[java] plugin management by reflection

loadPlugins

  // replace schedulerSettings ...
  try{
      String pluginsDirectory = schedulerSettings.getPluginsDirectory();
      Class placementClass = PluginsUtils.getClassFromDirectory(pluginsDirectory , placementPolicy);
      log_.debug(String.format("instantiate the placement policy %s from the jar",placementPolicy));
      Object placementObject = placementClass.getConstructor(ResourceDemandEstimator.class).newInstance(estimator);
      placement = (PlacementPolicy)placementObject;
  }
  catch (Exception e)
  {
     e.printStackTrace();
      log_.debug("Back to default placement policy" ) ;
      placement = new FirstFit(estimator);
  }                
}

/**
* Gets class from directory
*/
public static Class getClassFromDirectory(String pluginsDirectory, String classToLoad) 
            throws MalformedURLException, ClassNotFoundException
{
    
  log_.debug("Try to look into the plugins directory " + pluginsDirectory);
  File dir = new File(pluginsDirectory);
  File[] files = dir.listFiles(new FilenameFilter(){
     @Override
      public boolean accept(File dir, String name) {
          return name.endsWith(".jar");
      }
  });
  URL[] urls = new URL[files.length];
  
  int i = 0 ;
  for (File file:files)
  {
      log_.debug("file " + file.toURI().toURL().toString());
      urls[i] = file.toURI().toURL();
      i++; 
  }
  log_.debug("number of plugins found " + urls.length );
  ClassLoader loader = new URLClassLoader(urls);
  Class classLoaded = loader.loadClass(String.valueOf(classToLoad));
  
  return classLoaded;
}