Google GSON嵌套HashMaps反序列化 [英] Google GSON nested HashMaps deserialization

问题描述

在我当前的项目中，我在android中使用GSON库，并且遇到嵌套Maps反序列化问题。这是初始json的样子

  {
 
5：{
 ID：5，
name：初始名称，
image_url：uploads / 71d44b5247cc1a7c56e62fa51ca91d9b.png，
status：1，
 花：{
7：{
id：7，
category_id：5，
name：test，
description：一些描述，
price：1000，
image_url：uploads / test.png，
status：1 ，
color：red，
 
} 
} 
} 
} 
  pre> 
 
 
我的pojo's 
  class类别{
长ID; 
字符串名称; 
 String image_url; 
 HashMap< String，Flower>花卉; 
} 
  
和Flower类
  class Flower {
 long id; 
 String category_id; 
字符串名称; 
字符串描述; 
弦乐价格; 
 String image_url; 
字符串状态; 
} 
  
但是当我尝试反序列化这个对象时，我可以访问嵌套的hashmaps，示例代码是 
 
 
  public class TestJson {
 public static void main（String [] args）{
 Gson gson = new Gson（）; 
尝试{
 BufferedReader br = new BufferedReader（
 new FileReader（2.txt））; 
 HashMap< String，Category> map = gson.fromJson（br，HashMap.class）; 
收藏<类别> asd = map.values（）; 
 System.out.println（map.values（））; 
 
} catch（IOException e）{
 e.printStackTrace（）; 
} 
 
} 
} 
  
任何建议？
解决方案此 gson.fromJson（br，HashMap.class）; 告诉Gson你想反序列化为未知值类型的Map。你会试图指定像 Map< String，Category> .class 之类的东西，但是你不能在Java中这样做，所以解决方法是在Gson中使用他们所谓的TypeToken 。
 地图< String，Category> categoryMap = gson.fromJson（br，new TypeToken< Map< String，Category>>（）{}。getType（））; 
  
 
In my current project i use GSON library in android, and i've faced a problem of nested Maps deserializtion. This is how initial json looks like 
 {

"5":{
    "id":5,
    "name":"initial name",
    "image_url":"uploads/71d44b5247cc1a7c56e62fa51ca91d9b.png",
    "status":"1",
    "flowers":{
        "7":{
            "id":7,
            "category_id":"5",
            "name":"test",
            "description":"some description",
            "price":"1000",
            "image_url":"uploads/test.png",
            "status":"1",
            "color":"red",

        }
    }
  }
 }
And my pojo's
class Category {
long id;
String name;
String image_url;
HashMap<String,Flower> flowers;
}
And Flower class
class Flower {
long id;
String category_id;
String name;
String description;
String price;
String image_url;
String status;
}
But when i try to deserialize this objects, i can access nested hashmaps, the example code is 
public class TestJson {
public static void main(String[] args) {
  Gson gson = new Gson();
    try {
    BufferedReader br = new BufferedReader(
        new FileReader("2.txt"));
    HashMap<String,Category> map = gson.fromJson(br, HashMap.class);
    Collection<Category> asd = map.values();
            System.out.println(map.values());

       } catch (IOException e) {
        e.printStackTrace();
       }

    }
 }
Any suggestions?
解决方案
This gson.fromJson(br, HashMap.class); tells to Gson that you want to deserialize to a Map of unknown value type. You would be tempted to specifiy something like Map<String,Category>.class, but you can not do this in Java so the solution is to use what they called TypeToken in Gson.
Map<String, Category> categoryMap = gson.fromJson(br, new TypeToken<Map<String, Category>>(){}.getType());


                        
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