DATAREDIS-865 - Expose GenericJackson2JsonRedisSerializer.registerNullValueSerializer() for ObjectMapper customization.

We now expose registerNullValueSerializer(…) on GenericJackson2JsonRedisSerializer to allow customization of an externally provided ObjectMapper. NullValueSerializer was previously registered only within a constructor that takes classPropertyTypeName and provided no further possibilities to customize ObjectMapper.

Code wishing to provide a custom ObjectMapper can now call GenericJackson2JsonRedisSerializer.registerNullValueSerializer(objectMapper, …) and perform additional customizations before using ObjectMapper with GenericJackson2JsonRedisSerializer.

Original Pull Request: #376

src/main/java/org/springframework/data/redis/serializer/GenericJackson2JsonRedisSerializer.java

@@ -34,7 +34,10 @@ import com.fasterxml.jackson.databind.ser.SerializerFactory;
 import com.fasterxml.jackson.databind.ser.std.StdSerializer;
 
 /**
+ * Generic Jackson 2-based {@link RedisSerializer} that maps {@link Object objects} to JSON using dynamic typing.
+ *
  * @author Christoph Strobl
+ * @author Mark Paluch
  * @since 1.6
  */
 public class GenericJackson2JsonRedisSerializer implements RedisSerializer<Object> {
@@ -61,7 +64,7 @@ public class GenericJackson2JsonRedisSerializer implements RedisSerializer<Objec
 
 		// simply setting {@code mapper.disable(SerializationFeature.FAIL_ON_EMPTY_BEANS)} does not help here since we need
 		// the type hint embedded for deserialization using the default typing feature.
-		mapper.registerModule(new SimpleModule().addSerializer(new NullValueSerializer(classPropertyTypeName)));
+		registerNullValueSerializer(mapper, classPropertyTypeName);
 
 		if (StringUtils.hasText(classPropertyTypeName)) {
 			mapper.enableDefaultTypingAsProperty(DefaultTyping.NON_FINAL, classPropertyTypeName);
@@ -83,6 +86,22 @@ public class GenericJackson2JsonRedisSerializer implements RedisSerializer<Objec
 		this.mapper = mapper;
 	}
 
+	/**
+	 * Register {@link NullValueSerializer} in the given {@link ObjectMapper} with an optional
+	 * {@code classPropertyTypeName}. This method should be called by code that customizes
+	 * {@link GenericJackson2JsonRedisSerializer} by providing an external {@link ObjectMapper}.
+	 *
+	 * @param objectMapper the object mapper to customize.
+	 * @param classPropertyTypeName name of the type property. Defaults to {@code @class} if {@literal null}/empty.
+	 * @since 2.2
+	 */
+	public static void registerNullValueSerializer(ObjectMapper objectMapper, @Nullable String classPropertyTypeName) {
+
+		// simply setting {@code mapper.disable(SerializationFeature.FAIL_ON_EMPTY_BEANS)} does not help here since we need
+		// the type hint embedded for deserialization using the default typing feature.
+		objectMapper.registerModule(new SimpleModule().addSerializer(new NullValueSerializer(classPropertyTypeName)));
+	}
+
 	/*
 	 * (non-Javadoc)
 	 * @see org.springframework.data.redis.serializer.RedisSerializer#serialize(java.lang.Object)
@@ -140,7 +159,7 @@ public class GenericJackson2JsonRedisSerializer implements RedisSerializer<Objec
 	 * @author Christoph Strobl
 	 * @since 1.8
 	 */
-	private class NullValueSerializer extends StdSerializer<NullValue> {
+	private static class NullValueSerializer extends StdSerializer<NullValue> {
 
 		private static final long serialVersionUID = 1999052150548658808L;
 		private final String classIdentifier;

src/test/java/org/springframework/data/redis/serializer/GenericJackson2JsonRedisSerializerUnitTests.java

@@ -20,6 +20,7 @@ import static org.hamcrest.core.IsInstanceOf.*;
 import static org.hamcrest.core.IsNull.*;
 import static org.junit.Assert.*;
 import static org.mockito.Mockito.*;
+import static org.mockito.Mockito.any;
 import static org.springframework.test.util.ReflectionTestUtils.*;
 import static org.springframework.util.ObjectUtils.*;
 
@@ -31,15 +32,20 @@ import org.springframework.beans.BeanUtils;
 import org.springframework.cache.support.NullValue;
 
 import com.fasterxml.jackson.annotation.JsonTypeInfo;
+import com.fasterxml.jackson.annotation.JsonTypeInfo.As;
 import com.fasterxml.jackson.core.JsonGenerationException;
 import com.fasterxml.jackson.core.JsonProcessingException;
 import com.fasterxml.jackson.databind.JsonMappingException;
 import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.ObjectMapper.DefaultTyping;
 import com.fasterxml.jackson.databind.jsontype.TypeResolverBuilder;
 import com.fasterxml.jackson.databind.type.TypeFactory;
 
 /**
+ * Unit tests for {@link GenericJackson2JsonRedisSerializer}.
+ *
  * @author Christoph Strobl
+ * @author Mark Paluch
  */
 public class GenericJackson2JsonRedisSerializerUnitTests {
 
@@ -122,11 +128,28 @@ public class GenericJackson2JsonRedisSerializerUnitTests {
 		new GenericJackson2JsonRedisSerializer(objectMapperMock).deserialize(new byte[] { 1 });
 	}
 
-	@Test // DATAREDIS-553
+	@Test // DATAREDIS-553, DATAREDIS-865
 	public void shouldSerializeNullValueSoThatItCanBeDeserializedWithDefaultTypingEnabled() {
 
 		GenericJackson2JsonRedisSerializer serializer = new GenericJackson2JsonRedisSerializer();
 
+		serializeAndDeserializeNullValue(serializer);
+	}
+
+	@Test // DATAREDIS-865
+	public void shouldSerializeNullValueWithCustomObjectMapper() {
+
+		ObjectMapper mapper = new ObjectMapper();
+		mapper.enableDefaultTyping(DefaultTyping.NON_FINAL, As.PROPERTY);
+
+		GenericJackson2JsonRedisSerializer.registerNullValueSerializer(mapper, null);
+		GenericJackson2JsonRedisSerializer serializer = new GenericJackson2JsonRedisSerializer(mapper);
+
+		serializeAndDeserializeNullValue(serializer);
+	}
+
+	private static void serializeAndDeserializeNullValue(GenericJackson2JsonRedisSerializer serializer) {
+
 		NullValue nv = BeanUtils.instantiateClass(NullValue.class);
 
 		byte[] serializedValue = serializer.serialize(nv);