namespacesupport.java

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// NamespaceSupport.java - generic Namespace support for SAX.
// http://www.saxproject.org
// Written by David Megginson
// This class is in the Public Domain.  NO WARRANTY!
// $Id: NamespaceSupport.java,v 1.1 2004/02/15 11:07:14 epr Exp $

package org.xml.sax.helpers;

import java.util.EmptyStackException;
import java.util.Enumeration;
import java.util.Hashtable;
import java.util.Vector;


/**
 * Encapsulate Namespace logic for use by applications using SAX,
 * or internally by SAX drivers.
 *
 * <blockquote>
 * <em>This module, both source code and documentation, is in the
 * Public Domain, and comes with <strong>NO WARRANTY</strong>.</em>
 * See <a href='http://www.saxproject.org'>http://www.saxproject.org</a>
 * for further information.
 * </blockquote>
 *
 * <p>This class encapsulates the logic of Namespace processing:
 * it tracks the declarations currently in force for each context
 * and automatically processes qualified XML 1.0 names into their
 * Namespace parts; it can also be used in reverse for generating
 * XML 1.0 from Namespaces.</p>
 *
 * <p>Namespace support objects are reusable, but the reset method
 * must be invoked between each session.</p>
 *
 * <p>Here is a simple session:</p>
 *
 * <pre>
 * String parts[] = new String[3];
 * NamespaceSupport support = new NamespaceSupport();
 *
 * support.pushContext();
 * support.declarePrefix("", "http://www.w3.org/1999/xhtml");
 * support.declarePrefix("dc", "http://www.purl.org/dc#");
 *
 * parts = support.processName("p", parts, false);
 * System.out.println("Namespace URI: " + parts[0]);
 * System.out.println("Local name: " + parts[1]);
 * System.out.println("Raw name: " + parts[2]);
 *
 * parts = support.processName("dc:title", parts, false);
 * System.out.println("Namespace URI: " + parts[0]);
 * System.out.println("Local name: " + parts[1]);
 * System.out.println("Raw name: " + parts[2]);
 *
 * support.popContext();
 * </pre>
 *
 * <p>Note that this class is optimized for the use case where most
 * elements do not contain Namespace declarations: if the same
 * prefix/URI mapping is repeated for each context (for example), this
 * class will be somewhat less efficient.</p>
 *
 * <p>Although SAX drivers (parsers) may choose to use this class to
 * implement namespace handling, they are not required to do so.
 * Applications must track namespace information themselves if they
 * want to use namespace information.
 *
 * @since SAX 2.0
 * @author David Megginson
 * @version 2.0.1 (sax2r2)
 */
public class NamespaceSupport
{


    ////////////////////////////////////////////////////////////////////
    // Constants.
    ////////////////////////////////////////////////////////////////////


    /**
     * The XML Namespace URI as a constant.
     * The value is <code>http://www.w3.org/XML/1998/namespace</code>
     * as defined in the XML Namespaces specification.
     *
     * <p>This is the Namespace URI that is automatically mapped
     * to the "xml" prefix.</p>
     */
    public final static String XMLNS =
	"http://www.w3.org/XML/1998/namespace";


    /**
     * An empty enumeration.
     */
    private final static Enumeration EMPTY_ENUMERATION =
	new Vector().elements();


    ////////////////////////////////////////////////////////////////////
    // Constructor.
    ////////////////////////////////////////////////////////////////////


    /**
     * Create a new Namespace support object.
     */
    public NamespaceSupport ()
    {
	reset();
    }



    ////////////////////////////////////////////////////////////////////
    // Context management.
    ////////////////////////////////////////////////////////////////////


    /**
     * Reset this Namespace support object for reuse.
     *
     * <p>It is necessary to invoke this method before reusing the
     * Namespace support object for a new session.</p>
     */
    public void reset ()
    {
	contexts = new Context[32];
	contextPos = 0;
	contexts[contextPos] = currentContext = new Context();
	currentContext.declarePrefix("xml", XMLNS);
    }


    /**
     * Start a new Namespace context.
     * The new context will automatically inherit
     * the declarations of its parent context, but it will also keep
     * track of which declarations were made within this context.
     *
     * <p>Event callback code should start a new context once per element.
     * This means being ready to call this in either of two places.
     * For elements that don't include namespace declarations, the
     * <em>ContentHandler.startElement()</em> callback is the right place.
     * For elements with such a declaration, it'd done in the first
     * <em>ContentHandler.startPrefixMapping()</em> callback.
     * A boolean flag can be used to
     * track whether a context has been started yet.  When either of
     * those methods is called, it checks the flag to see if a new context
     * needs to be started.  If so, it starts the context and sets the
     * flag.  After <em>ContentHandler.startElement()</em>
     * does that, it always clears the flag.
     *
     * <p>Normally, SAX drivers would push a new context at the beginning
     * of each XML element.  Then they perform a first pass over the
     * attributes to process all namespace declarations, making
     * <em>ContentHandler.startPrefixMapping()</em> callbacks.
     * Then a second pass is made, to determine the namespace-qualified
     * names for all attributes and for the element name.
     * Finally all the information for the
     * <em>ContentHandler.startElement()</em> callback is available,
     * so it can then be made.
     *
     * <p>The Namespace support object always starts with a base context
     * already in force: in this context, only the "xml" prefix is
     * declared.</p>
     *
     * @see org.xml.sax.ContentHandler
     * @see #popContext
     */
    public void pushContext ()
    {
	int max = contexts.length;

	contexts [contextPos].declsOK = false;
	contextPos++;

				// Extend the array if necessary
	if (contextPos >= max) {
	    Context newContexts[] = new Context[max*2];
	    System.arraycopy(contexts, 0, newContexts, 0, max);
	    max *= 2;
	    contexts = newContexts;
	}

				// Allocate the context if necessary.
	currentContext = contexts[contextPos];
	if (currentContext == null) {
	    contexts[contextPos] = currentContext = new Context();
	}

				// Set the parent, if any.
	if (contextPos > 0) {
	    currentContext.setParent(contexts[contextPos - 1]);
	}
    }


    /**
     * Revert to the previous Namespace context.
     *
     * <p>Normally, you should pop the context at the end of each
     * XML element.  After popping the context, all Namespace prefix
     * mappings that were previously in force are restored.</p>
     *
     * <p>You must not attempt to declare additional Namespace
     * prefixes after popping a context, unless you push another
     * context first.</p>
     *
     * @see #pushContext
     */
    public void popContext ()
    {
	contexts[contextPos].clear();
	contextPos--;
	if (contextPos < 0) {
	    throw new EmptyStackException();
	}
	currentContext = contexts[contextPos];
    }



    ////////////////////////////////////////////////////////////////////
    // Operations within a context.
    ////////////////////////////////////////////////////////////////////


    /**
     * Declare a Namespace prefix.  All prefixes must be declared
     * before they are referenced.  For example, a SAX driver (parser)
     * would scan an element's attributes
     * in two passes:  first for namespace declarations,
     * then a second pass using {@link #processName processName()} to
     * interpret prefixes against (potentially redefined) prefixes.
     *
     * <p>This method declares a prefix in the current Namespace
     * context; the prefix will remain in force until this context
     * is popped, unless it is shadowed in a descendant context.</p>
     *
     * <p>To declare the default element Namespace, use the empty string as
     * the prefix.</p>
     *
     * <p>Note that you must <em>not</em> declare a prefix after
     * you've pushed and popped another Namespace context, or
     * treated the declarations phase as complete by processing
     * a prefixed name.</p>
     *
     * <p>Note that there is an asymmetry in this library: {@link
     * #getPrefix getPrefix} will not return the "" prefix,
     * even if you have declared a default element namespace.
     * To check for a default namespace,
     * you have to look it up explicitly using {@link #getURI getURI}.
     * This asymmetry exists to make it easier to look up prefixes
     * for attribute names, where the default prefix is not allowed.</p>
     *
     * @param prefix The prefix to declare, or the empty string to
     *	indicate the default element namespace.  This may never have
     *	the value "xml" or "xmlns".
     * @param uri The Namespace URI to associate with the prefix.
     * @return true if the prefix was legal, false otherwise
     * @exception IllegalStateException when a prefix is declared
     *	after looking up a name in the context, or after pushing
     *	another context on top of it.
     *
     * @see #processName
     * @see #getURI
     * @see #getPrefix
     */
    public boolean declarePrefix (String prefix, String uri)
    {
	if (prefix.equals("xml") || prefix.equals("xmlns")) {
	    return false;
	} else {
	    currentContext.declarePrefix(prefix, uri);
	    return true;
	}
    }


    /**
     * Process a raw XML 1.0 name, after all declarations in the current
     * context have been handled by {@link #declarePrefix declarePrefix()}.
     *
     * <p>This method processes a raw XML 1.0 name in the current
     * context by removing the prefix and looking it up among the
     * prefixes currently declared.  The return value will be the
     * array supplied by the caller, filled in as follows:</p>
     *
     * <dl>
     * <dt>parts[0]</dt>
     * <dd>The Namespace URI, or an empty string if none is
     *  in use.</dd>
     * <dt>parts[1]</dt>
     * <dd>The local name (without prefix).</dd>
     * <dt>parts[2]</dt>
     * <dd>The original raw name.</dd>
     * </dl>
     *
     * <p>All of the strings in the array will be internalized.  If
     * the raw name has a prefix that has not been declared, then
     * the return value will be null.</p>
     *
     * <p>Note that attribute names are processed differently than
     * element names: an unprefixed element name will received the
     * default Namespace (if any), while an unprefixed attribute name
     * will not.</p>
     *
     * @param qName The raw XML 1.0 name to be processed.
     * @param parts An array supplied by the caller, capable of
     *        holding at least three members.
     * @param isAttribute A flag indicating whether this is an
     *        attribute name (true) or an element name (false).
     * @return The supplied array holding three internalized strings 
     *        representing the Namespace URI (or empty string), the
     *        local name, and the raw XML 1.0 name; or null if there
     *        is an undeclared prefix.
     * @see #declarePrefix
     * @see java.lang.String#intern */
    public String [] processName (String qName, String parts[],
				  boolean isAttribute)
    {
	String myParts[] = currentContext.processName(qName, isAttribute);
	if (myParts == null) {
	    return null;
	} else {
	    parts[0] = myParts[0];
	    parts[1] = myParts[1];
	    parts[2] = myParts[2];
	    return parts;
	}
    }


    /**
     * Look up a prefix and get the currently-mapped Namespace URI.
     *
     * <p>This method looks up the prefix in the current context.
     * Use the empty string ("") for the default Namespace.</p>
     *
     * @param prefix The prefix to look up.
     * @return The associated Namespace URI, or null if the prefix
     *         is undeclared in this context.
     * @see #getPrefix
     * @see #getPrefixes
     */
    public String getURI (String prefix)
    {
	return currentContext.getURI(prefix);
    }


    /**
     * Return an enumeration of all prefixes currently declared.
     *
     * <p><strong>Note:</strong> if there is a default prefix, it will not be
     * returned in this enumeration; check for the default prefix
     * using the {@link #getURI getURI} with an argument of "".</p>
     *
     * @return An enumeration of all prefixes declared in the
     *         current context except for the empty (default)
     *         prefix.
     * @see #getDeclaredPrefixes
     * @see #getURI
     */
    public Enumeration getPrefixes ()
    {
	return currentContext.getPrefixes();
    }


    /**
     * Return one of the prefixes mapped to a Namespace URI.
     *
     * <p>If more than one prefix is currently mapped to the same
     * URI, this method will make an arbitrary selection; if you
     * want all of the prefixes, use the {@link #getPrefixes}
     * method instead.</p>
     *
     * <p><strong>Note:</strong> this will never return the empty (default) prefix;
     * to check for a default prefix, use the {@link #getURI getURI}
     * method with an argument of "".</p>
     *
     * @param uri The Namespace URI.
     * @param isAttribute true if this prefix is for an attribute