FactoryFinder.java
/*
* Copyright (c) 2010, 2017 Oracle and/or its affiliates. All rights reserved.
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Public License v. 2.0, which is available at
* http://www.eclipse.org/legal/epl-2.0.
*
* This Source Code may also be made available under the following Secondary
* Licenses when the conditions for such availability set forth in the
* Eclipse Public License v. 2.0 are satisfied: GNU General Public License,
* version 2 with the GNU Classpath Exception, which is available at
* https://www.gnu.org/software/classpath/license.html.
*
* SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
*/
package javax.ws.rs.sse;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Iterator;
import java.util.Properties;
import java.util.ServiceConfigurationError;
import java.util.ServiceLoader;
import java.util.logging.Level;
import java.util.logging.Logger;
/**
* Factory finder utility class.
*
* @author Paul Sandoz
* @author Marc Hadley
* @author Marek Potociar
* @since 2.1
*/
final class FactoryFinder {
private static final Logger LOGGER = Logger.getLogger(FactoryFinder.class.getName());
private FactoryFinder() {
// prevents instantiation
}
private static ClassLoader getContextClassLoader() {
return AccessController.doPrivileged((PrivilegedAction<ClassLoader>) () -> {
ClassLoader cl = null;
try {
cl = Thread.currentThread().getContextClassLoader();
} catch (SecurityException ex) {
LOGGER.log(
Level.WARNING,
"Unable to get context classloader instance.",
ex);
}
return cl;
});
}
/**
* Creates an instance of the specified class using the specified
* {@code ClassLoader} object.
*
* @param className name of the class to be instantiated.
* @param classLoader class loader to be used.
* @return instance of the specified class.
* @throws ClassNotFoundException if the given class could not be found
* or could not be instantiated.
*/
private static Object newInstance(final String className, final ClassLoader classLoader) throws ClassNotFoundException {
try {
Class<?> spiClass;
if (classLoader == null) {
spiClass = Class.forName(className);
} else {
try {
spiClass = Class.forName(className, false, classLoader);
} catch (ClassNotFoundException ex) {
LOGGER.log(
Level.FINE,
"Unable to load provider class " + className
+ " using custom classloader " + classLoader.getClass().getName()
+ " trying again with current classloader.",
ex);
spiClass = Class.forName(className);
}
}
return spiClass.getDeclaredConstructor().newInstance();
} catch (ClassNotFoundException x) {
throw x;
} catch (Exception x) {
throw new ClassNotFoundException("Provider " + className + " could not be instantiated: " + x, x);
}
}
/**
* Finds the implementation {@code Class} for the given factory name,
* or if that fails, finds the {@code Class} for the given fallback
* class name and create its instance. The arguments supplied MUST be
* used in order. If using the first argument is successful, the second
* one will not be used.
* <p>
* This method is package private so that this code can be shared.
*
* @param factoryId the name of the factory to find, which is
* a system property.
* @param fallbackClassName the implementation class name, which is
* to be used only if nothing else.
* is found; {@code null} to indicate that
* there is no fallback class name.
* @param service service to be found.
* @param <T> type of the service to be found.
* @return the instance of the specified service; may not be {@code null}.
* @throws ClassNotFoundException if the given class could not be found
* or could not be instantiated.
*/
static <T> Object find(final String factoryId, final String fallbackClassName, Class<T> service) throws ClassNotFoundException {
ClassLoader classLoader = getContextClassLoader();
try {
Iterator<T> iterator = ServiceLoader.load(service, FactoryFinder.getContextClassLoader()).iterator();
if(iterator.hasNext()) {
return iterator.next();
}
} catch (Exception | ServiceConfigurationError ex) {
LOGGER.log(Level.FINER, "Failed to load service " + factoryId + ".", ex);
}
try {
Iterator<T> iterator = ServiceLoader.load(service, FactoryFinder.class.getClassLoader()).iterator();
if(iterator.hasNext()) {
return iterator.next();
}
} catch (Exception | ServiceConfigurationError ex) {
LOGGER.log(Level.FINER, "Failed to load service " + factoryId + ".", ex);
}
// try to read from $java.home/lib/jaxrs.properties
FileInputStream inputStream = null;
String configFile = null;
try {
String javah = System.getProperty("java.home");
configFile = javah + File.separator + "lib" + File.separator + "jaxrs.properties";
File f = new File(configFile);
if (f.exists()) {
Properties props = new Properties();
inputStream = new FileInputStream(f);
props.load(inputStream);
String factoryClassName = props.getProperty(factoryId);
return newInstance(factoryClassName, classLoader);
}
} catch (Exception ex) {
LOGGER.log(Level.FINER, "Failed to load service " + factoryId
+ " from $java.home/lib/jaxrs.properties", ex);
} finally {
if (inputStream != null) {
try {
inputStream.close();
} catch (IOException ex) {
LOGGER.log(Level.FINER, String.format("Error closing %s file.", configFile), ex);
}
}
}
// Use the system property
try {
String systemProp = System.getProperty(factoryId);
if (systemProp != null) {
return newInstance(systemProp, classLoader);
}
} catch (SecurityException se) {
LOGGER.log(Level.FINER, "Failed to load service " + factoryId
+ " from a system property", se);
}
if (fallbackClassName == null) {
throw new ClassNotFoundException(
"Provider for " + factoryId + " cannot be found", null);
}
return newInstance(fallbackClassName, classLoader);
}
}