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Apache XML Security for Java supports XML-Signature Syntax and Processing, W3C Recommendation 12 February 2002, and XML Encryption Syntax and Processing, W3C Recommendation 10 December 2002. As of version 1.4, the library supports the standard Java API JSR-105: XML Digital Signature APIs.

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/**
 * 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.xml.security.utils;


/**
 * A Factory to return an XPathAPI instance. If Xalan is available it returns XalanXPathAPI. If not, then 
 * it returns JDKXPathAPI.
 */
public abstract class XPathFactory {

    private static boolean xalanInstalled;
    
    static {
        try {
            Class funcTableClass = 
                ClassLoaderUtils.loadClass("org.apache.xpath.compiler.FunctionTable", XPathFactory.class);
            if (funcTableClass != null) {
                xalanInstalled = true;
            }
        } catch (Exception e) { //NOPMD
            //ignore
        }
    }
    
    protected static synchronized boolean isXalanInstalled() {
        return xalanInstalled;
    }
    
    /**
     * Get a new XPathFactory instance
     */
    public static XPathFactory newInstance() {
        if (!isXalanInstalled()) {
            return new JDKXPathFactory();
        }
        // Xalan is available
        if (XalanXPathAPI.isInstalled()) {
            return new XalanXPathFactory();
        }
        // Some problem was encountered in fixing up the Xalan FunctionTable so fall back to the 
        // JDK implementation
        return new JDKXPathFactory();
    }

    /**
     * Get a new XPathAPI instance
     */
    public abstract XPathAPI newXPathAPI();

}