| /* |
| * 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.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; |
| |
| |
| /** |
| * 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>'\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 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<CodecSet> 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 |
| * 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 |
| */ |
| |
| public final class ServiceLoader<S> |
| implements Iterable<S> |
| { |
| |
| private static final String PREFIX = "META-INF/services/"; |
| |
| // The class or interface representing the service being loaded |
| private final Class<S> service; |
| |
| // The class loader used to locate, load, and instantiate providers |
| private final ClassLoader loader; |
| |
| // The access control context taken when the ServiceLoader is created |
| // Android-changed: do not use legacy security code. |
| // private final AccessControlContext acc; |
| |
| // Cached providers, in instantiation order |
| private LinkedHashMap<String,S> providers = new LinkedHashMap<>(); |
| |
| // The current lazy-lookup iterator |
| private LazyIterator lookupIterator; |
| |
| /** |
| * 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() { |
| providers.clear(); |
| lookupIterator = new LazyIterator(service, loader); |
| } |
| |
| private ServiceLoader(Class<S> svc, ClassLoader cl) { |
| service = Objects.requireNonNull(svc, "Service interface cannot be null"); |
| loader = (cl == null) ? ClassLoader.getSystemClassLoader() : cl; |
| // Android-changed: Do not use legacy security code. |
| // On Android, System.getSecurityManager() is always null. |
| // acc = (System.getSecurityManager() != null) ? AccessController.getContext() : null; |
| reload(); |
| } |
| |
| private static void fail(Class<?> service, String msg, Throwable cause) |
| throws ServiceConfigurationError |
| { |
| throw new ServiceConfigurationError(service.getName() + ": " + msg, |
| cause); |
| } |
| |
| 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 the names list. |
| // |
| private int parseLine(Class<?> service, URL u, BufferedReader r, int lc, |
| List<String> names) |
| 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 (!providers.containsKey(ln) && !names.contains(ln)) |
| names.add(ln); |
| } |
| return lc + 1; |
| } |
| |
| // Parse the content of the given URL as a provider-configuration file. |
| // |
| // @param service |
| // The service type for which providers are being sought; |
| // used to construct error detail strings |
| // |
| // @param u |
| // The URL naming the configuration file to be parsed |
| // |
| // @return 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 |
| // |
| // @throws ServiceConfigurationError |
| // If an I/O error occurs while reading from the given URL, or |
| // if a configuration-file format error is detected |
| // |
| private Iterator<String> parse(Class<?> service, URL u) |
| throws ServiceConfigurationError |
| { |
| InputStream in = null; |
| BufferedReader r = null; |
| ArrayList<String> 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)) >= 0); |
| } catch (IOException x) { |
| fail(service, "Error reading configuration file", x); |
| } finally { |
| try { |
| if (r != null) r.close(); |
| if (in != null) in.close(); |
| } catch (IOException y) { |
| fail(service, "Error closing configuration file", y); |
| } |
| } |
| return names.iterator(); |
| } |
| |
| // Private inner class implementing fully-lazy provider lookup |
| // |
| private class LazyIterator |
| implements Iterator<S> |
| { |
| |
| Class<S> service; |
| ClassLoader loader; |
| Enumeration<URL> configs = null; |
| Iterator<String> pending = null; |
| String nextName = null; |
| |
| private LazyIterator(Class<S> service, ClassLoader loader) { |
| this.service = service; |
| this.loader = loader; |
| } |
| |
| private boolean hasNextService() { |
| 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, "Error locating configuration files", x); |
| } |
| } |
| while ((pending == null) || !pending.hasNext()) { |
| if (!configs.hasMoreElements()) { |
| return false; |
| } |
| pending = parse(service, configs.nextElement()); |
| } |
| nextName = pending.next(); |
| return true; |
| } |
| |
| private S nextService() { |
| if (!hasNextService()) |
| throw new NoSuchElementException(); |
| String cn = nextName; |
| nextName = null; |
| Class<?> c = null; |
| try { |
| c = Class.forName(cn, false, loader); |
| } catch (ClassNotFoundException x) { |
| fail(service, |
| // Android-changed: Let the ServiceConfigurationError have a cause. |
| "Provider " + cn + " not found", x); |
| // "Provider " + cn + " not found"); |
| } |
| if (!service.isAssignableFrom(c)) { |
| // Android-changed: Let the ServiceConfigurationError have a cause. |
| ClassCastException cce = new ClassCastException( |
| service.getCanonicalName() + " is not assignable from " + c.getCanonicalName()); |
| fail(service, |
| "Provider " + cn + " not a subtype", cce); |
| // fail(service, |
| // "Provider " + cn + " not a subtype"); |
| } |
| try { |
| S p = service.cast(c.newInstance()); |
| providers.put(cn, p); |
| return p; |
| } catch (Throwable x) { |
| fail(service, |
| "Provider " + cn + " could not be instantiated", |
| x); |
| } |
| throw new Error(); // This cannot happen |
| } |
| |
| public boolean hasNext() { |
| // Android-changed: do not use legacy security code |
| /* if (acc == null) { */ |
| return hasNextService(); |
| /* |
| } else { |
| PrivilegedAction<Boolean> action = new PrivilegedAction<Boolean>() { |
| public Boolean run() { return hasNextService(); } |
| }; |
| return AccessController.doPrivileged(action, acc); |
| } |
| */ |
| } |
| |
| public S next() { |
| // Android-changed: do not use legacy security code |
| /* if (acc == null) { */ |
| return nextService(); |
| /* |
| } else { |
| PrivilegedAction<S> action = new PrivilegedAction<S>() { |
| public S run() { return nextService(); } |
| }; |
| return AccessController.doPrivileged(action, acc); |
| } |
| */ |
| } |
| |
| public void remove() { |
| throw new UnsupportedOperationException(); |
| } |
| |
| } |
| |
| /** |
| * 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 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 |
| * 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 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 Iterator<S> iterator() { |
| return new Iterator<S>() { |
| |
| Iterator<Map.Entry<String,S>> knownProviders |
| = providers.entrySet().iterator(); |
| |
| public boolean hasNext() { |
| if (knownProviders.hasNext()) |
| return true; |
| return lookupIterator.hasNext(); |
| } |
| |
| public S next() { |
| if (knownProviders.hasNext()) |
| return knownProviders.next().getValue(); |
| return lookupIterator.next(); |
| } |
| |
| public void remove() { |
| throw new UnsupportedOperationException(); |
| } |
| |
| }; |
| } |
| |
| /** |
| * 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> ServiceLoader<S> load(Class<S> service, |
| ClassLoader loader) |
| { |
| return new ServiceLoader<>(service, loader); |
| } |
| |
| /** |
| * 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> ServiceLoader<S> load(Class<S> service) { |
| ClassLoader cl = Thread.currentThread().getContextClassLoader(); |
| return ServiceLoader.load(service, cl); |
| } |
| |
| /** |
| * 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> ServiceLoader<S> loadInstalled(Class<S> service) { |
| ClassLoader cl = ClassLoader.getSystemClassLoader(); |
| ClassLoader prev = null; |
| while (cl != null) { |
| prev = cl; |
| cl = cl.getParent(); |
| } |
| return ServiceLoader.load(service, prev); |
| } |
| |
| // BEGIN Android-added: loadFromSystemProperty(), for internal use. |
| // Instantiates a class from a system property (used elsewhere in libcore). |
| /** |
| * Internal API to support built-in SPIs that check a system property first. |
| * Returns an instance specified by a property with the class' binary name, or null if |
| * no such property is set. |
| * @hide |
| */ |
| public static <S> S loadFromSystemProperty(final Class<S> service) { |
| try { |
| final String className = System.getProperty(service.getName()); |
| if (className != null) { |
| Class<?> c = ClassLoader.getSystemClassLoader().loadClass(className); |
| return (S) c.newInstance(); |
| } |
| return null; |
| } catch (Exception e) { |
| throw new Error(e); |
| } |
| } |
| // END Android-added: loadFromSystemProperty(), for internal use. |
| |
| /** |
| * Returns a string describing this service. |
| * |
| * @return A descriptive string |
| */ |
| public String toString() { |
| return "java.util.ServiceLoader[" + service.getName() + "]"; |
| } |
| |
| } |
