‣ Feature Flag

Overview

The Feature term is used to represent functionality or treatment in an application. It is identified by an unique identifier (uid).

A Feature represents a business logic that can potentially crosses every layer of applications from user interfaces to data access. Therefore, to implement a feature toggle mechanism, we must help you in each layer as shown with the picture on the right.

Feature toggle,or feature flag, purpose is to evaluate the state of features at runtime to drive the execution of your code. You can change the state of features at runtime (enable and disable, toggle ON/OFF).

Each feature is associated as a flag. Given a feature with identifier f1 we want to write in the code:

if (ff4j.check("f1")) {
  System.out.println("The feature 'f1' is 'ON'");
} else {
  System.out.println("The feature 'f1' is 'OFF'");    
}

Feature object

With the library FF4J, a feature is an object with multiple attributes (not only identifier and state):

• A text description to explain the purpose
• An optional groupName to toggle multiple features at once (see FeatureGroup)
• An optional set of permissions to implement RBAC access. (see Permissions)
• An optional flipping strategy to implement your predicates (see FlippingStrategy)

• A key/value map named customProperties to create some context

  classDiagram
  Feature --* FlippingStrategy
  Feature --* Property
  
  Feature : enable()
  Feature : disable()
  Feature : toJson()
  Feature : fromJson(...)  
  Feature : getters()
  Feature : setters()
  Feature : String uid
  Feature : boolean enable
  Feature : String description
  Feature : String group
  Feature : Set<String> permissions
  Feature : Map<String,Property> customProperties
  FlippingStrategy : getInitParams()
  FlippingStrategy : evaluate()
  Property : name
  Property : value

Sample codes

You can interact with the Feature object programmatically :

Feature f1 = new Feature("f1");
Feature f2 = new Feature("f2", false, "sample description");

• Feature with Permissions:

Set < String > permission = new HashSet<String>();
permission.add("BETA-TESTER");
permission.add("VIP");
Feature f3 = new Feature("f3", false, "desc", "GROUP_1", permission);

• Feature with Custom Properties:

Feature f4 = new Feature("f4");
f4.addProperty(new PropertyString("p1", "v1"));
f4.addProperty(new PropertyDouble("pie", Math.PI));
f4.addProperty(new PropertyInt("myAge", 12));

• Feature with FlippingStrategy

Feature f5 = new Feature("f5");
Calendar nextReleaseDate = Calendar.getInstance();
nextReleaseDate.set(Calendar.MONTH, Calendar.SEPTEMBER);
nextReleaseDate.set(Calendar.DAY_OF_MONTH, 1);
f5.setFlippingStrategy(new ReleaseDateFlipStrategy(nextReleaseDate.getTime()));

// Working with DarkLaunch Flipping Strategy
Feature f6 = new Feature("f6");
f6.setFlippingStrategy(new DarkLaunchStrategy(0.2d));        

// Working with White List Flipping Strategy
Feature f7 = new Feature("f7");
f7.setFlippingStrategy(new WhiteListStrategy("localhost"));

It is not likely that you do have to create the Features objects on your own (except for tests). They will be stored in the FeatureStore and purpose is really to check the status at runtime. You may want to create them through the webUI or configuration files. Attributes mentionned before are available in the edit modal:

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Last update: 2023-07-04