Head First Servlets & JSP book - JSP Question

[Alvin chew]

hi, good day , everyone .. my question is how javascript variable assign/save into java variable ?

following are jsp scriptlet and javascript example :

jsp:

<% Boolean flag = "false" %>

javascript :

<script language="javascript">
 
function disable()
{
if(myform.checkbox.checked == true)
{
document.myform.mybutton.disabled=true;
[B]can i assign variable to mydata variable as below?[/B]
   flag = myform.checkbox.checked;
}
else
{
document.myform.mybutton.disabled=false;
}
}
 
 
</script>
 

how do i save javascript variable under jsp ? thank you very much ~

[ October 21, 2004: Message edited by: Alvin chew ]
[ October 21, 2004: Message edited by: Alvin chew ]

[Nicholas Cheung]

If I have understood your question correctly, you want to assign a JavaScript variable into JSP variable, isnt it?

In this case, I dont think this action is possible because:
1. JSP variables are server-side, they are translated BEFORE the response is sent to the browser
2. JS variables are client-side, they WONT available until the browser received the response

Thus, when your JavaScript variable gets the value due to your action (mouse click, etc), the JSP variable has been gone already (being parsed and JSP is converted into HTML).

Nick

[David Ulicny]

But you could generate javascript with JSP, so you could assing variables on the server side.

[Chengwei Lee]

If you're thinking of doing it on the same JSP, the answer is no. But, if you're hoping to do it on other pages or servlets, you can.

Just use hidden field. You can, however, assign Java values to Javascript. BTW, your code <% Boolean flag = "false" %> is not correct. It could be <% boolean flag = false; %> or <% Boolean flag = new Boolean("false"); %>

HTH.

[Nicholas Cheung]

But you could generate javascript with JSP, so you could assing variables on the server side.

Yes, this works because JSP can generate JS in server-side, but then, you cannot generate JSP using JS in the client side.

Nick

[David Ulicny]

Absolutely right Nicholas

[Nicholas Cheung]

In fact, if you write an application that thinks you need to generate JSP via some JS variables, you may:
- either redesign the logic
- as other said, submit the variables and use it in next page
- submit the variables to the SAME page, and display it

Nick

[Alvin chew]

hi, thanks all for giving advices ,

- as other said, submit the variables and use it in next page
- submit the variables to the SAME page, and display it

as for above mentioned advice, can someone please show me some sample on it ? i not clear on the idea how to submit variable and use for next page ?

[David Ulicny]

You will need a form and the variables will be submitted with GET or POST.

[Nicholas Cheung]

You can use a form to submit the value to the server again, in case you wanna the *next page* or the *same page* to use the variable.

Next page means, since we have no way to set a JSP value by JS value, thus, if we submit the JS value back to the server, assign it to JSP value at the server, and then re-generate the page back to the browser, you can then get the JS value.

In fact, you may not necessary to use different page to display, you can use the same page, and thus, you just check, whether the JS value exist, if yes, use it, if no, use default.

HTH.

Nick

[Alvin chew]

Nicholas, do you mind to show me sample code on what you explain , i really new on javascript ? thank you , and hope you can help ..

[Nicholas Cheung]

You could try this:

In abc.jsp,

function doSubmit() {
    // click after you do everything in the form
}
 
<%! boolean flag %>
 
<!-- note: submit to same JSP -->
<form name="myform" action="abc.jsp">
 
<%
  // Assume checked
  if (request.getAttribute("checkbox")) != null) {
      flag = true;
  }
%>
<input type="checkbox" name="checkbox">
 
<input type="submit" on click="doSubmit()">
<!--
other trigger, not to reload the same page for getting the value of checkbox
-->
<input type="submit2" on click="document.forms[0].action="xyz.jsp">
</form>

Note that this is assume that, the 1st load of the page does NOT contain info for that CHECK button, so, if you really need to assign a checkbox value to the JSP variable, you do a submit to the SAME page.

After you do everything, you can click another submit.

HTH

Nick

[Alvin chew]

hi, nicholas, i finally get it ...i try on submit hidden as shown following code

<script language="javascript"> function disable(){
if(myform.checkbox.checked == true)
{
        document.myform.mybutton.disabled=true;[I] //how do i save several variable into array?? [/I]
        [B]myform.hidden1.value = myform.checkbox.checked;[/B]
}
 
        else
       {
         document.myform.mybutton.disabled=false;
}}  
</script> 

form action="get.jsp" method="post" name="myform">
<p>
  <input type="hidden" name="hidden1">
  <input type="submit" name="submit" value="Submit">
</p>

but , let say if i want to save several js variable ...then how i implement array in my case ?

and for get.jsp page , to get array ...can i using code like

String value[] = request.getParameter("hidden1"); 

thank you !

[ October 22, 2004: Message edited by: Alvin chew ]

[ October 22, 2004: Message edited by: Alvin chew ]
[ October 22, 2004: Message edited by: Alvin chew ]

[Nicholas Cheung]

You can use the same variable name for those form objects. The container will translate the values into a String[].

Nick