Add mapper feature to allow explicitly named properties to be renamed with PropertyNamingStrategy

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

@@ -331,6 +331,17 @@ public enum MapperFeature implements ConfigFeature
      */
     USE_STD_BEAN_NAMING(false),
 
+    /**
+     * Feature that when enabled will allow explicitly named properties (i.e., fields or methods
+     * annotated with {@link com.fasterxml.jackson.annotation.JsonProperty}("explicitName")) to
+     * be re-named by a {@link PropertyNamingStrategy}, if one is configured.
+     * <p>
+     * Feature is disabled by default.
+     *
+     * @since 2.6
+     */
+    ALLOW_EXPLICIT_PROPERTY_RENAMING(false),
+
     /*
     /******************************************************
     /* Other features

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

@@ -785,8 +785,9 @@ protected void _renameUsing(Map<String, POJOPropertyBuilder> propMap,
             PropertyName fullName = prop.getFullName();
             String rename = null;
             // As per [#428](https://github.com/FasterXML/jackson-databind/issues/428) need
-            // to skip renaming if property has explicitly defined name
-            if (!prop.isExplicitlyNamed()) {
+            // to skip renaming if property has explicitly defined name, unless feature
+            // is enabled
+            if (!prop.isExplicitlyNamed() || _config.isEnabled(MapperFeature.ALLOW_EXPLICIT_PROPERTY_RENAMING)) {
                 if (_forSerialization) {
                     if (prop.hasGetter()) {
                         rename = naming.nameForGetterMethod(_config, prop.getGetter(), fullName.getSimpleName());

src/test/java/com/fasterxml/jackson/databind/introspect/TestNamingStrategyStd.java

@@ -7,6 +7,7 @@
 
 import com.fasterxml.jackson.annotation.*;
 import com.fasterxml.jackson.databind.BaseMapTest;
+import com.fasterxml.jackson.databind.MapperFeature;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.databind.PropertyNamingStrategy;
 import com.fasterxml.jackson.databind.annotation.JsonNaming;
@@ -316,4 +317,41 @@ public void testNamingWithObjectNode() throws Exception
         assertEquals(2, result.json.size());
         assertEquals("bing", result.json.path("baz").asText());
     }
+
+    static class ExplicitBean {
+      @JsonProperty("firstName")
+      String userFirstName = "Peter";
+      @JsonProperty("lastName")
+      String userLastName = "Venkman";
+      @JsonProperty
+      String userAge = "35";
+    }
+
+    public void testExplicitRename() throws Exception {
+      ObjectMapper m = new ObjectMapper();
+      m.setPropertyNamingStrategy(PropertyNamingStrategy.CAMEL_CASE_TO_LOWER_CASE_WITH_UNDERSCORES);
+      m.enable(MapperFeature.SORT_PROPERTIES_ALPHABETICALLY);
+      // by default, renaming will not take place on explicitly named fields
+      assertEquals(aposToQuotes("{'firstName':'Peter','lastName':'Venkman','user_age':'35'}"),
+          m.writeValueAsString(new ExplicitBean()));
+
+      m = new ObjectMapper();
+      m.setPropertyNamingStrategy(PropertyNamingStrategy.CAMEL_CASE_TO_LOWER_CASE_WITH_UNDERSCORES);
+      m.enable(MapperFeature.SORT_PROPERTIES_ALPHABETICALLY);
+      m.enable(MapperFeature.ALLOW_EXPLICIT_PROPERTY_RENAMING);
+      // w/ feature enabled, ALL property names should get re-written
+      assertEquals(aposToQuotes("{'first_name':'Peter','last_name':'Venkman','user_age':'35'}"),
+          m.writeValueAsString(new ExplicitBean()));
+
+      // test deserialization as well
+      ExplicitBean bean =
+          m.readValue(aposToQuotes("{'first_name':'Egon','last_name':'Spengler','user_age':'32'}"),
+              ExplicitBean.class);
+
+      assertNotNull(bean);
+      assertEquals("Egon", bean.userFirstName);
+      assertEquals("Spengler", bean.userLastName);
+      assertEquals("32", bean.userAge);
+
+    }
 }