Fix #251

Author: cowtowncoder

datatypes/src/main/java/com/fasterxml/jackson/datatype/jdk8/Jdk8Deserializers.java

@@ -13,13 +13,29 @@ public class Jdk8Deserializers
 {
     private static final long serialVersionUID = 1L;
 
+    /**
+     * @since 2.14
+     */
+    protected final boolean _cfgReadAbsentAsNull;
+
+    public Jdk8Deserializers() {
+        // for backwards compatibility
+        this(Jdk8Module.DEFAULT_READ_ABSENT_AS_NULL);
+    }
+
+    public Jdk8Deserializers(boolean cfgReadAbsentAsNull) {
+        _cfgReadAbsentAsNull = cfgReadAbsentAsNull;
+    }
+    
     @Override // since 2.7
     public JsonDeserializer<?> findReferenceDeserializer(ReferenceType refType,
             DeserializationConfig config, BeanDescription beanDesc,
             TypeDeserializer contentTypeDeserializer, JsonDeserializer<?> contentDeserializer)
     {
         if (refType.hasRawClass(Optional.class)) {
-            return new OptionalDeserializer(refType, null, contentTypeDeserializer,contentDeserializer);
+            return new OptionalDeserializer(refType, null,
+                    contentTypeDeserializer,contentDeserializer,
+                    _cfgReadAbsentAsNull);
         }
         // 21-Oct-2015, tatu: Should probably consider possibility of custom deserializer being
         //    added to property; if so, `contentDeserializer` would not be null.

datatypes/src/main/java/com/fasterxml/jackson/datatype/jdk8/Jdk8Module.java

@@ -5,6 +5,8 @@
 
 public class Jdk8Module extends Module
 {
+    public final static boolean DEFAULT_READ_ABSENT_AS_NULL = false;
+
     /**
      * Configuration setting that determines whether `Optional.empty()` is
      * considered "same as null" for serialization purposes; that is, to be
@@ -22,17 +24,25 @@ public class Jdk8Module extends Module
      * criteria for filtering out absent optionals; this setting is mostly useful for
      * legacy use cases that predate version 2.6.
      */
-    protected boolean _cfgHandleAbsentAsNull = false;
+    protected boolean _cfgWriteAbsentAsNull = false;
+
+    /**
+     * See {@link #configureReadAbsentAsNull} for details of this configuration
+     * setting.
+     *
+     * @since 2.14
+     */
+    protected boolean _cfgReadAbsentAsNull = DEFAULT_READ_ABSENT_AS_NULL;
 
     @Override
     public void setupModule(SetupContext context) {
         context.addSerializers(new Jdk8Serializers());
-        context.addDeserializers(new Jdk8Deserializers());
+        context.addDeserializers(new Jdk8Deserializers(_cfgReadAbsentAsNull));
         // And to fully support Optionals, need to modify type info:
         context.addTypeModifier(new Jdk8TypeModifier());
 
         // Allow enabling "treat Optional.empty() like Java nulls"
-        if (_cfgHandleAbsentAsNull) {
+        if (_cfgWriteAbsentAsNull) {
             context.addBeanSerializerModifier(new Jdk8BeanSerializerModifier());
         }
     }
@@ -64,7 +74,25 @@ public Version version() {
      */
     @Deprecated
     public Jdk8Module configureAbsentsAsNulls(boolean state) {
-        _cfgHandleAbsentAsNull = state;
+        _cfgWriteAbsentAsNull = state;
+        return this;
+    }
+
+    /**
+     * Method for configuring handling of "absent" {@link java.util.Optional}
+     * values; absent meaning case where no value is found to pass via
+     * Creator method (constructor, factory method).
+     * If enabled (set to {@code true}) it will be deserialized as
+     * {@code null}; if disabled it will be read as "empty" {@code Optional}
+     * (same as if encountering actual JSON {@code null} value).
+     *<p>
+     * Default is {@code false} for backwards compatibility (retains behavior
+     * pre-2.14); for Jackson 3.0 default will likely be changed.
+     *
+     * @since 2.14
+     */
+    public Jdk8Module configureReadAbsentAsNull(boolean state) {
+        _cfgReadAbsentAsNull = state;
         return this;
     }
 

datatypes/src/main/java/com/fasterxml/jackson/datatype/jdk8/OptionalDeserializer.java

@@ -12,19 +12,35 @@ final class OptionalDeserializer
 {
     private static final long serialVersionUID = 1L;
 
+    protected final boolean _cfgReadAbsentAsNull;
+    
     /*
     /**********************************************************
     /* Life-cycle
     /**********************************************************
      */
 
+    /**
+     * @since 2.14
+     */
+    public OptionalDeserializer(JavaType fullType, ValueInstantiator inst,
+            TypeDeserializer typeDeser, JsonDeserializer<?> deser,
+            boolean cfgReadAbsentAsNull)
+    {
+        super(fullType, inst, typeDeser, deser);
+        _cfgReadAbsentAsNull = cfgReadAbsentAsNull;
+    }
+
     /**
      * @since 2.9
+     * @deprecated Since 2.14
      */
+    @Deprecated // @since 2.14
     public OptionalDeserializer(JavaType fullType, ValueInstantiator inst,
             TypeDeserializer typeDeser, JsonDeserializer<?> deser)
     {
-        super(fullType, inst, typeDeser, deser);
+        this(fullType, inst, typeDeser, deser,
+                Jdk8Module.DEFAULT_READ_ABSENT_AS_NULL);
     }
 
     /*
@@ -36,7 +52,7 @@ public OptionalDeserializer(JavaType fullType, ValueInstantiator inst,
     @Override
     public OptionalDeserializer withResolved(TypeDeserializer typeDeser, JsonDeserializer<?> valueDeser) {
         return new OptionalDeserializer(_fullType, _valueInstantiator,
-                typeDeser, valueDeser);
+                typeDeser, valueDeser, _cfgReadAbsentAsNull);
     }
 
     @Override
@@ -53,6 +69,21 @@ public Object getEmptyValue(DeserializationContext ctxt) throws JsonMappingExcep
         return getNullValue(ctxt);
     }
 
+    /**
+     * As of Jackson 2.14 we will either return either same as
+     * {@link #getNullValue} or {@code null}: see
+     * {@like Jdk8Module#configureReadAbsentLikeNull(boolean)} for
+     * details.
+     */
+    @Override // @since 2.14
+    public Object getAbsentValue(DeserializationContext ctxt) throws JsonMappingException {
+        // Note: actual `null` vs "null value" (which is coerced as "empty")
+        if (_cfgReadAbsentAsNull) {
+            return null;
+        }
+        return getNullValue(ctxt);
+    }
+
     @Override
     public Optional<?> referenceValue(Object contents) {
         return Optional.ofNullable(contents);

datatypes/src/test/java/com/fasterxml/jackson/datatype/jdk8/CreatorTest.java

@@ -5,6 +5,7 @@
 import com.fasterxml.jackson.annotation.JsonCreator;
 import com.fasterxml.jackson.annotation.JsonProperty;
 import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.json.JsonMapper;
 
 public class CreatorTest extends ModuleTestBase
 {
@@ -34,7 +35,7 @@ public CreatorWithOptionalStrings(@JsonProperty("a") Optional<String> a,
      * Test to ensure that creator parameters use defaulting
      * (introduced in Jackson 2.6)
      */
-    public void testCreatorWithOptional() throws Exception
+    public void testCreatorWithOptionalDefault() throws Exception
     {
         CreatorWithOptionalStrings bean = MAPPER.readValue(
                 a2q("{'a':'foo'}"), CreatorWithOptionalStrings.class);
@@ -45,4 +46,22 @@ public void testCreatorWithOptional() throws Exception
         assertFalse(bean.b.isPresent());
         assertEquals("foo", bean.a.get());
     }
+
+    public void testCreatorWithOptionalAbsentAsNull() throws Exception
+    {
+        Jdk8Module module = new Jdk8Module()
+                .configureReadAbsentAsNull(true);
+        final ObjectMapper mapper = JsonMapper.builder()
+                .addModule(module)
+                .build();
+        CreatorWithOptionalStrings bean = mapper.readValue(
+                a2q("{'a':'foo'}"), CreatorWithOptionalStrings.class);
+        assertNotNull(bean);
+        assertNotNull(bean.a);
+        assertTrue(bean.a.isPresent());
+        assertEquals("foo", bean.a.get());
+
+        // This is the config change
+        assertNull(bean.b);
+    }
 }

release-notes/VERSION-2.x

@@ -19,6 +19,8 @@ Modules:
  (contributed by (Maciej D)
 #242: Fix InstantSerializer ignoring the JsonFormat shape
  (contributed by KaseiFR@github)
+#251: Allow `Optional` deserialization for "absent" value as Java `null`
+ (like other Reference types), not "empty"
 
 2.13.4 (03-Sep-2022)
 2.13.3 (14-May-2022)