/*

 * Copyright (c) 2003, 2013, 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;

/**

 * <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@sun.com

 * @author Huizhe.Wang@oracle.com

 */

class FactoryFinder {

    private static final String DEFAULT_PACKAGE = "com.sun.org.apache.xerces.internal";

    /**

     * Internal debug flag.

     */

    private static boolean debug = false;

    /**

     */

    private static final Properties cacheProps = new Properties();

    /**

     * have been cached.

     */

    static volatile boolean firstTime = true;

    /**

     * Security support class use to check access control before

     * getting certain system resources.

     */

    private static final SecuritySupport ss = new SecuritySupport();

    // 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 = ss.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(String msg) {

        if (debug) {

            System.err.println("JAXP: " + msg);

        }

    }

    /**

     * 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 = ss.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.

     */

    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.newInstance();

            if (debug) {    // Extra check to avoid computing cl strings

                dPrint("created new instance of " + providerClass +

                       " using ClassLoader: " + cl);

            }

            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 = ss.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 {

            if (firstTime) {

                synchronized (cacheProps) {

                    if (firstTime) {

                        String configFile = ss.getSystemProperty("java.home") + File.separator +

                        File f = new File(configFile);

                        firstTime = false;

                        if (ss.doesFileExist(f)) {

                            dPrint("Read properties file "+f);

                            cacheProps.load(ss.getFileInputStream(f));

                        }

                    }

                }

            }

            final String factoryClassName = cacheProps.getProperty(factoryId);

            if (factoryClassName != null) {

                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;

        }

    }

}