fix #2675

Author: cowtowncoder

release-notes/VERSION-2.x

@@ -13,6 +13,7 @@ Project: jackson-databind
  (reported by Incara@github)
 #2091: `ReferenceType` does not expose valid containedType
  (reported by Nate B)
+#2675: Support use of `Void` valued properties (`MapperFeature.ALLOW_VOID_VALUED_PROPERTIES`)
 #2683: Explicitly fail (de)serialization of `java.time.*` types in absence of
   registered custom (de)serializers
 #2707: Improve description included in by `DeserializationContext.handleUnexpectedToken()`

src/main/java/com/fasterxml/jackson/databind/MapperFeature.java

@@ -213,6 +213,19 @@ public enum MapperFeature implements ConfigFeature
      */
     INFER_CREATOR_FROM_CONSTRUCTOR_PROPERTIES(true),
 
+    /**
+     * Feature that determines whether nominal property type of {@link Void} is
+     * allowed for Getter methods to indicate {@code null} valued pseudo-property
+     * or not. If enabled, such properties are recognized (see [databind#2675] for
+     * reasons -- mostly things related to frameworks, code generation); if disabled,
+     * such property accessors (or at least getters) are ignored.
+     *<p>
+     * Feature is disabled by default (in 2.12) for backwards compatibility.
+     *
+     * @since 2.12
+     */
+    ALLOW_VOID_VALUED_PROPERTIES(false),
+
     /*
     /******************************************************
     /* Access modifier handling

src/main/java/com/fasterxml/jackson/databind/introspect/AnnotatedMethod.java

@@ -215,10 +215,14 @@ public Class<?> getRawReturnType() {
      * false, otherwise true
      * 
      * @since 2.4
+     *
+     * @deprecated Since 2.12 (related to [databind#2675]), needs to be configurable
      */
+    @Deprecated
     public boolean hasReturnType() {
         Class<?> rt = getRawReturnType();
-        return (rt != Void.TYPE && rt != Void.class);
+        // also, as per [databind#2675], only consider `void` to be real "No return type"
+        return (rt != Void.TYPE);
     }
 
     /*

src/main/java/com/fasterxml/jackson/databind/introspect/POJOPropertiesCollector.java

@@ -580,10 +580,15 @@ protected void _addGetterMethod(Map<String, POJOPropertyBuilder> props,
             AnnotatedMethod m, AnnotationIntrospector ai)
     {
         // Very first thing: skip if not returning any value
-        if (!m.hasReturnType()) {
-            return;
+        // 06-May-2020, tatu: [databind#2675] changes handling slightly...
+        {
+            final Class<?> rt = m.getRawReturnType();
+            if ((rt == Void.TYPE) ||
+                    ((rt == Void.class) && !_config.isEnabled(MapperFeature.ALLOW_VOID_VALUED_PROPERTIES))) {
+                return;
+            }
         }
-        
+
         // any getter?
         // @JsonAnyGetter?
         if (Boolean.TRUE.equals(ai.hasAnyGetter(m))) {

src/main/java/com/fasterxml/jackson/databind/ser/BeanSerializerFactory.java

@@ -9,7 +9,6 @@
 
 import com.fasterxml.jackson.databind.*;
 import com.fasterxml.jackson.databind.cfg.SerializerFactoryConfig;
-import com.fasterxml.jackson.databind.deser.impl.UnsupportedTypeDeserializer;
 import com.fasterxml.jackson.databind.introspect.*;
 import com.fasterxml.jackson.databind.jsontype.NamedType;
 import com.fasterxml.jackson.databind.jsontype.TypeResolverBuilder;

src/test/java/com/fasterxml/jackson/databind/deser/jdk/VoidProperties2675Test.java

@@ -0,0 +1,61 @@
+package com.fasterxml.jackson.databind.deser.jdk;
+
+import com.fasterxml.jackson.databind.*;
+import com.fasterxml.jackson.databind.exc.InvalidDefinitionException;
+import com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException;
+
+// [databind#2675]: Void-valued "properties"
+public class VoidProperties2675Test extends BaseMapTest
+{
+    static class VoidBean {
+        protected Void value;
+
+        public Void getValue() { return null; }
+
+//        public void setValue(Void v) { }
+    }
+
+    /*
+    /**********************************************************************
+    /* Test methods
+    /**********************************************************************
+     */
+
+    private final ObjectMapper DEFAULT_MAPPER = sharedMapper();
+
+    private final ObjectMapper VOID_MAPPER = jsonMapperBuilder()
+            .enable(MapperFeature.ALLOW_VOID_VALUED_PROPERTIES)
+            .build();
+
+    public void testVoidBeanSerialization() throws Exception
+    {
+        // By default (2.x), not enabled:
+        try {
+            DEFAULT_MAPPER.writeValueAsString(new VoidBean());
+            fail("Should not pass");
+        } catch (InvalidDefinitionException e) {
+            verifyException(e, "no properties discovered");
+        }
+
+        // but when enabled
+        assertEquals("{\"value\":null}", VOID_MAPPER.writeValueAsString(new VoidBean()));
+    }
+
+    public void testVoidBeanDeserialization() throws Exception {
+        final String DOC = "{\"value\":null}";
+        VoidBean result;
+
+        // By default (2.x), not enabled:
+        try {
+            result = DEFAULT_MAPPER.readValue(DOC, VoidBean.class);
+            fail("Should not pass");
+        } catch (UnrecognizedPropertyException e) {
+            verifyException(e, "Unrecognized field \"value\"");
+        }
+
+        // but when enabled
+        result = VOID_MAPPER.readValue(DOC, VoidBean.class);
+        assertNotNull(result);
+        assertNull(result.getValue());
+    }
+}