Aspect Oriented Programming (AOP)¶

FF4j leverages on Spring AOP framework to provide a seamless integration for feature toggling using annotations, making it easier to manage and maintain feature toggles in a clean and efficient manner.

Overview¶

From the beginning of this guide, we use imperative statements within source code to perform feature toggle check like:

Snippet for checking the state of a feature

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

This approach is quite intrusive into source code. You can nest different feature toggles at you may consider to clean often your code and remove obsolete features.

A good alternative is to rely on Dependency Injection, also called Inversion of control (IoC) to choose the correct implementation of the service at runtime.

Ff4j provide the @Flip annotation to perform flipping on methods using AOP proxies. At runtime, the target service is proxied by the FF4j component which choose an implementation instead of another using feature status (enable/disable). It leverages on Spring AOP Framework.

Sample¶

Info

The complete sample is available in the ff4j-samples/ff4j-aop-sample repository.

1. Dependency2. Service interface3. Service implementation4. FF4j Configuration5. Test

Add the dependency ff4j-aop

pom.xml

<dependency>
  <groupId>org.ff4j</groupId>
  <artifactId>ff4j-aop</artifactId>
  <version>${ff4j.version}</version>
</dependency>

Create interface with the annotation @Flip on the method to be flipped

org.ff4j.sample.aop.service.GreetingService.java

package org.ff4j.sample.aop.service;

import org.ff4j.aop.Flip;

public interface GreetingService {

  @Flip(name = "language", alterBean = "greeting.french")
  String sayHello(String name);
}

We will define two implementations of the service, one for English and another for French. The @Flip annotation on the sayHello method indicates that the implementation will be switched based on the state of the "language" feature.

org.ff4j.sample.aop.service.EnglishGreetingService.java

package org.ff4j.sample.aop.service;

import org.springframework.context.annotation.Primary;
import org.springframework.stereotype.Component;

@Primary
@Component("greeting.english")
public class EnglishGreetingService implements GreetingService {

  @Override
  public String sayHello(String name) {
    return "Hello, " + name + "!";
  }
}

Note

The @Primary annotation on the EnglishGreetingService indicates that it will be the default implementation when the "language" feature is disabled.

org.ff4j.sample.aop.service.FrenchGreetingService.java

package org.ff4j.sample.aop.service;

import org.springframework.stereotype.Component;

@Component("greeting.french")
public class FrenchGreetingService implements GreetingService {

  @Override
  public String sayHello(String name) {
    return "Bonjour, " + name + "!";
  }
}

Create an FF4j configuration class to set up the FF4j bean and enable component scanning for the AOP package and your service package.

org.ff4j.sample.aop.config.FF4jConfig.java

package org.ff4j.sample.aop.config;

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

@Configuration
@ComponentScan({"org.ff4j.aop", "org.ff4j.sample.aop"})
public class FF4jConfig {

  @Bean
  public FF4j ff4j() {
    return new FF4j("ff4j-language-sample.xml");
  }
}

Create the FF4j configuration file to define the "language" feature, which will control the switching between English and French greetings.

resources/ff4j-language-sample.xml

<?xml version="1.0" encoding="UTF-8" ?>
<ff4j xmlns="https://www.ff4j.org/schema/ff4j"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="https://www.ff4j.org/schema/ff4j https://ff4j.org/schema/ff4j-1.4.0.xsd">
  <features>
    <feature uid="language" enable="false"></feature>
  </features>
</ff4j>

org.ff4j.sample.aop.FF4jAopTest.java

package org.ff4j.sample.aop;

import org.ff4j.FF4j;
import org.ff4j.sample.aop.config.FF4jConfig;
import org.ff4j.sample.aop.service.GreetingService;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit.jupiter.SpringExtension;

import static org.assertj.core.api.Assertions.assertThat;

@ExtendWith(SpringExtension.class)
@ContextConfiguration(classes = FF4jConfig.class)
class FF4jAopTest {

  @Autowired
  private FF4j ff4j;

  @Autowired
  private GreetingService greetingService;

  @Test
  void defaultEnglishGreeting() {
    // Given
    assertThat(ff4j.getFeatureStore().exist("language")).isTrue();
    assertThat(ff4j.check("language")).isFalse();
    // When
    String greeting = greetingService.sayHello("John");
    // Then
    assertThat(greeting).isEqualTo("Hello, John!");
  }

  @Test
  void toggleFrenchGreeting() {
    // Given
    assertThat(ff4j.getFeatureStore().exist("language")).isTrue();
    assertThat(ff4j.check("language")).isFalse();
    // When
    ff4j.enable("language");
    // Then
    assertThat(ff4j.check("language")).isTrue();
    // When
    String greeting = greetingService.sayHello("John");
    // Then
    assertThat(greeting).isEqualTo("Bonjour, John!");
  }
}