Fix #4896: deserialize enum from "" (#4923)

Author: cowtowncoder

release-notes/VERSION-2.x

@@ -41,6 +41,8 @@ Project: jackson-databind
 #4867: Add `Optional<JsonNode> JsonNode.asOptional()` convenience method
  (fix by Joo-Hyuk K)
 #4869: Add `JsonNode.values()` to replace `elements()`
+#4896: Coercion shouldn't be necessary for Enums specifying an empty string
+ (reported by @joaocanaverde-blue)
 
 2.18.3 (not yet released)
 

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

@@ -177,36 +177,8 @@ public boolean isAnnotationBundle(Annotation ann) {
     /**********************************************************
      */
 
-    /**
-     * Since 2.6, we have supported use of {@link JsonProperty} for specifying
-     * explicit serialized name
-     */
-    @Override
-    @Deprecated // since 2.8
-    public String findEnumValue(Enum<?> value)
-    {
-        // 11-Jun-2015, tatu: As per [databind#677], need to allow explicit naming.
-        //   Unfortunately cannot quite use standard AnnotatedClass here (due to various
-        //   reasons, including odd representation JVM uses); has to do for now
-        try {
-            // We know that values are actually static fields with matching name so:
-            Field f = value.getDeclaringClass().getField(value.name());
-            if (f != null) {
-                JsonProperty prop = f.getAnnotation(JsonProperty.class);
-                if (prop != null) {
-                    String n = prop.value();
-                    if (n != null && !n.isEmpty()) {
-                        return n;
-                    }
-                }
-            }
-        } catch (SecurityException e) {
-            // 17-Sep-2015, tatu: Anything we could/should do here?
-        } catch (NoSuchFieldException e) {
-            // 17-Sep-2015, tatu: should not really happen. But... can we do anything?
-        }
-        return value.name();
-    }
+    // @since 2.19 no longer overridden; been deprecated since 2.8
+    //public String findEnumValue(Enum<?> value)
 
     @Override // since 2.7
     @Deprecated // since 2.16
@@ -221,9 +193,12 @@ public String[] findEnumValues(Class<?> enumType, Enum<?>[] enumValues, String[]
                 continue;
             }
             String n = prop.value();
+            // 24-Jan-2025, tatu: [databind#4896] Should not skip "" with enums
+            /*
             if (n.isEmpty()) {
                 continue;
             }
+            */
             if (expl == null) {
                 expl = new HashMap<String,String>();
             }
@@ -251,7 +226,9 @@ public String[] findEnumValues(MapperConfig<?> config, AnnotatedClass annotatedC
             JsonProperty property = field.getAnnotation(JsonProperty.class);
             if (property != null) {
                 String propValue = property.value();
-                if (propValue != null && !propValue.isEmpty()) {
+                if (propValue != null) {
+                    // 24-Jan-2025, tatu: [databind#4896] Should not skip "" with enums
+                    // && !propValue.isEmpty()) {
                     enumToPropertyMap.put(field.getName(), propValue);
                 }
             }

src/main/java/com/fasterxml/jackson/databind/util/CompactStringObjectMap.java

@@ -96,7 +96,8 @@ private final static int findSize(int size)
         return result;
     }
 
-    public Object find(String key) {
+    public Object find(String key)
+    {
         int slot = key.hashCode() & _hashMask;
         int ix = (slot<<1);
         Object match = _hashArea[ix];

src/test/java/com/fasterxml/jackson/databind/deser/enums/EnumDeserializationTest.java

@@ -205,7 +205,6 @@ public Object deserializeKey(String key, DeserializationContext ctxt) throws IOE
         }
     }
 
-
     @JsonDeserialize(using = AnEnumDeserializer.class, keyUsing = AnEnumKeyDeserializer.class)
     public enum LanguageCodeMixin {
     }
@@ -279,6 +278,18 @@ public static Operation3006 forValue(final String idStr) {
         }
     }
 
+    // [databind#4896]
+    enum YesOrNoOrEmpty4896 {
+        @JsonProperty("")
+        EMPTY,
+
+        @JsonProperty("yes")
+        YES,
+
+        @JsonProperty("no")
+        NO;
+    }
+
     /*
     /**********************************************************
     /* Test methods
@@ -814,4 +825,15 @@ public void testEnumFeature_READ_ENUM_KEYS_USING_INDEX_isDisabledByDefault() {
             .isEnabled(EnumFeature.READ_ENUM_KEYS_USING_INDEX));
     }
 
+    // [databind#4896]
+    @Test
+    public void testEnumReadFromEmptyString() throws Exception {
+        // First, regular value
+        assertEquals(YesOrNoOrEmpty4896.YES,
+                MAPPER.readerFor(YesOrNoOrEmpty4896.class)
+                    .readValue(q("yes")));
+        assertEquals(YesOrNoOrEmpty4896.EMPTY,
+            MAPPER.readerFor(YesOrNoOrEmpty4896.class)
+                .readValue(q("")));
+    }
 }