Hello "Kobe BryantLuo"-
On your way in you may have missed that we have a
policy on screen names here at JavaRanch. Basically, it must consist of a first name, a space, and a last name, and not be obviously fictitious. Since yours does not conform with it, please take a moment to change it, which you can do
right here.
As to your question, the checkNull function should return false if there is an error.
I think it should be "form.item.value.length" instead of "form.item.length"; same for the file field.