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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

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 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

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 * accompanied this code).

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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>

 *

 * <p>The {@link XPathFactory} class is not thread-safe. In other words,

 * it is the application's responsibility to ensure that at most

 * one thread is using a {@link XPathFactory} object at any

 * given moment. Implementations are encouraged to mark methods

 * as <code>synchronized</code> to protect themselves from broken clients.

 *

 * <p>{@link XPathFactory} is not re-entrant. While one of the

 * <code>newInstance</code> methods is being invoked, applications

 * may not attempt to recursively invoke a <code>newInstance</code> method,

 * even from the same thread.

 *

 * @author  <a href="mailto:Norman.Walsh@Sun.com">Norman Walsh</a>

 * @author  <a href="mailto:Jeff.Suttor@Sun.com">Jeff Suttor</a>

 *

 * @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> Take care of restrictions imposed by java security model </p>

     */

    private static SecuritySupport ss = new SecuritySupport() ;

    /**

     * <p>Protected constructor as {@link #newInstance()} or {@link #newInstance(String uri)}

     * or {@link #newInstance(String uri, String factoryClassName, ClassLoader classLoader)}

     * 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>.

     *

     * @throws RuntimeException When there is a failure in creating an

     *   <code>XPathFactory</code> for the default object model.

     */

    public static 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}/conf/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>

    *     Use the service-provider loading facilities, defined by the

    *     {@link java.util.ServiceLoader} class, to attempt to locate and load an

    *     implementation of the service using the {@linkplain

    *     java.util.ServiceLoader#load(java.lang.Class) default loading mechanism}:

    *     the service-provider loading facility will use the {@linkplain

    *     java.lang.Thread#getContextClassLoader() current thread's context class loader}

    *     to attempt to load the service. If the context class

    *     loader is null, the {@linkplain

    *     ClassLoader#getSystemClassLoader() system class loader} will be used.

    *     <br>

    *     Each potential service provider is required to implement the method

    *     {@link #isObjectModelSupported(String objectModel)}.

    *     The first service provider found that supports the specified object

    *     model is returned.

    *     <br>

    *     In case of {@link java.util.ServiceConfigurationError} an

    *     {@link XPathFactoryConfigurationException} will be thrown.

    *   </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, or if there is a configuration error.

    * @throws NullPointerException If <code>uri</code> is <code>null</code>.

    * @throws IllegalArgumentException If <code>uri</code> is <code>null</code>

    *   or <code>uri.length() == 0</code>.

    */

    public static 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 = ss.getContextClassLoader();

        if (classLoader == null) {

            //use the current class loader

            classLoader = XPathFactory.class.getClassLoader();

        }

        XPathFactory xpathFactory = new XPathFactoryFinder(classLoader).newFactory(uri);

        if (xpathFactory == null) {

            throw new XPathFactoryConfigurationException(

                    "No XPathFactory implementation found for the object model: "

                    + uri);

        }

        return xpathFactory;

    }

    /**

     * <p>Obtain a new instance of a <code>XPathFactory</code> from a factory class name. <code>XPathFactory</code>

     * is returned if specified factory class supports the specified object model.

     * This function is useful when there are multiple providers in the classpath.

     * It gives more control to the application as it can specify which provider

     * should be loaded.</p>

     *

     *

     * <h2>Tip for Trouble-shooting</h2>

     * <p>Setting the <code>jaxp.debug</code> system property will cause

     * this method to print a lot of debug messages

     * to <code>System.err</code> about what it is doing and where it is looking at.</p>

     *

     * <p> If you have problems try:</p>

     * <pre>

     * java -Djaxp.debug=1 YourProgram ....

     * </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.

     *

     * @param factoryClassName fully qualified factory class name that provides implementation of <code>javax.xml.xpath.XPathFactory</code>.

     *

     * @param classLoader <code>ClassLoader</code> used to load the factory class. If <code>null</code>

     *                     current <code>Thread</code>'s context classLoader is used to load the factory class.

     *

     *

     * @return New instance of a <code>XPathFactory</code>

     *

     * @throws XPathFactoryConfigurationException

     *                   if <code>factoryClassName</code> is <code>null</code>, or

     *                   the factory class cannot be loaded, instantiated

     *                   or the factory class does not support the object model specified

     *                   in the <code>uri</code> parameter.

     *

     * @throws NullPointerException If <code>uri</code> is <code>null</code>.

     * @throws IllegalArgumentException If <code>uri</code> is <code>null</code>

     *          or <code>uri.length() == 0</code>.

     *

     * @see #newInstance()

     * @see #newInstance(String uri)

     *

     * @since 1.6

     */

    public static XPathFactory newInstance(String uri, String factoryClassName, ClassLoader classLoader)

        throws XPathFactoryConfigurationException{

        ClassLoader cl = classLoader;

        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 == \"\"");

        }

        if (cl == null) {

            cl = ss.getContextClassLoader();

        }

        XPathFactory f = new XPathFactoryFinder(cl).createInstance(factoryClassName);

        if (f == null) {

            throw new XPathFactoryConfigurationException(

                    "No XPathFactory implementation found for the object model: "

                    + uri);

        }

        //if this factory supports the given schemalanguage return this factory else thrown exception

        if (f.isObjectModelSupported(uri)) {

            return f;

        } else {

            throw new XPathFactoryConfigurationException("Factory "

                    + factoryClassName + " doesn't support given " + uri

                    + " object model");

        }

    }

    /**

     * <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();

}