getting null value, from a variable being sent from JavaScript in the page

[thor aniket]

I have a JSP file (trial.jsp). In that file, I'm taking username(any value) from user through a text box(name="username")
on submitting the form(name="form" onSubmit="call()") through submit button in HTML code, and then
accessing that username through a JavaScript function named "call()".

function call(){ var name=document.forms["form"]["username"].value; window.location.replace("trial.jsp?name="+name); }

Now, I'm accessing/printing these name variable in the JSP Scriptlet after the form in the same file .

String name=request.getParameter("name");

But I'm getting the null value of name in JSP scriptlet.
What could be the problem?

I have tried using

window.location.href =’trial.jsp?name='+name;

but problem persists. Would you help?

[Bear Bibeault]

What exactly is the problem? Just posting code without an explanation isn't very helpful.

From the topic title, I assume that you may need to read through this article.

[thor aniket]

Thank you very much, Bear Bibeault. I'm very glad to be here on JavaRanch. and I'm extremely sorry for not being reading instructions for creating new topic. I assure you I'll be taking work to be able to post a good readable topic with proper quotes. Sorry for inconvenience.

[thor aniket]

My problem is solved now, I got it right..!!!

When I use the input button type, 'button' instead of 'submit' type, my code worked. But I wish if it could work when input type was submit. any suggestion for that?

[Rob Spoor]

A submit button will actually submit the form. To send the variable you must include it as a (hidden) input field in your form.

[thor aniket]

But I haven't used any hidden variable here.. how did it worked? I got no idea.
so you mean, if we use submit button, I should make variable as hidden, right? viz.

<form name="myForm" onSubmit="return validate()" >
<input type="submit" value="submit" ></input>
</form>

or

<form name="myForm">
<input type="submit" value="submit" onSubmit="return validate()"></input>
</form>

and if we pass the variable to JSP Scriptlet from the JavaScirpt function validate(), will it work?
and I'm not getting what is hidden variable you're talking about, would you explain me further about it?

[Paul Clapham]

<input type="hidden" value="This is a basic HTML concept" />

[thor aniket]

Oh I see..!! Thank you Paul.. Thank you very much..!!
I think I need to get through HTML basics now specially about Hidden values and Submit button..

But would you tell me, what is the purpose for making that value as a hidden? Is it beneficial while sending values? or it has any other purpose..?
or Submit button has to anything to with Hidden value?

[Rob Spoor]

Submitting a form will only send values of the input fields (<input>, <select>, <textarea>) inside the form. Therefore, to send any value it needs to be the value of such an element. The <input type="hidden"> field is meant for values you want included when the form is submitted but that should not be visible on the screen.

[thor aniket]

oh I see. I got it now what hidden meant..!! Thanks Rob..But, why couldn't my code worked when using form's onSubmit event while sending the values to scriptlet, but it worked fine when I used button's onClick event. you have any idea or suggestion?

[Rob Spoor]

Buttons by default don't do anything (they're meant to have onclick event handlers), so when you clicked the button, all it did was execute the code you've attached to its onclick event.
Submit buttons by default submit the form, so when you clicked that button it executed the code and then still submitted the form. It wouldn't surprise me if your server logs would have shown an extra request for trial.jsp - as in, your code change the location, but then the browser changed it again because of the form.

You can stop the form from submitting by not using onclick but onsubmit for the form, and returning false from that method. Like you probably already do with validate().

[thor aniket]

Thank you very much Rob for the reply. Yes. Now, I'm getting a clearer difference between submit and click, and it has helped in this program too, like as the first way when using onClick button event on button itself and the second way while using submit button with form submit event way. I haven't tried second( submit button with form submit event ) thoroughly and knowingly, but now I'll try it to work correct. Thanks again.

[thor aniket]

So now, this is my permanent JavaScript function in (login.jsp) is as

function validate_form(){ var param1=document.forms["myForm"]["username"].value; var param2=document.forms["myForm"]["password"].value; window.location.replace("login.jsp?uname="+param1+"&pass="+param2); }

and now remaining JSP page in login.jsp, (1st way, i.e. using Button input type with onClick event) looks like,

<form name="myForm" > <center> User name:<input type="text" name="username"></input><br/> Password:<input type="password" name="password"></input><br/> <input type="button" value="Values, right?" onClick="validate_form()"> </center> </form> <% String value1=request.getParameter("uname"); String value2=request.getParameter("pass"); System.out.println("username is= "+value1+"\n"); out.println("password is= "+value2); %>

and it works fine, values(username and password) are getting printed through scriptlet.

[thor aniket]

But when I tried the same using 2nd way ( submit button with form's onSubmit event) as provided JAVASCRIPT function remains same,
login.jsp would change as,

<form name="myForm" onSubmit="validate_form()"> <center> User name:<input type="text" name="username"></input><br/> Password:<input type="password" name="password"></input><br/> <input type="submit" value="Values, right?"> </center> </form> <% String value1=request.getParameter("uname"); String value2=request.getParameter("pass"); System.out.println("username is= "+value1+"\n"); out.println("password is= "+value2); %>

it doesn't give me the values(username and password), rather they are shown as null. what could possibly go wrong above??
is their anything to do with action attribute in form, giving the same page link(login.jsp) to action as below,

<form name="myForm" onSubmit="validate_form()" action="login.jsp">

[Rob Spoor]

The form field names are called "username" and "password", not "uname" and "pass". Also, when using the form's own submit functionality, you don't need to call that method - the form does that for you. Well, assuming this page is login.jsp. Without an explicit "action" attribute it will open the current page.

[thor aniket]

are you saying, we don't have to call form's on Submit event explicitly, that event by default gets called when we hit submit button?? I didn't get it right. So how does Submit button come to know about the exact function name written in JavaScript? I'm confused now so much. please would you tell me in some other way.

I would re-write my exact code or my aim in the code, to be more explanatory. it's as follow,


actually, its not so very intentional program but just to make sure that we can pass variables from javascript to jsp. But specifically I would like to state step by step what I have coded in trial.jsp,
1.form field text box values, as named(username,password) are accessed through javascript in validate_form() function.
User name:<input type="text" name="username"></input><br/> Password:<input type="password" name="password"></input><br/> <input type="button" value="Values, right?" onClick="validate_form()">
2.stored in param1 and param2 variables their in validate_form() javascript function
function validate_form(){ var param1=document.forms["myForm"]["username"].value; var param2=document.forms["myForm"]["password"].value; window.location.replace("login.jsp?uname="+param1+"&pass="+param2); }
3. their, they are being sent to the JSP scriptlet written after <form>, using window.location.replace
(param1, param2-> uname, pass)
window.location.replace("login.jsp?uname="+param1+"&pass="+param2);
4.in JSP scriptlet, they are being accessed as ( uname, pass).
<% String value1=request.getParameter("uname"); String value2=request.getParameter("pass"); System.out.println("username is= "+value1+"\n"); out.println("password is= "+value2); %>

So, I have been trying successfully run the code and getting printed values of form fields in JSP scriptlet when I use button's onclick event. But when I use form's submit method, it doesn't work.
i was trying for submit button as
<form name="myForm" onSubmit="validate_form()" action="login.jsp">

[Rob Spoor]

When you submit a form, the page is automatically forwarded to the form's action (login.jsp) with all input fields, text area's and selects added as parameter key-value pairs. In this you would need to remove the onsubmit function, and change login.jsp to read parameters "username" and "password" instead of "uname" and "pass". Right now you're doing stuff manually that the form will already do for you.

[thor aniket]

Thanks Rob for the reply. I get what you're saying, like, we won't need onSubmit action to get input parameters. We just get it automatically with submit button. and yes, I've completely cleared that concept with your replies.
But, what you're saying is not my objective here, I don't want that input parameters to be printed directly in the jsp scriptlet. I'm sorry that I might have not cleared enough to know you the objective of my program.
My goal was to access input parameters in javascript function. and then send that input parameters to same or any other jsp and print their. In this case, I've been trying to print them on the same jsp(login.jsp). In case, parameters could have send to other jsp page too, to get printed.
I've attached the file for your ref in case.

[Rob Spoor]

In that case don't use the form's submit functionality but instead use a regular button with an onclick event like you've done previously. You still need to make sure that the names of the parameters you send through JavaScript match the names of the form fields.

[thor aniket]

Ok. You're right!! I think that its not possible at all while using the submit's functionality to reload the same page. and its of no further use. rather AJAX and Co. functionalists can solve my simliar problems. Thank you very much Rob for your kindly help. :)

[Rob Spoor]

You're welcome.