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 * Copyright (c) 2003, 2017, 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,
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 *
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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;

Implements pluggable Parsers.
This class is duplicated for each JAXP subpackage so keep it in
sync.  It is package private for secure class loading.
Author:
Santiago PericasGeertsen/**
 * <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.
/**
     * Internal debug flag.
     */
    private static boolean debug = false;

    
Cache for properties in java.home/conf/jaxp.properties
/**
     * 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.
/**
     * 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 null, 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
/**
     * 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
getProviderClass() in order to load the class.
Params:
type – Base class / Service interface  of the factory to
            instantiate.
className – Name of the concrete class corresponding to the
service provider
cl – ClassLoader used to load the factory class. If null
current Thread's context classLoader is used to load the factory class.
doFallback – True if the current ClassLoader should be tried as
a fallback if the class is not found using cl/**
     * 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
getProviderClass() in order to load the class.
Params:
type – Base class / Service interface  of the factory to
            instantiate.
className – Name of the concrete class corresponding to the
service provider
cl – ClassLoader used to load the factory class. If null
current Thread's context classLoader is used to load the factory class.
doFallback – True if the current ClassLoader should be tried as
a fallback if the class is not found using cl
useBSClsLoader – True if cl=null actually meant bootstrap classLoader. This parameter
is needed since DocumentBuilderFactory/SAXParserFactory defined null as context classLoader./**
     * 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.
     */
    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.
Params:
type –                  Base class / Service interface  of the
                             factory to find.
fallbackClassName –     Implementation class name, if nothing else
                             is found.  Use null to mean no fallback.
Package private so this code can be shared.
Returns:
Class object of factory, never null/**
     * 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
     */
    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;
        }
    }

}