https://xerces.apache.org/xerces2-j/: Xerces2 is the next generation of high performance, fully compliant XML parsers in the Apache Xerces family. This new version of Xerces introduces the Xerces Native Interface (XNI), a complete framework for building parser components and configurations that is extremely modular and easy to program. The Apache Xerces2 parser is the reference implementation of XNI but other parser components, configurations, and parsers can be written using the Xerces Native Interface. For complete design and implementation documents, refer to the XNI Manual. Xerces2 is a fully conforming XML Schema 1.0 processor. A partial experimental implementation of the XML Schema 1.1 Structures and Datatypes Working Drafts (December 2009) and an experimental implementation of the XML Schema Definition Language (XSD): Component Designators (SCD) Candidate Recommendation (January 2010) are provided for evaluation. For more information, refer to the XML Schema page. Xerces2 also provides a complete implementation of the Document Object Model Level 3 Core and Load/Save W3C Recommendations and provides a complete implementation of the XML Inclusions (XInclude) W3C Recommendation. It also provides support for OASIS XML Catalogs v1.1. Xerces2 is able to parse documents written according to the XML 1.1 Recommendation, except that it does not yet provide an option to enable normalization checking as described in section 2.13 of this specification. It also handles namespaces according to the XML Namespaces 1.1 Recommendation, and will correctly serialize XML 1.1 documents if the DOM level 3 load/save APIs are in use. 
/*
 * 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.
 */

package org.apache.xerces.dom;

import org.w3c.dom.DOMImplementation;
import org.w3c.dom.DocumentType;


The DOMImplementation class is description of a particular
implementation of the Document Object Model. As such its data is
static, shared by all instances of this implementation.


The DOM API requires that it be a real object rather than static
methods. However, there's nothing that says it can't be a singleton,
so that's how I've implemented it.

@xerces.internal
Version:$Id: PSVIDOMImplementationImpl.java 809736 2009-08-31 20:43:19Z mrglavas $
Since: PR-DOM-Level-1-19980818.
/**
 * The DOMImplementation class is description of a particular
 * implementation of the Document Object Model. As such its data is
 * static, shared by all instances of this implementation.
 * <P>
 * The DOM API requires that it be a real object rather than static
 * methods. However, there's nothing that says it can't be a singleton,
 * so that's how I've implemented it.
 * 
 * @xerces.internal

 *
 * @version $Id: PSVIDOMImplementationImpl.java 809736 2009-08-31 20:43:19Z mrglavas $
 * @since  PR-DOM-Level-1-19980818.
 */
public class PSVIDOMImplementationImpl extends DOMImplementationImpl {

    //
    // Data
    //

    // static

    
Dom implementation singleton. 
/** Dom implementation singleton. */
    static final PSVIDOMImplementationImpl singleton = new PSVIDOMImplementationImpl();

    //
    // Public methods
    //

    
NON-DOM: Obtain and return the single shared object 
/** NON-DOM: Obtain and return the single shared object */
    public static DOMImplementation getDOMImplementation() {
        return singleton;
    }  

    //
    // DOMImplementation methods
    //

    
Test if the DOM implementation supports a specific "feature" --
currently meaning language and level thereof.

Params:
  • feature –      The package name of the feature to test.
In Level 1, supported values are "HTML" and "XML" (case-insensitive).
At this writing, org.apache.xerces.dom supports only XML.
  • version –      The version number of the feature being tested.
This is interpreted as "Version of the DOM API supported for the
specified Feature", and in Level 1 should be "1.0"
Returns:   true iff this implementation is compatable with the specified
feature and version.
/** 
     * Test if the DOM implementation supports a specific "feature" --
     * currently meaning language and level thereof.
     * 
     * @param feature      The package name of the feature to test.
     * In Level 1, supported values are "HTML" and "XML" (case-insensitive).
     * At this writing, org.apache.xerces.dom supports only XML.
     *
     * @param version      The version number of the feature being tested.
     * This is interpreted as "Version of the DOM API supported for the
     * specified Feature", and in Level 1 should be "1.0"
     *
     * @return    true iff this implementation is compatable with the specified
     * feature and version.
     */
    public boolean hasFeature(String feature, String version) {
        return super.hasFeature(feature, version) ||
               feature.equalsIgnoreCase("psvi");
    } // hasFeature(String,String):boolean
    
    //
    // Protected methods
    //
    
    protected CoreDocumentImpl createDocument(DocumentType doctype) {
        return new PSVIDocumentImpl(doctype);
    }

} // class PSVIDOMImplementationImpl