/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

// $Id: FactoryFinder.java 670431 2008-06-23 01:40:03Z mrglavas $

package javax.xml.transform;

import java.io.BufferedReader;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.Properties;

This class is duplicated for each JAXP subpackage so keep it in
sync.  It is package private.
This code is designed to implement the JAXP 1.1 spec pluggability
feature and is designed to run on JDK version 1.1 and later including
JVMs that perform early linking like the Microsoft JVM in IE 5.  Note
however that it must be compiled on a JDK version 1.2 or later system
since it calls Thread#getContextClassLoader().  The code also runs both
as part of an unbundled jar file and when bundled as part of the JDK.
/**
 * This class is duplicated for each JAXP subpackage so keep it in
 * sync.  It is package private.
 *
 * This code is designed to implement the JAXP 1.1 spec pluggability
 * feature and is designed to run on JDK version 1.1 and later including
 * JVMs that perform early linking like the Microsoft JVM in IE 5.  Note
 * however that it must be compiled on a JDK version 1.2 or later system
 * since it calls Thread#getContextClassLoader().  The code also runs both
 * as part of an unbundled jar file and when bundled as part of the JDK.
 */
final class FactoryFinder {
    
    
Debug flag to trace loading process.
/**
     * <p>Debug flag to trace loading process.</p>
     */
    private static boolean debug = false;
    
    
Cache properties for performance.
/**
     * <p>Cache properties for performance.</p>
     */
    private static Properties cacheProps = new Properties();
    
    
First time requires initialization overhead.
/**
     * <p>First time requires initialization overhead.</p>
     */
    private static boolean firstTime = true;
    
    
Default columns per line.
/**
     * Default columns per line.
     */
    private static final int DEFAULT_LINE_LENGTH = 80;

    // 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 FactoryFinder() {}

    private static void dPrint(String msg) {
        if (debug) {
            System.err.println("JAXP: " + msg);
        }
    }
    
    
Create an instance of a class using the specified ClassLoader and
optionally fall back to the current ClassLoader if not found.
Params:
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/**
     * Create an instance of a class using the specified ClassLoader and
     * optionally fall back to the current ClassLoader if not found.
     *
     * @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
    {
        // assert(className != null);

        try {
            Class providerClass;
            if (cl == null) {
                // If classloader is null Use the bootstrap ClassLoader.  
                // Thus Class.forName(String) will use the current
                // ClassLoader which will be the bootstrap ClassLoader.
                providerClass = Class.forName(className);
            } else {
                try {
                    providerClass = cl.loadClass(className);
                } catch (ClassNotFoundException x) {
                    if (doFallback) {
                        // Fall back to current classloader
                        cl = FactoryFinder.class.getClassLoader();
                        if (cl != null) {
                            providerClass = cl.loadClass(className);
                        }
                        else {
                            providerClass = Class.forName(className);
                        }
                    } else {
                        throw x;
                    }
                }
            }
                        
            Object instance = providerClass.newInstance();
            if (debug) 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.
Params:
factoryId –             Name of the factory to find, same as
                             a property name
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 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
    {        

        // Figure out which ClassLoader to use for loading the provider
        // class.  If there is a Context ClassLoader then use it.
        
        ClassLoader classLoader = SecuritySupport.getContextClassLoader();
        
        if (classLoader == null) {
            // if we have no Context ClassLoader
            // so use the current ClassLoader
            classLoader = FactoryFinder.class.getClassLoader();
        }

        if (debug) dPrint("find factoryId =" + factoryId);
        
        // Use the system property first
        try {
            String systemProp = SecuritySupport.getSystemProperty(factoryId);
            if (systemProp != null && systemProp.length() > 0) {                
                if (debug) dPrint("found system property, value=" + systemProp);
                return newInstance(systemProp, classLoader, true);
            }
        } catch (SecurityException se) {
            //if first option fails due to any reason we should try next option in the
            //look up algorithm.
        }

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

            if(factoryClassName != null){
                if (debug) dPrint("found in $java.home/jaxp.properties, value=" + factoryClassName);
                return newInstance(factoryClassName, classLoader, 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);
        }

        if (debug) dPrint("loaded from fallback value: " + fallbackClassName);
        return newInstance(fallbackClassName, classLoader, 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 = SecuritySupport.getContextClassLoader();
        if (cl != null) {
            is = SecuritySupport.getResourceAsStream(cl, serviceId);

            // If no provider found then try the current ClassLoader
            if (is == null) {
                cl = FactoryFinder.class.getClassLoader();
                is = SecuritySupport.getResourceAsStream(cl, serviceId);
            }
        } else {
            // No Context ClassLoader, try the current
            // ClassLoader
            cl = FactoryFinder.class.getClassLoader();
            is = SecuritySupport.getResourceAsStream(cl, serviceId);
        }

        if (is == null) {
            // No provider found
            return null;
        }

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

        // Read the service provider name in UTF-8 as specified in
        // the jar spec.  Unfortunately this fails in Microsoft
        // VJ++, which does not implement the UTF-8
        // encoding. Theoretically, we should simply let it fail in
        // that case, since the JVM is obviously broken if it
        // doesn't support such a basic standard.  But since there
        // are still some users attempting to use VJ++ for
        // development, we have dropped in a fallback which makes a
        // second attempt using the platform's default encoding. In
        // VJ++ this is apparently ASCII, which is a subset of
        // UTF-8... and since the strings we'll be reading here are
        // also primarily limited to the 7-bit ASCII range (at
        // least, in English versions), this should work well
        // enough to keep us on the air until we're ready to
        // officially decommit from VJ++. [Edited comment from
        // jkesselm]
        BufferedReader rd;
        try {
            rd = new BufferedReader(new InputStreamReader(is, "UTF-8"), DEFAULT_LINE_LENGTH);
        } catch (java.io.UnsupportedEncodingException e) {
            rd = new BufferedReader(new InputStreamReader(is), DEFAULT_LINE_LENGTH);
        }
        
        String factoryClassName = null;
        try {
            // XXX Does not handle all possible input as specified by the
            // Jar Service Provider specification
            factoryClassName = rd.readLine();
        } 
        catch (IOException x) {
            // No provider found
            return null;
        }
        finally {
            try { 
                // try to close the reader. 
                rd.close(); 
            } 
            // Ignore the exception. 
            catch (IOException exc) {}
        }

        if (factoryClassName != null &&
            ! "".equals(factoryClassName)) {
            if (debug) 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.
/**
         * 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;
        }
    }

}