/**
* Constructs a PropertyConnector that synchronizes the two bound bean properties as specified by
* the given pairs of bean and associated property name. If <code>Bean1#property1Name</code>
* changes it updates <code>Bean2#property2Name</code> and vice versa. If a bean does not provide
* support for bound properties, changes will not be observed. If a bean property is read-only,
* this connector will not listen to the other bean's property and so won't update the read-only
* property.
*
* <p>In case you don't need the PropertyConnector instance, you better use the static method
* {@link #connect(Object, String, Object, String)}. This constructor may confuse developers if
* you just use the side effects performed in the constructor; this is because it is quite
* unconventional to instantiate an object that you never use.
*
* @param bean1 the bean that owns the first property
* @param property1Name the name of the first property
* @param bean2 the bean that owns the second property
* @param property2Name the name of the second property
* @throws NullPointerException if a bean or property name is <code>null</code>
* @throws IllegalArgumentException if the beans are identical and the property name are equal, or
* if both properties are read-only
*/
public PropertyConnector(Object bean1, String property1Name, Object bean2, String property2Name) {
if (bean1 == null) throw new NullPointerException("Bean1 must not be null.");
if (bean2 == null) throw new NullPointerException("Bean2 must not be null.");
if (property1Name == null) throw new NullPointerException("PropertyName1 must not be null.");
if (property2Name == null) throw new NullPointerException("PropertyName2 must not be null.");
if ((bean1 == bean2) && (property1Name.equals(property2Name)))
throw new IllegalArgumentException(
"Cannot connect a bean property to itself on the same bean.");
this.bean1 = bean1;
this.bean2 = bean2;
this.bean1Class = bean1.getClass();
this.bean2Class = bean2.getClass();
this.property1Name = property1Name;
this.property2Name = property2Name;
property1Descriptor = getPropertyDescriptor(bean1Class, property1Name);
property2Descriptor = getPropertyDescriptor(bean2Class, property2Name);
// Used to check if property2 shall be observed,
// i.e. if a listener shall be registered with property2.
boolean property1Writable = property1Descriptor.getWriteMethod() != null;
// Used to check if property1 shall be observed,
// i.e. if a listener shall be registered with property1.
boolean property2Writable = property2Descriptor.getWriteMethod() != null;
// Reject to connect to read-only properties
if (!property1Writable && !property2Writable)
throw new IllegalArgumentException("Cannot connect two read-only properties.");
boolean property1Observable = BeanUtils.supportsBoundProperties(bean1Class);
boolean property2Observable = BeanUtils.supportsBoundProperties(bean2Class);
// We do not reject the case where two unobservable beans
// are connected; this allows a hand-update using #updateProperty1
// and #updateProperty2.
// Observe property1 if and only if bean1 provides support for
// bound bean properties, and if updates can be written to property2.
if (property1Observable && property2Writable) {
property1ChangeHandler =
new PropertyChangeHandler(bean1, property1Descriptor, bean2, property2Descriptor);
addPropertyChangeHandler(bean1, bean1Class, property1ChangeHandler);
} else {
property1ChangeHandler = null;
}
// Observe property2 if and only if bean2 provides support for
// bound bean properties, and if updates can be written to property1.
if (property2Observable && property1Writable) {
property2ChangeHandler =
new PropertyChangeHandler(bean2, property2Descriptor, bean1, property1Descriptor);
addPropertyChangeHandler(bean2, bean2Class, property2ChangeHandler);
} else {
property2ChangeHandler = null;
}
}
/**
* Looks up, lazily initializes and returns a <code>PropertyDescriptor</code> for the given Java
* Bean and property name.
*
* @param beanClass the Java Bean class used to lookup the property from
* @param propertyName the name of the property
* @return the descriptor for the given bean and property name
* @throws PropertyNotFoundException if the property could not be found
*/
private static PropertyDescriptor getPropertyDescriptor(Class beanClass, String propertyName) {
try {
return BeanUtils.getPropertyDescriptor(beanClass, propertyName);
} catch (IntrospectionException e) {
throw new PropertyNotFoundException(propertyName, beanClass, e);
}
}
private void setValueSilently(
Object sourceBean,
PropertyDescriptor sourcePropertyDescriptor,
Object targetBean,
PropertyDescriptor targetPropertyDescriptor,
Object newValue) {
if (property1ChangeHandler != null) {
removePropertyChangeHandler(bean1, bean1Class, property1ChangeHandler);
}
if (property2ChangeHandler != null) {
removePropertyChangeHandler(bean2, bean2Class, property2ChangeHandler);
}
try {
// Set the new value in the target bean.
BeanUtils.setValue(targetBean, targetPropertyDescriptor, newValue);
} catch (PropertyVetoException e) {
// Silently ignore this situation here, will be handled below.
}
// The target bean setter may have modified the new value.
// Read the value set in the target bean.
Object value = BeanUtils.getValue(targetBean, targetPropertyDescriptor);
// If the new value and the value read differ,
// update the source bean's value.
// This ignores that the source bean setter may modify the value again.
// But we won't end in a loop.
if (!BindingUtils.equals(value, newValue)) {
boolean sourcePropertyWritable = sourcePropertyDescriptor.getWriteMethod() != null;
if (sourcePropertyWritable) {
try {
BeanUtils.setValue(sourceBean, sourcePropertyDescriptor, value);
} catch (PropertyVetoException e) {
// Ignore. The value set is a modified variant
// of a value that had been accepted before.
}
}
}
if (property1ChangeHandler != null) {
addPropertyChangeHandler(bean1, bean1Class, property1ChangeHandler);
}
if (property2ChangeHandler != null) {
addPropertyChangeHandler(bean2, bean2Class, property2ChangeHandler);
}
}
/**
* A property in the observed bean has changed. First checks, if this listener should handle the
* event, because the event's property name is the one to be observed or the event indicates
* that any property may have changed. In case the event provides no new value, it is read from
* the source bean.
*
* @param evt the property change event to be handled
*/
public void propertyChange(PropertyChangeEvent evt) {
String sourcePropertyName = sourcePropertyDescriptor.getName();
if ((evt.getPropertyName() == null) || (evt.getPropertyName().equals(sourcePropertyName))) {
Object newValue = evt.getNewValue();
if (newValue == null) {
newValue = BeanUtils.getValue(sourceBean, sourcePropertyDescriptor);
}
setValueSilently(
sourceBean, sourcePropertyDescriptor, targetBean, targetPropertyDescriptor, newValue);
}
}
/**
* Used to remove this class' PropertyChangeHandler from the given bean if it is not <code>null
* </code>.
*
* @param bean the bean to remove the property change listener from
* @param listener the property change listener to be removed
* @throws PropertyUnboundException if the bean does not support bound properties
* @throws PropertyNotBindableException if the property change handler cannot be removed
* successfully
*/
private static void removePropertyChangeHandler(
Object bean, Class beanClass, PropertyChangeListener listener) {
if (bean != null) {
BeanUtils.removePropertyChangeListener(bean, beanClass, listener);
}
}
/**
* Reads the value of the first bean property and sets it as new value of the second bean
* property.
*
* @see #updateProperty1()
*/
public void updateProperty2() {
Object property1Value = BeanUtils.getValue(bean1, property1Descriptor);
setValueSilently(bean1, property1Descriptor, bean2, property2Descriptor, property1Value);
}