* This module, both source code and documentation, is in the * Public Domain, and comes with NO WARRANTY. * See http://www.saxproject.org * for further information. ** *
This class encapsulates the logic of Namespace processing: it * tracks the declarations currently in force for each context and * automatically processes qualified XML names into their Namespace * parts; it can also be used in reverse for generating XML qnames * from Namespaces.
* *Namespace support objects are reusable, but the reset method * must be invoked between each session.
* *Here is a simple session:
* *
* 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();
*
*
* 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.
* *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 1.4, SAX 2.0
* @author David Megginson
*/
public class NamespaceSupport
{
////////////////////////////////////////////////////////////////////
// Constants.
////////////////////////////////////////////////////////////////////
/**
* The XML Namespace URI as a constant.
* The value is http://www.w3.org/XML/1998/namespace
* as defined in the "Namespaces in XML" * recommendation.
*
*
This is the Namespace URI that is automatically mapped * to the "xml" prefix.
*/ public final static String XMLNS = "http://www.w3.org/XML/1998/namespace"; /** * The namespace declaration URI as a constant. * The value ishttp://www.w3.org/xmlns/2000/, as defined
* in a backwards-incompatible erratum to the "Namespaces in XML"
* recommendation. Because that erratum postdated SAX2, SAX2 defaults
* to the original recommendation, and does not normally use this URI.
*
*
* This is the Namespace URI that is optionally applied to * xmlns and xmlns:* attributes, which are used to * declare namespaces.
* * @since 1.5, SAX 2.1alpha * @see #setNamespaceDeclUris * @see #isNamespaceDeclUris */ public final static String NSDECL = "http://www.w3.org/xmlns/2000/"; /** * 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. * *It is necessary to invoke this method before reusing the * Namespace support object for a new session. If namespace * declaration URIs are to be supported, that flag must also * be set to a non-default value. *
* * @see #setNamespaceDeclUris */ public void reset () { contexts = new Context[32]; namespaceDeclUris = false; 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. * *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 * ContentHandler.startElement() callback is the right place. * For elements with such a declaration, it'd done in the first * ContentHandler.startPrefixMapping() 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 ContentHandler.startElement() * does that, it always clears the flag. * *
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 * ContentHandler.startPrefixMapping() 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 * ContentHandler.startElement() callback is available, * so it can then be made. * *
The Namespace support object always starts with a base context * already in force: in this context, only the "xml" prefix is * declared.
* * @see org.xml.sax.ContentHandler * @see #popContext */ public void pushContext () { int max = contexts.length; 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. * *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.
* *You must not attempt to declare additional Namespace * prefixes after popping a context, unless you push another * context first.
* * @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. * *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.
* *To declare the default element Namespace, use the empty string as * the prefix.
* *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.
* * @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 * * @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 qualified name, after all declarations in the * current context have been handled by {@link #declarePrefix * declarePrefix()}. * *This method processes a raw XML qualified 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:
* *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.
* *Note that attribute names are processed differently than * element names: an unprefixed element name will receive the * default Namespace (if any), while an unprefixed attribute name * will not.
* * @param qName The XML qualified 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 XML qualified 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. * *This method looks up the prefix in the current context. * Use the empty string ("") for the default Namespace.
* * @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 whose declarations are * active in the current context. * This includes declarations from parent contexts that have * not been overridden. * *Note: 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 "".
* * @return An enumeration of prefixes (never empty). * @see #getDeclaredPrefixes * @see #getURI */ public Enumeration getPrefixes () { return currentContext.getPrefixes(); } /** * Return one of the prefixes mapped to a Namespace URI. * *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.
* *Note: this will never return the empty (default) prefix; * to check for a default prefix, use the {@link #getURI getURI} * method with an argument of "".
* * @param uri the namespace URI * @return one of the prefixes currently mapped to the URI supplied, * or null if none is mapped or if the URI is assigned to * the default namespace * @see #getPrefixes(java.lang.String) * @see #getURI */ public String getPrefix (String uri) { return currentContext.getPrefix(uri); } /** * Return an enumeration of all prefixes for a given URI whose * declarations are active in the current context. * This includes declarations from parent contexts that have * not been overridden. * *This method returns prefixes mapped to a specific Namespace * URI. The xml: prefix will be included. If you want only one * prefix that's mapped to the Namespace URI, and you don't care * which one you get, use the {@link #getPrefix getPrefix} * method instead.
* *Note: the empty (default) prefix is never included * in this enumeration; to check for the presence of a default * Namespace, use the {@link #getURI getURI} method with an * argument of "".
* * @param uri The Namespace URI. * @return An enumeration of prefixes (never empty). * @see #getPrefix * @see #getDeclaredPrefixes * @see #getURI */ public Enumeration getPrefixes (String uri) { Vector prefixes = new Vector(); Enumeration allPrefixes = getPrefixes(); while (allPrefixes.hasMoreElements()) { String prefix = (String)allPrefixes.nextElement(); if (uri.equals(getURI(prefix))) { prefixes.addElement(prefix); } } return prefixes.elements(); } /** * Return an enumeration of all prefixes declared in this context. * *The empty (default) prefix will be included in this * enumeration; note that this behaviour differs from that of * {@link #getPrefix} and {@link #getPrefixes}.
* * @return An enumeration of all prefixes declared in this * context. * @see #getPrefixes * @see #getURI */ public Enumeration getDeclaredPrefixes () { return currentContext.getDeclaredPrefixes(); } /** * Controls whether namespace declaration attributes are placed * into the {@link #NSDECL NSDECL} namespace * by {@link #processName processName()}. This may only be * changed before any contexts have been pushed. * * @since 1.5, SAX 2.1alpha * * @exception IllegalStateException when attempting to set this * after any context has been pushed. */ public void setNamespaceDeclUris (boolean value) { if (contextPos != 0) throw new IllegalStateException (); if (value == namespaceDeclUris) return; namespaceDeclUris = value; if (value) currentContext.declarePrefix ("xmlns", NSDECL); else { contexts[contextPos] = currentContext = new Context(); currentContext.declarePrefix("xml", XMLNS); } } /** * Returns true if namespace declaration attributes are placed into * a namespace. This behavior is not the default. * * @since 1.5, SAX 2.1alpha */ public boolean isNamespaceDeclUris () { return namespaceDeclUris; } //////////////////////////////////////////////////////////////////// // Internal state. //////////////////////////////////////////////////////////////////// private Context contexts[]; private Context currentContext; private int contextPos; private boolean namespaceDeclUris; //////////////////////////////////////////////////////////////////// // Internal classes. //////////////////////////////////////////////////////////////////// /** * Internal class for a single Namespace context. * *This module caches and reuses Namespace contexts, * so the number allocated * will be equal to the element depth of the document, not to the total * number of elements (i.e. 5-10 rather than tens of thousands). * Also, data structures used to represent contexts are shared when * possible (child contexts without declarations) to further reduce * the amount of memory that's consumed. *
*/ final class Context { /** * Create the root-level Namespace context. */ Context () { copyTables(); } /** * (Re)set the parent of this Namespace context. * The context must either have been freshly constructed, * or must have been cleared. * * @param context The parent Namespace context object. */ void setParent (Context parent) { this.parent = parent; declarations = null; prefixTable = parent.prefixTable; uriTable = parent.uriTable; elementNameTable = parent.elementNameTable; attributeNameTable = parent.attributeNameTable; defaultNS = parent.defaultNS; declSeen = false; } /** * Makes associated state become collectible, * invalidating this context. * {@link #setParent} must be called before * this context may be used again. */ void clear () { parent = null; prefixTable = null; uriTable = null; elementNameTable = null; attributeNameTable = null; defaultNS = null; } /** * Declare a Namespace prefix for this context. * * @param prefix The prefix to declare. * @param uri The associated Namespace URI. * @see org.xml.sax.helpers.NamespaceSupport#declarePrefix */ void declarePrefix (String prefix, String uri) { // Lazy processing... // if (!declsOK) // throw new IllegalStateException ( // "can't declare any more prefixes in this context"); if (!declSeen) { copyTables(); } if (declarations == null) { declarations = new Vector(); } prefix = prefix.intern(); uri = uri.intern(); if ("".equals(prefix)) { if ("".equals(uri)) { defaultNS = null; } else { defaultNS = uri; } } else { prefixTable.put(prefix, uri); uriTable.put(uri, prefix); // may wipe out another prefix } declarations.addElement(prefix); } /** * Process an XML qualified name in this context. * * @param qName The XML qualified name. * @param isAttribute true if this is an attribute name. * @return An array of three strings containing the * URI part (or empty string), the local part, * and the raw name, all internalized, or null * if there is an undeclared prefix. * @see org.xml.sax.helpers.NamespaceSupport#processName */ String [] processName (String qName, boolean isAttribute) { String name[]; Hashtable table; // Select the appropriate table. if (isAttribute) { table = attributeNameTable; } else { table = elementNameTable; } // Start by looking in the cache, and // return immediately if the name // is already known in this content name = (String[])table.get(qName); if (name != null) { return name; } // We haven't seen this name in this // context before. Maybe in the parent // context, but we can't assume prefix // bindings are the same. name = new String[3]; name[2] = qName.intern(); int index = qName.indexOf(':'); // No prefix. if (index == -1) { if (isAttribute) { if (qName == "xmlns" && namespaceDeclUris) name[0] = NSDECL; else name[0] = ""; } else if (defaultNS == null) { name[0] = ""; } else { name[0] = defaultNS; } name[1] = name[2]; } // Prefix else { String prefix = qName.substring(0, index); String local = qName.substring(index+1); String uri; if ("".equals(prefix)) { uri = defaultNS; } else { uri = (String)prefixTable.get(prefix); } if (uri == null || (!isAttribute && "xmlns".equals (prefix))) { return null; } name[0] = uri; name[1] = local.intern(); } // Save in the cache for future use. // (Could be shared with parent context...) table.put(name[2], name); return name; } /** * Look up the URI associated with a prefix in this context. * * @param prefix The prefix to look up. * @return The associated Namespace URI, or null if none is * declared. * @see org.xml.sax.helpers.NamespaceSupport#getURI */ String getURI (String prefix) { if ("".equals(prefix)) { return defaultNS; } else if (prefixTable == null) { return null; } else { return (String)prefixTable.get(prefix); } } /** * Look up one of the prefixes associated with a URI in this context. * *Since many prefixes may be mapped to the same URI, * the return value may be unreliable.
* * @param uri The URI to look up. * @return The associated prefix, or null if none is declared. * @see org.xml.sax.helpers.NamespaceSupport#getPrefix */ String getPrefix (String uri) { if (uriTable == null) { return null; } else { return (String)uriTable.get(uri); } } /** * Return an enumeration of prefixes declared in this context. * * @return An enumeration of prefixes (possibly empty). * @see org.xml.sax.helpers.NamespaceSupport#getDeclaredPrefixes */ Enumeration getDeclaredPrefixes () { if (declarations == null) { return EMPTY_ENUMERATION; } else { return declarations.elements(); } } /** * Return an enumeration of all prefixes currently in force. * *The default prefix, if in force, is not * returned, and will have to be checked for separately.
* * @return An enumeration of prefixes (never empty). * @see org.xml.sax.helpers.NamespaceSupport#getPrefixes */ Enumeration getPrefixes () { if (prefixTable == null) { return EMPTY_ENUMERATION; } else { return prefixTable.keys(); } } //////////////////////////////////////////////////////////////// // Internal methods. //////////////////////////////////////////////////////////////// /** * Copy on write for the internal tables in this context. * *This class is optimized for the normal case where most * elements do not contain Namespace declarations.
*/ private void copyTables () { if (prefixTable != null) { prefixTable = (Hashtable)prefixTable.clone(); } else { prefixTable = new Hashtable(); } if (uriTable != null) { uriTable = (Hashtable)uriTable.clone(); } else { uriTable = new Hashtable(); } elementNameTable = new Hashtable(); attributeNameTable = new Hashtable(); declSeen = true; } //////////////////////////////////////////////////////////////// // Protected state. //////////////////////////////////////////////////////////////// Hashtable prefixTable; Hashtable uriTable; Hashtable elementNameTable; Hashtable attributeNameTable; String defaultNS = null; //////////////////////////////////////////////////////////////// // Internal state. //////////////////////////////////////////////////////////////// private Vector declarations = null; private boolean declSeen = false; private Context parent = null; } } // end of NamespaceSupport.java