How to make a FlowLayout JPanel nested inside a ScrollPanel go down the next row when reaching a fixed width

Question

I have a JPanel with a FlowLayout inside of a viewPort of a JScrollPane. I can add components dinamically to this JPanel but when I reach the end of the JScrollPane what i want is for the components to go down the next row instead of continuing horizontally infinitly. I know that to make FlowLayout go down the next row you can set sizes but when its nested in a JScrollPane it doesnt work.

Heres some code

import java.awt.Color;
import java.awt.EventQueue;
import java.awt.FlowLayout;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.border.EmptyBorder;

public class prova extends JFrame {

    private static final long serialVersionUID = 1L;
    private JPanel contentPane;

    /**
     * Launch the application.
     */
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    prova frame = new prova();
                    frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     * Create the frame.
     */
    public prova() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 1040, 475);
        contentPane = new JPanel();
        contentPane.setBackground(new Color(255, 255, 255));
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));

        setContentPane(contentPane);
        contentPane.setLayout(null);

        JScrollPane scrollPane = new JScrollPane();
        scrollPane.setBounds(10, 11, 1004, 206);
        contentPane.add(scrollPane);

        JPanel panel = new JPanel();
                panel.setLayout(new FlowLayout(FlowLayout.LEFT));
        scrollPane.setViewportView(panel);

        JButton btnNewButton = new JButton("New button");
        panel.add(btnNewButton);

        JButton btnNewButton_1 = new JButton("New button");
        panel.add(btnNewButton_1);

        JButton btnNewButton_2 = new JButton("New button");
        panel.add(btnNewButton_2);

        JButton btnNewButton_3 = new JButton("New button");
        panel.add(btnNewButton_3);

        JButton btnNewButton_4 = new JButton("New button");
        panel.add(btnNewButton_4);

        JButton btnNewButton_5 = new JButton("New button");
        panel.add(btnNewButton_5);

        JButton btnNewButton_6 = new JButton("New button");
        panel.add(btnNewButton_6);

        JButton btnNewButton_7 = new JButton("New button");
        panel.add(btnNewButton_7);

        JButton btnNewButton_8 = new JButton("New button");
        panel.add(btnNewButton_8);

        JButton btnNewButton_9 = new JButton("New button");
        panel.add(btnNewButton_9);

                JButton btnNewButton_10 = new JButton("New button");
        panel.add(btnNewButton_10);
    }

}

The JButton are placeholders for the example, I want the last two of the buttons (9 and 10) to go down a row. Also can't use GridLayout because the components have different sizes and it would strech every cell to the biggest one.