Reliable object not resizing java JScrollPane

I'm trying to make a file view(JScrollPane) resizable for an ide, but when I try to resize it, It wont update unless I resize the window. I try looking it up but I could not find anything usefull. If you help me on this thank you so much.

Take a look fore yourself

public MainWindow(String title) {
        
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setLayout(new BorderLayout());
        this.setResizable(true);
        this.setSize(windowSize);
        this.setLocationRelativeTo(null);

        // ....

        JPanel fileView = new JPanel();
        fileView.setBackground(Color.WHITE.darker());

        JScrollPane fileScrollView = new JScrollPane(fileView);
        fileScrollView.setPreferredSize(new Dimension(100, 0));

        fileScrollView.addMouseMotionListener(new MouseMotionListener() {
            private int offset = 0;
            private boolean start = false;

            @Override
            public void mouseDragged(MouseEvent e) {
                int mouseX = e.getX() ;
                int left = fileScrollView.getX() + fileScrollView.getWidth();
                boolean resize = setCursor(left, mouseX);

                if (start) {
                    offset = left - mouseX;
                }

                if (resize) {
                    LOGGER.logInfo("OFFSET: " + offset);
                    fileScrollView.setPreferredSize(new Dimension(mouseX + offset, fileScrollView.getHeight()));

                    repaint();
                    doLayout();
                }
                start = false;
            }

            @Override
            public void mouseMoved(MouseEvent e) {
                start = true;
                setCursor(fileScrollView.getX() + fileScrollView.getWidth(), e.getX());
            }

            public boolean setCursor(int right, int mx) {
                if (mx > right - 20 && mx < right){
                    fileScrollView.setCursor(new Cursor(Cursor.E_RESIZE_CURSOR));
                    return true;
                } else {
                    fileScrollView.setCursor(Cursor.getDefaultCursor());
                    return false;
                }
            }
        });



        this.add(fileScrollView, BorderLayout.WEST);
    }