[英]Extract specific JSON field with Scala and Argonaut
我正在嘗試使用Scala和Argonaut解析json。
假設我從其他REST服務獲得JSON響應,但我不知道該響應中JSON字段的順序和字段數。 例如, http://headers.jsontest.com/返回具有五個字段的JSON,但我只想提取一個字段並刪除其他字段:
{
"Accept-Language": "ru-RU,ru;q=0.8,en-US;q=0.5,en;q=0.3",
"Host": "headers.jsontest.com",
"Referer": "http://www.jsontest.com/",
"User-Agent": "Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Firefox/31.0 Iceweasel/31.4.0",
"Accept": "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8"
}
所以我寫一些代碼:
object Service {
case class Address(headers: String, rest: Option[String])
implicit def AddressCodecJson: CodecJson[Address] =
casecodec2(Address.apply, Address.unapply)("headers", "rest")
def parse(data: String): Option[Address] = {
Parse.decodeOption[Address](data)
}
def main(args: Array[String]): Unit = {
val src = url("http://headers.jsontest.com/")
val response: Future[String] = Http(src OK as.String)
response onComplete {
case Success(content) => {
val userData: Option[Address] = parse(content)
println(s"Extracted IP address = ${userData.get.headers}")
}
case Failure(err) => {
println(s"Error: ${err.getMessage}")
}
}
}
}
但是當然,此代碼不起作用,可能是因為jsontest的答案無法與Address
case類進行比較。
我收到此錯誤消息:
java.util.NoSuchElementException: None.get
at scala.None$.get(Option.scala:313)
at scala.None$.get(Option.scala:311)
at micro.api.Service$$anonfun$main$1.apply(Service.scala:26)
at micro.api.Service$$anonfun$main$1.apply(Service.scala:23)
at scala.concurrent.impl.CallbackRunnable.run(Promise.scala:32)
at scala.concurrent.impl.ExecutionContextImpl$$anon$3.exec(ExecutionContextImpl.scala:107)
at scala.concurrent.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260)
at scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.pollAndExecAll(ForkJoinPool.java:1253)
at scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1346)
at scala.concurrent.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979)
at scala.concurrent.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107)
如何僅獲得由其名稱指定的一個字段?
您的代碼具有:
implicit def AddressCodecJson: CodecJson[Address] =
casecodec2(Address.apply, Address.unapply)("headers", "rest")
你說:
我替換以下行:
val userData: Option[Address] = parse(content) println(s"Extracted IP address = ${userData.get.headers}")
與println(content)
並得到:{ "Host": "headers.jsontest.com", "User-Agent": "Dispatch/0.11.1-SNAPSHOT", "Accept": "/" }
所以您的回應是:
{ "Host": "headers.jsontest.com", "User-Agent": "Dispatch/0.11.1-SNAPSHOT", "Accept": "/" }
並且您正在像這樣解碼它:
Parse.decodeOption[UserData](data).get
...這意味着您肯定會並且很顯然會返回None
。
—現在為什么要期望從不包含期望的headers
和rest
屬性的JSON字典中獲得非None
值?
(我假設您知道對擁有None
值的Option[T]
調用.get
會引發異常。)
PS我不確定與HTTP標頭有什么關系...? 從建模的角度說...。
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