Server side form validation

Question

Hi exprets.
How can i validate a form with jsp without the involvement of any client side script so that when a field is not filled properly it should display the form again with the data filled previously and a message against the incorrect field.
I have a generic asp code that can be used with any form. There are some complexities in it for me in converting it to jsp because I am very net to it.
Here is the asp code:
validateForm.asp
<%
const errorSymbol = "<font color=red><b>*</b></font>"
dim dicError
set dicError = server.createObject("scripting.dictionary")
sub checkForm
dim fieldName, fieldValue, pFieldValue
for each field in request.form
if left(field, 1) = "_" then
' is validation field , obtain field name
fieldName = right( field, len( field ) - 1)
' obtain field value
fieldValue = request.form(field)
select case lCase(fieldValue)
case "required"
if trim(request.form(fieldName)) = "" then
dicError(fieldName) = "<font size=-2 face=Verdana, Arial, Helvetica, sans-serif color=blue>" & fieldName & " is required</font>"
end if
case "date"
if Not isDate(request.form(fieldName)) then
dicError(fieldName) = "<font size=-2 face=Verdana, Arial, Helvetica, sans-serif color=blue>" & fieldName & "must be a date</font>"
end if
case "number"
pFieldValue=request.form(fieldName)
if Not isNumeric(pFieldValue) or (instr(pFieldValue,",")<>0) then
dicError(fieldName) = "<font size=-2 face=Verdana, Arial, Helvetica, sans-serif color=blue>" & fieldName & " must be a number</font>"
end if
case "intnumber"
pFieldValue=request.form(fieldName)
if Not isNumeric(pFieldValue) or (instr(pFieldValue,",")<>0) or (instr(pFieldValue,".")<>0) then
dicError(fieldName) = "<font size=-2 face=Verdana, Arial, Helvetica, sans-serif color=blue>" & fieldName & " must be an integer</font>"
end if
case "email"
if instr(request.form(fieldName),"@")=0 or instr(request.form(fieldName),".")=0 then
dicError(fieldName) = "<font size=-2 face=Verdana, Arial, Helvetica, sans-serif color=blue>" & fieldName & " must be an email</font>"
end if
case "phone"
pFieldValue=request.form(fieldName)
pFieldValue=replace(pFieldValue," ","")
pFieldValue=replace(pFieldValue,"-","")
pFieldValue=replace(pFieldValue,"(","")
pFieldValue=replace(pFieldValue,")","")
pFieldValue=replace(pFieldValue,"+","")
if Not isNumeric(pFieldValue) then
dicError(fieldName) = "<font size=-2 face=Verdana, Arial, Helvetica, sans-serif color=blue>" & fieldName & " must be a phone number</font>"
end if
case "login"
Dim i, ch, login
login = false
pFieldValue = request.Form(fieldName)
if len(pFieldValue) < 5 then
     login = false
else
          for i=1 to len(pFieldValue)     
          ch = Mid(pFieldValue, i, 1)
               if i=1 then
                    if(((ch >= "A") and (ch <= "Z")) or((ch >= "a") and (ch <= "z"))) then
                         login = true
                    else
                         login = false
                         exit for
                    end if
               end if
               if (i > 1) then
                    if(((ch >= "A")and(ch <= "Z"))or((ch >= "a")and(ch <= "z"))or((ch >= "0")and(ch <= "9"))or(ch = "_")) then
                         login = true
                    else
                         login = false
                         exit for
                    end if
               end if
          next
     end if
     if login = false then
dicError(fieldName) = "<font size=-2 face=Verdana, Arial, Helvetica, sans-serif color=blue>" & fieldName & " must start with an alphabet, having numbers (0-9), alphabets, the underscore and no spaces</font>"
end if
end select
end if
next
end sub
sub validateForm2(byVal successPage)
if request.ServerVariables("CONTENT_LENGTH") > 0 then
checkForm
' if no errors, then successPage
if dicError.Count = 0 then
' build success querystring
tString=Cstr("")
for each field in request.form
if left(field, 1) <> "_" then
fieldName = field
fieldValue = request.form(fieldName)
tString=tString &fieldName& "=" &Server.UrlEncode(fieldValue)& "&"
end if
next
Dim PageRed
PageRed= successPage&"?"& tString
response.Redirect(PageRed)
end if
end if
end sub
sub validateError
dim countRow
countRow=cInt(0)
for each field in dicError
if countRow=0 then
response.write "<br>"
end if
response.write "<br> - " & dicError(field)
countRow=countRow+1
next
if countRow>0 then
response.write "<br>"
end if
end sub
sub validate( byVal fieldName, byVal validType )
%> <input name="_<%=fieldName%>" type="hidden" value="<%=validType%>"> <%
if dicError.Exists(fieldName) then
response.write errorSymbol
end if
end sub
sub textbox(byVal fieldName , byVal fieldValue, byVal fieldSize, byVal fieldType, byVal fieldTitle, byVal maxLength, byVal action)
dim lastValue
lastValue = request.form(fieldName)
select case fieldType
case "textbox"
%>
<input name="<%=fieldName%>" size="<%=fieldSize%>" value="<%
if trim(fieldValue)<>"" then
response.write fieldValue
else
response.write Server.HTMLEncode(lastValue)
end if%>" style="BORDER-BOTTOM: black 1px solid; BORDER-LEFT: black 1px solid; BORDER-RIGHT: black 1px solid; BORDER-TOP: black 1px solid;"
title="<%=fieldTitle%>" maxlength="<%=maxLength%>" <%=action%>>
<%
case "hidden"
%>
<input type="hidden" name="<%=fieldName%>" size="<%=fieldSize%>" value="<%
if trim(fieldValue)<>"" then
response.write fieldValue
else
response.write Server.HTMLEncode(lastValue)
end if%>">
<%
case "password"
%><input name="<%=fieldName%>" type="password" size="<%=fieldSize%>" value="<%
if trim(fieldValue)<>"" then
response.write fieldValue
else
response.write server.HTMLEncode(lastValue)
end if%>" style="BORDER-BOTTOM: black 1px solid; BORDER-LEFT: black 1px solid; BORDER-RIGHT: black 1px solid; BORDER-TOP: black 1px solid;"
title="<%=fieldTitle%>" maxlength="<%=maxLength%>">
<%
case "textarea"
%>
<textarea name="<%=fieldName%>" rows="3" cols="<%=fieldSize%>" style="BORDER-BOTTOM: black 1px solid; BORDER-LEFT: black 1px solid; BORDER-RIGHT: black 1px solid; BORDER-TOP: black 1px solid;"
title="<%=fieldTitle%>" <%=action%>><%
if trim(fieldValue)<>"" then
response.write fieldValue
else
response.write Server.HTMLEncode(trim(lastValue))
end if
%></textarea>
<%
end select
end sub %>
End of validateform.asp
and I use it like this:
<!--#include file="includes/validateForm.asp" -->
<%
     on error resume next
%>
<body leftmargin="0" rightmargin="0" topmargin="0">
<%
     validateForm "addcustomer.asp"
%>
     <form action="" method="post" name="form1" >
<%validateError%>
Customer Name
<%textbox "Name", pName, 30, "textbox", "Customer Name", 50, ""%>
<%validate "Name", "required"%>
the last two scriptlets create a Name field which is required. If user does not fill it an error message appears against it.
Can someone help me please.
Sajid

Answer 1

Wow... some ASP code... its strange to see ASP these days as its been ages since i have coded in ASP.
Well to answer your question, there are couple of options to overcome this issue.
1) Make use of Struts Framework. It automatically takes care for the error handling(ok not automatically), but error handling of the type you are looking for is built into it and one needs to modify according to his/her own application.
2) The other option will be to submit the data to the servlet. Populate the data into the respective fields of a Bean and put the bean into session/request as per ur requirements. On the JSP page, check if there is some data in the bean. If yes, then populate the values of HTML controls from the BEAN and the one that is empty/has custom error that you might enter in servlet can be displayed as an error message to the user.
Hopefully this works for you. Give it a shot and its correctly said, that "necessity is the mother of invention"