Google gson LinkedTreeMap class cast to myclass in java

Google gson LinkedTreeMap class cast to myclass in java

When using Google Gson to parse JSON data in Java, you may encounter a situation where Gson deserializes JSON objects into LinkedTreeMap objects, especially when the structure of the JSON data does not directly match the structure of your target class. To cast a LinkedTreeMap to your custom class, you'll need to manually map the data from the LinkedTreeMap to your class. Here's an example of how to do this:

Suppose you have a JSON object like this:

{ "name": "John", "age": 30 }

And you want to deserialize it into a custom Person class:

public class Person { private String name; private int age; // Getters and setters (or use lombok, if available) }

You can use Gson to parse the JSON and then manually map the LinkedTreeMap to your Person class:

import com.google.gson.Gson; import com.google.gson.internal.LinkedTreeMap; public class GsonExample { public static void main(String[] args) { // Sample JSON data String json = "{\"name\":\"John\",\"age\":30}"; // Parse the JSON into a LinkedTreeMap Gson gson = new Gson(); LinkedTreeMap<String, Object> map = gson.fromJson(json, LinkedTreeMap.class); // Manually map the LinkedTreeMap to your custom class Person person = new Person(); person.setName((String) map.get("name")); person.setAge(((Double) map.get("age")).intValue()); // Now you have the data in your custom Person object System.out.println("Name: " + person.getName()); System.out.println("Age: " + person.getAge()); } }

In this example:

  1. We use Gson to parse the JSON data into a LinkedTreeMap using gson.fromJson(json, LinkedTreeMap.class).

  2. We then manually map the values from the LinkedTreeMap to the fields of our Person class.

    • Note that we cast the age value to Double and then use intValue() to convert it to an integer, as Gson deserializes numeric values as Double by default.

By manually mapping the LinkedTreeMap to your custom class, you can handle JSON data that may not directly match the structure of your class.

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