[BUG-8620] Make DefaultJsonSerializer resilient to init failures

core-api/src/main/java/com/optimizely/ab/event/internal/serializer/DefaultJsonSerializer.java

@@ -22,6 +22,8 @@
 import com.optimizely.ab.config.parser.MissingJsonParserException;
 
 import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+import java.util.concurrent.Callable;
 
 /**
  * Factory for generating {@link Serializer} instances, based on the json library available on the classpath.
@@ -48,22 +50,27 @@ public static Serializer getInstance() {
     private static @Nonnull
     Serializer create() {
         Serializer serializer;
-
-        if (isPresent("com.fasterxml.jackson.databind.ObjectMapper")) {
-            serializer = new JacksonSerializer();
-        } else if (isPresent("com.google.gson.Gson")) {
-            serializer = new GsonSerializer();
-        } else if (isPresent("org.json.simple.JSONObject")) {
-            serializer = new JsonSimpleSerializer();
-        } else if (isPresent("org.json.JSONObject")) {
-            serializer = new JsonSerializer();
-        } else {
-            throw new MissingJsonParserException("unable to locate a JSON parser. "
-                + "Please see <link> for more information");
+        if ((serializer = tryCreate("com.fasterxml.jackson.databind.ObjectMapper", JacksonSerializer::new)) != null ||
+            (serializer = tryCreate("com.google.gson.Gson", GsonSerializer::new)) != null ||
+            (serializer = tryCreate("org.json.simple.JSONObject", JsonSimpleSerializer::new)) != null ||
+            (serializer = tryCreate("org.json.JSONObject", JsonSerializer::new)) != null) {
+            logger.debug("using json serializer: {}", serializer.getClass().getSimpleName());
+            return serializer;
         }
+        throw new MissingJsonParserException("unable to locate a JSON parser. "
+            + "Please see <link> for more information");
+    }
 
-        logger.debug("using json serializer: {}", serializer.getClass().getSimpleName());
-        return serializer;
+    private static @Nullable Serializer tryCreate(String className, Callable<Serializer> factory) {
+        if (!isPresent(className)) {
+            return null;
+        }
+        try {
+            return factory.call();
+        } catch (Throwable t) {
+            logger.warn("{} found on classpath but serializer init failed, trying next option.", className, t);
+            return null;
+        }
     }
 
     private static boolean isPresent(@Nonnull String className) {

core-api/src/test/java/com/optimizely/ab/event/internal/serializer/DefaultJsonSerializerTest.java

@@ -0,0 +1,45 @@
+/**
+ *
+ *    Copyright 2026, Optimizely and contributors
+ *
+ *    Licensed under the Apache License, Version 2.0 (the "License");
+ *    you may not use this file except in compliance with the License.
+ *    You may obtain a copy of the License at
+ *
+ *        http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *    Unless required by applicable law or agreed to in writing, software
+ *    distributed under the License is distributed on an "AS IS" BASIS,
+ *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *    See the License for the specific language governing permissions and
+ *    limitations under the License.
+ */
+package com.optimizely.ab.event.internal.serializer;
+
+import org.junit.Test;
+import static org.junit.Assert.*;
+
+public class DefaultJsonSerializerTest {
+
+    @Test
+    public void getInstanceReturnsNonNull() {
+        Serializer serializer = DefaultJsonSerializer.getInstance();
+        assertNotNull("getInstance() should return a non-null serializer", serializer);
+    }
+
+    @Test
+    public void getInstanceReturnsSameInstance() {
+        Serializer first = DefaultJsonSerializer.getInstance();
+        Serializer second = DefaultJsonSerializer.getInstance();
+        assertSame("getInstance() should return the same singleton instance", first, second);
+    }
+
+    @Test
+    public void instanceCanSerialize() {
+        Serializer serializer = DefaultJsonSerializer.getInstance();
+        String result = serializer.serialize(java.util.Collections.singletonMap("test_key", "test_value"));
+        assertNotNull("Serializer should produce non-null output", result);
+        assertTrue("Serialized output should contain the key", result.contains("test_key"));
+        assertTrue("Serialized output should contain the value", result.contains("test_value"));
+    }
+}