package org.webslinger.lang;

 import java.net.URL;

 import java.util.ArrayList;

 import java.util.Enumeration;

 import java.util.List;

 import java.util.Properties;

 public final class ClassUtil {

     public static final Object NULL = new Object();

     public static Object loadImplementation(String label, String[] impls, ClassLoader loader) {

         for (String impl: impls) {

             try {

                 return Class.forName(impl, true, loader).newInstance();

             } catch (Throwable t) {

                 // ignore

             }

         }

         throw new UnsupportedOperationException(label);

     }

     public static List loadImplementationsProperties(String label, String propName, Class clz) {

         ArrayList<Class> list = new ArrayList<Class>();

         loadImplementationsPropertiesInternal(list, label, propName, clz.getClassLoader());

         loadImplementationsPropertiesInternal(list, label, propName, Thread.currentThread().getContextClassLoader());

         return list;

     }

     private static void loadImplementationsPropertiesInternal(List<Class> list, String label, String propName, ClassLoader loader) {

         if (loader == null) return;

         try {

             Enumeration<URL> props = loader.getResources(propName);

             while (props.hasMoreElements()) {

                 URL url = props.nextElement();

                 Properties properties = new Properties();

                 try {

                     properties.load(url.openConnection().getInputStream());

                     for (int i = 0; ; i++) {

                         String impl = properties.getProperty("impl." + i);

                         if (impl == null) break;

                         try {

                             list.add(Class.forName(impl, true, loader));

                         } catch (Throwable t) {

                             // ignore

                         }

                     }

                 } catch (Throwable t) {

                     // ignore

                 }

             }

         } catch (Throwable t) {

             // ignore

         }

     }

 }