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


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55
56
57
58 package com.sun.org.apache.xerces.internal.parsers;
59
60 import java.io.InputStream ;
61 import java.io.IOException ;
62 import java.io.File ;
63 import java.io.FileInputStream ;
64
65 import java.util.Properties ;
66 import java.io.BufferedReader ;
67 import java.io.InputStreamReader ;
68
69 /**
70  * This class is duplicated for each JAXP subpackage so keep it in sync.
71  * It is package private and therefore is not exposed as part of the JAXP
72  * API.
73  * <p>
74  * This code is designed to implement the JAXP 1.1 spec pluggability
75  * feature and is designed to run on JDK version 1.1 and
76  * later, and to compile on JDK 1.2 and onward.
77  * The code also runs both as part of an unbundled jar file and
78  * when bundled as part of the JDK.
79  * <p>
80  *
81  * @version $Id: ObjectFactory.java,v 1.3 2004/05/08 11:07:44 vk112360 Exp $
82  */
83 class ObjectFactory {
84
85     //
86 // Constants
87 //
88
89     // name of default properties file to look for in JDK's jre/lib directory
90 private static final String DEFAULT_PROPERTIES_FILENAME = "xerces.properties";
91
92     /** Set to true for debugging */
93     private static final boolean DEBUG = false;
94     
95     /**
96      * Default columns per line.
97      */
98     private static final int DEFAULT_LINE_LENGTH = 80;
99
100     /** cache the contents of the xerces.properties file.
101      * Until an attempt has been made to read this file, this will
102      * be null; if the file does not exist or we encounter some other error
103      * during the read, this will be empty.
104      */
105     private static Properties fXercesProperties = null;
106
107     /***
108      * Cache the time stamp of the xerces.properties file so
109      * that we know if it's been modified and can invalidate
110      * the cache when necessary.
111      */
112     private static long fLastModified = -1;
113
114     //
115 // static methods
116 //
117
118     /**
119      * Finds the implementation Class object in the specified order. The
120      * specified order is the following:
121      * <ol>
122      * <li>query the system property using <code>System.getProperty</code>
123      * <li>read <code>META-INF/services/<i>factoryId</i></code> file
124      * <li>use fallback classname
125      * </ol>
126      *
127      * @return Class object of factory, never null
128      *
129      * @param factoryId Name of the factory to find, same as
130      * a property name
131      * @param fallbackClassName Implementation class name, if nothing else
132      * is found. Use null to mean no fallback.
133      *
134      * @exception ObjectFactory.ConfigurationError
135      */
136     static Object createObject(String factoryId, String fallbackClassName)
137         throws ConfigurationError {
138         return createObject(factoryId, null, fallbackClassName);
139     } // createObject(String,String):Object
140
141     /**
142      * Finds the implementation Class object in the specified order. The
143      * specified order is the following:
144      * <ol>
145      * <li>query the system property using <code>System.getProperty</code>
146      * <li>read <code>$java.home/lib/<i>propertiesFilename</i></code> file
147      * <li>read <code>META-INF/services/<i>factoryId</i></code> file
148      * <li>use fallback classname
149      * </ol>
150      *
151      * @return Class object of factory, never null
152      *
153      * @param factoryId Name of the factory to find, same as
154      * a property name
155      * @param propertiesFilename The filename in the $java.home/lib directory
156      * of the properties file. If none specified,
157      * ${java.home}/lib/xerces.properties will be used.
158      * @param fallbackClassName Implementation class name, if nothing else
159      * is found. Use null to mean no fallback.
160      *
161      * @exception ObjectFactory.ConfigurationError
162      */
163     static Object createObject(String factoryId,
164                                       String propertiesFilename,
165                                       String fallbackClassName)
166         throws ConfigurationError
167     {
168         if (DEBUG) debugPrintln("debug is on");
169
170         SecuritySupport ss = SecuritySupport.getInstance();
171         ClassLoader cl = findClassLoader();
172
173         // Use the system property first
174 try {
175             String systemProp = ss.getSystemProperty(factoryId);
176             if (systemProp != null) {
177                 if (DEBUG) debugPrintln("found system property, value=" + systemProp);
178                 return newInstance(systemProp, cl, true);
179             }
180         } catch (SecurityException se) {
181             // Ignore and continue w/ next location
182 }
183
184         // Try to read from propertiesFilename, or $java.home/lib/xerces.properties
185 String factoryClassName = null;
186         // no properties file name specified; use $JAVA_HOME/lib/xerces.properties:
187 if (propertiesFilename == null) {
188             File propertiesFile = null;
189             boolean propertiesFileExists = false;
190             try {
191                 String javah = ss.getSystemProperty("java.home");
192                 propertiesFilename = javah + File.separator +
193                     "lib" + File.separator + DEFAULT_PROPERTIES_FILENAME;
194                 propertiesFile = new File (propertiesFilename);
195                 propertiesFileExists = ss.getFileExists(propertiesFile);
196             } catch (SecurityException e) {
197                 // try again...
198 fLastModified = -1;
199                 fXercesProperties = null;
200             }
201
202             synchronized (ObjectFactory.class) {
203                 boolean loadProperties = false;
204                 try {
205                     // file existed last time
206 if(fLastModified >= 0) {
207                         if(propertiesFileExists &&
208                                 (fLastModified < (fLastModified = ss.getLastModified(propertiesFile)))) {
209                             loadProperties = true;
210                         } else {
211                             // file has stopped existing...
212 if(!propertiesFileExists) {
213                                 fLastModified = -1;
214                                 fXercesProperties = null;
215                             } // else, file wasn't modified!
216 }
217                     } else {
218                         // file has started to exist:
219 if(propertiesFileExists) {
220                             loadProperties = true;
221                             fLastModified = ss.getLastModified(propertiesFile);
222                         } // else, nothing's changed
223 }
224                     if(loadProperties) {
225                         // must never have attempted to read xerces.properties before (or it's outdeated)
226 fXercesProperties = new Properties ();
227                         FileInputStream fis = ss.getFileInputStream(propertiesFile);
228                         fXercesProperties.load(fis);
229                         fis.close();
230                     }
231                 } catch (Exception x) {
232                     fXercesProperties = null;
233                     fLastModified = -1;
234                     // assert(x instanceof FileNotFoundException
235 // || x instanceof SecurityException)
236 // In both cases, ignore and continue w/ next location
237 }
238             }
239             if(fXercesProperties != null) {
240                 factoryClassName = fXercesProperties.getProperty(factoryId);
241             }
242         } else {
243             try {
244                 FileInputStream fis = ss.getFileInputStream(new File (propertiesFilename));
245                 Properties props = new Properties ();
246                 props.load(fis);
247                 fis.close();
248                 factoryClassName = props.getProperty(factoryId);
249             } catch (Exception x) {
250                 // assert(x instanceof FileNotFoundException
251 // || x instanceof SecurityException)
252 // In both cases, ignore and continue w/ next location
253 }
254         }
255         if (factoryClassName != null) {
256             if (DEBUG) debugPrintln("found in " + propertiesFilename + ", value=" + factoryClassName);
257             return newInstance(factoryClassName, cl, true);
258         }
259
260         // Try Jar Service Provider Mechanism
261 Object provider = findJarServiceProvider(factoryId);
262         if (provider != null) {
263             return provider;
264         }
265
266         if (fallbackClassName == null) {
267             throw new ConfigurationError(
268                 "Provider for " + factoryId + " cannot be found", null);
269         }
270
271         if (DEBUG) debugPrintln("using fallback, value=" + fallbackClassName);
272         return newInstance(fallbackClassName, cl, true);
273     } // createObject(String,String,String):Object
274
275     //
276 // Private static methods
277 //
278
279     /** Prints a message to standard error if debugging is enabled. */
280     private static void debugPrintln(String msg) {
281         if (DEBUG) {
282             System.err.println("JAXP: " + msg);
283         }
284     } // debugPrintln(String)
285
286     /**
287      * Figure out which ClassLoader to use. For JDK 1.2 and later use
288      * the context ClassLoader.
289      */
290     static ClassLoader findClassLoader()
291         throws ConfigurationError
292     {
293         SecuritySupport ss = SecuritySupport.getInstance();
294
295         // Figure out which ClassLoader to use for loading the provider
296 // class. If there is a Context ClassLoader then use it.
297 ClassLoader context = ss.getContextClassLoader();
298         ClassLoader system = ss.getSystemClassLoader();
299
300         ClassLoader chain = system;
301         while (true) {
302             if (context == chain) {
303                 // Assert: we are on JDK 1.1 or we have no Context ClassLoader
304 // or any Context ClassLoader in chain of system classloader
305 // (including extension ClassLoader) so extend to widest
306 // ClassLoader (always look in system ClassLoader if Xerces
307 // is in boot/extension/system classpath and in current
308 // ClassLoader otherwise); normal classloaders delegate
309 // back to system ClassLoader first so this widening doesn't
310 // change the fact that context ClassLoader will be consulted
311 ClassLoader current = ObjectFactory.class.getClassLoader();
312
313                 chain = system;
314                 while (true) {
315                     if (current == chain) {
316                         // Assert: Current ClassLoader in chain of
317 // boot/extension/system ClassLoaders
318 return system;
319                     }
320                     if (chain == null) {
321                         break;
322                     }
323                     chain = ss.getParentClassLoader(chain);
324                 }
325
326                 // Assert: Current ClassLoader not in chain of
327 // boot/extension/system ClassLoaders
328 return current;
329             }
330
331             if (chain == null) {
332                 // boot ClassLoader reached
333 break;
334             }
335
336             // Check for any extension ClassLoaders in chain up to
337 // boot ClassLoader
338 chain = ss.getParentClassLoader(chain);
339         };
340
341         // Assert: Context ClassLoader not in chain of
342 // boot/extension/system ClassLoaders
343 return context;
344     } // findClassLoader():ClassLoader
345
346     /**
347      * Create an instance of a class using the specified ClassLoader
348      */
349     static Object newInstance(String className, ClassLoader cl,
350                                       boolean doFallback)
351         throws ConfigurationError
352     {
353         // assert(className != null);
354 try{
355             Class providerClass = findProviderClass(className, cl, doFallback);
356             Object instance = providerClass.newInstance();
357             if (DEBUG) debugPrintln("created new instance of " + providerClass +
358                    " using ClassLoader: " + cl);
359             return instance;
360         } catch (ClassNotFoundException x) {
361             throw new ConfigurationError(
362                 "Provider " + className + " not found", x);
363         } catch (Exception x) {
364             throw new ConfigurationError(
365                 "Provider " + className + " could not be instantiated: " + x,
366                 x);
367         }
368     }
369
370     /**
371      * Find a Class using the specified ClassLoader
372      */
373     static Class findProviderClass(String className, ClassLoader cl,
374                                       boolean doFallback)
375         throws ClassNotFoundException , ConfigurationError
376     {
377         //throw security exception if the calling thread is not allowed to access the package
378 //restrict the access to package as speicified in java.security policy
379 SecurityManager security = System.getSecurityManager();
380         try{
381             if (security != null) {
382                 final int lastDot = className.lastIndexOf(".");
383                 String packageName = className;
384                 if (lastDot != -1) packageName = className.substring(0, lastDot);
385                 security.checkPackageAccess(packageName);
386             }
387         }catch(SecurityException e){
388             throw e ;
389         }
390         Class providerClass;
391         if (cl == null) {
392             // XXX Use the bootstrap ClassLoader. There is no way to
393 // load a class using the bootstrap ClassLoader that works
394 // in both JDK 1.1 and Java 2. However, this should still
395 // work b/c the following should be true:
396 //
397 // (cl == null) iff current ClassLoader == null
398 //
399 // Thus Class.forName(String) will use the current
400 // ClassLoader which will be the bootstrap ClassLoader.
401 providerClass = Class.forName(className);
402         } else {
403             try {
404                 providerClass = cl.loadClass(className);
405             } catch (ClassNotFoundException x) {
406                 if (doFallback) {
407                     // Fall back to current classloader
408 ClassLoader current = ObjectFactory.class.getClassLoader();
409                     if (current == null) {
410                         providerClass = Class.forName(className);
411                     } else if (cl != current) {
412                         cl = current;
413                         providerClass = cl.loadClass(className);
414                     } else {
415                         throw x;
416                     }
417                 } else {
418                     throw x;
419                 }
420             }
421         }
422
423         return providerClass;
424     }
425
426     /*
427      * Try to find provider using Jar Service Provider Mechanism
428      *
429      * @return instance of provider class if found or null
430      */
431     private static Object findJarServiceProvider(String factoryId)
432         throws ConfigurationError
433     {
434         SecuritySupport ss = SecuritySupport.getInstance();
435         String serviceId = "META-INF/services/" + factoryId;
436         InputStream is = null;
437
438         // First try the Context ClassLoader
439 ClassLoader cl = findClassLoader();
440
441         is = ss.getResourceAsStream(cl, serviceId);
442
443         // If no provider found then try the current ClassLoader
444 if (is == null) {
445             ClassLoader current = ObjectFactory.class.getClassLoader();
446             if (cl != current) {
447                 cl = current;
448                 is = ss.getResourceAsStream(cl, serviceId);
449             }
450         }
451
452         if (is == null) {
453             // No provider found
454 return null;
455         }
456
457         if (DEBUG) debugPrintln("found jar resource=" + serviceId +
458                " using ClassLoader: " + cl);
459
460         // Read the service provider name in UTF-8 as specified in
461 // the jar spec. Unfortunately this fails in Microsoft
462 // VJ++, which does not implement the UTF-8
463 // encoding. Theoretically, we should simply let it fail in
464 // that case, since the JVM is obviously broken if it
465 // doesn't support such a basic standard. But since there
466 // are still some users attempting to use VJ++ for
467 // development, we have dropped in a fallback which makes a
468 // second attempt using the platform's default encoding. In
469 // VJ++ this is apparently ASCII, which is a subset of
470 // UTF-8... and since the strings we'll be reading here are
471 // also primarily limited to the 7-bit ASCII range (at
472 // least, in English versions), this should work well
473 // enough to keep us on the air until we're ready to
474 // officially decommit from VJ++. [Edited comment from
475 // jkesselm]
476 BufferedReader rd;
477         try {
478             rd = new BufferedReader (new InputStreamReader (is, "UTF-8"), DEFAULT_LINE_LENGTH);
479         } catch (java.io.UnsupportedEncodingException e) {
480             rd = new BufferedReader (new InputStreamReader (is), DEFAULT_LINE_LENGTH);
481         }
482
483         String factoryClassName = null;
484         try {
485             // XXX Does not handle all possible input as specified by the
486 // Jar Service Provider specification
487 factoryClassName = rd.readLine();
488             rd.close();
489         } catch (IOException x) {
490             // No provider found
491 return null;
492         }
493
494         if (factoryClassName != null &&
495             ! "".equals(factoryClassName)) {
496             if (DEBUG) debugPrintln("found in resource, value="
497                    + factoryClassName);
498
499             // Note: here we do not want to fall back to the current
500 // ClassLoader because we want to avoid the case where the
501 // resource file was found using one ClassLoader and the
502 // provider class was instantiated using a different one.
503 return newInstance(factoryClassName, cl, false);
504         }
505
506         // No provider found
507 return null;
508     }
509
510     //
511 // Classes
512 //
513
514     /**
515      * A configuration error.
516      */
517     static class ConfigurationError
518         extends Error {
519
520         //
521 // Data
522 //
523
524         /** Exception. */
525         private Exception exception;
526
527         //
528 // Constructors
529 //
530
531         /**
532          * Construct a new instance with the specified detail string and
533          * exception.
534          */
535         ConfigurationError(String msg, Exception x) {
536             super(msg);
537             this.exception = x;
538         } // <init>(String,Exception)
539
540         //
541 // methods
542 //
543
544         /** Returns the exception associated to this error. */
545         Exception getException() {
546             return exception;
547         } // getException():Exception
548
549     } // class ConfigurationError
550
551 } // class ObjectFactory
552

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