Custom JSON Deserialization ด้วย Gson ใน Java

ไลบรารี Gson ให้วิธีระบุ Custom Deserializers โดย Register กับ GsonBuilder สร้าง Custom Deserializer โดย Override เมธอด deserialize() ของคลาส com.google.gson.JsonDeserializer

ตัวอย่าง: Custom Deserialization สำหรับ Password Field

import java.lang.reflect.Type;
import com.google.gson.*;

public class CustomJSONDeSerializerTest {
    public static void main(String[] args) {
        Gson gson = new GsonBuilder()
            .registerTypeAdapter(Password.class, new PasswordDeserializer())
            .setPrettyPrinting()
            .create();
        
        String jsonStr = "{" +
            "\"firstName\": \"Adithya\"," +
            "\"lastName\": \"Sai\"," +
            "\"age\": 25," +
            "\"address\": \"Pune\"," +
            "\"password\": \"admin@123\"" +
        "}";
        
        Student student = gson.fromJson(jsonStr, Student.class);
        System.out.println(student.getPassword().getPassword());
    }
}

class PasswordDeserializer implements JsonDeserializer<Password> {
    @Override
    public Password deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context)
            throws JsonParseException {
        String encryptedPwd = json.getAsString();
        return new Password(new StringBuffer(encryptedPwd).toString());
    }
}

// Student class
class Student {
    private String firstName;
    private String lastName;
    private int age;
    private String address;
    private Password password;
    
    // Constructors, getters, setters...
    public Password getPassword() { return password; }
    public void setPassword(Password password) { this.password = password; }
}

// Password class
class Password {
    private String password;
    
    public Password(String password) { this.password = password; }
    public String getPassword() { return password; }
    public void setPassword(String password) { this.password = password; }
}

ผลลัพธ์

admin@123

Use Cases:

• Decrypt/Decode ค่าระหว่าง Deserialize
• Map JSON Structure ที่ต่างจาก Java Class
• Custom Date/Time Parsing
• Handle Polymorphic Types

คู่คู่: Custom Serialization ใช้ JsonSerializer และ serialize() method