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package java.beans;

import java.lang.reflect.InvocationHandler;

import java.lang.reflect.InvocationTargetException;

import java.lang.reflect.Proxy;

import java.lang.reflect.Method;

import java.security.AccessControlContext;

import java.security.AccessController;

import java.security.PrivilegedAction;

import sun.reflect.misc.MethodUtil;

import sun.reflect.misc.ReflectUtil;

/**

 * The <code>EventHandler</code> class provides

 * support for dynamically generating event listeners whose methods

 * execute a simple statement involving an incoming event object

 * and a target object.

 * <p>

 * The <code>EventHandler</code> 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 <em>source</em>)

 * to an application logic bean (the <em>target</em>). The most effective

 * connections of this kind isolate the application logic from the user

 * interface.  For example, the <code>EventHandler</code> for a

 * connection from a <code>JCheckBox</code> 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.

 * <p>

 * Inner classes are another, more general way to handle events from

 * user interfaces.  The <code>EventHandler</code> class

 * handles only a subset of what is possible using inner

 * classes. However, <code>EventHandler</code> works better

 * with the long-term persistence scheme than inner classes.

 * Also, using <code>EventHandler</code> in large applications in

 * which the same interface is implemented many times can

 * reduce the disk and memory footprint of the application.

 * <p>

 * The reason that listeners created with <code>EventHandler</code>

 * have such a small

 * footprint is that the <code>Proxy</code> class, on which

 * the <code>EventHandler</code> relies, shares implementations

 * of identical

 * interfaces. For example, if you use

 * the <code>EventHandler</code> <code>create</code> methods to make

 * all the <code>ActionListener</code>s in an application,

 * all the action listeners will be instances of a single class

 * (one created by the <code>Proxy</code> class).

 * In general, listeners based on

 * the <code>Proxy</code> class require one listener class

 * to be created per <em>listener type</em> (interface),

 * whereas the inner class

 * approach requires one class to be created per <em>listener</em>

 * (object that implements the interface).

 *

 * <p>

 * You don't generally deal directly with <code>EventHandler</code>

 * instances.

 * Instead, you use one of the <code>EventHandler</code>

 * <code>create</code> methods to create

 * an object that implements a given listener interface.

 * This listener object uses an <code>EventHandler</code> 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</code> methods.

 *

 * <h2>Examples of Using EventHandler</h2>

 *

 * The simplest use of <code>EventHandler</code> is to install

 * a listener that calls a method on the target object with no arguments.

 * In the following example we create an <code>ActionListener</code>

 * that invokes the <code>toFront</code> method on an instance

 * of <code>javax.swing.JFrame</code>.

 *

 * <blockquote>

 *<pre>

 *myButton.addActionListener(

 *    (ActionListener)EventHandler.create(ActionListener.class, frame, "toFront"));

 *</pre>

 * </blockquote>

 *

 * When <code>myButton</code> is pressed, the statement

 * <code>frame.toFront()</code> 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</code>

 * interface and adding an instance of it to the button:

 *

 * <blockquote>

 *<pre>

//Equivalent code using an inner class instead of EventHandler.

 *myButton.addActionListener(new ActionListener() {

 *    public void actionPerformed(ActionEvent e) {

 *        frame.toFront();

 *    }

 *});

 *</pre>

 * </blockquote>

 *

 * The next simplest use of <code>EventHandler</code> 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</code> that

 * sets the <code>nextFocusableComponent</code> property of the target

 * (myButton) object to the value of the "source" property of the event.

 *

 * <blockquote>

 *<pre>

 *EventHandler.create(ActionListener.class, myButton, "nextFocusableComponent", "source")

 *</pre>

 * </blockquote>

 *

 * This would correspond to the following inner class implementation:

 *

 * <blockquote>

 *<pre>

//Equivalent code using an inner class instead of EventHandler.

 *new ActionListener() {

 *    public void actionPerformed(ActionEvent e) {

 *        myButton.setNextFocusableComponent((Component)e.getSource());

 *    }

 *}

 *</pre>

 * </blockquote>

 *

 * It's also possible to create an <code>EventHandler</code> that

 * just passes the incoming event object to the target's action.

 * If the fourth <code>EventHandler.create</code> argument is

 * an empty string, then the event is just passed along:

 *

 * <blockquote>

 *<pre>

 *EventHandler.create(ActionListener.class, target, "doActionEvent", "")

 *</pre>

 * </blockquote>

 *

 * This would correspond to the following inner class implementation:

 *

 * <blockquote>

 *<pre>

//Equivalent code using an inner class instead of EventHandler.

 *new ActionListener() {

 *    public void actionPerformed(ActionEvent e) {

 *        target.doActionEvent(e);

 *    }

 *}

 *</pre>

 * </blockquote>

 *

 * Probably the most common use of <code>EventHandler</code>

 * is to extract a property value from the

 * <em>source</em> 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</code> 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.

 *

 * <blockquote>

 *<pre>

 *EventHandler.create(ActionListener.class, myButton, "label", "source.text")

 *</pre>

 * </blockquote>

 *

 * This would correspond to the following inner class implementation:

 *

 * <blockquote>

 *<pre>

//Equivalent code using an inner class instead of EventHandler.

 *new ActionListener {

 *    public void actionPerformed(ActionEvent e) {

 *        myButton.setLabel(((JTextField)e.getSource()).getText());

 *    }

 *}

 *</pre>

 * </blockquote>

 *

 * 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.

 * <p>

 * For example, the following action listener

 *

 * <blockquote>

 *<pre>

 *EventHandler.create(ActionListener.class, target, "a", "b.c.d")

 *</pre>

 * </blockquote>

 *

 * might be written as the following inner class

 * (assuming all the properties had canonical getter methods and

 * returned the appropriate types):

 *

 * <blockquote>

 *<pre>

//Equivalent code using an inner class instead of EventHandler.

 *new ActionListener {

 *    public void actionPerformed(ActionEvent e) {

 *        target.setA(e.getB().getC().isD());

 *    }

 *}

 *</pre>

 * </blockquote>

 * The target property may also be "qualified" with an arbitrary number

 * of property prefixs delimited with the "." character.  For example, the

 * following action listener:

 * <pre>

 *   EventHandler.create(ActionListener.class, target, "a.b", "c.d")

 * </pre>

 * might be written as the following inner class

 * (assuming all the properties had canonical getter methods and

 * returned the appropriate types):

 * <pre>

 *   //Equivalent code using an inner class instead of EventHandler.

 *   new ActionListener {

 *     public void actionPerformed(ActionEvent e) {

 *         target.getA().setB(e.getC().isD());

 *    }

 *}

 *</pre>

 * <p>

 * As <code>EventHandler</code> 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</code> which is

 * defined as:

 * <pre>

 *   public class MyTarget {

 *     public void doIt(String);

 *     public void doIt(Object);

 *   }

 * </pre>

 * Then the method <code>doIt</code> 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</code> object;

     * you generally use one of the <code>create</code> 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</code> and <code>listenerMethodName</code>

     * 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</code> is null

     * @throws NullPointerException if <code>action</code> 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</code> 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</code>.

     *

     * @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<Object>() {

            public Object run() {

                return invokeInternal(proxy, method, arguments);

            }

        }, acc);

    }

    private Object invokeInternal(Object proxy, Method method, Object[] arguments) {

        String methodName = method.getName();

        if (method.getDeclaringClass() == Object.class)  {

            // Handle the Object public methods.

            if (methodName.equals("hashCode"))  {

                return new Integer(System.identityHashCode(proxy));

            } else if (methodName.equals("equals")) {

                return (proxy == arguments[0] ? Boolean.TRUE : Boolean.FALSE);

            } else if (methodName.equals("toString")) {

                return proxy.getClass().getName() + '@' + Integer.toHexString(proxy.hashCode());

            }

        }

        if (listenerMethodName == null || listenerMethodName.equals(methodName)) {

            Class[] argTypes = null;

            Object[] newArgs = null;

            if (eventPropertyName == null) {     // Nullary method.

                newArgs = new Object[]{};

                argTypes = new Class<?>[]{};

            }

            else {

                Object input = applyGetters(arguments[0], getEventPropertyName());

                newArgs = new Object[]{input};

                argTypes = new Class<?>[]{input == null ? null :

                                       input.getClass()};

            }

            try {

                int lastDot = action.lastIndexOf('.');

                if (lastDot != -1) {

                    target = applyGetters(target, action.substring(0, lastDot));

                    action = action.substring(lastDot + 1);

                }

                Method targetMethod = Statement.getMethod(

                             target.getClass(), action, argTypes);

                if (targetMethod == null) {

                    targetMethod = Statement.getMethod(target.getClass(),

                             "set" + NameGenerator.capitalize(action), argTypes);

                }

                if (targetMethod == null) {

                    String argTypeString = (argTypes.length == 0)

                        ? " with no arguments"

                        : " with argument " + argTypes[0];

                    throw new RuntimeException(

                        "No method called " + action + " on " +

                        target.getClass() + argTypeString);

                }

                return MethodUtil.invoke(targetMethod, target, newArgs);

            }

            catch (IllegalAccessException ex) {

                throw new RuntimeException(ex);

            }

            catch (InvocationTargetException ex) {

                Throwable th = ex.getTargetException();

                throw (th instanceof RuntimeException)

                        ? (RuntimeException) th

                        : new RuntimeException(th);

            }

        }

        return null;

    }

    /**

     * Creates an implementation of <code>listenerInterface</code> in which

     * <em>all</em> of the methods in the listener interface apply

     * the handler's <code>action</code> to the <code>target</code>. This

     * method is implemented by calling the other, more general,

     * implementation of the <code>create</code> method with both

     * the <code>eventPropertyName</code> and the <code>listenerMethodName</code>

     * taking the value <code>null</code>. Refer to

     * {@link java.beans.EventHandler#create(Class, Object, String, String)

     * the general version of create} for a complete description of

     * the <code>action</code> parameter.

     * <p>

     * To create an <code>ActionListener</code> that shows a

     * <code>JDialog</code> with <code>dialog.show()</code>,

     * one can write:

     *

     *<blockquote>

     *<pre>

     *EventHandler.create(ActionListener.class, dialog, "show")

     *</pre>

     *</blockquote>

     *

     * @param <T> the type to create

     * @param listenerInterface the listener interface to create a proxy for

     * @param target the object that will perform the action

     * @param action the name of a (possibly qualified) property or method on

     *        the target

     * @return an object that implements <code>listenerInterface</code>