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 }