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Java/Kotlin Server SDK

Server vs. Client

These docs are for using our Java/Kotlin SDK in a multi-user, server side context. For client side android applications, check out our Android SDK or one of the other client SDKs for your client side applications.

This SDK is written in Kotlin, but exposes methods and overrides to Java based applications.

Statsig server SDK for Java/Kotlin applications. This SDK is open source and hosted on github.

The Basics#

Get started in a few quick steps.

  1. Create a free account on
  2. Install the SDK
  3. Initialize the SDK
  4. Fetch Feature Gates, Dynamic Configs, or Experiments
  5. Log a custom event

Step 1 - Create a free account on

You could skip this for now, but you will need an SDK Key and some Feature Gates or Dynamic Configs to use with the SDK in just a minute.

Step 2 - Install the SDK#

You can install the SDK using JitPack. See the latest version and installation steps at

NOTE: There was a breaking API change in SDK v0.8.0: The singleton for interfacing with Statsig, StatsigServer was renamed to simply Statsig

See the release notes.

Step 3 - Initialize the SDK#

After installation, you will need to initialize the SDK using a Server Secret Key from the statsig console.


Do NOT embed your Server Secret Key in client side applications, or expose it in any external facing documents. However, if you accidentally exposed it, you can create a new one in Statsig console.

There is also an optional parameter options that allows you to pass in a StatsigOptions to customize the SDK.

import com.statsig.sdk.Statsig;
Future initFuture = Statsig.initializeAsync("server-secret-key");

initialize will perform a network request. After initialize completes, virtually all SDK operations will be synchronous1--the SDK will fetch updates from Statsig in the background, independently of your API calls.

Step 4 - Fetch Feature Gates, Dynamic Configs, or Experiments#

Now that your SDK is initialized, let's fetch a Feature Gate. Feature Gates can be used to create logic branches in code that can be rolled out to different users from the Statsig Console. Gates always CLOSED or OFF (think return false;) by default.

From this point on, all APIs will require you to specify the user (see Statsig user) associated with the request. For example, check a gate for a certain user like this:

StatsigUser user = new StatsigUser("user_id");
Future<Boolean> featureOn = Statsig.checkGateAsync(user, "use_new_feature");
Boolean isFeatureOn = featureOn.get()
if (isFeatureOn) {
// Gate is on, use new feature
} else {
// Gate is off

Feature Gates can be very useful for simple on/off switches, with optional but advanced user targeting. However, if you want to be able send a different set of values (strings, numbers, and etc.) to your clients based on specific user attributes, e.g. country, Dynamic Configs can help you with that. The API is very similar to Feature Gates, but you get an entire json object you can configure on the server and you can fetch typed parameters from it. For example:

Future<DynamicConfig> configFuture = Statsig.getConfig(user, "awesome_product_details");
DynamicConfig config = configFuture.get();
// The 2nd parameter is the default value to be used in case the given parameter name does not exist on
// the Dynamic Config object. This can happen when there is a typo, or when the user is offline and the
// value has not been cached on the client.
String itemName = config.getString("product_name", "Awesome Product v1");
Double price = config.getDouble("price", 10.0);
Boolean shouldDiscount = config.getBoolean("discount", false);

Then we have Experiments, which you can use to run A/B/n experiments and use advanced features like layers (coming soon) to avoid collision and enable quicker iterations with parameter reuse.

Future<DynamicConfig> configFuture = Statsig.getExperiment(user, "new_user_promo");
DynamicConfig expConfig = configFuture.get();
String promoTitle = expConfig.getString("title", "Welcome to Statsig! Use discount code WELCOME10OFF for 10% off your first purchase!");
Double discount = expConfig.getDouble("discount", 0.1);
Double price = msrp * (1 - discount);
Asynchronous APIs

We mentioned earlier that after calling initialize most SDK APIs would run synchronously, so why are getConfig and checkGate asynchronous?

The main reason is that older versions of the SDK might not know how to interpret new types of gate conditions. In such cases the SDK will make an asynchronous call to our servers to fetch the result of a check. This can be resolved by upgrading the SDK, and we will warn you if this happens.

For more details, read our blog post about SDK evaluations. If you have any questions, please ask them in our Feedback Repository.

Step 5 - Log a custom event#

Now that you have a Feature Gate or an Experiment set up, you may want to track some custom events and see how your new features or different experiment groups affect these events. This is super easy with Statsig - simply call the Log Event API and specify the user and event name to log; you additionally provide some value and/or an object of metadata to be logged together with the event:

Statsig.logEvent(user, "purchase", 2.99, Map.of("item_name", "remove_ads"));

Statsig User#

When calling APIs that require a user, you should pass as much information as possible in order to take advantage of advanced gate and config conditions (like country or OS/browser level checks), and correctly measure impact of your experiments on your metrics/events. The userID field is required because it's needed to provide a consistent experience for a given user (click here to understand further why it's important to always provide a userID).

Besides userID, we also have email, ip, userAgent, country, locale and appVersion as top-level fields on StatsigUser. In addition, you can pass any key-value pairs in an object/dictionary to the custom field and be able to create targeting based on them.

Have sensitive user PII data that should not be logged?#

No problem, we have a solution for it! On the StatsigUser object we also have a field called privateAttributes, which is a simple object/dictionary that you can use to set private user attributes. Any attribute set in privateAttributes will only be used for evaluation/targeting, and removed from any logs before they are sent to Statsig server.

For example, if you have feature gates that should only pass for users with emails ending in "", but do not want to log your users' email addresses to Statsig, you can simply add the key-value pair { email: "" } to privateAttributes on the user and that's it!

Statsig Options#

You can pass in an optional parameter options in addition to the server secret during initialization to customize the Statsig client. Here are the current options and we are always adding more to the list:

  1. initTimeoutMs: double, default 3000
    • used to decide how long the Statsig client waits for the initial network request to respond before calling the completion block. The Statsig client will return either cached values (if any) or default values if checkGate/getConfig/getExperiment is called before the initial network request completes.
    • if you always want to wait for the latest values fetched from Statsig server, you should set this to 0 so we do not timeout the network request.
    • unit is milliseconds.
  2. environment tier: Tier (enum), default null
    • used to signal the environment tier the user is currently in, and can be PRODUCTION, STAGING or DEVELOPMENT;
    • e.g. passing in a value of Tier.Staging will allow your users to pass any condition that pass for the staging environment tier, and fail any condition that only passes for other environment tiers.

Shutting down Statsig#

Because we batch and periodically flush events, some events may not have been sent when your app/server shuts down. To make sure all logged events are properly flushed, you should tell Statsig to shutdown when your app/server is closing:



How do I run experiments for logged out users?#

(Coming soon)