src/javax/xml/transform/TransformerFactory.java

/*
 * The Apache Software License, Version 1.1
 *
 *
 * Copyright (c) 1999 The Apache Software Foundation.  All rights 
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer. 
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:  
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Xalan" and "Apache Software Foundation" must
 *    not be used to endorse or promote products derived from this
 *    software without prior written permission. For written 
 *    permission, please contact apache@apache.org.
 *
 * 5. Products derived from this software may not be called "Apache",
 *    nor may "Apache" appear in their name, without prior written
 *    permission of the Apache Software Foundation.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation and was
 * originally based on software copyright (c) 1999, Lotus
 * Development Corporation., http://www.lotus.com.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 */
/**
 * $Id$
 */
package javax.xml.transform;

import java.io.IOException;
import java.io.File;
import java.io.FileInputStream;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.BufferedReader;

import java.util.Properties;
import java.util.Enumeration;


/**
 * A TransformerFactory instance can be used to create Transformer and Template
 * objects.
 *
 * <p>The system property that determines which Factory implementation
 * to create is named "javax.xml.transform.TransformerFactory". This
 * property names a concrete subclass of the TransformerFactory abstract
 *  class. If the property is not defined, a platform default is be used.</p>
 */
public abstract class TransformerFactory {

    /** The default property name according to the JAXP spec. */
    private static final String defaultPropName =
        "javax.xml.transform.TransformerFactory";

    /**
     * Default constructor is protected on purpose.
     */
    protected TransformerFactory() {}

    /**
     * Obtain a new instance of a <code>TransformerFactory</code>.
     * This static method creates a new factory instance 
     * This method uses the following ordered lookup procedure to determine
     * the <code>TransformerFactory</code> implementation class to
     * load:
     * <ul>
     * <li>
     * Use the <code>javax.xml.transform.TransformerFactory</code> system
     * property.
     * </li>
     * <li>
     * Use the JAVA_HOME(the parent directory where jdk is
     * installed)/lib/jaxp.properties for a property file that contains the
     * name of the implementation class keyed on the same value as the
     * system property defined above.
     * </li>
     * <li>
     * Use the Services API (as detailed in the JAR specification), if
     * available, to determine the classname. The Services API will look
     * for a classname in the file
     * <code>META-INF/services/javax.xml.transform.TransformerFactory</code>
     * in jars available to the runtime.
     * </li>
     * <li>
     * Platform default <code>TransformerFactory</code> instance.
     * </li>
     * </ul>
     *
     * Once an application has obtained a reference to a <code>
     * TransformerFactory</code> it can use the factory to configure
     * and obtain parser instances.
     *
     * @return new TransformerFactory instance, never null.
     *
     * @throws TransformerFactoryConfigurationError
     * if the implmentation is not available or cannot be instantiated.
     */
    public static TransformerFactory newInstance()
            throws TransformerFactoryConfigurationError {

        String classname =
            findFactory(defaultPropName,
                        "org.apache.xalan.processor.TransformerFactoryImpl");

        if (classname == null) {
            throw new TransformerFactoryConfigurationError(
                "No default implementation found");
        }

        TransformerFactory factoryImpl;

        try {
            Class clazz = getClassForName(classname);

            factoryImpl = (TransformerFactory) clazz.newInstance();
        } catch (ClassNotFoundException cnfe) {
            throw new TransformerFactoryConfigurationError(cnfe);
        } catch (IllegalAccessException iae) {
            throw new TransformerFactoryConfigurationError(iae);
        } catch (InstantiationException ie) {
            throw new TransformerFactoryConfigurationError(ie);
        }

        return factoryImpl;
    }


    
    /** a zero length Object array used in getClassForName() */
    private static final Object NO_OBJS[] = new Object[0];
    /** the Method object for getContextClassLoader */
    private static java.lang.reflect.Method getCCL;
    
    static {
	try { 
	    getCCL = Thread.class.getMethod("getContextClassLoader",
					    new Class[0]);
	} catch (Exception e) {
	    getCCL = null;
	}
    }
    
    private static Class getClassForName(String className )
        throws ClassNotFoundException
    {
	if (getCCL != null) {
	    try {
		ClassLoader contextClassLoader =
		    (ClassLoader) getCCL.invoke(Thread.currentThread(),
						NO_OBJS);
		return contextClassLoader.loadClass(className);
	    } catch (ClassNotFoundException cnfe) {
		// nothing, try again with Class.forName 
	    } catch (Exception e) {
		getCCL = null; // don't try again
		// fallback
	    }
	}
	
	return Class.forName(className);
    }
  
    /**
     * Process the Source into a Transformer object.  Care must
     * be given not to use this object in multiple threads running concurrently.
     * Different TransformerFactories can be used concurrently by different
     * threads.
     *
     * @param source An object that holds a URI, input stream, etc.
     *
     * @return A Transformer object that may be used to perform a transformation
     * in a single thread, never null.
     *
     * @exception TransformerConfigurationException May throw this during the parse
     *            when it is constructing the Templates object and fails.
     */
    public abstract Transformer newTransformer(Source source)
        throws TransformerConfigurationException;

    /**
     * Create a new Transformer object that performs a copy
     * of the source to the result.
     *
     * @param source An object that holds a URI, input stream, etc.
     *
     * @return A Transformer object that may be used to perform a transformation
     * in a single thread, never null.
     *
     * @exception TransformerConfigurationException May throw this during
     *            the parse when it is constructing the
     *            Templates object and fails.
     */
    public abstract Transformer newTransformer()
        throws TransformerConfigurationException;

    /**
     * Process the Source into a Templates object, which is a
     * a compiled representation of the source. This Templates object
     * may then be used concurrently across multiple threads.  Creating
     * a Templates object allows the TransformerFactory to do detailed
     * performance optimization of transformation instructions, without
     * penalizing runtime transformation.
     *
     * @param source An object that holds a URL, input stream, etc.
     *
     * @return A Templates object capable of being used for transformation purposes,
     * never null.
     *
     * @exception TransformerConfigurationException May throw this during the parse when it
     *            is constructing the Templates object and fails.
     */
    public abstract Templates newTemplates(Source source)
        throws TransformerConfigurationException;

    /**
     * Get the stylesheet specification(s) associated
     * via the xml-stylesheet processing instruction (see
     * http://www.w3.org/TR/xml-stylesheet/) with the document
     * document specified in the source parameter, and that match
     * the given criteria.  Note that it is possible to return several
     * stylesheets, in which case they are applied as if they were
     * a list of imports or cascades in a single stylesheet.
     *
     * @param source The XML source document.
     * @param media The media attribute to be matched.  May be null, in which
     *              case the prefered templates will be used (i.e. alternate = no).
     * @param title The value of the title attribute to match.  May be null.
     * @param charset The value of the charset attribute to match.  May be null.
     *
     * @return A Source object suitable for passing to the TransformerFactory.
     *
     * @throws TransformerConfigurationException.
     */
    public abstract Source getAssociatedStylesheet(
        Source source, String media, String title, String charset)
            throws TransformerConfigurationException;

    /**
     * Set an object that is used by default during the transformation
     * to resolve URIs used in xsl:import, or xsl:include.
     *
     * @param resolver An object that implements the URIResolver interface,
     * or null.
     */
    public abstract void setURIResolver(URIResolver resolver);

    /**
     * Get the object that is used by default during the transformation
     * to resolve URIs used in document(), xsl:import, or xsl:include.
     *
     * @return The URIResolver that was set with setURIResolver.
     */
    public abstract URIResolver getURIResolver();

    //======= CONFIGURATION METHODS =======

    /**
     * Look up the value of a feature.
     *
     * <p>The feature name is any absolute URI.</p>
     * @param name The feature name, which is an absolute URI.
     * @return The current state of the feature (true or false).
     */
    public abstract boolean getFeature(String name);

    /**
     * Allows the user to set specific attributes on the underlying
     * implementation.  An attribute in this context is defined to
     * be an option that the implementation provides.
     *
     * @param name The name of the attribute.
     * @param value The value of the attribute.
     * @throws IllegalArgumentException thrown if the underlying
     * implementation doesn't recognize the attribute.
     */
    public abstract void setAttribute(String name, Object value)
        throws IllegalArgumentException;

    /**
     * Allows the user to retrieve specific attributes on the underlying
     * implementation.
     * @param name The name of the attribute.
     * @return value The value of the attribute.
     * @throws IllegalArgumentException thrown if the underlying
     * implementation doesn't recognize the attribute.
     */
    public abstract Object getAttribute(String name)
        throws IllegalArgumentException;

    /**
     * Set the error event listener for the TransformerFactory, which
     * is used for the processing of transformation instructions,
     * and not for the transformation itself.
     *
     * @param listener The new error listener.
     * @throws IllegalArgumentException if listener is null.
     */
    public abstract void setErrorListener(ErrorListener listener)
        throws IllegalArgumentException;

    /**
     * Get the error event handler for the TransformerFactory.
     *
     * @return The current error handler, which should never be null.
     */
    public abstract ErrorListener getErrorListener();

    // -------------------- private methods --------------------

    /**
     * Avoid reading all the files when the findFactory
     * method is called the second time (cache the result of
     * finding the default impl).
     */
    private static String foundFactory = null;

    /**
     * Temp debug code - this will be removed after we test everything
     */
    private static boolean debug;
    static {
	try {
	    debug = System.getProperty("jaxp.debug") != null;
	} catch( SecurityException ex ) {}
    }

    /**
     * Private implementation method - will find the implementation
     * class in the specified order.
     *
     * @param factoryId   Name of the factory interface.
     * @param xmlProperties Name of the properties file based on JAVA/lib.
     * @param defaultFactory Default implementation, if nothing else is found.
     *
     * @return The factory class name.
     */
    private static String findFactory(String factoryId,
                                      String defaultFactory) {

        // Use the system property first
        try {
	    String systemProp = null;
	    try {
		systemProp = System.getProperty(factoryId);
	    } catch( SecurityException se ) {}

            if (systemProp != null) {
                if (debug) {
                    System.err.println("JAXP: found system property"
                                       + systemProp);
                }

                return systemProp;
            }
        } catch (SecurityException se) {}

        if (foundFactory != null) {
            return foundFactory;
        }

        // try to read from $java.home/lib/jaxp.properties
        try {
            String javah      = System.getProperty("java.home");
            String configFile = javah + File.separator + "lib"
                                + File.separator + "jaxp.properties";
            File   f          = new File(configFile);

            if (f.exists()) {
                Properties props = new Properties();

                props.load(new FileInputStream(f));

                foundFactory = props.getProperty(factoryId);

                if (debug) {
                    System.err.println("JAXP: found java.home property "
                                       + foundFactory);
                }

                if (foundFactory != null) {
                    return foundFactory;
                }
            }
        } catch (Exception ex) {
            if (debug) {
                ex.printStackTrace();
            }
        }

        String serviceId = "META-INF/services/" + factoryId;

        // try to find services in CLASSPATH
        try {
            ClassLoader cl = TransformerFactory.class.getClassLoader();
            InputStream is = null;

            if (cl == null) {
                is = ClassLoader.getSystemResourceAsStream(serviceId);
            } else {
                is = cl.getResourceAsStream(serviceId);
            }

            if (is != null) {
                if (debug) {
                    System.err.println("JAXP: found  " + serviceId);
                }

                BufferedReader rd =
                    new BufferedReader(new InputStreamReader(is));

                foundFactory = rd.readLine();

                rd.close();

                if (debug) {
                    System.err.println("JAXP: loaded from services: "
                                       + foundFactory);
                }

                if ((foundFactory != null) &&!"".equals(foundFactory)) {
                    return foundFactory;
                }
            }
        } catch (Exception ex) {
            if (debug) {
                ex.printStackTrace();
            }
        }

        return defaultFactory;
    }
}