求大神指点Scala 中 scala.collection.mutable.Map 怎么转json.

测试代码如下,求指点

import com.alibaba.fastjson.serializer.SerializerFeature
import com.alibaba.fastjson.{JSON, JSONObject}
import com.google.gson.Gson

/**
 * 测试所用
 */
object test01 {
  def main(args: Array[String]): Unit = {
    import scala.collection.JavaConverters._
    val s: String = "{\"userId\": 1, \"id\": 1, \"title\": \"delectus aut autem\", \"completed\": false}"
    //fast json 转对象
    val json: JSONObject = JSON.parseObject(s)
    //转为map
    val map: Map[String, AnyRef] = json.getInnerMap.asScala.toMap
    //输出map的值
    println(map)

    //使用fast json 把map转json
    val str: String = JSON.toJSONString(map, SerializerFeature.WriteMapNullValue)
    println(str)
    //得到结果为空
    //{"empty":false,"traversableAgain":true}

    //用 Gson
    val gson: Gson = new Gson
    val str1: String = gson.toJson(map)
    println(str1)
    //与相要的不符合
    //{"key1":"id","value1":1,"key2":"completed","value2":false,"key3":"title","value3":"delectus aut autem","key4":"userId","value4":1}
  }
}