371 lines
13 KiB
Java
371 lines
13 KiB
Java
/*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership.
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* The ASF licenses this file to You under the Apache License, Version 2.0
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* (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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// $Id: XPathFactoryFinder.java 670432 2008-06-23 02:02:08Z mrglavas $
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package javax.xml.xpath;
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import java.io.BufferedReader;
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import java.io.File;
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import java.io.FileInputStream;
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import java.io.IOException;
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import java.io.InputStream;
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import java.io.InputStreamReader;
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import java.net.URL;
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import java.util.Collections;
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import java.util.Enumeration;
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import java.util.Iterator;
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import java.util.Properties;
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import javax.xml.validation.SchemaFactory;
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import libcore.io.IoUtils;
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/**
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* Implementation of {@link XPathFactory#newInstance(String)}.
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*
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* @author <a href="Kohsuke.Kawaguchi@Sun.com">Kohsuke Kawaguchi</a>
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* @version $Revision: 670432 $, $Date: 2008-06-22 19:02:08 -0700 (Sun, 22 Jun 2008) $
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* @since 1.5
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*/
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final class XPathFactoryFinder {
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/** debug support code. */
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private static boolean debug = false;
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/**
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* Default columns per line.
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*/
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private static final int DEFAULT_LINE_LENGTH = 80;
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static {
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String val = System.getProperty("jaxp.debug");
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// Allow simply setting the prop to turn on debug
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debug = val != null && (! "false".equals(val));
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}
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/**
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* <p>Cache properties for performance. Use a static class to avoid double-checked
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* locking.</p>
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*/
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private static class CacheHolder {
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private static Properties cacheProps = new Properties();
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static {
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String javah = System.getProperty("java.home");
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String configFile = javah + File.separator + "lib" + File.separator + "jaxp.properties";
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File f = new File(configFile);
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if (f.exists()) {
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if (debug) debugPrintln("Read properties file " + f);
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try (FileInputStream inputStream = new FileInputStream(f)) {
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cacheProps.load(inputStream);
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} catch (Exception ex) {
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if (debug) {
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ex.printStackTrace();
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}
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}
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}
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}
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}
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/**
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* <p>Conditional debug printing.</p>
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*
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* @param msg to print
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*/
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private static void debugPrintln(String msg) {
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if (debug) {
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System.err.println("JAXP: " + msg);
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}
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}
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/**
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* <p><code>ClassLoader</code> to use to find <code>SchemaFactory</code>.</p>
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*/
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private final ClassLoader classLoader;
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/**
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* <p>Constructor that specifies <code>ClassLoader</code> to use
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* to find <code>SchemaFactory</code>.</p>
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*
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* @param loader
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* to be used to load resource, {@link SchemaFactory}, and
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* {@code SchemaFactoryLoader} implementations during
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* the resolution process.
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* If this parameter is null, the default system class loader
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* will be used.
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*/
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public XPathFactoryFinder(ClassLoader loader) {
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this.classLoader = loader;
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if (debug) {
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debugDisplayClassLoader();
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}
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}
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private void debugDisplayClassLoader() {
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if (classLoader == Thread.currentThread().getContextClassLoader()) {
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debugPrintln("using thread context class loader (" + classLoader + ") for search");
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return;
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}
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if (classLoader==ClassLoader.getSystemClassLoader()) {
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debugPrintln("using system class loader (" + classLoader + ") for search");
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return;
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}
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debugPrintln("using class loader (" + classLoader + ") for search");
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}
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/**
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* <p>Creates a new {@link XPathFactory} object for the specified
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* schema language.</p>
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*
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* @param uri
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* Identifies the underlying object model.
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*
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* @return <code>null</code> if the callee fails to create one.
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*
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* @throws NullPointerException
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* If the parameter is null.
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*/
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public XPathFactory newFactory(String uri) {
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if (uri == null) {
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throw new NullPointerException("uri == null");
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}
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XPathFactory f = _newFactory(uri);
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if (debug) {
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if (f != null) {
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debugPrintln("factory '" + f.getClass().getName() + "' was found for " + uri);
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} else {
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debugPrintln("unable to find a factory for " + uri);
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}
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}
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return f;
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}
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/**
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* <p>Lookup a {@link XPathFactory} for the given object model.</p>
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*
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* @param uri identifies the object model.
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*/
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private XPathFactory _newFactory(String uri) {
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XPathFactory xpf;
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String propertyName = SERVICE_CLASS.getName() + ":" + uri;
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// system property look up
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try {
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if (debug) debugPrintln("Looking up system property '"+propertyName+"'" );
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String r = System.getProperty(propertyName);
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if (r != null && r.length() > 0) {
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if (debug) debugPrintln("The value is '"+r+"'");
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xpf = createInstance(r);
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if(xpf!=null) return xpf;
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} else if (debug) {
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debugPrintln("The property is undefined.");
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}
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} catch (Exception e) {
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e.printStackTrace();
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}
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// try to read from $java.home/lib/jaxp.properties
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try {
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String factoryClassName = CacheHolder.cacheProps.getProperty(propertyName);
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if (debug) debugPrintln("found " + factoryClassName + " in $java.home/jaxp.properties");
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if (factoryClassName != null) {
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xpf = createInstance(factoryClassName);
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if(xpf != null){
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return xpf;
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}
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}
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} catch (Exception ex) {
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if (debug) {
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ex.printStackTrace();
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}
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}
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// try META-INF/services files
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for (URL resource : createServiceFileIterator()) {
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if (debug) debugPrintln("looking into " + resource);
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try {
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xpf = loadFromServicesFile(uri, resource.toExternalForm(), resource.openStream());
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if(xpf!=null) return xpf;
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} catch(IOException e) {
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if( debug ) {
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debugPrintln("failed to read "+resource);
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e.printStackTrace();
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}
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}
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}
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// platform default
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if(uri.equals(XPathFactory.DEFAULT_OBJECT_MODEL_URI)) {
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if (debug) debugPrintln("attempting to use the platform default W3C DOM XPath lib");
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return createInstance("org.apache.xpath.jaxp.XPathFactoryImpl");
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}
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if (debug) debugPrintln("all things were tried, but none was found. bailing out.");
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return null;
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}
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/**
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* <p>Creates an instance of the specified and returns it.</p>
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*
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* @param className
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* fully qualified class name to be instantiated.
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*
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* @return null
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* if it fails. Error messages will be printed by this method.
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*/
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XPathFactory createInstance( String className ) {
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try {
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if (debug) debugPrintln("instantiating "+className);
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Class clazz;
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if( classLoader!=null )
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clazz = classLoader.loadClass(className);
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else
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clazz = Class.forName(className);
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if(debug) debugPrintln("loaded it from "+which(clazz));
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Object o = clazz.newInstance();
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if( o instanceof XPathFactory )
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return (XPathFactory)o;
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if (debug) debugPrintln(className+" is not assignable to "+SERVICE_CLASS.getName());
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}
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// The VM ran out of memory or there was some other serious problem. Re-throw.
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catch (VirtualMachineError vme) {
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throw vme;
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}
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// ThreadDeath should always be re-thrown
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catch (ThreadDeath td) {
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throw td;
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}
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catch (Throwable t) {
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if (debug) {
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debugPrintln("failed to instantiate "+className);
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t.printStackTrace();
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}
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}
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return null;
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}
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/** Searches for a XPathFactory for a given uri in a META-INF/services file. */
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private XPathFactory loadFromServicesFile(String uri, String resourceName, InputStream in) {
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if (debug) debugPrintln("Reading " + resourceName );
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BufferedReader rd;
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try {
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rd = new BufferedReader(new InputStreamReader(in, "UTF-8"), DEFAULT_LINE_LENGTH);
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} catch (java.io.UnsupportedEncodingException e) {
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rd = new BufferedReader(new InputStreamReader(in), DEFAULT_LINE_LENGTH);
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}
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String factoryClassName;
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XPathFactory resultFactory = null;
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// See spec for provider-configuration files: http://java.sun.com/j2se/1.5.0/docs/guide/jar/jar.html#Provider%20Configuration%20File
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while (true) {
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try {
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factoryClassName = rd.readLine();
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} catch (IOException x) {
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// No provider found
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break;
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}
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if (factoryClassName != null) {
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// Ignore comments in the provider-configuration file
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int hashIndex = factoryClassName.indexOf('#');
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if (hashIndex != -1) {
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factoryClassName = factoryClassName.substring(0, hashIndex);
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}
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// Ignore leading and trailing whitespace
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factoryClassName = factoryClassName.trim();
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// If there's no text left or if this was a blank line, go to the next one.
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if (factoryClassName.length() == 0) {
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continue;
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}
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try {
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// Found the right XPathFactory if its isObjectModelSupported(String uri) method returns true.
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XPathFactory foundFactory = createInstance(factoryClassName);
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if (foundFactory.isObjectModelSupported(uri)) {
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resultFactory = foundFactory;
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break;
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}
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} catch (Exception ignored) {
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}
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}
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else {
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break;
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}
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}
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IoUtils.closeQuietly(rd);
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return resultFactory;
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}
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/**
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* Returns an {@link Iterator} that enumerates all
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* the META-INF/services files that we care.
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*/
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private Iterable<URL> createServiceFileIterator() {
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if (classLoader == null) {
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URL resource = XPathFactoryFinder.class.getClassLoader().getResource(SERVICE_ID);
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return Collections.singleton(resource);
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} else {
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try {
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Enumeration<URL> e = classLoader.getResources(SERVICE_ID);
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if (debug && !e.hasMoreElements()) {
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debugPrintln("no "+SERVICE_ID+" file was found");
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}
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return Collections.list(e);
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} catch (IOException e) {
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if (debug) {
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debugPrintln("failed to enumerate resources "+SERVICE_ID);
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e.printStackTrace();
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}
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return Collections.emptySet();
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}
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}
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}
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private static final Class SERVICE_CLASS = XPathFactory.class;
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private static final String SERVICE_ID = "META-INF/services/" + SERVICE_CLASS.getName();
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private static String which( Class clazz ) {
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return which( clazz.getName(), clazz.getClassLoader() );
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}
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/**
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* <p>Search the specified classloader for the given classname.</p>
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*
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* @param classname the fully qualified name of the class to search for
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* @param loader the classloader to search
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*
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* @return the source location of the resource, or null if it wasn't found
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*/
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private static String which(String classname, ClassLoader loader) {
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String classnameAsResource = classname.replace('.', '/') + ".class";
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if (loader==null) loader = ClassLoader.getSystemClassLoader();
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URL it = loader.getResource(classnameAsResource);
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return it != null ? it.toString() : null;
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}
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}
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