com.elsevier.xml.NamespaceContextMappings.java Source code

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Here is the source code for com.elsevier.xml.NamespaceContextMappings.java

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/*
 * Copyright (c)2015 Elsevier, Inc.
    
 * Licensed 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.
 *
 */
package com.elsevier.xml;

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map.Entry;
import java.util.Set;

import javax.xml.XMLConstants;
import javax.xml.namespace.NamespaceContext;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * Class which provides the ability to 'register' namespace prefix to namespace
 * uri mappings. This is necessary for the XPath/XQuery expression evaluation
 * when the xpath/xquery expression contains namespace prefixes. If the
 * xpath/xquery expression does not contain namespace prefixes, then there is no
 * need to register any mappings. Default mappings are provided for the
 * well-known namespace prefixes 'xml', 'fn', and 'xs'.
 * 
 * @author Darin McBeath
 * 
 */
public class NamespaceContextMappings implements NamespaceContext {

    // Namespace Prefix to Namespace URI mapping cache
    private volatile static HashMap<String, String> prefixNamespaceMap = null;

    // Logger
    private static Log log = LogFactory.getLog(NamespaceContextMappings.class);

    /**
     * Init the cache with the passed HashMap of prefixes and namespaces. 
     * 
     * @param initPrefixNamespaceMap HashMap of prefixes and namespaces
     */
    public static void init(HashMap<String, String> initPrefixNamespaceMap) {

        if (prefixNamespaceMap == null) {
            synchronized (NamespaceContextMappings.class) {
                if (prefixNamespaceMap == null) {

                    // Add the defaults
                    prefixNamespaceMap = new HashMap<String, String>();
                    prefixNamespaceMap.put("xml", XMLConstants.XML_NS_URI);
                    prefixNamespaceMap.put("fn", "http://www.w3.org/2005/xpath-functions");
                    prefixNamespaceMap.put("xs", "http://www.w3.org/2001/XMLSchema");

                    // Add those passed to init
                    prefixNamespaceMap.putAll(initPrefixNamespaceMap);

                    // Output the list of namespace prefix to uri mappings
                    Set<String> keys = prefixNamespaceMap.keySet();
                    Iterator<String> it = keys.iterator();
                    log.info("** Namespace Mappings **");
                    while (it.hasNext()) {
                        String key = it.next();
                        String val = prefixNamespaceMap.get(key);
                        log.info(key + "=" + val);
                    }

                }
            }
        }

    }

    /**
     * Clear the cache.
     */
    public static void emptyCache() {

        if (prefixNamespaceMap != null) {
            synchronized (NamespaceContextMappings.class) {
                if (prefixNamespaceMap != null) {
                    prefixNamespaceMap = null;
                }
            }
        }

    }

    /**
     * Get the Namespace Prefix to Uri Mappings. This will be used by the
     * XPathProcessor and XQueryProcessor when setting namespaces.
     * 
     * @return Mappings
     */
    public static Set<Entry<String, String>> getMappings() {

        if (prefixNamespaceMap != null) {
            return prefixNamespaceMap.entrySet();
        } else {
            return null;
        }

    }

    /**
     * Provide namespace prefix to namespace uri resolution capability. All of
     * the namespace prefixed declared in XPath Expressions should be mapped to
     * the correct URI (in the XML) otherwise the evaluation will not be
     * correct.
     * 
     * @param prefix Namespace prefix
     *            
     * @return Namespace uri
     */
    public String getNamespaceURI(String prefix) {

        if (prefix == null)
            throw new NullPointerException("Null prefix");
        String uri = prefixNamespaceMap.get(prefix);
        if (uri == null) {
            return XMLConstants.NULL_NS_URI;
        } else {
            return uri;
        }

    }

    public String getPrefix(String uri) {

        throw new UnsupportedOperationException();

    }

    public Iterator<String> getPrefixes(String uri) {

        throw new UnsupportedOperationException();

    }

}