Scala Jackson 使用经验总结

,

背景

主要记录 scala 使用 jackson 中的几个问题

  • long 型数据转换为 ZonedDateTime
  • 对 field 做自定义反序列化

以下面对 json 为例

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{
  "time": 1570712743943, //time 为 Long ，反序列化需要映射成 ZonedDateTime 
  "id": 1 // id 为 Integer，反序列化成 String
}

scala 代码示例

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import java.time.ZonedDateTime

import com.fasterxml.jackson.annotation.JsonInclude.Include
import com.fasterxml.jackson.core.JsonParser
import com.fasterxml.jackson.databind.annotation.JsonDeserialize
import com.fasterxml.jackson.databind.deser.std.StdDeserializer
import com.fasterxml.jackson.databind.{DeserializationContext, DeserializationFeature, ObjectMapper}
import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule
import com.fasterxml.jackson.module.scala.DefaultScalaModule
import com.fasterxml.jackson.module.scala.experimental.ScalaObjectMapper
import org.scalatest.FunSuite

class TestJackson extends FunSuite {
  lazy val mapper = {
      val mapper = new ObjectMapper() with ScalaObjectMapper
      mapper.registerModule(new JavaTimeModule())
      mapper.setSerializationInclusion(Include.NON_NULL)
      mapper.setSerializationInclusion(Include.NON_ABSENT)
      mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false)
      mapper.registerModule(DefaultScalaModule)
      mapper
    }

  test("jackson") {
    val json =
      """
        |{
        | "time": 1570712743943,
        | "id": 1
        |}
        |""".stripMargin

    val t = mapper.readValue(json, classOf[Test])

    println(s"time type: ${t.time.getClass.getSimpleName}")
    println(s"id   type: ${t.id.getClass.getSimpleName}")
  }

}

class IdDeserializer() extends StdDeserializer[String](classOf[String]) {
  override def deserialize(p: JsonParser, ctxt: DeserializationContext): String = {
    p.getValueAsString
  }
}

case class Test(time: ZonedDateTime, @JsonDeserialize(using = classOf[IdDeserializer]) id: String)

输出为

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time type: ZonedDateTime
id   type: String

回到问题

  • long 型数据转换为 ZonedDateTime

    • 通过 new JavaTimeModule() 来实现 java8 中特有的 ZonedDateTime 的映射

  • 对 field 实现自定义反序列化

    • 通过 @JsonDeserialize(using = classOf[IdDeserializer]) 指定需要自定义反序列化的 field
    • 通过 class IdDeserializer().deserialize 实现反序列化的逻辑

备注

sbt dependencies

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val jackson = Seq(
  "com.fasterxml.jackson.module" %% "jackson-module-scala" % "2.9.9",
  "com.fasterxml.jackson.datatype" % "jackson-datatype-jdk8" % "2.9.9",
  "com.fasterxml.jackson.datatype" % "jackson-datatype-jsr310" % "2.9.9"
)