Java > Open Source Codes > org > apache > xerces > dom > ObjectFactory


1 /*
2  * Copyright 2001-2005 The Apache Software Foundation.
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  * http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16
17 package org.apache.xerces.dom;
18
19 import java.io.InputStream ;
20 import java.io.IOException ;
21 import java.io.File ;
22 import java.io.FileInputStream ;
23
24 import java.util.Properties ;
25 import java.io.BufferedReader ;
26 import java.io.InputStreamReader ;
27
28 /**
29  * This class is duplicated for each JAXP subpackage so keep it in sync.
30  * It is package private and therefore is not exposed as part of the JAXP
31  * API.
32  * <p>
33  * This code is designed to implement the JAXP 1.1 spec pluggability
34  * feature and is designed to run on JDK version 1.1 and
35  * later, and to compile on JDK 1.2 and onward.
36  * The code also runs both as part of an unbundled jar file and
37  * when bundled as part of the JDK.
38  * <p>
39  *
40  * @xerces.internal
41  *
42  * @version $Id: ObjectFactory.java,v 1.11 2005/04/18 04:14:19 mrglavas Exp $
43  */
44 final class ObjectFactory {
45
46     //
47 // Constants
48 //
49
50     // name of default properties file to look for in JDK's jre/lib directory
51 private static final String DEFAULT_PROPERTIES_FILENAME = "xerces.properties";
52
53     /** Set to true for debugging */
54     private static final boolean DEBUG = false;
55
56     /**
57      * Default columns per line.
58      */
59     private static final int DEFAULT_LINE_LENGTH = 80;
60
61     /** cache the contents of the xerces.properties file.
62      * Until an attempt has been made to read this file, this will
63      * be null; if the file does not exist or we encounter some other error
64      * during the read, this will be empty.
65      */
66     private static Properties fXercesProperties = null;
67
68     /***
69      * Cache the time stamp of the xerces.properties file so
70      * that we know if it's been modified and can invalidate
71      * the cache when necessary.
72      */
73     private static long fLastModified = -1;
74
75     //
76 // static methods
77 //
78
79     /**
80      * Finds the implementation Class object in the specified order. The
81      * specified order is the following:
82      * <ol>
83      * <li>query the system property using <code>System.getProperty</code>
84      * <li>read <code>META-INF/services/<i>factoryId</i></code> file
85      * <li>use fallback classname
86      * </ol>
87      *
88      * @return Class object of factory, never null
89      *
90      * @param factoryId Name of the factory to find, same as
91      * a property name
92      * @param fallbackClassName Implementation class name, if nothing else
93      * is found. Use null to mean no fallback.
94      *
95      * @exception ObjectFactory.ConfigurationError
96      */
97     static Object createObject(String factoryId, String fallbackClassName)
98         throws ConfigurationError {
99         return createObject(factoryId, null, fallbackClassName);
100     } // createObject(String,String):Object
101
102     /**
103      * Finds the implementation Class object in the specified order. The
104      * specified order is the following:
105      * <ol>
106      * <li>query the system property using <code>System.getProperty</code>
107      * <li>read <code>$java.home/lib/<i>propertiesFilename</i></code> file
108      * <li>read <code>META-INF/services/<i>factoryId</i></code> file
109      * <li>use fallback classname
110      * </ol>
111      *
112      * @return Class object of factory, never null
113      *
114      * @param factoryId Name of the factory to find, same as
115      * a property name
116      * @param propertiesFilename The filename in the $java.home/lib directory
117      * of the properties file. If none specified,
118      * ${java.home}/lib/xerces.properties will be used.
119      * @param fallbackClassName Implementation class name, if nothing else
120      * is found. Use null to mean no fallback.
121      *
122      * @exception ObjectFactory.ConfigurationError
123      */
124     static Object createObject(String factoryId,
125                                       String propertiesFilename,
126                                       String fallbackClassName)
127         throws ConfigurationError
128     {
129         if (DEBUG) debugPrintln("debug is on");
130
131         SecuritySupport ss = SecuritySupport.getInstance();
132         ClassLoader cl = findClassLoader();
133
134         // Use the system property first
135 try {
136             String systemProp = ss.getSystemProperty(factoryId);
137             if (systemProp != null) {
138                 if (DEBUG) debugPrintln("found system property, value=" + systemProp);
139                 return newInstance(systemProp, cl, true);
140             }
141         } catch (SecurityException se) {
142             // Ignore and continue w/ next location
143 }
144
145         // Try to read from propertiesFilename, or $java.home/lib/xerces.properties
146 String factoryClassName = null;
147         // no properties file name specified; use $JAVA_HOME/lib/xerces.properties:
148 if (propertiesFilename == null) {
149             File propertiesFile = null;
150             boolean propertiesFileExists = false;
151             try {
152                 String javah = ss.getSystemProperty("java.home");
153                 propertiesFilename = javah + File.separator +
154                     "lib" + File.separator + DEFAULT_PROPERTIES_FILENAME;
155                 propertiesFile = new File (propertiesFilename);
156                 propertiesFileExists = ss.getFileExists(propertiesFile);
157             } catch (SecurityException e) {
158                 // try again...
159 fLastModified = -1;
160                 fXercesProperties = null;
161             }
162             
163             synchronized (ObjectFactory.class) {
164                 boolean loadProperties = false;
165                 FileInputStream fis = null;
166                 try {
167                     // file existed last time
168 if(fLastModified >= 0) {
169                         if(propertiesFileExists &&
170                                 (fLastModified < (fLastModified = ss.getLastModified(propertiesFile)))) {
171                             loadProperties = true;
172                         } else {
173                             // file has stopped existing...
174 if(!propertiesFileExists) {
175                                 fLastModified = -1;
176                                 fXercesProperties = null;
177                             } // else, file wasn't modified!
178 }
179                     } else {
180                         // file has started to exist:
181 if(propertiesFileExists) {
182                             loadProperties = true;
183                             fLastModified = ss.getLastModified(propertiesFile);
184                         } // else, nothing's changed
185 }
186                     if(loadProperties) {
187                         // must never have attempted to read xerces.properties before (or it's outdeated)
188 fXercesProperties = new Properties ();
189                         fis = ss.getFileInputStream(propertiesFile);
190                         fXercesProperties.load(fis);
191                     }
192                 } catch (Exception x) {
193                     fXercesProperties = null;
194                     fLastModified = -1;
195                     // assert(x instanceof FileNotFoundException
196 // || x instanceof SecurityException)
197 // In both cases, ignore and continue w/ next location
198 }
199                 finally {
200                     // try to close the input stream if one was opened.
201 if (fis != null) {
202                         try {
203                             fis.close();
204                         }
205                         // Ignore the exception.
206 catch (IOException exc) {}
207                     }
208                 }
209             }
210             if(fXercesProperties != null) {
211                 factoryClassName = fXercesProperties.getProperty(factoryId);
212             }
213         } else {
214             FileInputStream fis = null;
215             try {
216                 fis = ss.getFileInputStream(new File (propertiesFilename));
217                 Properties props = new Properties ();
218                 props.load(fis);
219                 factoryClassName = props.getProperty(factoryId);
220             } catch (Exception x) {
221                 // assert(x instanceof FileNotFoundException
222 // || x instanceof SecurityException)
223 // In both cases, ignore and continue w/ next location
224 }
225             finally {
226                 // try to close the input stream if one was opened.
227 if (fis != null) {
228                     try {
229                         fis.close();
230                     }
231                     // Ignore the exception.
232 catch (IOException exc) {}
233                 }
234             }
235         }
236         if (factoryClassName != null) {
237             if (DEBUG) debugPrintln("found in " + propertiesFilename + ", value=" + factoryClassName);
238             return newInstance(factoryClassName, cl, true);
239         }
240
241         // Try Jar Service Provider Mechanism
242 Object provider = findJarServiceProvider(factoryId);
243         if (provider != null) {
244             return provider;
245         }
246
247         if (fallbackClassName == null) {
248             throw new ConfigurationError(
249                 "Provider for " + factoryId + " cannot be found", null);
250         }
251
252         if (DEBUG) debugPrintln("using fallback, value=" + fallbackClassName);
253         return newInstance(fallbackClassName, cl, true);
254     } // createObject(String,String,String):Object
255
256     //
257 // Private static methods
258 //
259
260     /** Prints a message to standard error if debugging is enabled. */
261     private static void debugPrintln(String msg) {
262         if (DEBUG) {
263             System.err.println("JAXP: " + msg);
264         }
265     } // debugPrintln(String)
266
267     /**
268      * Figure out which ClassLoader to use. For JDK 1.2 and later use
269      * the context ClassLoader.
270      */
271     static ClassLoader findClassLoader()
272         throws ConfigurationError
273     {
274         SecuritySupport ss = SecuritySupport.getInstance();
275
276         // Figure out which ClassLoader to use for loading the provider
277 // class. If there is a Context ClassLoader then use it.
278 ClassLoader context = ss.getContextClassLoader();
279         ClassLoader system = ss.getSystemClassLoader();
280
281         ClassLoader chain = system;
282         while (true) {
283             if (context == chain) {
284                 // Assert: we are on JDK 1.1 or we have no Context ClassLoader
285 // or any Context ClassLoader in chain of system classloader
286 // (including extension ClassLoader) so extend to widest
287 // ClassLoader (always look in system ClassLoader if Xerces
288 // is in boot/extension/system classpath and in current
289 // ClassLoader otherwise); normal classloaders delegate
290 // back to system ClassLoader first so this widening doesn't
291 // change the fact that context ClassLoader will be consulted
292 ClassLoader current = ObjectFactory.class.getClassLoader();
293
294                 chain = system;
295                 while (true) {
296                     if (current == chain) {
297                         // Assert: Current ClassLoader in chain of
298 // boot/extension/system ClassLoaders
299 return system;
300                     }
301                     if (chain == null) {
302                         break;
303                     }
304                     chain = ss.getParentClassLoader(chain);
305                 }
306
307                 // Assert: Current ClassLoader not in chain of
308 // boot/extension/system ClassLoaders
309 return current;
310             }
311
312             if (chain == null) {
313                 // boot ClassLoader reached
314 break;
315             }
316
317             // Check for any extension ClassLoaders in chain up to
318 // boot ClassLoader
319 chain = ss.getParentClassLoader(chain);
320         };
321
322         // Assert: Context ClassLoader not in chain of
323 // boot/extension/system ClassLoaders
324 return context;
325     } // findClassLoader():ClassLoader
326
327     /**
328      * Create an instance of a class using the specified ClassLoader
329      */
330     static Object newInstance(String className, ClassLoader cl,
331                                       boolean doFallback)
332         throws ConfigurationError
333     {
334         // assert(className != null);
335 try{
336             Class providerClass = findProviderClass(className, cl, doFallback);
337             Object instance = providerClass.newInstance();
338             if (DEBUG) debugPrintln("created new instance of " + providerClass +
339                    " using ClassLoader: " + cl);
340             return instance;
341         } catch (ClassNotFoundException x) {
342             throw new ConfigurationError(
343                 "Provider " + className + " not found", x);
344         } catch (Exception x) {
345             throw new ConfigurationError(
346                 "Provider " + className + " could not be instantiated: " + x,
347                 x);
348         }
349     }
350
351     /**
352      * Find a Class using the specified ClassLoader
353      */
354     static Class findProviderClass(String className, ClassLoader cl,
355                                       boolean doFallback)
356         throws ClassNotFoundException , ConfigurationError
357     {
358         //throw security exception if the calling thread is not allowed to access the package
359 //restrict the access to package as speicified in java.security policy
360 SecurityManager security = System.getSecurityManager();
361         if (security != null) {
362             final int lastDot = className.lastIndexOf(".");
363             String packageName = className;
364             if (lastDot != -1) packageName = className.substring(0, lastDot);
365             security.checkPackageAccess(packageName);
366         }
367         Class providerClass;
368         if (cl == null) {
369             // XXX Use the bootstrap ClassLoader. There is no way to
370 // load a class using the bootstrap ClassLoader that works
371 // in both JDK 1.1 and Java 2. However, this should still
372 // work b/c the following should be true:
373 //
374 // (cl == null) iff current ClassLoader == null
375 //
376 // Thus Class.forName(String) will use the current
377 // ClassLoader which will be the bootstrap ClassLoader.
378 providerClass = Class.forName(className);
379         } else {
380             try {
381                 providerClass = cl.loadClass(className);
382             } catch (ClassNotFoundException x) {
383                 if (doFallback) {
384                     // Fall back to current classloader
385 ClassLoader current = ObjectFactory.class.getClassLoader();
386                     if (current == null) {
387                         providerClass = Class.forName(className);
388                     } else if (cl != current) {
389                         cl = current;
390                         providerClass = cl.loadClass(className);
391                     } else {
392                         throw x;
393                     }
394                 } else {
395                     throw x;
396                 }
397             }
398         }
399
400         return providerClass;
401     }
402
403     /*
404      * Try to find provider using Jar Service Provider Mechanism
405      *
406      * @return instance of provider class if found or null
407      */
408     private static Object findJarServiceProvider(String factoryId)
409         throws ConfigurationError
410     {
411         SecuritySupport ss = SecuritySupport.getInstance();
412         String serviceId = "META-INF/services/" + factoryId;
413         InputStream is = null;
414
415         // First try the Context ClassLoader
416 ClassLoader cl = findClassLoader();
417
418         is = ss.getResourceAsStream(cl, serviceId);
419
420         // If no provider found then try the current ClassLoader
421 if (is == null) {
422             ClassLoader current = ObjectFactory.class.getClassLoader();
423             if (cl != current) {
424                 cl = current;
425                 is = ss.getResourceAsStream(cl, serviceId);
426             }
427         }
428
429         if (is == null) {
430             // No provider found
431 return null;
432         }
433
434         if (DEBUG) debugPrintln("found jar resource=" + serviceId +
435                " using ClassLoader: " + cl);
436
437         // Read the service provider name in UTF-8 as specified in
438 // the jar spec. Unfortunately this fails in Microsoft
439 // VJ++, which does not implement the UTF-8
440 // encoding. Theoretically, we should simply let it fail in
441 // that case, since the JVM is obviously broken if it
442 // doesn't support such a basic standard. But since there
443 // are still some users attempting to use VJ++ for
444 // development, we have dropped in a fallback which makes a
445 // second attempt using the platform's default encoding. In
446 // VJ++ this is apparently ASCII, which is a subset of
447 // UTF-8... and since the strings we'll be reading here are
448 // also primarily limited to the 7-bit ASCII range (at
449 // least, in English versions), this should work well
450 // enough to keep us on the air until we're ready to
451 // officially decommit from VJ++. [Edited comment from
452 // jkesselm]
453 BufferedReader rd;
454         try {
455             rd = new BufferedReader (new InputStreamReader (is, "UTF-8"), DEFAULT_LINE_LENGTH);
456         } catch (java.io.UnsupportedEncodingException e) {
457             rd = new BufferedReader (new InputStreamReader (is), DEFAULT_LINE_LENGTH);
458         }
459
460         String factoryClassName = null;
461         try {
462             // XXX Does not handle all possible input as specified by the
463 // Jar Service Provider specification
464 factoryClassName = rd.readLine();
465         } catch (IOException x) {
466             // No provider found
467 return null;
468         }
469         finally {
470             try {
471                 // try to close the reader.
472 rd.close();
473             }
474             // Ignore the exception.
475 catch (IOException exc) {}
476         }
477
478         if (factoryClassName != null &&
479             ! "".equals(factoryClassName)) {
480             if (DEBUG) debugPrintln("found in resource, value="
481                    + factoryClassName);
482
483             // Note: here we do not want to fall back to the current
484 // ClassLoader because we want to avoid the case where the
485 // resource file was found using one ClassLoader and the
486 // provider class was instantiated using a different one.
487 return newInstance(factoryClassName, cl, false);
488         }
489
490         // No provider found
491 return null;
492     }
493
494     //
495 // Classes
496 //
497
498     /**
499      * A configuration error.
500      */
501     static final class ConfigurationError
502         extends Error {
503
504         /** Serialization version. */
505         static final long serialVersionUID = 1914065341994951202L;
506         
507         //
508 // Data
509 //
510
511         /** Exception. */
512         private Exception exception;
513
514         //
515 // Constructors
516 //
517
518         /**
519          * Construct a new instance with the specified detail string and
520          * exception.
521          */
522         ConfigurationError(String msg, Exception x) {
523             super(msg);
524             this.exception = x;
525         } // <init>(String,Exception)
526
527         //
528 // methods
529 //
530
531         /** Returns the exception associated to this error. */
532         Exception getException() {
533             return exception;
534         } // getException():Exception
535
536     } // class ConfigurationError
537
538 } // class ObjectFactory
539

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