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* The Apache Software License, Version 1.1
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package org.apache.commons.discovery.tools;
import java.util.Enumeration;
import org.apache.commons.discovery.ResourceClass;
import org.apache.commons.discovery.ResourceClassIterator;
import org.apache.commons.discovery.ResourceNameIterator;
import org.apache.commons.discovery.resource.ClassLoaders;
import org.apache.commons.discovery.resource.classes.DiscoverClasses;
import org.apache.commons.discovery.resource.names.DiscoverServiceNames;
/**
* [this was ServiceDiscovery12... the 1.1 versus 1.2 issue
* has been abstracted to org.apache.commons.discover.jdk.JDKHooks]
*
* <p>Implement the JDK1.3 'Service Provider' specification.
* ( http://java.sun.com/j2se/1.3/docs/guide/jar/jar.html )
* </p>
*
* This class supports any VM, including JDK1.1, via
* org.apache.commons.discover.jdk.JDKHooks.
*
* The caller will first configure the discoverer by adding ( in the desired
* order ) all the places to look for the META-INF/services. Currently
* we support loaders.
*
* The findResources() method will check every loader.
*
* @author Richard A. Sitze
* @author Craig R. McClanahan
* @author Costin Manolache
* @author James Strachan
*/
public class Service
{
/** Construct a new service discoverer
*/
protected Service() {
}
/**
* as described in
* sun/jdk1.3.1/docs/guide/jar/jar.html#Service Provider,
* Except this uses <code>Enumeration</code>
* instead of <code>Interator</code>.
*
* @return Enumeration of class instances (<code>Object</code>)
*/
public static Enumeration providers(Class spiClass) {
return providers(new SPInterface(spiClass), null);
}
/**
* This version lets you specify constructor arguments..
*
* @param spi SPI to look for and load.
* @param classLoaders loaders to use in search.
* If <code>null</code> then use ClassLoaders.getAppLoaders().
*/
public static Enumeration providers(final SPInterface spi,
ClassLoaders loaders)
{
if (loaders == null) {
loaders = ClassLoaders.getAppLoaders(spi.getSPClass(),
Service.class,
true);
}
ResourceNameIterator servicesIter =
(new DiscoverServiceNames(loaders)).findResourceNames(spi.getSPName());
final ResourceClassIterator services =
(new DiscoverClasses(loaders)).findResourceClasses(servicesIter);
return new Enumeration() {
private Object object = null;
public boolean hasMoreElements() {
if (object == null) {
object = getNextClassInstance();
}
return object != null;
}
public Object nextElement() {
Object obj = object;
object = null;
return obj;
}
private Object getNextClassInstance() {
while (services.hasNext()) {
ResourceClass info = services.nextResourceClass();
try {
return spi.newInstance(info.loadClass());
} catch (Exception e) {
// ignore
}
}
return null;
}
};
}
}