libjava/external/sax/org/xml/sax/helpers/XMLReaderFactory.java

   1 // XMLReaderFactory.java - factory for creating a new reader.
   2 // http://www.saxproject.org
   3 // Written by David Megginson
   4 // and by David Brownell
   5 // NO WARRANTY!  This class is in the Public Domain.
   6 // $Id: XMLReaderFactory.java,v 1.1 2005/02/02 00:41:54 tromey Exp $
   7
   8 package org.xml.sax.helpers;
   9 import java.io.BufferedReader;
  10 import java.io.InputStream;
  11 import java.io.InputStreamReader;
  12 import org.xml.sax.XMLReader;
  13 import org.xml.sax.SAXException;
  14
  15
  16 /**
  17  * Factory for creating an XML reader.
  18  *
  19  * <blockquote>
  20  * <em>This module, both source code and documentation, is in the
  21  * Public Domain, and comes with <strong>NO WARRANTY</strong>.</em>
  22  * See <a href='http://www.saxproject.org'>http://www.saxproject.org</a>
  23  * for further information.
  24  * </blockquote>
  25  *
  26  * <p>This class contains static methods for creating an XML reader
  27  * from an explicit class name, or based on runtime defaults:</p>
  28  *
  29  * <pre>
  30  * try {
  31  *   XMLReader myReader = XMLReaderFactory.createXMLReader();
  32  * } catch (SAXException e) {
  33  *   System.err.println(e.getMessage());
  34  * }
  35  * </pre>
  36  *
  37  * <p><strong>Note to Distributions bundled with parsers:</strong>
  38  * You should modify the implementation of the no-arguments
  39  * <em>createXMLReader</em> to handle cases where the external
  40  * configuration mechanisms aren't set up.  That method should do its
  41  * best to return a parser when one is in the class path, even when
  42  * nothing bound its class name to <code>org.xml.sax.driver</code> so
  43  * those configuration mechanisms would see it.</p>
  44  *
  45  * @since SAX 2.0
  46  * @author David Megginson, David Brownell
  47  * @version 2.0.1 (sax2r2)
  48  */
  49 final public class XMLReaderFactory
  50 {
  51     /**
  52      * Private constructor.
  53      *
  54      * <p>This constructor prevents the class from being instantiated.</p>
  55      */
  56     private XMLReaderFactory ()
  57     {
  58     }
  59
  60     private static final String property = "org.xml.sax.driver";
  61
  62     /**
  63      * Attempt to create an XMLReader from system defaults.
  64      * In environments which can support it, the name of the XMLReader
  65      * class is determined by trying each these options in order, and
  66      * using the first one which succeeds:</p> <ul>
  67      *
  68      * <li>If the system property <code>org.xml.sax.driver</code>
  69      * has a value, that is used as an XMLReader class name. </li>
  70      *
  71      * <li>The JAR "Services API" is used to look for a class name
  72      * in the <em>META-INF/services/org.xml.sax.driver</em> file in
  73      * jarfiles available to the runtime.</li>
  74      *
  75      * <li> SAX parser distributions are strongly encouraged to provide
  76      * a default XMLReader class name that will take effect only when
  77      * previous options (on this list) are not successful.</li>
  78      *
  79      * <li>Finally, if {@link ParserFactory#makeParser()} can
  80      * return a system default SAX1 parser, that parser is wrapped in
  81      * a {@link ParserAdapter}.  (This is a migration aid for SAX1
  82      * environments, where the <code>org.xml.sax.parser</code> system
  83      * property will often be usable.) </li>
  84      *
  85      * </ul>
  86      *
  87      * <p> In environments such as small embedded systems, which can not
  88      * support that flexibility, other mechanisms to determine the default
  89      * may be used. </p>
  90      *
  91      * <p>Note that many Java environments allow system properties to be
  92      * initialized on a command line.  This means that <em>in most cases</em>
  93      * setting a good value for that property ensures that calls to this
  94      * method will succeed, except when security policies intervene.
  95      * This will also maximize application portability to older SAX
  96      * environments, with less robust implementations of this method.
  97      * </p>
  98      *
  99      * @return A new XMLReader.
 100      * @exception org.xml.sax.SAXException If no default XMLReader class
 101      *            can be identified and instantiated.
 102      * @see #createXMLReader(java.lang.String)
 103      */
 104     public static XMLReader createXMLReader ()
 105         throws SAXException
 106     {
 107         String          className = null;
 108         ClassLoader     loader = NewInstance.getClassLoader ();
 109
 110         // 1. try the JVM-instance-wide system property
 111         try { className = System.getProperty (property); }
 112         catch (RuntimeException e) { /* normally fails for applets */ }
 113
 114         // 2. if that fails, try META-INF/services/
 115         if (className == null) {
 116             try {
 117                 String          service = "META-INF/services/" + property;
 118                 InputStream     in;
 119                 BufferedReader  reader;
 120
 121                 if (loader == null)
 122                     in = ClassLoader.getSystemResourceAsStream (service);
 123                 else
 124                     in = loader.getResourceAsStream (service);
 125
 126                 if (in != null) {
 127                     reader = new BufferedReader (
 128                             new InputStreamReader (in, "UTF8"));
 129                     className = reader.readLine ();
 130                     in.close ();
 131                 }
 132             } catch (Exception e) {
 133             }
 134         }
 135
 136         // 3. Distro-specific fallback
 137         if (className == null) {
 138 // BEGIN DISTRIBUTION-SPECIFIC
 139
 140             // EXAMPLE:
 141             // className = "com.example.sax.XmlReader";
 142             // or a $JAVA_HOME/jre/lib/*properties setting...
 143
 144 // END DISTRIBUTION-SPECIFIC
 145         }
 146
 147         // do we know the XMLReader implementation class yet?
 148         if (className != null)
 149             return loadClass (loader, className);
 150
 151         // 4. panic -- adapt any SAX1 parser
 152         try {
 153             return new ParserAdapter (ParserFactory.makeParser ());
 154         } catch (Exception e) {
 155             throw new SAXException ("Can't create default XMLReader; "
 156                     + "is system property org.xml.sax.driver set?");
 157         }
 158     }
 159
 160
 161     /**
 162      * Attempt to create an XML reader from a class name.
 163      *
 164      * <p>Given a class name, this method attempts to load
 165      * and instantiate the class as an XML reader.</p>
 166      *
 167      * <p>Note that this method will not be usable in environments where
 168      * the caller (perhaps an applet) is not permitted to load classes
 169      * dynamically.</p>
 170      *
 171      * @return A new XML reader.
 172      * @exception org.xml.sax.SAXException If the class cannot be
 173      *            loaded, instantiated, and cast to XMLReader.
 174      * @see #createXMLReader()
 175      */
 176     public static XMLReader createXMLReader (String className)
 177         throws SAXException
 178     {
 179         return loadClass (NewInstance.getClassLoader (), className);
 180     }
 181
 182     private static XMLReader loadClass (ClassLoader loader, String className)
 183     throws SAXException
 184     {
 185         try {
 186             return (XMLReader) NewInstance.newInstance (loader, className);
 187         } catch (ClassNotFoundException e1) {
 188             throw new SAXException("SAX2 driver class " + className +
 189                                    " not found", e1);
 190         } catch (IllegalAccessException e2) {
 191             throw new SAXException("SAX2 driver class " + className +
 192                                    " found but cannot be loaded", e2);
 193         } catch (InstantiationException e3) {
 194             throw new SAXException("SAX2 driver class " + className +
 195            " loaded but cannot be instantiated (no empty public constructor?)",
 196                                    e3);
 197         } catch (ClassCastException e4) {
 198             throw new SAXException("SAX2 driver class " + className +
 199                                    " does not implement XMLReader", e4);
 200         }
 201     }
 202 }