Update: Common Validation Module for Swing Application

In the last blog I have written how to build a common validation module by using the jxlayer, beansbinding, and hibernate validator. After discussing about it with the JXLayer Author Alexander Potochkin, I got a suggestion from him(thanks, Alexp :-)): we should not change the state of any component in the paint() method. This is a swing pattern.

The last version of the HibernateValidationUI contains Obviously an antipattern, where the tooltip is set in the paintLayer() method.

Today, I post here a updated version of the HibernateValidationUI and try to kill the antipattern.

/**
* @author Jing Ge
*/
public class HibernateValidationUI extends AbstractLayerUI<JTextComponent> {

   private Object object;
   private String propertyName;
   private ClassValidator validator;
   private ELProperty elProperty;
   private PropertyStateListener propertyChangeHandler;
   private JXLayer<JTextComponent> layer;

   public HibernateValidationUI(Object obj, String propertyName) {
       this.object = obj;
       this.propertyName = propertyName;
       propertyChangeHandler = new PropertyChangeHandler();
       validator = new ClassValidator(obj.getClass());

       elProperty = ELProperty.create("${" + propertyName + "}");
   }

   @Override
   public void installUI(JComponent c) {
        if (layer != null) {
            throw new IllegalStateException(getClass().getSimpleName() +
                    " can't be shared between multiple layers");
        }
       super.installUI(c);
       layer = (JXLayer<JTextComponent>) c;
       elProperty.addPropertyStateListener(object, propertyChangeHandler);
       validate();
   }

   @Override
   public void uninstallUI(JComponent c) {
       super.uninstallUI(c);
       layer = null;
       elProperty.removePropertyStateListener(object, propertyChangeHandler);
   }

   private void validate() {
       InvalidValue[] validationMessages = validator.getInvalidValues(object,
               propertyName);
       if (validationMessages.length > 0) {
           layer.getView().setToolTipText(validationMessages[0].getMessage());
           return;
       }
       layer.getView().setToolTipText(null);
   }

   @Override
   protected void paintLayer(Graphics2D g2, JXLayer<JTextComponent> l) {
       super.paintLayer(g2, l);
       if (!isValid()) {
           BufferedImage image = Java2DIconFactory.createErrorIcon();
           g2.drawImage(image, l.getWidth() - image.getWidth() - 1,
                   l.getHeight() - 8, null);
       }
   }

   boolean isValid() {
       return isBlank(layer.getView().getToolTipText());
   }

     /**
     * a copy from the apache common lang.
     * Just use the StringUtils if the common lang jar in your classpath.
     */
    private boolean isBlank(String str) {
        int strLen;
        if (str == null || (strLen = str.length()) == 0) {
            return true;
        }
        for (int i = 0; i < strLen; i++) {
            if ((Character.isWhitespace(str.charAt(i)) == false)) {
                return false;
            }
        }
        return true;
    }

    class PropertyChangeHandler implements PropertyStateListener {

        @Override
        public void propertyStateChanged(PropertyStateEvent pse) {
            validate();
            setDirty(true);
        }
    }
}

There are some changes in the class:

1. The class holds a reference of the JXlayer instance, because it will be used while we validate the property. The reference will be injected when installUI() method is called.
2. A new method validate() is added, which will validate the property and set the tooltip appropriately.
3. The validate() method should be called in two places. One is just after the JXLayer instance is injected and another is when the property is changed, i.e. in the propertyStateChange(PropertyStateEvent) method.
4. Now we simply use the tooltip text of the managed text component for checking whether the value of the property is valid.
5. In the paintLayer() method we will only paint the error icon(when the the content of the property is invalid). No state of any component will be changed here.
6. like the comment says, the isBlank() method is a copy from the apache common lang. If the common lang jar is in your classpath, just call the StringUtils.isBlank() method.