Allow configuring custom NullValueSerializer.

Closes #2878
Original pull request: #2905

Author: AnneMayor

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

@@ -134,6 +134,17 @@ public GenericJackson2JsonRedisSerializer(@Nullable String classPropertyTypeName
 		this.mapper.setDefaultTyping(typer);
 	}
 
+	/**
+	 * Factory method returning a {@literal Builder} used to construct and configure a {@link GenericJackson2JsonRedisSerializer}.
+	 *
+	 * @return new {@link GenericJackson2JsonRedisSerializer.GenericJackson2JsonRedisSerializerBuilder}.
+	 * @since 3.3
+	 */
+	public static GenericJackson2JsonRedisSerializerBuilder builder(ObjectMapper objectMapper, JacksonObjectReader reader,
+			JacksonObjectWriter writer) {
+		return new GenericJackson2JsonRedisSerializerBuilder(objectMapper, reader, writer);
+	}
+
 	/**
 	 * Setting a custom-configured {@link ObjectMapper} is one way to take further control of the JSON serialization
 	 * process. For example, an extended {@link SerializerFactory} can be configured that provides custom serializers for
@@ -396,6 +407,69 @@ public void serializeWithType(NullValue value, JsonGenerator jsonGenerator, Seri
 		}
 	}
 
+	/**
+	 * {@literal Builder} for creating a {@link GenericJackson2JsonRedisSerializer}.
+	 *
+	 * @author Anne Lee
+	 * @since 3.3
+	 */
+	public static class GenericJackson2JsonRedisSerializerBuilder {
+		@Nullable
+		private String classPropertyTypeName;
+		private JacksonObjectReader reader;
+		private JacksonObjectWriter writer;
+		private ObjectMapper mapper;
+		@Nullable
+		private StdSerializer<NullValue> nullValueSerializer;
+
+		private GenericJackson2JsonRedisSerializerBuilder(
+				ObjectMapper objectMapper,
+				JacksonObjectReader reader,
+				JacksonObjectWriter writer
+		) {
+			this.mapper = objectMapper;
+			this.reader = reader;
+			this.writer = writer;
+		}
+
+		/**
+		 * Configure a classPropertyName.
+		 *
+		 * @param classPropertyTypeName can be {@literal null}.
+		 * @return this {@link GenericJackson2JsonRedisSerializer.GenericJackson2JsonRedisSerializerBuilder}.
+		 * @since 3.3
+		 */
+		public GenericJackson2JsonRedisSerializerBuilder classPropertyTypeName(@Nullable String classPropertyTypeName) {
+			this.classPropertyTypeName = classPropertyTypeName;
+			return this;
+		}
+
+		/**
+		 * Register a nullValueSerializer.
+		 *
+		 * @param nullValueSerializer the {@link StdSerializer} to use for {@link NullValue} serialization. Can be {@literal null}.
+		 * @return this {@link GenericJackson2JsonRedisSerializer.GenericJackson2JsonRedisSerializerBuilder}.
+		 */
+		public GenericJackson2JsonRedisSerializerBuilder registerNullValueSerializer(@Nullable StdSerializer<NullValue> nullValueSerializer) {
+			this.nullValueSerializer = nullValueSerializer;
+			return this;
+		}
+
+		/**
+		 * Create new instance of {@link GenericJackson2JsonRedisSerializer} with configuration options applied.
+		 *
+		 * @return new instance of {@link GenericJackson2JsonRedisSerializer}.
+		 */
+		public GenericJackson2JsonRedisSerializer build() {
+			Assert.notNull(this.mapper, "ObjectMapper must not be null");
+			Assert.notNull(this.reader, "Reader must not be null");
+			Assert.notNull(this.writer, "Writer must not be null");
+
+			this.mapper.registerModule(new SimpleModule().addSerializer(this.nullValueSerializer != null ? this.nullValueSerializer : new NullValueSerializer(this.classPropertyTypeName)));
+			return new GenericJackson2JsonRedisSerializer(this.mapper, this.reader, this.writer, this.classPropertyTypeName);
+		}
+	}
+
 	/**
 	 * Custom {@link StdTypeResolverBuilder} that considers typing for non-primitive types. Primitives, their wrappers and
 	 * primitive arrays do not require type hints. The default {@code DefaultTyping#EVERYTHING} typing does not satisfy

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

@@ -40,6 +40,10 @@
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Consumer;
 
+import com.fasterxml.jackson.core.JsonGenerator;
+import com.fasterxml.jackson.databind.SerializerProvider;
+import com.fasterxml.jackson.databind.jsontype.TypeSerializer;
+import com.fasterxml.jackson.databind.ser.std.StdSerializer;
 import org.junit.jupiter.api.Test;
 import org.mockito.Mockito;
 
@@ -420,7 +424,7 @@ void deserializesJavaTimeFrimBytes() {
 	}
 
 	@Test // GH-2601
-	public void internalObjectMapperCustomization() {
+	void internalObjectMapperCustomization() {
 
 		GenericJackson2JsonRedisSerializer serializer = new GenericJackson2JsonRedisSerializer();
 
@@ -432,20 +436,63 @@ public void internalObjectMapperCustomization() {
 
 		assertThat(serializer.configure(configurer)).isSameAs(serializer);
 
-		verify(mockObjectMapper, times(1)).registerModule(eq(mockModule));
+		verify(mockObjectMapper, times(1)).registerModule(mockModule);
 		verifyNoMoreInteractions(mockObjectMapper);
 		verifyNoInteractions(mockModule);
 	}
 
 	@Test // GH-2601
-	public void configureWithNullConsumerThrowsIllegalArgumentException() {
+	void configureWithNullConsumerThrowsIllegalArgumentException() {
 
 		assertThatIllegalArgumentException()
 			.isThrownBy(() -> new GenericJackson2JsonRedisSerializer().configure(null))
 			.withMessage("Consumer used to configure and customize ObjectMapper must not be null")
 			.withNoCause();
 	}
 
+	@Test
+	void defaultSerializeAndDeserializeNullValueWithBuilderClass() {
+		GenericJackson2JsonRedisSerializer serializer = GenericJackson2JsonRedisSerializer.builder(
+				new ObjectMapper().enableDefaultTyping(DefaultTyping.EVERYTHING, As.PROPERTY),
+				JacksonObjectReader.create(), JacksonObjectWriter.create())
+				.classPropertyTypeName(null)
+				.registerNullValueSerializer(null)
+				.build();
+
+		serializeAndDeserializeNullValue(serializer);
+	}
+
+	@Test
+	void customSerializeAndDeserializeNullValueWithBuilderClass() {
+		GenericJackson2JsonRedisSerializer serializer = GenericJackson2JsonRedisSerializer.builder(
+				new ObjectMapper(), JacksonObjectReader.create(), JacksonObjectWriter.create())
+				.classPropertyTypeName(null)
+				.registerNullValueSerializer(new StdSerializer<>(NullValue.class) {
+					@Override
+					public void serialize(NullValue nullValue,
+					                      JsonGenerator jsonGenerator,
+					                      SerializerProvider serializerProvider) throws IOException {
+						jsonGenerator.writeNull();
+					}
+
+					@Override
+					public void serializeWithType(NullValue value, JsonGenerator jsonGenerator, SerializerProvider serializers,
+					                              TypeSerializer typeSerializer) throws IOException {
+
+						serialize(value, jsonGenerator, serializers);
+					}
+				})
+				.build();
+
+		NullValue nv = BeanUtils.instantiateClass(NullValue.class);
+
+		byte[] serializedValue = serializer.serialize(nv);
+		assertThat(serializedValue).isNotNull();
+
+		Object deserializedValue = serializer.deserialize(serializedValue);
+		assertThat(deserializedValue).isNull();
+	}
+
 	private static void serializeAndDeserializeNullValue(GenericJackson2JsonRedisSerializer serializer) {
 
 		NullValue nv = BeanUtils.instantiateClass(NullValue.class);