[JAVA] Introduction of library ff4j that realizes FeatureToggle with Spring Boot

What is Feature Toggle?

• This is a basic story, so if you know it, please skip it. FeatureToggle is simply a conditional branch that turns a feature on and off. It is also called Feature Flag.

For example, as shown below, prepare a boolean variable called ʻuseNewAlgorithm to use a new algorithm, and use it in situations where the new algorithm and the old algorithm are used properly according to the true / false of ʻuseNewAlgorithm.

  function reticulateSplines(){
    var useNewAlgorithm = false;
    // useNewAlgorithm = true; // UNCOMMENT IF YOU ARE WORKING ON THE NEW SR ALGORITHM
  
    if( useNewAlgorithm ){
      return enhancedSplineReticulation();
    }else{
      return oldFashionedSplineReticulation();
    }
  }
  
  function oldFashionedSplineReticulation(){
    // current implementation lives here
  }
  
  function enhancedSplineReticulation(){
    // TODO: implement better SR algorithm
  }

FeatureFlag is often used when providing new features with a fixed release timing, canary releases, A / B testing, etc.

FF4J

https://ff4j.github.io/

FF4j is a Java library that can easily implement FeatureToggle.

--Real-time Toggle switching using Web Console and REST API --Persistence of state using various storages --Feature usage monitoring

Various functions such as are provided.

Installation procedure

Creating a project

Create a project by selecting only Spring Reactive Web, lombok from Spring Initializr that everyone loves.

Introduction of FF4j

Add a dependency to pom.xml.

pom.xml

<dependency>
    <groupId>org.ff4j</groupId>
    <artifactId>ff4j-spring-boot-starter</artifactId>
    <version>1.8</version>
</dependency>

Create Bean definition & Feature for FF4j.

FF4JConfiguration.java

import org.ff4j.FF4j;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class FF4JConfiguration {
    @Bean
    public FF4j ff4j() {
        FF4j ff4j = new FF4j()
                .createFeature(awesomeFeature())
                .createFeature(greatFeature())
                .createFeature(excellentFeature());
        return ff4j;
    }

    private Feature awesomeFeature() {
        return new Feature("AwesomeFeature", true);
    }

    private Feature greatFeature() {
        return new Feature("GreatFeature", false);
    }

    private Feature excellentFeature() {
        return new Feature("ExcellentFeature", false);
    }
}

This time, we have defined three features, ʻAwesomeFeature, GreatFeature, and ʻExcellentFeature, and turned on only ʻAwesomeFeature`.

Implement Controller using FF4j. In the Controller that returns only a simple message, if the three defined features are turned on, it is added to the message according to the features.

GreetingController.java

@RestController
@RequiredArgsConstructor
public class GreetingController {

    //Constructor injection
    private final FF4j ff4j;

    @GetMapping
    public String greeting() {
        List<String> features = new ArrayList<>();
        addFeatures(features);
        String greeting = String.format("Hello, %s World!!", String.join(" ", features));

        return greeting;
    }

    //Processing of each feature
    private void addFeatures(List<String> features) {
        if(ff4j.check("AwesomeFeature")) {
            features.add("Awesome");
        }

        if(ff4j.check("GreatFeature")) {
            features.add("Great");
        }

        if(ff4j.check("ExcellentFeature")) {
            features.add("Excellent");
        }
    }
}

Launch the application and go to http: // localhost: 8080.

By default, ʻAwesome Feature is enabled, so the message will be displayed as Hello, Awesome World! `.

Introducing Web Console

Next, install the FF4j management console. In the previous state, it was necessary to switch Feature on / off on the source code, but by using WebConsole, it is possible to switch Feature on / off while the application is running.

Add a dependency to pom.xml.

<dependency>
	<groupId>org.ff4j</groupId>
	<artifactId>ff4j-web</artifactId>
	<version>1.8</version>
</dependency>
<dependency>
	<groupId>org.thymeleaf</groupId>
	<artifactId>thymeleaf</artifactId>
	<version>2.1.4.RELEASE</version>
</dependency>

Add a new bean definition.

@Configuration
@ConditionalOnClass({ConsoleServlet.class, FF4jDispatcherServlet.class})
@AutoConfigureAfter(FF4JConfiguration.class)
public class FF4JWebConfiguration extends SpringBootServletInitializer {

    @Bean
    public ServletRegistrationBean<FF4jDispatcherServlet> ff4jDispatcherServletRegistrationBean(FF4jDispatcherServlet ff4jDispatcherServlet)
    {
        ServletRegistrationBean<FF4jDispatcherServlet> bean = new ServletRegistrationBean<>(ff4jDispatcherServlet, "/ff4j-web-console/*");
        bean.setName("ff4j-console");
        bean.setLoadOnStartup(1);
        return bean;
    }

    @Bean
    @ConditionalOnMissingBean
    public FF4jDispatcherServlet getFF4jDispatcherServlet(FF4j ff4j) {
        FF4jDispatcherServlet ff4jDispatcherServlet = new FF4jDispatcherServlet();
        ff4jDispatcherServlet.setFf4j(ff4j);
        return ff4jDispatcherServlet;
    }

}

Start and access http: // localhost: 8080 / ff4j-web-console.

You can see the currently defined Features in the Features menu, Feature turns on / off as the toggle is turned on / off.

GIF animation demo

I will also post a demo of the contents explained above taken with GIF animation. For your reference.

Summary

I gave a brief introduction of FF4j. Feature Toggle is a powerful technique, but if you don't set an operation policy, a chaotic code base will be created, so I want to be careful when operating it. It is necessary to have a framework such as separating the features to be DI for each profile and defining coding standards and review points.

reference

martinFowler.com - FeatureToggle: https://martinfowler.com/articles/feature-toggles.html FF4j: https://ff4j.github.io/ Repository used this time: https://github.com/IshinFUKUOKA/ff4j-demo