Start work to support aliases

Author: cowtowncoder

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

@@ -62,7 +62,7 @@ public enum Type {
              * {@link com.fasterxml.jackson.annotation.JsonManagedReference}
              */
             MANAGED_REFERENCE
-    
+
             /**
              * Reference property that Jackson manages by suppressing it during serialization,
              * and reconstructing during deserialization.
@@ -570,6 +570,16 @@ public JsonFormat.Value findFormat(Annotated memberOrClass) {
      */
     public String findImplicitPropertyName(AnnotatedMember member) { return null; }
 
+    /**
+     * Method called to find if given property has alias(es) defined.
+     * 
+     * @return `null` if member has no information; otherwise a `List` (possibly
+     *   empty) of aliases to use.
+     *
+     * @since 2.9
+     */
+    public List<PropertyName> findPropertyAliases(Annotated ann) { return null; }
+
     /**
      * Method for finding optional access definition for a property, annotated
      * on one of its accessors. If a definition for read-only, write-only

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

@@ -433,7 +433,7 @@ public enum MapperFeature implements ConfigFeature
      * @since 2.9
      */
     IGNORE_MERGE_FOR_UNMERGEABLE(true)
-    
+
     ;
 
     private final boolean _defaultState;

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

@@ -465,9 +465,15 @@ public Integer findPropertyIndex(Annotated ann) {
     }
 
     @Override
-    public String findImplicitPropertyName(AnnotatedMember param) {
-        String r = _primary.findImplicitPropertyName(param);
-        return (r == null) ? _secondary.findImplicitPropertyName(param) : r;
+    public String findImplicitPropertyName(AnnotatedMember ann) {
+        String r = _primary.findImplicitPropertyName(ann);
+        return (r == null) ? _secondary.findImplicitPropertyName(ann) : r;
+    }
+
+    @Override
+    public List<PropertyName> findPropertyAliases(Annotated ann) {
+        List<PropertyName> r = _primary.findPropertyAliases(ann);
+        return (r == null) ? _secondary.findPropertyAliases(ann) : r;
     }
 
     @Override

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

@@ -335,7 +335,25 @@ public String findImplicitPropertyName(AnnotatedMember m) {
         PropertyName n = _findConstructorName(m);
         return (n == null) ? null : n.getSimpleName();
     }
-    
+
+    @Override
+    public List<PropertyName> findPropertyAliases(Annotated m) {
+        JsonAlias ann = _findAnnotation(m, JsonAlias.class);
+        if (ann == null) {
+            return null;
+        }
+        String[] strs = ann.value();
+        final int len = strs.length;
+        if (len == 0) {
+            return Collections.emptyList();
+        }
+        List<PropertyName> result = new ArrayList<>(len);
+        for (int i = 0; i < len; ++i) {
+            result.add(PropertyName.construct(strs[i]));
+        }
+        return result;
+    }
+
     @Override
     public boolean hasIgnoreMarker(AnnotatedMember m) {
         return _isIgnorable(m);

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

@@ -502,10 +502,8 @@ protected void _addCreatorParam(Map<String, POJOPropertyBuilder> props,
         boolean expl = (pn != null && !pn.isEmpty());
         if (!expl) {
             if (impl.isEmpty()) {
-                /* Important: if neither implicit nor explicit name, can not make use
-                 * of this creator parameter -- may or may not be a problem, verified
-                 * at a later point.
-                 */
+                // Important: if neither implicit nor explicit name, can not make use of
+                // this creator parameter -- may or may not be a problem, verified at a later point.
                 return;
             }
             // Also: if this occurs, there MUST be explicit annotation on creator itself
@@ -529,14 +527,13 @@ protected void _addCreatorParam(Map<String, POJOPropertyBuilder> props,
         prop.addCtor(param, pn, expl, true, false);
         _creatorProperties.add(prop);
     }
-    
+
     /**
      * Method for collecting basic information on all fields found
      */
     protected void _addMethods(Map<String, POJOPropertyBuilder> props)
     {
         final AnnotationIntrospector ai = _annotationIntrospector;
-        
         for (AnnotatedMethod m : _classDef.memberMethods()) {
             /* For methods, handling differs between getters and setters; and
              * we will also only consider entries that either follow the bean