Trying to give value to Java variable in JSP after checkbox's value

Question

I am creating a web interface in jsp. I have a java String variable (let's call it 'a') and some radio buttons, and I am trying to get the value of the checked one on click (without submiting the form) and give it's value to the variable.

I made a research on weather this can be done using only jsp and I could not find anything. So I assumed that I have to do this using Javascript. I am new in Javascript(so please excuse me if my question is stupid), but I wrote the following code.

HTML:

`<input type="radio" name="phase" value="value1" class="checkboxes" id="design_phase" onclick="getRadioValue(this.id)" />Value1
 <input type="radio" name="phase" value="value2" class="checkboxes"  id="development_phase" onclick="getRadioValue(this.id)" checked/>Value2`

Javascript:

      `function getRadioValue(id) {
        var radioBtn = document.getElementById(id);
        if(radioBtn.value=="value1"){
                            alert(radioBtn.value);
            <%a="value1";
            System.out.println("value1!");%>
        }
        else{
                            alert(radioBtn.value);
            <%a="value2";
            System.out.println("value2!");%>
        }
        }`

When I run this, both System.out contents are printed just when I load the page, before I even choose a checkbox. I have put the alert functions in order to make sure that javascript reads the values correctly, and it does indeed! So the problem seems to be with using js together with jsp.

Does anyone know what I am doing wrong, and how can this be done correctly?

Thanks in advance!

What functionality are you trying to code? It appears that you want to process the data selected from the radio button using Java. As Java is a server side technology you will need to send the data to the server hosting your application and process it using a servlet. This can be done by submitting the form to the servlet which then recuperates the data from the request object. If you don't want to submit the form you can use AJAX, which will send the data to the server without submitting the form. — Alex Theedom
– Alex Theedom, Commented Jun 29, 2013 at 16:26
I have a select input which gets values from a Java ArrayList, using JSP. I want to filter the values based on the radio button selection. The radio button and the select input are parts of the same form... Any ideas on how I can do this? — missrg
– missrg, Commented Jun 29, 2013 at 16:36
@missrg if you want the value of the radio to be saved in a jsp variable, it is necessay to submit the form — fmodos
– fmodos, Commented Jun 29, 2013 at 17:03
Why do you need the scripting variable, use javascript global variable. — Roman C
– Roman C, Commented Jun 29, 2013 at 17:07

Community · Accepted Answer · 2017-05-23 12:05:27Z

1

You should use AJAX (if you dont want to submit the form).

This is the methodology:

As soon as the user selects a radio button, an AJAX call is triggered that sends a request to a servlet. The servlet recuperates the option selected from the radio buttons (from the request object) and using this value it generates a response containing the values you want to display in the select (perhaps the values are stored in an array) and then sends the response to the client. The response is received and the values to be displayed in the select are recuperated and dynamically added to the DOM.

Have a look at this link for an explanation of how to do it: How to use Servlets and Ajax?

also here is a very simple example: Return JSON from one JSP to another?

edited May 23, 2017 at 12:05

CommunityBot

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answered Jun 29, 2013 at 18:23

Alex Theedom

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1 Comment

missrg Over a year ago

Thank you very much! I finally desided to send to request onclick using javascript and do the processing in a servlet and then send it back (because I was more familiar with JSP technology) but your answer was really on the point :)

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