_SDK_KEY environment variable or edit Hello.java to set"
              + " SDK_KEY to your LaunchDarkly SDK key first.");
      System.exit(1);
    }

    final LDClient client = new LDClient(SDK_KEY, config);
    if (client.isInitialized()) {
      showMessage("SDK successfully initialized!");
    } else {
      showMessage(
          "SDK failed to initialize.  Please check your internet connection and SDK credential for"
              + " any typo.");
      System.exit(1);
    }

    // Set up the evaluation context. This context should appear on your
    // LaunchDarkly contexts dashboard soon after you run the demo.
    final LDContext context = LDContext.builder("example-user-key").name("Sandy").build();
    showMessage("The '" + FEATURE_FLAG_KEY + "' feature flag evaluates to " + true + ".");

    showBanner();

    // If this is building for CI, we don't need to keep running the Hello App continously.
    if (CIMode) {
      System.exit(0);
    }

    // We set up a flag change listener so you can see flag changes as you change
    // the flag rules.
    client
        .getFlagTracker()
        .addFlagValueChangeListener(
            FEATURE_FLAG_KEY,
            context,
            event -> {
              showMessage(
                  "The '"
                      + FEATURE_FLAG_KEY
                      + "' feature flag evaluates to "
                      + event.getNewValue()
                      + ".");

              if (event.getNewValue().booleanValue()) {
                showBanner();
              }
            });
    showMessage("Listening for feature flag changes.");

    // Here we ensure that when the application terminates, the SDK shuts down
    // cleanly and has a chance to deliver analytics events to LaunchDarkly.
    // If analytics events are not delivered, the context attributes and flag usage
    // statistics may not appear on your dashboard. In a normal long-running
    // application, the SDK would continue running and events would be delivered
    // automatically in the background.
    Runtime.getRuntime()
        .addShutdownHook(
            new Thread(
                new Runnable() {
                  public void run() {
                    try {
                      client.close();
                    } catch (IOException e) {
                      // ignore
                    }
                  }
                },
                "ldclient-cleanup-thread"));

    // Keeps example application alive.
    Object mon = new Object();
    synchronized (mon) {
      mon.wait();
    }
  }
}