| // 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 1.10 2002/04/22 01:00:13 dbrownell Exp $ |
| |
| package org.xml.sax.helpers; |
| |
| import java.io.BufferedReader; |
| import java.io.InputStream; |
| import java.io.InputStreamReader; |
| import org.xml.sax.SAXException; |
| import org.xml.sax.XMLReader; |
| |
| |
| /** |
| * 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... |
| |
| // 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> |
| * |
| * @param className the name of the class that should be instantiated. |
| * |
| * <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); |
| } |
| } |
| } |