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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 are 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:

  • 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.
  • 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.
  • bootstrapValues: string?, default null
    • a string that represents all rules for all feature gates, dynamic configs and experiments. It can be provided to bootstrap the Statsig server SDK at initialization in case your server runs into network issue or Statsig server is down temporarily.
  • rulesUpdatedCallback: ((rules: String) -> Unit)?, default null
    • a callback function that's called whenever we have an update for the rules; it's called with a JSON string (used as is for bootstrapValues mentioned above) and a timestamp.
  • localMode - boolean, default false
    • Pass true to this option to turn on Local Mode for the SDK, which will stop the SDK from issuing any network requests and make it only operate with only local overrides and cache.

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:




* An object of properties relating to the current user
* Provide as many as possible to take advantage of advanced conditions in the Statsig console
* A dictionary of additional fields can be provided under the "custom" field
* @property userID - string - REQUIRED - a unique identifier for the user. Why is this required? See
* @property email - string - an email associated with the current user
* @property ip - string - the ip address of the requests for the user
* @property userAgent - string - the user agent of the requests for this user
* @property country - string - the two letter country code of the user
* @property locale - string - the locale for the user
* @property appVersion - string - the current version of the app
* @property custom - Map<string, string> - any additional custom user attributes for custom conditions in the console
* @property privateAttributes - Map<string, Object> - any user attributes that should be used in evaluation only and removed in any logs.
* @property customIDs - Map<string, string> - Map of ID name to ID value for custom identifiers
data class StatsigUser

StatsigOptions and StatsigEnvironment

class StatsigOptions(
var api: String =,
var initTimeoutMs: Long? = 3000L,
var bootstrapValues: String? = null,
var rulesUpdatedCallback: ((rules: String) -> unit)? = null,
var localMode: Boolean = false
) {

// to set the environment tier
fun setTier(tier : Tier);

enum class Tier {


How do I run experiments for logged out users?

You can run experiments for arbitrary unit IDs (sessionID, groupID, etc), rather than at the userID level, if you choose. These custom unit IDs must be predefined in your Statsig project, and then selected in the Experiment creation flow. For more information, see our guide on experimenting on custom ID types

How can I mock Statsig for testing?

The python server SDK, starting in version 1.18.0+, supports a few features to make testing easier.

First, there is a new StatsigOption parameter called localMode. Setting localMode to true will cause the SDK to never hit the network, and only return default values. This is perfect for dummy environments or test environments that should not access the network.

Next, there are the overrideGate and overrideConfig APIs on the global Statsig interface:

overrideGate(gateName: String, gateValue: Boolean)

overrideConfig(configName: String, configValue: Map<String, Any>)

These can be used to set a gate or config value to be be returned for the given name.

We suggest you enable localMode and then override gates/configs to specific values to test the various code flows you are building.

You can view LocalOverridesTest to see overrides being used in test.