jakarta.activation.FactoryFinder Maven / Gradle / Ivy
/*
* Copyright (c) 2021 Oracle and/or its affiliates. All rights reserved.
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Distribution License v. 1.0, which is available at
* http://www.eclipse.org/org/documents/edl-v10.php.
*
* SPDX-License-Identifier: BSD-3-Clause
*/
package jakarta.activation;
import java.lang.reflect.Method;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Iterator;
import java.util.logging.Level;
import java.util.logging.Logger;
class FactoryFinder {
private static final Logger logger = Logger.getLogger("jakarta.activation");
private static final ServiceLoaderUtil.ExceptionHandler EXCEPTION_HANDLER =
new ServiceLoaderUtil.ExceptionHandler() {
@Override
public RuntimeException createException(Throwable throwable, String message) {
return new RuntimeException(message, throwable);
}
};
/**
* Finds the implementation {@code Class} object for the given
* factory type. If it fails and {@code tryFallback} is {@code true}
* finds the {@code Class} object for the given default class name.
* The arguments supplied must be used in order
* Note the default class name may be needed even if fallback
* is not to be attempted in order to check if requested type is fallback.
*
* This method is package private so that this code can be shared.
*
* @return the {@code Class} object of the specified message factory;
* may not be {@code null}
*
* @param factoryClass factory abstract class or interface to be found
* @param defaultClassName the implementation class name, which is
* to be used only if nothing else
* is found; {@code null} to indicate
* that there is no default class name
* @param tryFallback whether to try the default class as a
* fallback
* @exception RuntimeException if there is no factory found
*/
static T find(Class factoryClass,
String defaultClassName,
boolean tryFallback) throws RuntimeException {
ClassLoader tccl = ServiceLoaderUtil.contextClassLoader(EXCEPTION_HANDLER);
String factoryId = factoryClass.getName();
// Use the system property first
String className = fromSystemProperty(factoryId);
if (className != null) {
T result = newInstance(className, defaultClassName, tccl);
if (result != null) {
return result;
}
}
// standard services: java.util.ServiceLoader
T factory = ServiceLoaderUtil.firstByServiceLoader(
factoryClass,
logger,
EXCEPTION_HANDLER);
if (factory != null) {
return factory;
}
// handling Glassfish/OSGi (platform specific default)
if (isOsgi()) {
T result = lookupUsingOSGiServiceLoader(factoryId);
if (result != null) {
return result;
}
}
// If not found and fallback should not be tried, throw RuntimeException.
if (!tryFallback) {
throw new RuntimeException(
"Provider for " + factoryId + " cannot be found", null);
}
// We didn't find the class through the usual means so try the default
// (built in) factory if specified.
if (defaultClassName == null) {
throw new RuntimeException(
"Provider for " + factoryId + " cannot be found", null);
}
return newInstance(defaultClassName, defaultClassName, tccl);
}
private static T newInstance(String className, String defaultClassName, ClassLoader tccl) throws RuntimeException {
return ServiceLoaderUtil.newInstance(
className,
defaultClassName,
tccl,
EXCEPTION_HANDLER);
}
private static String fromSystemProperty(String factoryId) {
String systemProp = getSystemProperty(factoryId);
return systemProp;
}
private static String getSystemProperty(final String property) {
logger.log(Level.FINE, "Checking system property {0}", property);
String value = AccessController.doPrivileged(new PrivilegedAction() {
@Override
public String run() {
return System.getProperty(property);
}
});
logFound(value);
return value;
}
private static void logFound(String value) {
if (value != null) {
logger.log(Level.FINE, " found {0}", value);
} else {
logger.log(Level.FINE, " not found");
}
}
private static final String OSGI_SERVICE_LOADER_CLASS_NAME = "org.glassfish.hk2.osgiresourcelocator.ServiceLoader";
private static boolean isOsgi() {
try {
Class.forName(OSGI_SERVICE_LOADER_CLASS_NAME);
return true;
} catch (ClassNotFoundException ignored) {
}
return false;
}
@SuppressWarnings({"unchecked"})
private static T lookupUsingOSGiServiceLoader(String factoryId) {
try {
// Use reflection to avoid having any dependency on HK2 ServiceLoader class
Class serviceClass = Class.forName(factoryId);
Class[] args = new Class[]{serviceClass};
Class target = Class.forName(OSGI_SERVICE_LOADER_CLASS_NAME);
Method m = target.getMethod("lookupProviderInstances", Class.class);
Iterator iter = ((Iterable) m.invoke(null, (Object[]) args)).iterator();
return iter.hasNext() ? (T) iter.next() : null;
} catch (Exception ignored) {
// log and continue
return null;
}
}
}