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How to validate the name of a hidden form field that is not present in an HTML form using servlet

I have two HTML forms that have a Hidden Field tag and the other has no tag. When validating the first HTML form containing a hidden field tag, I can validate in the servlet by getting the name and value of the field. example as below,

HTML form with hidden tag

<form action="/myServlet" method="post" enctype="multipart/form-data">  
<input type="hidden" name="myname" value="myvalue"/>
<input type="file" name="file"/>
<input type="submit" value="Submit"/>

Servlet checking hidden field

ServletFileUpload upload = new ServletFileUpload();
FileItemIterator iter;
iter = upload.getItemIterator(request);
while (iter.hasNext()) {
   item = iter.next();
   String fileName =  item.getName();
   String fieldName = item.getFieldName();
   if (item.isFormField()) {
   String fieldValue = Streams.asString(item.openStream());
   if (fieldName.equals("myname")){ //validating Hidden form tag name
         // some process goes here
   }
}

With the above code, I can validate a hidden form field, but if I have an HTML form like below that does not have a hidden tag, then how do I handle my servlet for validation.

HTML form without hidden tag

<form action="/myServlet" method="post" enctype="multipart/form-data"> 
//No hidden tag
<input type="file" name="file"/>
<input type="submit" value="Submit"/>

I would like to check these various cases:

  • Form with hidden field and some content in the request for the field: VALID
  • Form with empty hidden field: INVALID
  • Form without hidden field: VALID

The main problem is the difference between the last two cases.

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2 answers


If you just need to know if the myname attribute is present, you can set a flag to indicate this. Or store the value in a string that was initialized to zero.



    boolean hasMyName = false;

    while (iter.hasNext()) {
       item = iter.next();
       String fileName =  item.getName();
       String fieldName = item.getFieldName();
       if (item.isFormField()) {
          String fieldValue = Streams.asString(item.openStream());
          if (fieldName.equals("myname")){ //validating Hidden form tag name
             hasMyName = true;
          }
    }

    if ( hasMyName ) {
        // myname is present, do something
    }
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I haven't done this, but you can try:

  • Create a hidden field in your form in case you think it should exist. The name of the hint field is "myHiddenField".

  • Now try to see if there is any / w bit value of this field when trying to get it when:

and. He's gone.



b. It is empty.

Try to see if you have the ability to get some kind of distinction such as empty and empty. As I said, I haven't tried it myself. I may be wrong in my assumption here.

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