+ MyProject
  + FolderType1 (should have a type1 icon)
    - file1.json
    - file2.json
  + FolderType2 (should have a type2 icon)
    - file1.json
    - file2.json

	  @Override
	  public Object execute(ExecutionEvent event) throws ExecutionException {
		 // Get workbench window
		 IWorkbenchWindow window = HandlerUtil.getActiveWorkbenchWindowChecked(event);
		 // Set selection service
		 ISelectionService service = window.getSelectionService();
		 // Set structured selection
		 IStructuredSelection structured = (IStructuredSelection) service.getSelection();
		 Object first = structured.getFirstElement();
		 if (first instanceof IFolder) {
			 IFolder folder = (IFolder) first;
			 
                        // Change icon ...
		 }
		 return null;
	  }