org.apache.activemq.artemis.utils.FactoryFinder Maven / Gradle / Ivy
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* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.activemq.artemis.utils;
import java.io.BufferedInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
public class FactoryFinder {
/**
* The strategy that the FactoryFinder uses to find load and instantiate Objects
* can be changed out by calling the setObjectFactory method with a custom implementation of ObjectFactory.
*
* The default ObjectFactory is typically changed out when running in a specialized container
* environment where service discovery needs to be done via the container system. For example,
* in an OSGi scenario.
*/
public interface ObjectFactory {
/**
* @param path the full service path
* @return Object
* @throws IllegalAccessException illegal access
* @throws InstantiationException on instantiation error
* @throws IOException On IO Error
* @throws ClassNotFoundException On class not found error
*/
Object create(String path) throws IllegalAccessException, InstantiationException, IOException, ClassNotFoundException;
}
/**
* The default implementation of Object factory which works well in standalone applications.
*/
protected static class StandaloneObjectFactory implements ObjectFactory {
final ConcurrentMap classMap = new ConcurrentHashMap<>();
@Override
public Object create(final String path) throws InstantiationException, IllegalAccessException, ClassNotFoundException, IOException {
Class clazz = classMap.get(path);
if (clazz == null) {
clazz = loadClass(loadProperties(path));
classMap.put(path, clazz);
}
return clazz.newInstance();
}
static Class loadClass(Properties properties) throws ClassNotFoundException, IOException {
String className = properties.getProperty("class");
if (className == null) {
throw new IOException("Expected property is missing: class");
}
Class clazz = null;
ClassLoader loader = Thread.currentThread().getContextClassLoader();
if (loader != null) {
try {
clazz = loader.loadClass(className);
} catch (ClassNotFoundException e) {
// ignore
}
}
if (clazz == null) {
clazz = FactoryFinder.class.getClassLoader().loadClass(className);
}
return clazz;
}
public Properties loadProperties(String uri) throws IOException {
// lets try the thread context class loader first
ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
if (classLoader == null) {
classLoader = StandaloneObjectFactory.class.getClassLoader();
}
InputStream in = classLoader.getResourceAsStream(uri);
if (in == null) {
in = FactoryFinder.class.getClassLoader().getResourceAsStream(uri);
if (in == null) {
throw new IOException("Could not find factory class for resource: " + uri);
}
}
// lets load the file
try (BufferedInputStream reader = new BufferedInputStream(in)) {
Properties properties = new Properties();
properties.load(reader);
return properties;
}
}
}
// ================================================================
// Class methods and properties
// ================================================================
private static ObjectFactory objectFactory = new StandaloneObjectFactory();
public static ObjectFactory getObjectFactory() {
return objectFactory;
}
public static void setObjectFactory(ObjectFactory objectFactory) {
FactoryFinder.objectFactory = objectFactory;
}
// ================================================================
// Instance methods and properties
// ================================================================
private final String path;
public FactoryFinder(String path) {
this.path = path;
}
/**
* Creates a new instance of the given key
*
* @param key is the key to add to the path to find a text file containing
* the factory name
* @return a newly created instance
* @throws IllegalAccessException On illegal access
* @throws InstantiationException On can not instantiate exception
* @throws IOException On IOException
* @throws ClassNotFoundException When class not on class path
*/
public Object newInstance(String key) throws IllegalAccessException, InstantiationException, IOException, ClassNotFoundException {
return objectFactory.create(path + key);
}
}