code: /*******************************************************************************
   * Copyright 2018 572682
   * 
   * Licensed 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 us.dot.its.jpo.ode.plugin;
  
  import java.net.URL;
  import java.net.URLClassLoader;
  
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /** Return concrete implementations for specific, known interfaces. */
  public final class PluginFactory {
  
     private static Logger logger = LoggerFactory.getLogger(PluginFactory.class);
  
     private PluginFactory() {
        throw new UnsupportedOperationException();
     }
  
     /**
      * Read in configuration data that maps names of interfaces to names of
      * corresponding concrete implementation classes. Called early upon startup,
      * before any implementations are needed by the rest of the program.
      * 
      * <P>
      * Example of a possible entry in such a config file : myapp.TimeSource =
      * myapp.TimeSourceOneDayAdvance
      */
     public static void init() {
        // TODO
        // perhaps a properties file is read, perhaps some other source is used
     }
  
     /*
      * Another variation: allow the caller to swap in different implementation
      * classes at runtime, after calling init. This allows testing code to swap
      * in various implementations.
      */
  
     /**
      * Return the concrete implementation of a OdePlugin interface.
      * 
      * @param coderClassName
      * @throws IllegalAccessException
      * @throws InstantiationException
      * @throws ClassNotFoundException
      */
     public static OdePlugin getPluginByName(String coderClassName)
           throws ClassNotFoundException, InstantiationException, IllegalAccessException {
        logger.info("Getting Plugin: {}", coderClassName);
        OdePlugin result = (OdePlugin) buildObject(coderClassName);
  
        if (null != result) {
           String resultStr = result.toString();
           logger.info("Got Plugin: {}", resultStr);
        } else {
           logger.info("Failed to load plugin for {}", coderClassName);
        }
  
        return result;
     }
  
     private static Object buildObject(String aClassName)
           throws ClassNotFoundException, InstantiationException, IllegalAccessException {
        Object result = null;
        try {
           ClassLoader cl = Thread.currentThread().getContextClassLoader();
  
           printClasspath(cl);
  
           result = buildObject(cl, aClassName);
        } catch (Exception ex) {
           logger.error("Error instantiating an object of " + aClassName, ex);
  
           ClassLoader cl = ClassLoader.getSystemClassLoader();
           printClasspath(cl);
           result = buildObject(cl, aClassName);
        }
        return result;
     }
  
     private static Object buildObject(ClassLoader cl, String aClassName)
           throws ClassNotFoundException, InstantiationException, IllegalAccessException {
        Object result;
        logger.info("Getting class: {}", aClassName);
  
        // note that, with this style, the implementation needs to have a
        // no-argument constructor!
        Class<?> implClass = cl.loadClass(aClassName);
  
        logger.info("creating an instance of: {}", implClass);
        result = implClass.newInstance();
        return result;
     }
  
     private static void printClasspath(ClassLoader cl) {
        URL[] urls = ((URLClassLoader) cl).getURLs();
  
        for (URL url : urls) {
           logger.info("Classpath: {}", url.getFile());
        }
     }
  }
  