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. 
/*
 * Copyright (c) 2004 World Wide Web Consortium,
 *
 * (Massachusetts Institute of Technology, European Research Consortium for
 * Informatics and Mathematics, Keio University). All Rights Reserved. This
 * work is distributed under the W3C(r) Software License [1] in the hope that
 * it will be useful, but WITHOUT ANY WARRANTY; without even the implied
 * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 *
 * [1] http://www.w3.org/Consortium/Legal/2002/copyright-software-20021231
 */


package org.w3c.dom.bootstrap;

import java.util.StringTokenizer;
import java.util.Vector;
import org.w3c.dom.DOMImplementationSource;
import org.w3c.dom.DOMImplementationList;
import org.w3c.dom.DOMImplementation;
import java.io.InputStream;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.security.AccessController;
import java.security.PrivilegedAction;


A factory that enables applications to obtain instances of
DOMImplementation.


Example:



 // get an instance of the DOMImplementation registry
 DOMImplementationRegistry registry =
      DOMImplementationRegistry.newInstance();
 // get a DOM implementation the Level 3 XML module
 DOMImplementation domImpl =
      registry.getDOMImplementation("XML 3.0");




This provides an application with an implementation-independent starting
point. DOM implementations may modify this class to meet new security
standards or to provide *additional* fallbacks for the list of
DOMImplementationSources.



See Also:
Since:DOM Level 3
/**
 * A factory that enables applications to obtain instances of
 * <code>DOMImplementation</code>.
 *
 * <p>
 * Example:
 * </p>
 *
 * <pre class='example'>
 *  // get an instance of the DOMImplementation registry
 *  DOMImplementationRegistry registry =
 *       DOMImplementationRegistry.newInstance();
 *  // get a DOM implementation the Level 3 XML module
 *  DOMImplementation domImpl =
 *       registry.getDOMImplementation("XML 3.0");
 * </pre>
 *
 * <p>
 * This provides an application with an implementation-independent starting
 * point. DOM implementations may modify this class to meet new security
 * standards or to provide *additional* fallbacks for the list of
 * DOMImplementationSources.
 * </p>
 *
 * @see DOMImplementation
 * @see DOMImplementationSource
 * @since DOM Level 3
 */
public final class DOMImplementationRegistry {
    
The system property to specify the
DOMImplementationSource class names.

/**
     * The system property to specify the
     * DOMImplementationSource class names.
     */
    public static final String PROPERTY =
        "org.w3c.dom.DOMImplementationSourceList";
    
    
Default columns per line.

/**
     * Default columns per line.
     */
    private static final int DEFAULT_LINE_LENGTH = 80;
    
    
Default DOMImplementationSource.

/**
     * Default DOMImplementationSource.
     */
    private static final String DEFAULT_DOM_IMPLEMENTATION_SOURCE = "org.apache.xerces.dom.DOMXSImplementationSourceImpl";
    
    
The list of DOMImplementationSources.

/**
     * The list of DOMImplementationSources.
     */
    private Vector sources;
    
    
Private constructor.

Params:
  • srcs – Vector List of DOMImplementationSources
/**
     * Private constructor.
     * @param srcs Vector List of DOMImplementationSources
     */
    private DOMImplementationRegistry(final Vector srcs) {
        sources = srcs;
    }
    
    
Obtain a new instance of a DOMImplementationRegistry.
The DOMImplementationRegistry is initialized by the
application or the implementation, depending on the context, by
first checking the value of the Java system property
org.w3c.dom.DOMImplementationSourceList and
the the service provider whose contents are at
"META-INF/services/org.w3c.dom.DOMImplementationSourceList"
The value of this property is a white-space separated list of
names of availables classes implementing the
DOMImplementationSource interface. Each class listed
in the class name list is instantiated and any exceptions
encountered are thrown to the application.

Throws:
Returns:an initialized instance of DOMImplementationRegistry
/**
     * Obtain a new instance of a <code>DOMImplementationRegistry</code>.
     *
     
     * The <code>DOMImplementationRegistry</code> is initialized by the
     * application or the implementation, depending on the context, by
     * first checking the value of the Java system property
     * <code>org.w3c.dom.DOMImplementationSourceList</code> and
     * the the service provider whose contents are at
     * "<code>META-INF/services/org.w3c.dom.DOMImplementationSourceList</code>"
     * The value of this property is a white-space separated list of
     * names of availables classes implementing the
     * <code>DOMImplementationSource</code> interface. Each class listed
     * in the class name list is instantiated and any exceptions
     * encountered are thrown to the application.
     *
     * @return an initialized instance of DOMImplementationRegistry
     * @throws ClassNotFoundException
     *     If any specified class can not be found
     * @throws InstantiationException
     *     If any specified class is an interface or abstract class
     * @throws IllegalAccessException
     *     If the default constructor of a specified class is not accessible
     * @throws ClassCastException
     *     If any specified class does not implement
     * <code>DOMImplementationSource</code>
     */
    public static DOMImplementationRegistry newInstance()
    throws
    ClassNotFoundException,
    InstantiationException,
    IllegalAccessException,
    ClassCastException {
        Vector sources = new Vector();
        
        ClassLoader classLoader = getClassLoader();
        // fetch system property:
        String p = getSystemProperty(PROPERTY);
        
        //
        // if property is not specified then use contents of
        // META-INF/org.w3c.dom.DOMImplementationSourceList from classpath
        if (p == null || p.length() == 0) {
            p = getServiceValue(classLoader);
        } 
        if (p == null) {
            //
            // DOM Implementations can modify here to add *additional* fallback
            // mechanisms to access a list of default DOMImplementationSources.
            p = DEFAULT_DOM_IMPLEMENTATION_SOURCE;
        }
        if (p != null) {
            StringTokenizer st = new StringTokenizer(p);
            while (st.hasMoreTokens()) {
                String sourceName = st.nextToken();
                // Use context class loader, falling back to Class.forName
                // if and only if this fails...
                Class sourceClass = null;
                if (classLoader != null) {
                    sourceClass = classLoader.loadClass(sourceName);
                } else {
                    sourceClass = Class.forName(sourceName);
                }
                DOMImplementationSource source =
                    (DOMImplementationSource) sourceClass.newInstance();
                sources.addElement(source);
            }
        }
        return new DOMImplementationRegistry(sources);
    }
    
    
Return the first implementation that has the desired
features, or null if none is found.

Params:
  • features – 
           A string that specifies which features are required. This is
           a space separated list in which each feature is specified by
           its name optionally followed by a space and a version number.
           This is something like: "XML 1.0 Traversal +Events 2.0"
Returns:An implementation that has the desired features,
        or null if none found.
/**
     * Return the first implementation that has the desired
     * features, or <code>null</code> if none is found.
     *
     * @param features
     *            A string that specifies which features are required. This is
     *            a space separated list in which each feature is specified by
     *            its name optionally followed by a space and a version number.
     *            This is something like: "XML 1.0 Traversal +Events 2.0"
     * @return An implementation that has the desired features,
     *         or <code>null</code> if none found.
     */
    public DOMImplementation getDOMImplementation(final String features) {
        int size = sources.size();
        String name = null;
        for (int i = 0; i < size; i++) {
            DOMImplementationSource source =
                (DOMImplementationSource) sources.elementAt(i);
            DOMImplementation impl = source.getDOMImplementation(features);
            if (impl != null) {
                return impl;
            }
        }
        return null;
    }
    
    
Return a list of implementations that support the
desired features.

Params:
  • features – 
           A string that specifies which features are required. This is
           a space separated list in which each feature is specified by
           its name optionally followed by a space and a version number.
           This is something like: "XML 1.0 Traversal +Events 2.0"
Returns:A list of DOMImplementations that support the desired features.
/**
     * Return a list of implementations that support the
     * desired features.
     *
     * @param features
     *            A string that specifies which features are required. This is
     *            a space separated list in which each feature is specified by
     *            its name optionally followed by a space and a version number.
     *            This is something like: "XML 1.0 Traversal +Events 2.0"
     * @return A list of DOMImplementations that support the desired features.
     */
    public DOMImplementationList getDOMImplementationList(final String features) {
        final Vector implementations = new Vector();
        int size = sources.size();
        for (int i = 0; i < size; i++) {
            DOMImplementationSource source =
                (DOMImplementationSource) sources.elementAt(i);
            DOMImplementationList impls =
                source.getDOMImplementationList(features);
            for (int j = 0; j < impls.getLength(); j++) {
                DOMImplementation impl = impls.item(j);
                implementations.addElement(impl);
            }
        }
        return new DOMImplementationList() {
            public DOMImplementation item(final int index) {
                if (index >= 0 && index < implementations.size()) {
                    try {
                        return (DOMImplementation)
                        implementations.elementAt(index);
                    } catch (ArrayIndexOutOfBoundsException e) {
                        return null;
                    }
                }
                return null;
            }
            
            public int getLength() {
                return implementations.size();
            }
        };
    }
    
    
Register an implementation.

Params:
  • s – The source to be registered, may not be null
/**
     * Register an implementation.
     *
     * @param s The source to be registered, may not be <code>null</code>
     */
    public void addSource(final DOMImplementationSource s) {
        if (s == null) {
            throw new NullPointerException();
        }
        if (!sources.contains(s)) {
            sources.addElement(s);
        }
    }
    
    
Gets a class loader.

Returns:A class loader, possibly null
/**
     *
     * Gets a class loader.
     *
     * @return A class loader, possibly <code>null</code>
     */
    private static ClassLoader getClassLoader() {
        try {
            ClassLoader contextClassLoader = getContextClassLoader();
            
            if (contextClassLoader != null) {
                return contextClassLoader;
            }
        } catch (Exception e) {
            // Assume that the DOM application is in a JRE 1.1, use the
            // current ClassLoader
            return DOMImplementationRegistry.class.getClassLoader();
        }
        return DOMImplementationRegistry.class.getClassLoader();
    }
    
    
This method attempts to return the first line of the resource
META-INF/services/org.w3c.dom.DOMImplementationSourceList
from the provided ClassLoader.

Params:
  • classLoader – classLoader, may not be null.
Returns:first line of resource, or null
/**
     * This method attempts to return the first line of the resource
     * META-INF/services/org.w3c.dom.DOMImplementationSourceList
     * from the provided ClassLoader.
     *
     * @param classLoader classLoader, may not be <code>null</code>.
     * @return first line of resource, or <code>null</code>
     */
    private static String getServiceValue(final ClassLoader classLoader) {
        String serviceId = "META-INF/services/" + PROPERTY;
        // try to find services in CLASSPATH
        try {
            InputStream is = getResourceAsStream(classLoader, serviceId);
            
            if (is != null) {
                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);
                }		
                String serviceValue = null;
                try {
                    serviceValue = rd.readLine();
                }
                finally {
                    rd.close();
                }
                if (serviceValue != null && serviceValue.length() > 0) {
                    return serviceValue;
                }
            }
        } catch (Exception ex) {
            return null;
        }
        return null;
    }
    
    
A simple JRE (Java Runtime Environment) 1.1 test

Returns:true if JRE 1.1
/**
     * A simple JRE (Java Runtime Environment) 1.1 test
     *
     * @return <code>true</code> if JRE 1.1 
     */
    private static boolean isJRE11() {
        try {
            Class c = Class.forName("java.security.AccessController");
            // java.security.AccessController existed since 1.2 so, if no
            // exception was thrown, the DOM application is running in a JRE
            // 1.2 or higher
            return false;
        } catch (Exception ex) {
            // ignore 
        }
        return true;
    }
    
    
This method returns the ContextClassLoader or null if
running in a JRE 1.1

Returns:The Context Classloader
/**
     * This method returns the ContextClassLoader or <code>null</code> if
     * running in a JRE 1.1
     *
     * @return The Context Classloader
     */
    private static ClassLoader getContextClassLoader() {
        return isJRE11()
        ? null
                : (ClassLoader)
                AccessController.doPrivileged(new PrivilegedAction() {
                    public Object run() {
                        ClassLoader classLoader = null;
                        try {
                            classLoader =
                                Thread.currentThread().getContextClassLoader();
                        } catch (SecurityException ex) {
                        }
                        return classLoader;
                    }
                });
    }
    
    
This method returns the system property indicated by the specified name
after checking access control privileges. For a JRE 1.1, this check is
not done.
	 

Params:
  • name – the name of the system property
Returns:the system property
/**
     * This method returns the system property indicated by the specified name
     * after checking access control privileges. For a JRE 1.1, this check is
     * not done.
     * 	 
     * @param name the name of the system property	 
     * @return the system property
     */
    private static String getSystemProperty(final String name) {
        return isJRE11()
        ? (String) System.getProperty(name)
                : (String) AccessController.doPrivileged(new PrivilegedAction() {
                    public Object run() {
                        return System.getProperty(name);
                    }
                });
    }
    
    
This method returns an Inputstream for the reading resource
META-INF/services/org.w3c.dom.DOMImplementationSourceList after checking
access control privileges. For a JRE 1.1, this check is not done.

Params:
  • classLoader – classLoader
  • name – the resource
Returns:an Inputstream for the resource specified
/**
     * This method returns an Inputstream for the reading resource
     * META-INF/services/org.w3c.dom.DOMImplementationSourceList after checking
     * access control privileges. For a JRE 1.1, this check is not done.
     *
     * @param classLoader classLoader	 
     * @param name the resource 	 
     * @return an Inputstream for the resource specified
     */
    private static InputStream getResourceAsStream(final ClassLoader classLoader,
            final String name) {
        if (isJRE11()) {
            InputStream ris;
            if (classLoader == null) {
                ris = ClassLoader.getSystemResourceAsStream(name);
            } else {
                ris = classLoader.getResourceAsStream(name);
            }    
            return ris;
        } else {
            return (InputStream)
            AccessController.doPrivileged(new PrivilegedAction() {
                public Object run() {
                    InputStream ris;
                    if (classLoader == null) {
                        ris =
                            ClassLoader.getSystemResourceAsStream(name);
                    } else {
                        ris = classLoader.getResourceAsStream(name);
                    }
                    return ris;
                }
            });
        }
    }
}