fix_issus_3926 #3931

ban-xiu · 2026-01-03T11:52:05Z

What this PR does / why we need it?

Fix: 修复自定义 List 子类反序列化时元素类型解析为 JSONObject 的问题 issus_3926

恳请帮忙审查并合并此 PR，希望能为项目贡献一份力量

根本原因

在 ObjectReaderCreator.createFieldReader() 方法中，当字段类型是自定义 List 子类（如 MyList.class ）时：

fieldTypeResolved 不是 ParameterizedType ，无法提取泛型类型参数
fieldType 是普通 Class （不是 ParameterizedType ），也无法提取泛型类型参数
最终 itemType 被设置为 Object.class ，导致反序列化时创建 JSONObject

解决方案

在 ObjectReaderCreator.java 的 List 类型解析逻辑中，新增第三步类型解析策略：

第一步：从 fieldTypeResolved 提取类型参数（原有逻辑）
第二步：从 fieldType 提取类型参数（原有逻辑）
第三步：遍历 fieldType 的泛型超类层次结构，查找包含泛型类型参数的 Collection 超类
另外处理了fieldTypeResolved fieldClassResolved为空的情况

Summary of your change

core/src/main/java/com/alibaba/fastjson2/reader/ObjectReaderCreator.java，在 createFieldReader() 方法中，针对 List 类型的字段解析逻辑进行了增强

core/src/test/java/com/alibaba/fastjson2_demo/CustomListTest.java，添加了测试用例验证修复效果

Please indicate you've done the following:

Made sure tests are passing and test coverage is added if needed.
Made sure commit message follow the rule of Conventional Commits specification.
Considered the docs impact and opened a new docs issue or PR with docs changes if needed.

CLAassistant · 2026-01-03T11:52:11Z

All committers have signed the CLA.

jujn · 2026-01-03T12:25:42Z

谢谢你的支持，我最近也在研究这个，有几个建议供你参考：
①对于直接实现接口的场景（如下），目前的修复可能还存在一些缺陷

public class MyList implements List<String> { ... }

②单测可以补充一下 FieldBased 的场景：

MyDTO myDTO = JSON.parseObject("{\"myList\":[{\"name\":\"张三\"}]}", MyDTO.class, JSONReader.Feature.FieldBased);
MyObject myObject = myDTO.getMyList().get(0);

③单测类的命名、放置位置、编写风格可以参考下其它已合并的 PR

ban-xiu · 2026-01-03T12:29:41Z

@jujn 好的我研究一下

…interfaces

ban-xiu · 2026-01-04T10:31:57Z

@jujn hi，已经完成了接口解析的补充和自测，请问可以帮忙review一下吗

jujn · 2026-01-04T12:10:50Z

MyDTO myDTO = JSON.parseObject("{"myList":[{"name":"张三"}]}", MyDTO.class, JSONReader.Feature.FieldBased);
FieldBased 的场景也需要修复（在 ObjectReaderCreator 某一个 createFieldReader 中，你可以自己找一下hh），增加与 createFieldReaderMethod 相类似的逻辑即可。因为这两种情况，一个是基于setter解析，一个基于field。

ban-xiu · 2026-01-05T11:20:57Z

@jujn 搞定了辛苦帮忙看看

jujn · 2026-01-05T11:27:23Z

可以改成这样吗？

if (fieldTypeResolved instanceof ParameterizedType) {
  // 这里的逻辑不要动
  …… 
} else {
   调用 BeanUtils.resolveCollectionItemType
   ……
}

ban-xiu · 2026-01-05T11:45:22Z

已修改

jujn · 2026-01-05T11:54:09Z

resolveCollectionItemType 里可以复用 BeanUtils.getGenericSupertype 方法吗？（比如类似下面这样的逻辑）

    public static Type resolveCollectionItemType(Type fieldTypeResolved, Class<?> fieldClass) {
        Type contextType = fieldTypeResolved != null ? fieldTypeResolved : fieldClass;

        Type listType = getGenericSupertype(contextType, fieldClass, List.class);

        if (listType == null || listType == List.class) {
            listType = getGenericSupertype(contextType, fieldClass, Collection.class);
        }

        listType = BeanUtils.resolve(contextType, fieldClass, listType);

        if (listType instanceof ParameterizedType) {
            ParameterizedType parameterizedType = (ParameterizedType) listType;
            Type[] actualTypeArguments = parameterizedType.getActualTypeArguments();

            if (actualTypeArguments.length == 1) {
                return actualTypeArguments[0];
            }
        }
        return null;
    }

ban-xiu · 2026-01-05T12:14:17Z

感谢指正，确实有很多可以复用的方法

ban-xiu · 2026-01-05T13:24:12Z

已经做出修改

ban-xiu · 2026-01-05T14:11:57Z

不知道为什么，图片中的评论我展示不出来，现在调整过了

jujn · 2026-01-06T07:44:14Z

等温老师有时间来审核吧，这里我感觉很容易留下逻辑漏洞

wenshao · 2026-01-10T17:08:52Z

很好的改进，这个问题在Map上也有，欢迎继续提PR

* fix_issus_3926 * support generic type resolution for custom collection subclasses and interfaces * move test * fix field-based mode * use resolveCollectionItemType * fix resolveCollectionItemType * fix fieldReaderList * fix fieldReaderList return

ban-xiu · 2026-01-11T11:25:34Z

我尝试了以下这个例子，可以正常运行，似乎Map已经支持了

package com.alibaba.fastjson2.issues_3900;

import com.alibaba.fastjson2.JSON;
import org.junit.jupiter.api.Test;

import java.util.HashMap;

import static org.junit.jupiter.api.Assertions.assertEquals;

public class Issue3926_Map {
    /**
     * 测试Map的key和value类型被继承的情况
     */
    public static class MyDTO1 {
        private MyMap1 myMap1;

        public MyMap1 getMyMap1() {
            return myMap1;
        }

        public void setMyMap1(MyMap1 myMap1) {
            this.myMap1 = myMap1;
        }
    }

    /**
     * 自定义Map子类，使用继承的key和value类型
     */
    public static class MyMap1 extends HashMap<MyKey, MyValue> {
    }

    /**
     * 基础Key类
     */
    public static class BaseKey {
        protected int id;

        public int getId() {
            return id;
        }

        public void setId(int id) {
            this.id = id;
        }
    }

    /**
     * 自定义Key类，继承自BaseKey
     */
    public static class MyKey extends BaseKey {
        private String name;

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

        @Override
        public boolean equals(Object o) {
            if (this == o) {
                return true;
            }
            if (o == null || getClass() != o.getClass()) {
                return false;
            }
            MyKey myKey = (MyKey) o;
            return id == myKey.id && (name != null ? name.equals(myKey.name) : myKey.name == null);
        }

        @Override
        public int hashCode() {
            return 31 * id + (name != null ? name.hashCode() : 0);
        }
    }

    /**
     * 基础Value类
     */
    public static class BaseValue {
        protected String job;

        public String getJob() {
            return job;
        }

        public void setJob(String job) {
            this.job = job;
        }
    }

    /**
     * 自定义Value类，继承自BaseValue
     */
    public static class MyValue extends BaseValue {
        private int age;

        public int getAge() {
            return age;
        }

        public void setAge(int age) {
            this.age = age;
        }
    }

    /**
     * 测试Map的key和value类型被继承的情况
     */
    @Test
    public void testCustomMapWithInheritedTypes() {
        String json = "{\"myMap1\":{{\"name\":\"张三\"}:{\"job\":\"司机\",\"age\":30}}}";
        MyDTO1 myDTO1 = JSON.parseObject(json, MyDTO1.class);

        assertEquals(1, myDTO1.getMyMap1().size());

        for (java.util.Map.Entry<MyKey, MyValue> entry : myDTO1.getMyMap1().entrySet()) {
            MyKey key = entry.getKey();
            MyValue value = entry.getValue();

            // 验证值的属性
            assertEquals("张三", key.getName());
            assertEquals("司机", value.getJob());
            assertEquals(30, value.getAge());
        }
    }

    /**
     * 测试Map的key和value类型实现接口的情况
     */
    public static class MyDTO2 {
        private MyMap2 myMap2;

        public MyMap2 getMyMap2() {
            return myMap2;
        }

        public void setMyMap2(MyMap2 myMap2) {
            this.myMap2 = myMap2;
        }
    }

    /**
     * 自定义Map子类，使用实现接口的key和value类型
     */
    public static class MyMap2 extends HashMap<KeyImpl, ValueImpl> {
    }

    /**
     * Key接口
     */
    public interface KeyInterface {
        String getKey();
    }

    /**
     * 实现KeyInterface的类
     */
    public static class KeyImpl implements KeyInterface {
        private String key;

        @Override
        public String getKey() {
            return key;
        }

        public void setKey(String key) {
            this.key = key;
        }

        @Override
        public boolean equals(Object o) {
            if (this == o) {
                return true;
            }
            if (o == null || getClass() != o.getClass()) {
                return false;
            }
            KeyImpl keyImpl = (KeyImpl) o;
            return key != null ? key.equals(keyImpl.key) : keyImpl.key == null;
        }

        @Override
        public int hashCode() {
            return key != null ? key.hashCode() : 0;
        }
    }

    /**
     * Value接口
     */
    public interface ValueInterface {
        String getValue();
    }

    /**
     * 实现ValueInterface的类
     */
    public static class ValueImpl implements ValueInterface {
        private String value;

        @Override
        public String getValue() {
            return value;
        }

        public void setValue(String value) {
            this.value = value;
        }
    }

    /**
     * 测试Map的key和value类型实现接口的情况
     */
    @Test
    public void testCustomMapWithInterfaceTypes() {
        String json = "{\"myMap2\":{{\"key\":\"key1\"}:{\"value\":\"value1\"}}}";
        MyDTO2 myDTO2 = JSON.parseObject(json, MyDTO2.class);

        assertEquals(1, myDTO2.getMyMap2().size());

        for (java.util.Map.Entry<KeyImpl, ValueImpl> entry : myDTO2.getMyMap2().entrySet()) {
            KeyImpl key = entry.getKey();
            ValueImpl value = entry.getValue();

            // 验证值的属性
            assertEquals("key1", key.getKey());
            assertEquals("value1", value.getValue());
        }
    }
}

fix_issus_3926

655c223

ban-xiu added 2 commits January 3, 2026 21:01

support generic type resolution for custom collection subclasses and …

7876fef

…interfaces

move test

acfdd84

fix field-based mode

da650fb

use resolveCollectionItemType

1c2548b

fix resolveCollectionItemType

0750449

fix fieldReaderList

12789d3

fix fieldReaderList return

f037321

wenshao merged commit 6bbb2fd into alibaba:main Jan 10, 2026
21 checks passed

fix_issus_3926 #3931

fix_issus_3926 #3931

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