| /* |
| * 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); |
| } |
| |
| } |
