[FSSDK-9785] handle duplicate experiment keys with a warning (#535)

When duplicate experiment keys are found in a datafile, SDK returns a correct experimentMap in OptimizelyConfig:

- the experimentMap will contain the experiment later in the datafile experiments list.
- add a warning log about "Duplicate experiment keys found in datafile: {key-name}"

Author: jaeopt

Diff for: core-api/src/main/java/com/optimizely/ab/optimizelyconfig/OptimizelyConfigService.java

@@ -1,5 +1,5 @@
 /****************************************************************************
- * Copyright 2020-2021, Optimizely, Inc. and contributors                        *
+ * Copyright 2020-2021, 2023, Optimizely, Inc. and contributors             *
  *                                                                          *
  * Licensed under the Apache License, Version 2.0 (the "License");          *
  * you may not use this file except in compliance with the License.         *
@@ -18,6 +18,8 @@
 import com.optimizely.ab.annotations.VisibleForTesting;
 import com.optimizely.ab.config.*;
 import com.optimizely.ab.config.audience.Audience;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 import java.util.*;
 
@@ -31,6 +33,8 @@ public class OptimizelyConfigService {
     private Map<String, List<FeatureVariable>> featureIdToVariablesMap = new HashMap<>();
     private Map<String, OptimizelyExperiment> experimentMapByExperimentId = new HashMap<>();
 
+    private static final Logger logger = LoggerFactory.getLogger(OptimizelyConfigService.class);
+
     public OptimizelyConfigService(ProjectConfig projectConfig) {
         this.projectConfig = projectConfig;
         this.audiences = getAudiencesList(projectConfig.getTypedAudiences(), projectConfig.getAudiences());
@@ -125,6 +129,11 @@ Map<String, OptimizelyExperiment> getExperimentsMap() {
                 experiment.serializeConditions(this.audiencesMap)
             );
 
+            if (featureExperimentMap.containsKey(experiment.getKey())) {
+                // continue with this warning, so the later experiment will be used.
+                logger.warn("Duplicate experiment keys found in datafile: {}", experiment.getKey());
+            }
+
             featureExperimentMap.put(experiment.getKey(), optimizelyExperiment);
             experimentMapByExperimentId.put(experiment.getId(), optimizelyExperiment);
         }

Diff for: core-api/src/test/java/com/optimizely/ab/optimizelyconfig/OptimizelyConfigServiceTest.java

@@ -1,5 +1,5 @@
 /****************************************************************************
- * Copyright 2020-2021, Optimizely, Inc. and contributors                        *
+ * Copyright 2020-2021, 2023, Optimizely, Inc. and contributors             *
  *                                                                          *
  * Licensed under the Apache License, Version 2.0 (the "License");          *
  * you may not use this file except in compliance with the License.         *
@@ -15,23 +15,29 @@
  ***************************************************************************/
 package com.optimizely.ab.optimizelyconfig;
 
+import ch.qos.logback.classic.Level;
 import com.optimizely.ab.config.*;
 import com.optimizely.ab.config.audience.Audience;
+import com.optimizely.ab.internal.LogbackVerifier;
 import org.junit.Before;
+import org.junit.Rule;
 import org.junit.Test;
-import org.junit.runner.RunWith;
-import org.mockito.runners.MockitoJUnitRunner;
 
 import java.util.*;
 import static java.util.Arrays.asList;
 import static org.junit.Assert.*;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
 
 public class OptimizelyConfigServiceTest {
 
     private ProjectConfig projectConfig;
     private OptimizelyConfigService optimizelyConfigService;
     private OptimizelyConfig expectedConfig;
 
+    @Rule
+    public LogbackVerifier logbackVerifier = new LogbackVerifier();
+
     @Before
     public void initialize() {
         projectConfig = generateOptimizelyConfig();
@@ -46,6 +52,33 @@ public void testGetExperimentsMap() {
         assertEquals(expectedConfig.getExperimentsMap(), optimizelyExperimentMap);
     }
 
+    @Test
+    public void testGetExperimentsMapWithDuplicateKeys() {
+        List<Experiment> experiments = Arrays.asList(
+            new Experiment(
+                "first",
+                "duplicate_key",
+                null, null, Collections.<String>emptyList(), null,
+                Collections.<Variation>emptyList(), Collections.<String, String>emptyMap(), Collections.<TrafficAllocation>emptyList()
+            ),
+            new Experiment(
+                "second",
+                "duplicate_key",
+                null, null, Collections.<String>emptyList(), null,
+                Collections.<Variation>emptyList(), Collections.<String, String>emptyMap(), Collections.<TrafficAllocation>emptyList()
+            )
+        );
+
+        ProjectConfig projectConfig = mock(ProjectConfig.class);
+        OptimizelyConfigService optimizelyConfigService = new OptimizelyConfigService(projectConfig);
+        when(projectConfig.getExperiments()).thenReturn(experiments);
+
+        Map<String, OptimizelyExperiment> optimizelyExperimentMap = optimizelyConfigService.getExperimentsMap();
+        assertEquals("Duplicate keys should be overwritten", optimizelyExperimentMap.size(), 1);
+        assertEquals("Duplicate keys should be overwritten", optimizelyExperimentMap.get("duplicate_key").getId(), "second");
+        logbackVerifier.expectMessage(Level.WARN, "Duplicate experiment keys found in datafile: duplicate_key");
+    }
+
     @Test
     public void testRevision() {
         String revision = optimizelyConfigService.getConfig().getRevision();

Diff for: java-quickstart/src/main/java/com/optimizely/Example.java

@@ -56,7 +56,7 @@ private void processVisitor(String userId, Map<String, Object> attributes) {
 
     public static void main(String[] args) throws InterruptedException {
         Optimizely optimizely = OptimizelyFactory.newDefaultInstance("BX9Y3bTa4YErpHZEMpAwHm");
-
+        
         Example example = new Example(optimizely);
         Random random = new Random();