如何使用json将Java8 LocalDateTime序列化为日历对象

Question

我正在使用jackson-datatype-jsr310 310模块，它支持LocalDateTime序列化。但默认情况下，它将日期/时间序列化为"2022,6,29,17,15,54“。

但是，我需要重写这个行为，以便以"Calendar“格式(例如)序列化/反序列化它。作为json对象

"arrivalDate": {
  "month": "JUNE",
  "dayOfWeek": "WEDNESDAY",
  "dayOfYear": 180,
  "nano": 0,
  "year": 2022,
  "monthValue": 6,
  "dayOfMonth": 29,
  "hour": 12,
  "minute": 53,
  "second": 46,
  "chronology": {
    "id": "ISO",
    "calendarType": "iso8601"
  }
}

对于所有应用程序，该设置不应该是全局的，而仅用于内部特定的ObjectMapper实例化。

Answer 1

引言

让我们把Jackson 2.13.3作为当前版本。

分析

这样的特征似乎已被排除在外。

请参阅下面的源代码，并注意下面的注释：jackson-databind/BeanSerializerFactory.java at jackson-databind-2.13.3·FasterXML/jackson-databind

    protected JsonSerializer<?> _findUnsupportedTypeSerializer(SerializerProvider ctxt,
            JavaType type, BeanDescription beanDesc)
        throws JsonMappingException
    {
        // 05-May-2020, tatu: Should we check for possible Shape override to "POJO"?
        //   (to let users force 'serialize-as-POJO'?
        final String errorMsg = BeanUtil.checkUnsupportedType(type);

也许，打开适当的GitHub问题是值得的。

可能的解决办法

引入并使用自定义BeanSerializerFactory实现，该实现不会阻止对JSR 310类型( java.time包)和Joda类型( org.joda.time包)使用默认的Jackson序列化程序。

为了理解这个想法，请参考以下方法的实施：

• com.fasterxml.jackson.databind.ser.BeanSerializerFactory._findUnsupportedTypeSerializer()。
• com.fasterxml.jackson.databind.util.BeanUtil.checkUnsupportedType()。
• com.fasterxml.jackson.databind.util.BeanUtil.isJava8TimeClass()。

CustomBeanSerializerFactory类

import com.fasterxml.jackson.databind.BeanDescription;
import com.fasterxml.jackson.databind.JavaType;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.cfg.SerializerFactoryConfig;
import com.fasterxml.jackson.databind.ser.BeanSerializerFactory;

public final class CustomBeanSerializerFactory extends BeanSerializerFactory {
    protected CustomBeanSerializerFactory(final SerializerFactoryConfig config) {
        super(config);
    }

    @Override
    protected JsonSerializer<?> _findUnsupportedTypeSerializer(
        final SerializerProvider ctxt,
        final JavaType type,
        final BeanDescription beanDesc
    ) {
        return null;
    }
}

Schedule类

import java.time.LocalDateTime;

public final class Schedule {
    private final LocalDateTime arrivalDate;

    public Schedule(final LocalDateTime arrivalDate) {
        this.arrivalDate = arrivalDate;
    }

    public LocalDateTime getArrivalDate() {
        return arrivalDate;
    }
}

Program类

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import java.time.LocalDateTime;

public final class Program {
    public static void main(final String[] args) throws JsonProcessingException {
        final LocalDateTime localDateTime = LocalDateTime.of(
            2022, 1, 2, 3, 4, 5, 6
        );
        final Schedule schedule = new Schedule(localDateTime);

        final ObjectMapper objectMapper = new ObjectMapper();
        objectMapper.setSerializerFactory(
            new CustomBeanSerializerFactory(null)
        );
        final String jsonString = objectMapper.writeValueAsString(schedule);
        System.out.println(jsonString);
    }
}

程序输出：

{"arrivalDate":{"nano":6,"year":2022,"monthValue":1,"dayOfMonth":2,"hour":3,"minute":4,"second":5,"month":"JANUARY","dayOfWeek":"SUNDAY","dayOfYear":2,"chronology":{"id":"ISO","calendarType":"iso8601"}}}

附加参考资料

• GitHub杂志：默认情况下不支持.问题#26859 ./spring。

- Comment: [Spring Boot 2.5.0 and InvalidDefinitionException: Java 8 date/time type `java.time.Instant` not supported by default · Issue #26859 · spring-projects/spring-boot](https://github.com/spring-projects/spring-boot/issues/26859#issuecomment-869144674).

• GitHub杂志：没有注册自定义序列化器的类型·问题#2683·FasterXML/jackson数据库。