fix: resolve conflict where global Date writer overrides @JSONField format, for issue #3864

wenshao · wenshao · commit 49f44e36535a · 2025-12-26T10:15:15.000+08:00
diff --git a/core/src/main/java/com/alibaba/fastjson2/writer/ObjectWriterCreator.java b/core/src/main/java/com/alibaba/fastjson2/writer/ObjectWriterCreator.java
@@ -819,7 +819,7 @@ public <T> FieldWriter<T> createFieldWriter(
             // ignored
         }
 
-        if (initObjectWriter == null && provider != null) {
+        if (initObjectWriter == null && provider != null && (format == null || format.isEmpty() || fieldClass != Date.class)) {
             initObjectWriter = getInitWriter(provider, fieldClass);
         }
 
diff --git a/core/src/test/java/com/alibaba/fastjson2/issues_3800/Issue3864.java b/core/src/test/java/com/alibaba/fastjson2/issues_3800/Issue3864.java
@@ -0,0 +1,38 @@
+package com.alibaba.fastjson2.issues_3800;
+
+import com.alibaba.fastjson2.JSON;
+import com.alibaba.fastjson2.JSONFactory;
+import com.alibaba.fastjson2.annotation.JSONField;
+import com.alibaba.fastjson2.writer.ObjectWriterProvider;
+import lombok.Data;
+import org.junit.jupiter.api.Test;
+
+import java.util.Date;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class Issue3864 {
+    @Test
+    public void testSerializationPriority() {
+        ObjectWriterProvider provider = JSONFactory.getDefaultObjectWriterProvider();
+        try {
+            provider.register(Date.class, (jsonWriter, o, o1, type, l) -> jsonWriter.writeInt64(((Date) o).getTime()));
+
+            CustomDateDo dateDo = new CustomDateDo();
+            dateDo.setDate(new Date(1673861993477L));
+            dateDo.setDate2(new Date(1673861993477L));
+
+            String json = JSON.toJSONString(dateDo);
+            assertEquals("{\"date\":1673861993477,\"date2\":\"2023-01-16 17:39:53\"}", json);
+        } finally {
+            provider.unregister(Date.class);
+        }
+    }
+
+    @Data
+    public static class CustomDateDo {
+        private Date date;
+        @JSONField(format = "yyyy-MM-dd HH:mm:ss")
+        private Date date2;
+    }
+}

Original file line number	Diff line number	Diff line change
`@@ -819,7 +819,7 @@ public <T> FieldWriter<T> createFieldWriter(`
`819`	`819`	`// ignored`
`820`	`820`	`}`
`821`	`821`
`822`		`- if (initObjectWriter == null && provider != null) {`
	`822`	`+ if (initObjectWriter == null && provider != null && (format == null \|\| format.isEmpty() \|\| fieldClass != Date.class)) {`
`823`	`823`	`initObjectWriter = getInitWriter(provider, fieldClass);`
`824`	`824`	`}`
`825`	`825`