// $Id: XPathFactory.java,v 1.13.10.1 2004/05/07 00:34:05 jsuttor Exp $

/*
 * @(#)XPathFactory.java	1.7 04/07/26
 * 
 * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package javax.xml.xpath;

/**
 * <p>An <code>XPathFactory</code> instance can be used to create
 * {@link javax.xml.xpath.XPath} objects.</p>
 *
 *<p>See {@link #newInstance(String uri)} for lookup mechanism.</p>
 *
 * @author  <a href="mailto:Norman.Walsh@Sun.com">Norman Walsh</a>
 * @author  <a href="mailto:Jeff.Suttor@Sun.com">Jeff Suttor</a>
 * @version $Revision: 1.13.10.1 $, $Date: 2004/05/07 00:34:05 $
 * @since 1.5
 */
public abstract class XPathFactory {

    /**
     * <p>The default property name according to the JAXP spec.</p>
     */
    public static final String DEFAULT_PROPERTY_NAME = "javax.xml.xpath.XPathFactory";

    /**
     * <p>Default Object Model URI.</p>
     */
    public static final String DEFAULT_OBJECT_MODEL_URI = "http://java.sun.com/jaxp/xpath/dom";

    /**
     * <p>Protected constructor as {@link #newInstance()} or {@link #newInstance(String uri)}
     * should be used to create a new instance of an <code>XPathFactory</code>.</p>
     */
    protected XPathFactory() {
    }

    /**
     * <p>Get a new <code>XPathFactory</code> instance using the default object model,
     * {@link #DEFAULT_OBJECT_MODEL_URI},
     * the W3C DOM.</p>
     * 
     * <p>This method is functionally equivalent to:</p>
     * <pre>
     *   newInstance(DEFAULT_OBJECT_MODEL_URI)
     * </pre>
     * 
     * <p>Since the implementation for the W3C DOM is always available, this method will never fail.</p> 
     * 
     * @return Instance of an <code>XPathFactory</code>.
     */
    public static final XPathFactory newInstance() {
    	
    	try {
        	return newInstance(DEFAULT_OBJECT_MODEL_URI);
    	} catch (XPathFactoryConfigurationException xpathFactoryConfigurationException) {
    		throw new RuntimeException(
    			"XPathFactory#newInstance() failed to create an XPathFactory for the default object model: "
    			+ DEFAULT_OBJECT_MODEL_URI
    			+ " with the XPathFactoryConfigurationException: "
    			+ xpathFactoryConfigurationException.toString()
    		);
    	}
    }

    /**
    * <p>Get a new <code>XPathFactory</code> instance using the specified object model.</p>
    * 
    * <p>To find a <code>XPathFactory</code> object,
    * this method looks the following places in the following order where "the class loader" refers to the context class loader:</p>
    * <ol>
    *   <li>
    *     If the system property {@link #DEFAULT_PROPERTY_NAME} + ":uri" is present,
    *     where uri is the parameter to this method, then its value is read as a class name.
    *     The method will try to create a new instance of this class by using the class loader,
    *     and returns it if it is successfully created.
    *   </li>
    *   <li>
    *     ${java.home}/lib/jaxp.properties is read and the value associated with the key being the system property above is looked for.
    *     If present, the value is processed just like above.
    *   </li>
    *   <li>
    *     The class loader is asked for service provider provider-configuration files matching <code>javax.xml.xpath.XPathFactory</code>
    *     in the resource directory META-INF/services.
    *     See the JAR File Specification for file format and parsing rules.
    *     Each potential service provider is required to implement the method:
    *     <pre>
    *       {@link #isObjectModelSupported(String objectModel)}
    *     </pre>
    *     The first service provider found in class loader order that supports the specified object model is returned.
    *   </li>
    *   <li>
    *     Platform default <code>XPathFactory</code> is located in a platform specific way.
    *     There must be a platform default XPathFactory for the W3C DOM, i.e. {@link #DEFAULT_OBJECT_MODEL_URI}.
    *   </li>
    * </ol>
    * <p>If everything fails, an <code>XPathFactoryConfigurationException</code> will be thrown.</p>
    * 
    * <p>Tip for Trouble-shooting:</p>
    * <p>See {@link java.util.Properties#load(java.io.InputStream)} for exactly how a property file is parsed.
    * In particular, colons ':' need to be escaped in a property file, so make sure the URIs are properly escaped in it.
    * For example:</p>
    * <pre>
    *   http\://java.sun.com/jaxp/xpath/dom=org.acme.DomXPathFactory
    * </pre>
    * 
    * @param uri Identifies the underlying object model.
    *   The specification only defines the URI {@link #DEFAULT_OBJECT_MODEL_URI},
    *   <code>http://java.sun.com/jaxp/xpath/dom</code> for the W3C DOM,
    *   the org.w3c.dom package, and implementations are free to introduce other URIs for other object models.
    * 
    * @return Instance of an <code>XPathFactory</code>.
    * 
    * @throws XPathFactoryConfigurationException If the specified object model is unavailable.
    * @throws NullPointerException If <code>uri</code> is <code>null</code>. 
	 * @throws IllegalArgumentException If <code>uri.length() == 0</code>.
    */
    public static final XPathFactory newInstance(final String uri)
        throws XPathFactoryConfigurationException {
        	
        if (uri == null) {
        	throw new NullPointerException(
        		"XPathFactory#newInstance(String uri) cannot be called with uri == null"
        	);
        }

		if (uri.length() == 0) {
			throw new IllegalArgumentException(
				"XPathFactory#newInstance(String uri) cannot be called with uri == \"\""
			);
		}
		
		ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
		
		XPathFactory xpathFactory = new XPathFactoryFinder(classLoader).newFactory(uri);
		
		if (xpathFactory == null) {
			throw new XPathFactoryConfigurationException(
				"No XPathFctory implementation found for the object model: "
				+ uri
			);
		}
		
		return xpathFactory;
    }

	/**
	 * <p>Is specified object model supported by this <code>XPathFactory</code>?</p>
	 * 
	 * @param objectModel Specifies the object model which the returned <code>XPathFactory</code> will understand.
	 *  
	 * @return <code>true</code> if <code>XPathFactory</code> supports <code>objectModel</code>, else <code>false</code>.
	 * 
	 * @throws NullPointerException If <code>objectModel</code> is <code>null</code>.
	 * @throws IllegalArgumentException If <code>objectModel.length() == 0</code>.
	 */
	public abstract boolean isObjectModelSupported(String objectModel);

    /**
     * <p>Set a feature for this <code>XPathFactory</code> and <code>XPath</code>s created by this factory.</p>
     * 
     * <p>
     * Feature names are fully qualified {@link java.net.URI}s.
     * Implementations may define their own features.
     * An {@link XPathFactoryConfigurationException} is thrown if this <code>XPathFactory</code> or the <code>XPath</code>s
     *  it creates cannot support the feature.
     * It is possible for an <code>XPathFactory</code> to expose a feature value but be unable to change its state.
     * </p>
     * 
     * <p>
     * All implementations are required to support the {@link javax.xml.XMLConstants#FEATURE_SECURE_PROCESSING} feature.
     * When the feature is <code>true</code>, any reference to  an external function is an error.
     * Under these conditions, the implementation must not call the {@link XPathFunctionResolver}
     * and must throw an {@link XPathFunctionException}.
     * </p>
     * 
     * @param name Feature name.
     * @param value Is feature state <code>true</code> or <code>false</code>.
     *  
     * @throws XPathFactoryConfigurationException if this <code>XPathFactory</code> or the <code>XPath</code>s
     *   it creates cannot support this feature.
     * @throws NullPointerException if <code>name</code> is <code>null</code>.
     */
	public abstract void setFeature(String name, boolean value)
		throws XPathFactoryConfigurationException;

	/**
	 * <p>Get the state of the named feature.</p>
	 * 
     * <p>
     * Feature names are fully qualified {@link java.net.URI}s.
     * Implementations may define their own features.
     * An {@link XPathFactoryConfigurationException} is thrown if this <code>XPathFactory</code> or the <code>XPath</code>s
     * it creates cannot support the feature.
     * It is possible for an <code>XPathFactory</code> to expose a feature value but be unable to change its state.
     * </p>
     * 
	 * @param name Feature name.
	 * 
	 * @return State of the named feature.
	 * 
     * @throws XPathFactoryConfigurationException if this <code>XPathFactory</code> or the <code>XPath</code>s
     *   it creates cannot support this feature.
     * @throws NullPointerException if <code>name</code> is <code>null</code>.
	 */
	public abstract boolean getFeature(String name)
		throws XPathFactoryConfigurationException;

    /**
     * <p>Establish a default variable resolver.</p>
     *
     * <p>Any <code>XPath</code> objects constructed from this factory will use
     * the specified resolver by default.</p>
     * 
     * <p>A <code>NullPointerException</code> is thrown if <code>resolver</code> is <code>null</code>.</p>
     * 
     * @param resolver Variable resolver.
     * 
     *  @throws NullPointerException If <code>resolver</code> is <code>null</code>.
     */
    public abstract void setXPathVariableResolver(XPathVariableResolver resolver);

    /**
       * <p>Establish a default function resolver.</p>
       * 
       * <p>Any <code>XPath</code> objects constructed from this factory will use
       * the specified resolver by default.</p>
       *
       * <p>A <code>NullPointerException</code> is thrown if <code>resolver</code> is <code>null</code>.</p>
       * 
       * @param resolver XPath function resolver.
       * 
       * @throws NullPointerException If <code>resolver</code> is <code>null</code>.
       */
    public abstract void setXPathFunctionResolver(XPathFunctionResolver resolver);

    /**
    * <p>Return a new <code>XPath</code> using the underlying object
    * model determined when the <code>XPathFactory</code> was instantiated.</p>
    * 
    * @return New instance of an <code>XPath</code>.
    */
    public abstract XPath newXPath();
}