java 谷歌 GSON 嵌套 HashMaps 反序列化
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Google GSON nested HashMaps deserialization
提问by ilya.stmn
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
在我当前的项目中，我在 android 中使用 GSON 库，并且遇到了嵌套 Maps 反序列化的问题。这是初始 json 的样子
{
"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
还有我的 pojo
class Category {
long id;
String name;
String image_url;
HashMap<String,Flower> flowers;
}
And Flower class
和花类
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
但是当我尝试反序列化这个对象时，我可以访问嵌套的哈希图，示例代码是
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?
有什么建议？
回答by eugen
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.
这gson.fromJson(br, HashMap.class);告诉 Gson 您想要反序列化为未知值类型的 Map。您可能很想指定类似 的东西Map<String,Category>.class，但您不能在 Java 中执行此操作，因此解决方案是在 Gson 中使用他们所谓的 TypeToken。
Map<String, Category> categoryMap = gson.fromJson(br, new TypeToken<Map<String, Category>>(){}.getType());
