JSONObject对同一个key重新put时，新值就会取代旧值，没有set之类的方法
构建json string时，所有的引号都要转义
package xx; import com.alibaba.fastjson.JSON; import com.alibaba.fastjson.JSONObject; // 对JSONObject中的指定字段重新赋值 public class testJsonReplace { public static void main(String[] args) { String query_jsonstr = "{\"timezone\":\"GMT+0\",\"action\":\"front_BRAND\",\"format\":\"true\",\"lan\":\"en_us\",\"column\":[\"day\",\"impressions\",\"clicks\",\"ctr\",\"brand_estimated_ecpm\",\"pay_out\"],\"dimension\":[\"day\"],\"filter\":{\"posid\":{\"op\":\"in\",\"value\":\"2454105\"}},\"start\":1528761600000,\"end\":1529452800000}"; JSONObject query = JSON.parseObject(query_jsonstr); if (query.getJSONObject("filter") != null) { JSONObject posJson = new JSONObject(); posJson.put("op", "in"); posJson.put("value", "2454117"); query.getJSONObject("filter").put("posid", posJson); } String posid = query.getJSONObject("filter").getJSONObject("posid").getString("value"); String newJsonStr = query.toJSONString(); System.out.println(newJsonStr); } }