current/sdk/sdk_library/public/art.module.public.api_stub_sources/java/util/ServiceLoader.java

/*
 * Copyright (C) 2014 The Android Open Source Project
 * Copyright (c) 2005, 2013, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */


package java.util;

import java.util.Iterator;

/**
 * A simple service-provider loading facility.
 *
 * <p> 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
 * can 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 can also be made available by adding them to the
 * application's class path or by some other platform-specific means.
 *
 * <p> For the purpose of loading, a service is represented by a single type,
 * that is, a single interface or abstract class.  (A concrete class can be
 * used, but this is not recommended.)  A provider of a given service contains
 * one or more concrete classes that extend this <i>service type</i> with data
 * and code specific to the provider.  The <i>provider class</i> is typically
 * not the entire provider itself but rather a proxy which 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 type is
 * defined here.  The only requirement enforced by this facility is that
 * provider classes must have a zero-argument constructor so that they can be
 * instantiated during loading.
 *
 * <p><a name="format"> A service provider is identified by placing a
 * <i>provider-configuration file</i> in the resource directory
 * <tt>META-INF/services</tt>.</a>  The file's name is the fully-qualified <a
 * href="../lang/ClassLoader.html#name">binary name</a> of the service's type.
 * The file contains a list of fully-qualified binary names of concrete
 * provider classes, one per line.  Space and tab characters surrounding each
 * name, as well as blank lines, are ignored.  The comment character is
 * <tt>'#'</tt> (<tt>'&#92;u0023'</tt>,
 * <font style="font-size:smaller;">NUMBER SIGN</font>); on
 * each line all characters following the first comment character are ignored.
 * The file must be encoded in UTF-8.
 *
 * <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 are 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 from which the file was
 * actually loaded.
 *
 * <p> Providers are located and instantiated lazily, that is, on demand.  A
 * service loader maintains a cache of the providers that have been loaded so
 * far.  Each invocation of the {@link #iterator iterator} method returns an
 * iterator that first yields all of the elements of the cache, in
 * instantiation order, and then lazily locates and instantiates any remaining
 * providers, adding each one to the cache in turn.  The cache can be cleared
 * via the {@link #reload reload} method.
 *
 * <p> Service loaders always execute in the security context of the caller.
 * Trusted system code should typically invoke the methods in this class, and
 * the methods of the iterators which they return, from within a privileged
 * security context.
 *
 * <p> Instances of this class are not safe for use by multiple concurrent
 * threads.
 *
 * <p> Unless otherwise specified, passing a <tt>null</tt> argument to any
 * method in this class will cause a {@link java.lang.NullPointerException NullPointerException} to be thrown.
 *
 *
 * <p><span style="font-weight: bold; padding-right: 1em">Example</span>
 * Suppose we have a service type <tt>com.example.CodecSet</tt> which is
 * intended to represent sets of encoder/decoder pairs for some protocol.  In
 * this case it is an abstract class with two abstract methods:
 *
 * <blockquote><pre>
 * public abstract Encoder getEncoder(String encodingName);
 * public abstract Decoder getDecoder(String encodingName);</pre></blockquote>
 *
 * Each method returns an appropriate object or <tt>null</tt> if the provider
 * does not support the given encoding.  Typical providers support more than
 * one encoding.
 *
 * <p> If <tt>com.example.impl.StandardCodecs</tt> is an implementation of the
 * <tt>CodecSet</tt> service then its jar file also contains a file named
 *
 * <blockquote><pre>
 * META-INF/services/com.example.CodecSet</pre></blockquote>
 *
 * <p> This file contains the single line:
 *
 * <blockquote><pre>
 * com.example.impl.StandardCodecs    # Standard codecs</pre></blockquote>
 *
 * <p> The <tt>CodecSet</tt> class creates and saves a single service instance
 * at initialization:
 *
 * <blockquote><pre>
 * private static ServiceLoader&lt;CodecSet&gt; codecSetLoader
 *     = ServiceLoader.load(CodecSet.class);</pre></blockquote>
 *
 * <p> To locate an encoder for a given encoding name it defines a static
 * factory method which iterates through the known and available providers,
 * returning only when it has located a suitable encoder or has run out of
 * providers.
 *
 * <blockquote><pre>
 * public static Encoder getEncoder(String encodingName) {
 *     for (CodecSet cp : codecSetLoader) {
 *         Encoder enc = cp.getEncoder(encodingName);
 *         if (enc != null)
 *             return enc;
 *     }
 *     return null;
 * }</pre></blockquote>
 *
 * <p> A <tt>getDecoder</tt> method is defined similarly.
 *
 *
 * <p><span style="font-weight: bold; padding-right: 1em">Usage Note</span> If
 * the class path of a class loader that is used for provider loading includes
 * remote network URLs then those URLs will be dereferenced in the process of
 * searching for provider-configuration files.
 *
 * <p> This activity is normal, although it may cause puzzling entries to be
 * created in web-server logs.  If a web server is not configured correctly,
 * however, then this activity may cause the provider-loading algorithm to fail
 * spuriously.
 *
 * <p> A web server should return an HTTP 404 (Not Found) response when a
 * requested resource does not exist.  Sometimes, however, web servers are
 * erroneously configured to return an HTTP 200 (OK) response along with a
 * helpful HTML error page in such cases.  This will cause a {@link java.util.ServiceConfigurationError ServiceConfigurationError} to be thrown when this class attempts to parse
 * the HTML page as a provider-configuration file.  The best solution to this
 * problem is to fix the misconfigured web server to return the correct
 * response code (HTTP 404) along with the HTML error page.
 *
 * @param  <S>
 *         The type of the service to be loaded by this loader
 *
 * @author Mark Reinhold
 * @since 1.6
 */

@SuppressWarnings({"unchecked", "deprecation", "all"})
public final class ServiceLoader<S> implements java.lang.Iterable<S> {

private ServiceLoader() { throw new RuntimeException("Stub!"); }

/**
 * Clear this loader's provider cache so that all providers will be
 * reloaded.
 *
 * <p> After invoking this method, subsequent invocations of the {@link
 * #iterator() iterator} method will lazily look up and instantiate
 * providers from scratch, just as is done by a newly-created loader.
 *
 * <p> This method is intended for use in situations in which new providers
 * can be installed into a running Java virtual machine.
 */

public void reload() { throw new RuntimeException("Stub!"); }

/**
 * Lazily loads the available providers of this loader's service.
 *
 * <p> The iterator returned by this method first yields all of the
 * elements of the provider cache, in instantiation order.  It then lazily
 * loads and instantiates any remaining providers, adding each one to the
 * cache in turn.
 *
 * <p> To achieve laziness the actual work of parsing the available
 * provider-configuration files and instantiating providers must be done by
 * the iterator itself.  Its {@link java.util.Iterator#hasNext hasNext} and
 * {@link java.util.Iterator#next next} methods can therefore throw a
 * {@link java.util.ServiceConfigurationError ServiceConfigurationError} if a provider-configuration file
 * violates the specified format, or if it names a provider class that
 * cannot be found and instantiated, or if the result of instantiating the
 * class is not assignable to the service type, or if any other kind of
 * exception or error is thrown as the next provider is located and
 * instantiated.  To write robust code it is only necessary to catch {@link java.util.ServiceConfigurationError ServiceConfigurationError} when using a service iterator.
 *
 * <p> If such an error is thrown then subsequent invocations of the
 * iterator will make a best effort to locate and instantiate the next
 * available provider, but in general such recovery cannot be guaranteed.
 *
 * <blockquote style="font-size: smaller; line-height: 1.2"><span
 * style="padding-right: 1em; font-weight: bold">Design Note</span>
 * Throwing an error in these cases may seem extreme.  The rationale for
 * this behavior is that a malformed provider-configuration file, like a
 * malformed class file, indicates a serious problem with the way the Java
 * virtual machine is configured or is being used.  As such it is
 * preferable to throw an error rather than try to recover or, even worse,
 * fail silently.</blockquote>
 *
 * <p> The iterator returned by this method does not support removal.
 * Invoking its {@link java.util.Iterator#remove() remove} method will
 * cause an {@link java.lang.UnsupportedOperationException UnsupportedOperationException} to be thrown.
 *
 * @implNote When adding providers to the cache, the {@link #iterator
 * Iterator} processes resources in the order that the {@link
 * java.lang.ClassLoader#getResources(java.lang.String)
 * ClassLoader.getResources(String)} method finds the service configuration
 * files.
 *
 * @return  An iterator that lazily loads providers for this loader's
 *          service
 */

public java.util.Iterator<S> iterator() { throw new RuntimeException("Stub!"); }

/**
 * Creates a new service loader for the given service type and class
 * loader.
 *
 * @param  <S> the class of the service type
 *
 * @param  service
 *         The interface or abstract class representing the service
 *
 * @param  loader
 *         The class loader to be used to load provider-configuration files
 *         and provider classes, or <tt>null</tt> if the system class
 *         loader (or, failing that, the bootstrap class loader) is to be
 *         used
 *
 * @return A new service loader
 */

public static <S> java.util.ServiceLoader<S> load(java.lang.Class<S> service, java.lang.ClassLoader loader) { throw new RuntimeException("Stub!"); }

/**
 * Creates a new service loader for the given service type, using the
 * current thread's {@linkplain java.lang.Thread#getContextClassLoader
 * context class loader}.
 *
 * <p> An invocation of this convenience method of the form
 *
 * <blockquote><pre>
 * ServiceLoader.load(<i>service</i>)</pre></blockquote>
 *
 * is equivalent to
 *
 * <blockquote><pre>
 * ServiceLoader.load(<i>service</i>,
 *                    Thread.currentThread().getContextClassLoader())</pre></blockquote>
 *
 * @param  <S> the class of the service type
 *
 * @param  service
 *         The interface or abstract class representing the service
 *
 * @return A new service loader
 */

public static <S> java.util.ServiceLoader<S> load(java.lang.Class<S> service) { throw new RuntimeException("Stub!"); }

/**
 * Creates a new service loader for the given service type, using the
 * extension class loader.
 *
 * <p> This convenience method simply locates the extension class loader,
 * call it <tt><i>extClassLoader</i></tt>, and then returns
 *
 * <blockquote><pre>
 * ServiceLoader.load(<i>service</i>, <i>extClassLoader</i>)</pre></blockquote>
 *
 * <p> If the extension class loader cannot be found then the system class
 * loader is used; if there is no system class loader then the bootstrap
 * class loader is used.
 *
 * <p> This method is intended for use when only installed providers are
 * desired.  The resulting service will only find and load providers that
 * have been installed into the current Java virtual machine; providers on
 * the application's class path will be ignored.
 *
 * @param  <S> the class of the service type
 *
 * @param  service
 *         The interface or abstract class representing the service
 *
 * @return A new service loader
 */

public static <S> java.util.ServiceLoader<S> loadInstalled(java.lang.Class<S> service) { throw new RuntimeException("Stub!"); }

/**
 * Returns a string describing this service.
 *
 * @return  A descriptive string
 */

public java.lang.String toString() { throw new RuntimeException("Stub!"); }
}