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	/*
	* Copyright (c) 2003, 2021, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	package javax.xml.parsers;

	import java.io.File;
	import java.security.AccessController;
	import java.security.PrivilegedAction;
	import java.util.Iterator;
	import java.util.Properties;
	import java.util.ServiceConfigurationError;
	import java.util.ServiceLoader;
	import java.util.function.Supplier;
	import jdk.xml.internal.SecuritySupport;

	/**
	* <p>Implements pluggable Parsers.</p>
	*
	* <p>This class is duplicated for each JAXP subpackage so keep it in
	* sync. It is package private for secure class loading.</p>
	*
	* @author Santiago PericasGeertsen
	*/
	class FactoryFinder {
	private static final String DEFAULT_PACKAGE = "com.sun.org.apache.xerces.internal";
	/**
	* Internal debug flag.
	*/
	private static boolean debug = false;

	/**
	* Cache for properties in java.home/conf/jaxp.properties
	*/
	private static final Properties cacheProps = new Properties();

	/**
	* Flag indicating if properties from java.home/conf/jaxp.properties
	* have been cached.
	*/
	static volatile boolean firstTime = true;

	// Define system property "jaxp.debug" to get output
	static {
	// Use try/catch block to support applets, which throws
	// SecurityException out of this code.
	try {
	String val = SecuritySupport.getSystemProperty("jaxp.debug");
	// Allow simply setting the prop to turn on debug
	debug = val != null && !"false".equals(val);
	}
	catch (SecurityException se) {
	debug = false;
	}
	}

	private static void dPrint(Supplier<String> msgGen) {
	if (debug) {
	System.err.println("JAXP: " + msgGen.get());
	}
	}

	/**
	* Attempt to load a class using the class loader supplied. If that fails
	* and fall back is enabled, the current (i.e. bootstrap) class loader is
	* tried.
	*
	* If the class loader supplied is <code>null</code>, first try using the
	* context class loader followed by the current (i.e. bootstrap) class
	* loader.
	*
	* Use bootstrap classLoader if cl = null and useBSClsLoader is true
	*/
	static private Class<?> getProviderClass(String className, ClassLoader cl,
	boolean doFallback, boolean useBSClsLoader) throws ClassNotFoundException
	{
	try {
	if (cl == null) {
	if (useBSClsLoader) {
	return Class.forName(className, false, FactoryFinder.class.getClassLoader());
	} else {
	cl = SecuritySupport.getContextClassLoader();
	if (cl == null) {
	throw new ClassNotFoundException();
	}
	else {
	return Class.forName(className, false, cl);
	}
	}
	}
	else {
	return Class.forName(className, false, cl);
	}
	}
	catch (ClassNotFoundException e1) {
	if (doFallback) {
	// Use current class loader - should always be bootstrap CL
	return Class.forName(className, false, FactoryFinder.class.getClassLoader());
	}
	else {
	throw e1;
	}
	}
	}

	/**
	* Create an instance of a class. Delegates to method
	* <code>getProviderClass()</code> in order to load the class.
	*
	* @param type Base class / Service interface of the factory to
	* instantiate.
	*
	* @param className Name of the concrete class corresponding to the
	* service provider
	*
	* @param cl <code>ClassLoader</code> used to load the factory class. If <code>null</code>
	* current <code>Thread</code>'s context classLoader is used to load the factory class.
	*
	* @param doFallback True if the current ClassLoader should be tried as
	* a fallback if the class is not found using cl
	*/
	static <T> T newInstance(Class<T> type, String className, ClassLoader cl,
	boolean doFallback)
	throws FactoryConfigurationError
	{
	return newInstance(type, className, cl, doFallback, false);
	}

	/**
	* Create an instance of a class. Delegates to method
	* <code>getProviderClass()</code> in order to load the class.
	*
	* @param type Base class / Service interface of the factory to
	* instantiate.
	*
	* @param className Name of the concrete class corresponding to the
	* service provider
	*
	* @param cl <code>ClassLoader</code> used to load the factory class. If <code>null</code>
	* current <code>Thread</code>'s context classLoader is used to load the factory class.
	*
	* @param doFallback True if the current ClassLoader should be tried as
	* a fallback if the class is not found using cl
	*
	* @param useBSClsLoader True if cl=null actually meant bootstrap classLoader. This parameter
	* is needed since DocumentBuilderFactory/SAXParserFactory defined null as context classLoader.
	*/
	@SuppressWarnings("removal")
	static <T> T newInstance(Class<T> type, String className, ClassLoader cl,
	boolean doFallback, boolean useBSClsLoader)
	throws FactoryConfigurationError
	{
	assert type != null;
	// make sure we have access to restricted packages
	if (System.getSecurityManager() != null) {
	if (className != null && className.startsWith(DEFAULT_PACKAGE)) {
	cl = null;
	useBSClsLoader = true;
	}
	}

	try {
	Class<?> providerClass = getProviderClass(className, cl, doFallback, useBSClsLoader);
	if (!type.isAssignableFrom(providerClass)) {
	throw new ClassCastException(className + " cannot be cast to " + type.getName());
	}
	Object instance = providerClass.getConstructor().newInstance();
	final ClassLoader clD = cl;
	dPrint(()->"created new instance of " + providerClass +
	" using ClassLoader: " + clD);
	return type.cast(instance);
	}
	catch (ClassNotFoundException x) {
	throw new FactoryConfigurationError(x,
	"Provider " + className + " not found");
	}
	catch (Exception x) {
	throw new FactoryConfigurationError(x,
	"Provider " + className + " could not be instantiated: " + x);
	}
	}

	/**
	* Finds the implementation Class object in the specified order. Main
	* entry point.
	* @return Class object of factory, never null
	*
	* @param type Base class / Service interface of the
	* factory to find.
	* @param fallbackClassName Implementation class name, if nothing else
	* is found. Use null to mean no fallback.
	*
	* Package private so this code can be shared.
	*/
	static <T> T find(Class<T> type, String fallbackClassName)
	throws FactoryConfigurationError
	{
	final String factoryId = type.getName();
	dPrint(()->"find factoryId =" + factoryId);

	// Use the system property first
	try {
	String systemProp = SecuritySupport.getSystemProperty(factoryId);
	if (systemProp != null) {
	dPrint(()->"found system property, value=" + systemProp);
	return newInstance(type, systemProp, null, true);
	}
	}
	catch (SecurityException se) {
	if (debug) se.printStackTrace();
	}

	// try to read from $java.home/conf/jaxp.properties
	try {
	if (firstTime) {
	synchronized (cacheProps) {
	if (firstTime) {
	String configFile = SecuritySupport.getSystemProperty("java.home") + File.separator +
	"conf" + File.separator + "jaxp.properties";
	File f = new File(configFile);
	firstTime = false;
	if (SecuritySupport.doesFileExist(f)) {
	dPrint(()->"Read properties file "+f);
	cacheProps.load(SecuritySupport.getFileInputStream(f));
	}
	}
	}
	}
	final String factoryClassName = cacheProps.getProperty(factoryId);

	if (factoryClassName != null) {
	dPrint(()->"found in ${java.home}/conf/jaxp.properties, value=" + factoryClassName);
	return newInstance(type, factoryClassName, null, true);
	}
	}
	catch (Exception ex) {
	if (debug) ex.printStackTrace();
	}

	// Try Jar Service Provider Mechanism
	T provider = findServiceProvider(type);
	if (provider != null) {
	return provider;
	}
	if (fallbackClassName == null) {
	throw new FactoryConfigurationError(
	"Provider for " + factoryId + " cannot be found");
	}

	dPrint(()->"loaded from fallback value: " + fallbackClassName);
	return newInstance(type, fallbackClassName, null, true);
	}

	/*
	* Try to find provider using the ServiceLoader API
	*
	* @param type Base class / Service interface of the factory to find.
	*
	* @return instance of provider class if found or null
	*/
	@SuppressWarnings("removal")
	private static <T> T findServiceProvider(final Class<T> type) {
	try {
	return AccessController.doPrivileged(new PrivilegedAction<T>() {
	public T run() {
	final ServiceLoader<T> serviceLoader = ServiceLoader.load(type);
	final Iterator<T> iterator = serviceLoader.iterator();
	if (iterator.hasNext()) {
	return iterator.next();
	} else {
	return null;
	}
	}
	});
	} catch(ServiceConfigurationError e) {
	// It is not possible to wrap an error directly in
	// FactoryConfigurationError - so we need to wrap the
	// ServiceConfigurationError in a RuntimeException.
	// The alternative would be to modify the logic in
	// FactoryConfigurationError to allow setting a
	// Throwable as the cause, but that could cause
	// compatibility issues down the road.
	final RuntimeException x = new RuntimeException(
	"Provider for " + type + " cannot be created", e);
	final FactoryConfigurationError error =
	new FactoryConfigurationError(x, x.getMessage());
	throw error;
	}
	}

	}

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