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);