Parse partial JSON object

App.java

import com.google.gson.Gson;

public class App {
  public static void main(String[] args) {
    Gson gson = new Gson();
    String json = "{\"type\":\"bankaccount\",\"payload\":{\"bankAccountNo\":\"BE123\"}}";
    // String json = "{\"type\":\"newuser\",\"payload\":{\"firstName\":\"Sam\",\"lastName\":\"Wolfs\"}}";
    Message msg = gson.fromJson(json, Message.class);
    switch (msg.getType()) {
      case "bankaccount":
        ChangeBankAccount changeBA = gson.fromJson(msg.getPayload(), ChangeBankAccount.class);
        System.out.println(changeBA.getBankAccountNo());
        break;
      case "newuser":
        NewUser newUser = gson.fromJson(msg.getPayload(), NewUser.class);
        System.out.println(newUser.getFirstName() + " " + newUser.getLastName());
        break;
    
      default:
        break;
    }
  }
}

ChangeBankAccount.java

public class ChangeBankAccount {
  private String bankAccountNo;

  public String getBankAccountNo() {
    return bankAccountNo;
  }
}

Message.java

import com.google.gson.JsonObject;

public class Message {
  private String type;
  private JsonObject payload;

  public String getType() {
    return type;
  }

  public JsonObject getPayload() {
    return payload;
  }
}

NewUser.java

public class NewUser {
  private String firstName;
  private String lastName;

  public String getFirstName() {
    return firstName;
  }

  public String getLastName() {
    return lastName;
  }
}