java - 将 LocalDate 和 LocalDateTime 序列化为 Unix 时间戳

Question

我正在从使用 java.sql.Timestamp 和 java.util.GregorianCalendar 转向使用 java.time.* 新类在 Spring MVC 应用程序中。

所以我改变了一切

private GregorianCalendar field;

到

private LocalDate field;

或

private LocalDateTime field;

但是现在当序列化这些 bean 时，它们会像这样被序列化:

"field": {
      "year": 1970,
      "month": "JANUARY",
      "dayOfMonth": 18,
      "dayOfWeek": "SUNDAY",
      "era": "CE",
      "dayOfYear": 18,
      "leapYear": false,
      "monthValue": 1,
      "chronology": {
        "id": "ISO",
        "calendarType": "iso8601"
      }
    },

我找到了其他提到向 jackson-datatype-jsr310 添加依赖项的问题的答案并获得:

 "field": [
      1970,
      1,
      18
    ],

但是我在序列化时仍然需要一个 unix 时间戳，就像我在 GregorianCalendar 字段中得到的那样:我怎样才能实现它？我可以避免使用自定义序列化程序(和反序列化程序)吗？

这些与资源响应和请求主体(如 POST、PUT 等)相关，与请求参数无关。

Jackson ObjectMapper 配置如下:

jacksonConverter.getObjectMapper().enable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);
jacksonConverter.getObjectMapper().disable(SerializationFeature.WRITE_DATE_TIMESTAMPS_AS_NANOSECONDS);

Answer 1

在 JavaDoc 中为 JavaTimeModule (包含在jackson-datatype-jsr310库中)，我们可以读到以下内容:

Most java.time types are serialized as numbers (integers or decimals as appropriate) if the SerializationFeature.WRITE_DATES_AS_TIMESTAMPS feature is enabled [...]

[...] If SerializationFeature.WRITE_DATE_TIMESTAMPS_AS_NANOSECONDS is disabled, timestamps are written as a whole number of milliseconds. [...]

然后:

Some exceptions to this standard serialization/deserialization rule:

• [...]
• LocalDate, LocalTime, LocalDateTime, and OffsetTime, which cannot portably be converted to timestamps and are instead represented as arrays when WRITE_DATES_AS_TIMESTAMPS is enabled.

您确实可以看到 LocalDateTime 无法普遍转换为 Unix 时间戳，因为它的 toEpochSecond方法以 ZoneOffset 作为参数。

总而言之，看来您能做的最好的事情就是将 LocalDateTime 替换为 Instant(参见 this great answer 的解释) LocalDateTime 和 Instant 之间的区别。

除此之外，您确实需要自定义 JsonSerializer 和 JsonDeserializer。

---

这是一个工作代码示例:

public static void main(String[] args) throws Exception {
    ObjectMapper objectMapper = new ObjectMapper()
            .registerModule(new JavaTimeModule())
            .disable(SerializationFeature.WRITE_DATE_TIMESTAMPS_AS_NANOSECONDS);

    Entity entity = new Entity(Instant.now());

    StringWriter writer = new StringWriter();
    objectMapper.writeValue(writer, entity);
    System.out.println(writer.getBuffer());
}

@lombok.Value
static class Entity {
    Instant timestamp;
}