http://xml.apache.org/commons/components/external/: 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. 
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// $Id: XPathFactory.java 888889 2009-12-09 17:43:18Z mrglavas $

package javax.xml.xpath;


An XPathFactory instance can be used to create XPath objects.


See newInstance(String uri) for lookup mechanism.


Author: Norman Walsh,  Jeff Suttor
Version:$Revision: 888889 $, $Date: 2009-12-09 12:43:18 -0500 (Wed, 09 Dec 2009) $
Since:1.5
/**
 * <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: 888889 $, $Date: 2009-12-09 12:43:18 -0500 (Wed, 09 Dec 2009) $
 * @since 1.5
 */
public abstract class XPathFactory {

    
    
The default property name according to the JAXP spec.


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

    
Default Object Model URI.


/**
     * <p>Default Object Model URI.</p>
     */
    public static final String DEFAULT_OBJECT_MODEL_URI = "http://java.sun.com/jaxp/xpath/dom";
    
    
Protected constructor as newInstance(), newInstance(String uri) or newInstance(String uri, String factoryClassName, ClassLoader classLoader) should be used to create a new instance of an XPathFactory.


/**
     * <p>Protected constructor as {@link #newInstance()}, {@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() {
    }

    
Get a new XPathFactory instance using the default object model, DEFAULT_OBJECT_MODEL_URI, the W3C DOM.


This method is functionally equivalent to:


  newInstance(DEFAULT_OBJECT_MODEL_URI)



Since the implementation for the W3C DOM is always available, this method will never fail.
 

Returns:Instance of an 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()
    		);
    	}
    }

    
Get a new XPathFactory instance using the specified object model.


To find a XPathFactory object,
this method looks the following places in the following order where "the class loader" refers to the context class loader:


    
  
  1.  If the system property 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. 
    2. 
  
  2. 
    ${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.
  
    3. 
  
  3. 
    The class loader is asked for service provider provider-configuration files matching javax.xml.xpath.XPathFactory
    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:
    
     isObjectModelSupported(String objectModel) 
    
    The first service provider found in class loader order that supports the specified object model is returned.
  
    4. 
  
  4. 
    Platform default XPathFactory is located in a platform specific way. There must be a platform default XPathFactory for the W3C DOM, i.e. DEFAULT_OBJECT_MODEL_URI. 
    5. 



If everything fails, an XPathFactoryConfigurationException will be thrown.


Tip for Trouble-shooting:


See Properties.load(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:


  http\://java.sun.com/jaxp/xpath/dom=org.acme.DomXPathFactory



Params:
  • uri – Identifies the underlying object model. The specification only defines the URI DEFAULT_OBJECT_MODEL_URI, http://java.sun.com/jaxp/xpath/dom for the W3C DOM,
  the org.w3c.dom package, and implementations are free to introduce other URIs for other object models.
Throws:
Returns:Instance of an XPathFactory.
/**
    * <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 = SecuritySupport.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 XPathFctory implementation found for the object model: "
                + uri
            );
        }
        return xpathFactory;
    }
    
    
Throws:
Returns:Instance of an XPathFactory.
/**
     * @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 XPathFactory newInstance(String uri, String factoryClassName,
            ClassLoader classLoader) 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 == \"\""
            );
        }
        if (factoryClassName == null) {
            throw new XPathFactoryConfigurationException("factoryClassName cannot be null.");
        }
        if (classLoader == null) {
            classLoader = SecuritySupport.getContextClassLoader();
        }
        XPathFactory xpathFactory = new XPathFactoryFinder(classLoader).createInstance(factoryClassName);
        if (xpathFactory == null || !xpathFactory.isObjectModelSupported(uri)) {
            throw new XPathFactoryConfigurationException(
                "No XPathFctory implementation found for the object model: "
                + uri
            );
        }
        return xpathFactory;
    }

	
Is specified object model supported by this XPathFactory?


Params:
  • objectModel – Specifies the object model which the returned XPathFactory will understand.
Throws:
Returns:true if XPathFactory supports objectModel, else false.
/**
	 * <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);

    
Set a feature for this XPathFactory and XPaths created by this factory.


 Feature names are fully qualified URIs. Implementations may define their own features. An XPathFactoryConfigurationException is thrown if this XPathFactory or the XPaths
 it creates cannot support the feature.
It is possible for an XPathFactory to expose a feature value but be unable to change its state.



 All implementations are required to support the XMLConstants.FEATURE_SECURE_PROCESSING feature. When the feature is true, any reference to an external function is an error. Under these conditions, the implementation must not call the XPathFunctionResolver and must throw an XPathFunctionException. 


Params:
  • name – Feature name.
  • value – Is feature state true or false.
Throws:
/**
     * <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;

	
Get the state of the named feature.


 Feature names are fully qualified URIs. Implementations may define their own features. An XPathFactoryConfigurationException is thrown if this XPathFactory or the XPaths
it creates cannot support the feature.
It is possible for an XPathFactory to expose a feature value but be unable to change its state.



Params:
  • name – Feature name.
Throws:
Returns:State of the named feature.
/**
	 * <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;

    
Establish a default variable resolver.


Any XPath objects constructed from this factory will use
the specified resolver by default.


A NullPointerException is thrown if resolver is null.


Params:
  • resolver – Variable resolver.
 @throws NullPointerException If resolver is null.
/**
     * <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);

    
Establish a default function resolver.


Any XPath objects constructed from this factory will use
the specified resolver by default.


A NullPointerException is thrown if resolver is null.


Params:
  • resolver – XPath function resolver.
Throws:
/**
       * <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);

    
Return a new XPath using the underlying object
model determined when the XPathFactory was instantiated.


Returns:New instance of an XPath.
/**
    * <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();
}