fix bug for issue alibaba#3464 (alibaba#3501)

* Update ObjectWriterAdapter.java

fix bug for Issue3464

* Create Issue3464.java

fix bug for Issue3464

* Update ObjectWriterAdapter.java

Resolve Checkstyle Issues

* Update Issue3464.java

Resolve Checkstyle Issues

Author: jujn

core/src/main/java/com/alibaba/fastjson2/writer/ObjectWriterAdapter.java

@@ -675,6 +675,11 @@ public JSONObject toJSONObject(T object, long features) {
             if (fieldValue == object) {
                 fieldValue = jsonObject;
             }
+            if (fieldValue instanceof Enum) {
+                if ((features & WriteEnumsUsingName.mask) != 0) {
+                    fieldValue = ((Enum) fieldValue).name();
+                }
+            }
             if (fieldWriter instanceof FieldWriterObject && !(fieldValue instanceof Map)) {
                 ObjectWriter valueWriter = fieldWriter.getInitWriter();
                 if (valueWriter == null) {

core/src/test/java/com/alibaba/fastjson2/issues_3400/Issue3464.java

@@ -0,0 +1,27 @@
+package com.alibaba.fastjson2.issues_3400;
+
+import com.alibaba.fastjson2.JSON;
+import com.alibaba.fastjson2.JSONObject;
+import com.alibaba.fastjson2.JSONWriter;
+import lombok.AllArgsConstructor;
+import lombok.Getter;
+import org.junit.Test;
+
+import java.util.concurrent.TimeUnit;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class Issue3464 {
+    @Test
+    public void test() {
+        Data data = new Data(TimeUnit.MINUTES);
+        JSONObject json = (JSONObject) JSON.toJSON(data, JSONWriter.Feature.WriteEnumsUsingName);
+        assertEquals(json.get("unit").getClass().toString(), "class java.lang.String");
+    }
+
+    @Getter
+    @AllArgsConstructor
+    private static class Data {
+        private TimeUnit unit;
+    }
+}