001    /** 
002     * 
003     * Copyright 2004 Protique Ltd
004     * 
005     * Licensed under the Apache License, Version 2.0 (the "License"); 
006     * you may not use this file except in compliance with the License. 
007     * You may obtain a copy of the License at 
008     * 
009     * http://www.apache.org/licenses/LICENSE-2.0
010     * 
011     * Unless required by applicable law or agreed to in writing, software
012     * distributed under the License is distributed on an "AS IS" BASIS, 
013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 
014     * See the License for the specific language governing permissions and 
015     * limitations under the License. 
016     * 
017     **/
018    package org.activemq.util;
019    
020    import java.io.BufferedReader;
021    import java.io.IOException;
022    import java.io.InputStream;
023    import java.io.InputStreamReader;
024    import java.util.HashMap;
025    import java.util.Map;
026    
027    /**
028     * A helper class to discover protocols dynamically to ensure
029     * that the system is extensible and has minimum runtime dependencies
030     *
031     * @version $Revision: 1.1.1.1 $
032     */
033    public class FactoryFinder {
034        private String path;
035        private Map classes = new HashMap();
036    
037        public FactoryFinder(String path) {
038            this.path = path;
039        }
040    
041        /**
042         * Creates a new instance of the given key
043         *
044         * @param key is the key to add to the path to find a text file containing the factory name
045         * @return a newly created instance
046         */
047        public Object newInstance(String key) throws IllegalAccessException, InstantiationException, IOException, ClassNotFoundException {
048            Class type = findClass(key);
049            return type.newInstance();
050        }
051    
052        /**
053         * Loads the class for the given key
054         *
055         * @param key is the key to add to the path to find a text file containing the factory name
056         * @return the class for the given key
057         */
058        public Class findClass(String key) throws IOException, ClassNotFoundException {
059            Class answer = (Class) classes.get(key);
060            if (answer == null) {
061                answer = doFindClass(key);
062                classes.put(key, answer);
063            }
064            return answer;
065    
066        }
067    
068        private Class doFindClass(String key) throws IOException, ClassNotFoundException {
069            String uri = path + key;
070    
071            // lets try the thread context class loader first
072            InputStream in = Thread.currentThread().getContextClassLoader().getResourceAsStream(uri);
073            if (in == null) {
074                in = getClass().getClassLoader().getResourceAsStream(uri);
075                if (in == null) {
076                    throw new IOException("Could not find class for resource: " + uri);
077                }
078            }
079    
080            // lets load the file
081            BufferedReader reader = null;
082            try {
083                reader = new BufferedReader(new InputStreamReader(in));
084                String line = reader.readLine();
085                if (line == null) {
086                    throw new IOException("Empty file found for: " + uri);
087                }
088                line = line.trim();
089                Class answer = loadClass(line);
090                if (answer == null) {
091                    throw new ClassNotFoundException("Could not find class: " + line);
092                }
093                return answer;
094            }
095            finally {
096                try {
097                    reader.close();
098                }
099                catch (Exception e) {
100                    // ignore
101                }
102            }
103        }
104    
105        protected Class loadClass(String name) throws ClassNotFoundException {
106            try {
107                return Thread.currentThread().getContextClassLoader().loadClass(name);
108            }
109            catch (ClassNotFoundException e) {
110                return getClass().getClassLoader().loadClass(name);
111            }
112        }
113    }