[英]Mapping values to case class in json4s
说我有以下几点:
[ {
"job_id": "1",
"status": "running"
},
{
"job_id": "0",
"status": "finished"
}]
我可以以某种方式对json4s执行以下操作:
case class Job(job_id: Int, status: JobStatus)
abstract class JobStatus
case class JobFinished extends JobStatus
case class JobRunning extends JobStatus
... some magic is probably needed here
这样,提取第一个代码段将导致:
[ Job(1, JobRunning()), Job(0, JobFinished())]
我认为基于JSON创建scala case类的最佳方法是使用此站点,这增加了魔力,我通常使用此站点,您甚至可以更改分类的名称,因此在您的情况下,可以使用网站,然后管理班级之间的关系:
您可以使用一个枚举,然后通过json4s-ext将EnumSerializer
添加到您的formats
。 但是,您的枚举将被序列化为int(在您的情况下为0或1)。
除了我自己的答案外,您还可以使用EnumNameSerializer,它将序列化为您指定的枚举值(例如“运行”或“完成”)。
这是可能的,但是需要一些编码。 我将尝试以一些较小的步骤对其进行分解。
// Types
case class Job(jobId: Int, status: JobStatus)
// Sealed trait to make match exhaustive in helper functions
sealed trait JobStatus
// use case object to not create uneeded instances, also case class without () no longer allowed
case object JobFinished extends JobStatus
case object JobRunning extends JobStatus
import org.json4s._
import org.json4s.native.Serialization
import org.json4s.native.Serialization.{read, write}
// helper functions, could be improved by having a mapping
implicit def stringToJobStatus(in: String) : JobStatus = in match {
case "running" => JobRunning
case "finished" => JobFinished
}
implicit def jobStatusToString(jobStatus: JobStatus) : String = jobStatus match {
case JobRunning => "running"
case JobFinished => "finished"
}
// here is the "magic" a custom serializer
class JobSerializer extends CustomSerializer[Job](format => (
// unmarshal Function
{
case JObject( JField("job_id", JString(jobId)) :: JField("status", JString(status)) :: Nil ) => {
new Job(jobId.toInt, status)
}
},
// masrshal Function
{
case Job(jobId, status) => JObject(
JField("job_id", JString(jobId.toString)) ::
JField("status", JString(status)) :: Nil)
}
))
// Implicit formats for serialization and deserialization
implicit val formats = Serialization.formats(NoTypeHints) + new JobSerializer
val data = """
[
{
"job_id": "1",
"status": "running"
},
{
"job_id": "0",
"status": "finished"
}
]
"""
read[List[Job]](data)
res3: List[Job] = List(Job(1,JobRunning), Job(0,JobFinished))
尽管@Andres Neumann的回答相当不错,但它确实需要重新实现整个Job类的序列化(可能比示例中笨拙的Job类大很多),而实际上唯一需要序列化的是状态。 根据@Andreas的回答,所需的实际代码会短一些,并且不需要手动序列化Job中的每个字段。
// here is the "magic" a custom serializer
class JobStatusSerializer extends CustomSerializer[JobStatus](format => (
// unmarshal Function
{
case JString(status) => {
// helper functions, could be improved by having a mapping
def stringToJobStatus(in: String): JobStatus = in match {
case "running" => JobRunning
case "finished" => JobFinished
}
stringToJobStatus(status)
}
},
// marshal Function
{
case status: JobStatus => {
def jobStatusToString(jobStatus: JobStatus): String = jobStatus match {
case JobRunning => "running"
case JobFinished => "finished"
}
JString(jobStatusToString(status))
}
}
)
)
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