feature flag patterns

Author: thombergs

spring-boot/feature-flags/src/main/java/io/reflectoring/featureflags/FeatureFlagService.java

@@ -22,4 +22,6 @@ public interface FeatureFlagService {
      */
     Boolean isUserActionTargetedFeatureActive();
 
+    Boolean isNewServiceEnabled();
+
 }

spring-boot/feature-flags/src/main/java/io/reflectoring/featureflags/ff4j/FF4JFeatureFlagService.java

@@ -33,4 +33,9 @@ public Boolean isUserActionTargetedFeatureActive() {
         return null;
     }
 
+    @Override
+    public Boolean isNewServiceEnabled() {
+        return null;
+    }
+
 }

spring-boot/feature-flags/src/main/java/io/reflectoring/featureflags/launchdarkly/LaunchDarklyFeatureFlagService.java

@@ -4,11 +4,13 @@
 import com.launchdarkly.sdk.server.LDClient;
 import io.reflectoring.featureflags.FeatureFlagService;
 import io.reflectoring.featureflags.web.UserSession;
+import org.springframework.context.annotation.Primary;
 import org.springframework.stereotype.Component;
 
 import javax.annotation.PostConstruct;
 
 @Component("launchdarkly")
+@Primary
 public class LaunchDarklyFeatureFlagService implements FeatureFlagService {
 
     private final LDClient launchdarklyClient;
@@ -56,6 +58,11 @@ public Boolean isUserActionTargetedFeatureActive() {
         return launchdarklyClient.boolVariation("user-clicked-flag", getLaunchdarklyUserFromSession(), false);
     }
 
+    @Override
+    public Boolean isNewServiceEnabled() {
+        return true;
+    }
+
     private LDUser getLaunchdarklyUserFromSession() {
         return new LDUser.Builder(userSession.getUsername())
                 .custom("clicked", userSession.hasClicked())

spring-boot/feature-flags/src/main/java/io/reflectoring/featureflags/patterns/ifelse/Service.java

@@ -0,0 +1,22 @@
+package io.reflectoring.featureflags.patterns.ifelse;
+
+import io.reflectoring.featureflags.FeatureFlagService;
+import org.springframework.stereotype.Component;
+
+@Component
+class Service {
+
+    private final FeatureFlagService featureFlagService;
+
+    public Service(FeatureFlagService featureFlagService) {
+        this.featureFlagService = featureFlagService;
+    }
+
+    public int doSomething() {
+        if (featureFlagService.isNewServiceEnabled()) {
+            return 42;
+        } else {
+            return 1;
+        }
+    }
+}

spring-boot/feature-flags/src/main/java/io/reflectoring/featureflags/patterns/replacebean/FeatureFlagEvaluation.java

@@ -0,0 +1,8 @@
+package io.reflectoring.featureflags.patterns.replacebean;
+
+@FunctionalInterface
+public interface FeatureFlagEvaluation {
+
+    boolean evaluate();
+
+}

spring-boot/feature-flags/src/main/java/io/reflectoring/featureflags/patterns/replacebean/FeatureFlaggedBean.java

@@ -0,0 +1,42 @@
+package io.reflectoring.featureflags.patterns.replacebean;
+
+import org.springframework.beans.factory.FactoryBean;
+
+import java.lang.reflect.InvocationHandler;
+import java.lang.reflect.Proxy;
+
+public class FeatureFlaggedBean<T> implements FactoryBean<T> {
+
+    private final Class<T> targetClass;
+    private final FeatureFlagEvaluation featureFlagEvaluation;
+    private final T beanWhenTrue;
+    private final T beanWhenFalse;
+
+    public FeatureFlaggedBean(Class<T> targetClass, FeatureFlagEvaluation featureFlagEvaluation, T beanWhenTrue, T beanWhenFalse) {
+        this.targetClass = targetClass;
+        this.featureFlagEvaluation = featureFlagEvaluation;
+        this.beanWhenTrue = beanWhenTrue;
+        this.beanWhenFalse = beanWhenFalse;
+    }
+
+    @Override
+    public T getObject() {
+
+        InvocationHandler invocationHandler = (proxy, method, args) -> {
+            if (featureFlagEvaluation.evaluate()) {
+                return method.invoke(beanWhenTrue, args);
+            } else {
+                return method.invoke(beanWhenFalse, args);
+            }
+        };
+
+        Object proxy = Proxy.newProxyInstance(targetClass.getClassLoader(), new Class[]{targetClass}, invocationHandler);
+
+        return (T) proxy;
+    }
+
+    @Override
+    public Class<?> getObjectType() {
+        return targetClass;
+    }
+}

spring-boot/feature-flags/src/main/java/io/reflectoring/featureflags/patterns/replacebean/FeatureFlaggedService.java

@@ -0,0 +1,12 @@
+package io.reflectoring.featureflags.patterns.replacebean;
+
+import io.reflectoring.featureflags.FeatureFlagService;
+import org.springframework.stereotype.Component;
+
+@Component("replaceBeanFeatureFlaggedService")
+class FeatureFlaggedService extends FeatureFlaggedBean<Service> {
+
+    public FeatureFlaggedService(FeatureFlagService featureFlagService) {
+        super(Service.class, featureFlagService::isNewServiceEnabled, new NewService(), new OldService());
+    }
+}

spring-boot/feature-flags/src/main/java/io/reflectoring/featureflags/patterns/replacebean/NewService.java

@@ -0,0 +1,8 @@
+package io.reflectoring.featureflags.patterns.replacebean;
+
+class NewService implements Service {
+    @Override
+    public int doSomething() {
+        return 42;
+    }
+}

spring-boot/feature-flags/src/main/java/io/reflectoring/featureflags/patterns/replacebean/OldService.java

@@ -0,0 +1,8 @@
+package io.reflectoring.featureflags.patterns.replacebean;
+
+class OldService implements Service {
+    @Override
+    public int doSomething() {
+        return 1;
+    }
+}

spring-boot/feature-flags/src/main/java/io/reflectoring/featureflags/patterns/replacebean/Service.java

@@ -0,0 +1,7 @@
+package io.reflectoring.featureflags.patterns.replacebean;
+
+interface Service {
+
+    int doSomething();
+
+}