/* * Copyright (c) 1999, 2003, 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 sun.misc; import java.io.BufferedReader;import java.io.IOException;import java.io.InputStream;import java.io.InputStreamReader;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> 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> 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> 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> <b>Example:</b> Suppose we have a service class named * <tt>java.io.spi.CharCodec</tt>.  It has two abstract methods: * * <pre> *   public abstract CharEncoder getEncoder(String encodingName); *   public abstract CharDecoder getDecoder(String encodingName); * </pre> * * 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> 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: * * <pre> *   sun.io.StandardCodec    # Standard codecs for the platform * </pre> * * To locate an encoder for a given encoding name, the internal I/O code would * do something like this: * * <pre> *   CharEncoder getEncoder(String encodingName) { *       Iterator ps = Service.providers(CharCodec.class); *       while (ps.hasNext()) { *           CharCodec cc = (CharCodec)ps.next(); *           CharEncoder ce = cc.getEncoder(encodingName); *           if (ce != null) *               return ce; *       } *       return null; *   } * </pre> * * 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 * @since 1.3 */ public final class Service {     private static final String prefix = "META-INF/services/";     private Service() { }     private static void fail(Class service, String msg, Throwable cause)        throws ServiceConfigurationError    {        ServiceConfigurationError sce            = new ServiceConfigurationError(service.getName() + ": " + msg);        sce.initCause(cause);        throw sce;    }     private static void fail(Class service, String msg)        throws ServiceConfigurationError    {        throw new ServiceConfigurationError(service.getName() + ": " + msg);    }     private static void fail(Class service, URL u, int line, String msg)        throws ServiceConfigurationError    {        fail(service, 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.     */    private static int parseLine(Class service, URL u, BufferedReader r, int lc,                                 List names, Set returned)        throws IOException, ServiceConfigurationError    {        String ln = r.readLine();        if (ln == null) {            return -1;        }        int ci = ln.indexOf('#');        if (ci >= 0) ln = ln.substring(0, ci);        ln = ln.trim();        int n = ln.length();        if (n != 0) {            if ((ln.indexOf(' ') >= 0) || (ln.indexOf('\t') >= 0))                fail(service, u, lc, "Illegal configuration-file syntax");            int cp = ln.codePointAt(0);            if (!Character.isJavaIdentifierStart(cp))                fail(service, u, lc, "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(service, u, lc, "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.     *     * @param  service     *         The service class for which providers are being sought;     *         used to construct error detail strings     *     * @param  url     *         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     */    private static Iterator parse(Class service, URL u, Set returned)        throws ServiceConfigurationError    {        InputStream in = null;        BufferedReader r = null;        ArrayList names = new ArrayList();        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);        } finally {            try {                if (r != null) r.close();                if (in != null) in.close();            } catch (IOException y) {                fail(service, ": " + y);            }        }        return names.iterator();    }      /**     * Private inner class implementing fully-lazy provider lookup     */    private static class LazyIterator implements Iterator {         Class service;        ClassLoader loader;        Enumeration configs = null;        Iterator pending = null;        Set returned = new TreeSet();        String nextName = null;         private LazyIterator(Class service, ClassLoader loader) {            this.service = service;            this.loader = loader;        }         public boolean hasNext() throws ServiceConfigurationError {            if (nextName != null) {                return true;            }            if (configs == null) {                try {                    String fullName = prefix + service.getName();                    if (loader == null)                        configs = ClassLoader.getSystemResources(fullName);                    else                        configs = loader.getResources(fullName);                } catch (IOException x) {                    fail(service, ": " + x);                }            }            while ((pending == null) || !pending.hasNext()) {                if (!configs.hasMoreElements()) {                    return false;                }                pending = parse(service, (URL)configs.nextElement(), returned);            }            nextName = (String)pending.next();            return true;        }         public Object next() throws ServiceConfigurationError {            if (!hasNext()) {                throw new NoSuchElementException();            }            String cn = nextName;            nextName = null;            try {                return Class.forName(cn, true, loader).newInstance();            } catch (ClassNotFoundException x) {                fail(service,                     "Provider " + cn + " not found");            } catch (Exception x) {                fail(service,                     "Provider " + cn + " could not be instantiated: " + x,                     x);            }            return null;        /* This cannot happen */        }         public void remove() {            throw new UnsupportedOperationException();        }     }      /**     * Locates and incrementally instantiates the available providers of a     * given service using the given class loader.     *     * <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> 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     *     * @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.     *     * @throws ServiceConfigurationError     *         If a provider-configuration file violates the specified format     *         or names a provider class that cannot be found and instantiated     *     * @see #providers(java.lang.Class)     * @see #installedProviders(java.lang.Class)     */    public static Iterator providers(Class service, ClassLoader loader)        throws ServiceConfigurationError    {        return new LazyIterator(service, loader);    }      /**     * Locates and incrementally instantiates the available providers of a     * given service using the context class loader.  This convenience method     * is equivalent to     *     * <pre>     *   ClassLoader cl = Thread.currentThread().getContextClassLoader();     *   return Service.providers(service, cl);     * </pre>     *     * @param  service     *         The service's abstract service class     *     * @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.     *     * @throws ServiceConfigurationError     *         If a provider-configuration file violates the specified format     *         or names a provider class that cannot be found and instantiated     *     * @see #providers(java.lang.Class, java.lang.ClassLoader)     */    public static Iterator providers(Class service)        throws ServiceConfigurationError    {        ClassLoader cl = Thread.currentThread().getContextClassLoader();        return Service.providers(service, cl);    }      /**     * Locates and incrementally instantiates the available providers of a     * given service using the extension class loader.  This convenience method     * simply locates the extension class loader, call it     * <tt>extClassLoader</tt>, and then does     *     * <pre>     *   return Service.providers(service, extClassLoader);     * </pre>     *     * 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.     *     * @param  service     *         The service's abstract service class     *     * @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.     *     * @throws ServiceConfigurationError     *         If a provider-configuration file violates the specified format     *         or names a provider class that cannot be found and instantiated     *     * @see #providers(java.lang.Class, java.lang.ClassLoader)     */    public static Iterator installedProviders(Class service)        throws ServiceConfigurationError    {        ClassLoader cl = ClassLoader.getSystemClassLoader();        ClassLoader prev = null;        while (cl != null) {            prev = cl;            cl = cl.getParent();        }        return Service.providers(service, prev);    } }