001    /* java.beans.EventHandler
002       Copyright (C) 2004, 2005 Free Software Foundation, Inc.
003    
004    This file is part of GNU Classpath.
005    
006    GNU Classpath is free software; you can redistribute it and/or modify
007    it under the terms of the GNU General Public License as published by
008    the Free Software Foundation; either version 2, or (at your option)
009    any later version.
010     
011    GNU Classpath is distributed in the hope that it will be useful, but
012    WITHOUT ANY WARRANTY; without even the implied warranty of
013    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014    General Public License for more details.
015    
016    You should have received a copy of the GNU General Public License
017    along with GNU Classpath; see the file COPYING.  If not, write to the
018    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
019    02110-1301 USA.
020    
021    Linking this library statically or dynamically with other modules is
022    making a combined work based on this library.  Thus, the terms and
023    conditions of the GNU General Public License cover the whole
024    combination.
025    
026    As a special exception, the copyright holders of this library give you
027    permission to link this library with independent modules to produce an
028    executable, regardless of the license terms of these independent
029    modules, and to copy and distribute the resulting executable under
030    terms of your choice, provided that you also meet, for each linked
031    independent module, the terms and conditions of the license of that
032    module.  An independent module is a module which is not derived from
033    or based on this library.  If you modify this library, you may extend
034    this exception to your version of the library, but you are not
035    obligated to do so.  If you do not wish to do so, delete this
036    exception statement from your version. */
037    
038    
039    package java.beans;
040    
041    import java.lang.reflect.InvocationHandler;
042    import java.lang.reflect.InvocationTargetException;
043    import java.lang.reflect.Method;
044    import 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     */
061    public 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    }