fix to support old jackson versions too

Author: jaeopt

README.md

@@ -44,9 +44,9 @@ dependencies {
   compile 'com.optimizely.ab:core-api:{VERSION}'
   compile 'com.optimizely.ab:core-httpclient-impl:{VERSION}'
   // The SDK integrates with multiple JSON parsers, here we use Jackson.
-  compile 'com.fasterxml.jackson.core:jackson-core:2.7.1'
-  compile 'com.fasterxml.jackson.core:jackson-annotations:2.7.1'
-  compile 'com.fasterxml.jackson.core:jackson-databind:2.7.1'
+  compile 'com.fasterxml.jackson.core:jackson-core:2.13.5'
+  compile 'com.fasterxml.jackson.core:jackson-annotations:2.13.5'
+  compile 'com.fasterxml.jackson.core:jackson-databind:2.13.5'
 }
 ```
 

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

@@ -19,13 +19,51 @@
 import com.fasterxml.jackson.annotation.JsonInclude;
 import com.fasterxml.jackson.core.JsonProcessingException;
 import com.fasterxml.jackson.databind.ObjectMapper;
-import com.fasterxml.jackson.databind.PropertyNamingStrategies;
 
 class JacksonSerializer implements Serializer {
 
-    private ObjectMapper mapper =
-        new ObjectMapper().setPropertyNamingStrategy(
-            PropertyNamingStrategies.SNAKE_CASE);
+    private ObjectMapper mapper = createMapper();
+
+    /**
+     * Creates an ObjectMapper with snake_case naming strategy.
+     * Supports both Jackson 2.12+ (PropertyNamingStrategies) and earlier versions (PropertyNamingStrategy).
+     * Uses reflection to avoid compile-time dependencies on either API.
+     */
+    static ObjectMapper createMapper() {
+        ObjectMapper objectMapper = new ObjectMapper();
+        Object namingStrategy = getSnakeCaseStrategy();
+        
+        try {
+            // Use setPropertyNamingStrategy method (available in all versions)
+            objectMapper.getClass()
+                .getMethod("setPropertyNamingStrategy", 
+                    Class.forName("com.fasterxml.jackson.databind.PropertyNamingStrategy"))
+                .invoke(objectMapper, namingStrategy);
+        } catch (Exception e) {
+            throw new RuntimeException("Failed to set snake_case naming strategy", e);
+        }
+        
+        return objectMapper;
+    }
+
+    /**
+     * Gets the snake case naming strategy, supporting both Jackson 2.12+ and earlier versions.
+     */
+    private static Object getSnakeCaseStrategy() {
+        try {
+            // Try Jackson 2.12+ API first
+            Class<?> strategiesClass = Class.forName("com.fasterxml.jackson.databind.PropertyNamingStrategies");
+            return strategiesClass.getField("SNAKE_CASE").get(null);
+        } catch (ClassNotFoundException | NoSuchFieldException | IllegalAccessException e) {
+            try {
+                // Fall back to Jackson 2.11 and earlier (deprecated but compatible)
+                Class<?> strategyClass = Class.forName("com.fasterxml.jackson.databind.PropertyNamingStrategy");
+                return strategyClass.getField("SNAKE_CASE").get(null);
+            } catch (ClassNotFoundException | NoSuchFieldException | IllegalAccessException ex) {
+                throw new RuntimeException("Unable to find snake_case naming strategy in Jackson", ex);
+            }
+        }
+    }
 
     public <T> String serialize(T payload) {
         mapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);

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

@@ -18,7 +18,6 @@
 
 import com.fasterxml.jackson.databind.ObjectMapper;
 
-import com.fasterxml.jackson.databind.PropertyNamingStrategies;
 import com.optimizely.ab.event.internal.payload.EventBatch;
 
 import org.junit.Test;
@@ -36,14 +35,34 @@
 
 import static org.hamcrest.CoreMatchers.is;
 import static org.junit.Assert.assertThat;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.assertNotNull;
 
 public class JacksonSerializerTest {
 
     private JacksonSerializer serializer = new JacksonSerializer();
-    private ObjectMapper mapper =
-        new ObjectMapper().setPropertyNamingStrategy(
-            PropertyNamingStrategies.SNAKE_CASE);
+    private ObjectMapper mapper = JacksonSerializer.createMapper();
 
+    @Test
+    public void createMapperSucceeds() {
+        // Verify that createMapper() successfully creates an ObjectMapper with snake_case naming
+        // This tests that the reflection logic works for the current Jackson version
+        ObjectMapper testMapper = JacksonSerializer.createMapper();
+        assertNotNull("Mapper should be created successfully", testMapper);
+        
+        // Verify snake_case naming by serializing a simple object
+        class TestObject {
+            @SuppressWarnings("unused")
+            public String getMyFieldName() { return "test"; }
+        }
+        
+        try {
+            String json = testMapper.writeValueAsString(new TestObject());
+            assertTrue("Should use snake_case naming", json.contains("my_field_name"));
+        } catch (Exception e) {
+            throw new RuntimeException("Failed to serialize with snake_case naming", e);
+        }
+    }
 
     @Test
     public void serializeImpression() throws IOException {