Fix generic field deserialize, issue #3810

src/main/java/com/alibaba/fastjson/parser/deserializer/DefaultFieldDeserializer.java

@@ -64,7 +64,7 @@ public void parseField(DefaultJSONParser parser, Object object, Type objectType,
             }
             if (fieldType != objectType) {
                 fieldType = FieldInfo.getFieldType(this.clazz, objectType, fieldType);
-                if (fieldValueDeserilizer == null) {
+                if (fieldValueDeserilizer instanceof JavaObjectDeserializer) {
                     fieldValueDeserilizer = parser.getConfig().getDeserializer(fieldType);
                 }
             }

src/test/java/com/alibaba/json/bvt/issue_3800/Issue3810.java

@@ -0,0 +1,40 @@
+package com.alibaba.json.bvt.issue_3800;
+
+import com.alibaba.fastjson.JSONObject;
+import com.alibaba.fastjson.util.ParameterizedTypeImpl;
+import junit.framework.TestCase;
+import lombok.Data;
+
+import java.lang.reflect.Type;
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * https://github.com/alibaba/fastjson/issues/3810
+ *
+ * @author hnyyghk
+ * @date 2021/06/30 18:40
+ */
+public class Issue3810 extends TestCase {
+    @Data
+    static class TestA<T> {
+        T a;
+    }
+
+    @Data
+    static class TestB {
+        String b;
+    }
+
+    private final static String json = "{\"a\":[{\"b\":\"b\"}]}";
+
+    public void test_for_issue() throws Exception {
+        ParameterizedTypeImpl inner = new ParameterizedTypeImpl(new Type[]{TestB.class}, List.class, List.class);
+        ParameterizedTypeImpl outer = new ParameterizedTypeImpl(new Type[]{inner}, TestA.class, TestA.class);
+        JSONObject jo = JSONObject.parseObject(json);
+        TestA<List<?>> ret = jo.toJavaObject(outer);
+
+        assertEquals(ArrayList.class.getName(), ret.getA().getClass().getName());
+        assertEquals(TestB.class.getName(), ret.getA().get(0).getClass().getName());
+    }
+}