[BUG] 枚举类型变量反序列化后变成NULL

[yaozhihang]

问题描述

枚举类型变量反序列化后变成NULL

环境信息

请填写以下信息：

• OS信息： Windows 10
• JDK信息： Openjdk 17
• 版本信息：Fastjson 2:2.0.52

重现步骤

首先建立一个基于gradle的java项目，并且引入fastjson2依赖和另外一个开源库citygml4j

dependencies {
    implementation 'com.alibaba.fastjson2:fastjson2:2.0.52'
    implementation 'org.citygml4j:citygml4j-core:3.2.1'
}

在 module-info.java 设置模块

module org.example {
    requires com.alibaba.fastjson2;
    requires org.citygml4j.core;

    exports org.example;
}

然后建立一个简单的类, 里面只有一个枚举类型的变量 version.

package org.example;

import com.alibaba.fastjson2.JSONWriter;
import com.alibaba.fastjson2.annotation.JSONField;
import org.citygml4j.core.model.CityGMLVersion;

public class FOO {
    @JSONField(serializeFeatures = JSONWriter.Feature.WriteEnumUsingToString)
    private CityGMLVersion version;

    public CityGMLVersion getVersion() {
        return version;
    }

    public FOO setVersion(CityGMLVersion version) {
        this.version = version;
        return this;
    }

    public FOO setVersion(String version) {
        this.version = CityGMLVersion.fromValue(version);
        return this;
    }
}

接下来进行测试

package org.example;

import com.alibaba.fastjson2.JSON;

public class Main {
    public static void main(String[] args) {
        FOO foo = JSON.parseObject("{\n" +
                "  \"version\": \"2.0\"\n" +
                "}", FOO.class);

        System.out.println(foo.getVersion());
    }
}

结果输出是 null。但是如果使用以前的版本 2:2.0.49， 结果则是正确的 "2.0". 附上以上测试代码项目包。

test.zip

[wenshao]

这个你可以用Mixin的方式去解，比如：

public class Issue2820 {
    static class CityGMLVersionMixin {
        @JSONField(value = true)
        public String toValue() {
            return null;
        }
    }

    @Test
    public void test() {
        JSON.mixIn(CityGMLVersion.class, CityGMLVersionMixin.class);
        FOO foo = JSON.parseObject("{\n" +
                "  \"version\": \"2.0\"\n" +
                "}", FOO.class);

        System.out.println(foo.getVersion());
    }
    public class FOO {
        @JSONField(serializeFeatures = JSONWriter.Feature.WriteEnumUsingToString)
        private CityGMLVersion version;

        public CityGMLVersion getVersion() {
            return version;
        }

        public FOO setVersion(CityGMLVersion version) {
            this.version = version;
            return this;
        }

        public FOO setVersion(String version) {
            this.version = CityGMLVersion.fromValue(version);
            return this;
        }
    }
}

[clausnagel]

@wenshao, can you please explain what the proposed MixIn class and its toValue method actually do in the background to solve the issue?

I suppose your proposal is rather a workaround than a solution. At least with version fastjson2 2.0.49, the code worked without having to use a MixIn class. I haven't been using the static JSON.mixIn method before. It looks like this method is some sort of global configuration for the JSON de-/serialization, right? My concern is that this configuration can simply be overriden by any external user. We are building a Java library that uses fastjson2 and I want this library to behave in a stable way without offering users the possibilty to change behaviour via static methods. And this could be accomplished using 2.0.49.

[yaozhihang]

@wenshao 感谢回复，正如上面clausnagel提到的， 使用 JSON.mixIn 看起来只是一个临时替代方案。请问在接下来的版本中会修复这个bug吗?

[wenshao]

JSON.toJSONString(obj, JSONWriter.Feature.WriteEnumUsingToString)

@yaozhihang 也可以只用这个方法，未来的版本应该也是这个行为，缺省是name()

[yaozhihang]

不好意思，不是很理解。问题出现在反序列化的过程。您提上面到"缺省是name()" 是什么意思?

[clausnagel]

Agree with @yaozhihang. I guess, having a ReadEnumUsingToString feature for JSONReader would be a good solution. Strangely, it already worked with 2.0.49.

[wenshao]

https://github.com/alibaba/fastjson2/releases/tag/2.0.54
问题已修复，请用新版本