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// XMLReaderFactory.java - factory for creating a new reader. // http://www.saxproject.org // Written by David Megginson // and by David Brownell // NO WARRANTY! This class is in the Public Domain. // $Id: XMLReaderFactory.java,v 1.2.2.1 2005/07/31 22:48:08 jeffsuttor Exp $ package org.xml.sax.helpers; import java.io.BufferedReader; import java.io.InputStream; import java.io.InputStreamReader; import org.xml.sax.XMLReader; import org.xml.sax.SAXException; /** * Factory for creating an XML reader. * * <blockquote> * <em>This module, both source code and documentation, is in the * Public Domain, and comes with <strong>NO WARRANTY</strong>.</em> * See <a href='http://www.saxproject.org'>http://www.saxproject.org</a> * for further information. * </blockquote> * * <p>This class contains static methods for creating an XML reader * from an explicit class name, or based on runtime defaults:</p> * * <pre> * try { * XMLReader myReader = XMLReaderFactory.createXMLReader(); * } catch (SAXException e) { * System.err.println(e.getMessage()); * } * </pre> * * <p><strong>Note to Distributions bundled with parsers:</strong> * You should modify the implementation of the no-arguments * <em>createXMLReader</em> to handle cases where the external * configuration mechanisms aren't set up. That method should do its * best to return a parser when one is in the class path, even when * nothing bound its class name to <code>org.xml.sax.driver</code> so * those configuration mechanisms would see it.</p> * * @since SAX 2.0 * @author David Megginson, David Brownell * @version 2.0.1 (sax2r2) */ final public class XMLReaderFactory { /** * Private constructor. * * <p>This constructor prevents the class from being instantiated.</p> */ private XMLReaderFactory () { } private static final String property = "org.xml.sax.driver"; /** * Attempt to create an XMLReader from system defaults. * In environments which can support it, the name of the XMLReader * class is determined by trying each these options in order, and * using the first one which succeeds:</p> <ul> * * <li>If the system property <code>org.xml.sax.driver</code> * has a value, that is used as an XMLReader class name. </li> * * <li>The JAR "Services API" is used to look for a class name * in the <em>META-INF/services/org.xml.sax.driver</em> file in * jarfiles available to the runtime.</li> * * <li> SAX parser distributions are strongly encouraged to provide * a default XMLReader class name that will take effect only when * previous options (on this list) are not successful.</li> * * <li>Finally, if {@link ParserFactory#makeParser()} can * return a system default SAX1 parser, that parser is wrapped in * a {@link ParserAdapter}. (This is a migration aid for SAX1 * environments, where the <code>org.xml.sax.parser</code> system * property will often be usable.) </li> * * </ul> * * <p> In environments such as small embedded systems, which can not * support that flexibility, other mechanisms to determine the default * may be used. </p> * * <p>Note that many Java environments allow system properties to be * initialized on a command line. This means that <em>in most cases</em> * setting a good value for that property ensures that calls to this * method will succeed, except when security policies intervene. * This will also maximize application portability to older SAX * environments, with less robust implementations of this method. * </p> * * @return A new XMLReader. * @exception org.xml.sax.SAXException If no default XMLReader class * can be identified and instantiated. * @see #createXMLReader(java.lang.String) */ public static XMLReader createXMLReader () throws SAXException { String className = null; ClassLoader loader = NewInstance.getClassLoader (); // 1. try the JVM-instance-wide system property try { className = System.getProperty (property); } catch (RuntimeException e) { /* normally fails for applets */ } // 2. if that fails, try META-INF/services/ if (className == null) { try { String service = "META-INF/services/" + property; InputStream in; BufferedReader reader; if (loader == null) in = ClassLoader.getSystemResourceAsStream (service); else in = loader.getResourceAsStream (service); if (in != null) { reader = new BufferedReader ( new InputStreamReader (in, "UTF8")); className = reader.readLine (); in.close (); } } catch (Exception e) { } } // 3. Distro-specific fallback if (className == null) { // BEGIN DISTRIBUTION-SPECIFIC // EXAMPLE: // className = "com.example.sax.XmlReader"; // or a $JAVA_HOME/jre/lib/*properties setting... className = "com.sun.org.apache.xerces.internal.parsers.SAXParser"; // END DISTRIBUTION-SPECIFIC } // do we know the XMLReader implementation class yet? if (className != null) return loadClass (loader, className); // 4. panic -- adapt any SAX1 parser try { return new ParserAdapter (ParserFactory.makeParser ()); } catch (Exception e) { throw new SAXException ("Can't create default XMLReader; " + "is system property org.xml.sax.driver set?"); } } /** * Attempt to create an XML reader from a class name. * * <p>Given a class name, this method attempts to load * and instantiate the class as an XML reader.</p> * * <p>Note that this method will not be usable in environments where * the caller (perhaps an applet) is not permitted to load classes * dynamically.</p> * * @return A new XML reader. * @exception org.xml.sax.SAXException If the class cannot be * loaded, instantiated, and cast to XMLReader. * @see #createXMLReader() */ public static XMLReader createXMLReader (String className) throws SAXException { return loadClass (NewInstance.getClassLoader (), className); } private static XMLReader loadClass (ClassLoader loader, String className) throws SAXException { try { return (XMLReader) NewInstance.newInstance (loader, className); } catch (ClassNotFoundException e1) { throw new SAXException("SAX2 driver class " + className + " not found", e1); } catch (IllegalAccessException e2) { throw new SAXException("SAX2 driver class " + className + " found but cannot be loaded", e2); } catch (InstantiationException e3) { throw new SAXException("SAX2 driver class " + className + " loaded but cannot be instantiated (no empty public constructor?)", e3); } catch (ClassCastException e4) { throw new SAXException("SAX2 driver class " + className + " does not implement XMLReader", e4); } } }