/*
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* 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.
*/
/**
* 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
* 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 Service() { }
throws ServiceConfigurationError
{
throw sce;
}
throws ServiceConfigurationError
{
}
throws ServiceConfigurationError
{
}
/**
* 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.
*/
throws IOException, ServiceConfigurationError
{
return -1;
}
if (n != 0) {
}
}
}
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
*/
throws ServiceConfigurationError
{
BufferedReader r = null;
try {
in = u.openStream();
int lc = 1;
} catch (IOException x) {
} finally {
try {
} catch (IOException y) {
}
}
}
/**
* Private inner class implementing fully-lazy provider lookup
*/
}
return true;
}
try {
else
} catch (IOException x) {
}
}
if (!configs.hasMoreElements()) {
return false;
}
}
return true;
}
if (!hasNext()) {
throw new NoSuchElementException();
}
try {
} catch (ClassNotFoundException x) {
}
if (!service.isAssignableFrom(c)) {
}
try {
} catch (Throwable 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)
*/
throws ServiceConfigurationError
{
}
/**
* 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)
*/
throws ServiceConfigurationError
{
}
/**
* 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)
*/
throws ServiceConfigurationError
{
}
}
}