org.glassfish.jersey.core/jersey-common/2.30.1 : org/glassfish/jersey/internal/ServiceFinder.java

ServiceFinder
https://projects.eclipse.org/projects/ee4j.jersey/jersey-common: Jersey core common packages (Eclipse Foundation)
Petr Bouda
Pavel Bucek (Oracle Corporation)
Michal Gajdos
Petr Janouch
Libor Kramolis
Adam Lindenthal
Jakub Podlesak (Oracle Corporation)
Marek Potociar
Stepan Vavra
Roman Grigoriadi (Oracle Corporation)
Lukas Jungmann (Oracle Corporation)
Dmitry Kornilov (Oracle Corporation)
Tomas Kraus (Oracle Corporation)
Tomas Langer (Oracle Corporation)
Maxim Nesen (Oracle Corporation)
Santiago Pericas-Geertsen (Oracle Corporation)
Jan Supol (Oracle Corporation)
/*
 * Copyright (c) 2010, 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 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.
Author: Mark Reinhold, Jakub Podlesak, Marek Potociar
Type parameters: <T> – the type of the service instance./**
 * 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>The default service provider registration/lookup mechanism based
 * on <tt>META-INF/services</tt> files is described below.
 * For environments, where the basic mechanism is not suitable, clients
 * can enforce a different approach by setting their custom <tt>ServiceIteratorProvider</tt>
 * by calling <tt>setIteratorProvider</tt>. The call must be made prior to any lookup attempts.
 * </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 codec 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.
 *
 * @param <T> the type of the service instance.
 * @author Mark Reinhold
 * @author Jakub Podlesak
 * @author Marek Potociar
 */
public final class ServiceFinder<T> implements Iterable<T> {

    private static final Logger LOGGER = Logger.getLogger(ServiceFinder.class.getName());
    private static final String PREFIX = "META-INF/services/";
    private final Class<T> 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<URL> getResources(final ClassLoader loader, final String name) throws IOException {
        if (loader == null) {
            return getResources(name);
        } else {
            final Enumeration<URL> resources = loader.getResources(name);
            if ((resources != null) && resources.hasMoreElements()) {
                return resources;
            } else {
                return getResources(name);
            }
        }
    }

    private static Enumeration<URL> 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. 

Params: service – The service's abstract service class
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
Type parameters: <T> – the type of the service instance.
Throws: ServiceConfigurationError – If a provider-configuration file violates the specified format
                                  or names a provider class that cannot be found and instantiated
See Also: find(Class<Object>)
Returns: the service finder/**
     * 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)
     * @param <T> the type of the service instance.
     * @return the service finder
     */
    public static <T> ServiceFinder<T> find(final Class<T> 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. 

Params: service – The service's abstract service class
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
ignoreOnClassNotFound – If a provider cannot be loaded by the class loader
                             then move on to the next available provider.
Type parameters: <T> – the type of the service instance.
Throws: ServiceConfigurationError – If a provider-configuration file violates the specified format
                                  or names a provider class that cannot be found and instantiated
See Also: find(Class<Object>)
Returns: the service finder/**
     * 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
     * @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 <T> the type of the service instance.
     * @return the service finder
     */
    public static <T> ServiceFinder<T> find(final Class<T> service,
                                            final ClassLoader loader,
                                            final boolean ignoreOnClassNotFound) throws ServiceConfigurationError {
        return new ServiceFinder<T>(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);

Params: service – The service's abstract service class
Type parameters: <T> – the type of the service instance.
Throws: ServiceConfigurationError – If a provider-configuration file violates the specified format
                                  or names a provider class that cannot be found and instantiated
See Also: find(Class<Object>, ClassLoader)
Returns: the service finder/**
     * 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, false);
     * </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)
     * @param <T> the type of the service instance.
     * @return the service finder
     */
    public static <T> ServiceFinder<T> find(final Class<T> 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);

Params: service – The service's abstract service class
ignoreOnClassNotFound – If a provider cannot be loaded by the class loader
                             then move on to the next available provider.
Type parameters: <T> – the type of the service instance.
Throws: ServiceConfigurationError – If a provider-configuration file violates the specified format
                                  or names a provider class that cannot be found and instantiated
See Also: find(Class<Object>, ClassLoader)
Returns: the service finder/**
     * 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();
     *   boolean ingore = ...
     *   return Service.providers(service, cl, ignore);
     * </pre>
     * @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 <T> the type of the service instance.
     * @return the service finder
     */
    public static <T> ServiceFinder<T> find(final Class<T> 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.
Params: 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
Returns: the service finder/**
     * 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<Object>(Object.class, serviceName, _getContextClassLoader(), false);
    }

    Register the service iterator provider to iterate on provider instances
or classes.
 The default implementation registered, DefaultServiceIteratorProvider, looks up provider classes in META-INF/service files. 

This method must be called prior to any attempts to obtain provider
instances or classes.
Params: sip – the service iterator provider.
Throws: SecurityException – if the provider cannot be registered./**
     * Register the service iterator provider to iterate on provider instances
     * or classes.
     * <p>
     * The default implementation registered, {@link DefaultServiceIteratorProvider},
     * looks up provider classes in META-INF/service files.
     * <p>
     * This method must be called prior to any attempts to obtain provider
     * instances or classes.
     *
     * @param sip the service iterator provider.
     * @throws SecurityException if the provider cannot be registered.
     */
    public static void setIteratorProvider(final ServiceIteratorProvider sip) throws SecurityException {
        ServiceIteratorProvider.setInstance(sip);
    }

    private ServiceFinder(
            final Class<T> service,
            final ClassLoader loader,
            final boolean ignoreOnClassNotFound) {
        this(service, service.getName(), loader, ignoreOnClassNotFound);
    }

    private ServiceFinder(
            final Class<T> service,
            final String serviceName,
            final ClassLoader loader,
            final boolean ignoreOnClassNotFound) {
        this.serviceClass = service;
        this.serviceName = serviceName;
        this.classLoader = loader;
        this.ignoreOnClassNotFound = ignoreOnClassNotFound;
    }

    Returns discovered objects incrementally.
Returns: An Iterator that yields provider objects for the given
        service, in some arbitrary order.  The iterator will throw a
        ServiceConfigurationError if a provider-configuration
        file violates the specified format or if a provider class cannot
        be found and instantiated./**
     * 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.
     */
    @Override
    public Iterator<T> iterator() {
        return ServiceIteratorProvider.getInstance()
                .createIterator(serviceClass, serviceName, classLoader, ignoreOnClassNotFound);
    }

    Returns discovered objects all at once.
Throws: ServiceConfigurationError – If a provider-configuration file violates the specified format
                                  or names a provider class that cannot be found and instantiated
Returns: 
     can be empty but never null./**
     * Returns discovered objects all at once.
     *
     * @return
     *      can be empty but never null.
     *
     * @throws ServiceConfigurationError If a provider-configuration file violates the specified format
     *                                   or names a provider class that cannot be found and instantiated
     */
    @SuppressWarnings("unchecked")
    public T[] toArray() throws ServiceConfigurationError {
        final List<T> result = new ArrayList<T>();
        for (final T t : this) {
            result.add(t);
        }
        return result.toArray((T[]) Array.newInstance(serviceClass, result.size()));
    }

    Returns discovered classes all at once.
Throws: ServiceConfigurationError – If a provider-configuration file violates the specified format
                                  or names a provider class that cannot be found
Returns: 
     can be empty but never null./**
     * Returns discovered classes all at once.
     *
     * @return
     *      can be empty but never null.
     *
     * @throws ServiceConfigurationError If a provider-configuration file violates the specified format
     *                                   or names a provider class that cannot be found
     */
    @SuppressWarnings("unchecked")
    public Class<T>[] toClassArray() throws ServiceConfigurationError {
        final List<Class<T>> result = new ArrayList<Class<T>>();

        final ServiceIteratorProvider iteratorProvider = ServiceIteratorProvider.getInstance();
        final Iterator<Class<T>> i = iteratorProvider
                .createClassIterator(serviceClass, serviceName, classLoader, ignoreOnClassNotFound);
        while (i.hasNext()) {
            result.add(i.next());
        }
        return result.toArray((Class<T>[]) Array.newInstance(Class.class, result.size()));
    }

    private static void fail(final String serviceName, final String msg, final Throwable cause)
            throws ServiceConfigurationError {
        final ServiceConfigurationError sce = new ServiceConfigurationError(serviceName + ": " + msg);
        sce.initCause(cause);
        throw sce;
    }

    private static void fail(final String serviceName, final String msg)
            throws ServiceConfigurationError {
        throw new ServiceConfigurationError(serviceName + ": " + msg);
    }

    private static void fail(final String serviceName, final URL u, final int line, final String msg)
            throws ServiceConfigurationError {
        fail(serviceName, u + ":" + line + ": " + msg);
    }

    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.
/**
     * 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 String serviceName, 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(serviceName, u, lc, LocalizationMessages.ILLEGAL_CONFIG_SYNTAX());
            }
            int cp = ln.codePointAt(0);
            if (!Character.isJavaIdentifierStart(cp)) {
                fail(serviceName, u, lc, LocalizationMessages.ILLEGAL_PROVIDER_CLASS_NAME(ln));
            }
            for (int i = Character.charCount(cp); i < n; i += Character.charCount(cp)) {
                cp = ln.codePointAt(i);
                if (!Character.isJavaIdentifierPart(cp) && (cp != '.')) {
                    fail(serviceName, u, lc, LocalizationMessages.ILLEGAL_PROVIDER_CLASS_NAME(ln));
                }
            }
            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.
Params: serviceName –  The service class for which providers are being sought;
                    used to construct error detail strings
u –        The URL naming the configuration file to be parsed
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 Iterator.
Throws: ServiceConfigurationError – If an I/O error occurs while reading from the given URL, or
                                  if a configuration-file format error is detected
Returns: A (possibly empty) Iterator that will yield the
        provider-class names in the given configuration file that are
        not yet members of the returned set/**
     * Parse the content of the given URL as a provider-configuration file.
     *
     * @param serviceName  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(final String serviceName, final URL u, final Set<String> returned)
            throws ServiceConfigurationError {
        InputStream in = null;
        BufferedReader r = null;
        final ArrayList<String> names = new ArrayList<String>();
        try {
            final URLConnection uConn = u.openConnection();
            uConn.setUseCaches(false);
            in = uConn.getInputStream();
            r = new BufferedReader(new InputStreamReader(in, "utf-8"));
            int lc = 1;
            while ((lc = parseLine(serviceName, u, r, lc, names, returned)) >= 0) {
                // continue
            }
        } catch (final IOException x) {
            fail(serviceName, ": " + x);
        } finally {
            try {
                if (r != null) {
                    r.close();
                }
                if (in != null) {
                    in.close();
                }
            } catch (final IOException y) {
                fail(serviceName, ": " + y);
            }
        }
        return names.iterator();
    }

    private static class AbstractLazyIterator<T> {

        final Class<T> service;
        final String serviceName;
        final ClassLoader loader;
        final boolean ignoreOnClassNotFound;
        Enumeration<URL> configs = null;
        Iterator<String> pending = null;
        Set<String> returned = new TreeSet<String>();
        String nextName = null;

        private AbstractLazyIterator(
                final Class<T> service,
                final String serviceName,
                final ClassLoader loader,
                final boolean ignoreOnClassNotFound) {
            this.service = service;
            this.serviceName = serviceName;
            this.loader = loader;
            this.ignoreOnClassNotFound = ignoreOnClassNotFound;
        }

        protected final void setConfigs() {
            if (configs == null) {
                try {
                    final String fullName = PREFIX + serviceName;
                    configs = getResources(loader, fullName);
                } catch (final IOException x) {
                    fail(serviceName, ": " + x);
                }
            }
        }

        public boolean hasNext() throws ServiceConfigurationError {
            if (nextName != null) {
                return true;
            }
            setConfigs();

            while (nextName == null) {
                while ((pending == null) || !pending.hasNext()) {
                    if (!configs.hasMoreElements()) {
                        return false;
                    }
                    pending = parse(serviceName, configs.nextElement(), returned);
                }
                nextName = pending.next();
                if (ignoreOnClassNotFound) {
                    try {
                        AccessController.doPrivileged(ReflectionHelper.classForNameWithExceptionPEA(nextName, loader));
                    } catch (final ClassNotFoundException ex) {
                        handleClassNotFoundException();
                    } catch (final PrivilegedActionException pae) {
                        final Throwable thrown = pae.getException();
                        if (thrown instanceof ClassNotFoundException) {
                            handleClassNotFoundException();
                        } else if (thrown instanceof NoClassDefFoundError) {
                            // Dependent class of provider not found
                            if (LOGGER.isLoggable(Level.CONFIG)) {
                                // This assumes that ex.getLocalizedMessage() returns
                                // the name of a dependent class that is not found
                                LOGGER.log(Level.CONFIG,
                                        LocalizationMessages.DEPENDENT_CLASS_OF_PROVIDER_NOT_FOUND(
                                                thrown.getLocalizedMessage(), nextName, service));
                            }
                            nextName = null;
                        } else if (thrown instanceof ClassFormatError) {
                            // Dependent class of provider not found
                            if (LOGGER.isLoggable(Level.CONFIG)) {
                                LOGGER.log(Level.CONFIG,
                                        LocalizationMessages.DEPENDENT_CLASS_OF_PROVIDER_FORMAT_ERROR(
                                                thrown.getLocalizedMessage(), nextName, service));
                            }
                            nextName = null;
                        } else if (thrown instanceof RuntimeException) {
                            throw (RuntimeException) thrown;
                        } else {
                            throw new IllegalStateException(thrown);
                        }
                    }
                }
            }
            return true;
        }

        public void remove() {
            throw new UnsupportedOperationException();
        }

        private void handleClassNotFoundException() {
            // Provider implementation not found
            if (LOGGER.isLoggable(Level.CONFIG)) {
                LOGGER.log(Level.CONFIG,
                        LocalizationMessages.PROVIDER_NOT_FOUND(nextName, service));
            }
            nextName = null;
        }
    }

    private static final class LazyClassIterator<T> extends AbstractLazyIterator<T>
            implements Iterator<Class<T>> {

        private LazyClassIterator(
                final Class<T> service,
                final String serviceName,
                final ClassLoader loader,
                final boolean ignoreOnClassNotFound) {
            super(service, serviceName, loader, ignoreOnClassNotFound);
        }

        @Override
        public Class<T> next() {
            if (!hasNext()) {
                throw new NoSuchElementException();
            }
            final String cn = nextName;
            nextName = null;
            try {

                final Class<T> tClass = AccessController.doPrivileged(
                        ReflectionHelper.<T>classForNameWithExceptionPEA(cn, loader));

                if (LOGGER.isLoggable(Level.FINEST)) {
                    LOGGER.log(Level.FINEST, "Loading next class: " + tClass.getName());
                }

                return tClass;

            } catch (final ClassNotFoundException ex) {
                fail(serviceName,
                        LocalizationMessages.PROVIDER_NOT_FOUND(cn, service));
            } catch (final PrivilegedActionException pae) {

                final Throwable thrown = pae.getCause();

                if (thrown instanceof ClassNotFoundException) {
                    fail(serviceName,
                            LocalizationMessages.PROVIDER_NOT_FOUND(cn, service));
                } else if (thrown instanceof NoClassDefFoundError) {
                    fail(serviceName,
                            LocalizationMessages.DEPENDENT_CLASS_OF_PROVIDER_NOT_FOUND(
                                    thrown.getLocalizedMessage(), cn, service));
                } else if (thrown instanceof ClassFormatError) {
                    fail(serviceName,
                            LocalizationMessages.DEPENDENT_CLASS_OF_PROVIDER_FORMAT_ERROR(
                                    thrown.getLocalizedMessage(), cn, service));
                } else {
                    fail(serviceName,
                            LocalizationMessages.PROVIDER_CLASS_COULD_NOT_BE_LOADED(cn, service, thrown.getLocalizedMessage()),
                            thrown);
                }
            }

            return null;    /* This cannot happen */
        }
    }

    private static final class LazyObjectIterator<T> extends AbstractLazyIterator<T> implements Iterator<T> {

        private T t;

        private LazyObjectIterator(
                final Class<T> service,
                final String serviceName,
                final ClassLoader loader,
                final boolean ignoreOnClassNotFound) {
            super(service, serviceName, loader, ignoreOnClassNotFound);
        }

        @Override
        public boolean hasNext() throws ServiceConfigurationError {
            if (nextName != null) {
                return true;
            }
            setConfigs();

            while (nextName == null) {
                while ((pending == null) || !pending.hasNext()) {
                    if (!configs.hasMoreElements()) {
                        return false;
                    }
                    pending = parse(serviceName, configs.nextElement(), returned);
                }
                nextName = pending.next();
                try {
                    t = service.cast(AccessController.doPrivileged(
                            ReflectionHelper.classForNameWithExceptionPEA(nextName, loader)).newInstance());

                } catch (final InstantiationException ex) {
                    if (ignoreOnClassNotFound) {
                        if (LOGGER.isLoggable(Level.CONFIG)) {
                            LOGGER.log(Level.CONFIG,
                                    LocalizationMessages.PROVIDER_COULD_NOT_BE_CREATED(nextName, service,
                                            ex.getLocalizedMessage()));
                        }
                        nextName = null;
                    } else {
                        fail(serviceName,
                                LocalizationMessages.PROVIDER_COULD_NOT_BE_CREATED(nextName, service, ex.getLocalizedMessage()),
                                ex);
                    }
                } catch (final IllegalAccessException ex) {
                    fail(serviceName,
                            LocalizationMessages.PROVIDER_COULD_NOT_BE_CREATED(nextName, service, ex.getLocalizedMessage()),
                            ex);

                } catch (final ClassNotFoundException ex) {
                    handleClassNotFoundException();
                } catch (final NoClassDefFoundError ex) {
                    // Dependent class of provider not found
                    if (ignoreOnClassNotFound) {
                        if (LOGGER.isLoggable(Level.CONFIG)) {
                            // This assumes that ex.getLocalizedMessage() returns
                            // the name of a dependent class that is not found
                            LOGGER.log(Level.CONFIG,
                                    LocalizationMessages.DEPENDENT_CLASS_OF_PROVIDER_NOT_FOUND(
                                            ex.getLocalizedMessage(), nextName, service));
                        }
                        nextName = null;
                    } else {
                        fail(serviceName,
                                LocalizationMessages
                                        .DEPENDENT_CLASS_OF_PROVIDER_NOT_FOUND(ex.getLocalizedMessage(), nextName, service),
                                ex);
                    }

                } catch (final PrivilegedActionException pae) {
                    final Throwable cause = pae.getCause();
                    if (cause instanceof ClassNotFoundException) {
                        handleClassNotFoundException();
                    } else if (cause instanceof ClassFormatError) {
                        // Dependent class of provider not found
                        if (ignoreOnClassNotFound) {
                            if (LOGGER.isLoggable(Level.CONFIG)) {
                                LOGGER.log(Level.CONFIG,
                                        LocalizationMessages.DEPENDENT_CLASS_OF_PROVIDER_FORMAT_ERROR(
                                                cause.getLocalizedMessage(), nextName, service));
                            }
                            nextName = null;
                        } else {
                            fail(serviceName,
                                    LocalizationMessages
                                            .DEPENDENT_CLASS_OF_PROVIDER_FORMAT_ERROR(cause.getLocalizedMessage(), nextName,
                                                    service),
                                    cause);
                        }
                    } else {
                        fail(serviceName,
                                LocalizationMessages
                                        .PROVIDER_COULD_NOT_BE_CREATED(nextName, service, cause.getLocalizedMessage()),
                                cause);
                    }
                }
            }
            return true;
        }

        @Override
        public T next() {
            if (!hasNext()) {
                throw new NoSuchElementException();
            }
            nextName = null;
            if (LOGGER.isLoggable(Level.FINEST)) {
                LOGGER.log(Level.FINEST, "Loading next object: " + t.getClass().getName());
            }
            return t;
        }

        private void handleClassNotFoundException() throws ServiceConfigurationError {
            if (ignoreOnClassNotFound) {
                // Provider implementation not found
                if (LOGGER.isLoggable(Level.CONFIG)) {
                    LOGGER.log(Level.CONFIG,
                            LocalizationMessages.PROVIDER_NOT_FOUND(nextName, service));
                }
                nextName = null;
            } else {
                fail(serviceName,
                        LocalizationMessages.PROVIDER_NOT_FOUND(nextName, service));
            }
        }
    }

    Supports iteration of provider instances or classes.
 The default implementation looks up provider classes from META-INF/services files, see DefaultServiceIteratorProvider. This implementation may be overridden by invoking ServiceFinder.setIteratorProvider(ServiceIteratorProvider). /**
     * Supports iteration of provider instances or classes.
     * <p>
     * The default implementation looks up provider classes from META-INF/services
     * files, see {@link DefaultServiceIteratorProvider}.
     * This implementation may be overridden by invoking
     * {@link ServiceFinder#setIteratorProvider(org.glassfish.jersey.internal.ServiceFinder.ServiceIteratorProvider)}.
     */
    public abstract static class ServiceIteratorProvider {

        private static volatile ServiceIteratorProvider sip;
        private static final Object sipLock = new Object();

        private static ServiceIteratorProvider getInstance() {
            // TODO: check the following is a good practice: Double-check idiom for lazy initialization of fields.
            ServiceIteratorProvider result = sip;
            if (result == null) { // First check (no locking)
                synchronized (sipLock) {
                    result = sip;
                    if (result == null) { // Second check (with locking)
                        sip = result = new DefaultServiceIteratorProvider();
                    }
                }
            }
            return result;
        }

        private static void setInstance(final ServiceIteratorProvider sip) throws SecurityException {
            final SecurityManager security = System.getSecurityManager();
            if (security != null) {
                final ReflectPermission rp = new ReflectPermission("suppressAccessChecks");
                security.checkPermission(rp);
            }
            synchronized (sipLock) {
                ServiceIteratorProvider.sip = sip;
            }
        }

        Iterate over provider instances of a service.
Params: service – the service class.
serviceName – the service name.
loader – the class loader to utilize when loading provider
       classes.
ignoreOnClassNotFound – if true ignore an instance if the corresponding provider class if cannot be found, otherwise throw a ClassNotFoundException.
Type parameters: <T> – the type of the service.
Returns: the provider instance iterator./**
         * Iterate over provider instances of a service.
         *
         * @param <T> the type of the service.
         * @param service the service class.
         * @param serviceName the service name.
         * @param loader the class loader to utilize when loading provider
         *        classes.
         * @param ignoreOnClassNotFound if true ignore an instance if the
         *        corresponding provider class if cannot be found,
         *        otherwise throw a {@link ClassNotFoundException}.
         * @return the provider instance iterator.
         */
        public abstract <T> Iterator<T> createIterator(Class<T> service,
                                                       String serviceName, ClassLoader loader, boolean ignoreOnClassNotFound);

        Iterate over provider classes of a service.
Params: service – the service class.
serviceName – the service name.
loader – the class loader to utilize when loading provider
       classes.
ignoreOnClassNotFound – if true ignore the provider class if cannot be found, otherwise throw a ClassNotFoundException.
Type parameters: <T> – the type of the service.
Returns: the provider class iterator./**
         * Iterate over provider classes of a service.
         *
         * @param <T> the type of the service.
         * @param service the service class.
         * @param serviceName the service name.
         * @param loader the class loader to utilize when loading provider
         *        classes.
         * @param ignoreOnClassNotFound if true ignore the provider class if
         *        cannot be found,
         *        otherwise throw a {@link ClassNotFoundException}.
         * @return the provider class iterator.
         */
        public abstract <T> Iterator<Class<T>> createClassIterator(Class<T> service,
                                                                   String serviceName,
                                                                   ClassLoader loader,
                                                                   boolean ignoreOnClassNotFound);
    }

    The default service iterator provider that looks up provider classes in
META-INF/services files.
 This class may utilized if a ServiceIteratorProvider needs to reuse the default implementation. /**
     * The default service iterator provider that looks up provider classes in
     * META-INF/services files.
     * <p>
     * This class may utilized if a {@link ServiceIteratorProvider} needs to
     * reuse the default implementation.
     */
    public static final class DefaultServiceIteratorProvider extends ServiceIteratorProvider {

        @Override
        public <T> Iterator<T> createIterator(final Class<T> service, final String serviceName,
                                              final ClassLoader loader, final boolean ignoreOnClassNotFound) {
            return new LazyObjectIterator<T>(service, serviceName, loader, ignoreOnClassNotFound);
        }

        @Override
        public <T> Iterator<Class<T>> createClassIterator(final Class<T> service, final String serviceName,
                                                          final ClassLoader loader, final boolean ignoreOnClassNotFound) {
            return new LazyClassIterator<T>(service, serviceName, loader, ignoreOnClassNotFound);
        }
    }
}
Author:	Mark Reinhold, Jakub Podlesak, Marek Potociar
Type parameters:	<T> – the type of the service instance.
Params:	service – The service's abstract service class 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
Type parameters:	<T> – the type of the service instance.
Throws:	ServiceConfigurationError – If a provider-configuration file violates the specified format or names a provider class that cannot be found and instantiated
See Also:	find(Class<Object>)
Returns:	the service finder
Params:	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
Returns:	the service finder
Params:	sip – the service iterator provider.
Throws:	SecurityException – if the provider cannot be registered.
Params:	serviceName – The service class for which providers are being sought; used to construct error detail strings u – The URL naming the configuration file to be parsed 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 `Iterator`.
Throws:	ServiceConfigurationError – If an I/O error occurs while reading from the given URL, or if a configuration-file format error is detected
Returns:	A (possibly empty) `Iterator` that will yield the provider-class names in the given configuration file that are not yet members of the returned set
Params:	service – the service class. serviceName – the service name. loader – the class loader to utilize when loading provider classes. ignoreOnClassNotFound – if true ignore an instance if the corresponding provider class if cannot be found, otherwise throw a `ClassNotFoundException`.
Type parameters:	<T> – the type of the service.
Returns:	the provider instance iterator.
/

org.glassfish.jersey.core/ jersey-common/ 2.30.1/ org/glassfish/jersey/internal/ServiceFinder.java
