Java > Open Source Codes > com > sun > org > apache > xerces > internal > dom > ObjectFactory


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55
56
57 package com.sun.org.apache.xerces.internal.dom;
58
59 import java.io.InputStream ;
60 import java.io.IOException ;
61 import java.io.File ;
62 import java.io.FileInputStream ;
63
64 import java.util.Properties ;
65 import java.io.BufferedReader ;
66 import java.io.InputStreamReader ;
67
68 /**
69  * This class is duplicated for each JAXP subpackage so keep it in sync.
70  * It is package private and therefore is not exposed as part of the JAXP
71  * API.
72  * <p>
73  * This code is designed to implement the JAXP 1.1 spec pluggability
74  * feature and is designed to run on JDK version 1.1 and
75  * later, and to compile on JDK 1.2 and onward.
76  * The code also runs both as part of an unbundled jar file and
77  * when bundled as part of the JDK.
78  * <p>
79  *
80  * @version $Id: ObjectFactory.java,v 1.3 2004/05/08 11:07:40 vk112360 Exp $
81  */
82 class ObjectFactory {
83
84     //
85 // Constants
86 //
87
88     // name of default properties file to look for in JDK's jre/lib directory
89 private static final String DEFAULT_PROPERTIES_FILENAME = "xerces.properties";
90
91     /** Set to true for debugging */
92     private static final boolean DEBUG = false;
93
94     /**
95      * Default columns per line.
96      */
97     private static final int DEFAULT_LINE_LENGTH = 80;
98
99     /** cache the contents of the xerces.properties file.
100      * Until an attempt has been made to read this file, this will
101      * be null; if the file does not exist or we encounter some other error
102      * during the read, this will be empty.
103      */
104     private static Properties fXercesProperties = null;
105
106     /***
107      * Cache the time stamp of the xerces.properties file so
108      * that we know if it's been modified and can invalidate
109      * the cache when necessary.
110      */
111     private static long fLastModified = -1;
112
113     //
114 // static methods
115 //
116
117     /**
118      * Finds the implementation Class object in the specified order. The
119      * specified order is the following:
120      * <ol>
121      * <li>query the system property using <code>System.getProperty</code>
122      * <li>read <code>META-INF/services/<i>factoryId</i></code> file
123      * <li>use fallback classname
124      * </ol>
125      *
126      * @return Class object of factory, never null
127      *
128      * @param factoryId Name of the factory to find, same as
129      * a property name
130      * @param fallbackClassName Implementation class name, if nothing else
131      * is found. Use null to mean no fallback.
132      *
133      * @exception ObjectFactory.ConfigurationError
134      */
135     static Object createObject(String factoryId, String fallbackClassName)
136         throws ConfigurationError {
137         return createObject(factoryId, null, fallbackClassName);
138     } // createObject(String,String):Object
139
140     /**
141      * Finds the implementation Class object in the specified order. The
142      * specified order is the following:
143      * <ol>
144      * <li>query the system property using <code>System.getProperty</code>
145      * <li>read <code>$java.home/lib/<i>propertiesFilename</i></code> file
146      * <li>read <code>META-INF/services/<i>factoryId</i></code> file
147      * <li>use fallback classname
148      * </ol>
149      *
150      * @return Class object of factory, never null
151      *
152      * @param factoryId Name of the factory to find, same as
153      * a property name
154      * @param propertiesFilename The filename in the $java.home/lib directory
155      * of the properties file. If none specified,
156      * ${java.home}/lib/xerces.properties will be used.
157      * @param fallbackClassName Implementation class name, if nothing else
158      * is found. Use null to mean no fallback.
159      *
160      * @exception ObjectFactory.ConfigurationError
161      */
162     static Object createObject(String factoryId,
163                                       String propertiesFilename,
164                                       String fallbackClassName)
165         throws ConfigurationError
166     {
167         if (DEBUG) debugPrintln("debug is on");
168
169         SecuritySupport ss = SecuritySupport.getInstance();
170         ClassLoader cl = findClassLoader();
171
172         // Use the system property first
173 try {
174             String systemProp = ss.getSystemProperty(factoryId);
175             if (systemProp != null) {
176                 if (DEBUG) debugPrintln("found system property, value=" + systemProp);
177                 return newInstance(systemProp, cl, true);
178             }
179         } catch (SecurityException se) {
180             // Ignore and continue w/ next location
181 }
182
183         // Try to read from propertiesFilename, or $java.home/lib/xerces.properties
184 String factoryClassName = null;
185         // no properties file name specified; use $JAVA_HOME/lib/xerces.properties:
186 if (propertiesFilename == null) {
187             File propertiesFile = null;
188             boolean propertiesFileExists = false;
189             try {
190                 String javah = ss.getSystemProperty("java.home");
191                 propertiesFilename = javah + File.separator +
192                     "lib" + File.separator + DEFAULT_PROPERTIES_FILENAME;
193                 propertiesFile = new File (propertiesFilename);
194                 propertiesFileExists = ss.getFileExists(propertiesFile);
195             } catch (SecurityException e) {
196                 // try again...
197 fLastModified = -1;
198                 fXercesProperties = null;
199             }
200
201             synchronized (ObjectFactory.class) {
202                 boolean loadProperties = false;
203                 try {
204                     // file existed last time
205 if(fLastModified >= 0) {
206                         if(propertiesFileExists &&
207                                 (fLastModified < (fLastModified = ss.getLastModified(propertiesFile)))) {
208                             loadProperties = true;
209                         } else {
210                             // file has stopped existing...
211 if(!propertiesFileExists) {
212                                 fLastModified = -1;
213                                 fXercesProperties = null;
214                             } // else, file wasn't modified!
215 }
216                     } else {
217                         // file has started to exist:
218 if(propertiesFileExists) {
219                             loadProperties = true;
220                             fLastModified = ss.getLastModified(propertiesFile);
221                         } // else, nothing's changed
222 }
223                     if(loadProperties) {
224                         // must never have attempted to read xerces.properties before (or it's outdeated)
225 fXercesProperties = new Properties ();
226                         FileInputStream fis = ss.getFileInputStream(propertiesFile);
227                         fXercesProperties.load(fis);
228                         fis.close();
229                     }
230                 } catch (Exception x) {
231                     fXercesProperties = null;
232                     fLastModified = -1;
233                     // assert(x instanceof FileNotFoundException
234 // || x instanceof SecurityException)
235 // In both cases, ignore and continue w/ next location
236 }
237             }
238             if(fXercesProperties != null) {
239                 factoryClassName = fXercesProperties.getProperty(factoryId);
240             }
241         } else {
242             try {
243                 FileInputStream fis = ss.getFileInputStream(new File (propertiesFilename));
244                 Properties props = new Properties ();
245                 props.load(fis);
246                 fis.close();
247                 factoryClassName = props.getProperty(factoryId);
248             } catch (Exception x) {
249                 // assert(x instanceof FileNotFoundException
250 // || x instanceof SecurityException)
251 // In both cases, ignore and continue w/ next location
252 }
253         }
254         if (factoryClassName != null) {
255             if (DEBUG) debugPrintln("found in " + propertiesFilename + ", value=" + factoryClassName);
256             return newInstance(factoryClassName, cl, true);
257         }
258
259         // Try Jar Service Provider Mechanism
260 Object provider = findJarServiceProvider(factoryId);
261         if (provider != null) {
262             return provider;
263         }
264
265         if (fallbackClassName == null) {
266             throw new ConfigurationError(
267                 "Provider for " + factoryId + " cannot be found", null);
268         }
269
270         if (DEBUG) debugPrintln("using fallback, value=" + fallbackClassName);
271         return newInstance(fallbackClassName, cl, true);
272     } // createObject(String,String,String):Object
273
274     //
275 // Private static methods
276 //
277
278     /** Prints a message to standard error if debugging is enabled. */
279     private static void debugPrintln(String msg) {
280         if (DEBUG) {
281             System.err.println("JAXP: " + msg);
282         }
283     } // debugPrintln(String)
284
285     /**
286      * Figure out which ClassLoader to use. For JDK 1.2 and later use
287      * the context ClassLoader.
288      */
289     static ClassLoader findClassLoader()
290         throws ConfigurationError
291     {
292         SecuritySupport ss = SecuritySupport.getInstance();
293
294         // Figure out which ClassLoader to use for loading the provider
295 // class. If there is a Context ClassLoader then use it.
296 ClassLoader context = ss.getContextClassLoader();
297         ClassLoader system = ss.getSystemClassLoader();
298
299         ClassLoader chain = system;
300         while (true) {
301             if (context == chain) {
302                 // Assert: we are on JDK 1.1 or we have no Context ClassLoader
303 // or any Context ClassLoader in chain of system classloader
304 // (including extension ClassLoader) so extend to widest
305 // ClassLoader (always look in system ClassLoader if Xerces
306 // is in boot/extension/system classpath and in current
307 // ClassLoader otherwise); normal classloaders delegate
308 // back to system ClassLoader first so this widening doesn't
309 // change the fact that context ClassLoader will be consulted
310 ClassLoader current = ObjectFactory.class.getClassLoader();
311
312                 chain = system;
313                 while (true) {
314                     if (current == chain) {
315                         // Assert: Current ClassLoader in chain of
316 // boot/extension/system ClassLoaders
317 return system;
318                     }
319                     if (chain == null) {
320                         break;
321                     }
322                     chain = ss.getParentClassLoader(chain);
323                 }
324
325                 // Assert: Current ClassLoader not in chain of
326 // boot/extension/system ClassLoaders
327 return current;
328             }
329
330             if (chain == null) {
331                 // boot ClassLoader reached
332 break;
333             }
334
335             // Check for any extension ClassLoaders in chain up to
336 // boot ClassLoader
337 chain = ss.getParentClassLoader(chain);
338         };
339
340         // Assert: Context ClassLoader not in chain of
341 // boot/extension/system ClassLoaders
342 return context;
343     } // findClassLoader():ClassLoader
344
345     /**
346      * Create an instance of a class using the specified ClassLoader
347      */
348     static Object newInstance(String className, ClassLoader cl,
349                                       boolean doFallback)
350         throws ConfigurationError
351     {
352         // assert(className != null);
353 try{
354             Class providerClass = findProviderClass(className, cl, doFallback);
355             Object instance = providerClass.newInstance();
356             if (DEBUG) debugPrintln("created new instance of " + providerClass +
357                    " using ClassLoader: " + cl);
358             return instance;
359         } catch (ClassNotFoundException x) {
360             throw new ConfigurationError(
361                 "Provider " + className + " not found", x);
362         } catch (Exception x) {
363             throw new ConfigurationError(
364                 "Provider " + className + " could not be instantiated: " + x,
365                 x);
366         }
367     }
368
369     /**
370      * Find a Class using the specified ClassLoader
371      */
372     static Class findProviderClass(String className, ClassLoader cl,
373                                       boolean doFallback)
374         throws ClassNotFoundException , ConfigurationError
375     {
376         //throw security exception if the calling thread is not allowed to access the package
377 //restrict the access to package as speicified in java.security policy
378 SecurityManager security = System.getSecurityManager();
379         try{
380             if (security != null) {
381                 final int lastDot = className.lastIndexOf(".");
382                 String packageName = className;
383                 if (lastDot != -1) packageName = className.substring(0, lastDot);
384                 security.checkPackageAccess(packageName);
385             }
386         }catch(SecurityException e){
387             throw e ;
388         }
389         Class providerClass;
390         if (cl == null) {
391             // XXX Use the bootstrap ClassLoader. There is no way to
392 // load a class using the bootstrap ClassLoader that works
393 // in both JDK 1.1 and Java 2. However, this should still
394 // work b/c the following should be true:
395 //
396 // (cl == null) iff current ClassLoader == null
397 //
398 // Thus Class.forName(String) will use the current
399 // ClassLoader which will be the bootstrap ClassLoader.
400 providerClass = Class.forName(className);
401         } else {
402             try {
403                 providerClass = cl.loadClass(className);
404             } catch (ClassNotFoundException x) {
405                 if (doFallback) {
406                     // Fall back to current classloader
407 ClassLoader current = ObjectFactory.class.getClassLoader();
408                     if (current == null) {
409                         providerClass = Class.forName(className);
410                     } else if (cl != current) {
411                         cl = current;
412                         providerClass = cl.loadClass(className);
413                     } else {
414                         throw x;
415                     }
416                 } else {
417                     throw x;
418                 }
419             }
420         }
421
422         return providerClass;
423     }
424
425     /*
426      * Try to find provider using Jar Service Provider Mechanism
427      *
428      * @return instance of provider class if found or null
429      */
430     private static Object findJarServiceProvider(String factoryId)
431         throws ConfigurationError
432     {
433         SecuritySupport ss = SecuritySupport.getInstance();
434         String serviceId = "META-INF/services/" + factoryId;
435         InputStream is = null;
436
437         // First try the Context ClassLoader
438 ClassLoader cl = findClassLoader();
439
440         is = ss.getResourceAsStream(cl, serviceId);
441
442         // If no provider found then try the current ClassLoader
443 if (is == null) {
444             ClassLoader current = ObjectFactory.class.getClassLoader();
445             if (cl != current) {
446                 cl = current;
447                 is = ss.getResourceAsStream(cl, serviceId);
448             }
449         }
450
451         if (is == null) {
452             // No provider found
453 return null;
454         }
455
456         if (DEBUG) debugPrintln("found jar resource=" + serviceId +
457                " using ClassLoader: " + cl);
458
459         // Read the service provider name in UTF-8 as specified in
460 // the jar spec. Unfortunately this fails in Microsoft
461 // VJ++, which does not implement the UTF-8
462 // encoding. Theoretically, we should simply let it fail in
463 // that case, since the JVM is obviously broken if it
464 // doesn't support such a basic standard. But since there
465 // are still some users attempting to use VJ++ for
466 // development, we have dropped in a fallback which makes a
467 // second attempt using the platform's default encoding. In
468 // VJ++ this is apparently ASCII, which is a subset of
469 // UTF-8... and since the strings we'll be reading here are
470 // also primarily limited to the 7-bit ASCII range (at
471 // least, in English versions), this should work well
472 // enough to keep us on the air until we're ready to
473 // officially decommit from VJ++. [Edited comment from
474 // jkesselm]
475 BufferedReader rd;
476         try {
477             rd = new BufferedReader (new InputStreamReader (is, "UTF-8"), DEFAULT_LINE_LENGTH);
478         } catch (java.io.UnsupportedEncodingException e) {
479             rd = new BufferedReader (new InputStreamReader (is), DEFAULT_LINE_LENGTH);
480         }
481
482         String factoryClassName = null;
483         try {
484             // XXX Does not handle all possible input as specified by the
485 // Jar Service Provider specification
486 factoryClassName = rd.readLine();
487             rd.close();
488         } catch (IOException x) {
489             // No provider found
490 return null;
491         }
492
493         if (factoryClassName != null &&
494             ! "".equals(factoryClassName)) {
495             if (DEBUG) debugPrintln("found in resource, value="
496                    + factoryClassName);
497
498             // Note: here we do not want to fall back to the current
499 // ClassLoader because we want to avoid the case where the
500 // resource file was found using one ClassLoader and the
501 // provider class was instantiated using a different one.
502 return newInstance(factoryClassName, cl, false);
503         }
504
505         // No provider found
506 return null;
507     }
508
509     //
510 // Classes
511 //
512
513     /**
514      * A configuration error.
515      */
516     static class ConfigurationError
517         extends Error {
518
519         //
520 // Data
521 //
522
523         /** Exception. */
524         private Exception exception;
525
526         //
527 // Constructors
528 //
529
530         /**
531          * Construct a new instance with the specified detail string and
532          * exception.
533          */
534         ConfigurationError(String msg, Exception x) {
535             super(msg);
536             this.exception = x;
537         } // <init>(String,Exception)
538
539         //
540 // methods
541 //
542
543         /** Returns the exception associated to this error. */
544         Exception getException() {
545             return exception;
546         } // getException():Exception
547
548     } // class ConfigurationError
549
550 } // class ObjectFactory
551

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