/*

 * Copyright (c) 2003, 2006, 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.transform;

import java.io.File;

import java.io.FileInputStream;

import java.util.Properties;

import java.io.BufferedReader;

import java.io.IOException;

import java.io.InputStream;

import java.io.InputStreamReader;

import java.net.URL;

/**

 * <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@sun.com

 */

class FactoryFinder {

    /**

     * Internal debug flag.

     */

    private static boolean debug = false;

    /**

     * Cache for properties in java.home/lib/jaxp.properties

     */

    static Properties cacheProps = new Properties();

    /**

     * Flag indicating if properties from java.home/lib/jaxp.properties

     * have been cached.

     */

    static boolean firstTime = true;

    /**

     * Security support class use to check access control before

     * getting certain system resources.

     */

    static 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.

     */

    static private Class getProviderClass(String className, ClassLoader cl,

            boolean doFallback) throws ClassNotFoundException

    {

        try {

            if (cl == null) {

                cl = ss.getContextClassLoader();

                if (cl == null) {

                    throw new ClassNotFoundException();

                }

                else {

                    return cl.loadClass(className);

                }

            }

            else {

                return cl.loadClass(className);

            }

        }

        catch (ClassNotFoundException e1) {

            if (doFallback) {

                // Use current class loader - should always be bootstrap CL

                return Class.forName(className, true, 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 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

     */

    static Object newInstance(String className, ClassLoader cl, boolean doFallback)

        throws ConfigurationError

    {

        try {

            Class providerClass = getProviderClass(className, cl, doFallback);

            Object instance = providerClass.newInstance();

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

                dPrint("created new instance of " + providerClass +

                       " using ClassLoader: " + cl);

            }

            return instance;

        }

        catch (ClassNotFoundException x) {

            throw new ConfigurationError(

                "Provider " + className + " not found", x);

        }

        catch (Exception x) {

            throw new ConfigurationError(

                "Provider " + className + " could not be instantiated: " + x,

                x);

        }

    }

    /**

     * Finds the implementation Class object in the specified order.  Main

     * entry point.

     * @return Class object of factory, never null

     *

     * @param factoryId             Name of the factory to find, same as

     *                              a property name

     * @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 Object find(String factoryId, String fallbackClassName)

        throws ConfigurationError

    {

        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(systemProp, null, true);

            }

        }

        catch (SecurityException se) {

            if (debug) se.printStackTrace();

        }

        // try to read from $java.home/lib/jaxp.properties

        try {

            String factoryClassName = null;

            if (firstTime) {

                synchronized (cacheProps) {

                    if (firstTime) {

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

                            "lib" + File.separator + "jaxp.properties";

                        File f = new File(configFile);

                        firstTime = false;

                        if (ss.doesFileExist(f)) {

                            dPrint("Read properties file "+f);

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

                        }

                    }

                }

            }

            factoryClassName = cacheProps.getProperty(factoryId);

            if (factoryClassName != null) {

                dPrint("found in $java.home/jaxp.properties, value=" + factoryClassName);

                return newInstance(factoryClassName, null, true);

            }

        }

        catch (Exception ex) {

            if (debug) ex.printStackTrace();

        }

        // Try Jar Service Provider Mechanism

        Object provider = findJarServiceProvider(factoryId);

        if (provider != null) {

            return provider;

        }

        if (fallbackClassName == null) {

            throw new ConfigurationError(

                "Provider for " + factoryId + " cannot be found", null);

        }

        dPrint("loaded from fallback value: " + fallbackClassName);

        return newInstance(fallbackClassName, null, true);

    }

    /*

     * Try to find provider using Jar Service Provider Mechanism

     *

     * @return instance of provider class if found or null

     */

    private static Object findJarServiceProvider(String factoryId)

        throws ConfigurationError

    {

        String serviceId = "META-INF/services/" + factoryId;

        InputStream is = null;

        // First try the Context ClassLoader

        ClassLoader cl = ss.getContextClassLoader();

        if (cl != null) {

            is = ss.getResourceAsStream(cl, serviceId);

            // If no provider found then try the current ClassLoader

            if (is == null) {

                cl = FactoryFinder.class.getClassLoader();

                is = ss.getResourceAsStream(cl, serviceId);

            }

        } else {

            // No Context ClassLoader, try the current ClassLoader

            cl = FactoryFinder.class.getClassLoader();

            is = ss.getResourceAsStream(cl, serviceId);

        }

        if (is == null) {

            // No provider found

            return null;

        }

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

            dPrint("found jar resource=" + serviceId + " using ClassLoader: " + cl);

        }

        BufferedReader rd;

        try {

            rd = new BufferedReader(new InputStreamReader(is, "UTF-8"));

        }

        catch (java.io.UnsupportedEncodingException e) {

            rd = new BufferedReader(new InputStreamReader(is));

        }

        String factoryClassName = null;

        try {

            // XXX Does not handle all possible input as specified by the

            // Jar Service Provider specification

            factoryClassName = rd.readLine();

            rd.close();

        } catch (IOException x) {

            // No provider found

            return null;

        }

        if (factoryClassName != null && !"".equals(factoryClassName)) {

            dPrint("found in resource, value=" + factoryClassName);

            // Note: here we do not want to fall back to the current

            // ClassLoader because we want to avoid the case where the

            // resource file was found using one ClassLoader and the

            // provider class was instantiated using a different one.

            return newInstance(factoryClassName, cl, false);

        }

        // No provider found

        return null;

    }

    static class ConfigurationError extends Error {

        private Exception exception;

        /**

         * Construct a new instance with the specified detail string and

         * exception.

         */

        ConfigurationError(String msg, Exception x) {

            super(msg);

            this.exception = x;

        }

        Exception getException() {

            return exception;

        }

        /**

        * use the exception chaining mechanism of JDK1.4

        */

        @Override

        public Throwable getCause() {

            return exception;

        }

    }

}