jsonfield defaultValue support enum, for issue #2239

Author: wenshao

core/src/main/java/com/alibaba/fastjson2/reader/FieldReaderObject.java

@@ -125,8 +125,10 @@ public void readFieldValue(JSONReader jsonReader, T object) {
 
         Object value;
         try {
-            if (jsonReader.nextIfNull()) {
-                if (fieldClass == OptionalInt.class) {
+            if (jsonReader.nextIfNullOrEmptyString()) {
+                if (defaultValue != null) {
+                    value = defaultValue;
+                } else if (fieldClass == OptionalInt.class) {
                     value = OptionalInt.empty();
                 } else if (fieldClass == OptionalLong.class) {
                     value = OptionalLong.empty();

core/src/main/java/com/alibaba/fastjson2/reader/ObjectReaderCreator.java

@@ -2524,6 +2524,9 @@ public <T> FieldReader<T> createFieldReader(
             Field field,
             ObjectReader initReader
     ) {
+        if (defaultValue instanceof String && fieldClass.isEnum()) {
+            defaultValue = Enum.valueOf(fieldClass, (String) defaultValue);
+        }
         if (defaultValue != null && defaultValue.getClass() != fieldClass) {
             ObjectReaderProvider provider = JSONFactory
                     .getDefaultObjectReaderProvider();

core/src/test/java/com/alibaba/fastjson2/issues_2200/Issue2239.java

@@ -0,0 +1,25 @@
+package com.alibaba.fastjson2.issues_2200;
+
+import com.alibaba.fastjson2.JSON;
+import com.alibaba.fastjson2.annotation.JSONField;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class Issue2239 {
+    @Test
+    public void test() {
+        assertEquals(Type.NONE, JSON.parseObject("{}", Bean.class).type);
+        assertEquals(Type.NONE, JSON.parseObject("{\"type\":null}", Bean.class).type);
+        assertEquals(Type.NONE, JSON.parseObject("{\"type\":\"\"}", Bean.class).type);
+    }
+
+    public static class Bean {
+        @JSONField(defaultValue = "NONE")
+        public Type type;
+    }
+
+    public enum Type {
+        NONE, ONE, TWO
+    }
+}