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 null);
178 }
179 catch (NoSuchMethodException nsme1)
180 {
181 try {
182 // Look for regular property getter getProperty
183 getter = o.getClass().getMethod("get" + capitalize(prop),
184 null);
185 } catch(NoSuchMethodException nsme2) {
186 try {
187 // Finally look for a method of the name prop
188 getter = o.getClass().getMethod(prop, null);
189 } catch(NoSuchMethodException nsme3) {
190 // Ok, give up with an intelligent hint for the user.
191 throw new RuntimeException("Method not called: Could not find a property or method '" + prop
192 + "' in " + o.getClass() + " while following the property argument '" + property + "'.");
193 }
194 }
195 }
196 try {
197 Object val = getter.invoke(o, null);
198
199 if (rest != null)
200 return getProperty(val, rest);
201
202 return new Object[] {val, getter.getReturnType()};
203 } catch(InvocationTargetException ite) {
204 throw new RuntimeException("Method not called: Property or method '" + prop + "' has thrown an exception.", ite);
205 } catch(IllegalAccessException iae) {
206 // This cannot happen because we looked up method with Class.getMethod()
207 // which returns public methods only.
208 throw (InternalError) new InternalError("Non-public method was invoked.").initCause(iae);
209 }
210 }
211
212 /**
213 * Invokes the <code>EventHandler</code>.
214 *
215 * <p>This method is normally called by the listener's proxy implementation.</p>
216 *
217 * @param proxy The listener interface that is implemented using
218 * the proxy mechanism.
219 * @param method The method that was called on the proxy instance.
220 * @param arguments The arguments which where given to the method.
221 * @throws Throwable <code>NoSuchMethodException</code> is thrown when the EventHandler's
222 * action method or property cannot be found.
223 */
224 public Object invoke(Object proxy, Method method, Object[] arguments)
225 {
226 try {
227 // The method instance of the target object. We have to find out which
228 // one we have to invoke.
229 Method actionMethod = null;
230
231 // Listener methods that weren't specified are ignored. If listenerMethod
232 // is null, then all listener methods are processed.
233 if (listenerMethod != null && !method.getName().equals(listenerMethod))
234 return null;
235
236 // If a property is defined we definitely need a valid object at
237 // arguments[0] that can be used to retrieve a value to which the
238 // property of the target gets set.
239 if(property != null) {
240 // Extracts the argument. We will let it fail with a NullPointerException
241 // the caller used a listener method that has no arguments.
242 Object event = arguments[0];
243
244 // Obtains the property XXX propertyType keeps showing up null - why?
245 // because the object inside getProperty changes, but the ref variable
246 // can't change this way, dolt! need a better way to get both values out
247 // - need method and object to do the invoke and get return type
248 Object v[] = getProperty(event, property);
249 Object[] args = new Object[] { v[0] };
250
251 // Changes the class array that controls which method signature we are going
252 // to look up in the target object.
253 Class[] argTypes = new Class[] { initClass((Class) v[1]) };
254
255 // Tries to find a setter method to which we can apply the
256 while(argTypes[0] != null) {
257 try
258 {
259 // Look for a property setter for action.
260 actionMethod = targetClass.getMethod("set" + capitalize(action), argTypes);
261
262 return actionMethod.invoke(target, args);
263 }
264 catch (NoSuchMethodException e)
265 {
266 // If action as property didn't work, try as method later.
267 }
268
269 argTypes[0] = nextClass(argTypes[0]);
270 }
271
272 // We could not find a suitable setter method. Now we try again interpreting
273 // action as the method name itself.
274 // Since we probably have changed the block local argTypes array
275 // we need to rebuild it.
276 argTypes = new Class[] { initClass((Class) v[1]) };
277
278 // Tries to find a setter method to which we can apply the
279 while(argTypes[0] != null) {
280 try
281 {
282 actionMethod = targetClass.getMethod(action, argTypes);
283
284 return actionMethod.invoke(target, args);
285 }
286 catch (NoSuchMethodException e)
287 {
288 }
289
290 argTypes[0] = nextClass(argTypes[0]);
291 }
292
293 throw new RuntimeException("Method not called: Could not find a public method named '"
294 + action + "' in target " + targetClass + " which takes a '"
295 + v[1] + "' argument or a property of this type.");
296 }
297
298 // If property was null we will search for a no-argument method here.
299 // Note: The ordering of method lookups is important because we want to prefer no-argument
300 // calls like the JDK does. This means if we have actionMethod() and actionMethod(Event) we will
301 // call the first *EVEN* if we have a valid argument for the second method. This is behavior compliant
302 // to the JDK.
303 // If actionMethod() is not available but there is a actionMethod(Event) we take this. That makes us
304 // more specification compliant than the JDK itself because this one will fail in such a case.
305 try
306 {
307 actionMethod = targetClass.getMethod(action, null);
308 }
309 catch(NoSuchMethodException nsme)
310 {
311 // Note: If we want to be really strict the specification says that a no-argument method should
312 // accept an EventObject (or subclass I guess). However since the official implementation is broken
313 // anyways, it's more flexible without the EventObject restriction and we are compatible on everything
314 // else this can stay this way.
315 if(arguments != null && arguments.length >= 1/* && arguments[0] instanceof EventObject*/) {
316 Class[] targetArgTypes = new Class[] { initClass(arguments[0].getClass()) };
317
318 while(targetArgTypes[0] != null) {
319 try
320 {
321 // If no property exists we expect the first element of the arguments to be
322 // an EventObject which is then applied to the target method.
323
324 actionMethod = targetClass.getMethod(action, targetArgTypes);
325
326 return actionMethod.invoke(target, new Object[] { arguments[0] });
327 }
328 catch(NoSuchMethodException nsme2)
329 {
330
331 }
332
333 targetArgTypes[0] = nextClass(targetArgTypes[0]);
334 }
335
336 }
337 }
338
339 // If we do not have a Method instance at this point this means that all our tries
340 // failed. The JDK throws an ArrayIndexOutOfBoundsException in this case.
341 if(actionMethod == null)
342 throw new ArrayIndexOutOfBoundsException(0);
343
344 // Invoke target.action(property)
345 return actionMethod.invoke(target, null);
346 } catch(InvocationTargetException ite) {
347 throw new RuntimeException(ite.getCause());
348 } catch(IllegalAccessException iae) {
349 // Cannot happen because we always use getMethod() which returns public
350 // methods only. Otherwise there is something seriously broken in
351 // GNU Classpath.
352 throw (InternalError) new InternalError("Non-public method was invoked.").initCause(iae);
353 }
354 }
355
356 /**
357 * <p>Returns the primitive type for every wrapper class or the
358 * class itself if it is no wrapper class.</p>
359 *
360 * <p>This is needed because to be able to find both kinds of methods:
361 * One that takes a wrapper class as the first argument and one that
362 * accepts a primitive instead.</p>
363 */
364 private Class initClass(Class klass) {
365 if(klass == Boolean.class) {
366 return Boolean.TYPE;
367 } else if(klass == Byte.class) {
368 return Byte.TYPE;
369 } else if(klass == Short.class) {
370 return Short.TYPE;
371 } else if(klass == Integer.class) {
372 return Integer.TYPE;
373 } else if(klass == Long.class) {
374 return Long.TYPE;
375 } else if(klass == Float.class) {
376 return Float.TYPE;
377 } else if(klass == Double.class) {
378 return Double.TYPE;
379 } else {
380 return klass;
381 }
382 }
383
384 /**
385 *
386 *
387 * @param klass
388 * @return
389 */
390 private Class nextClass(Class klass) {
391 if(klass == Boolean.TYPE) {
392 return Boolean.class;
393 } else if(klass == Byte.TYPE) {
394 return Byte.class;
395 } else if(klass == Short.TYPE) {
396 return Short.class;
397 } else if(klass == Integer.TYPE) {
398 return Integer.class;
399 } else if(klass == Long.TYPE) {
400 return Long.class;
401 } else if(klass == Float.TYPE) {
402 return Float.class;
403 } else if(klass == Double.TYPE) {
404 return Double.class;
405 } else {
406 return klass.getSuperclass();
407 }
408 }
409
410 /**
411 * <p>Constructs an implementation of <code>listenerInterface</code>
412 * to dispatch events.</p>
413 *
414 * <p>You can use such an implementation to simply call a public
415 * no-argument method of an arbitrary target object or to forward
416 * the first argument of the listener method to the target method.</p>
417 *
418 * <p>Call this method like:</p>
419 * <code>
420 * button.addActionListener((ActionListener)
421 * EventHandler.create(ActionListener.class, target, "dispose"));
422 * </code>
423 *
424 * <p>to achieve the following behavior:</p>
425 * <code>
426 * button.addActionListener(new ActionListener() {
427 * public void actionPerformed(ActionEvent ae) {
428 * target.dispose();
429 * }
430 * });
431 * </code>
432 *
433 * <p>That means if you need a listener implementation that simply calls a
434 * a no-argument method on a given instance for <strong>each</strong>
435 * method of the listener interface.</p>
436 *
437 * <p>Note: The <code>action</code> is interpreted as a method name. If your target object
438 * has no no-argument method of the given name the EventHandler tries to find
439 * a method with the same name but which can accept the first argument of the
440 * listener method. Usually this will be an event object but any other object
441 * will be forwarded, too. Keep in mind that using a property name instead of a
442 * real method here is wrong and will throw an <code>ArrayIndexOutOfBoundsException</code>
443 * whenever one of the listener methods is called.<p/>
444 *
445 * <p>The <code>EventHandler</code> will automatically convert primitives
446 * to their wrapper class and vice versa. Furthermore it will call
447 * a target method if it accepts a superclass of the type of the
448 * first argument of the listener method.</p>
449 *
450 * <p>In case that the method of the target object throws an exception
451 * it will be wrapped in a <code>RuntimeException</code> and thrown out
452 * of the listener method.</p>
453 *
454 * <p>In case that the method of the target object cannot be found an
455 * <code>ArrayIndexOutOfBoundsException</code> will be thrown when the
456 * listener method is invoked.</p>
457 *
458 * <p>A call to this method is equivalent to:
459 * <code>create(listenerInterface, target, action, null, null)</code></p>
460 *
461 * @param listenerInterface Listener interface to implement.
462 * @param target Object to invoke action on.
463 * @param action Target property or method to invoke.
464 * @return A constructed proxy object.
465 */
466 public static <T> T create(Class<T> listenerInterface, Object target,
467 String action)
468 {
469 return create(listenerInterface, target, action, null, null);
470 }
471
472 /**
473 * <p>Constructs an implementation of <code>listenerInterface</code>
474 * to dispatch events.</p>
475 *
476 * <p>Use this method if you want to create an implementation that retrieves
477 * a property value from the <b>first</b> argument of the listener method
478 * and applies it to the target's property or method. This first argument
479 * of the listener is usually an event object but any other object is
480 * valid, too.</p>
481 *
482 * <p>You can set the value of <code>eventPropertyName</code> to "prop"
483 * to denote the retrieval of a property named "prop" from the event
484 * object. In case that no such property exists the <code>EventHandler</code>
485 * will try to find a method with that name.</p>
486 *
487 * <p>If you set <code>eventPropertyName</code> to a value like this "a.b.c"
488 * <code>EventHandler</code> will recursively evaluate the properties "a", "b"
489 * and "c". Again if no property can be found the <code>EventHandler</code>
490 * tries a method name instead. This allows mixing the names, too: "a.toString"
491 * will retrieve the property "a" from the event object and will then call
492 * the method "toString" on it.</p>
493 *
494 * <p>An exception thrown in any of these methods will provoke a
495 * <code>RuntimeException</code> to be thrown which contains an
496 * <code>InvocationTargetException</code> containing the triggering exception.</p>
497 *
498 * <p>If you set <code>eventPropertyName</code> to a non-null value the
499 * <code>action</code> parameter will be interpreted as a property name
500 * or a method name of the target object.</p>
501 *
502 * <p>Any object retrieved from the event object and applied to the
503 * target will converted from primitives to their wrapper class or
504 * vice versa or applied to a method that accepts a superclass
505 * of the object.</p>
506 *
507 * <p>Examples:</p>
508 * <p>The following code:</p><code>
509 * button.addActionListener(
510 * new ActionListener() {
511 * public void actionPerformed(ActionEvent ae) {
512 * Object o = ae.getSource().getClass().getName();
513 * textField.setText((String) o);
514 * }
515 * });
516 * </code>
517 *
518 * <p>Can be expressed using the <code>EventHandler</code> like this:</p>
519 * <p>
520 * <code>button.addActionListener((ActionListener)
521 * EventHandler.create(ActionListener.class, textField, "text", "source.class.name");
522 * <code>
523 * </p>
524 *
525 * <p>As said above you can specify the target as a method, too:</p>
526 * <p>
527 * <code>button.addActionListener((ActionListener)
528 * EventHandler.create(ActionListener.class, textField, "setText", "source.class.name");
529 * <code>
530 * </p>
531 *
532 * <p>Furthermore you can use method names in the property:</p>
533 * <p>
534 * <code>button.addActionListener((ActionListener)
535 * EventHandler.create(ActionListener.class, textField, "setText", "getSource.getClass.getName");
536 * <code>
537 * </p>
538 *
539 * <p>Finally you can mix names:</p>
540 * <p>
541 * <code>button.addActionListener((ActionListener)
542 * EventHandler.create(ActionListener.class, textField, "setText", "source.getClass.name");
543 * <code>
544 * </p>
545 *
546 * <p>A call to this method is equivalent to:
547 * <code>create(listenerInterface, target, action, null, null)</code>
548 * </p>
549 *
550 * @param listenerInterface Listener interface to implement.
551 * @param target Object to invoke action on.
552 * @param action Target property or method to invoke.
553 * @param eventPropertyName Name of property to extract from event.
554 * @return A constructed proxy object.
555 */
556 public static <T> T create(Class<T> listenerInterface, Object target,
557 String action, String eventPropertyName)
558 {
559 return create(listenerInterface, target, action, eventPropertyName, null);
560 }
561
562 /**
563 * <p>Constructs an implementation of <code>listenerInterface</code>
564 * to dispatch events.</p>
565 *
566 * <p>Besides the functionality described for {@link create(Class, Object, String)}
567 * and {@link create(Class, Object, String, String)} this method allows you
568 * to filter the listener method that should have an effect. Look at these
569 * method's documentation for more information about the <code>EventHandler</code>'s
570 * usage.</p>
571 *
572 * <p>If you want to call <code>dispose</code> on a <code>JFrame</code> instance
573 * when the <code>WindowListener.windowClosing()</code> method was invoked use
574 * the following code:</p>
575 * <p>
576 * <code>
577 * EventHandler.create(WindowListener.class, jframeInstance, "dispose", null, "windowClosing");
578 * </code>
579 * </p>
580 *
581 * <p>A <code>NullPointerException</code> is thrown if the <code>listenerInterface</code>
582 * or <code>target</code> argument are <code>null</code>.
583 *
584 * @param listenerInterface Listener interface to implement.
585 * @param target Object to invoke action on.
586 * @param action Target method name to invoke.
587 * @param eventPropertyName Name of property to extract from event.
588 * @param listenerMethodName Listener method to implement.
589 * @return A constructed proxy object.
590 */
591 public static <T> T create(Class<T> listenerInterface, Object target,
592 String action, String eventPropertyName,
593 String listenerMethodName)
594 {
595 // Create EventHandler instance
596 EventHandler eh = new EventHandler(target, action, eventPropertyName,
597 listenerMethodName);
598
599 // Create proxy object passing in the event handler
600 Object proxy = Proxy.newProxyInstance(listenerInterface.getClassLoader(),
601 new Class<?>[] {listenerInterface},
602 eh);
603
604 return (T) proxy;
605 }
606 }