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/*
 * Copyright (c) 2018 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0, which is available at
 * http://www.eclipse.org/legal/epl-2.0.
 *
 * This Source Code may also be made available under the following Secondary
 * Licenses when the conditions for such availability set forth in the
 * Eclipse Public License v. 2.0 are satisfied: GNU General Public License,
 * version 2 with the GNU Classpath Exception, which is available at
 * https://www.gnu.org/software/classpath/license.html.
 *
 * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
 */
package javax.xml.rpc;

import java.io.InputStream;
import java.io.IOException;
import java.io.File;
import java.io.FileInputStream;

import java.util.Properties;
import java.io.BufferedReader;
import java.io.InputStreamReader;

class FactoryFinder {

    /**
     * Creates an instance of the specified class using the specified 
     * ClassLoader object.
     *
     * @exception ServiceException if the given class could not be found
     *            or could not be instantiated
     */
    private static Object newInstance(String className,
                                      ClassLoader classLoader) throws ServiceException
    {
        try {
            Class spiClass;
            if (classLoader == null) {
                spiClass = Class.forName(className);
            } else {
                spiClass = classLoader.loadClass(className);
            }
            return spiClass.newInstance();
        } catch (ClassNotFoundException x) {
            throw new ServiceException(
                "Provider " + className + " not found", x);
        } catch (Exception x) {
            throw new ServiceException(
                "Provider " + className + " could not be instantiated: " + x,
                x);
        }
    }

    /**
     * Finds the implementation Class object for the given
     * factory name, or if that fails, finds the Class object
     * for the given fallback class name. The arguments supplied must be
     * used in order. If using the first argument is successful, the second
     * one will not be used.
     * 
     * This method is package private so that this code can be shared.
     *
     * @return the Class object of the specified message factory;
     *         may not be null
     *
     * @param factoryId             the name of the factory to find, which is
     *                              a system property
     * @param fallbackClassName     the implementation class name, which is
     *                              to be used only if nothing else
     *                              is found; null to indicate that
     *                              there is no fallback class name
     * @exception ServiceException if there is an error
     */
    static Object find(String factoryId, String fallbackClassName) throws ServiceException
    {
        ClassLoader classLoader;
        try {
            classLoader = Thread.currentThread().getContextClassLoader();
        } catch (Exception x) {
            throw new ServiceException(x.toString(), x);
        }

        // Use the system property first
        try {
            String systemProp =
                System.getProperty( factoryId );
            if( systemProp!=null) {
                return newInstance(systemProp, classLoader);
            }
        } catch (SecurityException se) {
        }

        // try to read from $java.home/lib/jaxrpc.properties
        try {
            String javah=System.getProperty( "java.home" );
            String configFile = javah + File.separator +
                "lib" + File.separator + "jaxrpc.properties";
            File f=new File( configFile );
            if( f.exists()) {
                Properties props=new Properties();
                props.load( new FileInputStream(f));
                String factoryClassName = props.getProperty(factoryId);
                return newInstance(factoryClassName, classLoader);
            }
        } catch(Exception ex ) {
        }

        String serviceId = "META-INF/services/" + factoryId;
        // try to find services in CLASSPATH
        try {
            InputStream is=null;
            if (classLoader == null) {
                is=ClassLoader.getSystemResourceAsStream(serviceId);
            } else {
                is=classLoader.getResourceAsStream(serviceId);
            }
        
            if( is!=null ) {
                BufferedReader rd =
                    new BufferedReader(new InputStreamReader(is, "UTF-8"));
        
                String factoryClassName = rd.readLine();
                rd.close();

                if (factoryClassName != null &&
                    ! "".equals(factoryClassName)) {
                    return newInstance(factoryClassName, classLoader);
                }
            }
        } catch( Exception ex ) {
        }

        if (fallbackClassName == null) {
            throw new ServiceException(
                "Provider for " + factoryId + " cannot be found", null);
        }

        return newInstance(fallbackClassName, classLoader);
    }
}