001/* java.beans.EventHandler
002   Copyright (C) 2004, 2005 Free Software Foundation, Inc.
003
004This file is part of GNU Classpath.
005
006GNU Classpath is free software; you can redistribute it and/or modify
007it under the terms of the GNU General Public License as published by
008the Free Software Foundation; either version 2, or (at your option)
009any later version.
010 
011GNU Classpath is distributed in the hope that it will be useful, but
012WITHOUT ANY WARRANTY; without even the implied warranty of
013MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014General Public License for more details.
015
016You should have received a copy of the GNU General Public License
017along with GNU Classpath; see the file COPYING.  If not, write to the
018Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
01902110-1301 USA.
020
021Linking this library statically or dynamically with other modules is
022making a combined work based on this library.  Thus, the terms and
023conditions of the GNU General Public License cover the whole
024combination.
025
026As a special exception, the copyright holders of this library give you
027permission to link this library with independent modules to produce an
028executable, regardless of the license terms of these independent
029modules, and to copy and distribute the resulting executable under
030terms of your choice, provided that you also meet, for each linked
031independent module, the terms and conditions of the license of that
032module.  An independent module is a module which is not derived from
033or based on this library.  If you modify this library, you may extend
034this exception to your version of the library, but you are not
035obligated to do so.  If you do not wish to do so, delete this
036exception statement from your version. */
037
038
039package java.beans;
040
041import java.lang.reflect.InvocationHandler;
042import java.lang.reflect.InvocationTargetException;
043import java.lang.reflect.Method;
044import java.lang.reflect.Proxy;
045
046/**
047 * <p>EventHandler forms a bridge between dynamically created listeners and
048 * arbitrary properties and methods.</p>
049 * 
050 * <p>You can use this class to easily create listener implementations for
051 * some basic interactions between an event source and its target. Using
052 * the three static methods named <code>create</code> you can create
053 * these listener implementations.</p>
054 * 
055 * <p>See the documentation of each method for usage examples.</p>
056 *  
057 * @author Jerry Quinn (jlquinn@optonline.net)
058 * @author Robert Schuster (thebohemian@gmx.net)
059 * @since 1.4
060 */
061public class EventHandler implements InvocationHandler
062{
063  // The name of the method that will be implemented.  If null, any method.
064  private String listenerMethod;
065
066  // The object to call action on.
067  private Object target;
068
069  // The name of the method or property setter in target.
070  private String action;
071
072  // The property to extract from an event passed to listenerMethod.
073  private String property;
074
075  // The target objects Class.
076  private Class targetClass;
077  
078  // String class doesn't already have a capitalize routine.
079  private String capitalize(String s)
080  {
081    return s.substring(0, 1).toUpperCase() + s.substring(1);
082  }
083
084  /**
085   * Creates a new <code>EventHandler</code> instance.
086   *
087   * <p>Typical creation is done with the create method, not by knewing an
088   * EventHandler.</p>
089   *
090   * <p>This constructs an EventHandler that will connect the method
091   * listenerMethodName to target.action, extracting eventPropertyName from
092   * the first argument of listenerMethodName. and sending it to action.</p>
093   * 
094   * <p>Throws a <code>NullPointerException</code> if the <code>target</code>
095   * argument is <code>null</code>. 
096   *
097   * @param target Object that will perform the action.
098   * @param action A property or method of the target.
099   * @param eventPropertyName A readable property of the inbound event.
100   * @param listenerMethodName The listener method name triggering the action.
101   */
102  public EventHandler(Object target, String action, String eventPropertyName,
103                      String listenerMethodName)
104  {
105    this.target = target;
106    
107    // Retrieving the class is done for two reasons:
108    // 1) The class object is needed very frequently in the invoke() method.
109    // 2) The constructor should throw a NullPointerException if target is null.
110    targetClass = target.getClass();
111    
112    this.action = action;       // Turn this into a method or do we wait till
113                // runtime
114    property = eventPropertyName;
115    listenerMethod = listenerMethodName;
116  }
117
118  /**
119   * Returns the event property name.
120   */
121  public String getEventPropertyName()
122  {
123    return property;
124  }
125
126  /**
127   * Returns the listener's method name.
128   */
129  public String getListenerMethodName()
130  {
131    return listenerMethod;
132  }
133
134  /**
135   * Returns the target object.
136   */
137  public Object getTarget()
138  {
139    return target;
140  }
141
142  /**
143   * Returns the action method name.
144   */
145  public String getAction()
146  {
147    return action;
148  }
149
150  // Fetch a qualified property like a.b.c from object o.  The properties can
151  // be boolean isProp or object getProp properties.
152  //
153  // Returns a length 2 array with the first entry containing the value
154  // extracted from the property, and the second entry contains the class of
155  // the method return type.
156  //
157  // We play this game because if the method returns a native type, the return
158  // value will be a wrapper.  If we then take the type of the wrapper and use
159  // it to locate the action method that takes the native type, it won't match.
160  private Object[] getProperty(Object o, String prop)
161  {
162    // Isolate the first property name from a.b.c.
163    int pos;
164    String rest = null;
165    if ((pos = prop.indexOf('.')) != -1)
166      {
167        rest = prop.substring(pos + 1);
168        prop = prop.substring(0, pos);
169      }
170
171    // Find a method named getProp.  It could be isProp instead.
172    Method getter;
173    try
174      {
175        // Look for boolean property getter isProperty
176        getter = o.getClass().getMethod("is" + capitalize(prop));
177      }
178    catch (NoSuchMethodException nsme1)
179      {
180        try {
181          // Look for regular property getter getProperty
182          getter = o.getClass().getMethod("get" + capitalize(prop));
183        } catch(NoSuchMethodException nsme2) {
184            try {
185            // Finally look for a method of the name prop
186            getter = o.getClass().getMethod(prop);
187            } catch(NoSuchMethodException nsme3) {
188                // Ok, give up with an intelligent hint for the user.
189                throw new RuntimeException("Method not called: Could not find a property or method '" + prop
190                        + "' in " + o.getClass() + " while following the property argument '" + property + "'.");
191            }
192        }
193      }
194    try {
195      Object val = getter.invoke(o);
196
197      if (rest != null)
198        return getProperty(val, rest);
199
200      return new Object[] {val, getter.getReturnType()};
201    } catch(InvocationTargetException ite) {
202        throw new RuntimeException("Method not called: Property or method '" + prop + "' has thrown an exception.", ite);
203    } catch(IllegalAccessException iae) {
204        // This cannot happen because we looked up method with Class.getMethod()
205        // which returns public methods only.
206        throw (InternalError) new InternalError("Non-public method was invoked.").initCause(iae);
207    }
208  }
209
210  /**
211   * Invokes the <code>EventHandler</code>.
212   * 
213   * <p>This method is normally called by the listener's proxy implementation.</p>
214   * 
215   * @param proxy The listener interface that is implemented using
216   * the proxy mechanism.
217   * @param method The method that was called on the proxy instance.
218   * @param arguments The arguments which where given to the method.
219   * @throws Throwable <code>NoSuchMethodException</code> is thrown when the EventHandler's
220   * action method or property cannot be found.
221   */
222  public Object invoke(Object proxy, Method method, Object[] arguments)
223  {
224      try {
225      // The method instance of the target object. We have to find out which
226      // one we have to invoke.
227      Method actionMethod = null;
228
229    // Listener methods that weren't specified are ignored.  If listenerMethod
230    // is null, then all listener methods are processed.
231    if (listenerMethod != null && !method.getName().equals(listenerMethod))
232      return null;
233
234    // If a property is defined we definitely need a valid object at
235    // arguments[0] that can be used to retrieve a value to which the
236    // property of the target gets set.
237    if(property != null) {
238      // Extracts the argument. We will let it fail with a NullPointerException
239      // the caller used a listener method that has no arguments.
240      Object event = arguments[0];
241
242      // Obtains the property XXX propertyType keeps showing up null - why?
243      // because the object inside getProperty changes, but the ref variable
244      // can't change this way, dolt!  need a better way to get both values out
245      // - need method and object to do the invoke and get return type
246      Object v[] = getProperty(event, property);
247      Object[] args = new Object[] { v[0] };
248      
249      // Changes the class array that controls which method signature we are going
250      // to look up in the target object.
251      Class[] argTypes = new Class[] { initClass((Class) v[1]) };
252    
253      // Tries to  find a setter method to which we can apply the
254      while(argTypes[0] != null) {
255      try
256      {
257        // Look for a property setter for action.
258        actionMethod = targetClass.getMethod("set" + capitalize(action), argTypes);
259
260        return actionMethod.invoke(target, args);
261      }
262    catch (NoSuchMethodException e)
263      {
264        // If action as property didn't work, try as method later.
265      }
266    
267      argTypes[0] = nextClass(argTypes[0]);
268      }
269      
270      // We could not find a suitable setter method. Now we try again interpreting
271      // action as the method name itself.
272      // Since we probably have changed the block local argTypes array 
273      // we need to rebuild it.
274      argTypes = new Class[] { initClass((Class) v[1]) };
275    
276      // Tries to  find a setter method to which we can apply the
277      while(argTypes[0] != null) {
278        try
279        {
280          actionMethod = targetClass.getMethod(action, argTypes);
281
282          return actionMethod.invoke(target, args);
283        }
284        catch (NoSuchMethodException e)
285        {
286        }
287        
288        argTypes[0] = nextClass(argTypes[0]);
289      }
290        
291        throw new RuntimeException("Method not called: Could not find a public method named '"
292                + action + "' in target " + targetClass + " which takes a '"
293                + v[1] + "' argument or a property of this type.");
294      }      
295  
296    // If property was null we will search for a no-argument method here.
297    // Note: The ordering of method lookups is important because we want to prefer no-argument
298    // calls like the JDK does. This means if we have actionMethod() and actionMethod(Event) we will
299    // call the first *EVEN* if we have a valid argument for the second method. This is behavior compliant
300    // to the JDK.
301    // If actionMethod() is not available but there is a actionMethod(Event) we take this. That makes us
302    // more specification compliant than the JDK itself because this one will fail in such a case.
303    try
304      {
305      actionMethod = targetClass.getMethod(action);
306      }
307    catch(NoSuchMethodException nsme)
308      {
309        // Note: If we want to be really strict the specification says that a no-argument method should
310        // accept an EventObject (or subclass I guess). However since the official implementation is broken
311        // anyways, it's more flexible without the EventObject restriction and we are compatible on everything
312        // else this can stay this way.
313        if(arguments != null && arguments.length >= 1/* && arguments[0] instanceof EventObject*/) {
314            Class[] targetArgTypes = new Class[] { initClass(arguments[0].getClass()) };
315            
316            while(targetArgTypes[0] != null) {
317                try
318                {
319                  // If no property exists we expect the first element of the arguments to be
320                  // an EventObject which is then applied to the target method.
321      
322                  actionMethod = targetClass.getMethod(action, targetArgTypes);
323              
324                  return actionMethod.invoke(target, new Object[] { arguments[0] });
325                }
326                catch(NoSuchMethodException nsme2)
327                {
328                    
329                }
330                
331                targetArgTypes[0] = nextClass(targetArgTypes[0]);
332            }
333          
334        }
335      }
336
337    // If we do not have a Method instance at this point this means that all our tries
338    // failed. The JDK throws an ArrayIndexOutOfBoundsException in this case.
339    if(actionMethod == null)
340      throw new ArrayIndexOutOfBoundsException(0);
341    
342    // Invoke target.action(property)
343    return actionMethod.invoke(target);
344      } catch(InvocationTargetException ite) {
345         throw new RuntimeException(ite.getCause());
346      } catch(IllegalAccessException iae) {
347          // Cannot happen because we always use getMethod() which returns public
348          // methods only. Otherwise there is something seriously broken in
349          // GNU Classpath.
350          throw (InternalError) new InternalError("Non-public method was invoked.").initCause(iae);
351      }
352  }
353  
354  /**
355   * <p>Returns the primitive type for every wrapper class or the
356   * class itself if it is no wrapper class.</p>
357   * 
358   * <p>This is needed because to be able to find both kinds of methods:
359   * One that takes a wrapper class as the first argument and one that
360   * accepts a primitive instead.</p>
361   */
362  private Class initClass(Class klass) {
363   if(klass == Boolean.class) {
364    return Boolean.TYPE;    
365   } else if(klass == Byte.class) {
366    return Byte.TYPE;   
367   } else if(klass == Short.class) {
368    return Short.TYPE;   
369   } else if(klass == Integer.class) {
370    return Integer.TYPE;   
371   } else if(klass == Long.class) {
372    return Long.TYPE;   
373   } else if(klass == Float.class) {
374    return Float.TYPE;   
375   } else if(klass == Double.class) {
376    return Double.TYPE;   
377   } else {
378    return klass;   
379   }
380  }
381
382  /**
383   * 
384   * 
385   * @param klass
386   * @return
387   */
388  private Class nextClass(Class klass) {
389    if(klass == Boolean.TYPE) {
390    return Boolean.class;    
391   } else if(klass == Byte.TYPE) {
392    return Byte.class;   
393   } else if(klass == Short.TYPE) {
394    return Short.class;   
395   } else if(klass == Integer.TYPE) {
396    return Integer.class;   
397   } else if(klass == Long.TYPE) {
398    return Long.class;   
399   } else if(klass == Float.TYPE) {
400    return Float.class;   
401   } else if(klass == Double.TYPE) {
402    return Double.class;   
403   } else {
404    return klass.getSuperclass();
405   }
406   }
407  
408  /**
409   * <p>Constructs an implementation of <code>listenerInterface</code>
410   * to dispatch events.</p>
411   * 
412   * <p>You can use such an implementation to simply call a public
413   * no-argument method of an arbitrary target object or to forward
414   * the first argument of the listener method to the target method.</p>
415   * 
416   * <p>Call this method like:</p>
417   * <code>
418   * button.addActionListener((ActionListener)
419   *    EventHandler.create(ActionListener.class, target, "dispose"));
420   * </code>
421   * 
422   * <p>to achieve the following behavior:</p>
423   * <code>
424   * button.addActionListener(new ActionListener() {
425   *    public void actionPerformed(ActionEvent ae) {
426   *        target.dispose();
427   *    }
428   * });
429   * </code>
430   * 
431   * <p>That means if you need a listener implementation that simply calls a
432   * a no-argument method on a given instance for <strong>each</strong>
433   * method of the listener interface.</p>
434   * 
435   * <p>Note: The <code>action</code> is interpreted as a method name. If your target object
436   * has no no-argument method of the given name the EventHandler tries to find
437   * a method with the same name but which can accept the first argument of the
438   * listener method. Usually this will be an event object but any other object
439   * will be forwarded, too. Keep in mind that using a property name instead of a
440   * real method here is wrong and will throw an <code>ArrayIndexOutOfBoundsException</code>
441   * whenever one of the listener methods is called.<p/>
442   *
443   * <p>The <code>EventHandler</code> will automatically convert primitives
444   * to their wrapper class and vice versa. Furthermore it will call
445   * a target method if it accepts a superclass of the type of the
446   * first argument of the listener method.</p>
447   * 
448   * <p>In case that the method of the target object throws an exception
449   * it will be wrapped in a <code>RuntimeException</code> and thrown out
450   * of the listener method.</p>
451   * 
452   * <p>In case that the method of the target object cannot be found an
453   * <code>ArrayIndexOutOfBoundsException</code> will be thrown when the
454   * listener method is invoked.</p>
455   * 
456   * <p>A call to this method is equivalent to:
457   * <code>create(listenerInterface, target, action, null, null)</code></p>
458   *
459   * @param listenerInterface Listener interface to implement.
460   * @param target Object to invoke action on.
461   * @param action Target property or method to invoke.
462   * @return A constructed proxy object.
463   */
464  public static <T> T create(Class<T> listenerInterface, Object target,
465                             String action)
466  {
467    return create(listenerInterface, target, action, null, null);
468  }
469
470  /**
471   * <p>Constructs an implementation of <code>listenerInterface</code>
472   * to dispatch events.</p>
473   *
474   * <p>Use this method if you want to create an implementation that retrieves
475   * a property value from the <b>first</b> argument of the listener method
476   * and applies it to the target's property or method. This first argument
477   * of the listener is usually an event object but any other object is
478   * valid, too.</p>
479   * 
480   * <p>You can set the value of <code>eventPropertyName</code> to "prop"
481   * to denote the retrieval of a property named "prop" from the event
482   * object. In case that no such property exists the <code>EventHandler</code>
483   * will try to find a method with that name.</p>
484   * 
485   * <p>If you set <code>eventPropertyName</code> to a value like this "a.b.c"
486   * <code>EventHandler</code> will recursively evaluate the properties "a", "b"
487   * and "c". Again if no property can be found the <code>EventHandler</code>
488   * tries a method name instead. This allows mixing the names, too: "a.toString"
489   * will retrieve the property "a" from the event object and will then call
490   * the method "toString" on it.</p>
491   * 
492   * <p>An exception thrown in any of these methods will provoke a
493   * <code>RuntimeException</code> to be thrown which contains an
494   * <code>InvocationTargetException</code> containing the triggering exception.</p>
495   * 
496   * <p>If you set <code>eventPropertyName</code> to a non-null value the
497   * <code>action</code> parameter will be interpreted as a property name
498   * or a method name of the target object.</p>
499   *   
500   * <p>Any object retrieved from the event object and applied to the
501   * target will converted from primitives to their wrapper class or
502   * vice versa or applied to a method that accepts a superclass
503   * of the object.</p>
504   *
505   * <p>Examples:</p>
506   * <p>The following code:</p><code>
507   * button.addActionListener(
508   *    new ActionListener() {
509   *        public void actionPerformed(ActionEvent ae) {
510   *            Object o = ae.getSource().getClass().getName();
511   *            textField.setText((String) o);
512   *        }
513   *    });
514   * </code>
515   * 
516   * <p>Can be expressed using the <code>EventHandler</code> like this:</p>
517   * <p>
518   * <code>button.addActionListener((ActionListener)
519   *    EventHandler.create(ActionListener.class, textField, "text", "source.class.name");
520   * <code>
521   * </p>
522   * 
523   * <p>As said above you can specify the target as a method, too:</p>
524   * <p>
525   * <code>button.addActionListener((ActionListener)
526   *    EventHandler.create(ActionListener.class, textField, "setText", "source.class.name");
527   * <code>
528   * </p>
529   * 
530   * <p>Furthermore you can use method names in the property:</p>
531   * <p>
532   * <code>button.addActionListener((ActionListener)
533   *    EventHandler.create(ActionListener.class, textField, "setText", "getSource.getClass.getName");
534   * <code>
535   * </p>
536   * 
537   * <p>Finally you can mix names:</p>
538   * <p>
539   * <code>button.addActionListener((ActionListener)
540   *    EventHandler.create(ActionListener.class, textField, "setText", "source.getClass.name");
541   * <code>
542   * </p>
543   * 
544   * <p>A call to this method is equivalent to:
545   * <code>create(listenerInterface, target, action, null, null)</code>
546   * </p>
547   *
548   * @param listenerInterface Listener interface to implement.
549   * @param target Object to invoke action on.
550   * @param action Target property or method to invoke.
551   * @param eventPropertyName Name of property to extract from event.
552   * @return A constructed proxy object.
553   */
554  public static <T> T create(Class<T> listenerInterface, Object target,
555                             String action, String eventPropertyName)
556  {
557    return create(listenerInterface, target, action, eventPropertyName, null);
558  }
559
560  /**
561   * <p>Constructs an implementation of <code>listenerInterface</code>
562   * to dispatch events.</p>
563   *
564   * <p>Besides the functionality described for {@link create(Class, Object, String)}
565   * and {@link create(Class, Object, String, String)} this method allows you
566   * to filter the listener method that should have an effect. Look at these
567   * method's documentation for more information about the <code>EventHandler</code>'s
568   * usage.</p>
569   * 
570   * <p>If you want to call <code>dispose</code> on a <code>JFrame</code> instance
571   * when the <code>WindowListener.windowClosing()</code> method was invoked use
572   * the following code:</p>
573   * <p>
574   * <code>
575   * EventHandler.create(WindowListener.class, jframeInstance, "dispose", null, "windowClosing");
576   * </code>
577   * </p>
578   * 
579   * <p>A <code>NullPointerException</code> is thrown if the <code>listenerInterface</code>
580   * or <code>target</code> argument are <code>null</code>.
581   * 
582   * @param listenerInterface Listener interface to implement.
583   * @param target Object to invoke action on.
584   * @param action Target method name to invoke.
585   * @param eventPropertyName Name of property to extract from event.
586   * @param listenerMethodName Listener method to implement.
587   * @return A constructed proxy object.
588   */
589  public static <T> T create(Class<T> listenerInterface, Object target,
590                             String action, String eventPropertyName,
591                             String listenerMethodName)
592  {
593    // Create EventHandler instance
594    EventHandler eh = new EventHandler(target, action, eventPropertyName,
595                                       listenerMethodName);
596
597    // Create proxy object passing in the event handler
598    Object proxy = Proxy.newProxyInstance(listenerInterface.getClassLoader(),
599                                          new Class<?>[] {listenerInterface},
600                                          eh);
601
602    return (T) proxy;
603  }
604}