Question

I’ve been having problems passing parameters from one .jsp to another.

I have two .jsp (1 and 2). In 1 I get some data from a database and show the user a bunch of checkboxes (depending on the data I got before). The user has to check one or more of the checkboxes, the selected will be deleted in my database in 2. (It´s something like “Select the numbers you want to delete”).

I don’t know how to pass the selected checkboxes and the value from 1 to 2.
I tried with javascript/jQuery, trying to know if a checkbox is checked and its value, add the value to a hidden field and use the request in 2 to get it.

1.jsp

<%
    HttpSession sesion = request.getSession();

    Company company = (Company) sesion.getAttribute("company");
    List<Phone> phones = company.getTelefonos();
%>
<form id="formulario" method="POST" action="desMul_Final.jsp">
<fieldset>
    <legend>Numbers</legend>
    <%
        Iterator<Phone> it1 = phones.iterator();
        while(it1.hasNext()){
            Phone t = it1.next();
            String number = t.getNumero();
    %>
    <p>
        <input name=check id="t_<%=number%>" type=checkbox value="<%=number%>" /> <%=number%>.
    </p>
    <%
        }
    %>
</fieldset>
<p class="buttons">
    <button type=submit onclick="javascript: pick();">Continue</button>
</p>
</form>

Javascript/jQuery

function pick(){
var counter = 0;
$("#formulario fieldset p").each(function(index){
    var field;
    $(this).children("input").each(function() {
        if($this.is(':checked')){
            field = $(this).val();
        }
    });
    index = index + 1;

    texto = "<input type=hidden name=phone_"+index+" value="+field+" />";
    $("#formulario").append(texto);

    counter = index;
});
cant = "<input type=hidden name=amount id=amount value="+counter+" />";
$("#formulario").append(cant);
}

2.jsp (here I only try to know if I have the info)

<%
    int amount = Integer.valueOf(request.getParameter("amount"));
    System.out.println(amount);

    for(int i = 1; i <= amount; i++){
            String s = request.getParameter("phone_"+i);
        System.out.println(s);
    }
%>

When I try to access to request.getParameter("amount") I get an java.lang.NumberFormatException: null so I think my Javascript/jQuery is wrong.

How can I solve this?.

Answer 1

Well, I finally found the solution and I didn’t need any Javascript. Searching in the API I found a method of the request called getParameterNames() that returns an Enumeration of String objects containing the names of the parameters contained in this request.

And I understood that when you submit the form, the checkbox value will be sent if the control is checked. Otherwise, nothing will be sent. So with this information and the method, I changed the way the checkboxes were constructed and use the enumeration to get the values.

BEFORE  
<input name=check id="t_<%=number%>" type=checkbox value="<%=number%>" /> <%=number%>.

NOW  
<input name="<%=number%>" type=checkbox /> <%=number%>.

So in my second .jsp I get a Enumeration with the names of the selected checkboxes, which are the phone numbers.

java.util.Enumeration enu = request.getParameterNames();
java.util.List<String> numbers = new java.util.ArrayList<String>();
while(enu.hasMoreElements()){
   String s = (String)(enu.nextElement());
   System.out.println(s);
   numbers.add(s);
}