public class IronDoor
  extends JavaPlugin
  implements Listener
{
  public void onEnable()
  {
    getServer().getPluginManager().registerEvents(this, this);
    logInfo("Plugin enabled.");
  }

  public void logInfo(String message)
  {
    getLogger().info(message);
  }

  @EventHandler
  public void onEntityExplode(EntityExplodeEvent event)
  {
    List<Block> destroy = event.blockList();
    Iterator<Block> it = destroy.iterator();
    while (it.hasNext())
    {
      Block b = (Block)it.next();

      Location loc = b.getLocation();
      loc.setY(loc.getY() - 2);

      int block = loc.getWorld().getBlockTypeIdAt(loc);
      Block blo = loc.getWorld().getBlockAt(loc);

      if (b.getType() == Material.IRON_DOOR) {
        if(blo.getType() == Material.OBSIDIAN) {

        it.remove();
        }
      }
    }
  }
}