public class MyService {
    private Connection connection = null;

    public void save(Book book) {
        try {
            Class.forName("com.mysql.jdbc.Driver");
            connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/mydb", "root", "password");

            PreparedStatement stmt = connection.prepareStatement("INSERT INTO PUBLISHER (CODE, PUBLISHER_NAME) VALUES (?, ?)");
            stmt.setString(1, book.getPublisher().getCode());
            stmt.setString(2, book.getPublisher().getName());
            stmt.executeUpdate();

            stmt.close(); //1

            stmt = connection.prepareStatement("INSERT INTO BOOK (ISBN, BOOK_NAME, PUBLISHER_CODE) VALUES (?, ?, ?)");
            stmt.setString(1, book.getIsbn());
            stmt.setString(2, book.getName());
            stmt.setString(3, book.getPublisher().getCode());
            stmt.executeUpdate();

            stmt.close(); //2
        } catch (ClassNotFoundException e) { e.printStackTrace(); } catch (SQLException e) { e.printStackTrace(); }
        finally { connection.close(); }
    }
}

try (Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/mydb", "root", "password")) {

    try (PreparedStatement stmt = connection.prepareStatement("INSERT INTO PUBLISHER (CODE, PUBLISHER_NAME) VALUES (?, ?)")) {
        stmt.setString(1, book.getPublisher().getCode());
        stmt.setString(2, book.getPublisher().getName());
        stmt.executeUpdate();
    }
    // stmt is auto closed here, even if SQLException is thrown

    try (PreparedStatement stmt = connection.prepareStatement("INSERT INTO BOOK (ISBN, BOOK_NAME, PUBLISHER_CODE) VALUES (?, ?, ?)");
        stmt.setString(1, book.getIsbn());
        stmt.setString(2, book.getName());
        stmt.setString(3, book.getPublisher().getCode());
        stmt.executeUpdate();
    }
    // stmt is auto closed here, even if SQLException is thrown
}
// connection is auto closed here, even if SQLException is thrown

try{
             String insertIntoCust = "insert into NORTHWIND_CUSTOMER(CUSTOMER_ID,FIRST_NAME,LAST_NAME,ADDRESS,CITY,STATE,POSTAL_CODE) values(?,?,?,?,?,?)";
             pst = connect.prepareStatement(insertIntoCust);
             pst.setString(1, txtCustomerId.getText());
             pst.setString(2, txtFirstName.getText());
             pst.setString(3, txtLastName.getText());
             pst.setString(4, txtAddress2.getText());
             pst.setString(5, txtCity.getText());
             pst.setString(6, txtState.getText());
             pst.setString(7, txtPostalCode.getText());

             pst.execute();

             String insertIntoOrder = "insert into NORTHWIND_ORDER(ORDER_ID,ORDER_DATE) values(?,?)";
             pst = connect.prepareStatement(insertIntoOrder);
             pst.setString(1, txtOrderId.getText());
             pst.setString(2, txtOrderDate.getText());

             pst.execute();
             JOptionPane.showMessageDialog(null, "Saved");
         }catch(Exception e){
             JOptionPane.showMessageDialog(null, e);
         }