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package com.sun.xml.internal.ws.policy.privateutil;

import java.io.BufferedReader;

import java.io.IOException;

import java.io.InputStream;

import java.io.InputStreamReader;

import java.lang.reflect.Array;

import java.net.URL;

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;

/**

 *

 * A simple service-provider lookup mechanism.  A <i>service</i> is a

 * well-known set of interfaces and (usually abstract) classes.  A <i>service

 * provider</i> 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.

 * <p/>

 * <p> 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 <i>service class</i> with data and code specific to

 * the provider.  This <i>provider class</i> 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.

 * <p/>

 * <p> A service provider identifies itself by placing a provider-configuration

 * file in the resource directory <tt>META-INF/services</tt>.  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 <tt>'#'</tt>

 * (<tt>0x23</tt>); on each line all characters following the first comment

 * character are ignored.  The file must be encoded in UTF-8.

 * <p/>

 * <p> 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.

 * <p/>

 * <p> <b>Example:</b> Suppose we have a service class named

 * <tt>java.io.spi.CharCodec</tt>.  It has two abstract methods:

 * <p/>

 * <pre>

 *   public abstract CharEncoder getEncoder(String encodingName);

 *   public abstract CharDecoder getDecoder(String encodingName);

 * </pre>

 * <p/>

 * Each method returns an appropriate object or <tt>null</tt> if it cannot

 * translate the given encoding.  Typical <tt>CharCodec</tt> providers will

 * support more than one encoding.

 * <p/>

 * <p> If <tt>sun.io.StandardCodec</tt> is a provider of the <tt>CharCodec</tt>

 * service then its jar file would contain the file

 * <tt>META-INF/services/java.io.spi.CharCodec</tt>.  This file would contain

 * the single line:

 * <p/>

 * <pre>

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

 * </pre>

 * <p/>

 * To locate an encoder for a given encoding name, the internal I/O code would

 * do something like this:

 * <p/>

 * <pre>

 *   CharEncoder getEncoder(String encodingName) {

 *       for( CharCodec cc : ServiceFinder.find(CharCodec.class) ) {

 *           CharEncoder ce = cc.getEncoder(encodingName);

 *           if (ce != null)

 *               return ce;

 *       }

 *       return null;

 *   }

 * </pre>

 * <p/>

 * 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.

 *

 * @author Mark Reinhold

 * @version 1.11, 03/12/19

 * @since 1.3

 */

final class ServiceFinder<T> implements Iterable<T> {

    private static final PolicyLogger LOGGER = PolicyLogger.getLogger(ServiceFinder.class);

    private static final String prefix = "META-INF/services/";

    private final Class<T> serviceClass;

    private final ClassLoader classLoader;

    /**

     * Locates and incrementally instantiates the available providers of a

     * given service using the given class loader.

     * <p/>

     * <p> This method transforms the name of the given service class into a

     * provider-configuration filename as described above and then uses the

     * <tt>getResources</tt> 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.

     * <p/>

     * <p> 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. <p>

     *

     * @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 <tt>null</tt> 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)

     */

    static <T> ServiceFinder<T> find(final Class<T> service, final ClassLoader loader) {

        if (null==service) {

            throw LOGGER.logSevereException(new NullPointerException(LocalizationMessages.WSP_0032_SERVICE_CAN_NOT_BE_NULL()));

        }

        return new ServiceFinder<T>(service,loader);

    }

    /**

     * Locates and incrementally instantiates the available providers of a

     * given service using the context class loader.  This convenience method

     * is equivalent to

     * <p/>

     * <pre>

     *   ClassLoader cl = Thread.currentThread().getContextClassLoader();

     *   return Service.providers(service, cl);

     * </pre>

     *

     * @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)

     */

    public static <T> ServiceFinder<T> find(final Class<T> service) {

        return find(service,Thread.currentThread().getContextClassLoader());

    }

    private ServiceFinder(Class<T> service, ClassLoader loader) {

        this.serviceClass = service;

        this.classLoader = loader;

    }

    /**

     * Returns discovered objects incrementally.

     *

     * @return An <tt>Iterator</tt> that yields provider objects for the given

     *         service, in some arbitrary order.  The iterator will throw a

     *         <tt>ServiceConfigurationError</tt> if a provider-configuration

     *         file violates the specified format or if a provider class cannot

     *         be found and instantiated.

     */

    public Iterator<T> iterator() {

        return new LazyIterator<T>(serviceClass,classLoader);

    }

    /**

     * Returns discovered objects all at once.

     *

     * @return

     *      can be empty but never null.

     *

     * @throws ServiceConfigurationError

     */

    @SuppressWarnings({"unchecked"})

    public T[] toArray() {

        List<T> result = new ArrayList<T>();

        for (T t : this) {

            result.add(t);

        }

        return result.toArray((T[])Array.newInstance(serviceClass,result.size()));

    }

    private static void fail(final Class service, final String msg, final Throwable cause)

        throws ServiceConfigurationError {

        final ServiceConfigurationError sce

            = new ServiceConfigurationError(LocalizationMessages.WSP_0025_SPI_FAIL_SERVICE_MSG(service.getName(), msg));

        if (null != cause) {

            sce.initCause(cause);

        }

        throw LOGGER.logSevereException(sce);

    }

/*    private static void fail(Class service, String msg)

        throws ServiceConfigurationError {

        throw new ServiceConfigurationError(LocalizationMessages.WSP_0025_SPI_FAIL_SERVICE_MSG(service.getName(), msg));

    }*/

    private static void fail(final Class service, final URL u, final int line, final String msg, final Throwable cause)

        throws ServiceConfigurationError {

        fail(service, LocalizationMessages.WSP_0024_SPI_FAIL_SERVICE_URL_LINE_MSG(u , line, msg), cause);

    }

    /**

     * Parse a single line from the given configuration file, adding the name

     * on the line to both the names list and the returned set iff the name is

     * not already a member of the returned set.

     */

    private static int parseLine(final Class service, final URL u, final BufferedReader r, final int lc,

                                 final List<String> names, final Set<String> returned)

        throws IOException, ServiceConfigurationError {

        String ln = r.readLine();

        if (ln == null) {

            return -1;

        }

        final int ci = ln.indexOf('#');

        if (ci >= 0) ln = ln.substring(0, ci);

        ln = ln.trim();

        final int n = ln.length();

        if (n != 0) {

            if ((ln.indexOf(' ') >= 0) || (ln.indexOf('\t') >= 0))

                fail(service, u, lc, LocalizationMessages.WSP_0067_ILLEGAL_CFG_FILE_SYNTAX(), null);

            int cp = ln.codePointAt(0);

            if (!Character.isJavaIdentifierStart(cp))

                fail(service, u, lc, LocalizationMessages.WSP_0066_ILLEGAL_PROVIDER_CLASSNAME(ln), null);

            for (int i = Character.charCount(cp); i < n; i += Character.charCount(cp)) {

                cp = ln.codePointAt(i);

                if (!Character.isJavaIdentifierPart(cp) && (cp != '.'))

                    fail(service, u, lc, LocalizationMessages.WSP_0066_ILLEGAL_PROVIDER_CLASSNAME(ln), null);

            }

            if (!returned.contains(ln)) {

                names.add(ln);

                returned.add(ln);

            }

        }

        return lc + 1;

    }

    /**

     * Parse the content of the given URL as a provider-configuration file.

     *

     * @param service  The service class for which providers are being sought;

     *                 used to construct error detail strings

     * @param u        The URL naming the configuration file to be parsed

     * @param returned A Set containing the names of provider classes that have already

     *                 been returned.  This set will be updated to contain the names

     *                 that will be yielded from the returned <tt>Iterator</tt>.

     * @return A (possibly empty) <tt>Iterator</tt> that will yield the

     *         provider-class names in the given configuration file that are

     *         not yet members of the returned set

     * @throws ServiceConfigurationError If an I/O error occurs while reading from the given URL, or

     *                                   if a configuration-file format error is detected

     */

    @SuppressWarnings({"StatementWithEmptyBody"})

    private static Iterator<String> parse(Class service, URL u, Set<String> returned)

        throws ServiceConfigurationError {

        InputStream in = null;

        BufferedReader r = null;

        ArrayList<String> names = new ArrayList<String>();

        try {

            in = u.openStream();

            r = new BufferedReader(new InputStreamReader(in, "utf-8"));

            int lc = 1;

            while ((lc = parseLine(service, u, r, lc, names, returned)) >= 0) ;

        } catch (IOException x) {

            fail(service, ": " + x, x);

        } finally {

            try {

                if (r != null) r.close();

                if (in != null) in.close();

            } catch (IOException y) {

                fail(service, ": " + y, y);

            }

        }

        return names.iterator();

    }

    /**

     * Private inner class implementing fully-lazy provider lookup

     */

    private static class LazyIterator<T> implements Iterator<T> {

        Class<T> service;

        ClassLoader loader;

        Enumeration<URL> configs = null;

        Iterator<String> pending = null;

        Set<String> returned = new TreeSet<String>();

        String nextName = null;

        private LazyIterator(Class<T> service, ClassLoader loader) {

            this.service = service;

            this.loader = loader;

        }

        public boolean hasNext() throws ServiceConfigurationError {

            if (nextName != null) {

                return true;

            }

            if (configs == null) {

                try {

                    final String fullName = prefix + service.getName();

                    if (loader == null)

                        configs = ClassLoader.getSystemResources(fullName);

                    else

                        configs = loader.getResources(fullName);

                } catch (IOException x) {

                    fail(service, ": " + x, x);

                }

            }

            while ((pending == null) || !pending.hasNext()) {

                if (!configs.hasMoreElements()) {

                    return false;

                }

                pending = parse(service, configs.nextElement(), returned);

            }

            nextName = pending.next();

            return true;

        }

        public T next() throws ServiceConfigurationError {

            if (!hasNext()) {

                throw new NoSuchElementException();

            }

            final String cn = nextName;

            nextName = null;

            try {

                return service.cast(Class.forName(cn, true, loader).newInstance());

            } catch (ClassNotFoundException x) {

                fail(service, LocalizationMessages.WSP_0027_SERVICE_PROVIDER_NOT_FOUND(cn), x);

            } catch (Exception x) {

                fail(service, LocalizationMessages.WSP_0028_SERVICE_PROVIDER_COULD_NOT_BE_INSTANTIATED(cn), x);

            }

            return null;    /* This cannot happen */

        }

        public void remove() {

            throw new UnsupportedOperationException();

        }

    }

}