src/main/java/org/apache/servicemix/finder/FactoryFinder.java

/*
 * 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.servicemix.finder;

import java.io.BufferedInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.Map;
import java.util.Properties;

import java.util.concurrent.ConcurrentHashMap;

public class FactoryFinder {

    private final String path;

    private final Map<String, Class<?>> classMap = new ConcurrentHashMap<String, Class<?>>();

    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
     */
    public Object newInstance(String key) throws IllegalAccessException, InstantiationException, IOException,
            ClassNotFoundException {
        return newInstance(key, null);
    }

    public Object newInstance(String key, String propertyPrefix) throws IllegalAccessException, InstantiationException,
            IOException, ClassNotFoundException {
        if (propertyPrefix == null) {
            propertyPrefix = "";
        }
        Class clazz = classMap.get(propertyPrefix + key);
        if (clazz == null) {
            clazz = newInstance(doFindFactoryProperies(key), propertyPrefix);
            classMap.put(propertyPrefix + key, clazz);
        }
        return clazz.newInstance();
    }

    private Class newInstance(Properties properties, String propertyPrefix) throws ClassNotFoundException, IOException {

        String className = properties.getProperty(propertyPrefix + "class");
        if (className == null) {
            throw new IOException("Expected property is missing: " + propertyPrefix + "class");
        }
        Class clazz;
        try {
            clazz = Thread.currentThread().getContextClassLoader().loadClass(className);
        } catch (ClassNotFoundException e) {
            clazz = FactoryFinder.class.getClassLoader().loadClass(className);
        }

        return clazz;
    }

    private Properties doFindFactoryProperies(String key) throws IOException {
        String uri = path + key;

        // lets try the thread context class loader first
        InputStream in = Thread.currentThread().getContextClassLoader().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
        BufferedInputStream reader = null;
        try {
            reader = new BufferedInputStream(in);
            Properties properties = new Properties();
            properties.load(reader);
            return properties;
        } finally {
            try {
                reader.close();
            } catch (Exception e) {
                // Do nothing
            }
        }
    }
}