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 }