Fixed #1990

release-notes/CREDITS-2.x

@@ -768,6 +768,10 @@ roeltje25@github
     infinite loop
    (2.9.5)
 
+Freddy Boucher (freddyboucher@github)
+  * Reported #1990: MixIn `@JsonProperty` for `Object.hashCode()` is ignored
+   (2.9.6)
+
 Ondrej Zizka (OndraZizk@github)
   * Reported #1999: "Duplicate property" issue should mention which class it complains about
    (2.9.6)

release-notes/VERSION-2.x

@@ -11,6 +11,8 @@ Project: jackson-databind
 #1964: Failed to specialize `Map` type during serialization where key type
   incompatibility overidden via "raw" types
  (reported by ptirador@github)
+#1990: MixIn `@JsonProperty` for `Object.hashCode()` is ignored
+ (reported by Freddy B)
 #1998: Removing "type" attribute with Mixin not taken in account if
   using ObjectMapper.copy()
  (reported by SBKila@github)

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

@@ -49,37 +49,40 @@ AnnotatedMethodMap collect(TypeFactory typeFactory, TypeResolutionContext tc,
                     type.getRawClass(), methods, mixin);
         }
         // Special case: mix-ins for Object.class? (to apply to ALL classes)
-        /*
+        boolean checkJavaLangObject = false;
         if (_mixInResolver != null) {
             Class<?> mixin = _mixInResolver.findMixInClassFor(Object.class);
             if (mixin != null) {
-                _addMethodMixIns(tc, mainType.getRawClass(), memberMethods, mixin, mixins);
+                _addMethodMixIns(tc, mainType.getRawClass(), methods, mixin); //, mixins);
+                checkJavaLangObject = true;
             }
         }
 
         // Any unmatched mix-ins? Most likely error cases (not matching any method);
         // but there is one possible real use case: exposing Object#hashCode
         // (alas, Object#getClass can NOT be exposed)
-        if (_intr != null) {
-            if (!mixins.isEmpty()) {
-                Iterator<AnnotatedMethod> it = mixins.iterator();
-                while (it.hasNext()) {
-                    AnnotatedMethod mixIn = it.next();
-                    try {
-                        Method m = Object.class.getDeclaredMethod(mixIn.getName(), mixIn.getRawParameterTypes());
-                        if (m != null) {
-                            // Since it's from java.lang.Object, no generics, no need for real type context:
-                            AnnotatedMethod am = _constructMethod(tc, m);
-                            _addMixOvers(mixIn.getAnnotated(), am, false);
-                            memberMethods.add(am);
-                        }
-                    } catch (Exception e) { }
+        // Since we only know of that ONE case, optimize for it
+        if (checkJavaLangObject && (_intr != null) && !methods.isEmpty()) {
+            // Could use lookup but probably as fast or faster to traverse
+            for (Map.Entry<MemberKey,MethodBuilder> entry : methods.entrySet()) {
+                MemberKey k = entry.getKey();
+                if (!"hashCode".equals(k.getName()) || (0 != k.argCount())) {
+                    continue;
                 }
+                try {
+                    // And with that, we can generate it appropriately
+                    Method m = Object.class.getDeclaredMethod(k.getName());
+                    if (m != null) {
+                        MethodBuilder b = entry.getValue();
+                        b.annotations = collectDefaultAnnotations(b.annotations,
+                                m.getDeclaredAnnotations());
+                        b.method = m;
+                   }
+                } catch (Exception e) { }
             }
         }
-        */
 
-        // And then let's 
+        // And then let's create the lookup map
         if (methods.isEmpty()) {
             return new AnnotatedMethodMap();
         }

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

@@ -68,7 +68,8 @@ protected final AnnotationCollector collectFromBundle(AnnotationCollector c, Ann
     // // // Defaulting ("mix under")
 
     // Variant that only adds annotations that are missing
-    protected final AnnotationCollector collectDefaultAnnotations(AnnotationCollector c, Annotation[] anns) {
+    protected final AnnotationCollector collectDefaultAnnotations(AnnotationCollector c,
+            Annotation[] anns) {
         for (int i = 0, end = anns.length; i < end; ++i) {
             Annotation ann = anns[i];
             if (!c.isPresent(ann)) {
@@ -81,7 +82,8 @@ protected final AnnotationCollector collectDefaultAnnotations(AnnotationCollecto
         return c;
     }
 
-    protected final AnnotationCollector collectDefaultFromBundle(AnnotationCollector c, Annotation bundle) {
+    protected final AnnotationCollector collectDefaultFromBundle(AnnotationCollector c,
+            Annotation bundle) {
         Annotation[] anns = ClassUtil.findClassAnnotations(bundle.annotationType());
         for (int i = 0, end = anns.length; i < end; ++i) {
             Annotation ann = anns[i];

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

@@ -31,14 +31,21 @@ public MemberKey(String name, Class<?>[] argTypes)
         _argTypes = (argTypes == null) ? NO_CLASSES : argTypes;
     }
 
+    public String getName() {
+        return _name;
+    }
+
+    public int argCount() {
+        return _argTypes.length;
+    }
+
     @Override
     public String toString() {
         return _name + "(" + _argTypes.length+"-args)";
     }
 
     @Override
-    public int hashCode()
-    {
+    public int hashCode() {
         return _name.hashCode() + _argTypes.length;
     }
 

src/test/java/com/fasterxml/jackson/databind/mixins/TestMixinDeserForClass.java

@@ -10,12 +10,6 @@
 public class TestMixinDeserForClass
     extends BaseMapTest
 {
-    /*
-    /**********************************************************
-    /* Helper bean classes
-    /**********************************************************
-     */
-
     static class BaseClass
     {
         /* property that is always found; but has lower priority than
@@ -35,6 +29,21 @@ static class LeafClass
     @JsonAutoDetect(setterVisibility=Visibility.NONE, fieldVisibility=Visibility.NONE)
     interface MixIn { }
 
+    // [databind#1990]
+    public interface HashCodeMixIn {
+        @Override
+        @JsonProperty
+        public int hashCode();
+    }
+
+    public class Bean1990WithoutHashCode {
+    }
+
+    public class Bean1990WithHashCode {
+        @Override
+        public int hashCode() { return 13; }
+    }
+
     /*
     /**********************************************************
     /* Unit tests
@@ -48,18 +57,16 @@ public void testClassMixInsTopLevel() throws IOException
         LeafClass result = m.readValue("{\"a\":\"value\"}", LeafClass.class);
         assertEquals("XXXvalue", result.a);
 
-        /* Then with leaf-level mix-in; without (method) auto-detect, should
-         * use field
-         */
+        // Then with leaf-level mix-in; without (method) auto-detect,
+        // should use field
         m = new ObjectMapper();
         m.addMixIn(LeafClass.class, MixIn.class);
         result = m.readValue("{\"a\":\"value\"}", LeafClass.class);
         assertEquals("value", result.a);
     }
 
-    /* and then a test for mid-level mixin; should have no effect
-     * when deserializing leaf (but will if deserializing base class)
-     */
+    // and then a test for mid-level mixin; should have no effect
+    // when deserializing leaf (but will if deserializing base class)
     public void testClassMixInsMidLevel() throws IOException
     {
         ObjectMapper m = new ObjectMapper();
@@ -95,4 +102,22 @@ public void testClassMixInsForObjectClass() throws IOException
             assertEquals("XXX", result.a);
         }
     }
+
+    // [databind#1990]: can apply mix-in to `Object#hashCode()` to force serialization
+    public void testHashCodeViaObject() throws Exception
+    {
+        ObjectMapper mapper = new ObjectMapper()
+                .addMixIn(Object.class, HashCodeMixIn.class);
+
+        // First, with something that overrides hashCode()
+        assertEquals( "{\"hashCode\":13}",
+                mapper.writeValueAsString(new Bean1990WithHashCode()));
+
+        // and then special case of accessing Object#hashCode()
+        String prefix = "{\"hashCode\":";
+        String json = mapper.writeValueAsString(new Bean1990WithoutHashCode());
+        if (!json.startsWith(prefix)) {
+            fail("Should start with ["+prefix+"], does not: ["+json+"]");
+        }
+    }
 }