Check file before upload with h: inputFile and javax.servlet.http.Part in JSF

I am working on a JSF web project that uses the h: inputFile facility to upload files. I am binding the h: inputFile value to a base bean property of type javax.servelt.http.Part

<h:inputFile id="inputfile" validator="#{bean.validateFile}" value="#{bean.part}"/>

      

        
        
        
      

    

Also I use the following file validation strategy in the same bean backing:

 public void validateFile(FacesContext con, UIComponent comp, Object value) {
    Part p = (Part) value;
    List<FacesMessage> list = new ArrayList<>();
    if (p.getSize() == 0) {
        list.add(new FacesMessage("File Size too small"));
    }
    if (p.getSize()>MAXSIZE) {
        list.add(new FacesMessage("File Size too Big"));
    }
    if (!list.isEmpty()) {
        throw new ValidatorException(list);
    }
}

      

        
        
        
      

    

My question is: Does the Part interface use the whole file that will be uploaded to the server and THEN it will receive confirmation (i.e. its size) when the form is submitted?

As I experience this on localhost (Glass fish v.4), I see a message in the left corner of the Chrome browser indicating the file upload process, and after that, in case of a file validation error, I get a confirmation message.I am worried in real life situations (e.g. slow internet connections), this is a rather inconvenient way to send a size check error after uploading a file!

Please help me and if this is the way I am guessing please post an alternative solution.

Thanks in advance!