public class MyHandler extends AbstractHandler implements IHandler {

  @Override
  public Object execute(ExecutionEvent event) throws ExecutionException {

    final XtextEditor xtextEditor = (XtextEditor) HandlerUtil.getActiveEditor(event);

    final String info = xtextEditor.getDocument().readOnly(new IUnitOfWork<String,XtextResource>() {
			
      @Override
      public String exec(XtextResource state) throws Exception {

        TreeIterator<EObject> iter = state.getAllContents();
        String res = "";

        while (iter.hasNext()) {

	  EObject obj = iter.next();

	  if (...) {

            res = obj.getMyFeature();

          }

        }
        return res;

      }
			
    });


    //do some work here...

    //and then:
    xtextEditor.getDocument().modify(new IUnitOfWork.Void<XtextResource>() {

      @Override
      public void process(XtextResource state) throws Exception {

        TreeIterator<EObject> iter = state.getAllContents();

        while (iter.hasNext()) {

	  EObject obj = iter.next();

	  if (...) {

            obj.setMyFeature(info);

          }

        }

      }

    });

  }

}