在寫spark項目時遇到scala對象與json對象之間轉(zhuǎn)換的問題焰盗，花點時間總結(jié)一下蝎毡。
Json4s介紹
Json4s下面有兩個類型的包
- Lift Json
import org.json4s._
import org.json4s.native.JsonMethods._
native package具有l(wèi)ift-json的所有功能。
- Jackson
import org.json4s._
import org.josn4s.jackson.JsonMethods._
與native package不同的是壶熏，jackson包含了大部分jackson-module-scala的功能，也可以使用lift-json下的所有功能。在這個項目中我們使用jackson翰意。
Json AST
lift-json library 的核心就是Json AST，它將Json對象轉(zhuǎn)換成了語法樹。
sealed abstract class JValue
case object JNothing extends JValue // 'zero' for JValue
case object JNull extends JValue
case class JString(s: String) extends JValue
case class JDouble(num: Double) extends JValue
case class JDecimal(num: BigDecimal) extends JValue
case class JInt(num: BigInt) extends JValue
case class JBool(value: Boolean) extends JValue
case class JObject(obj: List[JField]) extends JValue
case class JArray(arr: List[JValue]) extends JValue
type JField = (String, JValue)
轉(zhuǎn)換的常見方式有：
- Json DSL(implicit)
- String parse
- case class
下面一一介紹冀偶。
Json4s安裝
- SBT users
- native support
val json4sNative = "org.json4s" %% "json4s-native" % "{latestVersion}"
- jackson support
val json4sJackson = "org.json4s" %% "json4s-jackson" % "{latestVersion}"
- Maven users
- native support
<dependency>
<groupId>org.json4s</groupId>
<artifactId>json4s-native_${scala.version}</artifactId>
<version>{latestVersion}</version>
</dependency>
- jackson support
<dependency>
<groupId>org.json4s</groupId>
<artifactId>json4s-jackson_${scala.version}</artifactId>
<version>{latestVersion}</version>
</dependency>
JSON轉(zhuǎn)換
這里我們都以jackson為例醒第，native support請參考http://json4s.org/
一個有效的json對象可以轉(zhuǎn)換成AST格式
String parse
import org.json4s._
import org.json4s.jackson.JsonMethods._
parse("""{ "numbers" : [1, 2, 3, 4] }""")
parse("""{"name":"Toy","price":35.35}""", useBigDecimalForDouble = true)
DSL Parse
任意scala原始對象與json原始對象之間的轉(zhuǎn)換
#List to json
scala> val json = List(1, 2, 3)
scala> compact(render(json))
res0: String = [1,2,3]
#Map to json
scala> val json = ("name" -> "joe")
scala> compact(render(json))
res1: String = {"name":"joe"}
#當有多行數(shù)據(jù)時，用~符號連接
scala> val json = ("name" -> "joe") ~ ("age" -> 35)
scala> compact(render(json))
res2: String = {"name":"joe","age":35}
case class
當你有自定義的數(shù)據(jù)類型想進行轉(zhuǎn)換時进鸠，可以使用下面的方法
type DslConversion = T => JValue
object JsonExample extends App {
import org.json4s._
import org.json4s.JsonDSL._
import org.json4s.jackson.JsonMethods._
#定義類 Winner, Lotto
case class Winner(id: Long, numbers: List[Int])
case class Lotto(id: Long, winningNumbers: List[Int], winners: List[Winner], drawDate: Option[java.util.Date])
val winners = List(Winner(23, List(2, 45, 34, 23, 3, 5)), Winner(54, List(52, 3, 12, 11, 18, 22)))
val lotto = Lotto(5, List(2, 45, 34, 23, 7, 5, 3), winners, None)
#轉(zhuǎn)換json
val json =
("lotto" ->
("lotto-id" -> lotto.id) ~
("winning-numbers" -> lotto.winningNumbers) ~
("draw-date" -> lotto.drawDate.map(_.toString)) ~
("winners" ->
lotto.winners.map { w =>
(("winner-id" -> w.id) ~
("numbers" -> w.numbers))}))
println(compact(render(json)))
}
scala> JsonExample
{"lotto":{"lotto-id":5,"winning-numbers":[2,45,34,23,7,5,3],"winners":
[{"winner-id":23,"numbers":[2,45,34,23,3,5]},{"winner-id":54,"numbers":[52,3,12,11,18,22]}]}}
如果想將結(jié)果打印出來稠曼，可以使用
scala> pretty(render(JsonExample.json))
{
"lotto":{
"lotto-id":5,
"winning-numbers":[2,45,34,23,7,5,3],
"winners":[{
"winner-id":23,
"numbers":[2,45,34,23,3,5]
},{
"winner-id":54,
"numbers":[52,3,12,11,18,22]
}]
}
}
