Symfony Serializer反序列化JSON至PHP类返回NULL问题求助

问题根源 #

1. 私有属性无访问器：Symfony Serializer的ObjectNormalizer默认无法直接操作私有属性，必须通过getter/setter、反射配置或元数据组件识别属性。
2. 嵌套对象类型未被识别：Low/Medium/High类的私有属性和嵌套结构缺少元数据支持，Serializer无法自动实例化这些对象并赋值。
3. 构造函数映射缺失：FeeClass的构造参数虽对应JSON键，但若无属性元数据，Serializer无法将JSON值绑定到构造参数。

解决方案 #

方案一：添加访问器并启用PropertyInfo组件（推荐生产环境）

1. 为Low/Medium/High类添加getter/setter，确保属性可被Serializer访问：

class Low {
    private $networkFee;

    public function getNetworkFee(): ?string
    {
        return $this->networkFee;
    }

    public function setNetworkFee(string $networkFee): void
    {
        $this->networkFee = $networkFee;
    }
}

// Medium和High类复制上述代码，替换类名即可

2. 安装Symfony PropertyInfo组件，用于识别属性类型和元数据：

composer require symfony/property-info

3. 配置Serializer时注入PropertyInfo提取器：

use Symfony\Component\PropertyInfo\Extractor\PhpDocExtractor;
use Symfony\Component\PropertyInfo\Extractor\ReflectionExtractor;
use Symfony\Component\PropertyInfo\PropertyInfoExtractor;
use Symfony\Component\Serializer\Normalizer\ObjectNormalizer;
use Symfony\Component\Serializer\Serializer;
use Symfony\Component\Serializer\Encoder\JsonEncoder;

// 初始化属性信息提取器
$phpDocExtractor = new PhpDocExtractor();
$reflectionExtractor = new ReflectionExtractor();
$propertyInfoExtractor = new PropertyInfoExtractor(
    [$reflectionExtractor],
    [$phpDocExtractor, $reflectionExtractor],
    [$phpDocExtractor],
    [$reflectionExtractor]
);

// 配置Serializer
$normalizers = [new ObjectNormalizer(null, null, null, $propertyInfoExtractor)];
$encoders = [new JsonEncoder()];
$serializer = new Serializer($normalizers, $encoders);

// 执行反序列化
$parsed = $serializer->deserialize((string)$response->getBody(), FeeClass::class, 'json');

方案二：临时改为公开属性（仅用于测试）

若需快速验证，可将类属性改为公开（不推荐生产环境，违反封装原则）：

class Low {
    public $networkFee;
}

class Medium {
    public $networkFee;
}

class High {
    public $networkFee;
}

class FeeClass {
    public $low;
    public $medium;
    public $high;
}

方案三：使用注解配置属性映射

1. 安装注解组件：

composer require symfony/annotation

2. 为类添加序列化注解：

use Symfony\Component\Serializer\Annotation\SerializedName;

class Low {
    /**
     * @SerializedName("networkFee")
     */
    private $networkFee;

    // 对应getter/setter
}

class FeeClass {
    /**
     * @SerializedName("low")
     */
    private $low;

    /**
     * @SerializedName("medium")
     */
    private $medium;

    /**
     * @SerializedName("high")
     */
    private $high;

    public function __construct(Low $low, Medium $medium, High $high) {
        $this->low = $low;
        $this->medium = $medium;
        $this->high = $high;
    }
}

3. 配置Serializer启用注解加载：

use Symfony\Component\Serializer\Mapping\Factory\ClassMetadataFactory;
use Symfony\Component\Serializer\Mapping\Loader\AnnotationLoader;
use Doctrine\Common\Annotations\AnnotationReader;
use Symfony\Component\Serializer\Normalizer\ObjectNormalizer;
use Symfony\Component\Serializer\Serializer;
use Symfony\Component\Serializer\Encoder\JsonEncoder;

$classMetadataFactory = new ClassMetadataFactory(new AnnotationLoader(new AnnotationReader()));
$normalizers = [new ObjectNormalizer($classMetadataFactory)];
$encoders = [new JsonEncoder()];
$serializer = new Serializer($normalizers, $encoders);

内容的提问来源于stack exchange，提问作者Russo