Java example source code file (NamespaceSupport.java)
The NamespaceSupport.java Java example source code
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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 1.5 2004/11/03 22:53:09 jsuttor 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.
* See <a href='http://www.saxproject.org'>http://www.saxproject.org
* 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 names into their Namespace
* parts; it can also be used in reverse for generating XML qnames
* 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:
*
* <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
*/
public class NamespaceSupport
{
////////////////////////////////////////////////////////////////////
// Constants.
////////////////////////////////////////////////////////////////////
/**
* The XML Namespace URI as a constant.
* The value is <code>http://www.w3.org/XML/1998/namespace
* as defined in the "Namespaces in XML" * recommendation.
*
* <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";
/**
* The namespace declaration URI as a constant.
* The value is <code>http://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.
*
*
* <p>This is the Namespace URI that is optionally applied to
* <em>xmlns and xmlns:* attributes, which are used to
* declare namespaces. </p>
*
* @since 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.
*
* <p>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.
* </p>
*
* @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.
*
* <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() callback is the right place.
* For elements with such a declaration, it'd done in the first
* <em>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 <em>ContentHandler.startElement()
* 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() 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() 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;
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 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
*
* @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()}.
*
* <p>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:</p>
*
* <dl>
* <dt>parts[0]
* <dd>The Namespace URI, or an empty string if none is
* in use.</dd>
* <dt>parts[1]
* <dd>The local name (without prefix).
* <dt>parts[2]
* <dd>The original raw name.
* </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 receive the
* default Namespace (if any), while an unprefixed attribute name
* will not.</p>
*
* @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.
*
* <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 whose declarations are
* active in the current context.
* This includes declarations from parent contexts that have
* not been overridden.
*
* <p>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 "".</p>
*
* @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.
*
* <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>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 "".</p>
*
* @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.
*
* <p>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.</p>
*
* <p>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 "".</p>
*
* @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.
*
* <p>The empty (default) prefix will be included in this
* enumeration; note that this behaviour differs from that of
* {@link #getPrefix} and {@link #getPrefixes}.</p>
*
* @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 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 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.
*
* <p>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.
* </p>
*/
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.
*
* <p>Since many prefixes may be mapped to the same URI,
* the return value may be unreliable.</p>
*
* @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.
*
* <p>The default prefix, if in force, is not
* returned, and will have to be checked for separately.</p>
*
* @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.
*
* <p>This class is optimized for the normal case where most
* elements do not contain Namespace declarations.</p>
*/
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
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