Retain data, set next event and show errors

trying to figure out how I can accomplish this below. if I have errors then I need to do the following

  • send to action category.edit
  • retain any data that was entered
  • show error messages

public void function save(){
var rc = event.getCollection();
var cat = populateModel(model=categoryService.get(rc.id),exclude=“id”);

if( validationService.validate(cat) ){
categoryService.save(cat);
getPlugin(“messagebox”).setMessage(“info”,“Category saved!”);
setNextEvent(‘category/list’);
} else {

// send to action category.edit

// retain any data that was entered

// show error messages

}

}