ro.isdc.wro.util.provider.ProviderFinder Maven / Gradle / Ivy
package ro.isdc.wro.util.provider;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import javax.imageio.spi.ServiceRegistry;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import ro.isdc.wro.WroRuntimeException;
import ro.isdc.wro.util.Ordered;
/**
* Helps to find available providers of any supported type.
*
* @author Alex Objelean
* @created 16 Jun 2012
* @since 1.4.7
*/
public class ProviderFinder {
private static final Logger LOG = LoggerFactory.getLogger(ProviderFinder.class);
private final Class type;
/**
* @VisibleForTesting.
* @param type
* the type of providers to find.
*/
ProviderFinder(final Class type) {
this.type = type;
}
/**
* Creates a {@link ProviderFinder} which will find providers of type provided as argument..
*
* @param type
* the type of providers to search.
* @return {@link ProviderFinder} handling providers lookup.
*/
public static ProviderFinder of(final Class type) {
return new ProviderFinder(type);
}
/**
* @return the list of all providers found in classpath. The returned list is sorted according to the {@link Ordered} interface (from {@link Ordered#LOWEST} to {@link Ordered#HIGHEST}.
*/
public List find() {
final List providers = new ArrayList();
try {
final Iterator iterator = lookupProviders(type);
for (; iterator.hasNext();) {
final T provider = iterator.next();
LOG.debug("found provider: {}", provider);
providers.add(provider);
}
collectConfigurableProviders(providers);
} catch (final Exception e) {
LOG.error("Failed to discover providers using ServiceRegistry. Cannot continue...", e);
throw WroRuntimeException.wrap(e);
}
Collections.sort(providers, Ordered.DESCENDING_COMPARATOR);
LOG.debug("found providers: {}", providers);
return providers;
}
/**
* Collects also providers of type {@link ConfigurableProvider} if the T type is a supertype of
* {@link ConfigurableProvider}. If the type is already {@link ConfigurableProvider}, it will be ignored to avoid
* adding of duplicate providers.
*
* @param providers
* the list where found providers will be added.
*/
@SuppressWarnings("unchecked")
private void collectConfigurableProviders(final List providers) {
if (type.isAssignableFrom(ConfigurableProvider.class) && (type != ConfigurableProvider.class)) {
final Iterator iterator = lookupProviders(ConfigurableProvider.class);
for (; iterator.hasNext();) {
final T provider = (T) iterator.next();
LOG.debug("found provider: {}", provider);
providers.add(provider);
}
}
}
/**
* This method is useful for mocking the lookup operation. The implementation will try to use java.util.ServiceLoader
* by default (available in jdk6) and will fallback to ServiceRegistry for earlier JDK versions. The reason for this
* is to support GAE environment which doesn't contain the ServiceRegistry in its whitelist.
*
* @param providerClass
* the class of the provider to lookup.
* @VisibleForTesting
* @return the iterator of found providers.
*/
@SuppressWarnings("unchecked")
Iterator
lookupProviders(final Class
providerClass) {
LOG.debug("searching for providers of type : {}", providerClass);
try {
final Class serviceLoader = getClass().getClassLoader().loadClass("java.util.ServiceLoader");
LOG.debug("using {} to lookupProviders", serviceLoader.getName());
return ((Iterable
) serviceLoader.getMethod("load", Class.class).invoke(serviceLoader, providerClass)).iterator();
} catch (final Exception e) {
LOG.debug("ServiceLoader is not available. Falling back to ServiceRegistry.", e);
}
LOG.debug("using {} to lookupProviders", ServiceRegistry.class.getName());
return ServiceRegistry.lookupProviders(providerClass);
}
}