* The {@code EventHandler} class is intended to be used by interactive tools, such as * application builders, that allow developers to make connections between * beans. Typically connections are made from a user interface bean * (the event source) * to an application logic bean (the target). The most effective * connections of this kind isolate the application logic from the user * interface. For example, the {@code EventHandler} for a * connection from a {@code JCheckBox} to a method * that accepts a boolean value can deal with extracting the state * of the check box and passing it directly to the method so that * the method is isolated from the user interface layer. *
* Inner classes are another, more general way to handle events from * user interfaces. The {@code EventHandler} class * handles only a subset of what is possible using inner * classes. However, {@code EventHandler} works better * with the long-term persistence scheme than inner classes. * Also, using {@code EventHandler} in large applications in * which the same interface is implemented many times can * reduce the disk and memory footprint of the application. *
* The reason that listeners created with {@code EventHandler} * have such a small * footprint is that the {@code Proxy} class, on which * the {@code EventHandler} relies, shares implementations * of identical * interfaces. For example, if you use * the {@code EventHandler create} methods to make * all the {@code ActionListener}s in an application, * all the action listeners will be instances of a single class * (one created by the {@code Proxy} class). * In general, listeners based on * the {@code Proxy} class require one listener class * to be created per listener type (interface), * whereas the inner class * approach requires one class to be created per listener * (object that implements the interface). * *
* You don't generally deal directly with {@code EventHandler} * instances. * Instead, you use one of the {@code EventHandler} * {@code create} methods to create * an object that implements a given listener interface. * This listener object uses an {@code EventHandler} object * behind the scenes to encapsulate information about the * event, the object to be sent a message when the event occurs, * the message (method) to be sent, and any argument * to the method. * The following section gives examples of how to create listener * objects using the {@code create} methods. * *
** * When {@code myButton} is pressed, the statement * {@code frame.toFront()} will be executed. One could get * the same effect, with some additional compile-time type safety, * by defining a new implementation of the {@code ActionListener} * interface and adding an instance of it to the button: * **myButton.addActionListener( * (ActionListener)EventHandler.create(ActionListener.class, frame, "toFront")); **
*
//Equivalent code using an inner class instead of EventHandler.
*myButton.addActionListener(new ActionListener() {
* public void actionPerformed(ActionEvent e) {
* frame.toFront();
* }
*});
*
*
*
* The next simplest use of {@code EventHandler} is
* to extract a property value from the first argument
* of the method in the listener interface (typically an event object)
* and use it to set the value of a property in the target object.
* In the following example we create an {@code ActionListener} that
* sets the {@code nextFocusableComponent} property of the target
* (myButton) object to the value of the "source" property of the event.
*
* ** * This would correspond to the following inner class implementation: * **EventHandler.create(ActionListener.class, myButton, "nextFocusableComponent", "source") **
*
//Equivalent code using an inner class instead of EventHandler.
*new ActionListener() {
* public void actionPerformed(ActionEvent e) {
* myButton.setNextFocusableComponent((Component)e.getSource());
* }
*}
*
*
*
* It's also possible to create an {@code EventHandler} that
* just passes the incoming event object to the target's action.
* If the fourth {@code EventHandler.create} argument is
* an empty string, then the event is just passed along:
*
* ** * This would correspond to the following inner class implementation: * **EventHandler.create(ActionListener.class, target, "doActionEvent", "") **
*
//Equivalent code using an inner class instead of EventHandler.
*new ActionListener() {
* public void actionPerformed(ActionEvent e) {
* target.doActionEvent(e);
* }
*}
*
*
*
* Probably the most common use of {@code EventHandler}
* is to extract a property value from the
* source of the event object and set this value as
* the value of a property of the target object.
* In the following example we create an {@code ActionListener} that
* sets the "label" property of the target
* object to the value of the "text" property of the
* source (the value of the "source" property) of the event.
*
* ** * This would correspond to the following inner class implementation: * **EventHandler.create(ActionListener.class, myButton, "label", "source.text") **
*
//Equivalent code using an inner class instead of EventHandler.
*new ActionListener {
* public void actionPerformed(ActionEvent e) {
* myButton.setLabel(((JTextField)e.getSource()).getText());
* }
*}
*
*
*
* The event property may be "qualified" with an arbitrary number
* of property prefixes delimited with the "." character. The "qualifying"
* names that appear before the "." characters are taken as the names of
* properties that should be applied, left-most first, to
* the event object.
* * For example, the following action listener * *
** * might be written as the following inner class * (assuming all the properties had canonical getter methods and * returned the appropriate types): * **EventHandler.create(ActionListener.class, target, "a", "b.c.d") **
*
//Equivalent code using an inner class instead of EventHandler.
*new ActionListener {
* public void actionPerformed(ActionEvent e) {
* target.setA(e.getB().getC().isD());
* }
*}
*
*
* The target property may also be "qualified" with an arbitrary number
* of property prefixs delimited with the "." character. For example, the
* following action listener:
* * EventHandler.create(ActionListener.class, target, "a.b", "c.d") ** might be written as the following inner class * (assuming all the properties had canonical getter methods and * returned the appropriate types): *
* //Equivalent code using an inner class instead of EventHandler.
* new ActionListener {
* public void actionPerformed(ActionEvent e) {
* target.getA().setB(e.getC().isD());
* }
*}
*
* * As {@code EventHandler} ultimately relies on reflection to invoke * a method we recommend against targeting an overloaded method. For example, * if the target is an instance of the class {@code MyTarget} which is * defined as: *
* public class MyTarget {
* public void doIt(String);
* public void doIt(Object);
* }
*
* Then the method {@code doIt} is overloaded. EventHandler will invoke
* the method that is appropriate based on the source. If the source is
* null, then either method is appropriate and the one that is invoked is
* undefined. For that reason we recommend against targeting overloaded
* methods.
*
* @see java.lang.reflect.Proxy
* @see java.util.EventObject
*
* @since 1.4
*
* @author Mark Davidson
* @author Philip Milne
* @author Hans Muller
*
*/
public class EventHandler implements InvocationHandler {
private Object target;
private String action;
private final String eventPropertyName;
private final String listenerMethodName;
private final AccessControlContext acc = AccessController.getContext();
/**
* Creates a new {@code EventHandler} object;
* you generally use one of the {@code create} methods
* instead of invoking this constructor directly. Refer to
* {@link java.beans.EventHandler#create(Class, Object, String, String)
* the general version of create} for a complete description of
* the {@code eventPropertyName} and {@code listenerMethodName}
* parameter.
*
* @param target the object that will perform the action
* @param action the name of a (possibly qualified) property or method on
* the target
* @param eventPropertyName the (possibly qualified) name of a readable property of the incoming event
* @param listenerMethodName the name of the method in the listener interface that should trigger the action
*
* @throws NullPointerException if {@code target} is null
* @throws NullPointerException if {@code action} is null
*
* @see EventHandler
* @see #create(Class, Object, String, String, String)
* @see #getTarget
* @see #getAction
* @see #getEventPropertyName
* @see #getListenerMethodName
*/
@ConstructorProperties({"target", "action", "eventPropertyName", "listenerMethodName"})
public EventHandler(Object target, String action, String eventPropertyName, String listenerMethodName) {
this.target = target;
this.action = action;
if (target == null) {
throw new NullPointerException("target must be non-null");
}
if (action == null) {
throw new NullPointerException("action must be non-null");
}
this.eventPropertyName = eventPropertyName;
this.listenerMethodName = listenerMethodName;
}
/**
* Returns the object to which this event handler will send a message.
*
* @return the target of this event handler
* @see #EventHandler(Object, String, String, String)
*/
public Object getTarget() {
return target;
}
/**
* Returns the name of the target's writable property
* that this event handler will set,
* or the name of the method that this event handler
* will invoke on the target.
*
* @return the action of this event handler
* @see #EventHandler(Object, String, String, String)
*/
public String getAction() {
return action;
}
/**
* Returns the property of the event that should be
* used in the action applied to the target.
*
* @return the property of the event
*
* @see #EventHandler(Object, String, String, String)
*/
public String getEventPropertyName() {
return eventPropertyName;
}
/**
* Returns the name of the method that will trigger the action.
* A return value of {@code null} signifies that all methods in the
* listener interface trigger the action.
*
* @return the name of the method that will trigger the action
*
* @see #EventHandler(Object, String, String, String)
*/
public String getListenerMethodName() {
return listenerMethodName;
}
private Object applyGetters(Object target, String getters) {
if (getters == null || getters.equals("")) {
return target;
}
int firstDot = getters.indexOf('.');
if (firstDot == -1) {
firstDot = getters.length();
}
String first = getters.substring(0, firstDot);
String rest = getters.substring(Math.min(firstDot + 1, getters.length()));
try {
Method getter = null;
if (target != null) {
getter = Statement.getMethod(target.getClass(),
"get" + NameGenerator.capitalize(first),
new Class[]{});
if (getter == null) {
getter = Statement.getMethod(target.getClass(),
"is" + NameGenerator.capitalize(first),
new Class[]{});
}
if (getter == null) {
getter = Statement.getMethod(target.getClass(), first, new Class[]{});
}
}
if (getter == null) {
throw new RuntimeException("No method called: " + first +
" defined on " + target);
}
Object newTarget = MethodUtil.invoke(getter, target, new Object[]{});
return applyGetters(newTarget, rest);
}
catch (Exception e) {
throw new RuntimeException("Failed to call method: " + first +
" on " + target, e);
}
}
/**
* Extract the appropriate property value from the event and
* pass it to the action associated with
* this {@code EventHandler}.
*
* @param proxy the proxy object
* @param method the method in the listener interface
* @return the result of applying the action to the target
*
* @see EventHandler
*/
public Object invoke(final Object proxy, final Method method, final Object[] arguments) {
AccessControlContext acc = this.acc;
if ((acc == null) && (System.getSecurityManager() != null)) {
throw new SecurityException("AccessControlContext is not set");
}
return AccessController.doPrivileged(new PrivilegedAction