xml/namespace/QName.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

// $Id: QName.java 754581 2009-03-15 01:32:39Z mrglavas $

package javax.xml.namespace;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.Serializable;
import javax.xml.XMLConstants;

/**
 * <p><code>QName</code> represents a <strong>qualified name</strong>
 * as defined in the XML specifications: <a
 * href="http://www.w3.org/TR/xmlschema-2/#QName">XML Schema Part2:
 * Datatypes specification</a>, <a
 * href="http://www.w3.org/TR/REC-xml-names/#ns-qualnames">Namespaces
 * in XML</a>, <a
 * href="http://www.w3.org/XML/xml-names-19990114-errata">Namespaces
 * in XML Errata</a>.</p>
 *
 * <p>The value of a <code>QName</code> contains a <strong>Namespace
 * URI</strong>, <strong>local part</strong> and
 * <strong>prefix</strong>.</p>
 *
 * <p>The prefix is included in <code>QName</code> to retain lexical
 * information <strong><em>when present</em></strong> in an {@link
 * javax.xml.transform.Source XML input source}. The prefix is
 * <strong><em>NOT</em></strong> used in {@link #equals(Object)
 * QName.equals(Object)} or to compute the {@link #hashCode()
 * QName.hashCode()}.  Equality and the hash code are defined using
 * <strong><em>only</em></strong> the Namespace URI and local part.</p>
 *
 * <p>If not specified, the Namespace URI is set to {@link
 * javax.xml.XMLConstants#NULL_NS_URI XMLConstants.NULL_NS_URI}.
 * If not specified, the prefix is set to {@link
 * javax.xml.XMLConstants#DEFAULT_NS_PREFIX
 * XMLConstants.DEFAULT_NS_PREFIX}.</p>
 *
 * <p><code>QName</code> is immutable.</p>
 *
 * @author <a href="mailto:Jeff.Suttor (at) Sun.com">Jeff Suttor</a>
 * @version $Revision: 754581 $, $Date: 2009-03-14 18:32:39 -0700 (Sat, 14 Mar 2009) $
 * @see <a href="http://www.w3.org/TR/xmlschema-2/#QName">XML Schema Part2: Datatypes specification</a>
 * @see <a href="http://www.w3.org/TR/REC-xml-names/#ns-qualnames">Namespaces in XML</a>
 * @see <a href="http://www.w3.org/XML/xml-names-19990114-errata">Namespaces in XML Errata</a>
 * @since 1.5
 */

public class QName implements Serializable {

    /**
     * <p>Stream Unique Identifier.</p>
     *
     * <p>To enable the compatibility <code>serialVersionUID</code>
     * set the System Property
     * <code>org.apache.xml.namespace.QName.useCompatibleSerialVersionUID</code>
     * to a value of "1.0".</p>
     */
    private static final long serialVersionUID;

    /**
     * <p>The original default Stream Unique Identifier.</p>
     */
    private static final long defaultSerialVersionUID = -9120448754896609940L;

    /**
     * <p>The compatibility Stream Unique Identifier that was introduced
     * with Java 5 SE SDK.</p>
     */
    private static final long compatibilitySerialVersionUID = 4418622981026545151L;

    static {
        String compatPropValue = System.getProperty("org.apache.xml.namespace.QName.useCompatibleSerialVersionUID");
        // If 1.0 use compatibility serialVersionUID
        serialVersionUID = !"1.0".equals(compatPropValue) ? defaultSerialVersionUID : compatibilitySerialVersionUID;
    }

    /**
     * <p>Namespace URI of this <code>QName</code>.</p>
     */
    private final String namespaceURI;

    /**
     * <p>local part of this <code>QName</code>.</p>
     */
    private final String localPart;

    /**
     * <p>prefix of this <code>QName</code>.</p>
     */
    private String prefix;

    /**
     * <p><code>String</code> representation of this <code>QName</code>.</p>
     */
    private transient String qNameAsString;

    /**
     * <p><code>QName</code> constructor specifying the Namespace URI
     * and local part.</p>
     *
     * <p>If the Namespace URI is <code>null</code>, it is set to
     * {@link javax.xml.XMLConstants#NULL_NS_URI
     * XMLConstants.NULL_NS_URI}.  This value represents no
     * explicitly defined Namespace as defined by the <a
     * href="http://www.w3.org/TR/REC-xml-names/#ns-qualnames">Namespaces
     * in XML</a> specification.  This action preserves compatible
     * behavior with QName 1.0.  Explicitly providing the {@link
     * javax.xml.XMLConstants#NULL_NS_URI
     * XMLConstants.NULL_NS_URI} value is the preferred coding
     * style.</p>
     *
     * <p>If the local part is <code>null</code> an
     * <code>IllegalArgumentException</code> is thrown.
     * A local part of "" is allowed to preserve
     * compatible behavior with QName 1.0. </p>
     *
     * <p>When using this constructor, the prefix is set to {@link
     * javax.xml.XMLConstants#DEFAULT_NS_PREFIX
     * XMLConstants.DEFAULT_NS_PREFIX}.</p>
     *
     * <p>The Namespace URI is not validated as a
     * <a href="http://www.ietf.org/rfc/rfc2396.txt">URI reference</a>.
     * The local part is not validated as a
     * <a href="http://www.w3.org/TR/REC-xml-names/#NT-NCName">NCName</a>
     * as specified in <a href="http://www.w3.org/TR/REC-xml-names/">Namespaces
     * in XML</a>.</p>
     *
     * @param namespaceURI Namespace URI of the <code>QName</code>
     * @param localPart    local part of the <code>QName</code>
     *
     * @see #QName(String namespaceURI, String localPart, String
     * prefix) QName(String namespaceURI, String localPart, String
     * prefix)
     */
    public QName(final String namespaceURI, final String localPart) {
        this(namespaceURI, localPart, XMLConstants.DEFAULT_NS_PREFIX);
    }

    /**
     * <p><code>QName</code> constructor specifying the Namespace URI,
     * local part and prefix.</p>
     *
     * <p>If the Namespace URI is <code>null</code>, it is set to
     * {@link javax.xml.XMLConstants#NULL_NS_URI
     * XMLConstants.NULL_NS_URI}.  This value represents no
     * explicitly defined Namespace as defined by the <a
     * href="http://www.w3.org/TR/REC-xml-names/#ns-qualnames">Namespaces
     * in XML</a> specification.  This action preserves compatible
     * behavior with QName 1.0.  Explicitly providing the {@link
     * javax.xml.XMLConstants#NULL_NS_URI
     * XMLConstants.NULL_NS_URI} value is the preferred coding
     * style.</p>
     *
     * <p>If the local part is <code>null</code> an
     * <code>IllegalArgumentException</code> is thrown.
     * A local part of "" is allowed to preserve
     * compatible behavior with QName 1.0. </p>
     *
     * <p>If the prefix is <code>null</code>, an
     * <code>IllegalArgumentException</code> is thrown.  Use {@link
     * javax.xml.XMLConstants#DEFAULT_NS_PREFIX
     * XMLConstants.DEFAULT_NS_PREFIX} to explicitly indicate that no
     * prefix is present or the prefix is not relevant.</p>
     *
     * <p>The Namespace URI is not validated as a
     * <a href="http://www.ietf.org/rfc/rfc2396.txt">URI reference</a>.
     * The local part and prefix are not validated as a
     * <a href="http://www.w3.org/TR/REC-xml-names/#NT-NCName">NCName</a>
     * as specified in <a href="http://www.w3.org/TR/REC-xml-names/">Namespaces
     * in XML</a>.</p>
     *
     * @param namespaceURI Namespace URI of the <code>QName</code>
     * @param localPart    local part of the <code>QName</code>
     * @param prefix       prefix of the <code>QName</code>
     */
    public QName(String namespaceURI, String localPart, String prefix) {

        // map null Namespace URI to default to preserve compatibility with QName 1.0
        if (namespaceURI == null) {
            this.namespaceURI = XMLConstants.NULL_NS_URI;
        } else {
            this.namespaceURI = namespaceURI;
        }

        // local part is required.  "" is allowed to preserve compatibility with QName 1.0
        if (localPart == null) {
            throw new IllegalArgumentException("local part cannot be \"null\" when creating a QName");
        }
        this.localPart = localPart;

        // prefix is required
        if (prefix == null) {
            throw new IllegalArgumentException("prefix cannot be \"null\" when creating a QName");
        }
        this.prefix = prefix;
    }

    /**
     * <p><code>QName</code> constructor specifying the local part.</p>
     *
     * <p>If the local part is <code>null</code> an
     * <code>IllegalArgumentException</code> is thrown.
     * A local part of "" is allowed to preserve
     * compatible behavior with QName 1.0. </p>
     *
     * <p>When using this constructor, the Namespace URI is set to
     * {@link javax.xml.XMLConstants#NULL_NS_URI
     * XMLConstants.NULL_NS_URI} and the prefix is set to {@link
     * javax.xml.XMLConstants#DEFAULT_NS_PREFIX
     * XMLConstants.DEFAULT_NS_PREFIX}.</p>
     *
     * <p><em>In an XML context, all Element and Attribute names exist
     * in the context of a Namespace.  Making this explicit during the
     * construction of a <code>QName</code> helps prevent hard to
     * diagnosis XML validity errors.  The constructors {@link
     * #QName(String namespaceURI, String localPart) QName(String
     * namespaceURI, String localPart)} and
     * {@link #QName(String namespaceURI, String localPart, String prefix)}
     * are preferred.</em></p>
     *
     * <p>The local part is not validated as a
     * <a href="http://www.w3.org/TR/REC-xml-names/#NT-NCName">NCName</a>
     * as specified in <a href="http://www.w3.org/TR/REC-xml-names/">Namespaces
     * in XML</a>.</p>
     *
     * @param localPart local part of the <code>QName</code>
     * @see #QName(String namespaceURI, String localPart) QName(String
     * namespaceURI, String localPart)
     * @see #QName(String namespaceURI, String localPart, String
     * prefix) QName(String namespaceURI, String localPart, String
     * prefix)
     */
    public QName(String localPart) {
        this(
            XMLConstants.NULL_NS_URI,
            localPart,
            XMLConstants.DEFAULT_NS_PREFIX);
    }

    /**
     * <p>Get the Namespace URI of this <code>QName</code>.</p>
     *
     * @return Namespace URI of this <code>QName</code>
     */
    public String getNamespaceURI() {
        return namespaceURI;
    }

    /**
     * <p>Get the local part of this <code>QName</code>.</p>
     *
     *  @return local part of this <code>QName</code>
     */
    public String getLocalPart() {
        return localPart;
    }

    /**
     * <p>Get the prefix of this <code>QName</code>.</p>
     *
     * <p>The prefix assigned to a <code>QName</code> might
     * <strong><em>NOT</em></strong> be valid in a different
     * context. For example, a <code>QName</code> may be assigned a
     * prefix in the context of parsing a document but that prefix may
     * be invalid in the context of a different document.</p>
     *
     *  @return prefix of this <code>QName</code>
     */
    public String getPrefix() {
        return prefix;
    }

    /**
     * <p>Test this <code>QName</code> for equality with another
     * <code>Object</code>.</p>
     *
     * <p>If the <code>Object</code> to be tested is not a
     * <code>QName</code> or is <code>null</code>, then this method
     * returns <code>false</code>.</p>
     *
     * <p>Two <code>QName</code>s are considered equal if and only if
     * both the Namespace URI and local part are equal. This method
     * uses <code>String.equals()</code> to check equality of the
     * Namespace URI and local part. The prefix is
     * <strong><em>NOT</em></strong> used to determine equality.</p>
     *
     * <p>This method satisfies the general contract of {@link
     * java.lang.Object#equals(Object) Object.equals(Object)}</p>
     *
     * @param objectToTest the <code>Object</code> to test for
     * equality with this <code>QName</code>
     * @return <code>true</code> if the given <code>Object</code> is
     * equal to this <code>QName</code> else <code>false</code>
     */
    public final boolean equals(Object objectToTest) {
        // Is this the same object?
        if (objectToTest == this) {
            return true;
        }
        // Is this a QName?
        if (objectToTest instanceof QName) {
            QName qName = (QName) objectToTest;
            return localPart.equals(qName.localPart) && namespaceURI.equals(qName.namespaceURI);
        }
        return false;
    }

    /**
     * <p>Generate the hash code for this <code>QName</code>.</p>
     *
     * <p>The hash code is calculated using both the Namespace URI and
     * the local part of the <code>QName</code>.  The prefix is
     * <strong><em>NOT</em></strong> used to calculate the hash
     * code.</p>
     *
     * <p>This method satisfies the general contract of {@link
     * java.lang.Object#hashCode() Object.hashCode()}.</p>
     *
     * @return hash code for this <code>QName</code> <code>Object</code>
     */
    public final int hashCode() {
        return namespaceURI.hashCode() ^ localPart.hashCode();
    }

    /**
     * <p><code>String</code> representation of this
     * <code>QName</code>.</p>
     *
     * <p>The commonly accepted way of representing a <code>QName</code>
     * as a <code>String</code> was <a href="http://jclark.com/xml/xmlns.htm">defined</a>
     * by James Clark.  Although this is not a <em>standard</em>
     * specification, it is in common use,  e.g. {@link javax.xml.transform.Transformer#setParameter(String name, Object value)}.
     * This implementation represents a <code>QName</code> as:
     * "{" + Namespace URI + "}" + local part.  If the Namespace URI
     * <code>.equals(XMLConstants.NULL_NS_URI)</code>, only the
     * local part is returned.  An appropriate use of this method is
     * for debugging or logging for human consumption.</p>
     *
     * <p>Note the prefix value is <strong><em>NOT</em></strong>
     * returned as part of the <code>String</code> representation.</p>
     *
     * <p>This method satisfies the general contract of {@link
     * java.lang.Object#toString() Object.toString()}.</p>
     *
     * @return <code>String</code> representation of this <code>QName</code>
     */
    public String toString() {
        String _qNameAsString = qNameAsString;
        if (_qNameAsString == null) {
            final int nsLength = namespaceURI.length();
            if (nsLength == 0) {
                _qNameAsString = localPart;
            }
            else {
                StringBuilder buffer = new StringBuilder(nsLength + localPart.length() + 2);
                buffer.append('{');
                buffer.append(namespaceURI);
                buffer.append('}');
                buffer.append(localPart);
                _qNameAsString = buffer.toString();
            }
            qNameAsString = _qNameAsString;
        }
        return _qNameAsString;
    }

    /**
     * <p><code>QName</code> derived from parsing the formatted
     * <code>String</code>.</p>
     *
     * <p>If the <code>String</code> is <code>null</code> or does not conform to
     * {@link #toString() QName.toString()} formatting, an
     * <code>IllegalArgumentException</code> is thrown.</p>
     *
     * <p><em>The <code>String</code> <strong>MUST</strong> be in the
     * form returned by {@link #toString() QName.toString()}.</em></p>
     *
     * <p>The commonly accepted way of representing a <code>QName</code>
     * as a <code>String</code> was <a href="http://jclark.com/xml/xmlns.htm">defined</a>
     * by James Clark.  Although this is not a <em>standard</em>
     * specification, it is in common use,  e.g. {@link javax.xml.transform.Transformer#setParameter(String name, Object value)}.
     * This implementation parses a <code>String</code> formatted
     * as: "{" + Namespace URI + "}" + local part.  If the Namespace
     * URI <code>.equals(XMLConstants.NULL_NS_URI)</code>, only the
     * local part should be provided.</p>
     *
     * <p>The prefix value <strong><em>CANNOT</em></strong> be
     * represented in the <code>String</code> and will be set to
     * {@link javax.xml.XMLConstants#DEFAULT_NS_PREFIX
     * XMLConstants.DEFAULT_NS_PREFIX}.</p>
     *
     * <p>This method does not do full validation of the resulting
     * <code>QName</code>.
     * <p>The Namespace URI is not validated as a
     * <a href="http://www.ietf.org/rfc/rfc2396.txt">URI reference</a>.
     * The local part is not validated as a
     * <a href="http://www.w3.org/TR/REC-xml-names/#NT-NCName">NCName</a>
     * as specified in
     * <a href="http://www.w3.org/TR/REC-xml-names/">Namespaces in XML</a>.</p>
     *
     * @param qNameAsString <code>String</code> representation
     * of the <code>QName</code>
     * @return <code>QName</code> corresponding to the given <code>String</code>
     * @see #toString() QName.toString()
     */
    public static QName valueOf(String qNameAsString) {

        // null is not valid
        if (qNameAsString == null) {
            throw new IllegalArgumentException("cannot create QName from \"null\" or \"\" String");
        }

        // "" local part is valid to preserve compatible behavior with QName 1.0
        if (qNameAsString.length() == 0) {
            return new QName(
                XMLConstants.NULL_NS_URI,
                qNameAsString,
                XMLConstants.DEFAULT_NS_PREFIX);
        }

        // local part only?
        if (qNameAsString.charAt(0) != '{') {
            return new QName(
                XMLConstants.NULL_NS_URI,
                qNameAsString,
                XMLConstants.DEFAULT_NS_PREFIX);
        }

        // Namespace URI improperly specified?
        if (qNameAsString.startsWith("{" + XMLConstants.NULL_NS_URI + "}")) {
            throw new IllegalArgumentException(
                "Namespace URI .equals(XMLConstants.NULL_NS_URI), "
                + ".equals(\"" + XMLConstants.NULL_NS_URI + "\"), "
                + "only the local part, "
                + "\"" + qNameAsString.substring(2 + XMLConstants.NULL_NS_URI.length()) + "\", "
                + "should be provided.");
        }

        // Namespace URI and local part specified
        int endOfNamespaceURI = qNameAsString.indexOf('}');
        if (endOfNamespaceURI == -1) {
            throw new IllegalArgumentException(
                "cannot create QName from \""
                    + qNameAsString
                    + "\", missing closing \"}\"");
        }
        return new QName(
            qNameAsString.substring(1, endOfNamespaceURI),
            qNameAsString.substring(endOfNamespaceURI + 1),
            XMLConstants.DEFAULT_NS_PREFIX);
    }

    /*
     * For old versions of QName which didn't have a prefix field,
     * <code>ObjectInputStream.defaultReadObject()</code> will initialize
     * the prefix to <code>null</code> instead of the empty string. This
     * method fixes up the prefix field if it didn't exist in the serialized
     * object.
     */
    private void readObject(ObjectInputStream in)
        throws IOException, ClassNotFoundException {
        in.defaultReadObject();
        if (prefix == null) {
            prefix = XMLConstants.DEFAULT_NS_PREFIX;
        }
    }
}