let jsonbody : [String : Any] = [
            "name" : "jiajia",
            "age" : 18
        ]
        //json 的可用性判断
        if !JSONSerialization.isValidJSONObject(jsonbody) {
            print("不能转化")
            return
        }
        //json 字符串转换为data
        guard let data = try? JSONSerialization.data(withJSONObject: jsonbody, options: .prettyPrinted) else { return }
        //data 转为字符串
        let jsonstr = String(data: data, encoding: .utf8)
        print("Json Str" + jsonstr!)
        
        //.allowFragment 允许json字符串最外层不是array 或 dictionary  但必须是有效的json格式
        //.mutableContainers 返回可变容器   array 或 dictionary
        
        if let json = try? JSONSerialization.jsonObject(with: data, options: .allowFragments) as! [String : Any] {
            print("jsonDic:",json)
            let name = json["name"]
            let age = json["age"]
            print("name:\(name),age:\(age)")
        }