[BUG]反序列化空EnumSet可能导致异常

[superinkfish]

问题描述

简要描述您碰到的问题。
一个含有EnumSet的空集合，在JSON序列化后，再用FastJSON2反序列化，会报异常。

环境信息

• OS信息： Windows 11 & CentOS 7u2
• JDK信息： Openjdk 1.8.0
• 版本信息：fastjson2=2.0.42

重现步骤

1. 复现源码：

import java.util.EnumSet;
import java.util.concurrent.TimeUnit;

public class TestFastJson {

    public static void main(String[] args) {
        Bean bean = new Bean();
        System.out.println("Source: \n" + bean);

        String jsonStr = com.alibaba.fastjson.JSON.toJSONString(bean);
        System.out.println("\nFastJSON:\n" + jsonStr);
        System.out.println(com.alibaba.fastjson.JSON.parseObject(jsonStr, Bean.class));

        jsonStr = com.alibaba.fastjson2.JSON.toJSONString(bean);
        System.out.println("\nFastJSON2:\n" + jsonStr);
        System.out.println(com.alibaba.fastjson2.JSON.parseObject(jsonStr, Bean.class));
    }
}

class Bean {
    private EnumSet<TimeUnit> unit = EnumSet.noneOf(TimeUnit.class);

    public EnumSet<TimeUnit> getUnit() {
        return unit;
    }

    public void setUnit(EnumSet<TimeUnit> unit) {
        this.unit = unit;
    }

    @Override
    public String toString() {
        return "Bean [unit=" + unit + "]";
    }
}

在使用FastJSON时运行正常，FastJSON2反序列化时抛出异常：

Source: 
Bean [unit=[]]

FastJSON:
{"unit":[]}
Bean [unit=[]]

FastJSON2:
{"unit":[]}
Exception in thread "main" java.lang.IllegalArgumentException: Collection is empty
	at java.util.EnumSet.copyOf(EnumSet.java:174)
	at com.alibaba.fastjson2.reader.ObjectReaderImplList.lambda$of$0(ObjectReaderImplList.java:98)
	at com.alibaba.fastjson2.reader.ObjectReaderImplList.readObject(ObjectReaderImplList.java:626)
	at com.alibaba.fastjson2.reader.ORG_1_1_Bean.readObject(Unknown Source)
	at com.alibaba.fastjson2.JSON.parseObject(JSON.java:726)
	at TestFastJson.main(TestFastJson.java:16)

期待的正确结果

期望反序列化后能生成和原始bean相等的对象。

附加信息

• 问题原因：
  在com.alibaba.fastjson2.reader.ObjectReaderImplList.of(Type, Class, long)中，第96~98行有代码：

        } else if (listClass == EnumSet.class) {
            instanceClass = HashSet.class;
            builder = (o) -> EnumSet.copyOf((Collection) o);

这里的EnumSet.copyOf(Collection<E> c)的c隐含的是Nonnull，而空EnumSet的o为空集合，因此抛异常。
修复，把96~98行改为如下代码：

        } else if (listClass == EnumSet.class) {
            instanceClass = HashSet.class;
            final Class<Enum> clazz;
            try {
                clazz = (Class<Enum>)Class.forName(itemType.getTypeName());
            } catch (ClassNotFoundException e) {
                throw new IllegalStateException(e.getMessage(), e);
            }
            builder = (o) -> {
                if (((Collection<?>)o).isEmpty()) {
                    return EnumSet.noneOf(clazz);
                }
                return EnumSet.copyOf((Collection)o);
            };

再次执行，问题消除。

Source: 
Bean [unit=[]]

FastJSON:
{"unit":[]}
Bean [unit=[]]

FastJSON2:
{"unit":[]}
Bean [unit=[]]

[superinkfish]

在最新版的fastjson2 2.0.48中验证问题也存在。
同样，如果把EnumSet换成EnumMap，问题一样存在。
源码：

import java.util.EnumMap;
import java.util.concurrent.TimeUnit;

public class TestFastJson {

    public static void main(String[] args) {
        Bean bean = new Bean();
        System.out.println("Source: \n" + bean);

        String jsonStr = com.alibaba.fastjson.JSON.toJSONString(bean);
        System.out.println("\nFastJSON:\n" + jsonStr);
        System.out.println(com.alibaba.fastjson.JSON.parseObject(jsonStr, Bean.class));

        jsonStr = com.alibaba.fastjson2.JSON.toJSONString(bean);
        System.out.println("\nFastJSON2:\n" + jsonStr);
        System.out.println(com.alibaba.fastjson2.JSON.parseObject(jsonStr, Bean.class));
    }
}

class Bean {
    private EnumMap<TimeUnit, Integer> map = new EnumMap<>(TimeUnit.class);

    public EnumMap<TimeUnit, Integer> getMap() {
        return map;
    }

    public void setMap(EnumMap<TimeUnit, Integer> map) {
        this.map = map;
    }

    @Override
    public String toString() {
        return "Bean [map=" + map + "]";
    }
}

运行结果：

Source: 
Bean [map={}]

FastJSON:
{"map":{}}
Bean [map={}]

FastJSON2:
{"map":{}}
Exception in thread "main" com.alibaba.fastjson2.JSONException: create map error
	at com.alibaba.fastjson2.reader.ObjectReaderImplMapTyped.createInstance(ObjectReaderImplMapTyped.java:154)
	at com.alibaba.fastjson2.reader.ObjectReaderImplMapTyped.readObject(ObjectReaderImplMapTyped.java:308)
	at com.alibaba.fastjson2.reader.ORG_1_1_Bean.readObject(Unknown Source)
	at com.alibaba.fastjson2.JSON.parseObject(JSON.java:786)
	at TestFastJson.main(TestFastJson.java:16)
Caused by: java.lang.InstantiationException: java.util.EnumMap
	at java.lang.Class.newInstance(Class.java:427)
	at com.alibaba.fastjson2.reader.ObjectReaderImplMapTyped.createInstance(ObjectReaderImplMapTyped.java:152)
	... 4 more
Caused by: java.lang.NoSuchMethodException: java.util.EnumMap.<init>()
	at java.lang.Class.getConstructor0(Class.java:3082)
	at java.lang.Class.newInstance(Class.java:412)
	... 5 more

问题在com.alibaba.fastjson2.reader.ObjectReaderImplMapTyped.createInstance(long)中的instanceType.newInstance()，EnumMap没有无参构造器。
若在fastjson2 2.0.48的com.alibaba.fastjson2.reader.ObjectReaderImplMapTyped.readObject(JSONReader, Type, Object, long)第307行} else {前加入：

        } else if (EnumMap.class.isAssignableFrom(instanceType)) {
            try {
                object = EnumMap.class.getConstructor(Class.class).newInstance(Class.forName(keyType.getTypeName()));
            } catch (InstantiationException | IllegalAccessException | IllegalArgumentException
                | InvocationTargetException | NoSuchMethodException | SecurityException | ClassNotFoundException e) {
                throw new IllegalStateException(e.getMessage(), e);
            }

则测试代码能正常运行通过。

[wenshao]

https://oss.sonatype.org/content/repositories/snapshots/com/alibaba/fastjson2/fastjson2/2.0.49-SNAPSHOT/
问题已经修复，请帮忙用2.0.49-SNAPSHOT版本验证，2.0.49版本预计在本周末（4月14日）前发布

[wenshao]

https://github.com/alibaba/fastjson2/releases/tag/2.0.49
请用新版本