How can I convert an Icon to an Image

Question

I'm trying to convert an Icon (javax.swing.Icon) to an Image (java.awt.Image) using this code:

private Image iconToImage(Icon icon)
{
    if(icon instanceof ImageIcon)
    {
        return ((ImageIcon) icon).getImage();
    }
    else
    {
        BufferedImage image = new BufferedImage(icon.getIconWidth(), icon.getIconHeight(), BufferedImage.TYPE_INT_RGB);
        icon.paintIcon(null, image.getGraphics(), 0, 0);
        return image;
    }
}

The thing is, the paintIcon function throws a NullPointerException on the image.getGraphics().

For the record, the icon value is the default CheckBox icon (obtained via UIManager.getIcon("CheckBox.icon"))

Here are the details of the exception thrown :

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at com.sun.java.swing.plaf.windows.WindowsIconFactory$CheckBoxIcon.paintIcon(WindowsIconFactory.java:306)
    at utils.WarningRenderer.iconToImage(WarningRenderer.java:50)
    at utils.WarningRenderer.<init>(WarningRenderer.java:38)
    at deliveryexpress.DeliveryExpressView.setWarnings(DeliveryExpressView.java:278)
    at deliveryexpress.DeliveryExpressView.updateLists(DeliveryExpressView.java:218)
    at deliveryexpress.DeliveryExpressView.access$1100(DeliveryExpressView.java:47)
    at deliveryexpress.DeliveryExpressView$5.addCheck(DeliveryExpressView.java:183)
    at org.japura.gui.model.DefaultListCheckModel.fireCheckListModelListeners(Unknown Source)
    at org.japura.gui.model.DefaultListCheckModel.fireAddCheckListModelListeners(Unknown Source)
    at org.japura.gui.model.DefaultListCheckModel.addCheck(Unknown Source)
    at org.japura.gui.CheckList$1.mouseClicked(Unknown Source)
    at java.awt.AWTEventMulticaster.mouseClicked(AWTEventMulticaster.java:253)
    at java.awt.Component.processMouseEvent(Component.java:6292)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
    at java.awt.Component.processEvent(Component.java:6054)
    at java.awt.Container.processEvent(Container.java:2041)
    at java.awt.Component.dispatchEventImpl(Component.java:4652)
    at java.awt.Container.dispatchEventImpl(Container.java:2099)
    at java.awt.Component.dispatchEvent(Component.java:4482)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4577)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4247)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4168)
    at java.awt.Container.dispatchEventImpl(Container.java:2085)
    at java.awt.Window.dispatchEventImpl(Window.java:2478)
    at java.awt.Component.dispatchEvent(Component.java:4482)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:644)
    at java.awt.EventQueue.access$000(EventQueue.java:85)
    at java.awt.EventQueue$1.run(EventQueue.java:603)
    at java.awt.EventQueue$1.run(EventQueue.java:601)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:98)
    at java.awt.EventQueue$2.run(EventQueue.java:617)
    at java.awt.EventQueue$2.run(EventQueue.java:615)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:614)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

If you need more details, just tell me, I'll edit my post to add them.

Thanks!

Answer 1

Just found a code snippet which might help if you want to wrap those misbehaving LAF provided icons more often:

/**
 * Some ui-icons misbehave in that they unconditionally class-cast to the 
 * component type they are mostly painted on. Consequently they blow up if 
 * we are trying to paint them anywhere else (f.i. in a renderer).  
 * 
 * This Icon is an adaption of a cool trick by Darryl Burke/Rob Camick found at
 * http://tips4java.wordpress.com/2008/12/18/icon-table-cell-renderer/#comment-120
 * 
 * The base idea is to instantiate a component of the type expected by the icon, 
 * let it paint into the graphics of a bufferedImage and create an ImageIcon from it.
 * In subsequent calls the ImageIcon is used. 
 * 
 */
public static class SafeIcon implements Icon {

    private Icon wrappee;
    private Icon standIn;

    public SafeIcon(Icon wrappee) {
        this.wrappee = wrappee;
    }

    @Override
    public int getIconHeight() {
        return wrappee.getIconHeight();
    }

    @Override
    public int getIconWidth() {
        return wrappee.getIconWidth();
    }

    @Override
    public void paintIcon(Component c, Graphics g, int x, int y) {
        if (standIn == this) {
            paintFallback(c, g, x, y);
        } else if (standIn != null) {
            standIn.paintIcon(c, g, x, y);
        } else {
            try {
               wrappee.paintIcon(c, g, x, y); 
            } catch (ClassCastException e) {
                createStandIn(e, x, y);
                standIn.paintIcon(c, g, x, y);
            }
        }
    }

    /**
     * @param e
     */
    private void createStandIn(ClassCastException e, int x, int y) {
        try {
            Class<?> clazz = getClass(e);
            JComponent standInComponent = getSubstitute(clazz);
            standIn = createImageIcon(standInComponent, x, y);
        } catch (Exception e1) {
            // something went wrong - fallback to this painting
            standIn = this;
        } 
    }

    private Icon createImageIcon(JComponent standInComponent, int x, int y) {
        BufferedImage image = new BufferedImage(getIconWidth(),
                getIconHeight(), BufferedImage.TYPE_INT_ARGB);
          Graphics g = image.createGraphics();
          try {
              wrappee.paintIcon(standInComponent, g, 0, 0);
              return new ImageIcon(image);
          } finally {
              g.dispose();
          }
    }

    /**
     * @param clazz
     * @throws IllegalAccessException 
     */
    private JComponent getSubstitute(Class<?> clazz) throws IllegalAccessException {
        JComponent standInComponent;
        try {
            standInComponent = (JComponent) clazz.newInstance();
        } catch (InstantiationException e) {
            standInComponent = new AbstractButton() {

            };
            ((AbstractButton) standInComponent).setModel(new DefaultButtonModel());
        } 
        return standInComponent;
    }

    private Class<?> getClass(ClassCastException e) throws ClassNotFoundException {
        String className = e.getMessage();
        className = className.substring(className.lastIndexOf(" ") + 1);
        return Class.forName(className);

    }

    private void paintFallback(Component c, Graphics g, int x, int y) {
        g.drawRect(x, y, getIconWidth(), getIconHeight());
        g.drawLine(x, y, x + getIconWidth(), y + getIconHeight());
        g.drawLine(x + getIconWidth(), y, x, y + getIconHeight());
    }

}

To use in your snippet, simply pass in an arbitrary component:

    icon = new SafeIcon(icon);
    BufferedImage image = new BufferedImage(icon.getIconWidth(), icon.getIconHeight(), BufferedImage.TYPE_INT_RGB);
    icon.paintIcon(new JPanel(), image.getGraphics(), 0, 0);