HarmonyOS Json字符串在ArkTS中怎么单独把key和value拼接成字符串

参考如下代码：

let paramContent = "{ \"userName\":\"张三\",\"age\":5, \"subList\":[ { \"subName\":\"Sub张三\", \"subAge\":10 , \"childList\":[{\"childName\":\"child张三\",\"childAge\":20 }]}] }";
let obj: object = JSON.parse(paramContent);
let reStr:string = ''
let targetMap: Map<string, object> = new Map<string, object>(Object.entries(obj));
targetMap.forEach((value,key) => {
  if (key != undefined && value != undefined) {
    console.log("key:" + key + '    value:' + value)
    reStr += key + '='+JSON.stringify(value)+'&'
  }
})
reStr = reStr.slice(0,reStr.length-1)
console.log("reStr:" + reStr)