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. + *
+ *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 encoder 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
+ * @version 1.11, 03/12/19
+ * @since 1.3
+ */
+final class ServiceFinderThis 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.
+ *
+ * @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 null 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)
+ */
+ static
+ * ClassLoader cl = Thread.currentThread().getContextClassLoader();
+ * return Service.providers(service, cl);
+ *
+ *
+ * @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)
+ */
+ public static