@xtccc 2017-06-26T13:05:11.000000Z 字数 14332 阅读 3862

JSON

此处输入图片的描述

开发技巧

1. 基本用法

1.1 遍历Json中的key-value pairs

参考 Read JSON with JAVA using Google-gson library

public class Student {
    public String name;
    public String age;
    public String home;
    public String gender;
    public Student() {
    }
    public Student(String name, String age, String home, String gender) {
        this.name = name;
        this.age = age;
        this.home = home;
        this.gender = gender;
    }
}
public static void main(String[] args) {
        Student t = new Student("xiao", "31", null, "");
        String json = obj2Json(t);
        System.out.println(json);
        System.out.println("--------------------");
        IterateJson(json);
    }
    public static String obj2Json(Student t) {
        return new Gson().toJson(t);
    }
    /**
     * 遍历JSON中的元素（只在第一层遍历）
     */
    public static void IterateJson(String json) {
        JsonParser parser = new JsonParser();
        JsonElement jsonElem = parser.parse(new StringReader(json));
        JsonObject jsonObj = (JsonObject)jsonElem;
        Set<Map.Entry<String, JsonElement>> ens =  jsonObj.entrySet();
        for (Map.Entry<String, JsonElement> en : ens) {
            System.out.println(en.getKey() + " -> " + en.getValue());
        }
}

运行结果为：
QQ20151117-0@2x.png-18.9kB

2. 构造JSON

2.1 Primary Date Type -> JSON

对于常见的基本数据类型（如Array, Map），可以将其直接转换为JSON。

import com.google.gson.Gson
val gson = new Gson()
val a = new Array[Int](5)
for (i <- 0 until a.size)
  a(i) = i * 100
var json = gson.toJson(a)
println(s"a is converted to $json")
val b = new java.util.TreeMap[String, Array[Int]]()
b.put("张三", Array.fill[Int](3)(3))
b.put("李四", Array.fill[Int](4)(4))
b.put("王五", Array.fill[Int](5)(5))
json = gson.toJson(b)
println(s"b is converted to $json")

运行结果为：
QQ20160229-0@2x.png-22.9kB

2.2 Custom Data Type -> JSON

如果是较为特殊的数据类型，例如：

{   "name"  : "Jack",
    "weight": 76.6,
    "salaries" : {
        "January" : 11111.1,
        "February": 22222.2,
        "March"   : 33333.3
    },
    "children" : [
        "Tom","Merry","Rose"
    ]
}

我们可以使用case class来很方便地实现以上需求。

/** 使用case class来定义我们的custom data type */
case class Person(name: String, weight: Float,
                  salaries: util.HashMap[String, Float],
                  children: Array[String]) {}
def Serialize_CustomTypes(): Unit = {
  val salaries = new util.HashMap[String, Float]()
  salaries.put("January"  , 11111.1f)
  salaries.put("February" , 22222.2f)
  salaries.put("March"    , 33333.3f)
  val children = Array("Tom", "Merry", "Rose")
  val jack = Person("Jack", 76.6f, salaries, children)
  val json = new Gson().toJson(jack)
  println(s"jack is converted to $json")
}

注意： case class的定义不要放在 Serialize_CustomTypes 中，否则会报异常 java.lang.InternalError: Malformed class name

3. Spary Json

在Scala语言中，利用spray-json可以更加简单地处理JSON，参考 Scala and JSON generation

3.1 Object -> JSON

CaseClass.scala

import spray.json.DefaultJsonProtocol
case class Record(id: Int, description: String)
case class MoreRecord(ip: String, r: Record)
object MyJsonProtocol extends DefaultJsonProtocol {
  implicit val recordFormat     = jsonFormat2(Record)
  implicit val moreRecordFormat = jsonFormat2(MoreRecord)
}

TestSprayJson.scala

import MyJsonProtocol._
import spray.json._
object TestSprayJson {
  def main(args: Array[String]): Unit = {
    val record        = Record(1, "description here")
    val moreRecord    = MoreRecord("127.0.0.1", record)
    val json: JsValue = moreRecord.toJson
    val jsonString    = json.toString()
    println(jsonString)
  }
}

3.2 在HttpRequest中转换Json

Def.scala

import spray.httpx.SprayJsonSupport
import spray.json.DefaultJsonProtocol
case class RequestClusterParams(
   accessKey      : String,
   secreteKey     : String,
   userName       : String,
   region         : String,
   price          : String,
   slaveNodes     : String,
   instanceType   : String,
   amiID          : String,
   launchGroup    : String,
   securityKey    : String,
   securityGroup  : String,
   subnetID       : String)
case class SubmitRequestResult(
  status  : Boolean,
  message : String,
  params  : RequestClusterParams )
object JsonProtocol extends DefaultJsonProtocol with SprayJsonSupport{
  implicit val RequestClusterParamsFormat = jsonFormat12(RequestClusterParams)
  implicit val SubmitRequestResultFormat  = jsonFormat3(SubmitRequestResult)
}

SprayServer.scala

import akka.actor.{Actor, ActorLogging}
import spray.http.{HttpEntity, _}
import spray.routing.HttpService
import JsonProtocol._
import spray.json._
class Server extends Actor with RouteService with ActorLogging {
  def actorRefFactory = context
  def receive = runRoute(myRoute)
}
trait RouteService extends HttpService {
  this: Server =>
  val myRoute = { pathPrefix("v1") {
    path("request-path") {
      (post & entity(as[RequestClusterParams])) { params =>
        val result = SubmitRequestResult(····)
        complete(HttpResponse(StatusCodes.OK, 
            HttpEntity(ContentTypes.`application/json`, result.toJson.prettyPrint.getBytes)))
      }
    }
  }
 }
}

当收到的POST请求的BODY为一个JSON字符串时，会试图将其转换成对应的RequestClusterParams;当我们在程序中创建一个类型为RequestClusterParams的实例result之后，通过result.toJson.toString可以将其转换成JSON字符串。

值得注意的是，如果在定义object JsonProtocol时，没有让它扩展trait SprayJsonSupport，则可以会出现错误：

could not find implicit value for parameter um: spray.httpx.unmarshalling.FromRequestUnmarshaller[RequestClusterParams]
(post & entity(as[RequestClusterParams])) { params =>

因为trait SprayJsonSupport提供了自动的JSON marshalling/unmarshalling

3.3 JSON -> Object

import spray.json.DefaultJsonProtocol
import spray.json._
case class CA(flag: String, list: List[Int])
case class Bean(a: String, b: Int, ca: CA)
object BeanJsonProtocol extends DefaultJsonProtocol {
  implicit val CAFormat   = jsonFormat2(CA)
  implicit val BeanFormat = jsonFormat3(Bean)
}
import BeanJsonProtocol._
object  Deserialize extends App {
  val json =
    """
      { "a": "A",
        "b": 100,
        "ca" : {
            "flag" : "FLAG!!",
            "list": [1,2,3,4,5]
        }
      }"""
  // get Abstract Syntax Tree
  val ast: JsValue = json.parseJson
  // convert AST to object
  val obj: Bean = ast.convertTo[Bean]
  println(obj)
}

3.4 处理 non case class

上面展示了怎样处理Scala中的case class，如果想处理其他的class呢？例如想处理Java实现的org.joda.time.DateTimeZone类。。。

我们需要自己为org.joda.time.DateTimeZone实现一个format，这个format里面要实现write（序列化）和read两种方法（反序列化）。

由于DateTimeFormat的核心数据是id，因此我们只需要利用id即可创建出一个新的实例。

package cn.gridx.scala.lang.json.sprayjson
import org.joda.time.DateTimeZone
import spray.json._
object DateTimeZoneFormat extends RootJsonFormat[DateTimeZone] {
  // 序列化
  def write(tz: DateTimeZone): JsValue = {
    JsObject("id" -> JsString(tz.getID))
  }
  // 反序列化
  def read(value: JsValue): DateTimeZone = {
    value.asJsObject.getFields("id") match {
      case Seq(JsString(id)) =>
        DateTimeZone.forID(id)
      case _ =>
        throw new RuntimeException("ERROR")
    }
  }
}
object JavaJsonProtocols extends DefaultJsonProtocol {
  implicit val __DateTimeZone = DateTimeZoneFormat
}
/**
  * Created by tao on 1/11/17.
  */
object customization extends App {
  import JavaJsonProtocols._
  val tz = DateTimeZone.forID("America/Los_Angeles")
  val json = tz.toJson
  val jString = json.toString
  println("序列化后的字符为:")
  println(jString)
  println("\n反序列化的结果为:")
  val ast = jString.parseJson
  val obj = ast.convertTo[DateTimeZone]
  println(obj)
}

运行结果为

序列化后的字符为:
{"id":"America/Los_Angeles"}

反序列化的结果为:
America/Los_Angeles

也可以通过json4s来实现对non-case class的序列化和反序列化
参考 Serializing non-supported types

import org.json4s._
import org.json4s.native.Serialization.{write, writePretty}
class A(val a1: String, val a2: Int, val a3: Option[Boolean]) {
}
class SA extends CustomSerializer[A](format => (
  { // deserialize
    case JObject(JField("a1", JString(a1)) :: JField("a2", JInt(a2)) 
        :: JField("a3", JObject(a3)) :: Nil ) =>
      new A(a1, a2.intValue(), 
            if (a3 == JNothing) None else Some(a3.asInstanceOf[Boolean]))
  },
  { // srialize
    case a: A =>
      JObject(JField("a1", JString(a.a1)) ::
              JField("a2", JInt(a.a2))    ::
              JField("a3", if (a.a3.isEmpty) JNothing else JBool(a.a3.get))   ::
        Nil)
  }
  )
)
object TestSerialize {
  def main(args: Array[String]): Unit = {
    implicit val formats =  DefaultFormats + new SA()
    val a = new A("AAAA", 100, None)
    println(write(a))
    println(writePretty(a))
  }
}

4. GSON

4.1. 自定义Serializer

4.1.1 重命名Field Name

在将一个class转换成json时，key一般就是class field的名字。如果希望将key进行自定义，那么可以通过@SerializedName的方式来实现 :

public class ST {
    @SerializedName("my name")
    public String Name;
    @SerializedName("my age")
    public int Age;
    public ST(String name, int age) {
        this.Name = name;
        this.Age = age;
    }
};
String json = new Gson().toJson(new ST("Jack Tomcat", 300));

生成的json是：

    {"my name":"Jack Tomcat","my age":300}

4.2 使用JsonSerializer

参考

GSON SERIALISER EXAMPLE

重命名field name是非常简单的需求，我们可以通过JsonSerializer来实现对一个给定class定义更加复杂的序列化机制，使得在将该class转化为JSON串时，能够自定义其格式和内容（包括：rename fields, add/delete fields, format contents等）。

import java.lang.reflect.Type
import com.google.gson._
val car = Car("BMW", "X5", 3.0F, 88F, Array[String]("张三", "李四", "王二"), false)
val gsonBuilder = new GsonBuilder
// 为该class注册自定义的json serializer
gsonBuilder.registerTypeAdapter(classOf[Car], new CarSerializer)
gsonBuilder.setPrettyPrinting
val gson = gsonBuilder.create
val json = gson.toJson(car)
println(json)
// 给定的class
case class Car(brand: String, series: String, displacement: Float,
             price: Float, owners: Array[String], newCar: Boolean)
// 为类Car自定义json serializer
class CarSerializer extends JsonSerializer[Car] {
    override def serialize(car: Car, typeOfSrc: Type, 
        context: JsonSerializationContext): JsonElement = {
      val ret = new JsonObject
      ret.addProperty("品 牌", car.brand)
      ret.addProperty("是否新车", if (car.newCar) "Yes" else "No")
      ret.addProperty("历任车主数量", car.owners.size)
      val jsonArr = new JsonArray
      for (owner <- car.owners)
        jsonArr.add(new JsonPrimitive(owner))
      ret.add("车主 (包含二手车主)", jsonArr)
      val gson = new Gson()
      // 加入Map类型的项
      // `JsonObject#add` 可以加入一个 `JsonElement` 类型的property
      // 借此, 可以加入map等复杂类型
      val map = new util.HashMap[String, Double]()
      map.put("人民币", car.price)
      map.put("美  元", car.price/8)
      map.put("英  镑", car.price/10.4)
      ret.add("价 格", gson.toJsonTree(map))
      ret
    }
}

输出为：

{
  "品 牌": "BMW",
  "是否新车": "No",
  "历任车主数量": 3,
  "车主 (包含二手车主)": [
    "张三",
    "李四",
    "王二"
  ],
  "价 格": {
    "人民币": 880000.0,
    "英  镑": 84615.38461538461,
    "美  元": 110000.0
  }
}

5. JSON4S

JSON4S是最灵活、最强大的json工具，值得一看。

参考

WORKING WITH JSON IN SCALA USING THE JSON4S LIBRARY: Part 1

5.1 序列化

5.2 反序列化

import org.json4s._
import org.json4s.jackson.JsonMethods
implicit val format = org.json4s.DefaultFormats
val obj  = JsonMethods.parse("""["a","b"]""").extract[List[String]]
println(obj)

5.3 Field Serializer

有时，一个case class里面的某个field是自定义的类型，没有现成的serializer，我们可以为它单独添加一个serializer。

例如，DateTimeZone没有现成的serializer，如果它是某个class的field，则该class无法直接被json4s序列化：

import org.joda.time.DateTimeZone
import org.json4s._
import org.json4s.jackson.Json
/**
  * Created by tao on 4/10/17.
  */
object SerializeFields {
  implicit val formats  = org.json4s.DefaultFormats 
  val JSON              = Json(formats)
  def main(args: Array[String]): Unit = {
    val req = GlobalDataRequest("A", 100, DateTimeZone.forID("America/Los_Angeles"))
    val json: String = JSON.writePretty(req)
    println(json)
    val x = JSON.parse(json).extract[GlobalDataRequest]
    println(x)
  }
}
case class GlobalDataRequest(a: String, b: Int, c: DateTimeZone)

运行结果： image_1bedl25tt1kb1lr04rq1tdc1otgg.png-470.6kB

现增加一个field serializer：

import org.joda.time.DateTimeZone
import org.json4s._
import org.json4s.jackson.Json
object SerializeFields {
  implicit val formats  = org.json4s.DefaultFormats + DateTimeZoneSerializer
  val JSON              = Json(formats)
  def main(args: Array[String]): Unit = {
    val req = GlobalDataRequest("A", 100, DateTimeZone.forID("America/Los_Angeles"))
    val json: String = JSON.writePretty(req)
    println(json)
    val x = JSON.parse(json).extract[GlobalDataRequest]
    println(x)
  }
}
/**
 *  这就是field serializer
 */
case object DateTimeZoneSerializer extends CustomSerializer[DateTimeZone](format => (
  {
    case JString(s) => DateTimeZone.forID(s)
    case JNull      => null
  },
  {
    case tz: DateTimeZone => JString(tz.getID)
  }
))
case class GlobalDataRequest(a: String, b: Int, c: DateTimeZone)

现在可以通过json4s正常地对GlobalDataRequest实现序列化和反序列化。

5.4 对枚举（enum）实现序列化/反序列化

对Scala Enumeration的序列化和反序列化不能通过自定义的Filed Serializer来实现，而是需要借助于org.json4s.ext.EnumNameSerializer。

参考： Serialize and Deserialize scala enumerations or case objects using json4s

import org.json4s._
import org.json4s.ext.EnumNameSerializer
import org.json4s.jackson.Json
import org.json4s.jackson.JsonMethods._
object TestEnumeration {
  implicit lazy val formats  = org.json4s.DefaultFormats  + new EnumNameSerializer(WeekDay)
  val JSON = Json(formats)
  def main(args: Array[String]): Unit = {
    testSerialization()
    testDeserialization()
  }
  def testSerialization(): Unit = {
    val today = WeekDay.Mon
    val json = JSON.writePretty(Map("TODAY" -> today))
    println(json)
  }
  def testDeserialization(): Unit = {
    val json =
      """{
        |  "TODAY" : "Monday"
        |}
      """.stripMargin
    val today = parse(json).extract[Map[String, WeekDay]]
    println(today)
  }
}
///////////////////////////////////////////////////////////
object WeekDay extends Enumeration {
  type WeekDay = Value
  val Mon = Value(0, "Monday")
  val Tue = Value(1, "Tuesday")
  val Wed = Value(2, "Wednesday")
  val Thu = Value(3, "Tuesday")
  val Fri = Value(4, "Friday")
  val Sat = Value(5, "Saturday")
  val Sun = Value(6, "Sunday")
}

5.5 只从JSON中取出某一个field

假如有这样一个JSON string:

    val str = """
        |{
        |  "error": "not_authorised",
        |  "reason": "User not authorised to access virtual host",
        |  "extra" : {
        |     "a" : "A",
        |     "b" : "B"
        |   }
        |
        |} """.stripMargin

我们只想取出其中的extra，其他的不关心，怎么做？

val json = parse(str)
val value_error : JValue = json\\"error"
val value_errors: JValue = json\\"errors"
val value_extra : JValue = json\\"extra"
println("field error  : " + value_error.extractOpt[String])
println("field reason : " + value_errors.extractOpt[String])
println("field extra  : " + value_extra.extractOpt[Map[String, String]])

输出结果为：

field error  : Some(not_authorised)
field reason : None
field extra  : Some(Map(a -> A, b -> B))

同名field的带来的问题

对于下面的JSON:

{
    "meta": {
        "code": 200
    },
    "data": {
        "results": {
            "status": "success",
            "responseTime": 3452,
            "billStatus": [
                {
                    "status": "success"
                },
                {
                    "status": "success"
                }
            ]
        }
    }
}

使用下面的代码没法取出 data\results\status:

val jVal = org.json4s.jackson.JsonMethods.parse(respBody)
val status = (jVal \\ "data" \\ "results" \\ "status").extractOpt[String]
println(s"status = $status")

输出是 None.

解决方法
使用单反斜杠（\），而不是双反斜杠(\):

val jVal = org.json4s.jackson.JsonMethods.parse(respBody)
val status = (jVal \ "data" \ "results" \ "status").extractOpt[String]
println(s"status = $status")

6. JSON4S对特殊类型的定制序列化

对于有些类型，JSON4S不能自动地正确实现序列化，例如HashMap和java.util.TreeMap，举例:

object TestJson {
  implicit val formats = org.json4s.DefaultFormats 
  def main(args: Array[String]): Unit = {
    val tree = new java.util.TreeMap[Any, Any]()
    tree.put("bill_category", "CARE_Combined")
    tree.put("bill_presentation_category", "audit")
    tree.put("bill_super_category", 12)
    val in1 = HashMap("y" -> tree)
    val in2 = HashMap(tree -> "x")
    println("tree = " + org.json4s.jackson.Serialization.write(tree))
    println("in1  = " + org.json4s.jackson.Serialization.write(in1))
    println("in2  = " + org.json4s.jackson.Serialization.write(in2))
  }
}

运行结果：
image_1bji7bjej966tecn11agu18ag9.png-101.1kB

我们需要对Map和TreeMap实现自定义的序列化

object MySerializer extends CustomSerializer[Any] (thisFormat =>
  (
    {
      case x =>
        throw new RuntimeException("不感兴趣")
    },
    {
      case m: scala.collection.immutable.HashMap[Any, Any] =>
        implicit val formats = org.json4s.DefaultFormats
        JObject(
          m.map({
            case (k, v) =>
              JField(k.toString, Extraction.decompose(v)(thisFormat))
          }).toList
        )
      case m: scala.collection.mutable.HashMap[Any, Any] =>
        implicit val formats = org.json4s.DefaultFormats
        JObject(
          m.map({
            case (k, v) =>
              JField(k.toString, Extraction.decompose(v)(thisFormat))
          }).toList
        )
      case m: java.util.TreeMap[Any, Any] =>
        implicit val formats = org.json4s.DefaultFormats
        JObject({
          val con = ArrayBuffer[JField]()
          val it = m.keySet().iterator()
          while (it.hasNext) {
            val key = it.next()
            con.append(JField(key.toString, Extraction.decompose(m.get(key))(thisFormat)))
          }
          con.toList
        }
        )
    }
  )
)
object TestJson {
  implicit val formats = org.json4s.DefaultFormats + MySerializer
  def main(args: Array[String]): Unit = {
     ... // 相同的测试内容
     ...
  }
}

运行结果：

tree = {"bill_category":"CARE_Combined","bill_presentation_category":"audit","bill_super_category":12}
in1  = {"y":{"bill_category":"CARE_Combined","bill_presentation_category":"audit","bill_super_category":12}}
in2  = {"{bill_category=CARE_Combined, bill_presentation_category=audit, bill_super_category=12}":"x"}