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/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 *
 * Copyright (c) 2010-2015 Oracle and/or its affiliates. All rights reserved.
 *
 * The contents of this file are subject to the terms of either the GNU
 * General Public License Version 2 only ("GPL") or the Common Development
 * and Distribution License("CDDL") (collectively, the "License").  You
 * may not use this file except in compliance with the License.  You can
 * obtain a copy of the License at
 * http://glassfish.java.net/public/CDDL+GPL_1_1.html
 * or packager/legal/LICENSE.txt.  See the License for the specific
 * language governing permissions and limitations under the License.
 *
 * When distributing the software, include this License Header Notice in each
 * file and include the License file at packager/legal/LICENSE.txt.
 *
 * GPL Classpath Exception:
 * Oracle designates this particular file as subject to the "Classpath"
 * exception as provided by Oracle in the GPL Version 2 section of the License
 * file that accompanied this code.
 *
 * Modifications:
 * If applicable, add the following below the License Header, with the fields
 * enclosed by brackets [] replaced by your own identifying information:
 * "Portions Copyright [year] [name of copyright owner]"
 *
 * Contributor(s):
 * If you wish your version of this file to be governed by only the CDDL or
 * only the GPL Version 2, indicate your decision by adding "[Contributor]
 * elects to include this software in this distribution under the [CDDL or GPL
 * Version 2] license."  If you don't indicate a single choice of license, a
 * recipient has the option to distribute your version of this file under
 * either the CDDL, the GPL Version 2 or to extend the choice of license to
 * its licensees as provided above.  However, if you add GPL Version 2 code
 * and therefore, elected the GPL Version 2 license, then the option applies
 * only if the new code is made subject to such option by the copyright
 * holder.
 */
package org.glassfish.jersey.internal;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.lang.reflect.Array;
import java.lang.reflect.ReflectPermission;
import java.net.URL;
import java.net.URLConnection;
import java.security.AccessController;
import java.security.PrivilegedActionException;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;
import java.util.Set;
import java.util.TreeSet;
import java.util.logging.Level;
import java.util.logging.Logger;

import org.glassfish.jersey.internal.util.ReflectionHelper;

/**
 * A simple service-provider lookup mechanism.  A service is a
 * well-known set of interfaces and (usually abstract) classes.  A service
 * provider is a specific implementation of a service.  The classes in a
 * provider typically implement the interfaces and subclass the classes defined
 * in the service itself.  Service providers may be installed in an
 * implementation of the Java platform in the form of extensions, that is, jar
 * files placed into any of the usual extension directories.  Providers may
 * also be made available by adding them to the applet or application class
 * path or by some other platform-specific means.
 * 

 * 
 In this lookup mechanism a service is represented by an interface or an
 * abstract class.  (A concrete class may be used, but this is not
 * recommended.)  A provider of a given service contains one or more concrete
 * classes that extend this service class with data and code specific to
 * the provider.  This provider class will typically not be the entire
 * provider itself but rather a proxy that contains enough information to
 * decide whether the provider is able to satisfy a particular request together
 * with code that can create the actual provider on demand.  The details of
 * provider classes tend to be highly service-specific; no single class or
 * interface could possibly unify them, so no such class has been defined.  The
 * only requirement enforced here is that provider classes must have a
 * zero-argument constructor so that they may be instantiated during lookup.
 * 

 * 
The default service provider registration/lookup mechanism based
 * on META-INF/services files is described below.
 * For environments, where the basic mechanism is not suitable, clients
 * can enforce a different approach by setting their custom ServiceIteratorProvider
 * by calling setIteratorProvider. The call must be made prior to any lookup attempts.
 * 
 * 
 A service provider identifies itself by placing a provider-configuration
 * file in the resource directory META-INF/services.  The file's name
 * should consist of the fully-qualified name of the abstract service class.
 * The file should contain a list of fully-qualified concrete provider-class
 * names, one per line.  Space and tab characters surrounding each name, as
 * well as blank lines, are ignored.  The comment character is '#'
 * (0x23); on each line all characters following the first comment
 * character are ignored.  The file must be encoded in UTF-8.
 * 

 * 
 If a particular concrete provider class is named in more than one
 * configuration file, or is named in the same configuration file more than
 * once, then the duplicates will be ignored.  The configuration file naming a
 * particular provider need not be in the same jar file or other distribution
 * unit as the provider itself.  The provider must be accessible from the same
 * class loader that was initially queried to locate the configuration file;
 * note that this is not necessarily the class loader that found the file.
 * 

 * 
 Example: Suppose we have a service class named
 * java.io.spi.CharCodec.  It has two abstract methods:
 * 

 * 
 *   public abstract CharEncoder getEncoder(String encodingName);
 *   public abstract CharDecoder getDecoder(String encodingName);
 * 
 * 

 * Each method returns an appropriate object or null if it cannot
 * translate the given encoding.  Typical CharCodec providers will
 * support more than one encoding.
 * 

 * 
 If sun.io.StandardCodec is a provider of the CharCodec
 * service then its jar file would contain the file
 * META-INF/services/java.io.spi.CharCodec.  This file would contain
 * the single line:
 * 

 * 
 *   sun.io.StandardCodec    # Standard codecs for the platform
 * 
 * 

 * To locate an codec for a given encoding name, the internal I/O code would
 * do something like this:
 * 

 * 
 *   CharEncoder getEncoder(String encodingName) {
 *       for( CharCodec cc : ServiceFinder.find(CharCodec.class) ) {
 *           CharEncoder ce = cc.getEncoder(encodingName);
 *           if (ce != null)
 *               return ce;
 *       }
 *       return null;
 *   }
 * 
 * 

 * The provider-lookup mechanism always executes in the security context of the
 * caller.  Trusted system code should typically invoke the methods in this
 * class from within a privileged security context.
 *
 * @param  the type of the service instance.
 * @author Mark Reinhold
 * @author Jakub Podlesak
 * @author Marek Potociar
 */
public final class ServiceFinder implements Iterable {

    private static final Logger LOGGER = Logger.getLogger(ServiceFinder.class.getName());
    private static final String PREFIX = "META-INF/services/";
    private final Class serviceClass;
    private final String serviceName;
    private final ClassLoader classLoader;
    private final boolean ignoreOnClassNotFound;

    static {
        final OsgiRegistry osgiRegistry = ReflectionHelper.getOsgiRegistryInstance();

        if (osgiRegistry != null) {
            LOGGER.log(Level.CONFIG, "Running in an OSGi environment");

            osgiRegistry.hookUp();
        } else {
            LOGGER.log(Level.CONFIG, "Running in a non-OSGi environment");
        }
    }

    private static Enumeration getResources(final ClassLoader loader, final String name) throws IOException {
        if (loader == null) {
            return getResources(name);
        } else {
            final Enumeration resources = loader.getResources(name);
            if ((resources != null) && resources.hasMoreElements()) {
                return resources;
            } else {
                return getResources(name);
            }
        }
    }

    private static Enumeration getResources(final String name) throws IOException {
        if (ServiceFinder.class.getClassLoader() != null) {
            return ServiceFinder.class.getClassLoader().getResources(name);
        } else {
            return ClassLoader.getSystemResources(name);
        }
    }

    private static ClassLoader _getContextClassLoader() {
        return AccessController.doPrivileged(ReflectionHelper.getContextClassLoaderPA());
    }

    /**
     * Locates and incrementally instantiates the available providers of a
     * given service using the given class loader.
     * 

     * 
 This method transforms the name of the given service class into a
     * provider-configuration filename as described above and then uses the
     * getResources method of the given class loader to find all
     * available files with that name.  These files are then read and parsed to
     * produce a list of provider-class names.  The iterator that is returned
     * uses the given class loader to lookup and then instantiate each element
     * of the list.
     * 

     * 
 Because it is possible for extensions to be installed into a running
     * Java virtual machine, this method may return different results each time
     * it is invoked. 

     * @param service The service's abstract service class
     * @param loader The class loader to be used to load provider-configuration files
     *                and instantiate provider classes, or null if the system
     *                class loader (or, failing that the bootstrap class loader) is to
     *                be used
     * @throws ServiceConfigurationError If a provider-configuration file violates the specified format
     *                                   or names a provider class that cannot be found and instantiated
     * @see #find(Class)
     * @param  the type of the service instance.
     * @return the service finder
     */
    public static  ServiceFinder find(final Class service, final ClassLoader loader)
            throws ServiceConfigurationError {
        return find(service,
                loader,
                false);
    }

    /**
     * Locates and incrementally instantiates the available providers of a
     * given service using the given class loader.
     * 

     * 
 This method transforms the name of the given service class into a
     * provider-configuration filename as described above and then uses the
     * getResources method of the given class loader to find all
     * available files with that name.  These files are then read and parsed to
     * produce a list of provider-class names.  The iterator that is returned
     * uses the given class loader to lookup and then instantiate each element
     * of the list.
     * 

     * 
 Because it is possible for extensions to be installed into a running
     * Java virtual machine, this method may return different results each time
     * it is invoked. 

     * @param service The service's abstract service class
     * @param loader The class loader to be used to load provider-configuration files
     *                and instantiate provider classes, or null if the system
     *                class loader (or, failing that the bootstrap class loader) is to
     *                be used
     * @param ignoreOnClassNotFound If a provider cannot be loaded by the class loader
     *                              then move on to the next available provider.
     * @throws ServiceConfigurationError If a provider-configuration file violates the specified format
     *                                   or names a provider class that cannot be found and instantiated
     * @see #find(Class)
     * @param  the type of the service instance.
     * @return the service finder
     */
    public static  ServiceFinder find(final Class service,
                                            final ClassLoader loader,
                                            final boolean ignoreOnClassNotFound) throws ServiceConfigurationError {
        return new ServiceFinder(service,
                loader,
                ignoreOnClassNotFound);
    }

    /**
     * Locates and incrementally instantiates the available providers of a
     * given service using the context class loader.  This convenience method
     * is equivalent to
     * 

     * 
     *   ClassLoader cl = Thread.currentThread().getContextClassLoader();
     *   return Service.providers(service, cl, false);
     * 
     * @param service The service's abstract service class
     * @throws ServiceConfigurationError If a provider-configuration file violates the specified format
     *                                   or names a provider class that cannot be found and instantiated
     * @see #find(Class, ClassLoader)
     * @param  the type of the service instance.
     * @return the service finder
     */
    public static  ServiceFinder find(final Class service)
            throws ServiceConfigurationError {
        return find(service,
                _getContextClassLoader(),
                false);
    }

    /**
     * Locates and incrementally instantiates the available providers of a
     * given service using the context class loader.  This convenience method
     * is equivalent to
     * 

     * 
     *   ClassLoader cl = Thread.currentThread().getContextClassLoader();
     *   boolean ingore = ...
     *   return Service.providers(service, cl, ignore);
     * 
     * @param service The service's abstract service class
     * @param ignoreOnClassNotFound If a provider cannot be loaded by the class loader
     *                              then move on to the next available provider.
     * @throws ServiceConfigurationError If a provider-configuration file violates the specified format
     *                                   or names a provider class that cannot be found and instantiated
     * @see #find(Class, ClassLoader)
     * @param  the type of the service instance.
     * @return the service finder
     */
    public static  ServiceFinder find(final Class service,
                                            final boolean ignoreOnClassNotFound) throws ServiceConfigurationError {
        return find(service,
                _getContextClassLoader(),
                ignoreOnClassNotFound);
    }

    /**
     * Locates and incrementally instantiates the available classes of a given
     * service file using the context class loader.
     *
     * @param serviceName the service name correspond to a file in
     *        META-INF/services that contains a list of fully qualified class
     *        names
     * @throws ServiceConfigurationError If a service file violates the specified format
     *                                   or names a provider class that cannot be found and instantiated
     * @return the service finder
     */
    public static ServiceFinder find(final String serviceName) throws ServiceConfigurationError {
        return new ServiceFinder