Gson 轉換對象屬性null 保留屬性方法。

Map<String,Object> map = new HashMap<>();
 map.put("key",null);
 map.put("val","yeasd");
Gson gson = new GsonBuilder().serializeNulls().create();
String s = gson.toJson(map);
System.out.println("ok123:"+s);
Map<String,Object> user =  gson.fromJson(s,new TypeToken<HashMap<String,Object>>() {}.getType());
System.out.println(""+user);