org.xml.sax.helpers.XMLReaderFactory Maven / Gradle / Ivy
// 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);
}
}
}