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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 1.10 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 java.nio.charset.StandardCharsets;
import org.xml.sax.SAXException;
import org.xml.sax.XMLReader;


/**
 * Factory for creating an XML reader.
 *
 * 
* This module, both source code and documentation, is in the * Public Domain, and comes with NO WARRANTY. * See http://www.saxproject.org * for further information. *
* *

This class contains static methods for creating an XML reader * from an explicit class name, or based on runtime defaults:

* *
 * try {
 *   XMLReader myReader = XMLReaderFactory.createXMLReader();
 * } catch (SAXException e) {
 *   System.err.println(e.getMessage());
 * }
 * 
* *

Note to Distributions bundled with parsers: * You should modify the implementation of the no-arguments * createXMLReader 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 org.xml.sax.driver so * those configuration mechanisms would see it.

* * @since SAX 2.0 * @author David Megginson, David Brownell * @version 2.0.1 (sax2r2) */ final public class XMLReaderFactory { /** * Private constructor. * *

This constructor prevents the class from being instantiated.

*/ 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:

    * *
  • If the system property org.xml.sax.driver * has a value, that is used as an XMLReader class name.
  • * *
  • The JAR "Services API" is used to look for a class name * in the META-INF/services/org.xml.sax.driver file in * jarfiles available to the runtime.
  • * *
  • 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.
  • * *
  • 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 org.xml.sax.parser system * property will often be usable.)
  • * *
* *

In environments such as small embedded systems, which can not * support that flexibility, other mechanisms to determine the default * may be used.

* *

Note that many Java environments allow system properties to be * initialized on a command line. This means that in most cases * 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. *

* * @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, StandardCharsets.UTF_8)); 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. * *

Given a class name, this method attempts to load * and instantiate the class as an XML reader.

* * @param className the name of the class that should be instantiated. * *

Note that this method will not be usable in environments where * the caller (perhaps an applet) is not permitted to load classes * dynamically.

* * @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); } } }




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