Java Feature Flag Resources/Solutions
- LaunchDarkly Java Feature Flag SDK – LaunchDarkly
- Togglz – Christian Kaltepoth
- “Togglz is an implementation of the Feature Toggles pattern for Java. Feature Toggles are a very common agile development practices in the context of continuous deployment and delivery. The basic idea is to associate a toggle with each new feature you are working on. This allows you to enable or disable these features at application runtime, even for individual users.”
- GitHub Repo
- FF4J – Cédrick Lunven
- “Feature Toggle is the capability for an application, a system or a product to enable and/or disable features through configuration (files, databases,…) and possibly at runtime. FF4J, stands as Feature Flipping for Java, is an implementation of this pattern for the Java platform.”
- GitHub Repo
- Flip – Petric Coroli
- “Flip makes it simple to use Feature Toggle, (also known as Feature Flags, Feature Bits, Feature Switches, etc) in your Java application. Feature toggles can be used for many purposes, including: Reducing the need to branch by feature in your source control system by having all work done on the main code line. Features that are not ready for production can simply be disabled. New features can be rolled out to a subset of users (e.g. by group membership, canary testing, etc) Should a feature become problematic, we can turn it off without requiring a build and deploy.”
- GitHub Repo
- Fitchy – Andreas Kaubisch
- “A simple java library to use feature toggles / feature switches in your application. It provides a simple annotation based configuration to implement toggles into your code. Currently it supports only simple java projects where you manually add toggle support to a class. You mustn’t use annotation to enable toggling, you can also use an anonymous class that provide a possibility to switch between enabled and disabled status. With this early version you have the ability to configure your provided features in a property file an load it at runtime. There is also a possibility to configure your feature with pure java only. This library uses two types of proxy mechanics to enable toggles on an object. You can configure your fitchy to proxying an object with cglib or just the standard java proxy. The default behaviour is to create a proxy with the standard java library.”
- GitHub Repo
LaunchDarkly Java SDK Reference
Our Java SDK is intended for use in trusted server environments only, and should not be distributed to untrusted mobile users.
If you want to use LaunchDarkly in an Android application, see our Android SDK Reference Guide.
If you haven’t taken a look at our Quickstart guide yet, we recommend starting there to see how install our SDK into your Java application.
Once the SDK is installed, you’ll want to create a single, shared instance of
LDClient must be a singleton
It’s important to make this a singleton– internally, the client instance maintains internal state that allows us to serve feature flags without making any remote requests. Be sure that you’re not instantiating a new client with every request.
Customizing your client
You can also pass custom parameters to the client by creating a custom configuration object:
Let’s walk through this snippet. The first argument to the builder is the user’s key– in this case we’ve used the hash
"aa0ceb". The user key is the only mandatory user attribute. The key should also uniquely identify each user. You can use a primary key, an e-mail address, or a hash, as long as the same user always has the same key. We recommend using a hash if possible.
All of the other attributes (like
custom attributes) are optional. The attributes you specify will automatically appear on our dashboard, meaning that you can start segmenting and targeting users with these attributes.
Our Javadoc for LDUser.Builder shows you all the attributes that LaunchDarkly supports by default. In addition to these, you can pass us any of your own user data by passing
custom attributes, like the
groups attribute in the example above.
A note on types
Most of our built-in attributes (like names and e-mail addresses) expect string values. Custom attributes values can be strings, booleans (like true or false), numbers, or lists of strings, booleans or numbers.
If you enter a custom value on our dashboard that looks like a number or a boolean, it’ll be interpreted that way. The Java SDK is strongly typed, so be aware of this distinction.
Custom attributes are one of the most powerful features of LaunchDarkly. They let you target users according to any data that you want to send to us– organizations, groups, account plans– anything you pass to us becomes available instantly on our dashboard.
You can also distinguish logged-in users from anonymous users in the SDK, as follows:
You will still need to generate a unique key for anonymous users– session IDs or UUIDs work best for this.
Anonymous users work just like regular users, except that they won’t appear on your Users page in LaunchDarkly. You also can’t search for anonymous users on your Features page, and you can’t search or autocomplete by anonymous user keys. This is actually a good thing– it keeps anonymous users from polluting your Users page!
variation method determines which variation of a feature flag a user receives. In Java, there is a
variationmethod for each type (e.g.
variation calls take the feature flag key, an
LDUser, and a default value.
The default value will only be returned if an error is encountered– for example, if the feature flag key doesn’t exist or the user doesn’t have a key specified.
variation call will automatically create a user in LaunchDarkly if a user with that user key doesn’t exist already. There’s no need to create users ahead of time (but if you do need to, take a look at Identify).
allFlags method produces a map of feature flag keys to their values for a specific user.
track method allows you to record actions your users take on your site. This lets you record events that take place on your server. In LaunchDarkly, you can tie these events to goals in A/B tests. Here’s a simple example:
You can also attach custom JSON data to your event by passing an extra parameter to
identify creates or updates users on LaunchDarkly, making them available for targeting and autocomplete on the dashboard. In most cases, you won’t need to call
variation call will automatically create users on the dashboard for you.
identify can be useful if you want to pre-populate your dashboard before launching any features.
Secure mode hash
Internally, the LaunchDarkly SDK keeps an event buffer for
identify calls. These are flushed periodically in a background thread. In some situations (for example, if you’re testing out the SDK in a REPL), you may want to manually call
flush to process events immediately.
Note that the flush interval is configurable– if you need to change the interval, you can do so via
In some situations, you might want to stop making remote calls to LaunchDarkly and fall back to default values for your feature flags. For example, if your software is both cloud-hosted and distributed to customers to run on premise, it might make sense to fall back to defaults when running on premise. You can do this by setting
offlinemode in the client’s
LDConfig config = new LDConfig.Builder() .offline(true) .build(); LDClient ldClient = new LDClient("YOUR_SDK_KEY", config); ldClient.boolVariation("any.feature.flag", user, false) // will always return the default value (false)
Close safely shuts down the client instance and releases all resources associated with the client. In most long-running applications, you should not have to call close.