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xml-commons provides an Apache-hosted set of DOM, SAX, and
JAXP interfaces for use in other xml-based projects. Our hope is that we
can standardize on both a common version and packaging scheme for these
critical XML standards interfaces to make the lives of both our developers
and users easier. The External Components portion of xml-commons contains
interfaces that are defined by external standards organizations. For DOM,
that's the W3C; for SAX it's David Megginson and sax.sourceforge.net; for
JAXP it's Sun.
// 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 670295 2008-06-22 01:46:43Z mrglavas $
package org.xml.sax.helpers;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import org.xml.sax.XMLReader;
import org.xml.sax.SAXException;
/**
* 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";
/**
* Default columns per line.
*/
private static final int DEFAULT_LINE_LENGTH = 80;
/**
* 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 = SecuritySupport.getSystemProperty (property); }
catch (Exception e) { /* normally fails for applets */ }
// 2. if that fails, try META-INF/services/
if (className == null || className.length() == 0) {
String service = "META-INF/services/" + property;
InputStream is = null;
className = null;
// First try the Context ClassLoader
ClassLoader cl = SecuritySupport.getContextClassLoader();
if (cl != null) {
is = SecuritySupport.getResourceAsStream(cl, service);
// If no provider found then try the current ClassLoader
if (is == null) {
cl = XMLReaderFactory.class.getClassLoader();
is = SecuritySupport.getResourceAsStream(cl, service);
}
} else {
// No Context ClassLoader or JDK 1.1 so try the current
// ClassLoader
cl = XMLReaderFactory.class.getClassLoader();
is = SecuritySupport.getResourceAsStream(cl, service);
}
if (is != null) {
// Read the service provider name in UTF-8 as specified in
// the jar spec. Unfortunately this fails in Microsoft
// VJ++, which does not implement the UTF-8
// encoding. Theoretically, we should simply let it fail in
// that case, since the JVM is obviously broken if it
// doesn't support such a basic standard. But since there
// are still some users attempting to use VJ++ for
// development, we have dropped in a fallback which makes a
// second attempt using the platform's default encoding. In
// VJ++ this is apparently ASCII, which is a subset of
// UTF-8... and since the strings we'll be reading here are
// also primarily limited to the 7-bit ASCII range (at
// least, in English versions), this should work well
// enough to keep us on the air until we're ready to
// officially decommit from VJ++. [Edited comment from
// jkesselm]
BufferedReader rd;
try {
rd = new BufferedReader(new InputStreamReader(is, "UTF-8"), DEFAULT_LINE_LENGTH);
} catch (java.io.UnsupportedEncodingException e) {
rd = new BufferedReader(new InputStreamReader(is), DEFAULT_LINE_LENGTH);
}
try {
// XXX Does not handle all possible input as specified by the
// Jar Service Provider specification
className = rd.readLine();
}
catch (Exception x) {
// No provider found
}
finally {
try {
// try to close the reader.
rd.close();
}
// Ignore the exception.
catch (IOException exc) {}
}
}
}
// 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 = "org.apache.xerces.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.
*
* Given a class name, this method attempts to load
* and instantiate the class as an XML reader.
*
* 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);
}
}
}