Jukebox JavaFX Tutorial

package jukebox.model;

import com.google.gson.Gson;
import java.io.*;
import java.util.ArrayList;
import java.util.List;

public class Database {
    public User user = new User();
    public List<Album> albums = new ArrayList<>();
    
    public void saveData() { ... }
    public void loadData() { ... }
}

public void saveData() {
    // 1. Create a Gson instance - this handles JSON serialization
    Gson gson = new Gson();
    
    // 2. Convert this entire Database object to a JSON string
    // This includes all user data and all albums with their songs
    String json = gson.toJson(this);
    
    // 3. Print the JSON to console for debugging purposes
    System.out.println("Serialized JSON: " + json);
    
    // 4. Create a FileWriter to write to the database.json file
    FileWriter writer = null;
    try {
        // 5. Open the file for writing (creates or truncates existing file)
        writer = new FileWriter("database.json");
        
        // 6. Use Gson to write the JSON directly to the file
        // This is more efficient than writing the string we already created
        gson.toJson(this, writer);
        
        // 7. Flush the writer to ensure all data is written to disk
        writer.flush();
        
        // 8. Log success message
        System.out.println("JSON written to database.json");
    } catch (IOException e) {
        // 9. If we can't write to the file, print an error message
        // Common causes: file permissions, disk full, path doesn't exist
        System.out.println("couldnt write to file!");
    }
}

public void loadData() {
    // 1. Create a Gson instance for deserialization
    Gson gson = new Gson();
    FileReader reader = null;
    try {
        // 2. Try to open the database.json file for reading
        reader = new FileReader("database.json");
        
        // 3. Deserialize the JSON file into a Database object
        // Gson automatically maps JSON fields to Java object fields
        Database database = gson.fromJson(reader, Database.class);
        
        // 4. Copy the loaded data into this instance
        // This replaces our empty/default data with the persisted data
        user = database.user;
        albums = database.albums;
    } catch (FileNotFoundException e) {
        // 5. File doesn't exist yet - this is normal on first run
        System.out.println("couldnt read from file!, creating new one");
        
        // 6. Create a new empty database.json file
        // This will contain an empty user and empty albums list
        saveData();
    }
    // Note: Other IOExceptions are not caught here, they would propagate up
    // but in practice this method is called from main() so they'd crash the app
}

{
  "user": {
    "username": ""
  },
  "albums": [
    {
      "name": "The Dark Side of the Moon",
      "artist": "Pink Floyd",
      "genre": "ROCK",
      "songs": [
        {
          "title": "Speak to Me",
          "lengthSeconds": 90
        },
        {
          "title": "Breathe",
          "lengthSeconds": 163
        }
      ]
    }
  ]
}

// In Jukebox.java
public static Database database;

public static void main(String[] args) {
    // Initialize the database - this holds all our application data
    database = new Database();
    
    // Load data from the JSON file into our database object
    database.loadData();
    
    // Launch the JavaFX application
    launch(args);
}

// When saving is needed:
Jukebox.database.saveData();