Fix #47, one of oldest open bugs (yay!): support @JsonValue for Map keys

Author: cowtowncoder

release-notes/VERSION

@@ -6,6 +6,7 @@ Project: jackson-databind
 
 2.5.0 (not yet released)
 
+#47: Support `@JsonValue` for (Map) key serialization 
 #113: Problem deserializing polymorphic types with @JsonCreator
 #408: External type id does not allow use of 'visible=true'
 #421: @JsonCreator not used in case of multiple creators with parameter names

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

@@ -653,7 +653,7 @@ public final boolean isEnabled(JsonParser.Feature f, JsonFactory factory) {
         }
         return factory.isEnabled(f);
     }
-    
+
     /**
      * "Bulk" access method for checking that all features specified by
      * mask are enabled.
@@ -673,7 +673,7 @@ public final int getDeserializationFeatures() {
     /* Other configuration
     /**********************************************************
      */
-    
+
     /**
      * Method for getting head of the problem handler chain. May be null,
      * if no handlers have been added.

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

@@ -10,7 +10,6 @@
 
 import com.fasterxml.jackson.annotation.JsonFormat;
 import com.fasterxml.jackson.annotation.JsonInclude;
-
 import com.fasterxml.jackson.databind.*;
 import com.fasterxml.jackson.databind.annotation.JsonSerialize;
 import com.fasterxml.jackson.databind.cfg.SerializerFactoryConfig;
@@ -206,6 +205,7 @@ public JsonSerializer<Object> createKeySerializer(SerializationConfig config,
             JavaType keyType, JsonSerializer<Object> defaultImpl)
     {
         // We should not need any member method info; at most class annotations for Map type
+        // ... at least, not here.
         BeanDescription beanDesc = config.introspectClassAnnotations(keyType.getRawClass());
         JsonSerializer<?> ser = null;
         // Minor optimization: to avoid constructing beanDesc, bail out if none registered
@@ -221,7 +221,20 @@ public JsonSerializer<Object> createKeySerializer(SerializationConfig config,
         if (ser == null) {
             ser = defaultImpl;
             if (ser == null) {
-                ser = StdKeySerializers.getStdKeySerializer(keyType);
+                ser = StdKeySerializers.getStdKeySerializer(config, keyType.getRawClass(), false);
+                // As per [databind#47], also need to support @JsonValue
+                if (ser == null) {
+                    beanDesc = config.introspect(keyType);
+                    AnnotatedMethod am = beanDesc.findJsonValueMethod();
+                    if (am != null) {
+                        final Class<?> rawType = am.getRawReturnType();
+                        JsonSerializer<?> delegate = StdKeySerializers.getStdKeySerializer(config,
+                                rawType, true);
+                        ser = new JsonValueSerializer(am.getAnnotated(), delegate);
+                    } else {
+                        ser = StdKeySerializers.getDefault();
+                    }
+                }
             }
         }
 

src/main/java/com/fasterxml/jackson/databind/ser/std/JsonValueSerializer.java

@@ -7,7 +7,6 @@
 import java.lang.reflect.Type;
 
 import com.fasterxml.jackson.core.*;
-
 import com.fasterxml.jackson.databind.*;
 import com.fasterxml.jackson.databind.annotation.JacksonStdImpl;
 import com.fasterxml.jackson.databind.jsonFormatVisitors.JsonFormatVisitable;
@@ -60,11 +59,12 @@ public class JsonValueSerializer
      *    {@link com.fasterxml.jackson.databind.annotation.JsonSerialize#using}), otherwise
      *    null
      */
-    public JsonValueSerializer(Method valueMethod, JsonSerializer<Object> ser)
+    @SuppressWarnings("unchecked")
+    public JsonValueSerializer(Method valueMethod, JsonSerializer<?> ser)
     {
-        super(Object.class);
+        super(valueMethod.getReturnType(), false);
         _accessorMethod = valueMethod;
-        _valueSerializer = ser;
+        _valueSerializer = (JsonSerializer<Object>) ser;
         _property = null;
         _forceTypeInformation = true; // gets reconsidered when we are contextualized
     }
@@ -294,8 +294,7 @@ protected boolean isNaturalTypeWithStdHandling(Class<?> rawType, JsonSerializer<
      */
 
     @Override
-    public String toString()
-    {
+    public String toString() {
         return "(@JsonValue serializer for method " + _accessorMethod.getDeclaringClass() + "#" + _accessorMethod.getName() + ")";
     }
 }

src/main/java/com/fasterxml/jackson/databind/ser/std/StdKeySerializer.java

@@ -20,9 +20,9 @@
 public class StdKeySerializer extends StdSerializer<Object>
 {
     public StdKeySerializer() { super(Object.class); }
-    
+
     @Override
-    public void serialize(Object value, JsonGenerator jgen, SerializerProvider provider) throws IOException, JsonGenerationException {
+    public void serialize(Object value, JsonGenerator jgen, SerializerProvider provider) throws IOException {
         if (value instanceof Date) {
             provider.defaultSerializeDateKey((Date) value, jgen);
         } else {
@@ -34,7 +34,7 @@ public void serialize(Object value, JsonGenerator jgen, SerializerProvider provi
     public JsonNode getSchema(SerializerProvider provider, Type typeHint) throws JsonMappingException {
         return createSchemaNode("string");
     }
-    
+
     @Override
     public void acceptJsonFormatVisitor(JsonFormatVisitorWrapper visitor, JavaType typeHint) throws JsonMappingException {
         visitor.expectStringFormat(typeHint);

src/main/java/com/fasterxml/jackson/databind/ser/std/StdKeySerializers.java

@@ -5,10 +5,7 @@
 import java.util.Date;
 
 import com.fasterxml.jackson.core.*;
-
-import com.fasterxml.jackson.databind.JavaType;
-import com.fasterxml.jackson.databind.JsonSerializer;
-import com.fasterxml.jackson.databind.SerializerProvider;
+import com.fasterxml.jackson.databind.*;
 
 public class StdKeySerializers
 {
@@ -20,33 +17,47 @@ public class StdKeySerializers
 
     private StdKeySerializers() { }
 
+    /**
+     * @param config Serialization configuration in use, may be needed in choosing
+     *    serializer to use
+     * @param rawKeyType Type of key values to serialize
+     * @param useDefault If no match is found, should we return fallback deserializer
+     *    (true), or null (false)?
+     */
     @SuppressWarnings("unchecked")
-    public static JsonSerializer<Object> getStdKeySerializer(JavaType keyType)
+    public static JsonSerializer<Object> getStdKeySerializer(SerializationConfig config,
+            Class<?> rawKeyType, boolean useDefault)
     {
-        if (keyType == null) {
-            return DEFAULT_KEY_SERIALIZER;
-        }
-        Class<?> cls = keyType.getRawClass();
-        if (cls == String.class) {
-            return DEFAULT_STRING_SERIALIZER;
-        }
-        if (cls == Object.class || cls.isPrimitive() || Number.class.isAssignableFrom(cls)) {
-            return DEFAULT_KEY_SERIALIZER;
-        }
-        if (Date.class.isAssignableFrom(cls)) {
-            return (JsonSerializer<Object>) DateKeySerializer.instance;
-        }
-        if (Calendar.class.isAssignableFrom(cls)) {
-            return (JsonSerializer<Object>) CalendarKeySerializer.instance;
+        if (rawKeyType != null) {
+            if (rawKeyType == String.class) {
+                return DEFAULT_STRING_SERIALIZER;
+            }
+            if (rawKeyType == Object.class || rawKeyType.isPrimitive()
+                    || Number.class.isAssignableFrom(rawKeyType)) {
+                return DEFAULT_KEY_SERIALIZER;
+            }
+            if (Date.class.isAssignableFrom(rawKeyType)) {
+                return (JsonSerializer<Object>) DateKeySerializer.instance;
+            }
+            if (Calendar.class.isAssignableFrom(rawKeyType)) {
+                return (JsonSerializer<Object>) CalendarKeySerializer.instance;
+            }
         }
-        /* 14-Mar-2014, tatu: Should support @JsonValue, as per #47; but that
-         *   requires extensive introspection, and passing in more information
-         *   to this method.
-         */
-        // If no match, just use default one:
-        return DEFAULT_KEY_SERIALIZER;
+        return useDefault ? DEFAULT_KEY_SERIALIZER : null;
+    }
+
+    /**
+     * @deprecated Since 2.5
+     */
+    @Deprecated
+    public static JsonSerializer<Object> getStdKeySerializer(JavaType keyType) {
+        return getStdKeySerializer(null, keyType.getRawClass(), true);
     }
 
+    public static JsonSerializer<Object> getDefault() {
+        return DEFAULT_KEY_SERIALIZER;
+    }
+    
     /*
     /**********************************************************
     /* Standard implementations

src/test/java/com/fasterxml/jackson/failing/TestMapJsonValueKey47.java

@@ -41,6 +41,6 @@ public void testMapJsonValueKey()
 
         ObjectMapper mapper = new ObjectMapper();
         String json = mapper.writeValueAsString(input);
-        assertEquals(aposToQuotes("{'3':'true'}"), json);
+        assertEquals(aposToQuotes("{'3':true}"), json);
     }
 }