code: public static String getIconClasses(CmsExplorerTypeSettings typeSettings, String resourceName, boolean small) {
  
          String result = null;
          if (typeSettings == null) {
              typeSettings = OpenCms.getWorkplaceManager().getExplorerTypeSetting(
                  (resourceName != null) && CmsResource.isFolder(resourceName)
                  ? CmsResourceTypeUnknownFile.RESOURCE_TYPE_NAME
                  : CmsResourceTypeUnknownFolder.RESOURCE_TYPE_NAME);
          }
          if (!typeSettings.getIconRules().isEmpty() && (resourceName != null)) {
              String extension = CmsResource.getExtension(resourceName);
              if (extension != null) {
                  // check for a matching sub type icon rule
                  CmsIconRule rule = typeSettings.getIconRules().get(extension);
                  if (rule != null) {
                      result = small ? rule.getSmallIconStyle() : rule.getBigIconStyle();
                  }
              }
          }
          if (result == null) {
              if (small && (typeSettings.getSmallIconStyle() != null)) {
                  result = typeSettings.getSmallIconStyle();
              } else if (small && (typeSettings.getIcon() == null)) {
                  result = CmsExplorerTypeSettings.ICON_STYLE_DEFAULT_SMALL;
              } else if (!small && (typeSettings.getBigIconStyle() != null)) {
                  result = typeSettings.getBigIconStyle();
              } else if (!small && (typeSettings.getBigIcon() == null)) {
                  result = CmsExplorerTypeSettings.ICON_STYLE_DEFAULT_BIG;
              }
  
              if (result != null) {
                  result = CmsGwtConstants.TYPE_ICON_CLASS + " " + result;
              } else {
                  result = getResourceIconClasses(typeSettings.getName(), resourceName, small);
              }
          }
          return result;
      }
docs: Returns the resource type icon CSS classes for the given type.<p>
  Use within ADE context only.<p>
  
  @param typeSettings the explorer type settings
  @param resourceName the resource name
  @param small <code>true</code> to get the small icon classes
  
  @return the icon CSS classes