转载自:https://blog.csdn.net/jdsjlzx/article/details/76785239 有时在解析json数据中的字段key是动态可变的时候，由于Gson是使用静态注解的方式来设置实体对象的，因此我们很难直接对返回的类型来判断。但Gson在解析过程中如果不知道解析的字段，就会将所有变量存储在一个Map中，我们只要实例化这个map就能动态地取出key和value了。 先给出一段jsondata，这是天气预报的数据，其中day_20151002这种key是随日期而变化的，在实体类中就不能当做静态变量来处理，我们就通过map来取出其映射对象。

{"resultcode": "200","reason": "successed!","result": {"sk": {"temp": "24","wind_direction": "东北风","wind_strength": "2级","humidity": "28%","time": "17:38"},"today": {"temperature": "15℃~26℃","weather": "多云转晴","wind": "东北风微风","week": "星期日","city": "桂林","date_y": "2015年10月11日","dressing_index": "舒适","dressing_advice": "建议着长袖T恤、衬衫加单裤等服装。年老体弱者宜着针织长袖衬衫、马甲和长裤。","uv_index": "弱","comfort_index": "","wash_index": "较适宜","travel_index": "较适宜","exercise_index": "较适宜","drying_index": ""},"future": {"day_20151011": {"temperature": "15℃~26℃","weather": "多云转晴","wind": "东北风微风","week": "星期日","date": "20151011"},"day_20151012": {"temperature": "16℃~27℃","weather": "晴转多云","wind": "微风","week": "星期一","date": "20151012"},"day_20151013": {"temperature": "16℃~26℃","weather": "多云转晴",,"wind": "微风","week": "星期二","date": "20151013"},"day_20151014": {"temperature": "17℃~27℃","weather": "晴","wind": "北风微风","week": "星期三","date": "20151014"},"day_20151015": {"temperature": "17℃~28℃","weather": "晴","wind": "北风微风","week": "星期四","date": "20151015"},"day_20151016": {"temperature": "17℃~30℃","weather": "晴","wind": "北风微风","week": "星期五","date": "20151016"},"day_20151017": {"temperature": "17℃~30℃","weather": "晴","wind": "北风微风","week": "星期六","date": "20151017"}}},"error_code": 0
}
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相关的实体类如下：

public class FutureDay {private String temperature;private String weather;private String wind;private String week;private String date;
}public class Result {private Sk sk;private Today today;private Map<String,FutureDay> future;
}
public class Sk {private String temp;private String wind_direction;private String wind_strength;private String humidity;private String time;
}
public class Today {private String temperature;private String weather;private String week;private String city;private String date_y;private String dressing_index;private String dressing_advice;private String uv_index;private String comfort_index;private String wash_index;private String travel_index;private String exercise_index;private String drying_index;
}
public class Response {private String resultcode;private String reason;private String error_code;private Result result;
}
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具体解析过程如下代码所示：

import java.io.BufferedReader;
import java.io.FileReader;
import java.util.Map;
import weather.*;
import com.google.gson.Gson;public class GsonParseDynamicKey {public static  void main( String args []){String jsondata = readJsonFile();//从文件中读取出json字符串，并打印出来Gson gson = new Gson();System.out.println("Start Gson parse jsondata");   Response response = gson.fromJson(jsondata, Response.class);        System.out.println(response.toString());System.out.println(response.getResult().getSk().toString());System.out.println(response.getResult().getToday().toString());Map<String, FutureDay> future = response.getResult().getFuture(); //对动态的key，来创建map，间接从中取出实体类futrue。System.out.println("Keyset method");                     //这里取出value的方法有两种keySet() entrySet().都给出了遍历的方法for (String key:future.keySet()){                        //遍历取出key，再遍历map取出value。System.out.println("key:"+key); System.out.println(future.get(key).toString());}System.out.println("Entryset method");for (Map.Entry<String,FutureDay> pair:future.entrySet()){//遍历取出键值对，调用getkey()，getvalue()取出key和value。System.out.println("key:"+pair.getKey());System.out.println(pair.getValue().toString());}
}
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这里顺便一提遍历Map的两种方法keySet()，entrySet()的差别。 keySet()方法返回的是key的集合set，entrySet()返回的是键值对的集合set。虽然两者从set遍历取出元素的方法是一样的，但是根据这个元素取出value的效率有些不同。前者取出的元素是key，还要去原map中遍历取出value。 后者取出的元素是键值对，直接调用getkey()，getvalue()方法就能快速取出key和value。显然在map中存在大量键值对时，使用entrySet()来取出value的效率更高。