How to Handle NULL Values in JDBC?

// Java Program to Handle NULL values in JDBC
package geeksforgeeks;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;

// Driver Class
public class RetrieveDataExample {
    // Main Function
    public static void main(String[] args)
    {
        try {
            // Load the MySQL JDBC driver
            Class.forName("com.mysql.cj.jdbc.Driver");

            // Establish a connection to the database
            Connection con = DriverManager.getConnection(
                "jdbc:mysql://localhost:3306/books", "root",
                "password");

            if (con != null) {
                // Insert a new book into the 'book' table
                String insertQuery
                    = "INSERT INTO book (id, author, name, price) VALUES (?, ?, ?, ?)";
              
                PreparedStatement insertStatement
                    = con.prepareStatement(insertQuery);

                insertStatement.setInt(1, 500);

                // Set author to NULL
                insertStatement.setNull(
                    2, java.sql.Types.VARCHAR);

                // Set name to NULL
                insertStatement.setNull(
                    3, java.sql.Types.VARCHAR);

                // Set price to NULL
                insertStatement.setNull(
                    4, java.sql.Types.VARCHAR);
                int rowsInserted
                    = insertStatement.executeUpdate();

                // Check if the insertion was successful
                if (rowsInserted > 0) {
                    System.out.println(rowsInserted + " row(s) inserted successfully.");
                }
                else {
                    System.out.println("Insert failed.");
                }

                // Retrieve all data from the 'book' table
                String selectQuery = "SELECT * FROM book";
                PreparedStatement selectStatement = con.prepareStatement(selectQuery);
                ResultSet resultSet = selectStatement.executeQuery();

                System.out.println("The Available Data\n");

                // Iterate over the result set and print the
                // retrieved data
                while (resultSet.next()) {
                    int id = resultSet.getInt("id");

                    // Check for NULL values and replace
                    // them with a default value
                    String author_name = resultSet.getString("author");
                    if (resultSet.wasNull()) {
                        // Or any default value you prefer
                        author_name = "N/A";
                    }

                    String book_name = resultSet.getString("name");
                    if (resultSet.wasNull()) {
                        // Or any default value you prefer
                        book_name = "N/A";
                    }

                    String book_price = resultSet.getString("price");
                    if (resultSet.wasNull()) {
                        // Or any default value you prefer
                        book_price = "N/A";
                    }

                    System.out.println(
                        "ID: " + id
                        + ", Author_Name: " + author_name
                        + ", Book_Name: " + book_name
                        + ", Book_Price " + book_price);
                }
            }
            else {
                System.out.println("Not Connected...");
            }
        }
        catch (Exception e) {
            // Print any exceptions that occur during
            // database access
            System.out.println("Exception is " + e.getMessage());
        }
    }
}