clime.messadmin.providers.ProviderUtils Maven / Gradle / Ivy
/**
*
*/
package clime.messadmin.providers;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import clime.messadmin.providers.spi.BaseProvider;
/**
* Fetches and caches Services (== Providers)
* @author Cédrik LIME
*/
public class ProviderUtils {
/**
* This is a cache of Providers, keyed by its Interface, and by a ClassLoader.
* This enables different WebApps (different ClassLoaders) to have their own set of plugins (same Interface).
*/
private static final Map/*>>*/ PROVIDERS_CACHE = new SoftHashMap();//FIXME do we need soft values too?
private static final Comparator priorityComparator = new Comparator() {
/** {@inheritDoc} */
public int compare(Object o1, Object o2) {
return ((BaseProvider)o1).getPriority() - ((BaseProvider)o2).getPriority();
}
};
/**
*
*/
private ProviderUtils() {
super();
}
/**
* Implementation note: keep this method unsynchronized, as it would be a contention point otherwise.
* We don't care if the cache is filled multiple times.
* @param clazz
* @return list of providers for clazz, sorted by priority
*/
public static /**/ List/**/ getProviders(final Class/**/ clazz) {
ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
Map providersByInterface = (Map) PROVIDERS_CACHE.get(classLoader);
if (providersByInterface == null) {
fillProvidersCache(clazz);
providersByInterface = (Map) PROVIDERS_CACHE.get(classLoader);
}
List providers = (List) providersByInterface.get(clazz);
if (providers == null) {
fillProvidersCache(clazz);
providers = (List) providersByInterface.get(clazz);
}
return providers;
}
/**
* @param clazz
*/
private static synchronized void fillProvidersCache(final Class/**/ clazz) {
ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
Map providersByInterface = (Map) PROVIDERS_CACHE.get(classLoader);
if (providersByInterface == null) {
providersByInterface = new SoftHashMap/*>*/();
providersByInterface.put(clazz, new ArrayList/**/());
// put resulting Map in cache as *last operation* (after filling said Map)
PROVIDERS_CACHE.put(classLoader, providersByInterface);
}
List providers = (List) providersByInterface.get(clazz);
if (providers == null) {
providers = new ArrayList();
Iterator ps = Service.providers(clazz, classLoader);
if (! ps.hasNext() && classLoader != clazz.getClassLoader()) {
ps = Service.providers(clazz, clazz.getClassLoader());
}
while (ps.hasNext()) {
try {
BaseProvider provider = (BaseProvider) ps.next();
providers.add(provider);
} catch (RuntimeException rte) {
// error while fetching provider; skipping
System.err.println("ERROR while fetching MessAdmin Provider (skipped): " + rte.getLocalizedMessage());
} catch (LinkageError le) {
// error while fetching provider; skipping
System.err.println("ERROR while fetching MessAdmin Provider (skipped): " + le.getLocalizedMessage());
}
}
Collections.sort(providers, priorityComparator);
// put resulting List in cache as *last operation* (after filling said List)
providersByInterface.put(clazz, providers);
}
}
/**
* Clear this service's provider cache.
*
* After invoking this method, subsequent invocations of the
* iterator method will lazily look up and instantiate
* providers from scratch, just as is done by a newly-created instance of
* this class.
*
*
This method is intended for use in situations in which new providers
* can be installed into a running Java virtual machine.
*/
public static void reload() {
PROVIDERS_CACHE.clear();
}
/**
* Clear this service's provider cache for the current ClassLoader.
*
*
After invoking this method, subsequent invocations of the
* iterator method will lazily look up and instantiate
* providers from scratch, just as is done by a newly-created instance of
* this class.
*
*
This method is intended for use in situations in which new providers
* can be installed into a running Java virtual machine.
*/
public static void deregisterCurrent() {
PROVIDERS_CACHE.remove(Thread.currentThread().getContextClassLoader());
}
/**
* Finalizes this object prior to garbage collection. The
* deregisterAll method is called to deregister all
* currently registered service providers. This method should not
* be called from application code.
*
* @exception Throwable if an error occurs during superclass
* finalization.
* @see java.lang.Object#finalize()
*/
protected void finalize() throws Throwable {
reload();
super.finalize();
}
}