对象转化为json格式字符串，json格式字符串转化为JSONObject对象，取出JSONObject对象里的key值

json格式字符串jsonString：

{
    "code":"S0A00000",
    "data":{

        "userBaseInfo":{

            "group":{

                "companyId":"10000",

                "eshopCode":"11",

                "eshopTmp":"eshopTmp",

                "officeId":"10000",

                "userId":101

            },

            "role":{

                "roleCode":"crt_shzx_admin,crt_dszx_admin,crt_cxzx_admin",

                "userId":101

            },

            "user":{

                "firstName":"uat-admin1",

                "lastName":"uat-admin1",

                "optCounter":0,

                "userEml":"qq@qq.com",

                "userId":101,

                "userMbl":"18012345678",

                "userName":"uat-admin1",

                "userType":"1,2,3"

            }

        }

    },
    "msg":"成功",
    "transactionUuid":"b4d9a1220ddc4a8fba1bf921d218517b"
}

import com.alibaba.fastjson.JSON;

import com.alibaba.fastjson.JSONArray;

import com.alibaba.fastjson.JSONObject;

// json格式字符串jsonString转化为JSONObject对象

JSONObject jsonObj = JSON.parseObject(jsonString);

//从jsonObj对象里取出key是data的对象

JSONObject data = jsonObj.getJSONObject("data");

if(data != null){

//从data对象里取出userBaseInfo对象
JSONObject userBaseInfo = data.getJSONObject("userBaseInfo");

//从userBaseInfo对象里取出group对象
JSONObject group = userBaseInfo.getJSONObject("group");

//从group
对象里取出key值为companyId的值
Long merchantId = Long.valueOf(group.getString("companyId"));

}