Unleash Client SDK for Java

This is the Unleash Client SDK for Java. It is compatible with the Unleash-hosted.com SaaS offering and Unleash Open-Source.

Getting started

This section shows you how to get started quickly and explains some common configuration scenarios. For a full overview of Unleash configuration options, check out the Configuration options section.

Add the Unleash client to your class path

You will require unleash on your class path, pop it in to your pom:

<dependency>
    <groupId>io.getunleash</groupId>
    <artifactId>unleash-client-java</artifactId>
    <version>Latest version here</version>
</dependency>

Create a new Unleash instance

It is easy to get a new instance of Unleash. In your app you typically just want one instance of Unleash, and inject that where you need it. You will typically use a dependency injection frameworks such as Spring or Guice to manage this.

To create a new instance of Unleash you need to pass in a config object:

UnleashConfig config = UnleashConfig.builder()
            .appName("java-test")
            .instanceId("instance x")
            .unleashAPI("http://unleash.herokuapp.com/api/")
            .apiKey("API token")
            .build();

Unleash unleash = new DefaultUnleash(config);

Awesome feature toggle API

It is really simple to use unleash.

if(unleash.isEnabled("AwesomeFeature")) {
  //do some magic
} else {
  //do old boring stuff
}

Calling unleash.isEnabled("AwesomeFeature") is the equivalent of calling unleash.isEnabled("AwesomeFeature", false). Which means that it will return false if it cannot find the named toggle.

If you want it to default to true instead, you can pass true as the second argument:

unleash.isEnabled("AwesomeFeature", true)

Activation strategies

The Java client comes with implementations for the built-in activation strategies provided by unleash.

• DefaultStrategy
• UserWithIdStrategy
• GradualRolloutRandomStrategy
• GradualRolloutUserWithIdStrategy
• GradualRolloutSessionIdStrategy
• RemoteAddressStrategy
• ApplicationHostnameStrategy

Read more about the strategies in the activation strategies documentation.

Custom strategies

You may also specify and implement your own strategy. The specification must be registered in the Unleash UI and you must register the strategy implementation when you wire up unleash.

Strategy s1 = new MyAwesomeStrategy();
Strategy s2 = new MySuperAwesomeStrategy();
Unleash unleash return new DefaultUnleash(config, s1, s2);

Unleash context

In order to use some of the common activation strategies you must provide an Unleash context. This client SDK provides two ways of provide the unleash-context:

1. As part of isEnabled call

This is the simplest and most explicit way of providing the unleash context. You just add it as an argument to the isEnabled call.

UnleashContext context = UnleashContext.builder()
  .userId("[email protected]").build();

unleash.isEnabled("someToggle", context);

2. Via an UnleashContextProvider

This is a more advanced approach, where you configure an Unleash context provider. With a context provider, you don't need to rebuild or pass the Unleash context to every unleash.isEnabled call.

The provider typically binds the context to the same thread as the request. If you use Spring, the UnleashContextProvider will typically be a 'request scoped' bean.

UnleashContextProvider contextProvider = new MyAwesomeContextProvider();

UnleashConfig config = new UnleashConfig.Builder()
            .appName("java-test")
            .instanceId("instance x")
            .unleashAPI("http://unleash.herokuapp.com/api/")
            .customHttpHeader("Authorization", "API token")
            .unleashContextProvider(contextProvider)
            .build();

Unleash unleash = new DefaultUnleash(config);

// Anywhere in the code unleash will get the unleash context from your registered provider.
unleash.isEnabled("someToggle");

Custom HTTP headers

If you want the client to send custom HTTP Headers with all requests to the Unleash API you can define that by setting them via the UnleashConfig.

UnleashConfig unleashConfig = UnleashConfig.builder()
                .appName("my-app")
                .instanceId("my-instance-1")
                .unleashAPI(unleashAPI)
                .apiKey("12312Random")
                .build();

Dynamic custom HTTP headers

If you need custom http headers that change during the lifetime of the client, a provider can be defined via the UnleashConfig.

public class CustomHttpHeadersProviderImpl implements CustomHttpHeadersProvider {
    @Override
    public Map<String, String> getCustomHeaders() {
        String token = "Acquire or refresh token";
        return new HashMap() {{ put("Authorization", "Bearer "+token); }};
    }
}

CustomHttpHeadersProvider provider = new CustomHttpHeadersProviderImpl();

UnleashConfig unleashConfig = UnleashConfig.builder()
                .appName("my-app")
                .instanceId("my-instance-1")
                .unleashAPI(unleashAPI)
                .apiKey("API token")
                .customHttpHeadersProvider(provider)
                .build();

Subscriber API

(Introduced in 3.2.2)

Sometimes you want to know when Unleash updates internally. This can be achieved by registering a subscriber. An example on how to configure a custom subscriber is shown below. Have a look at UnleashSubscriber.java to get a complete overview of all methods you can override.

UnleashConfig unleashConfig = UnleashConfig.builder()
    .appName("my-app")
    .instanceId("my-instance-1")
    .unleashAPI(unleashAPI)
    .apiKey("API token")
    .subscriber(new UnleashSubscriber() {
        @Override
        public void onReady(UnleashReady ready) {
            System.out.println("Unleash is ready");
        }
        @Override
        public void togglesFetched(FeatureToggleResponse toggleResponse) {
            System.out.println("Fetch toggles with status: " + toggleResponse.getStatus());
        }

        @Override
        public void togglesBackedUp(ToggleCollection toggleCollection) {
            System.out.println("Backup stored.");
        }

    })
    .build();

Options

• appName - Required. Should be a unique name identifying the client application using Unleash.
• synchronousFetchOnInitialisation - Allows the user to specify that the unleash-client should do one synchronous fetch to the unleash-api at initialisation. This will slow down the initialisation (the client must wait for a http response). If the unleash-api is unavailable the client will silently move on and assume the api will be available later.
• disablePolling - Stops the client from polling. If used without synchronousFetchOnInitialisation will cause the client to never fetch toggles from the unleash-api.
• fetchTogglesInterval - Sets the interval (in seconds) between each poll to the unleash-api. Set this to 0 to do a single fetch and then stop refreshing while the process lives.

HTTP Proxy with Authentication

The Unleash Java client uses HttpURLConnection as HTTP Client which already recognizes the common JVM proxy settings such as http.proxyHost and http.proxyPort. So if you are using a Proxy without authentication, everything works out of the box. However, if you have to use Basic Auth authentication with your proxy, the related settings such as http.proxyUser and http.proxyPassword do not get recognized by default. In order to enable support for basic auth against a http proxy, you can simply enable the following option on the configuration builder:

UnleashConfig config = UnleashConfig.builder()
    .appName("my-app")
    .unleashAPI("http://unleash.org")
    .apiKey("API token")
    .enableProxyAuthenticationByJvmProperties()
    .build();

Toggle fetcher

The Unleash Java client now supports using your own toggle fetcher. The Config builder has been expanded to accept a io.getunleash.util.UnleashFeatureFetcherFactory which should be a Function<UnleashConfig, FeatureFetcher>. If you want to use OkHttp instead of HttpURLConnection you'll need a dependency on okhttp

<dependency>
    <groupId>com.squareup.okhttp3</groupId>
    <artifactId>okhttp</artifactId>
    <version>4.10+</version>
</dependency>

Then you can change your config to

UnleashConfig config = UnleashConfig.builder()
    .appName("my-app")
    .unleashAPI("http://unleash.org")
    .apiKey("API token")
    .unleashFeatureFetcherFactory(OkHttpFeatureFetcher::new)
    .build();

This will then start using OkHttp instead of HttpURLConnection.

Metrics sender

The Unleash Java client now supports using your own metrics sender. The Config builder has been expanded to accept a io.getunleash.util.MetricsSenderFactory which should be a Function<UnleashConfig, MetricsSender>.

If you want to use OkHttp instead of HttpURLConnection you'll need a dependency on okhttp

<dependency>
    <groupId>com.squareup.okhttp3</groupId>
    <artifactId>okhttp</artifactId>
    <version>4.10+</version>
</dependency>

Then you can change your config to

UnleashConfig config = UnleashConfig.builder()
    .appName("my-app")
    .unleashAPI("http://unleash.org")
    .customHttpHeader("Authorization", "API token")
    .unleashMetricsSenderFactory(OkHttpMetricsSender::new)
    .build();

This will then start using OkHttp instead of HttpURLConnection to send metrics

Local backup

By default unleash-client fetches the feature toggles from unleash-server every 10s, and stores the result in unleash-repo.json which is located in the java.io.tmpdir directory. This means that if the unleash-server becomes unavailable, the unleash-client will still be able to toggle the features based on the values stored in unleash-repo.json. As a result of this, the second argument of isEnabled will be returned in two cases:

• When unleash-repo.json does not exists
• When the named feature toggle does not exist in unleash-repo.json

Bootstrapping

• Unleash supports bootstrapping from a JSON string.
• Configure your own custom provider implementing the ToggleBootstrapProvider interface's single method String read(). This should return a JSON string in the same format returned from /api/client/features
• Example bootstrap files can be found in the json files located in src/test/resources
• Our assumption is this can be use for applications deployed to ephemeral containers or more locked down file systems where Unleash's need to write the backup file is not desirable or possible.

Provided Bootstrappers

ToggleBootstrapFileProvider

• Unleash comes configured with a ToggleBootstrapFileProvider which implements the ToggleBootstrapProvider interface.
• It is the default implementation used if not overridden via the setToggleBootstrapProvider on UnleashConfig.

Configure ToggleBootstrapFileProvider

• The ToggleBootstrapFileProvider reads the file located at the path defined by the UNLEASH_BOOTSTRAP_FILE environment variable.
• It supports both classpath: paths and absolute file paths.

Unit testing

You might want to control the state of the toggles during unit-testing. Unleash do come with a FakeUnleash implementation for doing this.

Some examples on how to use it below:

// example 1: everything on
FakeUnleash fakeUnleash = new FakeUnleash();
fakeUnleash.enableAll();

assertThat(fakeUnleash.isEnabled("unknown"), is(true));
assertThat(fakeUnleash.isEnabled("unknown2"), is(true));

// example 2
FakeUnleash fakeUnleash = new FakeUnleash();
fakeUnleash.enable("t1", "t2");

assertThat(fakeUnleash.isEnabled("t1"), is(true));
assertThat(fakeUnleash.isEnabled("t2"), is(true));
assertThat(fakeUnleash.isEnabled("unknown"), is(false));

// example 3: variants
FakeUnleash fakeUnleash = new FakeUnleash();
fakeUnleash.enable("t1", "t2");
fakeUnleash.setVariant("t1", new Variant("a", (String) null, true));

assertThat(fakeUnleash.getVariant("t1").getName(), is("a"));

Se more in FakeUnleashTest.java

Development

Build:

mvn clean install

Jacoco coverage reports:

mvn jacoco:report

The generated report will be available at target/site/jacoco/index.html

Formatting

• We're using AOSP Java code style, enforced by spotless. For formatting, use mvn spotless:apply and spotless will do the job for you
• It should apply spotless automatically upon compilation for you, but only on code that is changed since origin/main
• For Intelij you can use https://plugins.jetbrains.com/plugin/8527-google-java-format
• For VSCode you can use https://marketplace.visualstudio.com/items?itemName=wx-chevalier.google-java-format
• For VIM there's https://github.com/google/vim-codefmt

Releasing

Deployment

• You'll need an account with Sonatype's JIRA - https://issues.sonatype.org
• In addition your account needs access to publish under io.getunleash

GPG signing

• You'll need gpg installed and a configured gpg key for signing the artifacts

Example settings.xml

• In ~/.m2/settings.xml put

<settings>
    ...
    <profiles>
        ...
        <profile>
            <id>ossrh</id>
            <activation>
                <activeByDefault>true</activeByDefault>
            </activation>
            <properties>
                <gpg.executable>gpg</gpg.executable> <!-- Where to find gpg -->
                <gpg.passphrase>[PASSPHRASE FOR YOUR GPG KEY]</gpg.passphrase>
            </properties>
        </profile>
    </profiles>
    ...
    <servers>
        ...
        <server>
            <id>sonatype-nexus-snapshots</id>
            <username>[YOUR_SONATYPE_JIRA_USERNAME]</username>
            <password>[YOUR_SONATYPE_JIRA_PASSWORD]</password>
        </server>
        <server>
            <id>ossrh</id>
            <username>[YOUR_SONATYPE_JIRA_USERNAME]</username>
            <password>[YOUR_SONATYPE_JIRA_PASSWORD]</password>
        </server>
        <server>
            <id>sonatype-nexus-staging</id>
            <username>[YOUR_SONATYPE_JIRA_USERNAME]</username>
            <password>[YOUR_SONATYPE_JIRA_PASSWORD]</password>
        </server>
    </servers>
</settings>

More information

• https://central.sonatype.org/pages/ossrh-guide.html

Configuration options

The UnleashConfigBuilder class (created via UnleashConfig.builder()) exposes a set of builder methods to configure your Unleash client. The available options are listed below with a description of what they do. For the full signatures, take a look at the UnleashConfig class definition.

Method name	Description	Required	Default value
apiKey	The api key to use for authenticating against the Unleash API.	Yes	null
appName	The name of the application as shown in the Unleash UI. Registered applications are listed on the Applications page.	Yes	null
backupFile	The path to the file where local backups get stored.	No	Synthesized from your system's java.io.tmpdir and your appName: "<java.io.tmpdir>/unleash-<appName>-repo.json"
customHttpHeader	Add a custom HTTP header to the list of HTTP headers that will the client sends to the Unleash API. Each method call will add a new header. Note: in most cases, you'll need to use this method to provide an API token.	No	N/A
customHttpHeadersProvider	Add a custom HTTP header provider. Useful for dynamic custom HTTP headers.	No	null
disablePolling	A boolean indicating whether the client should poll the unleash api for updates to toggles.
disableMetrics	A boolean indicating whether the client should disable sending usage metrics to the Unleash server.	No	false
enableProxyAuthenticationByJvmProperties	Enable support for using JVM properties for HTTP proxy authentication.	No	false
environment	The name of the current environment.	No	null
fallbackStrategy	A strategy implementation that the client can use if it doesn't recognize the strategy type returned from the server.	No	null
fetchTogglesInterval	How often (in seconds) the client should check for toggle updates. Set to 0 if you want to only check once.	No	10
instanceId	A unique(-ish) identifier for your instance. Typically a hostname, pod id or something similar. Unleash uses this to separate metrics from the client SDKs with the same appName.	Yes	null
namePrefix	If provided, the client will only fetch toggles whose name starts with the provided value.	No	null
projectName	If provided, the client will only fetch toggles from the specified project. (This can also be achieved with an API token).	No	null
proxy	A Proxy object. Use this to configure a third-party proxy that sits between your client and the Unleash server.	No	null
scheduledExecutor	A custom executor to control timing and running of tasks (such as fetching toggles, sending metrics).	No	UnleashScheduledExecutorImpl
sendMetricsInterval	How often (in seconds) the client should send metrics to the Unleash server. Ignored if you disable metrics with the disableMetrics method.	No	60
subscriber	Register a subscriber to Unleash client events.	No	null
synchronousFetchOnInitialisation	Whether the client should fetch toggle configuration synchronously (in a blocking manner).	No	false
toggleBootstrapProvider	Add a bootstrap provider (must implement the ToggleBootstrapProvider interface)	No
unleashAPI	The URL of the Unleash API.	Yes	null
unleashContextProvider	An Unleash context provider used to configure Unleash.	No	null
unleashFeatureFetcherFactory	A factory providing a FeatureFetcher implementation.	No	HttpFeatureFetcher::new
unleashMetricsSenderFactory	A factory providing a MetricSender implementation.	No	JavaHttpMetricsSender::new

When you have set all the desired options, initialize the configuration with the build method. You can then pass the configuration to the Unleash client constructor. As an example:

UnleashConfig config = UnleashConfig.builder()
            .appName("your app name")
            .instanceId("instance id")
            .unleashAPI("http://unleash.herokuapp.com/api/")
            .apiKey("API token")
            // ... more configuration options
            .build();

Unleash unleash = new DefaultUnleash(config);