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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * accompanied this code).
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package javax.xml.datatype;

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 Datatypes.
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 Datatypes.</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 final static 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.
     */
    private 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  DatatypeConfigurationException
    {
        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 to use to load the class, null means to use
the bootstrap ClassLoader
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 ClassLoader to use to load the class, null means to use
     * the bootstrap ClassLoader
     *
     * @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 DatatypeConfigurationException
    {
        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 DatatypeConfigurationException(
                "Provider " + className + " not found", x);
        }
        catch (Exception x) {
            throw new DatatypeConfigurationException(
                "Provider " + className + " could not be instantiated: " + x,
                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 DatatypeConfigurationException
    {
        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
        final T provider = findServiceProvider(type);
        if (provider != null) {
            return provider;
        }
        if (fallbackClassName == null) {
            throw new DatatypeConfigurationException(
                "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)
            throws DatatypeConfigurationException
    {
        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) {
            final DatatypeConfigurationException error =
                    new DatatypeConfigurationException(
                        "Provider for " + type + " cannot be found", e);
            throw error;
        }
    }

}